Indole-3-butyric acid mediates antioxidative defense systems to promote adventitious rooting in mung bean seedlings under cadmium and drought stresses

In vitro experiments were performed to determine whether auxin can mediate the formation of adventitious roots in response to heavy metal and drought stresses using a model rooting plant, mung bean [Vigna radiata (L.) Wilczek]. The treatments with CdCl2 or mannitol alone significantly inhibited the formation and growth of adventitious roots in mung bean seedlings. In contrast, when CdCl2 or mannitol was applied together with indole-3-butyric acid (IBA), IBA considerably cancelled the inhibition of adventitious rooting by stresses. Treatment with CdCl2 or mannitol alone significantly increased the soluble protein and malondialdehyde (MDA) contents. CdCl2 and mannitol stress each induced differentially significant changes in the activities of antioxidative enzyme and antioxidant levels during adventitious rooting. Notably, both CdCl2 and mannitol stress strongly reduced the peroxidase (POD) and ascorbate peroxidase (APX) activities and glutathione (GSH) and phenols levels. Catalase and superoxide dismutase (SOD) activity were enhanced by CdCl2 but reduced by mannitol. CdCl2 increased the ascorbate acid (ASA) level, which was decreased by mannitol. Furthermore, when CdCl2 or mannitol was applied together with IBA, IBA counteracted the CdCl2- or mannitol-induced increase or decrease in certain antioxidants, MDA, and antioxidative enzymes. These results suggest that Cd and mannitol stress inhibition of adventitious rooting is associated with the regulation of antioxidative enzymes and antioxidants in cells to defense the oxidative stress. Moreover, IBA alleviates the effects of Cd and mannitol stress on the rooting process partially through the regulation of antioxidative defense systems.