Cobalt chloride-induced lateral root formation in rice: The role of heme oxygenase

Lateral roots (LRs) perform the essential tasks of providing water, nutrients, and physical support to plants. Therefore, understanding the regulation of LR development is of agronomic importance. Recent findings suggest that heme oxygenase (HO) plays an important role in LR development. In this study, we examined the effect of cobalt chloride (CoCl2) on LR formation and HO expression in rice. Treatment with CoCl2 induced LR formation and HO activity. We further observed that CoCl2 could induce the expression of OsHO1 but not OsHO2. CoCl2-increased HO activity occurred before LR formation. Zinc protoporphyrin IX (ZnPPIX, the specific inhibitor of HO) and hemoglobin (the carbon monoxide/nitric oxide scavenger) reduced LR formation, HO activity, and OsHO1 expression. Application of biliverdin, a product of HO-catalyzed reaction, to CoCl2-treated rice seedlings reversed the ZnPPIX-inhibited LR formation and ZnPPIX-decreased HO activity. CoCl2 had no effect on H2O2 content and nitric oxide production. Moreover, application of ascorbate, a H2O2 scavenger, failed to affect CoCl2-promoted LR formation and HO activity. It is concluded that HO is required for CoCl2-promoted LR formation in rice.