Salt stress mitigation in chickpea seedlings: a comparative study of zinc oxide nano and bulk particles

Nanotechnology plays a vital role in enhancing plant tolerance to salt stress; however, comparative studies on zinc oxide bulk particles (ZnO bulk) and zinc oxide nanoparticles (ZnO NPs) in this context remain unexplored. Since zinc (Zn) is an essential micronutrient involved in enzyme activation, photosynthesis, and antioxidant responses, it is important to understand how ZnO bulk and ZnO NPs influence chickpea growth under salt stress. This study investigated the morphological and physiological responses of chickpea seedlings treated with ZnO bulk (50 mg/L) and ZnO NPs (50 mg/L) under varying salt concentrations (20, 40, 80, and 120 mmol/L). Salt stress significantly inhibited chickpea growth, reducing the relative growth rate, net assimilation rate, total chlorophyll content, and potassium (K) and zinc ion levels while increasing sodium (Na), chlorine (Cl), malondialdehyde (MDA), and proline content. However, the application of ZnO bulk and ZnO NPs improved these parameters, mitigating the negative effects of salt stress. Furthermore, exogenous ZnO bulk and ZnO NPs to salt-stressed (20, 40, 80, and 120 mmol/L) chickpea resulted in decreased malondialdehyde content by 30, 32, 47, 34%, and 58, 31, 48, 47%, proline content by 4, 6, 1.6, 4% and 22, 21, 22, 28%, respectively, in comparison to the control. Notably, ZnO bulk and ZnO NPs enhanced antioxidant enzyme activities, including superoxide dismutase, catalase, ascorbate peroxidase, glutathione peroxidase, and glutathione reductase. These findings suggest that foliar application of ZnO bulk and ZnO NPs helps alleviate salt stress in chickpeas, promoting better growth and physiological performance under saline conditions.