Hydrogen sulfide and proline cooperate to alleviate cadmium stress in foxtail millet seedlings

Hydrogen sulfide (H₂S) and some functional amino acids in crops have been involved in the defense system against heavy-metal pollution. Here we report the relationships and functions of H₂S and proline to cadmium (Cd) stress. Sodium hydrosulfide (NaHS) pretreatment decreased the electrolytic leakage and the malondialdehyde and hydrogen peroxide contents while enhancing photosynthesis in Cd-treated seedlings. Furthermore, pretreatment with NaHS markedly exacerbated Cd-induced alterations in proline content, the activities of proline-5-carboxylate reductase (P5CR) and proline dehydrogenase (PDH), and the transcript levels of P5CR and PDH. When endogenous H₂S was scavenged or inhibited by various H₂S modulators, the Cd-induced increase in endogenous proline was weakened. Combined pretreatment with H₂S and proline was moderately higher in the Cd-stressed growth status, stomata movements and oxidative damage of seedlings compared to a single treatment with H₂S or proline. These results suggest that H₂S and proline cooperate to alleviate Cd-damage in foxtail millet.