The Possible Roles of Priming with ZnO Nanoparticles in Mitigation of Salinity Stress in Lupine (Lupinus termis) Plants

To our knowledge, little attention has been paid to evaluating ZnO nanoparticles (ZNPs) roles in plants grown under salinity stress. In this study, seeds of lupine (Lupinus termis) plants were grown in plastic pots and exposed to 0 (control) and 150 (S) mM NaCl with or without priming with different concentrations of ZnO [20 mg L-1 (ZNPs1), 40 mg L-1 (ZNPs2), and 60 mg L-1 (ZNPs3)] for 20 days. Salinized plants showed a reduction in plant growth parameters (root length, shoot length, fresh weight, and dry weight) and in the contents of photosynthetic pigments (chlorophyll a and b, and carotenoids) and Zn, as well as in the activity of catalase (CAT) against control plants. On the other side, salinity stress boosted the contents of organic solutes (soluble sugar, soluble protein, total free amino acids, and proline), total phenols, malondialdehyde (MDA), ascorbic acid and Na, as well as the activities of superoxide dismutase (SOD), peroxidase (POD), and ascorbate peroxidase (APX) in stressed plants over control plants. However, seed-priming with ZNPs mostly stimulated growth of stressed plants, which was accompanied by reinforcement in the levels of photosynthetic pigments, organic solutes, total phenols, ascorbic acid and Zn, as well as in the activities of SOD, CAT, POD, and APX enzymes over stressed plants alone. On the contrary, priming with ZNPs caused a decrement in the contents of MDA and Na in stressed plants relative to salinized plants alone. It is worthy to mention that, this improvement in salt tolerance of plants primed with ZNPs was more obvious in plants primed with ZNPs3 and grown both in unstressed and stressed regimes. Thus, our findings suggest that seed-priming with ZNPs, especially 60 mg L-1 ZnO is an effective strategy that can be used to enhance salt tolerance of lupine plants.