Hydrogen sulfide improves photosynthetic efficiency by regulating light energy dissipation and reversible phosphorylation of thylakoid proteins in rice under salt stress

Hydrogen sulfide (H₂S) has been regarded as a small gasotransmitter associated with physiological and biochemical regulation in plant responses to environmental stresses. However, the regulatory mechanisms of H₂S in photosynthesis under adverse conditions remains poorly understood in plants. Here, the role of H₂S in the regulation of photosystem I (PSI) and photosystem II (PSII) was investigated in rice seedlings subjected to salt stress. Our results showed that NaHS (H₂S donor) pretreatment significantly enhanced photosynthetic pigment content, gas exchange parameters, and the photochemical capacity of both PSI and PSII, while the application of H₂S scavenger hypotaurine (HT) or inhibitor hydroxylamine (HA) with NaHS resulted in the decline in photosynthetic efficiency in rice under salt stress. NaHS-pretreated plants displayed the rapid energy dissipation and an elevated electron transport rate (ETR), whereas HA and HT treatments further suppressed these processes under salt stress. Furthermore, we found that the protective mechanism of H₂S against salt stress was associated with the elevated levels of several PSII proteins, rapidly reversible phosphorylation of thylakoid proteins, and the stabilization of PSII-LHCII supercomplexes and PSI-PSII dimers. Collectively, our results demonstrate that H₂S can contribute to salt tolerance of photosynthetic machinery by optimizing electron transport efficiency and the coordinated regulation of PSII protein phosphorylation in rice.