Enhanced salinity tolerance in Alfalfa through foliar nano-zinc oxide application: Mechanistic insights and potential agricultural applications

Abstract

The field of nanoscience and nanotechnology has experienced rapid advancements, leading to the widespread utilization of zinc oxide nanoparticles (nano-ZnO) owing to their distinct physical and chemical properties. However, till date the comparative role of nano and bulk ZnO in the salt stress regulation in alfalfa is remained largely unaddressed. In this study, nano and bulk ZnO at 25 and 50 mg L−1 were sprayed on alfalfa which was subjected to three levels of salinity; S0, S50, and S100 (NaCl) mg kg−1 of soil. Nano-ZnO at 50 mg L−1 significantly enhanced the shoot and root growth by 29% and 28.4% respectively. The increased alfalfa growth and development could be associated with the regulatory effects of nano-ZnO, including photosynthesis, antioxidant enzyme activities and relative water content. Additionally, foliar application of nano-ZnO 50 mg L−1 in alfalfa dramatically up-regulated the levels of osmolytes (proline, total soluble sugar, and total soluble protein) by 36%, 61% and 32% respectively, leading towards better alfalfa salinity tolerance. The absorption and translocation of ZnO studied by TEM images indicated that nano-ZnO was mainly located in vacuoles and chloroplasts. These results provide noteworthy information for a mechanistic understanding of the biological impact of nano-ZnO on plant physiology and metabolism; this understanding paves the way for the judicious implementation of nanoparticles in agriculture.