Foliar Application of Ascorbic Acid and Tocopherol in Conferring Salt Tolerance in Rapeseed by Enhancing K+/Na+ Homeostasis, Osmoregulation, Antioxidant Defense, and Glyoxalase System

Abstract

This study explored the role of exogenous α-Toc (0.5 mM) and Asc (1 mM) in alleviating the damaging effects of salt stress in rapeseed plants (Brassica campestris cv. BARI Sarisha-17). Exposure of 21-day-old plants to different levels of salt stress (75 mM and 150 mM NaCl) resulted in the higher accumulation of sodium ions (Na+), reduced potassium ion (K+) levels, lower K+/Na+ ratio, increased oxidative damage, chlorophyll (Chl) breakdown, and disrupted antioxidant and glyoxalase systems. Phenotype responses to salt stress included reductions in plant height, shoot fresh weight, dry weight, number of siliques plant−1, silique length, number of seeds silique−1, 1000-seed weight, and seed yield plant−1. Exogenous α-Toc and Asc applications enhanced the levels of endogenous ascorbate, glutathione (GSH), AsA/dehydroascorbate ratios, GSH/glutathione disulfide, ascorbate peroxidase, monodehydroascorbate reductase, glutathione reductase, glutathione peroxidase, and catalase activities in the salt-stressed plants. Exogenous α-Toc and Asc enhanced antioxidant defense system components and insured better oxidative stress tolerance, as indicated by reduced hydrogen peroxide generation, membrane lipid peroxidation, and electrolyte leakage. Exogenous α-Toc and Asc increased glyoxalase I and glyoxalase II activities in the salt-affected plants. Moreover, they regulated proline levels and increased the leaf relative water content, as well as the Chl level. Exogenous α-Toc and Asc also restored growth and improved yield attributes and seed yield per plants in the salt-affected rapeseed.