Hydrogen sulfide (H(2)S) plays a crucial role in human and animal physiology. Its ubiquity and versatile properties have recently caught the attention of plant physiologists and biochemists. Two cysteine desulfhydrases (CDes), L-cysteine desulfhydrase and D-cysteine desulfhydrase, were identified as being mainly responsible for the degradation of cysteine in order to generate H(2)S. This study investigated the expression regulation of these genes and their relationship to drought tolerance in Arabidopsis. First, the expression pattern of CDes in Arabidopsis was investigated. The expression levels of CDes gradually increased in an age-dependent manner. The expression of CDes was significantly higher in stems and cauline leaves than in roots, rosette leaves and flowers. Second, the protective effect of H(2)S against drought was evaluated. The expression pattern of CDes was similar to the drought associated genes induced by dehydration, and H(2)S fumigation was found to stimulate further the expression of drought associated genes. Drought also significantly induced increased H(2)S production, a process that was reversed by rewatering. In addition, seedlings after treatment with NaHS (a H(2)S donor) showed a higher survival rate and displayed a significant reduction in the size of the stomatal aperture compared to the control. These findings provide evidence that H(2)S, as a gasotransmitter, improves drought resistance in Arabidopsis. (C) 2011 Elsevier Inc. All rights reserved.