# How silicon alleviates the effect of abiotic stresses during seed germination: A review

Ahmed El Moukhtari, Mariem Ksiaa, Walid Zorrig, Cécile Cabassa, Chedly

Abdelly, Mohamed Farissi, Arnould Savoure

► To cite this version:

Ahmed El Moukhtari, Mariem Ksiaa, Walid Zorrig, Cécile Cabassa, Chedly Abdelly, et al. How silicon alleviates the effect of abiotic stresses during seed germination: A review. Journal of Plant Growth Regulation, 2023, 42, pp.3323-3341. 10.1007/s00344-022-10794-z. http://dx.doi.org/10.1007/s00344-022-10794-z

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Submitted on 31 Aug 2022

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**Abstract**

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Rapid synchronized seed germination is desirable to ensure seedling establishment and improve crop yield.

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However, abiotic stresses from drought, salinity, and heavy metals have a negative impact on seed germination.

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The application of silicon (Si) has emerged as a promising approach for improving seed germination, especially under unfavorable conditions. However, the mechanisms of Si action have not been systematically studied in germinating seeds under conditions of abiotic stress. Considering the potential importance of sustainable agriculture, here we review recent findings of how seeds of numerous species, including several important crops, respond to Si treatment under abiotic stress. Exogenous Si has multiple effects on embryo viability, reserve mobilization, hormone/enzyme activity, membrane integrity, antioxidant metabolism, and regulation of gene expression in seed germination.

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Keywords: Silicon, salinity, drought, heavy metals, seed germination, tolerance mechanisms.

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41 **Introduction**

42 Seed germination is the crucial stage when individual progeny of plant sexual reproduction become established
43 (Waterworth et al. 2019) and the environment of the future growth and development of the plant is determined
44 (Hubbard et al. 2012; Ali and Elozeiri 2017). Germination is naturally very sensitive to abiotic stresses, including
45 those caused by heavy metals, salinity, and drought (Dehnavi et al. 2020; Farissi et al. 2011; Ghavami and Ramin
46 2007; Seneviratne et al. 2017; Xiao et al. 2016). Abiotic stresses either delay or entirely prevent seed germination
47 through osmotic stress and/or ionic toxicity (Debez et al. 2018; Haghighi et al. 2012; Farissi et al. 2011). Some
48 abiotic stresses also increase reactive oxygen species (ROS), such as hydrogen peroxide (H₂O₂) and superoxide
49 anion (O₂⁻) in seeds (Bailly 2019), that may be produced during desiccation, germination, and aging (Pulido et al.
50 2009). In imbibed seeds, it has been reported that the metabolic activity in the different cell compartments such as
51 NADPH oxidase activity in the plasma membrane, respiratory activity in mitochondria, purine catabolism in
52 peroxisomes and lipid metabolism in glyoxysomes contribute to ROS production (Bailly 2004; Gomes and Garcia
53 2013). ROS disturb cellular metabolism by causing the peroxidation of proteins, lipids, and nucleic acids leading
54 to seed deterioration and germination failure (Parvin et al. 2019). The exposure of seeds to salinity, drought, or
55 heavy metals therefore induces modifications in protein structure, which diminishes hydrolytic enzyme activities
56 so mobilization of seed reserves is compromised (Farissi et al. 2011; Hameed et al. 2021; Kranner and Colville
57 2011; Liu et al. 2018; Muscolo et al. 2014; Seneviratne et al. 2017).

58 Si is the second most abundant element after oxygen in the earth's crust. Exogenous application of Si has
59 improved seed germination and embryo viability under various abiotic stresses (El Moukhtari et al. 2021;
60 Lamsaadi et al. 2022; Rizwan et al. 2015; Siddiqui et al. 2020). An example of Si improving the seed viability of
61 *Medicago sativa* L. under salt stress is illustrated in Fig. 1. Under drought, salinity, or heavy metal stresses, the
62 addition of Si was found to improve seed germination rates in various plant species by influencing reserve
63 mobilization, membrane integrity, ROS detoxification, antioxidant system, phytohormone metabolism, and gene
64 expression (Ayed et al. 2021; Delavar et al. 2017; Gou et al. 2020; Khan and Gupta 2018). The beneficial effects
65 of exogenous Si on plant tolerance to various abiotic stresses have been the subject of several reviews (El
66 Moukhtari et al. 2021; Rizwan et al. 2015; Siddiqui et al. 2020) covering effects on plant growth, photosynthesis,
67 water nutrition, and productivity of different crops under various abiotic stresses. Here we focus on reviewing the
68 effect of exogenous Si on seed germination under abiotic stresses. First, we briefly highlight how different abiotic
69 stresses affect seed germination, purposely considering evidence from a wide range of species. Then within this
70 framework, the possible modes of Si action on seed germination are critically reviewed. Future areas of research
71 to deepen our understanding of the mechanisms triggered by Si during seed germination are discussed.
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<figure><img src="image_2.png" /><figcaption>**Fig. 1** Germination (a, b, and c) and embryo viability (d, e, and f) of seeds of the Moroccan *Medicago sativa* L. Demnate 201 variety treated with water (a, d), with 200 mM NaCl (b, e), or with 200 mM NaCl and 3 mM silicon in the form of CaSiO₃ (c, f). The germination rates were (a) 100%, (b) 51%, and (c) 85% after seven days of treatment. Embryo viability was evaluated after 12 hours of treatment using the 2,3,5 triphenyltetrazolium chloride (TTC) method in which viable embryos are stained red due to the reduction of TTC by respiratory activity of the cells. Images were taken under a binocular magnifying glass with 10x magnification.</figcaption></figure>

**Relationship between seed dormancy and germination**

Seed formation itself is a key strategy adopted by plants, especially annuals, to overcome unfavorable environments (Boesewinkel and Bouman 1984). Mature seeds are spread from the mother plant into the soil, where they germinate or stay dormant. Seeds can sense the surrounding environment and cannot germinate in the absence of appropriate environmental conditions (Baskin and Baskin 2004; Finch-Savage and Footitt 2017). Environmental factors such as temperature, nitrate, light, water, oxygen, smoke, and allelochemicals may all form an integrative signal to determine whether and when seeds germinate or stay dormant (Graeber et al. 2012; Sano and Marion-Poll 2021; Yan and Chen 2020).

Seed dormancy is an orchestrated process during which the germination of viable seeds is blocked or delayed to withstand unfavorable environmental conditions (Finkelstein et al. 2008), which is key for the survival of the offspring. Dormancy is established during seed maturation and reaches a maximum level in freshly harvested seeds (Nakabayashi and Leubner-Metzger 2021). Seed dormancy therefore counters the phenomenon of preharvest sprouting, which is a major detrimental issue in cereal production (Tai et al. 2021). Abscisic acid (ABA) initiates and maintains dormancy (Koornneef et al. 2002). Carles et al. (2002) found that ABA-deficient *A. thaliana* seeds (*abi4-1*, *abi5-2* and *abi5-5*) germinated under osmotic stress, even with as much as 175 mM NaCl or 300 mM mannitol in the growth medium, but the seedlings died 7 days after germination. This example shows that ABA serves to inhibit germination in environmental conditions that are too extreme for the proper establishment of the seedlings. In contrast, it is well-known that gibberellic acid (GA) breaks seed dormancy and triggers seed
germination (e.g. Stejskalová et al. 2015). For example, seeds of the GA biosynthesis *A. thaliana* mutant *ga1-3* only germinate if exogenous GA is applied (Hauvermale and Steber 2020). A key step in the germination process is the rupture of seed coat by the emerging radicle and GA stimulates radicle growth by mediating the activation of cell division in the embryonic root apical meristem (Ravindran and Kumar 2019). In tomato and Arabidopsis, GA promotes embryo growth and weakens the structures surrounding the embryo (Yamaguchi and Kamiya 2001). GA also stimulates the synthesis and translation of specific mRNAs, particularly those encoding α-amylase, a hydrolytic enzyme required for the digestion of seed reserves needed for germination (Ali and Elozeiri 2017; Muralikrishna and Nirmala 2005).

## Overview of the effects of abiotic stresses on seed germination

### Drought stress

Water is a major factor necessary for the imbibition and germination of seeds (Bradford 2017). Drought decreases external water potential, limiting the seed's ability to take up water and impairing germination (Balestrazzi et al. 2011; Campos et al. 2020). This effect has been observed in numerous Fabaceae species, including *Medicago sativa* (Han et al. 2017; Wang et al. 2009), *Glycine max* (Wijewardana et al. 2018, 2019), and *Lens culinaris* (Aniat-ul-Haq and Agnihotri 2010). Water stress was found to reduce several positive seed germination traits in some crop species of the Poaceae, Solanaceae, Asteraceae and Brassicaceae families. For example, germination percentage, germination rate, and vigor index are lowered by water stress in *Triticum aestivum* (Kizilgeci et al. 2017), *Hordeum vulgare* (Barati et al. 2015), *Oryza sativa* (Ali et al. 2020), *Solanum lycopersicum* (Galviz-Fajardo et al. 2020), *Helianthus annuus* (Toscano et al. 2017) and *Brassica napus* (Xiong et al. 2018). According to Llanes et al. (2015), drought stress can influence seed germination by changing endogenous plant growth regulator levels. For example, water deficit mediated by PEG treatment triggered an increase in ABA and a decrease in GA in *Trifolium repens*, impairing seed germination (Hassan et al. 2021). When less GA is available under water shortage, reserve mobilization is compromised, because the synthesis of various hydrolytic enzymes is not stimulated (Bewley 2001). In fact, Muscolo et al. (2014) and Hameed et al. (2021) reported that water deficiency significantly impaired the activities of α-amylase, β-amylase and proteases in the endosperm of lentil and wheat seeds, respectively, which consequently hampered seed reserve mobilization. In *Medicago truncatula* water deficit also alters embryo respiration and seed viability (Balestrazzi et al. 2011). In drought-stressed wheat, a decrease in germination rate appeared to result from the induction of oxidative stress, where a higher level of malonyldialdehyde (MDA) was noted together with an increase in H₂O₂ and O₂⁻ (Guo et al. 2017).

### Salinity stress

Salinity causes serious abiotic stress, severely hindering seed germination and delaying seedling emergence. When seeds are germinated on filter paper, salinity affects indexes such as percentage, rate, and speed of germination of various plant species, including *Sorghum bicolor* (Dehnavi et al. 2020), *M. sativa* (Farissi et al. 2011), *Silybum marianum* (Ghavami and Ramin 2007), *Suaeda salsa* and *Phragmites australis* (Xiao et al. 2016), *Buchloe dactyloides* and *Bouteloua gracilis* (Zhang et al. 2012). Salinity is even reported to delay the germination of some halophytes such as *Cakile maritime* (Debez et al. 2004, 2018), *Salicornia europaea* (Calone et al. 2020), *Spartina maritima*, and *Spartina densiflora* (Infante-Izquierdo et al. 2019) as the times for 50% germination of viable seeds (T₅₀) are longer when the level of salt stress is high.
Salinity inhibits seed germination through various metabolic changes. In addition to the effects of osmotic stress, salinity may induce ionic toxicity due to an excess of Na⁺ and Cl⁻ (de Oliveira et al. 2013). Salinity drastically decreased the activities of α- and β-amylase in *Amaranthus caudatus* (Białecka and Kępczyński 2009), with negative consequences on seed reserve mobilization (Farissi et al. 2011). A similar effect was observed in *O. sativa*, where salinity reduced the expression of the α-amylase gene and the activity of the enzyme (Liu et al. 2018). Similarly, catabolism of starch and lipids during *Cucumis sativus* seed germination was inhibited and delayed under salinity (Zhang et al. 2017). In *Pancratium maritimum* seeds, salinity affects cell division and causes DNA fragmentation, micronucleus formation, and chromosomal abnormalities (Mohamed et al. 2018). Salt can also disturb the homeostasis of phytohormones leading to failure of seed germination (Miransari and Smith 2014). Moreover, either through osmotic stress and/or ionic toxicity, salinity mediates an over-accumulation of ROS, leading to damage of nucleic acids, lipids, proteins, and carbohydrates which limits seed germination (Ibrahim 2016).

## Heavy metals

Heavy metals have been shown to negatively influence seed germination and seedling growth of various plant species (El Rasafi et al. 2020; Seneviratne et al. 2017). There have been numerous descriptions of cadmium (Cd) delaying or completely inhibiting germination. For example, wheat grain germination was reduced by 47% at 0.12 mM Cd (Guilherme et al. 2015), while no *O. sativa* grains germinated at 1 mM Cd (Ahsan et al. 2007). Mercury (Hg), another toxic metal, is known to suppress seed germination and seedling growth. In *Vigna radiata*, 7 mM Hg reduced seed germination, seedling elongation, and dry weight accumulation by 42%, 70%, and 47%, respectively, compared to the control (Muhammad et al. 2015). Copper (Cu) also has a harmful impact on seed germination, even at low concentrations. For example, 10 µM Cu reduced seed germination of *H. vulgare*, *T. aestivum*, and *O. sativa* by more than 7%, 39%, and 63%, respectively (Mahmood et al. 2007). When *M. sativa* seeds were sown on solid media, 24% fewer seeds germinated when treated with 40 ppm nickel (Ni) (Aydinalp and Marinova 2009). Lead (Pb) inhibits seed germination in various plant species, including *L. culinaris* (Cokkizgin and Cokkizgin 2010). When 4.5 mM Pb was applied to lentil seeds, the germination percentage and vigor index were 67% and 83% lower than controls without Pb, respectively, and the mean germination time was 17% longer. Seed germination inhibition by other metalloids has been reported, including aluminum (Al) (Rodrigues et al. 2019), arsenic (As) (Mridha et al. 2021), and chromium (Cr) (Khan et al. 2020).

