Abstract
As a dominant mangrove species, Kandelia obovata is distributed in an intertidal marsh with an active H(2)S release. Whether H(2)S participates in the salt tolerance of mangrove plants is still ambiguous, although increasing evidence has demonstrated that H(2)S functions in plant responses to multiple abiotic stresses. In this study, NaHS was used as an H(2)S donor to investigate the regulatory mechanism of H(2)S on the salt tolerance of K. obovata seedlings by using a combined physiological and proteomic analysis. The results showed that the reduction in photosynthesis (Pn) caused by 400 mM of NaCl was recovered by the addition of NaHS (200 μM). Furthermore, the application of H(2)S enhanced the quantum efficiency of photosystem II (PSII) and the membrane lipid stability, implying that H(2)S is beneficial to the survival of K. obovata seedlings under high salinity. We further identified 37 differentially expressed proteins by proteomic approaches under salinity and NaHS treatments. Among them, the proteins that are related to photosynthesis, primary metabolism, stress response and hormone biosynthesis were primarily enriched. The physiological and proteomic results highlighted that exogenous H(2)S up-regulated photosynthesis and energy metabolism to help K. obovata to cope with high salinity. Specifically, H(2)S increased photosynthetic electron transfer, chlorophyll biosynthesis and carbon fixation in K. obovata leaves under salt stress. Furthermore, the abundances of other proteins related to the metabolic pathway, such as antioxidation (ascorbic acid peroxidase (APX), copper/zinc superoxide dismutase (CSD2), and pancreatic and duodenal homeobox 1 (PDX1)), protein synthesis (heat-shock protein (HSP), chaperonin family protein (Cpn) 20), nitrogen metabolism (glutamine synthetase 1 and 2 (GS2), GS1:1), glycolysis (phosphoglycerate kinase (PGK) and triosephosphate isomerase (TPI)), and the ascorbate-glutathione (AsA-GSH) cycle were increased by H(2)S under high salinity. These findings provide new insights into the roles of H(2)S in the adaptations of the K. obovata mangrove plant to high salinity environments.