bluuebunny/crossref_metadata_2025 huggingface dataset:
Desiccation tolerance in two species with recalcitrant seeds: Clausena lansium (Lour.) and Litchi chinensis (Sonn.)
Authors: Fu J. R. , Jin J. P. , Peng Y. F. , Xia Q. H.
Published: September 2008

Seeds were collected at weekly intervals from mid-maturation to the fully ripened stage. As seed development progressed, desiccation tolerance increased. Desiccation tolerance of C. lansium seeds was greatest at 67 days after anthesis (DAA), when they tolerated air drying for 9 days; 74 DAA was considered as physiological maturity, and their full viability was only maintained for up to 3 days of drying; overripened seeds (88 DAA) had the lowest desiccation tolerance. In L. chinensis, the desiccation sensitivity of seeds at 98 DAA (fully mature) was higher than that at 84 and 91 DAA (less mature); among the excised embryonic axes at different developmental stages, the less mature ones were less sensitive to desiccation than the fully mature ones; excised embryonic axes of the same stage were more tolerant of desiccation than whole seeds.
α-Amylase isoenzymes and BASI-like proteins in seeds of different grass species
Authors: Cornford C. A. , Hill R. D.
Published: September 2008

Seeds from an assortment of 28 grass species (including two cereals), chiefly representing different tribes of the sub-family Pooideae were tested for the presence of BASI-like proteins using Western blotting techniques and antisera raised against the barley amylase/subtilisin inhibitor. A single protein species of the same molecular weight as the BASI protein was detected in each member of the tribes Triticeae and Bromeae tested. Members of the Triticeae and Bromeae were the only species to produce high pi α-amylase isoenzymes following germination of the grain in addition to low pl forms which were present in all species tested. Anti-BASI antibody binding patterns for the other grasses examined were variable with the strongest staining being observed for Lolium species. In these species, either a double or single protein band fractionally larger than the BASI protein was recognized. In most other cases antibody binding was barely or not detectable. Inhibitor preparations from Hordeum vulgare and Lolium perenne were effective at inhibiting wheat α-amylase but neither had any effect against enzyme produced by germinating L. perenne.
Molybdenum deficiency in wheat results in lower dormancy levels via reduced ABA
Authors: Modi A. T. , Cairns A. L. P.
Published: September 2008

Wheat which was grown in acid-washed sand and irrigated with a molybdenum-free nutrient solution was treated with various concentrations of molybdenum (Mo) as a foliar spray at the flag leaf stage. At maturity, dormancy levels and abscisic acid (ABA) content of the seed were determined. Seed dormancy and ABA content increased with increasing rates of Mo application. In a field experiment, wheat (cv. SST 66) was treated with 100 ppm Mo by foliar application at the flag leaf stage. Embryos were tested for sensitivity to exogenously applied ABA. Embryos from Mo-treated plants showed enhanced sensitivity to ABA-induced inhibition of germination. The Mo application also resulted in significantly higher levels of endogenous ABA and Mo in the seeds. It is postulated that Mo deficiency leads to a lack of dormancy in wheat via reduced synthesis of ABA.
Conifer zygotic embryogenesis, somatic embryogenesis, and seed germination: Biochemical and molecular advances
Authors: Misra Santosh
Published: September 2008

The development of techniques for somatic embryogenesis in conifers has led to rapid advances in the ability to culture conifer tissuein vitro.Somatic embryogenesis now provides a means to clonally propagate commercially valuable conifers of several species and offers anin vitroexperimental system for studying embryogenesis. As a result of these developments, the conifer zygotic and somatic embryo system has recently attracted the attention not only of the cell biologist but also of biochemists and molecular biologists. In this review I have attempted to consolidate the recent information on ultrastructure, biochemical and molecular aspects of conifer zygotic and somatic embryogenesis. In the first section, salient features of zygotic embryogenesis are highlighted followed by biochemical and ultrastructural characterization of development with reference to storage reserve deposition. In the second section, detailed characterization of seed storage proteins, changes in gene expression with emphasis on storage protein genes and Lea genes during zygotic and somatic embryogenesis are described. Effect of culture treatments such as abscisic acid, osmoticum and desiccation on storage protein gene expression in somatic embryos is discussed. Based on these studies, comparisons are presented between angiosperm and gymnosperm embryogeny regarding the unique morphological and developmental patterns of conifer embryogenesis. Finally, a brief discussion of recent progress in biochemical and molecular characterization of conifer seed germination is presented.
The mineral nutrient composition of wheat grains from ears grown to maturity in the field or cultured in media containing different concentrations of P, Mg, K and Ca
Authors: Batten Graeme D. , Ockenden Irene , Lott John N. A.
Published: September 2008