How heavy metal stress prevents seed germination is a complex biochemical process. Heavy metals can block aquaporins by binding to a cysteine residue close to the pore of the protein (Daniels et al. 1994) thereby impeding water uptake by seed cells and limiting seed imbibition (Cardoso et al. 2015; Lefèvre et al. 2009). Similar effects have been observed in *Pisum sativum* under HgCl₂ and ZnCl₂ stresses (Kshetrimayum et al. 2017). Furthermore, enzymes participating in reserve mobilization, such as α- and β-amylases, proteases, leucine amino peptidases as well as cysteine-, aspartic-, and metallo-proteases, are altered by heavy metals, resulting in lower enzyme activity that has a negative effect on germination (Seneviratne et al. 2017). Heavy metal stress may also alter endogenous phytohormone homeostasis in seeds (Seneviratne et al. 2017). In *Cicer arietinum*, the negative effect of Pb or zinc (Zn) stress on seed germination was due to an increase in ABA and a decrease in GA content (Atici et al. 2005). Heavy metals can also reduce seed germination by inducing oxidative stress, reducing cell viability, and altering embryo growth (Gonzalez-Mendoza et al. 2009; Li et al. 2005; Sethy and Ghosh 2013).
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To summarize, abiotic stresses, including drought, salinity and heavy metals, have a significant negative impact on seed germination of various species of plants. The negative effects include altered ion and water uptake, reduced reserve mobilization, modifications of proteins/enzymes and oxidative stress resulting in reduced seed viability and vigor (Table 1).
<table><caption>Table 1 Effects of abiotic stresses on germinating seeds of different plant species compared to non-stressed controls</caption><thead><tr><th colspan="3">Abiotic stress</th><th rowspan="2">Plant species</th><th rowspan="2">Effects on germination</th><th rowspan="2">References</th></tr><tr><th>Type of stress</th><th>Agent</th><th>Stress level</th></tr></thead><tbody><tr><td rowspan="12">Drought stress</td><td rowspan="3">Mannitol</td><td rowspan="3">-0.3, -0.6, -1.2 and -2.4 MPa</td><td rowspan="3">Glycine max</td><td>Lower germination indexes</td><td rowspan="3">Machado Neto et al. (2004)</td></tr><tr><td>Shorter hypocotyl and root</td></tr><tr><td>More abnormal seedlings</td></tr><tr><td rowspan="5">PEG</td><td rowspan="5">15%</td><td rowspan="5">Brassica napus</td><td>Lower germination indexes</td><td rowspan="5">Xiong et al. (2018)</td></tr><tr><td>Lower seed vigor index</td></tr><tr><td>More ROS accumulation</td></tr><tr><td>More lipid peroxidation</td></tr><tr><td>More non-enzymatic antioxidants</td></tr><tr><td rowspan="2">More ABA</td><td rowspan="2"></td><td rowspan="2"></td><td>Increased activity of antioxidant enzymes</td></tr><tr><td>Delayed water absorption capacity of testa</td></tr><tr><td rowspan="4">PEG</td><td rowspan="4">10%</td><td rowspan="4">Gossypium hirsutum</td><td>Lower germination indexes</td><td rowspan="4">Bai et al. (2020)</td></tr><tr><td>Increased ABA/GA ratio</td></tr><tr><td>Less α-amylase</td></tr><tr><td>More ROS accumulation</td></tr><tr><td rowspan="2">More lipid peroxidation</td><td rowspan="2"></td><td rowspan="2"></td><td>Delayed water absorption capacity of testa</td></tr><tr><td>More ABA</td></tr><tr><td rowspan="4">PEG</td><td rowspan="4">13.6 and 20.4%</td><td rowspan="4">Hordeum vulgars</td><td>Lower germination indexes</td><td rowspan="4">Barati et al. (2015)</td></tr><tr><td>Fewer primary roots</td></tr><tr><td>Shorter maximum root length</td></tr><tr><td>Shorter shoots</td></tr><tr><td rowspan="6">PEG</td><td rowspan="6">0.5-2.5 MPa</td><td rowspan="6">Juglans regia</td><td>Lower germination indexes</td><td rowspan="6">Lotfi et al. (2019)</td></tr><tr><td>Less water in radicle and plumule</td></tr><tr><td>More lipid peroxidation</td></tr><tr><td>Increased activity of antioxidant enzymes</td></tr><tr><td>More antioxidant compounds</td></tr><tr><td>More ABA, SA and JA</td></tr><tr><td rowspan="3">More proline</td><td rowspan="3"></td><td rowspan="3"></td><td>Less GA and IAA</td></tr><tr><td>Less proline</td></tr><tr><td>More ABA, SA and JA</td></tr><tr><td rowspan="2">PEG</td><td rowspan="2">10-21%</td><td rowspan="2">Lens culinaris</td><td>Lower germination indexes</td><td rowspan="2">Muscolo et al. (2014)</td></tr><tr><td>Less water in germinating seeds</td></tr><tr><td rowspan="2">PEG</td><td rowspan="2">10-21%</td><td rowspan="2">Lens culinaris</td><td>Less α-amylase</td><td rowspan="2"></td></tr><tr><td>More proline</td></tr></tbody></table>
<table><tbody><tr><td>PEG</td><td>-0.40, -0.50 and -0.75 MPa</td><td><i>Lens culinaris</i></td><td>Lower germination percentage<br>Reduced seedling survival<br>Shorter root and shoot</td><td>Aniat-ul-Haq and Agnihotri (2010)</td></tr><tr><td>PEG</td><td>35%</td><td><i>Medicago sativa</i></td><td>Lower germination indexes<br>More ROS accumulation<br>More lipid peroxidation<br>Increased activity of antioxidant enzymes</td><td>Wang et al. (2009)</td></tr><tr><td>PEG</td><td>20%</td><td><i>Oryza sativa</i></td><td>Lower germination indexes<br>Less water in seeds<br>More ROS accumulation<br>More lipid peroxidation<br>More ABA<br>Upregulated <i>OsNCED3</i> expression<br>Upregulated SOD and CAT related gene expression</td><td>Liu et al. (2019)</td></tr><tr><td>PEG</td><td>-0.3, -0.6 and -0.9 MPa</td><td><i>Oryza sativa</i></td><td>Lower germination indexes<br>Shorter plumules<br>Shorter roots<br>Shorter seedlings</td><td>Ali et al. (2020)</td></tr><tr><td>PEG</td><td>17%</td><td><i>Trifolium repens</i></td><td>Lower germination indexes<br>Less cytokinin<br>More ABA<br>Less β-amylase<br>Less total amylase<br>More starch and soluble sugar<br>More ROS accumulation<br>More lipid peroxidation<br>Increased CAT activity</td><td>Hassan et al. (2021)</td></tr><tr><td>AlCl<sub>3</sub></td><td>30 mmol L<sup>-1</sup></td><td><i>Triticum aestivum</i></td><td>Lower germination indexes<br>Lower amylase and esterase activity<br>More ROS accumulation<br>More lipid peroxidation</td><td>Zhang et al. (2010)</td></tr><tr><td>AlCl<sub>3</sub></td><td>2 mmol L<sup>-1</sup></td><td><i>Oryza sativa</i></td><td>Lower germination indexes<br>Lower GA/ABA ratio<br>Downregulation of the expression of ABA catabolism genes (<i>OsABA8ox1</i> and <i>OsABA8ox2</i>)<br>Lower α- and β-amylase activity<br>More lipid peroxidation<br>Increased antioxidant enzyme activity</td><td>Xu et al. (2017)</td></tr></tbody></table>
<table><tr><td>Cd</td><td>100-500 µM</td><td>Brassica napus</td><td>Induced ROS accumulation<br>Induced lipid peroxidation<br>Ultrastructural changes in cells of germinating seeds</td><td>Ali et al. (2015)</td></tr><tr><td>CdCl<sub>2</sub></td><td>5 mM</td><td>Phaseolus vulgaris</td><td>Lower germination indexes<br>Reduced embryo growth<br>Lower α-amylase and invertase activity<br>Induced lipid peroxidation</td><td>Sfaxi-Bousbih et al. (2010)</td></tr><tr><td>CdCl<sub>2</sub></td><td>10-30 mg L<sup>-1</sup></td><td>Trigonella foenum-graecum</td><td>Lower germination indexes</td><td>Espanany et al. (2015)</td></tr><tr><td>CdCl<sub>2</sub></td><td>1-5 mM</td><td>Triticum aestivum</td><td>Lower germination indexes<br>Shorter coleoptile and radicles<br>Lower amylase activity<br>Induced lipid peroxidation</td><td>Hu et al. (2015)</td></tr><tr><td>CuSO<sub>4</sub></td><td>100-500 µM</td><td>Hordeum vulgare</td><td>Lower germination indexes<br>Shorter radicles<br>Lower α- and β-amylase, acid phosphatase, and alkaline phosphatase activities<br>Induced lipid peroxidation<br>Induced proline accumulation</td><td>Kalai et al. (2014)</td></tr><tr><td>Cr<sup>3+</sup></td><td>50-800 mg L<sup>-1</sup></td><td>Arabidopsis thaliana</td><td>Lower germination indexes<br>Less embryo viability<br>Increased seed coat permeability</td><td>de Silva et al. (2021)</td></tr><tr><td>Cr (VI)</td><td>100 µM</td><td>Triticum aestivum</td><td>Lower germination indexes<br>Lower α-amylase activity<br>Fewer free amino acids<br>Induced ROS accumulation<br>Induced lipid peroxidation</td><td>Lei et al. (2021)</td></tr><tr><td>K<sub>2</sub>Cr<sub>2</sub>O<sub>7</sub></td><td>30-300 mg L<sup>-1</sup></td><td>Lepidium sativum</td><td>Lower germination indexes</td><td>Pavel et al. (2013)</td></tr><tr><td>PbCl<sub>2</sub></td><td>0.5-4.5 mM</td><td>Lens culinaris</td><td>Lower germination indexes<br>Shorter plumules and radicles</td><td>Cokkizgin and Cokkizgin (2010)</td></tr><tr><td>Pb (NO<sub>3</sub>)<sub>2</sub></td><td>0.05-1 g L<sup>-1</sup></td><td>Triticum aestivum</td><td>Induced lipid peroxidation,<br>Increased proline accumulation<br>Lower α-amylase activity<br>Increased antioxidant enzyme activities</td><td>Lamhamdi et al. (2011)</td></tr><tr><td>Salinity</td><td>NaCl</td><td>Arabidopsis thaliana</td><td>Lower germination indexes<br>Induced ROS accumulation<br>Induced lipid peroxidation</td><td>Luo et al. (2021)</td></tr></table>
<table><tr><td></td><td></td><td></td><td>Less embryo viability</td><td></td></tr><tr><td>NaCl</td><td>150 mM</td><td>Gossypium hirsutum</td><td>Lower germination indexes<br>Less α-amylase and β-galactosidase<br>Lower GA/ABA ratio<br>Less melatonin</td><td>Chen et al. (2021)</td></tr><tr><td>NaCl</td><td>150 mM</td><td>Gossypium hirsutum</td><td>Lower germination indexes<br>Downregulated ABA catabolism (CYP707A2) and GA biosynthesis (GA20ox1) genes<br>Upregulated ABA biosynthesis (NCED2, NCED5 and NCED9) and GA catabolism (GA2ox1) genes</td><td>Kong et al. (2017)</td></tr><tr><td>NaCl</td><td>50 and 100 mmol dm<sup>-3</sup></td><td>Gossypium hirsutum</td><td>Lower germination indexes<br>Lower α-amylase activity<br>Less reduced-sugar<br>Less total amino acids</td><td>Ashraf et al. (2002)</td></tr><tr><td>NaCl</td><td>100 mM</td><td>Lactuca sativa</td><td>Lower germination indexes<br>Lower phosphatase and phytase activities</td><td>Nasri et al. (2012)</td></tr><tr><td>NaCl</td><td>200 mM</td><td>Limonium bicolor</td><td>Reduced germination indexes<br>Lower GA/ABA ratio<br>Lower amylase and α-amylase activities<br>Decreased GA20ox, GA3ox and CYP707A1 gene expression<br>Increased NCED1 and NCED3 gene expression<br>More Na<sup>+</sup> and Cl<sup>-</sup></td><td>Li et al. (2019)</td></tr><tr><td>NaCl</td><td>50-200 mM</td><td>Medicago sativa</td><td>Lower germination indexes<br>Less reserve mobilization<br>Ionic toxicity</td><td>Farissi et al. (2011)</td></tr><tr><td>NaCl</td><td>100-200 mM</td><td>Sorghum bicolor</td><td>Lower germination indexes<br>Lower salinity tolerance index<br>Higher stress susceptibility index</td><td>Dehnavi et al. (2020)</td></tr><tr><td>NaCl</td><td>200 mM</td><td>Trigonella foenum-graecum</td><td>Lower germination indexes<br>Less seed reserve mobilization<br>Reduced seed viability<br>Induced ROS accumulation<br>Induced lipid peroxidation<br>Ionic toxicity</td><td>Lamsaadi et al. (2022)</td></tr><tr><td>NaCl</td><td>60 and 120 mM</td><td>Triticum aestivum</td><td>Lower germination indexes<br>Less water uptake<br>Lower α-amylase activity</td><td>El-Hendawy et al. (2019)</td></tr></table>
<table><tr><td>NaCl</td><td>120 mM</td><td>Oryza sativa</td><td>Lower germination indexes<br>Less bioactive GA<br>Lower α-amylase activity<br>Downregulated α-amylase gene expression</td><td>Liu et al. (2018)</td></tr><tr><td>NaCl</td><td>50-200 mM</td><td>Pancratium maritimum</td><td>Lower germination indexes<br>Affects cell division<br>DNA fragmentation, micronucleus formation, and<br>chromosomal abnormalities</td><td>Mohamed et al. (2018)</td></tr><tr><td>Na₂CO₃</td><td>50 mM</td><td>Oryza sativa</td><td>Lower germination indexes<br>Less bioactive GA<br>Lower α-amylase content</td><td>Li et al. (2019)</td></tr><tr><td>NaHCO₃</td><td>90 mmol L⁻¹</td><td>Cucumis sativus</td><td>Lower germination indexes<br>Shorter hypocotyl and radicles<br>Lower α- and β-amylase activity<br>Increased lipid peroxidation</td><td>Sun and Luo (2014)</td></tr></table>

