Pharmacological, laser scanning confocal microscopic (LSCM), real-time PCR and spectrophotographic approaches are used to study the roles of hydrogen sulfide (H 2 S) and nitric oxide (NO) in signaling transduction of stomatal movement response to ethylene in Arabidopsis thaliana. In the present study, inhibitors of H 2 S synthesis were found to block ethylene-induced stomatal closure of Arabidopsis. Treatment with ethylene induced H 2 S generation and increased L-/D-cysteine desulfhydrase (pyridoxalphosphate-dependent enzyme) activity in leaves. Quantitative PCR analysis showed AtL-CDes and AtD-CDes transcripts were induced by ethylene. It is suggested that ethylene-induced H 2 S levels and L-/D-cysteine desulfhydrase activity decreased when NO was compromised. The data clearly show that ethylene was able to induce H 2 S generation and stomatal closure in Atnoa1 plants, but failed in the Atnia1,nia2 mutant. Inhibitors of H 2 S synthesis had no effect on ethylene-induced NO accumulation and nitrate reductase (NR) activity in guard cells or leaves of Arabidopsis, whereas ethylene was able to induce NO synthesis. Therefore, we conclude that H 2 S and NO are involved in the signal transduction pathway of ethylene-induced stomatal closure. In Arabidopsis, H 2 S may represent a novel downstream indicator of NO during ethylene-induced stomatal movement. hydrogen sulfide, nitric oxide, L-/D-cysteine desulfhydrase, Arabidopsis thaliana, ethylene, stomatal closure Citation: Liu J, Hou L X, Liu G H, et al. Hydrogen sulfide induced by nitric oxide mediates ethylene-induced stomatal closure of Arabidopsis thaliana.