Chen J, FH Wu, WH Wang, CJ Zheng, GH Lin, XJ Dong, JX He, ZM Pei and HL Zheng.Journal of Experimental Botany, 2011. 62: 4481-4493.Hydrogen sulphide (H₂S) is emerging as a potential messenger molecule involved in modulation of physiological processes in animals and plants. In this report, the role of H₂S in modulating photosynthesis ofSpinacia oleraceaseedlings was investigated. The main results are as follows. (i) NaHS, a donor of H₂S, was found to increase the chlorophyll content in leaves. (ii) Seedlings treated with different concentrations of NaHS for 30 d exhibited a significant increase in seedling growth, soluble protein content, and photosynthesis in a dose-dependent manner, with 100mMNaHS being the optimal concentration. (iii) The number of grana lamellae stacking into the functional chloroplasts was also markedly increased by treatment with the optimal NaHS concentration. (iv) The light saturation point (Lsp), maximum net photosynthetic rate (Pmax), carboxylation efficiency (CE), and maximal photochemical efficiency of photosystem II (F_v/F_m) reached their maximal values, whereas the light compensation point (Lcp) and dark respiration (Rd) decreased significantly under the optimal NaHS concentration. (v) The activity of ribulose-1,5-bisphosphate carboxylase (RuBISCO) and the protein expression of the RuBISCO large subunit (RuBISCO LSU) were also significantly enhanced by NaHS. (vi) The total thiol content, glutathione and cysteine levels, internal concentration of H₂S, andO-acetylserine(thiol)lyase and L-cysteine desulphydrase activities were increased to some extent, suggesting that NaHS also induced the activity of thiol redox modification. (vii) Further studies using quantitative real-time PCR showed that the gene encoding the RuBISCO large subunit (RBCL), small subunit (RBCS), ferredoxin thioredoxin reductase (FTR), ferredoxin (FRX), thioredoxin m (TRX-m), thioredoxin f (TRX-f), NADP-malate dehydrogenase (NADP-MDH), andO-acetylserine(thiol)lyase (OAS) were up-regulated, but genes encoding serine acetyltransferase (SERAT), glycolate oxidase (GYX), and cytochrome oxidase (CCO) were downregulated after exposure to the optimal concentration of H₂S. These findings suggest that increases in RuBISCO activity and the function of thiol redox modification may underlie the amelioration of photosynthesis and that H₂S plays an important role in plant photosynthesis regulation by modulating the expression of genes involved in photosynthesis and thiol redox modification.