PEG, polyethelene glycol; GA, gibberellic acid; ABA, abscisic acid; Na₂CO₃, sodium carbonate; NaHCO₃, sodium hydrogen carbonate; Pb(NO₃)₂, lead (II) nitrate; PbCl₂, lead chloride; Cr(VI), chromium hexavalent; Cr³⁺, chromium; CuSO₄, copper sulfate; CdCl₂, cadmium chloride; Cd, cadmium; AlCl₃, aluminum chloride.

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213 Si improves seed germination under abiotic stresses

214 Si has repeatedly been found to have a positive effect on seed germination under abiotic stress (e.g. Rizwan et al. 2015; Siddiqui et al. 2020), and several of the reports are listed in Table 2. Elemental Si increases seed germination percentage, germination index, and seedling vigor of *C. sativus* exposed to stress caused by 200 mM NaCl (Gou et al. 2020). Investigations by Almutairi (2016) indicate that 1 mM nano-silicon increased germination percentage and germination rate of *S. lycopersicum* seeds under different NaCl concentrations (150-200 mM). In a different study by Zhang et al. (2015), germination rate, germination index, and vitality indexes of *Glycyrrhiza uralensis* seeds grown under salt stress (150 mM NaCl) were all improved upon Si treatment. In *Trigonella foenum-graecum* seeds germinating under NaCl induced salinity stress, the application of CaSiO₃ improved the germination percentage, germination speed, velocity index, germination energy, peak value and vitality index, all in a shorter mean germination time (Lamsaadi et al. 2022). Alsaeedi et al. (2017) showed that Si in the form of nano-silica restricted Na⁺ uptake by *Phaseolus vulgaris* seeds resulting in a final germination percentage and germination rate that were 19.7% and 22.6% higher, respectively, than Na⁺-stressed *P. vulgaris* seeds not supplied with Si. Toxicity of NaCl on germination of *T. aestivum* (Azeem et al. 2015), *Zea mays* (Naguib and Abdalla 2019), and *L. sativa* (Alves et al. 2020) was alleviated by Si application.

228 Si added as an exogenous compound was also beneficial as it improved seed germination under other abiotic stresses, such as drought and heavy metal stress (Arif et al. 2021). Under drought stress, Ayed et al. (2021) reported that Si in the form of sodium metasilicate (Na₂SiO₃H₂O) increased germination percentage, germination, and seedling vigor indexes of *T. turgidum* by 22%, 62%, and 39%, respectively. Furthermore, under 100 µM Cd stress, SiO₂ supplements improved *Phyllostachys edulis* seed germination (Emamverdian et al. 2021). In *O. sativa*, 5 mM silicic acid increased germination percentage under 150 µM As stress from 56% to 78% (Khan and Gupta 2018). In seed germination experiments with *Z. mays*, the toxic effects of Al were alleviated by exogenous application of Si (Delavar et al. 2017). Si in the form of Na₂SiO₃ can also augment seed germination in *C. sativus* under 3-phenylpropionic acid induced stress (Bu et al. 2018) and in *C. melo* under autotoxicity stress (Zhang et al. 2020). The studies above indicate that Si has an amelioratory effect on the germination of seeds grown under various abiotic stressors.
<table><caption>Table 2 Potential modes of Si action during seed germination under various abiotic stresses</caption><thead><tr><th rowspan="2">Plant species</th><th colspan="3">Si</th><th colspan="2">Stress</th><th rowspan="2">Mode of action</th><th rowspan="2">References</th></tr><tr><th>Form</th><th>Technique</th><th>Concentration</th><th>Type</th><th>Level</th></tr></thead><tbody><tr><td>Cucumis melo</td><td>Na<sub>2</sub>SiO<sub>3</sub></td><td>Soaking</td><td>2 mM</td><td>MPWE</td><td>20 mg L<sup>-1</sup></td><td>Germination traits<br>Reserve mobilization<br>Gene expression<br>Antioxidant activities<br>Membrane integrity</td><td>Zhang et al. (2020)</td></tr><tr><td>Cucumis sativus</td><td>Na<sub>2</sub>SiO<sub>3</sub></td><td>Soaking</td><td>2 mM</td><td>3-PPA</td><td>2 mM</td><td>Germination traits<br>Reserve mobilization<br>Gene expression</td><td>Bu et al. (2018)</td></tr><tr><td>Cucumis sativus</td><td>Na<sub>2</sub>SiO<sub>3</sub></td><td>Soaking</td><td>0.3 mM</td><td>NaCl</td><td>200 mM</td><td>Germination traits<br>Reserve mobilization<br>Membrane integrity<br>ROS detoxification<br>Antioxidant activities<br>Phytohormones<br>Gene expression</td><td>Gou et al. (2020)</td></tr><tr><td>Lactuca sativa</td><td>Ca<sub>2</sub>SiO<sub>4</sub></td><td>Priming</td><td>0.05-0.1 mM</td><td>NaCl</td><td>50 mM</td><td>Germination traits<br>Antioxidant activities<br>Membrane stability</td><td>Alves et al. (2020)</td></tr><tr><td>Lathyrus odoratus</td><td>nano-Si</td><td>Priming</td><td>20 mg L<sup>-1</sup></td><td>NaCl</td><td>21.60 dS m<sup>-1</sup></td><td>Germination traits</td><td>El-Serafy et al. (2021)</td></tr><tr><td>Lens culinaris</td><td>Na<sub>2</sub>SiO<sub>3</sub></td><td>Soaking</td><td>2 mM</td><td>PEG</td><td>18%</td><td>Germination traits<br>Reserve mobilization<br>Antioxidant activities<br>ROS detoxification<br>Membrane stability</td><td>Biju et al. (2017)</td></tr><tr><td>Oryza sativa</td><td>H<sub>4</sub>SiO<sub>2</sub><sup>-</sup></td><td>Priming</td><td>5 mM</td><td>As</td><td>150 uM</td><td>Germination traits<br>Antioxidant activities<br>Gene expression</td><td>Khan and Gupta (2018)</td></tr><tr><td>Oryza sativa</td><td>SiO<sub>2</sub></td><td>Priming</td><td>350 mg L<sup>-1</sup></td><td>PEG</td><td>-0.9 Mpa</td><td>Germination traits<br>Antioxidant activities<br>Membrane stability</td><td>Gana Ali et al. (2021)</td></tr><tr><td>Phaseolus vulgaris</td><td>nano-Si</td><td>Soaking</td><td>300 mg L<sup>-1</sup></td><td>Na<sup>+</sup></td><td>1-5 g L<sup>-1</sup></td><td>Germination traits<br>Nutrient homeostasis</td><td>Alsaeedi et al. (2017)</td></tr></tbody></table>
<table><thead><tr><th></th><th></th><th></th><th></th><th></th><th></th><th></th><th></th></tr></thead><tbody><tr><td>Phyllostachys edulis</td><td>nano-Si</td><td>Soaking</td><td>200 µM</td><td>Cd</td><td>100 µM</td><td>Germination traits</td><td>Emamverdian et al. (2021)</td></tr><tr><td>Solanum lycopersicum</td><td>Na<sub>2</sub>SiO<sub>3</sub></td><td>Soaking</td><td>0.5 mM</td><td>PEG</td><td>10%</td><td>Germination traits<br>Antioxidant activities<br>ROS detoxification<br>Membrane integrity</td><td>Shi et al. (2014)</td></tr><tr><td>Solanum lycopersicum</td><td>nano-Si</td><td>Soaking</td><td>0.5-3 mM</td><td>NaCl</td><td>150-200 mM</td><td>Germination traits<br>Gene expression</td><td>Almutairi (2016)</td></tr><tr><td>Trigonella foenum-graecum</td><td>CaSiO<sub>3</sub></td><td>Soaking</td><td>3 mM</td><td>NaCl</td><td>200 mM</td><td>Germination traits<br>Reserve mobilization<br>Embryo viability<br>Antioxidant activities<br>ROS detoxification<br>Membrane integrity<br>Compatible osmolytes<br>K<sup>+</sup>/Na<sup>+</sup> ratio</td><td>Lamsaadi et al. (2022)</td></tr><tr><td>Triticum aestivum</td><td>K<sub>2</sub>SiO<sub>3</sub></td><td>Priming</td><td>1.5 mM</td><td>NaCl</td><td>up to 20 dS m<sup>-1</sup></td><td>Germination traits</td><td>Feghhenabi et al. (2020)</td></tr><tr><td>Triticum turgidum</td><td>Na<sub>2</sub>SiO<sub>3</sub></td><td>Priming</td><td>15-20 mg L<sup>-1</sup></td><td>PEG</td><td>150 g L-1</td><td>Germination traits</td><td>Ayed et al. (2021)</td></tr><tr><td>Zea mays</td><td>Na<sub>2</sub>SiO<sub>3</sub></td><td>Soaking</td><td>2 mM</td><td>NaCl</td><td>75 mM</td><td>Germination traits<br>Phytohormones<br>Reserve mobilization</td><td>Delavar et al. (2017)</td></tr><tr><td>Zea mays</td><td>Na<sub>2</sub>SiO<sub>3</sub></td><td>Soaking</td><td>2 mM</td><td>Al</td><td>10 mM</td><td>Germination traits<br>Phytohormones<br>Reserve mobilization</td><td>Delavar et al. (2017)</td></tr><tr><td>Zea mays</td><td>nano-Si</td><td>Priming</td><td>10 mg L<sup>-1</sup></td><td>NaCl</td><td>150 mM</td><td>Germination traits<br>Embryo respiration<br>Reserve mobilization<br>Antioxidant activities<br>Phytohormones<br>Membrane integrity<br>ROS detoxification</td><td>Naguib and Abdalla (2019)</td></tr></tbody></table>

MPWE: Melon plant water extract; PEG: Polyethylene glycol; 3-PPA: 3-phenyl-propionic acid
241 **Si treatment enhances seed reserve mobilization under abiotic stress**

242 Si application improves the germination of seeds under abiotic stress conditions by modulating reserve mobilization (Fig. 2). For example, in drought-stressed germinating seeds of *Eleusine coracana*, Mundada et al. (2021) recently found that Si increased the breakdown of glucose to acetyl CoA via pyruvate, which was diverted to lipid biosynthesis instead of the tricarboxylic acid cycle. This is good evidence that Si has a role in lipid metabolism. Additionally, Si augmented the activity of α-amylase, β-amylase, and α-glucosidase in osmotically stressed seeds of *L. culinaris* (Biju et al. 2017). Similar findings were reported in *C. sativus* (Ning et al. 2020). In wheat, seed priming with Si nanoparticles increased amylase activity under drought stress (Rai-Kalal et al. 2021). Similarly, in *C. sativus* under salt stress, application of 0.3 mM sodium silicate alleviated the negative effects of 200 mM NaCl and significantly increased α-amylase activity (Gou et al. 2020). Recently, Lamsaadi et al. (2022) observed that the enhanced seed germination rate of Si-treated *Trigonella foenum-graecum* seeds under salt stress was due to better reserve mobilization and embryo viability. Seed priming with nano-silica improved embryo respiration by increasing aldolase and isocitrate lyase activities (Naguib and Abdalla 2019). Under Al stress, the activity of amylase was 45% higher in Al-stressed seed with NaSiO₃ compared to Al-stressed seed without the addition of Si (Delavar et al. 2017). In a study of *C. melo* seeds, the application of Si increased α-, β- and total-amylase activities under autotoxicity stress (Zhang et al., 2020). The same was observed under 3-phenylpropionic acid induced stress in *C. sativus*, where Si supplementation improved α-, β- and total-amylase activities, and finally seed germination (Bu et al. 2018). Exogenous Si may therefore alleviate the negative effects of abiotic stresses on seed germination by promoting reserve mobilization, but more detailed studies, including testing for embryo viability and monitoring gene expression and the activity of other enzymes related to reserve mobilization, are required.

