Improvement of photosynthesis in rice (Oryza sativa L.) as a result of an increase in stomatal aperture and density by exogenous hydrogen sulfide treatment

Hydrogen sulfide (H2S) is considered to be the third gaseous signaling molecule after NO and CO, and it plays an active role in regulating the physiological processes of plants and animals. In this work, rice cultivar 'IIyou 084' seedlings were treated with NaHS, which is a donor of H2S, for 10 days, and its effects on growth and physiology, including photosynthesis, photorespiration, chlorophyll fluorescence, and stomata, were investigated. The data revealed that 0.01 mM of H2S improved rice biomass and chlorophyll content, while higher concentrations of H2S had an adverse effect on these parameters. Photosynthetic rate, stomatal conductance, and ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39) activity also increased under 0.01 mM H2S treatment. However, photosynthetic oxygen evolution rate, photosynthetic electron transfer, and photochemical efficiency of PSII were not affected by H2S treatment. In addition, photosynthesis oxygen sensitivity, CO2 compensation point, and glycolate oxidase (EC 1.1.3.1) activity reduced by H2S treatment, and thus photorespiration was down-regulated. Under light, stomatal aperture and density increased by treatment with 0.01 mM H2S. On the basis of these results, it can be deduced that 0.01 mM of H2S treatment improved photosynthesis in rice by increasing its stomatal aperture and density, which may result from reduced photorespiration.