Increased evidence has shown that hydrogen sulfide (H₂S), a novel gasotransmitter, could enhance drought resistance in plants by inducing stomatal closure, with concurrent enhancement of photosynthetic efficiency, but little is known about the mechanism behind this contradictory phenomenon. This study examined the regulating mechanism of H₂S in response to drought stress from stomatal and non-stomatal factors in Chinese cabbage. The results showed that exogenous H₂S could increase the accumulation of photosynthetic pigments and alleviate the damage caused by drought stress. It also regulated the expression in transcriptional level and the activity of ribulose 1,5-bisphosphate carboxylase/oxygenase (BrRuBisCO) under drought stress. The large subunit of BrRuBisCO was found to be modified by S-sulfhydration, which might be the reason for its increased enzyme activity. The fluxes of Cl−, K+, and H+ in the guard cells were detected by non-invasive micro-test techniques while under drought stress. The results indicated that H₂S signaling induced a transmembrane Cl− and H+ efflux and inhibited K+ influx, and the Cl− channel was the main responders for H₂S-regulated stomatal movement. In conclusion, H₂S signal not only activated the ion channel proteins located in the guard cell membrane to induce stomatal closure, but also regulated the transcriptional expression and the activity of RuBisCO, a non-stomatal factor to enhance the photosynthetic efficiency of leaves. There is therefore a beneficial balance between the regulation of H₂S signaling on stomatal factors and non-stomatal factors due to drought stress, which needs to be better understood to apply it practically to increase crop yields.

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