Melatonin and hemin co-application reprograms lipolysis, oleosin accumulation and H2S metabolism in NaCl-stressed sunflower seedlings.

Salt stress adversely affects seed germination and lipid mobilization in germinating sunflower seedlings. Notably, recovery in the rate of lipolysis is crucial to promote stress tolerance, thereby imparting longevity to the seedlings. Melatonin has been previously reported to regulate lipolysis in NaCl-stressed sunflower seedling cotyledons. While hemin (oxidized form of heme) is known to function as a metabolic regulator in plants, no substantial reports are available to understand the combined impact of melatonin and hemin application in the regulation of lipid mobilization during seed germination. The present work hypothesizes that melatonin and hemin co-application escalates lipolysis thereby accompanying changes in proteolytic activity and H2S metabolism in NaCl-stressed sunflower seedling cotyledons. Seedlings exhibited reduced activity of lipolytic enzymes (fatty acyl-ester hydrolase, lipoxygenase, and phospholipase) accompanying a slower oil body mobilization under salinity stress. However, co-application of melatonin and hemin significantly reversed these effects thereby suggesting a faster rate of oil body degradation and lipid mobilization. Electrophoretic analysis of the lipolytic enzymes revealed isoform-specific changes in their expression in different treatment regimes. Confocal laser scanning microscopic analysis and spectrofluorometric estimation revealed intense H2S accumulation under NaCl stress, melatonin and hemin treatment which was correlated with the up-regulation of a 43 kDa L-cysteine desulfhydrase isoform. To sum up, the present work bears agronomic importance for the regulatory role of melatonin and hemin in modulating lipid mobilization and salt-sensitivity of oil seed crops.