Synergistic interplay between melatonin and hydrogen sulfide enhances cadmium-induced oxidative stress resistance in stock ( L.).

Ornamental crops particularly cut flowers are considered sensitive to heavy metals (HMs) induced oxidative stress condition. Melatonin (MLT) is a versatile phytohormone with the ability to mitigate abiotic stresses induced oxidative stress in plants. Similarly, signaling molecules such as hydrogen sulfide (HS) have emerged as potential options for resolving HMs related problems in plants. The mechanisms underlying the combined application of MLT and HS are not yet explored. Therefore, we evaluated the ability of individual and combined applications of MLT (100 μM) and HS in the form of sodium hydrosulfide (NaHS), a donor of HS, (1.5 mM) to alleviate cadmium (Cd) stress (50 mg L) in stock ( L.) plants by measuring various morpho-physiological and biochemical characteristics. The results depicted that Cd-stress inhibited growth, photosynthesis and induced Cd-associated oxidative stress as depicted by excessive ROS accumulation. Combined application of MLT and HS efficiently recovered all these attributes. Furthermore, Cd stress-induced oxidative stress markers including electrolyte leakage, malondialdehyde, and hydrogen peroxide are partially reversed in Cd-stressed plants by MLT and HS application. This might be attributed to MLT or HS induced antioxidant plant defense activities, which effectively reduce the severity of oxidative stress indicators. Overall, MLT and HS supplementation, favorably regulated Cd tolerance in stock; yet, the combined use had a greater effect on Cd tolerance than the independent application.