Methyl jasmonate-induced lateral root formation in rice: the role of heme oxygenase and calcium.

Lateral roots (LRs) play important roles in increasing the absorptive capacity of roots as well as to anchor the plant in the soil. Therefore, understanding the regulation of LR development is of agronomic importance. In this study, we examined the effect of methyl jasmonate (MJ) on LR formation in rice. Treatment with MJ induced LR formation and heme oxygenase (HO) activity. As well, MJ could induce OsHO1 mRNA expression. Zinc protoporphyrin IX (the specific inhibitor of HO) and hemoglobin [the carbon monoxide/nitric oxide (NO) scavenger] reduced LR formation, HO activity and OsHO1 expression. LR formation and HO activity induced by MJ was reduced by the specific NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-oxide. The effects of Ca2+ chelators, Ca2+-channel inhibitors, and calmodulin (CaM) antagonists on LR formation induced by MJ were also examined. All these inhibitors were effective in reducing the action of MJ. However, Ca2+ chelators and Ca2+ channel inhibitors induced HO activity when combining with MJ further. It is concluded that Ca2+ may regulate MJ action mainly through CaM-dependent mechanism.