preprint Open access
Papers open inside SciRah from the original publisher or repository; SciRah never hosts them.
The contribution of nanotechnology to agriculture has become the new subject of concern for plant physiologists since it is effective relative to the conventional means of fertilization. Zinc oxide nanoparticles (ZnO-NPs) are recognized to have a critical role in the abiotic stress tolerance of plants, nevertheless, their comparative effects with bulk-ZnO in alfalfa against salt stress have not been examined. In this study, different concentrations (25 and 50 mg L-1) of two different ZnO sources (nano and bulk) were sprayed on alfalfa which was subjected to three levels of salinity; S0, S50, and S100 (NaCl) mg kg-1 of soil. Plants responded favorably to 50 mg L-1 nanoparticles (NPs) treatment, which increased the growth and resistance towards salinity. Whereas salt stress increased the quantity of proline, hydrogen peroxide, and superoxide anion radical. Exogenously applied foliar spray of nano-ZnO significantly evoked the activities of antioxidants and levels of osmolytes to mitigate the shocks of salinity stress at S100. Consequently, among all other concentrations of nano and bulk, 50 mg L-1 nano-ZnO was statistically found efficient in improving the overall shoot growth, morphology, and physiology of alfalfa in the presence of salt stress. Spray of NPs to the stressed plants even further improved the antioxidant enzymatic system and other physiochemical processes as compared to bulk counterpart. The absorption and translocation of ZnO studied by transmission electron microscopy (TEM) techniques indicated that nano-ZnO was mainly located in vacuoles and chloroplasts. Results further suggested that application of ZnO-NPs boosted the development and physiology of the plant and also strengthened the salt tolerance capability of the plant in contrast to bulk treatments. Better growth and greater stress tolerance of alfalfa plants owing to ZnO-NP application might be attributed to higher activities of antioxidant enzymes, greater accumulation of osmolytes, and improved relative water content level.