Melatonin priming elevates hydrogen sulfide metabolism, reduces Na+ uptake and reprograms NaCl stress-induced metabolic signatures in sunflower seedling leaves

Abstract

Present work demonstrates the effect of melatonin priming on the modulation of NaCl-stress induced physiological and biochemical changes in sunflower seedlings. Seed priming with melatonin in optimized doses can be a cost-effective and convenient alternative for developing physiological tolerance to NaCl stress in sunflower (Helianthus annuus L.) plants. The present work substantiates the potential role of melatonin priming (50 μM) in the alleviation of NaCl stress (120 mM) in sunflower (Helianthus annuus L. var KBSH 88) seedlings as manifested by the elevation of H₂S metabolism and reprogramming of metabolic signatures in leaves. Melatonin priming brings about lower accumulation of Na⁺, improved K⁺ content (under NaCl stress), enhanced glutathione (GSH) metabolism, modulates antioxidative defense and slows down lipolysis in NaCl-stressed sunflower seedlings. Seedlings also exhibit adaptive response by lowering down membrane lipid peroxidation under NaCl stress which is manifested by a reduction in MDA content. Important correlations have been observed for physiological events in the cotyledons of sunflower seedlings as evident from changes in total neutral lipid content, accompanying differential distribution of ROS and H₂S in the cotyledonary leaf cells. Analysis of total neutral lipid content in the present work provides cue to the salt-sensitivity towards lipolysis in cotyledons from 20 d old sunflower seedlings. The physiological and biochemical parameters investigated in the present work, therefore, indicate towards better seedling performance and longevity in the early vegetative stage of sunflower plants subjected to NaCl stress and melatonin priming.

Keywords: Antioxidant enzymes; Hydrogen sulfide; Melatonin; NaCl stress; Priming; Sunflower.