Alleviation of salt toxicity by melatonin supplementation in eggplant involves the up-regulation of ascorbate–glutathione and glyoxalase system

Abstract

Eggplant is considered an important vegetable to evaluate the abiotic stress responses, especially salt stress, that compromise the growth as well as development of plants. Melatonin (MT) has recently surfaced as an emerging stress-alleviating molecule that can relief salinity-triggered toxicity in plants. Nonetheless, the probable mechanism involved in functioning of MT under saline stress has not yet been demonstrated to full extent in plants. Hence, we experimented to get insight into the crucial mechanisms involved in MT-triggered saline stress tolerance using eggplant. Biomass production and growth traits are substantially reduced under saline stress due to impairment of photosynthesis, hindering photosystem function, and accumulation of secondary metabolites. In contrast, application of MT remarkably enhanced the growth attributes, improved photosynthetic efficiency, maximum PSII efficacy (Fv/Fm), gas exchange parameters, elevated uptake of Potassium (K+) and reduced accumulation of Sodium (Na+) ion. Furthermore, MT efficiency recovered integrity of the cell [reduced malondialdehyde (MDA) and relative electrolyte leakage (REL)] through inducing the activities of antioxidant enzymes and regulating AsA-GSH pool, tightened the production of superoxide radical (O2•−) and hydrogen peroxide (H2O2). In particular, MT treatment increased Gly 1 enzyme activity and reduced MG enzyme activity in the leaves of eggplant seedling. In addition, proline, soluble sugar, and protein contents in eggplant leaves are enhanced as a result of MT treatment. We conclude that our research findings define the important role of MT in mitigating the toxicity triggered in eggplants due to salinity by improving photosynthesis, redox balance, and uptake of nutrients, secondary metabolism and hence increased biomass synthesis.