Exogenous melatonin‐mediated regulation of K⁺/Na⁺ transport, H⁺‐ATPase activity and enzymatic antioxidative defence operate through endogenous hydrogen sulphide signalling in NaCl‐stressed tomato seedling roots

Abstract

Melatonin (Mel) and hydrogen sulphide (H2S) have emerged as potential regulators of plant metabolism during abiotic stress. Presence of excess NaCl in the soil is one of the main causes of reduced crop productivity worldwide. The present investigation examines the role of exogenous Mel and endogenous H2S in tomato seedlings grown under NaCl stress. Effect of 30 µm Mel on endogenous synthesis of H2S was examined in roots of NaCl‐stressed (200 mm) tomato seedlings. Also, the impact of treatments on the oxidative stress markers, transport of K+ and Na+, and activity of H+‐ATPase and antioxidant enzymes was assessed. Results show that NaCl‐stressed seedlings supplemented with 30 µm Mel had increased levels of endogenous H2S through enhanced L‐cysteine desulfhydrase activity. Mel in association with H2S overcame the deleterious effect of NaCl and induced retention of K+ that maintained a higher K+/Na+ ratio. Use of plasma membrane inhibitors and an H2S scavenger revealed that Mel‐induced regulation of K+/Na+ homeostasis in NaCl‐stressed seedling roots operates through endogenous H2S signalling. Synergistic effects of Mel and H2S also reduced the generation of ROS and oxidative destruction through the enhanced activity of antioxidant enzymes. Thus, it is suggested that the protective function of Mel against NaCl stress operates through an endogenous H2S‐dependent pathway, wherein H+‐ATPase‐energized secondary active transport regulates K+/Na+ homeostasis.

Crosstalk between Melatonin and Reactive Oxygen Species in Plant Abiotic Stress Responses: An Update

“…It was also shown that H 2 S plays a vital role in enhancing plant tolerance to abiotic stress and alleviating its detrimental effects [ 89 , 90 , 91 , 92 ]. Melatonin increased the activities of the H 2 S-produced enzymes ( D -cysteine desulfhydrase (DCD), L -cysteine desulfhydrase (LCD)), thus improving H 2 S accumulation [ 93 , 94 , 95 ]. Further, application of hypotaurine (HT, H 2 S scavenger) reversed the contribution of melatonin in alleviation of the salinity and heat damages by reestablishing the redox homeostasis in tomato, cucumber, and wheat seedlings [ 44 , 94 , 95 ].…”

Melatonin Confers Plant Cadmium Tolerance: An Update

“…H 2 S enhanced photosynthesis and antioxidant enzyme activity, and up-regulated the transcripts of PC genes to alleviate Cd stress in tobacco [33]. Moreover, H 2 S homeostasis and L-cysteine desulfhydrase activity were involved in melatonin-modulated salt stress tolerance in tomato and cucumber seedlings [31,34,35]. Crosstalk of melatonin and H 2 S in alleviating heat stress was also suggested in wheat [36].…”

“…Exogenous melatonin regulated the endogenous H 2 S homeostasis by modulating the L-DES activity in salt-stressed tomato cotyledons [31]. Moreover, an endogenous H 2 S-dependent pathway was involved in melatonin-mediated salt stress tolerance in tomato seedling roots [34]. Synergistic effects of melatonin and H 2 S regulated K + /Na + homeostasis, and reduced excessive accumulation of ROS by enhancing the activity of antioxidant enzymes.…”

“…Various pharmacological, enzyme activity, and gene expression investigations revealed the crosstalk of H 2 S-melatonin in response to salt and heat stress in tomato and cucumber [34][35][36]. Exogenous melatonin induced the H 2 S generation by activating the L-cysteine desulfhydrase (L-CDes) activity, which was encoded by LCD, DCD, and DES1 [31,35].…”

“…Exogenous melatonin induced the H 2 S generation by activating the L-cysteine desulfhydrase (L-CDes) activity, which was encoded by LCD, DCD, and DES1 [31,35]. Then, the interaction of H 2 S and melatonin enhanced the antioxidant defense, and regulated carbohydrate metabolism and ion homeostasis [34][35][36]118]. Similar pharmacological experiments with an effective concentration range of 1-200 µM in exogenous melatonin, 10-100 µM in 4-Chloro-DL-phenylalanine (p-CPA, melatonin synthesis inhibitor), 10-100 µM in hypotaurine (HT, H 2 S inhibitor), and 10-100 µM in NaHS (H 2 S donor) could be used to investigate the crosstalk of H 2 S-melatonin during Cd stress.…”