Hydrogen sulfide and potassium synergistically induce osmotic stress tolerance through regulation of H+-ATPase activity and sugar metabolism in tomato seedlings

Abstract Potassium (K) is an essential macronutrient which is known to regulate key metabolic processes, modulate enzyme activity and plays a decisive role in osmotic adjustment in plants. Present work evaluates the role of K in the regulation of endogenous hydrogen sulfide (H2S) signaling in modulating the tolerance of tomato (Solanum lycopersicum L. Mill.) seedlings to osmotic stress. The findings reveal that exposure of seedlings to 15% (w/v) polyethylene glycol 8000 (PEG) led to a substantial decrease in leaf K content which was associated with reduced H+-ATPase activity. Exogenous application of K to the stressed seedlings significantly improved endogenous K content. Treatment with sodium orthovanadate (SOV, PM H+-ATPase inhibitor) and tetraethylammonium chloride (TEA, K channel blocker) suggests that exogenous K stimulated H+-ATPase activity that further regulated endogenous K content in tomato seedlings subjected to osmotic stress. Moreover, reduction in H+-ATPase activity by hypotaurine (H2S scavenger) substantiates the role of endogenous H2S in the regulation of H+-ATPase activity. Elevation in endogenous K content enhanced the biosynthesis of hydrogen sulfide (H2S) through enhancing the synthesis of cysteine, the H2S precursor. Synergistic action of H2S and K effectively neutralized osmotic stress by regulating sugar metabolism that resulted in osmotic adjustment, as witnessed by reduced water loss and improved hydration level of the stressed seedlings. Cross talk of H2S and K also assisted the seedlings in the activation of antioxidant enzymes that controlled the generation of reactive oxygen species and led to the protection against oxidative stress. The integrative role of H2S and K signaling was validated using hypotaurine (H2S scavenger) and TEA (K channel blocker) which weakened the protection against osmotic stress induced impairments. In conclusion, exogenous K and endogenous H2S regulate H+-ATPase activity which plays a decisive role in the maintenance of endogenous K homeostasis. Thus, present work reveals that K and H2S crosstalk is essential for modulation of osmotic stress tolerance in tomato seedlings.