A study was conducted to assess the effect of the supply of phosphorus and the major cations on the mineral nutrient composition of whole mature wheat grains and the electron-dense globoid crystals found in the aleurone cells. Ears of wheat plants, growing in the field, were detached after anthesis. The ears were cultured to maturity in a sterile control solution which contained all essential elements. Other ears were cultured in solutions which contained no phoshorus, no calcium, no magnesium, combinations of these (−P, −Ca; −P, −Mg) or a solution which contained additional potassium but no phosphorus, calcium or magnesium. Ears cultured in the control solution produced grains with higher concentrations of P, Mg, K and Ca than grains from ears which matured on plants in the field. All the −P treatments produced grains with lower concentrations of P and higher concentrations of Mg, K and Ca than the plants grown in the field. The appearance and elemental composition of the globoid crystals in the aleurone cells support the hypotheses that the size of globoid crystals is regulated, in part, by the amount of phosphorus deposited in the grain and also by the relative proportions of K, Mg and Ca in the tissue. The culture of individual ears of cereal plants is a useful technique by which to study the transfer to and deposition of mineral nutrients in cereal grains.
Seed stability during storage: Raffinose content and seed glassy state
Authors: Bernal-Lugo I. , Leopold A. C.
Published: September 2008

It has been proposed that sucrose and raffinose play a role in the storability of maize seeds. The levels of these sugars in the embryos and the glassy state were compared in maize seeds of contrasting storage stability to determine the relationship between sugar composition, glassy state and the storability of the seed. Sucrose was the predominant sugar but its content was not correlated with good storage. The content of raffinose as a mass fraction of total sugars and the magnitude of the glassy state showed positive correlations with storage stability. It is suggested that in maize seeds dry storage stability is a reflection not of the total soluble sugars, but of the mixture of sucrose with raffinose. Apparently raffinose amplifies the magnitude of the glass signal and this in turn is associated with enhanced storability.
A comparison of the synthesis of DNA, RNA and proteins in the embryos of after-ripened and thermo- or FR-dormantAgrostemma githagoL. seeds
Authors: Gerth U. , Bernhardt D.
Published: September 2008

Imbibed embryos of after-ripened and secondarily thermo- and FR-dormantAgrostemma githagoseeds were investigated as to their ability to synthesize DNA, RNA and proteins with the aim of finding characteristic differences connected with the induction and maintenance of developmental arrest. A gradual decrease in DNA synthesis was observed during the induction of thermodormancy. However, DNA synthesis was stimulated up to that of embryos of 30–h-imbibed after-ripened seeds within 24 h approximately after transferring the thermodormant seeds into temperatures which normally allow germination. DNA synthesis of embryos of FR-dormant seeds remained constant at a relatively low level during 7 d FR and another 7 d dark incubation. RNA synthesis decreased to different extents during induction of thermo- and FR-dormancy when it was arrested at a relatively low level in seeds transferred to temperatures which normally allow germination. Processes leading to an increase in RNA synthesis such as in embryos of after-ripened seeds appeared to be quantitatively and/or qualitatively repressed. Interestingly, protein synthesis was extremely depressed during induction of thermodormancy whereas it was slightly stimulated during induction of FR-dormancy. Nevertheless two-dimensional protein PAGE revealed several polypeptides which were new, increased, decreased or not synthesized predominantly in axes of thermo- and FR-dormant seeds in comparison to germinating after-ripened seeds. It is suggested that a connection exists between these polypeptides and the repression of germination. After transferring seconarily dormant seeds to temperatures which normally allow germination, a temporary stimulation of protein synthesis could be observed in both cases.
Development of the strophiole in seeds of white clover (Trifolium repens L.)
Authors: Martens Helle , Jakobsen Henrik B. , Lyshede Ole B.
Published: September 2008

The seed coat of Trifolium repens L. was studied with special emphasis on the development of the strophiole, which is the site for water entry during imbibition in leguminous seeds. The epidermal cells of the strophiole are longer than the cells in the remainder of the seed epidermis in the mature ovule. During seed development the median cells of the strophiolar epidermis divide periclinally into an outer layer of palisade cells and an inner layer of isodiametric cells. Prior to maturity a fissure is formed between some of the palisade cells in the centre of the strophiole. It is suggested that tension develops between the palisade cells and the iso-diametrical cells during later maturation stages causing the formation of the fissure which it is believed functions in water uptake. It is indicated that the ‘light line’ is caused by alteration of cellulose microfibrillar orientation in palisade cell walls. It is confirmed that removal of the epicuticular wax from hard seeds by rinsing in absolute alcohol or hexane does not induce water imbibition. Only when seed coats are mechanically abraded do hard seeds germinate.
A comparison of desiccation-related proteins (dehydrin and QP47) in peas (Pisum sativum)
Authors: Baker Ellen H. , Bradford Kent J. , Bryant John A. , Rost Thomas L.
Published: September 2008

