Exogenous Potassium (K⁺) Positively Regulates Na⁺/H⁺ Antiport System, Carbohydrate Metabolism, and Ascorbate–Glutathione Cycle in H₂S-Dependent Manner in NaCl-Stressed Tomato Seedling Roots

• Main Authors: M. Nasir Khan, Soumya Mukherjee, Asma A. Al-Huqail, Riyadh A. Basahi, Hayssam M. Ali, Bander M. A. Al-Munqedhi, Manzer H. Siddiqui, Hazem M. Kalaji
• Format: Article
• Language: English
• Published: MDPI AG 2021-05-01
• Series: Plants
• Subjects: hydrogen sulfide; ionic homeostasis; Na⁺/H⁺ antiport; oxidative stress; potassium; salinity
• Online Access: https://www.mdpi.com/2223-7747/10/5/948
• ISSN: 2223-7747

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 (H₂S). The present investigation was carried out to unravel the role of K⁺ and H₂S 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 H₂S, 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 H₂S 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, H₂S 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 H₂S scavenger HT reversed the effect of K⁺, suggesting H₂S-dependent functioning of K⁺ under NaCl stress. Therefore, the present findings report that K⁺, in association with H₂S, alleviates NaCl-induced impairments by regulating the Na⁺/H⁺ antiport system, carbohydrate metabolism, and antioxidative defense system.