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<figure><img src="image_3.png" /><figcaption>Fig. 2 Proposed effects of Si on seed reserve mobilization during seed germination under abiotic stresses. TAG, triacylglycerol</figcaption></figure>

282 **Exogenous Si mediates seed germination by modulating phytohormone balance**

283 The effects of Si on phytohormone synthesis in stressed plants during vegetative growth have been reviewed by El Moukhtari et al. (2021) and Rizwan et al. (2015). Only a few reports show a link between Si treatment and plant hormone metabolism during seed germination (Fig. 3). A recent study demonstrated that seed priming with nano-silica increased *Z. mays* seed germination under 150 mM NaCl stress, and this was correlated with a higher GA/ABA ratio (Naguib and Abdalla 2019). The authors also revealed that changes in hormone metabolism were
sufficient to explain the effect of Si on seed germination, particularly under unfavorable conditions. Another interesting study demonstrated that under 75 mM NaCl or 10 mM Al stress, *Z. mays* seeds that were soaked in 2 mM Na₂SiO₃ solution contained more GA and less ABA compared to the control, leading to a higher germination rate (Delavar et al. 2017). According to Gou et al. (2020), the increased GA in NaCl-treated *C. sativus* treated with Si was the result of downregulated expression of GA catabolism gene *GA2ox*, while the decreased ABA was the result of downregulated expression of ABA anabolism genes such as *NCED1* and *NCED2*. The combined effect was to raise the GA/ABA ratio to the level needed for dormancy release and germination. In PEG-stressed seeds of *E. coracana*, the application of Si modulates jasmonic acid (JA) synthesis during germination, especially under stressed conditions (Mundada et al. 2021). These results provide evidence that Si is effective in improving seed germination through the modulation of GA, ABA, and JA metabolism. Further investigations are necessary to understand the mode of action of Si and any signaling crosstalk in modulating phytohormones in seeds during abiotic stress.

<figure><img src="image_4.png" /><figcaption>Fig. 3 Proposed effects of exogenous Si application on phytohormone balance during seed germination under abiotic stresses. *NCED*, nine-cis-Epoxycarotenoid dioxygenases; *GA2ox*, Gibberellin 2-oxidases; GA, gibberellic acid; ABA, abscisic acid</figcaption></figure>

**Si enhances antioxidant machinery and improves integrity, functionality, and stability of membranes during seed germination**

During environmental stresses, the generation of ROS is enhanced (Nadarajah 2020). At high levels, ROS causes proteins, lipids, and nucleic acid peroxidation, hence causing cell damage and death (Hasanuzzaman et al. 2020). Maintaining membrane integrity and functionality during environmental change is a challenge for sessile plants (Rogowska and Szakiel 2020). Antioxidative defense systems, including both enzymatic and non-enzymatic antioxidants, play a major role preventing ROS build-up in cells (Kasote et al. 2015). Si has been reported to lower ROS activity and restore damaged plant membranes during seed germination by enhancing the antioxidant system (Debona et al. 2017; Mostofa et al. 2021). In drought-stressed *S. lycopersicum* (Shi et al. 2014) and *L. culinaris* (Biju et al. 2017), Na₂SiO₃ increased the activity of ascorbate peroxidase (APX), peroxidase (POX), catalase (CAT), and superoxide dismutase (SOD), consequently decreasing how much H₂O₂, O₂⁻, and malondialdehyde were generated, with less lipid peroxidation as a result. Parallel evidence using the Evans Blue method is that under 200 mM NaCl *C. sativus* seed membrane integrity was improved by Si-treatment (Gou et al. 2020). The latter effect was linked to the ability of Si to limit ROS generation by modulating the activity of SOD, POX, CAT and APX. Likewise, *Trigonella foenum graecum* seeds supplied with 3 mM CaSiO₃ and exposed to 200 mM NaCl
solution showed increased SOD and polyphenol oxidase (PPO) activities, and a greater content of total polyphenol, flavonoids, glycine betaine and proline, while displaying lowered levels of H₂O₂, O₂⁻, MDA and electrolyte leakage (Lamsaadi et al. 2022). Similar findings were reported by Naguib and Abdalla (2019), who showed that the decreases in both lipid peroxidation and ROS accumulation in salt-stressed *Z. mays* seeds were associated with the higher activities of SOD, POX, and PPO in response to nano-silica applied as a priming agent. Again as a priming agent, Si stimulated the activities of antioxidant enzymes, particularly CAT, decreasing lipid peroxidation in Cd-stressed lettuce seeds (Pereira et al. 2021). Si supplementation to *C. melo* seeds triggered an increased SOD, CAT and POD activities and a reduced MDA content under autotoxicity stress (Zhang et al. 2020). It is clear from the above studies that Si improves seed germination under multiple abiotic constraints by enhancing enzymatic and non-enzymatic antioxidant activities and thus maintaining the integrity and stability of membranes. Currently studies related to the molecular mechanisms and the metabolic pathways of Si-mediated stress tolerance are still limited.

## Si modulates gene expression during seed germination

The complex process of seed germination is governed by the expression of specific sets of genes (Rajjou et al. 2012). Si has been reported to regulate transcript levels of various abiotic stress-related genes during seed germination. The example of 0.3 mM Na₂SiO₃ downregulating the expression of *NCED1* and *NCED2* encoding nine-cis-epoxycarotenoid dioxygenases involved in ABA synthesis and *GA2ox* encoding gibberellin 2-oxidase, which deactivates bioactive Gas, was already cited (Gou et al. 2020). In another case, as ABA is known to activate *Mitogen-activated protein kinase (MAPK)* expression, which are genes involved in signal transduction pathways (Lu et al. 2002), the lower levels of ABA due to Si treatment (Delavar et al. 2017) may be the reason *MAPK2* and *MAPK3* are downregulated in Si-treated salt-stressed *S. lycopersicum* (Almutairi 2016). ABA was also shown to regulate the expression of *Ethylene response factor (ERF)*, a key transcription factor in abiotic stress signaling (Müller and Munné-Bosch 2015). In *S. lycopersicum*, the application of Si downregulates the expression of *Ethylene response factor 5 (ERF5)*, and this was associated with lower levels of ABA (Almutairi 2016). Moreover, *ERF* controls *Respiratory burst oxidase (RBOH)* (Yao et al. 2017), and the reduction of *ERF5* expression in salt-stressed *S. lycopersicum* in response to Si treatment downregulates *RBOH1* (Almutairi 2016).

The accumulation of compatible osmolytes, including proline, is one of the most common strategies to overcome adverse environmental conditions (El Moukhtari et al. 2020). This response is mediated by several genes, including *delta-1-Pyrroline5-carboxylate synthetase (P5CS)* involved in proline biosynthesis (Szabadoz and Savouré 2010). In a study by Almutairi (2016), the application of Si increased the expression of *P5CS* in *S. lycopersicum* during NaCl-induced salinity stress. This suggests that Si may be involved in mediating osmotic adjustment in germinating seeds during osmotic stress. Another mechanism of plant resistance to salt stress is to decrease Na⁺ uptake and accumulation (Bargaz et al. 2015) through the action of the *Na⁺/H⁺* antiporters of the plasma membrane (Rizwan et al. 2015). To investigate how Si controls Na⁺ uptake by the seeds, Almutairi (2016) studied the effect of Si on the expressions of *Na⁺/H⁺* antiporter 6 (*NHX6*) in salt-stressed seeds of *S. lycopersicum*. The results showed that Si under salt stress up-regulated this gene expression, preventing Na⁺ uptake by the seeds. Abscisic Acid-Responsive Element-Binding Protein (AREB) is required for the establishment of *Arabidopsis* seedlings (Sharma et al. 2011). During salinity stress, Si-treatment upregulated AREB expression in *S. lycopersicum* as compared to controls (Almutairi 2016). Acid phosphatase and esterases belonging to a group of
hydrolytic enzymes that catalyze the hydrolysis of the seed reserve are required for the germination process (Kantharaju and Murth 2014; Senna et al. 2006). In Cd-stressed lettuce, the use of Si as a priming agent triggered the expression of genes associated with esterase and acid phosphatase (Pereira et al. 2021). The upregulation of *Low silicon 2* (*OsLSi2*) and *OsLSi6* genes and the downregulation of the *OsLSi1* gene, which all encode Si-transporters, were reported in *O. sativa* supplemented with Si under 150 µM As stress (Khan and Gupta 2018). These findings indicate that *O. sativa* seeds may take Si up from the soil via OsLsi2 and/or OsLSi6 transporters. Moreover, seven days after rice seed imbibition, Si upregulated the expression of genes encoding Nitrate reductase (NR), Nitrite reductase (NiR), Glutamine synthetase (GS), Glutamate synthase (GOGAT), high affinity Nitrate transporter protein (NRT2), high affinity Ammonium transporter protein (AMT1), high affinity Phosphate transporters 1 and 2 (*PHT1*, *PHT2*), Acid phosphatases (*APase*), Potassium channel protein (*KAT1*) and Potassium transporter protein (*HAK10*) during As induced stress (Khan and Gupta 2018). In *C. sativus*, expression of *AMY* and *BMY* genes encoding α-amylase and β-amylase, respectively, were upregulated after 36h of stress from 10% PEG in the presence of Si, indicating that Si contributes to reserve mobilization of the embryo (Ning et al. 2020). In line with this, the positive effects of 2 mM Si on *C. sativus* under toxicity induced by 2 mM 3-phenylpropionic acid were attributed to the higher *AMY* and *BMY* transcript levels (Bu et al. 2018).

## Si uptake by germinating seeds

Si has been reported to be taken up by plants in three different modes: active, passive, and rejective (Rizwan et al. 2015; Zhu and Gong 2014). Si assimilation by plants from soil was reported to be facilitated by the specialized Si-transporters Lsi1 and Lsi2 (Coskun et al. 2021). *Lsi1* was first discovered in *O. sativa* by Ma et al. (2006), where the suppression of its expression resulted in less Si uptake. Soon after another gene named *Lsi2* was identified in a rice mutant which accumulates less Si than the wild type and does not display any deleterious symptoms when grown in the presence of germanium, a toxic analog of Si (Ma et al. 2007). Other Si transporters, Lsi3 and Lsi6, have since been documented (Ahire et al. 2021). Most of the studies have investigated the uptake of Si by plants during vegetative stages, showing particularly that Si transporters are localized in roots. However, there is little information on the presence and role of functional Si-transporters in seeds. Strong evidence comes from a report by Khan and Gupta (2018) who demonstrated that Si supplementation to *O. sativa* seeds germinating under As stress upregulated the expression of *Lsi1*, *Lsi2* together and *Lsi6* (analog to *Lsi1*). These findings indicate that seeds express Si-transporter genes potentially allowing Si uptake.

## Investigation of Si application for improvement of seed germination

Numerous reports have documented a beneficial effect of Si on seed germination of several plant species, particularly under unfavorable conditions (Ayed et al. 2021; Pereira et al. 2021; Sun et al. 2021). Si has the potential to induce various physiological changes inside seeds, but the effects on seed germination may depend on how Si is applied. To date, the most widespread method is to soak seeds in a solution with an optimal concentration of Si (Haghighi et al. 2012; Zhang et al. 2020). For example, the germination percentage of *L. culinus* seeds under 18% PEG stress was higher if they were soaked in 2 mM Na₂SiO₃ (Biju et al. 2017). The authors suggested that the induction of seed reserve mobilization mediated the improved seed germination. Under salinity stress, the improved germination percentage observed for *G. uralensis* seeds soaked in low Si concentrations was mediated by better membrane integrity and antioxidant systems (Zhang et al. 2015). Soaking *C. sativus* seeds in 0.3 mM
NaSiO₃ increased seed germination under 200 mM NaCl by triggering the expression of some genes related to dormancy release and seed germination (Gou et al., 2020). Soaking seeds with Si was also reported to increase seed germination by modulating plant hormone metabolism, especially ABA and GA (Delavar et al. 2017).

Priming seeds with Si is another method (Khan and Gupta 2018) that is widely used to synchronize the germination of individual seeds in a population, resulting in enhanced, faster, and more vigorous germination (Marthandan et al. 2020; Sharma et al. 2014). With this method, Si generally enhances the metabolic processes in the seed, which makes it efficient in responding more quickly to abiotic stress (Abdel Latef and Tran 2016; Hameed et al. 2013). For example, *Triticum turgidum* seeds primed with sodium metasilicates showed improved germination parameters, including germination percentage, germination index, and seedling vigor index under drought stress compared to unprimed seeds (Ayed et al. 2021). Consistent with this, Alves et al. (2020) observed that seed priming with 0.05 mM Ca₂SiO₄ increased the germination percentage and germination rate index of *Lactuca sativa* exposed to 50 mM salinity stress. According to Pereira et al. (2021), Si priming affects seed metabolism at both physiological and molecular levels. The authors demonstrated that primed seeds showed an improved antioxidant response and upregulation of stress alleviation genes. The positive impact of seed priming with Si was also reported in *O. sativa* under As stress (Khan and Gupta 2018).