Dehydrin and QP47, proteins present in mature pea seeds (Pisum sativum), have been proposed to play protective roles during desiccation. To identify possible relationships between these proteins and desiccation tolerance, their tissue locations and patterns of synthesis and degradation have been examined during germination. Tissue locations were determined by immunocytochemistry using polyclonal antibodies raised against a conserved dehydrin amino acid sequence and against purified QP47. In embryonic axis and cotyledon cells, QP47 and dehydrin were distributed uniformly with no apparent nuclear or organellar specificity. Both proteins were present in 24 h-imbibed axes that had not initiated radicle growth but were completely absent from 24 h-imbibed axes that had begun to grow. The amounts of QP47 and dehydrin in embryonic axes decreased with time after the start of imbibition and were undetectable by 48 h. When germination was prevented by polyethylene glycol (PEG) or abscisic acid (ABA), both proteins remained at their original amounts. Thus, both QP47 and dehydrin disappeared coincidently with the beginning of growth and not simply as a function of the time after imbibition. QP47 persisted in cotyledons until at least 31 days into seedling growth, whereas dehydrin was not detectable in cotyledons after 7 days. Dehydrin, but not QP47, could be re-induced in pea shoots and cotyledons by dehydration. The timing of degradation of both proteins was correlated with the loss of desiccation tolerance during germination of pea axes.
Germination of 110-year-old cereal and weed seeds, the Vienna Sample of 1877. Verification of effective ultra-dry storage at ambient temperature
Authors: Steiner A.M. , Ruckenbauer P.
Published: September 2008

After 110 years of hermetic sealed storage at temperatures between 10 and 15°C and at a moisture content of 3.12%, Hordeum vulgare showed 90% germination and Avena sativa 81%. In addition, some seeds of Agrostemma githago, Lolium temulentum, Sinapis alba, Sinapis arvensis, and Vaccaria hispanica were still capable of germinating. This demonstrates that ultra-dry, long-term seed storage under ambient temperature conditions can successfully be achieved with the intention of cutting down risks and costs in germplasm conservation.
Characterization of carboxypeptidase I of mung bean seeds
Authors: Wilson Karl A. , Russell Mary , Quackenbush John F. , Tan-Wilson Anna L.
Published: September 2008

There is a carboxypeptidase in mung bean seeds that is localized in the protein bodies, the same vacuoles in which seed storage proteins are sequestered. This carboxypeptidase, called carboxypeptidase I (or Cpase I) has been purified by a series of ion-exchange and gel filtration columns. The pure enzyme consists of a single polypeptide chain with a MW of 41700 by SDS-PAGE or 42000 by size-exclusion HPLC. It has a pl of 4.36 and is a serine carboxypeptidase as shown by its inactivation by phenylmethylsulfonyl fluoride, and its resistance to other proteolytic inhibitory reagents. A survey of its activity with Cbz-dipeptides shows preference for C-terminal amino acids that are large, hydrophobic residues, and a small aliphatic amino acid such as alanine, but not glycine, at the penultimate amino acid residue. Cpase I can convert a trypsin inhibitor of the mung bean to its proteolytic intermediate lacking four amino acid residues at its C-terminus. This proteolytic intermediate is detected in the mung bean cotyledons during early growth. Levels of both the activity and immunological cross-reacting forms of this enzyme start high and decrease during early growth.
Seed production environment and storage longevity of japonica rices (Oryza sativa L.)
Authors: Kameswara Rao N. , Jackson M.T.
Published: September 2008

Changes in seed dry weight, moisture content and germinability of three japonica cultivars of rice during development and maturation in the dry season (November–May) field multiplication at Los Baños, Philippines were compared with those in a cooler controlled environment (24°/18°C). Under field conditions, maximum dry weight accumulation, which indicates mass maturity, was attained 18–21 days after flowering in all cultivars. In the cooler environment however, mass maturity was achieved 21 days after flowering in Fujisaka 5 and Minehikare, and 28 days in Shuang cheng nuo. The moisture content of the seeds at mass maturity varied between 28 and 35% among cultivars in the two environments. Although the ability of seeds to germinate differed in early harvests (7 and 14 days) among cultivars and across two environments, germination of the mature seeds was similar in all. There were no significant differences in potential longevity of the seeds harvested at 28, 35 and 42 days after flowering within each cultivar, which was determined by the germination of seeds that had been hermetically stored with 15% moisture content at 35°C. Differences among cultivars within each seed production environment were also not significant. However, potential longevity of the seeds harvested from the cooler environment was higher than those from the field (P<0.05), which confirmed that japonica cultivars which evolved under temperate regions are sensitive to warmer seed production environments. However, the magnitude of differences in potential seed longevity between the two environments was not high. This indicates that the seed production environment during the dry season at Los Baños is not harsh for japonica cultivars.
Seed storage of plant genetic resources
Authors: Praciak Andrew
Published: September 2008

The need to conserve plant genetic resources can no longer be in doubt. The destruction of natural habitats, the replacement of multiple cropping systems with monocultures, the replacement of traditional varieties with uniform high-yielding cultivars all lead to genetic erosion and the loss of crop and plant diversity. Genetic resources are vital for crop breeding programmes as sources of new genes for, for example, disease and pest resistance. They are also vital as sources of pharmaceutical and novel industrial and food products. In their own right they may have potential as new crops.
Operational and philosophical decisions in seed dormancy research
Authors: Cohn Marc Alan
Published: September 2008

