Recent advancements in the mechanism of nitric oxide signaling associated with hydrogen sulfide and melatonin crosstalk during ethylene-induced fruit ripening in plants

The current review focuses on the significant role of nitric oxide (NO) in modulating ethylene-induced fruit ripening responses in plants. In this context, hydrogen sulfide (H₂S) and melatonin mediated crosstalk mechanisms have been discussed with recent updates. Physiological and biochemical events associated with climacteric fruit ripening involves a plethora of effects mediated by these biomolecules. In the last few years of progress in fruit ripening physiology, the involvement of hydrogen sulfide in relation to NO remains as a nascent field of research. The importance of nitric oxide as a freely diffusible and membrane permeable biomolecule leads to its applications in post-harvest fruit storage. The process of field to market transition of edible fruits involves various intermediate stages of post-harvest storage and transport. Fruits harvested in the pre-climacteric stage are intended to be stored and transported for longer durations. However, this does not confer proper development of aroma and flavor in the post-harvest stages. Nitric oxide and ethylene crosstalk is mediated by hydrogen sulfide and melatonin activity which regulate various metabolic pathways associated with fruit ripening. A surge in the reactive nitrogen species (RNS), sugar metabolism, and plastid biogenesis are the plausible effects of NO-ethylene crosstalk. NO-mediated regulations of carbon metabolism and phytohormone levels are essential components of fruit ripening process. Melatonin by the virtue of its functional group possesses strong anti-oxidative properties. Recent updates suggest crosstalk mechanisms associated with melatonin-ethylene and nitric oxide in plants. The present review briefly summarizes the current understandings of fruit ripening physiology manifested by the effects of NO, H₂S and melatonin signaling. The agri-horticultural applications of exogenous NO/H₂S donors and melatonin treatment impose major benefits for delaying postharvest fruit senescence.