Si has also been used as a coating agent (Rufino et al. 2017). This method is generally used to protect seeds against biotic stress (Pedrini et al. 2017). For example, Nguyen et al. (2016) showed that coating soybean seeds with Ag/SiO₂ nano-composites provided antifungal activity against *Fusarium oxysporium* and *Rhizoctonia solani*. The authors also showed that seed coating with Si was able to increase soybean seed germination to 100% in the presence of *F. oxysporium* and to between 98% to 100% in the presence of *R. solani*. Additionally, under normal non-stressed conditions, Corlett et al. (2014) demonstrated that Si-coated barley seeds exhibited a greater emergence speed index than that of the non-coated control without affecting the physiological quality of the seed. The authors hypothesized that seed coating with Si would be a promising way to protect barley seeds against pathogens without affecting the rate of seedling emergence nor the physiological quality of the seed. When seeds of *Z. mays* were coated with 20 mg H₂SiO₃ kg⁻¹, the established plants showed better growth and yield in terms of plant height, cob length and diameter, thousand-grain weight, and grain yield, more photosynthetic pigments, and enhanced enzymatic and non-enzymatic antioxidant activities under 120 mM NaCl stress compared to those from uncoated seeds (ur Rehman et al. 2020).

## Conclusions and perspectives

In this review, we intended to bring together evidence of how Si mediates seed germination under abiotic stresses. The literature shows that the application of Si improves seed germination, reduces germination time, and synchronizes germination under abiotic stressors. Si likely ameliorates seed germination under abiotic stresses through different modes of action, passing by ion and water uptake, reserve mobilization, phytohormone balance, reduction in oxidative stress by enhancing the activities of antioxidant defense system, and upregulation of gene expression (Fig. 4).

Previous investigations showed that Si is beneficial to plant abiotic stress tolerance (Debona et al. 2017; El Moukhtari et al. 2021; Rizwan et al. 2015), but the mechanisms of Si action are still unclear. Some authors hypothesized that Si can protect plant by forming a mechanical barrier (Coskun et al. 2019). Others suggested that soluble Si can be taken up by the roots and act as a secondary messenger to modulate defense responses (Coskun
et al. 2019; Fauteux et al. 2005; Van Bockhaven et al. 2013). However, these hypotheses assume plants absorb Si from the soil solution. In roots, Si is taken up from the soil solution by an influx transporter encoded by *Lsi1* (for review see Ma and Yamaji 2015). However, to date, little is known about active Si transporters in seeds. Therefore, more studies are needed to identify and characterize Si transporter activity in seeds to understand better the mechanisms underlying the role of Si during seed germination.

Seed germination is a complex process governed by the expression of specific sets of genes (Rajjou et al. 2012). Several works have shown that Si has amazing beneficial effects on seed germination under various abiotic stresses (Biju et al. 2017; Delavar et al. 2017; Lamsaadi et al. 2022). How Si treatment works in reducing the detrimental effect of abiotic stress during seed germination is, however, still not well understood and further researches are needed. Transcriptomic, proteomic and metabolomic analyses have been widely applied to explore mechanisms involved in plant adaptation to abiotic stresses (Hao et al. 2021). These approaches will be essential to identify targets of Si. This is a prerequisite to potentially manipulate genes in order to improve plant tolerance to adverse environmental conditions and at different developmental stages, including germination. Therefore, new studies are required to identify and characterize molecular mechanisms involved in Si perception by cells to trigger better germination and development under adverse conditions.

Several studies showed the beneficial concentration-dependent effects of various compounds of Si, including CaSiO₃, NaSiO₃, K₂SiO₃, and silicon nanoparticles, on seed germination (El Moukhtari et al. 2021; Rizwan et al. 2015; Siddiqui et al. 2020). However, according to Voogt and Sonneveld (2001), silicate salts, like NaSiO₃ and K₂SiO₃, used as sources of Si in growth media, are highly alkaline and if not carefully handled, may cause precipitation issues. Furthermore, many authors have reported that plants absorb Si from soil or nutrient solutions only in the form of Si(OH)₄ (Coskun et al. 2019). Therefore, it would be interesting to conduct more studies using different Si forms at varying doses to determine the optimal Si form and concentration that farmers could use to improve seed germination under abiotic stress.

In summary, the application of Si is a promising strategy to improve seed germination under abiotic stresses, but more specific research is needed in different crop species to show how Si acts in diverse agricultural contexts with optimal modes of application.
<figure><img src="image_5.png" /><figcaption>**Fig. 4** Schematic summarizing the modes of action of silicon during seed germination under different abiotic stresses. Silicon upregulates hydrolytic enzyme activities, modulates phytohormone homeostasis, enhances ion and water uptake, induces antioxidant enzyme activities and improves membrane integrity, and upregulates the expression of abiotic stress tolerance genes. GA, gibberellic acid; ABA, abscisic acid</figcaption></figure>

**Statements and Declarations**

**Author Contributions**

Conceptualization: A.E.M and A.S.; Literature review: A.E.M.; Original draft: A.E.M. and M.K.; Review editing: A.S., M.F., C.C., C.A., and W.Z.; Funding acquisition: A.S., M.F., and C.A.; Supervision: A.S. and M.F.; All authors read and approved the final manuscript.

**Competing Interests**

The authors declare that the research was conducted without any commercial or financial relationships that could be construed as a potential conflict of interest.
499 References

500 Abdel Latef AA, Tran L-SP (2016) Impacts of priming with silicon on the growth and tolerance of maize plants to alkaline stress. Front Plant Sci 7:243. https://doi.org/10.3389/FPLS.2016.00243

501 Ahire M, Mundada P, Nikam T, Bapat V, Suprasanna P (2021) Multifaceted roles of silicon in mitigating environmental stresses in plants. Plant Physiol Biochem 169:291-310. https://doi.org/10.1016/j.plaphy.2021.11.010

502 Ahsan N, Lee SH, Lee DG, Lee H, Lee SW, Bahk JD, Lee BH (2007) Physiological and protein profiles alternation of germinating rice seedlings exposed to acute cadmium toxicity. C R Biol 330:735-746. https://doi.org/10.1016/j.CRVI.2007.08.001

503 Ali B, Deng X, Hu X, Gill RA, Ali S, Wang S, Zhou W (2015) Deteriorative effects of cadmium stress on antioxidant system and cellular structure in germinating seeds of Brassica napus L. J Agr Sci Tech 17: 63-74

504 Ali AS, Elozeiri AA (2017) Metabolic processes during seed germination. In: Advances in Seed Biology. pp 141-166

505 Ali LG, Nulit R, İbrahim MH, Yien CYS (2020) Enhancement of germination and early seedling growth of rice (Oryza sativa) var. FARO44 by seed priming under normal and drought stressed conditions. J Plant Nutr 43:1579-1593. https://doi.org/10.1080/01904167.2020.1739298

506 Almutairi ZM (2016) Effect of nano-silicon application on the expression of salt tolerance genes in germinating tomato (Solanum lycopersicum L.) seedlings under salt stress. Plant Omics 9:106-114

507 Alsaeedi AH, El-Ramady H, Alshaal T, El-Garawani M, Elhawat N, Almohsen M (2017) Engineered silica nanoparticles alleviate the detrimental effects of Na⁺ stress on germination and growth of common bean (Phaseolus vulgaris). Environ Sci Pollut Res 24:21917-21928. https://doi.org/10.1007/s11356-017-9847-y

508 Alves R de C, Nicolau MCM, Checchio MV, Sousa Junior GS, de Oliveira FA, Prado RM, Gratão PL (2020) Salt stress alleviation by seed priming with silicon in lettuce seedlings: An approach based on enhancing antioxidant responses. Bragantia 79:19-29. https://doi.org/10.1590/1678-4499.20190360

509 Aniat-ul-Haq R, Agnihotri R (2010) Effect of osmotic stress (PEG) on germination and seedling survival of lentil (Lens culinaris Medik.). Res J Agric Sci 1:201-204

510 Arif Y, Singh P, Bajguz A, Alam P, Hayat S (2021) Silicon mediated abiotic stress tolerance in plants using physio-biochemical, omic approach and cross-talk with phytohormones. Plant Physiol Biochem 166:278-289. https://doi.org/10.1016/j.PLAPHY.2021.06.002

511 Ashraf MY, Afaf R, Qureshi MS, Sarwar G, Naqvi MH (2002) Salinity induced changes in α-amylase and protease activities and associated metabolism in cotton varieties during germination and early seedling growth stages. Acta Physiol Plant 24: 37-44. https://doi.org/10.1007/s11738-002-0019-3

512 Atici Ö, Ağar G, Battal P (2005) Changes in phytohormone contents in chickpea seeds germinating under lead or zinc stress. Biol Plant 49:215-222. https://doi.org/10.1007/s10535-005-5222-9

513 Aydinalp C, Marinova S (2009) The effects of heavy metals on seed germination and plant growth on alfalfa plant (Medicago sativa). Bulg J Agric Sci 15:347-350

514 Ayed S, Othmani A, Bouhaouel I, Rasâa N, Othmani S, Amara HS (2021) Effect of silicon (Si) seed priming on germination and effectiveness of its foliar supplies on durum wheat (Triticum turgidum L. ssp. durum) genotypes under semi-arid environment. Silicon 1-11. https://doi.org/10.1007/s12633-021-00963-2

515 Azeem M, Iqbal N, Kausar S, Javed MT, Akram MS, Sajid MA (2015) Efficacy of silicon priming and fertigation to modulate seedling's vigor and ion homeostasis of wheat (Triticum aestivum L.) under saline environment. Environ Sci Pollut Res 22:14367-14371. https://doi.org/10.1007/S11356-015-4983-8

516 Bai Y, Xiao S, Zhang Z, Zhang Y, Sun H, Zhang K, Wang X, Bai Z, Li C, Liu L (2020) Melatonin improves the germination rate of cotton seeds under drought stress by opening pores in the seed coat. PeerJ 8: e9450. https://doi.org/10.7717/peerj.9450

517 Bailly C (2004) Active oxygen species and antioxidants in seed biology. Seed Sci Res 14:93-107. https://doi.org/10.1079/SSR2004159

518 Bailly C (2019) The signalling role of ROS in the regulation of seed germination and dormancy. Biochem J 476:3019-3032. https://doi.org/10.1042/BCJ20190159

519 Balestrazzi A, Confalonieri M, Macovei A, Carbonera D (2011) Seed imbibition in *Medicago truncatula* Gaertn.: Expression profiles of DNA repair genes in relation to PEG-mediated stress. J Plant Physiol 168:706-713. https://doi.org/10.1016/j.JPLPH.2010.10.008

520 Barati M, Majidi MM, Mirlohi A, Pirnajmodini F, Sharif-Moghaddam N (2015) Response of cultivated and wild Barley germplasm to drought stress at different developmental stages. Crop Sci 55:2668-2681. https://doi.org/10.2135/cropsci2015.04.0229

521 Bargaz A, Zaman-Allah M, Farissi M, Lazali M, Drevon JJ, Maougal RT, Georg C (2015) Physiological and molecular aspects of tolerance to environmental constraints in grain and forage legumes. Int J Mol Sci 16: 18976-19008. https://doi.org/10.3390/ijms160818976

522 Baskin JM, Baskin CC (2004) A classification system for seed dormancy. Seed Sci Res 14:1-16.
559 https://doi.org/10.1079/ssr2003150

560 Bewley JD (2001) Seed germination and reserve mobilization. *Encycl Life Sci* 1–7.

561 https://doi.org/10.1038/npg.els.0002047

562 BiaŁcka B, Kępczyński J (2009) Effect of ethephon and gibberellin A3 on *Amaranthus caudatus* seed germination and alpha-and beta-amylase activity under salinity stress. *Acta Biol Cracoviensia Ser Bot* 2:119–125

565 Biju S, Fuentes S, Gupta D (2017) Silicon improves seed germination and alleviates drought stress in lentil crops by regulating osmolytes, hydrolytic enzymes and antioxidant defense system. *Plant Physiol Biochem* 119:250–264. https://doi.org/10.1016/j.PLAPHY.2017.09.001

568 Boesewinkel F, Bouman F (1984) Embryology of angiosperms. In: Media. SS& B (ed) Embryology of angiosperms

570 Bradford KJ (2017) Water relations in seed germination. *Seed Dev Germination* 351–396.

571 https://doi.org/10.1201/9780203740071-13

572 Bu R, Xiao X, Liao W, Hu Y, Li J, Lv J, Wang R, Xie J (2018) Exogenous Si alleviation of autotoxicity in cucumber (*Cucumis sativus* L.) seed germination is correlated with changes in carbohydrate metabolism. *J Plant Growth Regul* 37:784–793. https://doi.org/10.1007/s00344-017-9773-8