Many research questions focused upon seed dormancy and germination remain unanswered due to problems created by inappropriate assumptions concerning the design and implementation of experiments. Lack of attention to the genetic background and growing conditions required for seed production and subsequent storage may compromise an investigator's ability to pool data or assimilate data trends due to variability in seed performance from year to year. Seed aging events during the afterripening process can be mistaken for those involved in the transition from the dormant to nondormant state. After imbibition, inaccurate criteria for and scoring of the germination event may lead to confusion of seed vs. seedling physiology and biochemistry. In addition, a sufficient number and proper spacing of data points during timecourse experiments are required to properly stage a sequence of events. Studies comparing dormant vs. nondormant seeds must be supplemented with kinetic experiments examining the effect of a dormancy-breaking treatment upon the transition between the dormant and nondormant states. In comparisons of the relative efficacy of various dormancy-breaking chemical treatments, the physical properties of substances under evaluation (e.g. lipophilicity) should be considered. In addition, since many dormancy-breaking chemicals are toxic to vegetative growth, there is a danger of introducing pharmacological artifacts that confuse interpretation of the results obtained. These toxic properties also necessitate the use of viability tests during construction of dose-response curves to avoid confusing seed death with dormancy. Seed scientists must also avail themselves of the extensive literature on developmental arrest in other organisms, which may generate fresh ideas for experimentation.
Species differences in seed water status during seed maturation and germination
Authors: Egli D.B. , TeKrony D.M.
Published: September 2008

Maize (Zea maysL., cv. B73 × Mo17), wheat (Triticum aestivumL., cv. Clark), and soybean (Glycine maxL. Merrill, cv. Elgin 87) were grown in the field and seed samples were collected at frequent intervals for the determination of seed fresh and dry weight and water potential of excised embryos (maize and wheat) and axes (soybean). Seed water concentration declined during seed development and the concentration at physiological maturity (PM, maximum seed dry weight) was highest in soybean (550–590 g kg−1FW), lowest in maize (326–377 g kg−1) and intermediate in wheat (437 g kg−1). The embryo/axis water potential was relatively constant during much of seed filling before decreasing rapidly as the seeds approached PM and there was little variation among species (soybean −1.52 to −1.63 MPa, maize −1.61 to −1.99 MPa and wheat −1.66 MPa). Seed water concentration when 10% of the seeds germinated (radicle ≥3 mm) was highest in soybean (514 g kg−1), lowest in maize (332 g kg−1) and intermediate in wheat (345 g kg−1) while the water potential of the embryo/axis varied from −2.07 to −2.20 MPa across the three species. There was little variation in the water potential of the embryo/axis among species at the end of seed growth (PM) or at the beginning of germination. This similarity is consistent with the suggestion that the water status of critical seed structures may play a regulatory role in seed growth and germination.
Phytochrome promotion of mannan-degrading enzyme activities in the micropylar endosperm of Datura ferox seeds requires the presence of the embryo and gibberellin synthesis
Authors: Sánchez R. A. , de Miguel L.
Published: September 2008

It has been shown that endosperm weakening, a necessary step in the light induction of germination in Datura ferox seeds, is related to the hydrolysis of cell wall mannose polysaccharides. It is demonstrated that the activities of two enzymes involved in mannan degradation (β-mannanase and β-mannosidase) are strongly promoted in the micropylar endosperm, after Pfr formation but long before radicle protrusion. An increase in enzyme activities occurred in dissected seed parts at similar rates to those in whole seeds, but only when at least a portion of the embryonic axis was present during incubation. De-embryonation of seed parts prevented the Pfr-induced increase in hydrolase activities. Exogenous GA3 promoted mannan-degrading enzyme activities both in the micropylar region of far red-treated whole seeds and those of isolated and deembryonated endosperm sections. The response to Pfr and GA3 was far more pronounced in the micropylar portion than in the rest of the endosperm. Pfr promotion of hydrolase activities and germination was blocked by paclobutrazol, an inhibitor of gibberellin synthesis. A close correlation was found between β-mannanase activity measured 45 h after Pfr formation and germination scored 24 h later. These results support the hypothesis that in D. ferox, endosperm softening is promoted by Pfr via the production in the embryonic axis of a factor, probably a gibberellin, which moves to the endosperm where it stimulates cell wall-mannan hydrolytic enzyme activities.
The requirement for DNA repair in desiccation tolerance of germinating embryos
Authors: Boubriak Ivan , Kargiolaki Haroula , Lyne Linden , Osborne Daphne J.
Published: September 2008

It is proposed that desiccation tolerance in the embryo of seeds depends upon the capacity to repair damage to genomic DNA when the desiccated embryo is rehydrated. From a study of imbibed and hydrated embryos of rye (Secale cereale) and wild oat (Avena fatua) evidence is provided that it is neither the extent of water uptake by the cells, the ensuing stability of the DNA to desiccation, nor the onset of S-phase DNA synthesis in the first cell cycle of germination that determines whether the desiccated embryo will survive. It is shown that when α- and β-polymerases of DNA repair are inhibited by aphidicolin and dideoxythymidine-5'-triphosphate, respectively, a γ-irradiation-induced DNA fragmentation cannot be fully repaired. It is shown that in hydrated embryos, at a stage when desiccation tolerance is lost, embryo cells still repair irradiation-induced damage, but this repaired DNA is unstable to desiccation and cannot be rerepaired when water is again made available. The failure to re-repair on rehydration appears to be critical to embryo survival and successful germination.
Response of the recalcitrant seeds of Avicennia marina to hydrated storage: events occurring at the root primordia
Authors: Motete Nthabiseng , Pammenter N. W. , Berjak Patricia , Frédéric Jillian C.
Published: September 2008

