**5. Seed nanopriming in abiotic stress mitigation**

Due to the increase in pollution and climate changes, seeds are exposed to biotic and abiotic stress, which has a negative effect on their growth and development [83]. These stressors can cause physicochemical changes in various cellular levels.

*Seed Nanopriming to Mitigate Abiotic Stresses in Plants DOI: http://dx.doi.org/10.5772/intechopen.110087*

Stress can sense *via* cellular compartments such as cell wall and membrane, cytoplasm, chloroplast, mitochondria, endoplasmic reticulum, and peroxisomes [84]. In response to stress, gene transcription, transcription, translation, and post-translational modifications (PTMs) of proteins are altered, leading to the production and modification of proteins that play various roles in stress response [84].

In non-stressed conditions, the seed activates the GA signaling pathway and the transcription factors of hydrolytic enzymes by absorbing water; both processes break down the endosperm and release soluble sugar for seed growth, whereas, in stress conditions, the seed is unable to absorb water. In contrast, it activates the ABA signaling pathway, overproduces ROS, and prevents endosperm breakdown, which directly either slows down or delays seed germination [27]. In stressful conditions, nanoparticles can reduce seed ROS levels and thus seed cell damage due to increased activity of enzymes such as superoxidase dismutase, catalase [14].

#### **5.1 Seed nanopriming under salt stress**

Salinity is abiotic stress that threatens to impede plant growth and thereby affect crop yield [85]. Salinity in seeds causes osmotic and oxidative stress, which is associated with slowing down and prolonging the germination period [27]. Seed priming with Mn nanoparticles increases root length, alters the redistribution of macro-/ micronutrients including Mn, Na, and Ca, and increases salt tolerance of *Capsicum annuum* [10]. However, under the pressure of salinity, maize seeds and *Paeonia suffruticosa* were enhanced germination by TiO2, vigor index, shoot and root length, seedling biomass, RWC, total phenol, antioxidant enzyme function [44, 67]. In addition, priming rapeseed with cerium oxide increased germination, water absorption, SOD, POD, α-amylase activities, total soluble sugar content, and Na+/K+ ratio while reducing accumulation of ROS and improved salt tolerance [86–88]. Additionally, lentil seeds containing iron nanochelates [89], cucumber seeds containing NPs from water treatment residues [90], and milk thistle containing NPs of chitosan [38] reduced salt stress by enhancing physiological salt stress. Latef et al. (2017) showed that priming of lupine seed with ZnO NPs increased photosynthetic pigments, total phenols, Zn and APX, POD, SOD, and CAT activities, and decreased MDA content and Na + under salt stress conditions [91]. Similarly, ZnO nanopriming improved wheat salt tolerance by activating the antioxidants to reduce oxidative explosion and increased photosynthetic electron transport efficiency and sucrose production in plants under stress [9]. Priming lettuce seeds with water-soluble carbon NPs (CNPs) increased seed germination and Chl content under salt stress [57].

#### **5.2 Seed nanopriming in drought stress**

Drought stress inhibits plant growth and reduces crop yields [92]. NP-mediated priming had a great effect on the growth of different plants to reduce drought stress. Seed priming with multi-walled carbon nanotubes increased the germination rate, root index, and root-shoot growth of alnus subcordata (*Caucasian alder*) under dry conditions [93]. In addition, Cape (*Catharanthus roseus* L.) seeds under drought stress with chitosan nanoparticles improved aggregation, membrane integrity, and plant growth [94]. In addition, corn seeds prepared with Cu nanoparticles increased RWC, Chl, and carotenoid and anthocyanin content and decreased ROS accumulation during drought stress [78]. Priming marigold seeds (*Calendula officinalis* L.) with silicon NPs increased quercetin, total flavonoid content, and antioxidant activity

under drought stress conditions [95]. Nanozymes, Fe3O4 magnetite, and γ-Fe2O3 magnetite are magnetic nanoparticles that are effective in the development of plant growth under drought stress. For example, γ-Fe2O3 nanoparticles in rapeseed reduced H2O2 and lipid peroxidation and increased growth under drought stress. It has been reported that nanozymes reduce plant stress by removing ROS and increasing enzyme capacity [96].

#### **5.3 Seed nanopriming in heavy metal stress**

Metal toxicity is one of the abiotic stressors that disrupts plant growth. NP priming reduces the accumulation of toxic metals and adverse effects in various agricultural productions. For example, in sunflower seeds primed with green synthetic sulfur under Mn stress (*Helianthus annuus* L.), it activates antioxidant enzymes and reduces ROS and lipid peroxidation [97]. Under cadmium (Cd) stress, priming of zinc nanoparticles increased amylase, POD and SOD activities, and seedling growth in rice [67]. Furthermore, wheat seeds pretreated with TiO2 enhanced germination rate, seedling growth, and water holding capacity under Cd stress. In maize seed priming with zinc oxide nanoparticles under cobalt stress, ROS and MDA decreased and plant growth, biomass and photosynthesis were improved [46]. In general, NPs reduce the adverse effects of HM by modulating plant physiological and biochemical parameters [98].
