Hydrogen Peroxide is Involved in Salicylic Acid-Induced Adventitious Rooting in Cucumber Under Cadmium Stress

Cadmium (Cd) stress can cause system disorders in plants, affect the absorption of some nutrients. The roles and their relationship of salicylic acid (SA) and hydrogen peroxide (H2O2) in adventitious root formation (ARF) of cucumber (Cucumis sativus L.) under Cd stress were studied. The results showed that the exogenous SA and H2O2 in enhancing ARF in cucumber explants under Cd stress was concentration-dependent, with an optimal biological effect at 0.1 µM SA or 50 µM H2O2. Under Cd stress, SA-induced ARF was significantly reversed by H2O2 scavenger and inhibitor, indicating that endogenous H2O2 may be involved in SA-induced ARF under Cd stress. In addition, endogenous H2O2 levels were also promoted by SA in cucumber explants. The application of SA promoted pectin content and decreased pectin methylesterification degree under Cd stress. Moreover, we founded that SA and SA + H2O2 up-regulated the expression level of CsQUA and CsPME under Cd stress, respectively. However, the application of H2O2 scavenger and inhibitor could significantly reverse the effects of SA on the expression of the above genes. These results suggested that SA might play an important role in ARF in cucumber under Cd stress via enhancing endogenous H2O2 levels.