This study was undertaken to test the hypotheses that germinative metabolism of recalcitrant seeds in storage induces a requirement for additional water, which may result in the development of mild water stress, and that a reduction of the rate of this germinative metabolism will increase the storage lifespan of recalcitrant seeds. Studies were undertaken on seeds of Avicennia marina (Forssk.) Vierh. and concentrated on root primordia as these constitute the tissue that undergoes most change during storage. Encapsulating seeds from which the pericarp had been removed (naked seeds) in an alginate gel increased storage lifespan fourfold compared with naked seeds. Measures of metabolic rate such as time to first germination in storage and rate of protein synthesis did not indicate differences between alginate-coated and naked seeds, although ultrastructural observations indicated that both germinative and deteriorative processes were occurring more slowly in the alginate-coated seeds. Measures of water content and water and turgor potentials did not reveal signs of a mild water stress in either treatment. However, the number of seeds visibly contaminated with fungi and the rapidity with which this contamination became apparent were much reduced in alginate-coated seeds. It is suggested that fungal contamination constitutes a major cause of deterioration in stored, hydrated seeds of A. marina (and possibly other recalcitrant seed species) and the main effect of the alginate coating was to reduce the incidence of fungal contamination.
Desiccation sensitivity of recalcitrant seeds—a study on tropical fruit species
Authors: Normah M. N. , Ramiya Saraswathy D. , Gintangga Mainah
Published: September 2008

Mangosteen (Garcinia mangostana L.), rambai (Baccaurea motleyana Muell.- Arg.) and jelentik (Baccaurea polyneura Hook. f.) are tropical fruit species believed to have recalcitrant seeds. The seeds showed no dormancy; they germinated easily. At harvest, the mean moisture contents (fresh weight basis) were 53.54, 51.20 and 44.90% for G. mangostana, B. motleyana and B. polyneura, respectively. G. mangostana seeds lost viability when their moisture content fell to about 24% while B. motleyana seeds lost viability below 35.5% moisture content. However, for B. polyneura, the seeds could be dried to low moisture content with high survival. The viability was still high when the moisture content was reduced to 13.46%. At this moisture content, the percentage germination was 91.76% and it was found that the seeds survived cyopreservation with 8.3% viability. For B. motleyana axes, the loss of viability occurred when their moisture content fell to about 36% (15% viability with predominantly callus formation) while for B. polyneura axes, viability was reduced to 33-67% when the moisture was 27–30%. At various moisture contents, the seeds of the fruit species studied were exposed for 48 h to 7°C and −4°C. G. mangostana seeds did not survive either temperature. Baccaurea seeds survived 7°C but failed to survive −4°C. No axes from B. motleyana seeds at various moisture contents survived cryopreservation. However, some viability (20–30%) was observed in B. polyneura axes cryopreserved at a moisture content of about 27%. At this moisture content no normal growth was obtained; callus formation was observed. It appears that the seeds vary in the degree of desiccation sensitivity. They also vary in size. Seeds of G. mangostana are larger than Baccaurea seeds and thus, more sensitive to desiccation. Seed and embryonic axis structure may also play a role in desiccation sensitivity.
A comparative study of the seed germination biology of a narrow endemic and two geographically-widespread species ofSolidago(Asteraceae). 2. Germination responses of buried seeds in relation to seasonal temperature cycles
Authors: Walck Jeffrey L. , Baskin Jerry M. , Baskin Carol C.
Published: September 2008

Seeds of the narrow-endemicSolidago shortiiand of the geographically-widespreadS. altissimaandS. nemoraliscollected and buried in 1992 and 1993 were incubated in light and in darkness at 15/6°, 20/10°, 25/15°, 30/15° or 35/20°C following various periods of burial in soil in a non-temperature-controlled glasshouse. At maturity in November, seeds of the three species germinated to 0–1% in light at 15/6°C and to 10–77% at 20/10°, 25/15°, 30/15° and 35/20°C. Seeds exhumed each April from 1993 to 1996 and incubated in light at 15/6° and 20/10°C germinated to ≥83% and ≥90%, respectively, whereas those exhumed each September of 1993–96 germinated to ≤2%and ≤40%, respectively. At 25/15°, 30/15° and 35/20°C in light, seeds of S.altissimaandS. shortiigerminated to ≥52% and those of S.nemoralisto ≥19/, regardless of when they were exhumed. Timson's index, which integrates percentages, rates and times for onset of germination, was higher at all temperature regimes for seeds exhumed in April 1995 than for those exhumed in September 1995. Freshly-matured seeds of the three species germinated to 0–11% in darkness. Furthermore, regardless of when they were exhumed, seeds ofS. altissimaandS. nemoralisincubated in darkness germinated mostly to only 0–9% over the range of temperature regimes. In contrast, ≤88% and ≤6% of the seeds ofS. shortiiexhumed and incubated in darkness each April and September of 1993–96, respectively, germinated, ≤1% of them germinating while buried in soil. Thus, although buried seeds of all three species exhibited an annual conditional dormancy/non-dormancy cycle, only those ofS. shortiiexhibited cyclic changes in their germination response in darkness.
Effects of advancement on nucleic acids in sugarbeet (Beta vulgaris) seeds
Authors: Redfearn M. , Osborne D. J.
Published: September 2008

