IBA-induced changes in antioxidant enzymes during adventitious rooting in mung bean seedlings: The role of H2O2

The changes in antioxidant enzyme activity during the induction of adventitious roots in mung bean seedlings treated with Indole-3-butyric acid (IBA), hydrogen peroxide (H2O2), ascorbic acid (ASA) and diphenylene iodonium (DPI) were investigated. As compared with the controls, treatments of seedlings with 10 mu M IBA significantly decreased POD activity by 55% and 49.6% at 3 h and 12 h of incubation, respectively, and significantly increased by 49.8% at 36h of incubation; treatments of seedlings with 10 mM H2O2 significantly decreased POD activity by 42%, 60%, 39% and 38% at 3 h, 12 h, 24 h and 48 h of incubation, respectively, the changes in ROD activity were coincident with those in IBA-treated seedlings during the 0-12 h incubation period: treatments of seedlings with 2 mM ASA significantly decreased APX activities by 27% only at 3 h of incubation, the varying trend of POD activity was similar to incubation with water; 10 mu M DPI treatments significantly decreased POD activity by 42%, 40%, 54% and 28% at 3 h, 6 h, 12 h and 48 h of treatment, respectively. CAT activities remained at relatively stable levels and no major changes occurred from 0 h to 48 h during the incubation phase of adventitious rooting. The results may imply that CAT, an H2O2-metabolizing enzyme, is inactivated by H2O2 during the formation of adventitious roots. As compared with the controls, IBA treatments significantly decreased APX activities by 48%, 53% and 66% at 3 h, 9 h and 12 h of treatment, respectively; H2O2 treatments significantly decreased APX activities by 59%, 51% and 57% at 3 h. 12 h and 36 h of incubation, respectively; ASA treatments significantly decreased APX activities by 37% only at 3 h of incubation; DPI treatments significantly decreased APX activities by 54%, 53% and 63% at 3 h, 6 h and 12 h of incubation, respectively, and significantly increased APX activity by 106% at 24 h. These results indicated that the influence of IBA, H2O2, ASA and DPI on the changes in APX activity were the same as on the changes in POD activity. Furthermore, similar trends in the changes of APX activity and POD activity were observed during the induction and initiation rooting phase. This finding implies that APX and POD serve the same functions, possibly related to the level of H2O2, during the formation of adventitious roots, The early decrease of POD and APX activities in the initiation phase of IBA- and H2O2-treated seedlings may be one mechanism underlying the IBA- and H2O2-mediated facilitation of adventitious rooting. (C) 2009 Elsevier B.V. All rights reserved.