Hydrogen peroxide involvement in formation and development of adventitious roots in cucumber

Hydrogen peroxide (H2O2), an active oxygen species, is widely generated in many biological systems. The present study demonstrates that H2O2 was generated in seedling explants after the primary roots were removed, and it mediates the auxin response prior to adventitious root formation in cucumber (Cucumis sativus L. Ganfeng 8). When compared with the controls, treatment of cucumber seedling explants after primary roots removal with either 20-40 mM H2O2 or 10 mu M IAA significantly increased the number of adventitious roots, and treatment with 10-50 mM H2O2 significantly increased the fresh weight of adventitious roots. The effects of H2O2 on promoting the formation and growth of adventitious roots were eliminated by 2 mM ascorbic acid, 100 U CAT or 1 mu M DPI, and the effects of IAA were eliminated by 4 mM ascorbic acid, 100 U CAT or 5 mu M DPI. Treatment with either 4 mM ascorbic acid or 1-5 mu M DPI inhibited the formation and growth of adventitious roots, and these inhibitory effects were partly reversed by exogenous H2O2.Furthermore, a higher concentration of endogenous H2O2 was detected in seedling explants 3 h after the primary roots were removed. However, in 10 mu M DPI-treated seedling explants, the concentration of endogenous H2O2 was markedly reduced by DPI. Results obtained suggest that H2O2 may function as a signaling molecule, involved in the formation and development of adventitious roots in cucumber.