Sugarbeet (Beta vulgaris) seeds which had undergone an advancement treatment germinated more quickly and showed greater germination in a standard test at 9°C than seeds which had been steeped in water. Both treatments included the fungicide, thiram (tetramethyl thiuram disulphide). Advanced seeds also emerged more quickly and showed higher establishment in the field. The levels of extractable high molecular weight (HMW) RNA and DNA from advanced, thiram-steeped and untreated seeds were compared. Advanced seeds contained significantly (P > 0.05) more HMW RNA and DNA than thiram-steeped or untreated seeds. Extractable DNA levels were higher from thiram-steeped seeds than untreated seeds but not significantly so. Cell-cycle studies on advanced seeds demonstrated an increase from 2% to 24% of root-tip nuclei with DNA contents of 4C and above. This indicates that DNA replication occurred during the advancement treatment. There was no evidence of cell division occurring, indicating that: (1) advanced seeds were arrested post-S-phase and (2) the period following DNA synthesis in sugarbeet seeds is desiccation tolerant.
Physiological and biochemical changes induced in sunflower seeds by osmopriming and subsequent drying, storage and aging
Authors: Chojnowski M. , Corbineau F. , Côme D.
Published: September 2008

Sunflower (Helianthus annuusL.) seeds show more germination at high temperatures (25–30°C) than at temperatures below 20°C. Osmopriming with polyethylene glycol-6000 for 3–5 days at 15°C strongly increases germination at suboptimal temperatures. This stimulatory effect of priming persists after seed redrying and during subsequent storage at 20°C (55% RH) for at least 14 weeks. However, primed seeds deteriorate faster than untreated seeds during accelerated aging (45°C, 100% RH). The longer the priming treatment, the higher is the amount of germination but at the same time the higher is the sensitivity of seeds to accelerated aging. Priming enhances the respiratory activity of seeds transferred onto water and their ability to convert 1-aminocyclopropane-1-carboxylic acid (ACC) to ethylene. These effects remain after drying the seeds and are maintained in part during dry storage, whereas they disappear during accelerated aging. These results suggest that ACC-dependent ethylene production might be a good indicator of seed vigour; it increases with duration of priming and decreases very early during aging, well before significant loss of seed viability. Decrease in ACC conversion to ethylene indicates that aging is probably associated with membrane deterioration sincein vivoACC oxidase activity depends on membrane properties. However, no increase in electrolyte leakage is observed during aging.
Identification of biotinylated proteins in soybean [Glycine max (L.) Merrill] seeds and their characterization during germination and seedling growth
Authors: Shatters Robert G. , Boo Soon P. , França Neto José B. , West S. H.
Published: September 2008

Biotin is an important vitamin. It is biologically active as a protein prosthetic group, where it functions in enzymatically catalysed carboxylation reactions. It has previously been shown that the ability to synthesize biotin is not necessary for germination of Arabidopsis thaliana seeds, but that this process is required for early seedling growth. This research was conducted to determine if changes in the detection of biotinylated proteins could be observed that reflect changes in the need for biotin-mediated enzyme reactions observed during early soybean seedling growth. A seed specific 75-kDa biotinylated protein present in the embryonic axes and the cotyledons was lost during the first 3 d of germination. Seed specificity, and pattern of expression during germination suggest that this protein is a homologue of the seed specific 65-kDa biotinylated protein previously identified in pea (Pisum sativum). If samples were not treated with 2-mercaptoethanol, three equally spaced proteins at approx. 85 kDa were visible. In the presence of 2-ME these proteins appeared as a single 85-kDa band. This triplet was distinct only in the embryonic axes of dry seeds and not in imbibed seeds or in other plant parts. This demonstrates that imbibitional changes do occur in the pool of biotinylated proteins present in dry soybean seeds, and that 2-ME treatment can inhibit complete identification of the biotinylated proteins present in seed tissues.
Induced dormancy and colour polymorphism in seeds of the bull thistleCirsium vulgare(Savi) Ten.
Authors: Doucet Colleen , Cavers Paul B.
Published: September 2008

To colonize newly disturbed areas, weedy species must disperse their seeds in space and/or in time.Cirsium vulgarehas poor dispersal in space, but can form a persistent seed bank. Fresh seeds are capable of germinating in either light/dark or constant dark conditions under favourable diurnal temperatures of 25°C: 10°C. Despite this lack of dormancy, a large proportion of seeds do not germinate in the autumn after dispersal. Variation in germination requirements according to seed colour was also examined. Fresh seeds were placed under one of two overwintering treatments at 5°C, alternating light/dark or constant darkness. Some seeds of all colours: white, light, intermediate, dark and black germinated under these conditions. Six months later, ungerminated seeds subjected to the light/dark treatment did not require light for germination when placed under optimal temperatures. However, most seeds that had overwintered in constant darkness required light for germination. In the field, this induced dormancy would prevent seeds from germinating if buried or located in deep shade. Such seeds have the potential of forming a persistent seed bank. The proportion of dormant seeds did not appear to be associated with seed colour. Seeds incubated at 10°C following overwintering under light/dark conditions germinated to a higher percentage than seeds overwintered in darkness, regardless of the light conditions for germination. The results of this study help to explain the contradiction between delayed germination in the field and the lack of seed dormancy.
Survival of a lowland heathland seed bank after a 33-year burial
Authors: Thompson Ken , Band Stuart R.
Published: September 2008

