## 2 Nanomaterials in Improving Plant Growth and Yield  
Currently, around 1300 nanomaterials, with widespread potential applications, are available [13; 14]. Nanoparticles can penetrate the cell wall because the cell wall is porous to 3.5-20 nm macromolecules. Nanoparticles can enter through stomatal openings. When stomata are present at the lower surface of leaves, the entry of nanoparticles (NPs) becomes difficult [15]. It is reported that nanoparticles of size \(\leq\)43 nm can penetrate and enter into stomata [16; 17]. The effect of nanoparticles on crop plants is concentration-based. Many plant processes such as seed germination and plant growth are affected by NP concentration [18]. Many NPs have been reported to be beneficial for plant growth. [PERSON] et al. [19] used  
Figure 1: Schematic presentation of nanomaterials in agriculture [12]. Figure 2: Various applications of nanotechnology in agriculture taken from [12]. Zn, B, Si, zeolite NPs on a potato plant and found that these nanoparticles have a positive effect on potato plants and they improve the plant growth. [PERSON] and [PERSON] [20] treated eggplant with ZnONPs and found a foliar spray of ZnONPs causes the highest improvement in eggplant growth. [PERSON] et al. [21] reported that ZnONPs have a positive effect on seed germination in the _Triticum aestivum_ plant. Zinc oxide nanoparticles (ZnONPs) can enhance plant biomass and agriculture production [22]. [PERSON] et al. [23] also showed that nanocalcite (CaCO\({}_{3}\)) application with Fe\({}_{2}\)O\({}_{3}\), nano SiO\({}_{2}\), and MgO improved the uptake of Mg, Ca, and Fe, and also notably enhanced the intake of P with micronutrients Zn and Mn. [PERSON] et al. [24] found that ZnONPs increase in photosynthetic pigment in the _Leucena leucocephala_ plant. [PERSON] et al. [25] reported high chlorophyll-a', chlorophyll-b' and total chlorophyll content in the _Sesamum indicum_ plant when treated with ZnO NPs. [PERSON] et al. [26] observed that treatment of ZnONPs increases the increase in shoot dry matter in _Zea mays_. [PERSON] et al. [27] found that ZnONPs enhanced shoot and grain yield in the _Pennisetum glaucum_ plant. The application of titanium dioxide (TiO\({}_{2}\)) on crops promotes plant growth parameters and can enhance the photosynthetic rate. [PERSON] et al. [28] usedTiO\({}_{2}\) and ZnONPs on beet root plants. They found that both NPs increased chlorophyll and carotenoid content, improved plant growth, and also improved super oxide dismutase (SOD), catalase (CAT), H\({}_{2}\)O\({}_{2}\), and proline content in plants. ZnONPs were found to be better than TiO\({}_{2}\)NPs on beetroot plants. [PERSON] et al. [29] reported that TiO\({}_{2}\)NPs treatment improved shoots in the _Vigna radiate_ plant. [PERSON] and [PERSON] [30] observed that TiO\({}_{2}\)NPs at a lower concentration enhanced seed germination and seedling growth in onion plants. [PERSON] et al. [31] found a positive effect of TiO\({}_{2}\)NPs on the _Triticum aestivum_ plant. [PERSON] et al. [32] found a positive effect of TiO\({}_{2}\)NPs on the seed germination of the _Brassica napus_ plant. [PERSON] et al. [33] reported that treatment of TiO\({}_{2}\)NPs promotes photosynthetic rate in tomato plants. Silicon is an important element that plays a key role in several metabolic and physiological activities in plants [34]. SiO\({}_{2}\)nanoparticles have the potential to enhance the germination and seedling growth of _Agropyron elongatum_[35]. Nano-SiO\({}_{2}\) can be used to produce effective fertilizers for crops and to minimize the loss of fertilizer through slow and controlled release, allowing for regulated, responsive, and timely delivery [36]. [PERSON] et al. [37] found improved seed germination in the _Cucurbita pepo_ plant after treatment with Nano SiO\({}_{2}\). [PERSON] and [PERSON] [38] reported that Nano Si treatment on the tomato plant improves photosynthetic rate in treated plants. Copper is an essential element for plant growth and development. Copper plays a key role in the activity of many plant enzymes.