Hydrogen sulfide is already recognized as an important signaling molecule in mammalian systems, and emerging data suggest that H 2S is a signaling molecule just as important as nitric oxide (NO) and H 2O 2 in plants. Although sulfide is generated in chloroplasts and mitochondria, it is present predominantly in the charged HS (-) form due to the basic pH inside both organelles, thus requiring an active transporter, which is yet to be identified, to be released. In Arabidopsis, we found that the cytosolic L-cysteine desulfhydrase DES1 is involved in the degradation of cysteine, and therefore responsible for the generation of H 2S in this cellular compartment. DES1 deficiency leads to the induction of autophagy. Moreover, we have demonstrated that sulfide in particular exerts a general effect on autophagy through negative regulation, in a way unrelated to nutrient deficiency. The mechanisms of H 2S action and its molecular targets are largely unknown, although in animal systems, protein S-sulfhydration has been proposed as a mechanism for sulfide-mediated signaling.