575 Calone R, Sanoubar R, Noli E, Barbanti L (2020) Assessing *Salicornia europaea* tolerance to salinity at seed germination stage. *Agriculture* 10:29. https://doi.org/10.3390/AGRICULTURE10020029

577 Campos H, Trejo C, Pena-Validiva CB, Gracia-Nava R, Conde-Martinez VF, Cruz-Ortega R (2020) Water availability effects on germination, membrane stability and initial root growth of *Agave lechuguilla* and *A. salmiana*. *flora* 268:151606. https://doi.org/10.1016/j.flora.2020.151606

580 Cardoso AÁ, Euclydes De Lima E Borges E, Aparecida De Souza G, Jovelina Da Silva C, Maria De Oliveira Pires R, Fernandes DC, Dias S (2015) Seed imbibition and germination of *Plathymenia reticulata* Benth. (Fabaceae) affected by mercury: Possible role of aquaporins. *Acta Bot Brasilica* 29:285–291. https://doi.org/10.1590/0102-33062014abb0038

584 Carles C, Bies-Etheve N, Aspart L, Léon-Kloosterziel KM, Koornneef M, Echeverria M, Delseny M (2002) Regulation of Arabidopsis thaliana Em genes: role of ABI5. *Plant J* 30: 373-383. https://doi.org/10.1046/j.1365-313X.2002.01295.x

587 Chen L, Lu B, Liu L, Duan W, Jiang D, Li J, Zhang K, Sun H, Zhang Y, Li C, Bai Z (2021) Melatonin promotes seed germination under salt stress by regulating ABA and GA3 in cotton (*Gossypium hirsutum* L.). *Plant Physiol Biochem* 162: 506-516. https://doi.org/10.1016/j.plaphy.2021.03.029

590 Cokkizgin A, Cokkizgin H (2010) Effects of lead (PbCl2) stress on germination of lentil (*Lens culinaris* Medic.) lines. *African J Biotechnol* 9:8608–8612. https://doi.org/10.4314/ajb.v9i50.

592 Corlett FMF, Rufino C de A, Vieira JF, Tavares LC, Tunes LVM, Barros ACSA (2014) The influence of seed coating on the vigor and early seedling growth of barley. *Cienc e Investig Agrar* 41:129–135. https://doi.org/10.4067/S0718-16202014000100013

595 Coskun D, Deshmukh R, Shivaraj S, Isenring P, Bélanger R (2021) Lsi2: A black box in plant silicon transport. *Plant Soil* 466:1–20. https://doi.org/10.1007/s11104-021-05061-1

597 Coskun D, Deshmukh R, Sonah H, Menzies JG, Reynolds O, Ma JF, Kronzucker HJ, Bélanger RR (2019) The controversies of silicon's role in plant biology. *New Phytol* 221:67–85. https://doi.org/10.1111/nph.15343

599 Daniels MJ, Mirkov TE, Chrispeels MJ (1994) The plasma membrane of *Arabidopsis thaliana* contains a mercury-insensitive aquaporin that is a homolog of the tonoplast water channel protein TIP. *Plant Physiol* 106:1325–1333. https://doi.org/10.1104/PP.106.4.1325

602 de Oliveira AB, Mendes Alencar NL, Gomes-Filho E (2013) Comparison between the water and salt stress effects on plant growth and development. *Responses Org to Water Stress*. https://doi.org/10.5772/54223

604 de Silva NDG, Boutin C, Lukina AO, Western TL, Molina I, Rowland O (2021) Seed coat suberin forms a barrier against chromium (Cr³⁺) during early seed germination in *Arabidopsis thaliana*. *Environ Exp Bot* 191: 104632. https://doi.org/10.1016/j.envexpbot.2021.104632

607 Debez A, Belghith I, Pich A, Taamalli W, Abdelly C, Braun HP (2018) High salinity impacts germination of the halophyte *Cakile maritima* but primes seeds for rapid germination upon stress release. *Physiol Plant* 164:134–144. https://doi.org/10.1111/ppl.12679

610 Debez A, Ben Hamed K, Grignon C, Abdelly C (2004) Salinity effects on germination, growth, and seed production of the halophyte *Cakile maritima*. *Plant Soil* 262:179–189. https://doi.org/10.1023/B:PLSO.0000037034.47247.67

613 Debona D, Rodrigues FA, Datnoff LE (2017) Silicon's role in abiotic and biotic plant stresses. *Annu Rev Plant Biol* 55:85–107. https://doi.org/10.1146/ANNUREV-PHYTO-080516-035312

615 Dehnavi AR, Zahedi M, Ludwiczak A, Perez SC, Piernik A (2020) Effect of salinity on seed germination and seedling development of sorghum (*Sorghum bicolor* (L.) Moench) genotypes. *Agronomy* 10:859. https://doi.org/10.3390/agronomy10060859

618 Delavar K, Ghanati F, Zare-Maivan H, Behmanesh M (2017) Effects of silicon on the growth of maize seedlings
619 under normal, aluminum, and salinity stress conditions. J Plant Nutr 40:1475-1484.

620 https://doi.org/10.1080/01904167.2016.1269344

621 El-Hendawy S, Elshafei A, Al-Suhaibani N, Alotabi M, Hassan W, Dewir YH, Abdella K (2019) Assessment of the salt tolerance of wheat genotypes during the germination stage based on germination ability parameters and associated SSR markers. J Plant Interact 14: 151-163. https://doi.org/10.1080/17429145.2019.1603406

622 El-Serafy R, El-Sheshtawy A, Atteya AKG, Al-Hashimi A, Abbasi AM, Al-Ashkar I (2021) Seed priming with silicon as a potential to increase salt stress tolerance in *Lathyrus odoratus*. Plants 10:2140. https://doi.org/10.3390/plants10102140

623 El Moukhtari A, Lamsaadi N, Oubenali A, Mouradi M, Savoure A, Farissi M (2021) Exogenous silicon application promotes tolerance of legumes and their N₂ fixing symbiosis to salt stress. Silicon 1-18. https://doi.org/10.1007/s12633-021-01466-w

624 El Moukhtari A, Cabassa-Hourton C, Farissi M, Savouré A (2020) How does proline treatment promote salt stress tolerance during crop plant development?. Front Plant Sci 11: 1127. https://doi.org/10.3389/fpls.2020.01127

625 El Rasafi T, Oukarroum A, Haddioui A, Song H, Kwon EE, Bolan N, Tack FMG, Sebastian A, Prasad MNV, Rinklebe J (2020) Cadmium stress in plants: A critical review of the effects, mechanisms, and tolerance strategies. Crit Rev Environ Sci Technol 1-52. https://doi.org/10.1080/10643389.2020.1835435

626 Emamverdian A, Ding Y, Mokhberdoran F, Ahmad Z, Xie Y (2021) The effect of silicon nanoparticles on the seed germination and seedling growth of moso bamboo (*Phyllostachys edulis*) under cadmium stress. Polish J Environ Stud 30:3033-3042. https://doi.org/10.15244/pjoes/129683

627 Espanany A, Fallah S, Tadayyon A (2015) The effect of halopriming and salicylic acid on the germination of fenugreek (*Trigonella foenum-graecum*) under different cadmium concentrations. Not Sci Biol 7: 322-329. https://doi.org/10.15835/nsb739563

628 Farissi M, Bouizgaren A, Faghire M, Bargaz A, Ghoulam C (2011) Agro-physiological responses of Moroccan alfalfa (*Medicago sativa* L.) populations to salt stress during germination and early seedling stages. Seed Sci Technol 39:389-401. https://doi.org/10.15258/SST.2011.39.2.11

629 Fauteux F, Rémus-Borel W, Menzies JG, Bélanger RR (2005) Silicon and plant disease resistance against pathogenic fungi. FEMS Microbiol Lett 249:1-6. https://doi.org/10.1016/j.femsle.2005.06.034

630 Feghhenabi F, Hadi H, Khodaverdiloo H, van Genuchten MT (2020) Seed priming alleviated salinity stress during germination and emergence of wheat (*Triticum aestivum* L.). Agric Water Manag 231:106022. https://doi.org/10.1016/J.AGWAT.2020.106022

631 Finch-Savage WE, Footitt S (2017) Seed dormancy cycling and the regulation of dormancy mechanisms to time germination in variable field environments. J Exp Bot 68:843-856. https://doi.org/10.1093/jxb/erw477

632 Finkelstein R, Reeves W, Ariizumi T, Steber C (2008) Molecular aspects of seed dormancy. Annu Rev Plant Biol 59:387-415. https://doi.org/10.1146/annurev.arplant.59.032607.092740

633 Galviz-Fajardo YC, Bortolin GS, Deuner S, Amarante LD, Reolon F, de Moraes DM (2020) Seed priming with salicylic acid potentiates water restriction- induced effects in tomato seed germination and early seedling growth. J Seed Sci 42:e202042031. https://doi.org/10.2135/1984.physiologicalbasis.c4

634 Gana Ali L, Nulit R, Hafiz Ibrahim M, Yong C (2021) Potassium nitrate and silicon dioxide priming improve germination, seedling growth and protective enzymes of rice var. FARO44 under drought. J Plant Nutr 1-14. https://doi.org/10.1080/01904167.2021.1921201

635 Ghavami N, Ramin AA (2007) Salinity and temperature effects on seed germination of milk thistle. Commun Soil Sci Plant Anal 38:2681-2691. https://doi.org/10.1080/00103620701662901

636 Gomes MP, Garcia QS (2013) Reactive oxygen species and seed germination. Biologia (Bratisl) 68:351-357. https://doi.org/10.2478/s11756-013-0161-y

637 Gonzalez-Mendoza D, Quiroz-Moreno A, Medrano REG, Grimaldo-Juarez O, Zapata-Perez O (2009) Cell viability and leakage of electrolytes in *Avicennia germinans* exposed to heavy metals. Zeitschrift fur Naturforsch - Sect C J Biosci 64:391-394. https://doi.org/10.1515/znc-2009-5-615

638 Gou T, Chen X, Han R, Liu J, Zhu Y, Gong H (2020) Silicon can improve seed germination and ameliorate oxidative damage of bud seedlings in cucumber under salt stress. Acta Physiol Plant 42:12. https://doi.org/10.1007/s11738-019-3007-6

639 Graeber K, Nakabayashi K, Miatton E, Leubner-Metzger G, Soppe WJJ (2012) Molecular mechanisms of seed dormancy. Plant, Cell Environ 35:1769-1786. https://doi.org/10.1111/j.1365-3040.2012.02542.x

640 Guilherme M de F de S, de Oliveira HM, da Silva E (2015) Cadmium toxicity on seed germination and seedling growth of wheat *Triticum aestivum*. Biol Sci 37:499-504. https://doi.org/10.4025/actascibiolsci.v37i4.28148

641 Guo Q, Wang Y, Zhang H, Qu G, Wang T, Sun Q, Liang D (2017) Alleviation of adverse effects of drought stress on wheat seed germination using atmospheric dielectric barrier discharge plasma treatment. Sci Rep 7:1-14. https://doi.org/10.1038/s41598-017-16944-8

642 Haghighi M, Afifipour Z, Mozafarian M (2012) The alleviation effect of silicon on seed germination and seedling growth of tomato under salinity stress. Veg Crop Res Bull 76:119-126. https://doi.org/10.2478/v10032-012-0008-z
679 Hameed A, Farooq T, Hameed A, Sheikh MA (2021) Sodium nitroprusside mediated priming memory invokes water-deficit stress acclimation in wheat plants through physio-biochemical alterations. Plant Physiol Biochem 160:329–340. https://doi.org/10.1016/J.PLAPHY.2021.01.037

680
681
682 Hameed A, Sheikh MA, Jamil A, Basra SMA (2013) Seed priming with sodium silicate enhances seed germination and seedling growth in wheat (*Triticum aestivum* L.) under water deficit stress induced by polyethylene glycol. Pakistan J Life Soc Sci 11:19–24

683
684
685 Han R, Gao G, Li Z, Dong Z, Guo Z (2017) Effects of exogenous 5-aminolevulinic acid on seed germination of alfalfa (*Medicago varia* Martyn.) under drought stress. Grassl Sci 46:100–107. https://doi.org/10.1111/grs.12189

686
687
688 Hao L, Shi S, Guo H, Zhang J, Li P, Feng Y (2021) Transcriptome analysis reveals differentially expressed MYB transcription factors associated with silicon response in wheat. Scientific reports 11:1-9. https://doi.org/10.1038/s41598-021-83912-8

691
692
693 Hasanuzzaman M, Bhuyan MHMB, Zulfiqar F, Raza A, Mohsin SM, Mahmud JA, Fujita M, Fotopoulos V (2020) Reactive oxygen species and antioxidant defense in plants under abiotic stress: Revisiting the crucial role of a universal defense regulator. Antioxidants 9:681. https://doi.org/10.3390/ANTIOX9080681

