Exogenous Potassium (K(+)) Positively Regulates Na(+)/H(+) Antiport System, Carbohydrate Metabolism, and Ascorbate–Glutathione Cycle in H(2)S-Dependent Manner in NaCl-Stressed Tomato Seedling Roots

Potassium (K(+)) is one of the vital macronutrients required by plants for proper growth and blossoming harvest. In addition, K(+) also plays a decisive role in promoting tolerance to various stresses. Under stressful conditions, plants deploy their defense system through various signaling molecules, including hydrogen sulfide (H(2)S). The present investigation was carried out to unravel the role of K(+) and H(2)S in plants under NaCl stress. The results of the study show that NaCl stress caused a reduction in K(+) and an increase in Na(+) content in the tomato seedling roots which coincided with a lower H(+)-ATPase activity and K(+)/Na(+) ratio. However, application of 5 mM K(+), in association with endogenous H(2)S, positively regulated the Na(+)/H(+) antiport system that accelerated K+ influx and Na+ efflux, resulting in the maintenance of a higher K(+)/Na(+) ratio. The role of K(+) and H(2)S in the regulation of the Na(+)/H(+) antiport system was validated by applying sodium orthovanadate (plasma membrane H(+)-ATPase inhibitor), tetraethylammonium chloride (K(+) channel blocker), amiloride (Na(+)/H(+) antiporter inhibitor), and hypotaurine (HT, H(2)S scavenger). Application of 5 mM K(+) positively regulated the ascorbate–glutathione cycle and activity of antioxidant enzymes that resulted in a reduction in reactive oxygen species generation and associated damage. Under NaCl stress, K(+) also activated carbohydrate metabolism and proline accumulation that caused improvement in osmotic tolerance and enhanced the hydration level of the stressed seedlings. However, inclusion of the H(2)S scavenger HT reversed the effect of K(+), suggesting H(2)S-dependent functioning of K(+) under NaCl stress. Therefore, the present findings report that K(+), in association with H(2)S, alleviates NaCl-induced impairments by regulating the Na(+)/H(+) antiport system, carbohydrate metabolism, and antioxidative defense system.