**4. Effects of seed nanopriming on plants**

Nanopriming can improve the seed germination, stability, growth, and physiology of plant species by changing absorption, biochemical processes, antioxidants, photosynthesis [62, 63]. Various investigations demonstrate that nanoprimed seeds can better maintenance of cell balance and photosynthetic capacity [47, 62], increasing nutrient uptake and photosynthetic efficiency [59, 62], increased chlorophyll capacity and antioxidant activity, defense mechanisms (e.g., changes in osmotic pressure, stomatal movements) [64, 65]. It also removes the absorption of heavy metals (copper, cadmium, and zinc) and thus reduces toxicity [66].

Seed priming by NPs was discovered as a novel approach for regulating antioxidant enzymes in plants [67]. Plant antioxidant systems include non-enzymatic compounds and various enzymes, such as catalase (CAT), peroxidase (POX), ascorbate peroxidase (APX), superoxide dismutase (SOD), phenylalanine ammonia lyase (PAL), and glutathione. Priming of corn seeds with sodium metasilicate increased the activities of SOD, CAT, and POX under salt stress [68]. Similarly, maize seeds primed with TiO2 NPs increased SOD, CAT, and PAL activity [44]. Priming rice seeds with ZnO NPs enhances SOD and POD activity [67]. In addition, priming of Egyptian roselle (*Hibiscus sabdariffa* L.) seeds with Al2O3 NPs enhanced SOD, CAT, POD, and APX functions [69]. Priming of lavender (*Lavandula angustifolia* Mill.) by silver nanoparticles improved the performance of APX, POX, and SOD [70]. Wheat seeds primed with Si NPs increased SOD, POD, and CAT functions in cadmium stress [71]. Antioxidants produce ROS in response to environmental stressors. Antioxidant enzymes determine how ROS indirectly helps germination of nanoprimed seeds [72]. However, studies on the modulation of antioxidant enzymes by NPs priming are very few.

ROS as a by-product has a signaling role in germination and reducing seed dormancy [73]. This can occur by activating GA synthesis [74]. The accumulation of ROS such as superoxide (O2•-), hydrogen peroxide (H2O2), and hydroxyl radicals (OH) causes oxidative stress [73, 75]. Seeds generally receive NPs as extrinsic factors [72], and accumulation in the seed coat causes ROS production [34]. The increase of ROS in non-primed seeds is connected to the increase of abscisic acid (ABA), which caused disruption of seed dormancy and seed germination [76]. Furthermore, nanopriming increased ROS levels in plant cells, disrupted seed endosperm cell wall junctions, and promoted rapid and healthy seed germination [77]. Nanopriming can regulate ROS under normal and stress conditions, and seed nanopriming can regulate ROS production for faster seed germination. Under conditions, seeds accumulate ROS, and nanopriming can regulate ROS hemostasis *via* increased antioxidant activity for faster seed germination and improve plant stress tolerance [3]. Similarly, priming of maize seeds with copper NPs reduced ROS levels to drought stress [78]. Furthermore, *Lathyrus odoratus* seeds primed with Si-NPs reduced ROS and MDA levels under salt stress [79].

Stress and accumulation of ROS can affect membrane lipids, leading to lipid peroxidation, and loss of quality, germination, and seed viability [80, 81]. In stress conditions, an important lipid peroxidation reagent is malondialdehyde (MDA) [47, 82]. Studies have demonstrated that nanoparticle treatment by reducing lipid peroxidation stabilizes the cell membrane in various plants under abiotic stress [47], which is caused by the increased activity of antioxidant enzymes [83]. However, further research is necessary to elucidate the regulatory role of nanoparticle priming in ROS and membrane damage repair in different plants.