Soil samples were collected from the original land surface beneath an experimental earthwork, constructed in 1963 at Morden Bog, Dorset, England, and excavated in 1996. Large numbers of seeds of Calluna vulgaris, Erica cinerea and E. tetralix germinated from the samples, but other species present in the original flora, including Ulex minor and several grasses, were absent. The results confirm the previously-documented longevity of Calluna and E. tetralix, and for the first time demonstrate similar longevity in E. cinerea.
Spatial patterns of the germinable soil seed bank in northern Patagonia
Authors: Bertiller Mónica B.
Published: September 2008

The spatial variation of the soil seed bank in the steppe ofLarrea divaricataandStipaspp. was evaluated in relation to the spatial pattern of the established vegetation, over two years. Plant distribution was expected to affect the spatial pattern of the soil seed bank. It was hypothesized that patches of bare soil are seed-limited, while soil beneath the external crown of vegetation patches contains greater numbers of seeds. The soil seed bank of the steppe ofLarrea divaricataandStipaspp. displayed a patchy distribution associated with the spatial pattern of above-ground vegetation. Seed banks in areas of bare soil showed lower numbers of seeds than those beneath vegetation. The soil seed bank was dominated by annuals, both in open areas of soil and under vegetation canopies. The relative composition of the soil seed bank varied spatially. Annuals (dicots and grasses) were more abundant in grass-shrub patches (GSP) and grass patches (GP) than in incipient grass-shrub patches (IGSP) and bare soil (BS). Seeds of perennial grasses were more abundant under GP, less abundant under grass-shrub mixed canopies (IGSP and GSP) and practically absent in BS. In addition, seeds of perennial dicots were more frequent in grass-shrub mixed canopies, scarcely represented in GP and absent in BS. The concentration of seeds of perennial grasses in GP and GSP indicates that these are essential for the maintenance of the size of grass populations. Sustainable management should be focused to maintain the structure and function of these types of vegetation patches.
Heat-shock proteins in monitoring aging and heat-induced tolerance in germinating wheat and barley embryos
Authors: Dell'Aquila A. , Corona M. G. , Di Turi M.
Published: September 2008

Wheat and barley seeds were subjected to accelerated aging conditions at 12% moisture content and 35°C temperature over 28 days of storage, and to heat-shock treatment carried out by 4 h of incubation at 40°C following 16 h of imbibition at 20°C. Heat-treated, aged seeds showed altered germination behaviour and increasing leakage electroconductivity as well as a reduced incorporation of [35S]-methionine into embryo proteins, in comparison with the corresponding untreated seeds. Two-dimensional electrophoresis of labelled proteins from embryos gave evidence of further quantitative and qualitative changes: (a) ‘normal’ germination protein synthesis in wheat and barley was slightly modified by age, but following heat-shock treatment a general reduction of most of the control polypeptides occurred; (b) heat-shock response resulted in the production of several HSPs with different MW and pl, but a uniform general decline in their synthesis was not observed. Highly labelled HSPs (e.g., those with MW 66.7 or 89.3–66.7 kDa in wheat or barley, respectively) did not change over the entire period of aging, while some smaller HSPs with MW >29 kDa either decreased in intensity or disappeared. Conversely, specific low molecular weight HSPs (MW 17–14.2 kDa) were synthesized more in extremely aged embryos of both species. The hypothesis that these polypeptides may be used as biochemical markers in monitoring both vigour loss and heat-shock induced tolerance in aged seeds is discussed.
Manipulating dormancy of capeweed (Arctotheca calendulaL.) seed
Authors: Chaharsoghi Ali Tadayyon , Jacobs Brent
Published: September 2008

Capeweed (Arctotheca calendula) seeds were found to be dormant at harvest. Effects of duration and temperature of storage under ‘laboratory’ and ‘natural’ conditions, growth regulators, stratification and age of seeds, were studied on the germination of dormant seeds. Three factors imposed on seeds were found to promote germination of capeweed: (i) allowing seed to age, either in storage, buried in soil or during stratification (germination of 18-month-old seeds was up to 60% higher than that of fresh seeds); (ii) the presence of light (the average germination percentage of seeds exposed to light during storage was 3.2-fold greater than that of seed stored in the dark); and (iii) the application of growth regulators, particularly gibberellic acid, enhanced by scarification (GA3and ethephon promoted germination by up to 58% when applied to scarified seeds). Other factors, e.g. temperature and depth of storage, influenced germination but were less critical to its success. These results provide a preliminary assessment of the importance of these factors in controlling dormancy in seeds of capeweed.
Biophysical, physiological and biochemical processes regulating seed germination
Authors: Welbaum G. E. , Bradford K. J. , Yim Kyu-Ock , Booth D. T. , Oluoch M. O.
Published: September 2008

