Thymol confers tolerance to salt stress by activating anti-oxidative defense and modulating Na+ homeostasis in rice root.

Modulation of plant salt tolerance has been drawing great attention. Thymol is a kind of natural chemical that has been developed as anti-microbial reagent and medicine. To date, we still have limited knowledge about thymol-modulated plant physiology. In this work, physiological, histochemical, and biochemical methods were adopted to study thymol-conferred salt resistance in the root of rice (Oryza sativa). Thymol significantly rescued root growth under salt stress. Thymol ameliorated cell membrane damage, oxidative stress, ROS accumulation, and cell death in roots under salt stress. Thymol-attenuated oxidative stress may be resulted from the activation of anti-oxidative capacity, including both enzymatic and non-enzymatic system. Thymol treatment significantly decreased Na⁺ content in root cells upon salt stress, which might be ascribed to the upregulation of OsSOS1 (salt overly sensitive 1) facilitating Na⁺ exclusion. In addition, thymol stimulated the expression of genes encoding tonoplast OsNHX (Na⁺/H⁺antiporter), which may help root cells to compartmentalize Na⁺ in vacuole. The results of these works evidenced that thymol was capable of inducing salt tolerance by reestablishing ROS homeostasis and modulating cellular Na⁺ flux in rice roots. These findings may be applicable to improve crop growth in salinity area.