In higher plants, hydrogen sulfide (H2S) is a recognized signaling molecule that performs multiple regulatory functions. The enzyme L-cysteine desulfhydrase (LCD) catalyzes the conversion of L-cysteine (L-Cys) to pyruvate and ammonium with the concomitant generation of H₂S, and it is considered one of the main sources of H2S in plants. Using non-denaturing polyacrylamide gel electrophoresis (PAGE) in combination with a specific assay for LCD activity, this study aims to identify the potential LCD isozymes in wild-type Arabidopsis thaliana seedlings of 16 days old grown under in vitro conditions, and to evaluate the potential impact of nitric oxide (NO) and H2S on these LCD isozymes. For this purpose, an Atnoa1 mutant characterized to have a low endogenous NO content as well as the exogenous application of H2S were used. Five LCD isozymes were detected, with LCD IV being the isozyme that has the highest activity. However, the LCD V activity was the only one that was positively modulated in the Atnoa1 mutants and by exogenous H2S. To our knowledge, this is the first report showing the different LCD isozymes present in Arabidopsis seedlings and how their activity is affected by NO and H2S content.