In the physiological sense, germination begins with seed water uptake and ends with the initiation of elongation by the embryonic axis, usually the radicle. The driving forces and constraints on expansion by the embryo are examined, particularly for seeds in which the embryo is surrounded by endosperm and testa tissues that restrict growth. Models have been developed to predict germination based on thermal time, hydrotime and combined hydrothermal time. These population-based models indicate that the timing of germination is closely tied to physiologically determined temperature and water potential thresholds for radicle emergence which vary among individual seeds in a population. The restraint imposed by tissues surrounding the radicle is a major determinant of the threshold water potential. Enzymatic weakening of these tissues is a key event regulating the timing of radicle emergence. Considerable evidence suggests that endo-β-mannanase is involved in this process in a number of species, although it is doubtful that it is the sole determinant of when radicle emergence occurs. Molecular and biochemical studies are revealing the complexity of events occurring in endosperm and embryo cells associated with the completion of germination. Unique permeability properties and the presence of enzymes associated with pathogen resistance suggest additional functional roles for the tissues enclosing the embryo. The insights gained from physiology and modelling are being extended by the application of molecular techniques to identify and determine the function of genes expressed in association with germination. Single-seed assay methods,in vivoreporters, specific modification of gene expression and mutagenesis will be critical technologies for advancing our understanding of germination
Genetic basis for seed dormancy
Authors: Foley Michael E. , Fennimore Steven A.
Published: September 2008

Seed dormancy is an important physiological stage in the life cycle of many seed-bearing plants. In an ever-changing environment, dormancy increases survival by distributing germination over time. In general, seed dormancy is a quantitative trait that is influenced by environmental factors. Depending on the species and accession, dormancy is controlled by nuclear factors, maternal factors or both, and dormancy can be genetically the dominant or recessive form of the trait. Wild oat (Avena fatua) is a well developed system for dormancy investigations. Dormancy in wild oat is regulated by three major genes as well as environmental factors, and dormancy is conditionally the recessive form of the trait. This paper summarizes current knowledge on genetic and environmental factors, and the interaction of these factors, on seed dormancy in several cereal grain and dicotyledonous species. Some applications of this knowledge to improve crops and manage weeds are outlined.
Protein kinases in seeds
Authors: Walker-Simmons M. K.
Published: September 2008

Reversible phosphorylation is catalysed by protein kinases that transfer the γ-phosphate from ATP to amino acid residues of proteins. The process can be reversed by protein phosphatases. Phosphorylation can dramatically activate or inhibit enzymes and affect protein-protein interaction. Through phosphorylation protein kinases can amplify and propagate cellular signals. In plants and now seeds, protein kinases involved in hormone, defence and environmental stress responses are being identified. Increasingly, these protein kinases are being cloned and characterized, demonstrating the major role of reversible protein phosphorylation in seeds.
Real-time assessment of seed dormancy and seedling growth for weed management
Authors: Forcella Frank
Published: September 2008

Computer software called WeedCast was developed to simulate weed seed dormancy, timing of seedling emergence, and seedling height growth in crop environments in real-time and using actual or forecasted weather data. Weather data include daily rainfall and minimum and maximum air temperatures. Air temperatures are converted to average daily soil temperature at 5-cm soil depth using a series of equations that are specific for soil type, tillage system and previous year's crop-residue type. Daily rainfall and soil temperature estimates are combined to determine soil water potential (in megapascals) at 5-cm depth. Daily estimated soil water potential or soil temperatures are matched to empirically-derived threshold values that induce secondary dormancy in seeds of certain species. Soil growing degree days (GDD), calculated from soil temperatures, are used to project maximum emergence rates of weed seedlings. Emergence ceases on days when soil water potential falls below threshold values specific to each species. GDD based on air temperatures are used to estimate post-emergence seedling height growth. All three types of simulation provide information that allows users to answer important weed management questions in real-time. These types of questions include but are not limited to the following: (1) Are soil-applied treatments necessary? (2) How late can pre-emergence herbicides be applied? (3) When should mechanical control be implemented? (4) When should field-scouting commence and end? (5) When should post-emergence herbicides be applied?
Understanding the mechanisms and kinetics of seed aging
Authors: Walters Christina
Published: September 2008

When seeds deteriorate, they lose vigour and become more sensitive to stresses upon germination. Eventually seeds lose the ability to germinate. The factors which determine the rate of this ‘aging’ are the temperature and moisture content at which seeds are stored and an ill-defined parameter, seed quality. While it has been known for many years that manipulation of these factors influences the longevity of seeds, the precise interactions among them are so poorly understood as to preclude the prediction of longevity for a particular seed lot. Concepts from studies of materials and food stability can be applied to seed aging research, and this may help us take a more integrative approach to understanding the kinetics of seed deterioration. These concepts describe the physical environment of the seed matrix in response to changing water contents and temperature. Water activity models describe the state of water in the seed, while the glass models describe the state of the aqueous solution. Both models presume that changes of state affect the nature and kinetics of chemical reactions. Thus, the physical and chemical environment within the seed are inextricably linked.