**2. Role of nanoparticles in salinity stress**

Salinity has a negative impact on crops in various physiological and biochemical processes that decrease crop production drastically [13]. Water scarcity in the soil causes low osmotic potential and ionic toxicity of Cl− and Na+ in plant cells [14]. It is also seen that salt stress results in decreased concentration of photosynthetic pigments, reduced stomatal flow, lack of efficiency of photosystem II, and increased production of ROS.

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

Salt stress causes chlorophyll concentration leads to membrane disintegration and the rate of photosynthesis is significantly decreased. It also causes injury in thylakoid and grana that results in limited starch content [15]. Lupine (*Luminus termis*) was protected in saline conditions by priming with ZnO NPs, which enhanced the photosynthetic pigments, antioxidant responses, and growth [16]. ZnO NPs treatment also increased the antioxidant enzymes in *Zea mays* [17]. When *Abelmoschus esculentus* was treated with ZnO NPs, it increased the SOD and CAT activities and photosynthetic pigment [18]. Canola (*Brassica napus*) plant treated with ZnO NPs, alleviated the harmful effects of salt by upregulating the osmolyte biosynthesis, ionic regulation,

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

and antioxidant system under saline conditions [19]. *Gossypium hirsutum* plants treated with ZnO NPs enhanced the contents of carotenoids, chlorophyll a and b, and total chlorophyll under salt stress conditions [20, 21]. When salt-stressed citrus plants (*Citrus reticulata*) were treated with ZnO NPs, it results in decreased accumulation of total soluble sugars and proline contents that help in the osmoregulation of plants and maintain the growth rate of treated plants [22].
