Involvement of hydrogen peroxide and nitric oxide in expression of the ipomoelin gene from sweet potato

The IPO (ipomoelin) gene was isolated from sweet potato (Ipomoea batatas cv Tainung 57) and used as a molecular probe to investigate its regulation by hydrogen peroxide (H2O2) and nitric oxide (NO) after sweet potato was wounded. The expression of the IPO gene was stimulated by H2O2 whether or not the plant was wounded, but its expression after wounding was totally suppressed by the presence of diphenylene iodonium, an inhibitor of NADPH oxidase, both in the local and systemic leaves of sweet potato. These results imply that a signal transduction resulting from the mechanical wounding of sweet potato may involve NADPH oxidase, which produces endogenous H2O2 to stimulate the expression of the IPO gene. The production of H2O2 was also required for methyl jasmonate to stimulate the IPO gene expression. On the contrary, NO delayed the expression of the IPO gene, whereas N-G-monomethyl-L-arginine monoacetate, an inhibitor of NO synthase, enhanced the expression of the IPO gene after the plant was wounded. This study also demonstrates that the production of H2O2 stained with 3,3'-diaminobenzidine hydrochloride could be stimulated by wounding but was suppressed in the presence of NO. Meanwhile, the generation of NO was visualized by confocal scanning microscope in the presence of 4,5-diaminofluorescein diacetate after sweet potato was wounded. In conclusion, when sweet potato was wounded, both H2O2 and NO were produced to modulate the plant's defense system. Together, H2O2 and NO regulate the expression of the IPO gene, and their interaction might further stimulate plants to protect themselves from invasions by pathogens and herbivores.