694
695
696
697 Hassan MJ, Geng W, Zeng W, Raza MA, Khan I, Iqbal MZ, Peng Y, Zhu Y, Li Z (2021) Diethyl aminoethyl hexanoate priming ameliorates seed germination via involvement in hormonal changes, osmotic adjustment, and dehydrins accumulation in white clover under drought stress. Front Plant Sci 12:709187. https://doi.org/10.3389/fpls.2021.709187

698
699
700 Hauvermale AL, Steber CM (2020) GA signaling is essential for the embryo-to-seedling transition during Arabidopsis seed germination, a ghost story. Plant Signal Behav 15: 1705028. https://doi.org/10.1080/15592324.2019.1705028

701
702
703 Hu K-D, Bai G-S, Li W-J, Yan H, Hu L-Y, Li Y-H, Zhang H (2015) Sulfur dioxide promotes germination and plays an antioxidant role in cadmium-stressed wheat seeds. Plant Growth Regul 75: 271–280. https://doi.org/10.1007/s10725-014-9951-7

704
705 Hubbard M, Germida J, Vujanovic V (2012) Fungal endophytes improve wheat seed germination under heat and drought stress. Botany 90:137–149. https://doi.org/10.1139/B11-091

706
707 Ibrahim EA (2016) Seed priming to alleviate salinity stress in germinating seeds. J Plant Physiol 192:38–46. https://doi.org/10.1016/J.JPLPH.2015.12.011

708
709
710 Infante-Izquierdo MD, Castillo JM, Grewell BJ, Nieva FJJ, Muñoz-Rodríguez AF (2019) Differential effects of increasing salinity on germination and seedling growth of native and exotic invasive cordgrasses. Plants 8:372. https://doi.org/10.3390/PLANTS8100372

711
712
713 Kalai T, Khamassi K, Teixeira da Silva JA, Gouia H, Bettaieb Ben-Kaab L (2014) Cadmium and copper stress affect seedling growth and enzymatic activities in germinating barley seeds. Arch Agron Soil Sci 60: 765–783. https://doi.org/10.1080/03650340.2013.838001

714
715 Kantharaju S, Murthy KS (2014) Characterization of esterases of *Tamarindus indica* seeds. J Biosci Med 2: 54-62. http://dx.doi.org/10.4236/jbm.2014.24009

716
717 Kasote DM, Katyare SS, Hegde M V, Bae H (2015) Significance of antioxidant potential of plants and its relevance to therapeutic applications. Int J Biol Sci 11:982–991. https://doi.org/10.7150/ijbs.12096

718
719
720 Khan E, Gupta M (2018) Arsenic–silicon priming of rice (*Oryza sativa* L.) seeds influence mineral nutrient uptake and biochemical responses through modulation of Lsi-1, Lsi-2, Lsi-6 and nutrient transporter genes. Sci Rep 8:10301. https://doi.org/10.1038/s41598-018-28712-3

721
722
723 Khan MN, Alamri S, Al-Amri AA, Alsubaie QD, Al-Munqedi B, Ali HM, Singh VP, Siddiqui MH (2020) Effect of nitric oxide on seed germination and seedling development of tomato under chromium toxicity. J Plant Growth Regul 1–13. https://doi.org/10.1007/s00344-020-10212-2

724
725
726 Kizilgeci F, Tazebay N, Namili M, Albayrak O, Yildirim M (2017) The drought effect on seed germination and seedling growth in bread wheat (*Triticum aestivum* L.). Int J Agric Environ Food Sci 1:33–37. https://doi.org/10.31015/jaefs.17005

727
728
729 Kong X, Luo Z, Zhang Y, Li W, Dong H (2017) Soaking in H₂O₂ regulates ABA biosynthesis and GA catabolism in germinating cotton seeds under salt stress. Acta Physiol Plant 39: 1-10. https://doi.org/10.1007/s11738-016-2299-z

730 Koornneef M, Bentsink L, Hilhorst H (2002) Seed dormancy and germination. Curr Opin Plant Biol 5:33–36. https://doi.org/10.5860/choice.26-5658

731
732 Kranner I, Colville L (2011) Metals and seeds: Biochemical and molecular implications and their significance for seed germination. Environ Exp Bot 72:93–105. https://doi.org/10.1016/j.envexpbot.2010.05.005

733
734 Kshetrimayum E, Sahoo DP, Mitra J, Kumar Panda S (2017) Regulation of seed germination and the role of aquaporins under abiotic stress. Int J Environ Agric Biotechnol 2:238710. https://doi.org/10.22161/ijeab/2.2.7

735
736 Lamhamdi M, Bakrim A, Aarab A, Lafont R, Sayah F (2011) Lead phytotoxicity on wheat (*Triticum aestivum* L.) seed germination and seedlings growth. C R Biol 334: 118–126. https://doi.org/10.1016/j.crvi.2010.12.006
739

Lamsaadi N, El Moukhtari A, Oubenali A, Farissi M (2022) Exogenous silicon improves salt tolerance of Fenugreek (*Trigonella foenum-graecum* L.) during seed germination and early seedling stages. *Biologia*.
https://doi.org/10.1007/s11756-022-01035-5

741

742

Lefèvre I, Marchal G, Corréal E, Zanuzzi A, Lutts S (2009) Variation in response to heavy metals during vegetative growth in *Dorycnium pentaphyllum* Scop. Plant Growth Regul 2009 591 59:1-11.
https://doi.org/10.1007/S10725-009-9382-Z

743

744

745

Lei K, Sun S, Zhong K, Li S, Hu H, Sun C, Zheng Q, Tian Z, Dai T, Sun J (2021) Seed soaking with melatonin promotes seed germination under chromium stress via enhancing reserve mobilization and antioxidant metabolism in wheat. *Ecotoxicol Environ Saf* 220: 112241. https://doi.org/10.1016/j.ecoenv.2021.112241

746

747

748

Li Q, Yang A, Zhang WH (2019) Higher endogenous bioactive gibberellins and α-amylase activity confer greater tolerance of rice seed germination to saline-alkaline stress. *Environ Exp Bot* 162: 357-363.
https://doi.org/10.1016/j.envexpbot.2019.03.015

749

750

751

Li W, Khan MA, Yamaguchi S, Kamiya Y (2005) Effects of heavy metals on seed germination and early seedling growth of *Arabidopsis thaliana*. Plant Growth Regul 46:45-50. https://doi.org/10.1007/s10725-005-6324-2

752

753

Li J, Zhao C, Zhang M, Yuan F, Chen M (2019) Exogenous melatonin improves seed germination in *Limonium bicolor* under salt stress. Plant Signal Behav 14: 1659705. https://doi.org/10.1080/15592324.2019.1659705

754

755

Liu L, Xia W, Li H, Zeng H, Wei B, Han S, Yin C (2018) Salinity inhibits rice seed germination by reducing α-amylase activity via decreased bioactive gibberellin content. *Front Plant Sci* 9:275.
https://doi.org/10.3389/FPLS.2018.00275

756

757

758

Liu J, Hasanuzzaman M, Wen H, Zhang J, Peng T, Sun H, Zhao Q (2019) High temperature and drought stress cause abscisic acid and reactive oxygen species accumulation and suppress seed germination growth in rice. *Protoplasma* 256: 1217-1227. https://doi.org/10.1016/j.scienta.2019.02.060

759

760

761

Llanes A, Andrade A, Masciarelli O, Alemano S, Luna V (2015) Drought and salinity alter endogenous hormonal profiles at the seed germination phase. *Seed Sci Res* 26:1-13. https://doi.org/10.1017/S0960258515000331

762

763

Lotfi N, Soleimani A, Vahdati K, Çakmakçı R (2019) Comprehensive biochemical insights into the seed germination of walnut under drought stress. *Sci Hortic* 250: 329-343

764

765

Lu C, Han MH, Guevara-Garcia A, Fedoroff NV (2002) Mitogen-activated protein kinase signaling in postgermination arrest of development by abscisic acid. *Proc Natl Acad Sci* 99: 15812-15817.
https://doi.org/10.1073/pnas.242607499

766

767

768

Luo X, Dai Y, Zheng C, Yang Y, Chen W, Wang Q, Chandrasekaran U, Du J, Liu W, Shu K (2021) The ABI4-Rbohd/VTC2 regulatory module promotes reactive oxygen species (ROS) accumulation to decrease seed germination under salinity stress. *New Phytol* 229: 950-962. https://doi.org/10.1111/nph.16921

769

770

771

Ma FJ, Yamaji N, Mitani N, Tamai K, Konishi S, Fujiwara T, Katsuhara M, Yano M (2007) An efflux transporter of silicon in rice. *Nature* 448:209-212. https://doi.org/10.1038/nature05964

772

773

Ma JF, Tamai K, Yamaji N, Mitani N, Konishi S, Katsuhara M, Ishiguro M, Murata Y, Yano M (2006) A silicon transporter in rice. *Nature* 440:688-691. https://doi.org/10.1038/nature04590

774

775

Ma JF, Yamaji N (2015) A cooperative system of silicon transport in plants. *Trends Plant Sci* 20:435-442. https://doi.org/10.1016/j.tplants.2015.04.007

776

777

Machado Neto NB, Saturnino SM, Bomfim DC, Custódio CC (2004) Water stress induced by mannitol and sodium chloride in soybean cultivars. *Braz Arch Biol Technol* 47: 521-529. http://dx.doi.org/10.1590/S1516-891320040000400004

778

779

780

Mahmood T, Islam KR, Muhammad S (2007) Toxic effects of heavy metals on early growth and tolerance of cereal crops. Pakistan J Bot 39:451-462

781

782

Marthandan V, Geetha R, Kumutha K, Renganathan VG, Karthikeyan A, Ramalingam J (2020) Seed priming: A feasible strategy to enhance drought tolerance in crop plants. *Int J Mol Sci* 21:8258. https://doi.org/10.3390/ijms21218258

783

784

785

Miransari M, Smith DL (2014) Plant hormones and seed germination. *Environ Exp Bot* 99:110-121. https://doi.org/10.1016/J.ENVEXPBOT.2013.11.005

786

787

Mohamed E, Kasem AMM, Farghali KA (2018) Seed germination of Egyptian *Pancratium maritimum* under salinity with regard to cytology, antioxidant and reserve mobilization enzymes, and seed anatomy. *Flora* 242:120-127. https://doi.org/10.1016/J.FLORA.2018.03.011

788

789

790

Mostofa MG, Rahman MM, Ansary MMU, Keya SS, Abdelrahman M, Miah MG, Phan Tran LS (2021) Silicon in mitigation of abiotic stress-induced oxidative damage in plants. *Crit Rev Biotechnol* 41:918-934. https://doi.org/10.1080/07388551.2021.1892582

791

792

793

Mridha D, Paul I, De A, Ray I, Das A, Joardar M, Chowdhury NR, Bhadoria PBS, Roychowdhury T (2021) Rice seed (IR64) priming with potassium humate for improvement of seed germination, seedling growth and antioxidant defense system under arsenic stress. *Ecotoxicol Environ Saf* 219:112313. https://doi.org/10.1016/J.ECOENV.2021.112313

794

795

796

797

Muhammad ZI, Maria KS, Mohammad A, Muhammad S, Zia-ur-Rehman F, Muhammad KABIR (2015) Effect of mercury on seed germination and seedling growth of Mungbean (*Vigna radiata* (L.) Wilczek). *J Appl Sci*

798
799 Environ Manag 19: 191-199.

800 Müller M, Munné-Bosch S (2015) Ethylene response factors: a key regulatory hub in hormone and stress signaling.

801 Plant physiol 169: 32-41. https://doi.org/10.1104/pp.15.00677

802 Mundada PS, Barvkar VT, Umdale SD, Anil Kumar S, Nikam TD, Ahire ML (2021) An insight into the role of silicon on retaliation to osmotic stress in finger millet (Eleusine coracana (L.) Gaertn). J Hazard Mater 403:124078. https://doi.org/10.1016/j.JHAZMAT.2020.124078

805 Muralikrishna G, Nirmala M (2005) Cereal α-amylases—an overview. Carbohydrate polymers 60: 163-173. https://doi.org/10.1016/j.carbpol.2004.12.002

807 Muscolo A, Sidari M, Anastasi U, Santonoceto C, Maggio A (2014) Effect of PEG-induced drought stress on seed germination of four lentil genotypes. J Plant Interact 9:354-363.

809 https://doi.org/10.1080/17429145.2013.835880

810 Nadarajah KK (2020) ROS homeostasis in abiotic stress tolerance in plants. Int J Mol Sci 21:5208. https://doi.org/10.3390/ijms21155208

812 Naguib DM, Abdalla H (2019) Metabolic status during germination of nano silica primed Zea mays seeds under salinity stress. J Crop Sci Biotechnol 22:415-423. https://doi.org/10.1007/s12892-019-0168-0

814 Nakabayashi K, Leubner-Metzger G (2021) Seed dormancy and weed emergence: From simulating environmental change to understanding trait plasticity, adaptive evolution, and population fitness. J Exp Bot 72:4181-4185.

