**3. Role of NPS in drought tolerance**

Water crisis is one of the several issues that have been afflicted by climate change and global warming. Water is crucial for plant vitality as it has a role in the transportation of nutrients. Therefore, water deficit results in drought stress, which harshly affects the survival of plants and reduces agricultural production [54]. Therefore, a key solution in relation to sustainable agriculture is the identification of resistant crop varieties or improving drought tolerance in plants. Crop management and coping with various environmental challenges are possible by the new features of nanotechnology. The negative impacts of a restricted water supply on agriculture have been attempted to be reduced utilizing nano-materials. Farmers may be able to identify the effects of stress on plants at an early stage by using nano-sensors in global positioning systems that produce satellite photographs of fields [55]. Crop production in drought-prone locations may rise if soils have been given better waterretention capabilities [56]. Using nanoparticle-based plant modifications, conventional technologies may be used to improve crop plants by increasing the capacity of food crops to retain water, and nanoparticles improve the effectiveness of water consumption in the plants [57].

### **3.1 Silicon nanoparticles (SNPs)**

Only a few studies have documented the biological activity of silica, an element that makes up a major portion of the Earth's crust and is found as silicon [58]. The tolerance of Hawthorn (*Crataegus* sp.) plants to drought stress is increased by applying various concentrations of silica nanoparticles [59]. The findings indicated that pretreating SNPs had a favorable impact on the photosynthetic metrics, RWC, malondialdehyde, membrane electrolyte leakage, as well as the levels of carbohydrate and proline. Two *Sorghum bicolor* cultivars treated with silicon demonstrated enhanced drought tolerance by reducing their shoot-to-root ratio, which may have indicated enhanced root development and retention of photosynthetic rate. This suggests that increasing plant water uptake efficiency will increase resistance to drought [60]. Using sodium silicate at 1.0 mM enabled the reduction of the effects of drought stress on wheat [61]. Although the precise process is unknown but silicon helps stressed plants to boost shoot growth, preserve RWC, and chlorophyll content, and reduce the membrane lipid peroxidation.

*Improvement of Abiotic Stress Tolerance in Plants with the Application of Nanoparticles DOI: http://dx.doi.org/10.5772/intechopen.110201*

#### **3.2 Zinc nanoparticles (ZnO NPs)**

Application of Zn plays a role in increasing the radical growth and seed viability along with the establishment of germinated seeds, especially in Zinc deficient areas. Soybean seeds subjected to water stress showed that nano-zinc oxide has improved seed germination [62]. A composite of ZnO, B2O3, and CuO NPs reduced the effects of drought stress on soybean [63] and increased grain production and shoot growth by 36 and 33%, respectively, and improved nitrate and phosphorus uptake. By boosting the activity of the antioxidant enzymes SOD and CAT in wheat, ZnO NPs improved drought resistance. Zn and Cu NPs also increased the antioxidative enzyme activity, decreased lipid peroxidation, stabilized the photosynthetic pigments with increased RWC, and enhanced drought tolerance in wheat [64]. CuO and ZnO NPs modified the root morphology of plants colonized by *Triticum aestivum*, a beneficial pseudomonad, altering the plants to withstand drought [65]. CuO NPs boosted the production of lateral roots in wheat seedlings, and ZnO NPs stimulated the growth of extended root hairs proximal to the root tip. Drought stress severely affected eggplant development and production [66]. Exogenous ZnO NPs with 50 and 100 ppm, boosted the RWC and membrane stability index, improved stem and leaf morphology and better photosynthesis in water-stressed eggplant and yield rose by 12.2 and 22.6%, respectively.