816 https://doi.org/10.1093/JXB/ERAB150

817 Nasri N, Mahmoudi H, Baatour O, M'rah S, Kaddour R, Lachâal M (2012) Effect of exogenous gibberellic acid on germination, seedling growth and phosphatase activities in lettuce under salt stress. Afr J Biotechnol 11: 11967-11971

820 Nguyen HC, Nguyen TT, Dao TH, Ngo QB, Pham HL, Nguyen TBN (2016) Preparation of Ag/SiO₂ nanocomposite and assessment of its antifungal effect on soybean plant (a Vietnamese species DT-26). Adv Nat Sci Nanosci Nanotechnol 7:45014. https://doi.org/10.1088/2043-6262/7/4/045014

823 Ning J, Jian L, Jihua Y, Jianming X, Li J, Guobin Z, Zhi F (2020) Effect of exogenous silicon on seed germination and expression of related genes in cucumber under osmotic stress. Acta Hortic Sin 47:41

825 Parvin K, Nahar K, Hasanuzzaman M, Bhuyan MHMB, Fujita M (2019) Calcium-mediated growth regulation and abiotic stress tolerance in plants. Nature, Springer

827 Pavel VL, Sobariu DL, Diaconu M, Stătescu F, Gavrilescu M (2013) Effects of heavy metals on Lepidium sativum germination and growth. Environ Eng Manag J 12: 727-733

829 Pedrini S, Merritt DJ, Stevens J, Dixon K (2017) Seed coating: Science or marketing spin? Trends Plant Sci 22:106-116. https://doi.org/10.1016/j.TPLANTS.2016.11.002

831 Pereira ADES, Oliveira HC, Fraceto LF, Santaella C (2021) Nanotechnology potential in seed priming for sustainable agriculture. Nanomaterials 11:267. https://doi.org/10.3390/nano11020267

833 Pulido P, Cazalis R, Cejudo FJ (2009) An antioxidant redox system in the nucleus of wheat seed cells suffering oxidative stress. Plant J 57:132-145. https://doi.org/10.1111/j.1365-313X.2008.03675.x

835 Rai-Kalal P, Tomar RS, Jajoo A, Rai-Kalal P, Tomar RS, Jajoo A (2021) Seed nanopriming by silicon oxide improves drought stress alleviation potential in wheat plants. Funct Plant Biol 48:905-915.

837 https://doi.org/10.1071/FP21079

838 Rajjou L, Duval M, Gallardo K, Catusse J, Bally J, Job C, Job D (2012) Seed germination and vigor. Annu Rev Plant Biol 63:507-533. https://doi.org/10.1146/annurev-arplant-042811-105550

840 Ravindran P, Kumar PP (2019) Regulation of seed germination: The involvement of multiple forces exerted via gibberellic acid signaling. Mol Plant 12:24-26. https://doi.org/10.1016/j.molp.2018.12.013

842 Rizwan M, Ali S, Ibrahim M, Farid M, Adrees M, Bharwana SA, Zia-ur-Rehman M, Qayyum MF, Abbas F (2015) Mechanisms of silicon-mediated alleviation of drought and salt stress in plants: A review. Environ Sci Pollut Res 22:15416-15431. https://doi.org/10.1007/S11356-015-5305-X

845 Rodrigues AA, Filho SCV, Müller C, Rodrigues DA, Sales JF, Zuchi J, Costa AC, Rodrigues CL, Silva AA, Barbosa DP (2019) Tolerance of Eugenia dysenterica to aluminum: Germination and plant growth. Plants 8:317. https://doi.org/10.3390/PLANTS8090317

848 Rogowska A, Szakiel A (2020) The role of sterols in plant response to abiotic stress. Phytochem Rev 19: 1525-1538. https://doi.org/10.1007/s11101-020-09708-2

850 Rufino C de A, Tavares LC, Martín-Ramos P, Fernandes-Vieira J, Abreu Júnior JS, Silva FJA, Fernandes-Correa M, Martín-Gil J (2017) Performance of soybean seedlings upon nutrient application by seed coating. Brazilian Arch Biol Technol 60:1-11. https://doi.org/10.1590/1678-4324-2017160128

853 Sano N, Marion-Poll A (2021) ABA metabolism and homeostasis in seed dormancy and germination. Int J Mol Sci 22:5069. https://doi.org/10.3390/ijms22105069

855 Seneviratne M, Rajakaruna N, Rizwan M, Madawala HMSP, Ok YS, Vithanage M (2017) Heavy metal-induced oxidative stress on seed germination and seedling development: A critical review. Environ Geochem Health 41:1813-1831. https://doi.org/10.1007/s10653-017-0005-8

858 Senna R, Simonin V, Silva-Neto MAC, Fialho E (2006) Induction of acid phosphatase activity during germination
859

of maize (Zea mays) seeds.

Plant

Physiol

Biochem

44: 467-473.

861

https://doi.org/10.1016/j.plaphy.2006.03.008

862

https://doi.org/10.4103/0976-9668.116964

863

Sfaxi-Bousbih A, Chaoui A, El Ferjani E (2010) Cadmium impairs mineral and carbohydrate mobilization during

864

the germination of bean seeds. Ecotoxicol Environ Saf 73: 1123-1129.

865

https://doi.org/10.1016/j.ecoenv.2010.01.005

866

Sharma AD, Rathore SVS, Srinivasan K, Tyagi RK (2014) Comparison of various seed priming methods for seed

867

germination, seedling vigour and fruit yield in okra (Abelmoschus esculentus L. Moench). Sci Hortic

868

(Amsterdam) 165:75-81. https://doi.org/10.1016/J.SCIENTA.2013.10.044

869

Sharma PD, Singh N, Ahuja PS, Reddy TV (2011) Abscisic acid response element-binding factor 1 is required for

870

establishment of *Arabidopsis* seedlings during winter. Mol Biol Rep 38: 5147-5159.

871

https://doi.org/10.1007/s11033-010-0664-3

872

Shi Y, Zhang Y, Yao H, Wu J, Sun H, Gong H (2014) Silicon improves seed germination and alleviates oxidative

873

stress of bud seedlings in tomato under water deficit stress. Plant Physiol Biochem 78:27-36.

874

https://doi.org/10.1016/J.PLAPHY.2014.02.009

875

Siddiqui H, Ahmed KBM, Sami F, Hayat S (2020) Silicon nanoparticles and plants: Current knowledge and future

876

perspectives. In: Sustainable Agriculture Reviews 41. Springer, Cham, pp 129-142

877

Stejskalová J, Kupka I, Miltner S (2015) Effect of gibberellic acid on germination capacity and emergence rate of

878

*Sycamore maple* (*Acer pseudoplatanus* L.) seeds. J For Sci 61:325-331. https://doi.org/10.17221/22/2015-

879

JFS

880

Sun YD, Luo WR (2014) Effects of exogenous hydrogen sulphide on seed germination and seedling growth of

881

cucumber (*Cucumis sativus*) under sodium bicarbonate stress. Seed Sci Technol 42: 126-131.

882

https://doi.org/10.15258/sst.2014.42.2.02

883

Sun Y, Xu J, Miao X, Lin X, Liu W, Ren H (2021) Effects of exogenous silicon on maize seed germination and

884

seedling growth. Sci Rep 11:1-13. https://doi.org/10.1038/s41598-020-79723-y

885

Szabados L, Savouré A (2010) Proline: a multifunctional amino acid. Trends Plant Sci 15: 89-97.

886

https://doi.org/10.1016/j.tplants.2009.11.009

887

Tai L, Wang H-J, Xu X-J, Sun W-H, Ju L, Liu W-T, Li W-Q, Sun J, Chen K-M (2021) Pre-harvest sprouting in

888

cereals: Genetic and biochemical mechanisms. J Exp Bot 72:2857-2876.

889

https://doi.org/10.1093/JXB/ERAB024

890

Toscano S, Romano D, Tribulato A, Patanè C (2017) Effects of drought stress on seed germination of ornamental

891

sunflowers. Acta Physiol Plant 39:184. https://doi.org/10.1007/s11738-017-2484-8

892

ur Rehman A, Qamar R, Rehman A, Wasaya A, Farooq O, Sarwar N, Iqbal MM, Ahmad S (2020) Silicon coating

893

on maize seed mitigates saline stress in yermosols of southern punjab. Silicon 1-11.

894

https://doi.org/10.1007/s12633-020-00737-2

895

Van Bockhaven J, De Vleesschauwer D, Höfte M (2013) Towards establishing broad-spectrum disease resistance

896

in plants: Silicon leads the way. J Exp Bot 64:1281-1293. https://doi.org/10.1093/jxb/ers329

897

Voogt W, Sonneveld C (2001) Silicon in horticultural crops grown in soilless culture. Stud Plant Sci 8:115-131.

898

https://doi.org/10.1016/S0928-3420(01)80010-0

899

Wang W-B, Kim Y-H, Lee H-S, Kim K-Y, Deng X-P, Kwak S-S (2009) Analysis of antioxidant enzyme activity

900

during germination of alfalfa under salt and drought stresses. Plant Physiol Biochem 47:570-577.

901

https://doi.org/10.1016/j.plaphy.2009.02.009

902

Waterworth WM, Bray CM, West CE (2019) Seeds and the art of genome maintenance. Front Plant Sci 10:706.

903

https://doi.org/10.3389/fpls.2019.00706

904

Wijewardana C, Alsajri FA, Reddy KR (2018) Soybean seed germination response to in vitro osmotic stress. Seed

905

Technol 39:143-154

906

Wijewardana C, Reddy RK, Krutz JL, Gao W, Bellaloui N (2019) Drought stress has transgenerational effects on

907

soybean seed germination and seedling vigor. PLoS One 14:e0214977.

908

https://doi.org/10.1371/journal.pone.0214977

909

Xiao Y, Sun J, Liu F, Xu T (2016) Effects of salinity and sulphide on seed germination of three coastal plants.

910

Flora - Morphol Distrib Funct Ecol Plants 218:86-91. https://doi.org/10.1016/J.FLORA.2015.12.002

911

Xiong J-L, Li J, Wang H-C, Zhang C-L, Naeem MA (2018) Fullerol improves seed germination, biomass

912

accumulation, photosynthesis and antioxidant system in *Brassica napus* L. under water stress. Plant Physiol

913

Biochem 129:130-140. https://doi.org/10.1016/j.plaphy.2018.05.026

914

Xu D, Cao H, Fang W, Pan J, Chen J, Zhang J, Shen W (2017) Linking hydrogen-enhanced rice aluminum

915

tolerance with the reestablishment of GA/ABA balance and miRNA-modulated gene expression: A case

916

study on germination. Ecotoxicol Environ Saf 145: 303-312. https://doi.org/10.1016/j.ecoenv.2017.07.055

917

Yamaguchi S, Kamiya Y (2001) Gibberellins and light-stimulated seed germination. J Plant Growth Regul 20:369-

918

376. https://doi.org/10.1007/s003440010035
919 Yan A, Chen Z (2020) The control of seed dormancy and germination by temperature, light and nitrate. Bot Rev 86:39-75. https://doi.org/10.1007/s12229-020-09220-4
920
921 Yao Y, He RJ, Xie QL, Zhao XH, Deng XM, He JB, Song L, He J, Marchant A, Chen X-Y, Wu AM (2017) *Ethylene Response Factor 74 (ERF74)* plays an essential role in controlling a *respiratory burst oxidase homolog D (RbohD)*-dependent mechanism in response to different stresses in *Arabidopsis*. New Phytol 213: 1667-1681. https://doi.org/10.1111/nph.14278
922
923
924
925 Zhang H, Tan Z-Q, Hu L-Y, Wang S-H, Luo J-P, Jones RL (2010) Hydrogen sulfide alleviates aluminum toxicity in germinating wheat seedlings. J Integr Plant Biol 52: 556-567. https://doi.org/10.1111/j.1744-7909.2010.00946.x
926
927
928 Zhang N, Zhang H-J, Sun Q-Q, Cao Y-Y, Li X, Zhao B, Wu P, Guo Y-D (2017) Proteomic analysis reveals a role of melatonin in promoting cucumber seed germination under high salinity by regulating energy production. Sci Reports 7:1-15. https://doi.org/10.1038/s41598-017-00566-1
929
930
931 Zhang Q, Rue K, Wang S (2012) Salinity effect on seed germination and growth of two warm-season native grass species. HortScience 47:527-530. https://doi.org/10.21273/hortsci.47.4.527
932
933 Zhang XH, Zhou D, Cui JJ, Ma HL, Lang DY, Wu XL, Wang ZS, Qiu HY, Li M (2015) Effect of silicon on seed germination and the physiological characteristics of *Glycyrrhiza uralensis* under different levels of salinity. J Hortic Sci Biotechnol 90:439-443. https://doi.org/10.1080/14620316.2015.11513207
934
935
936 Zhang Z, Fan J, Wu J, Zhang L, Wang J, Zhang B, Wang-Pruski G (2020) Alleviating effect of silicon on melon seed germination under autotoxicity stress. Ecotoxicol Environ Saf 188:109901. https://doi.org/10.1016/J.ECOENV.2019.109901
937
938
939 Zhu Y, Gong H (2014) Beneficial effects of silicon on salt and drought tolerance in plants. Agron Sustain Dev 34:455-472. https://doi.org/10.1007/s13593-013-0194-1
940
941