Role and relationship of nitric oxide and hydrogen peroxide in adventitious root development of marigold

Several lines of evidence suggest that nitric oxide (NO) and hydrogen peroxide (H2O2) are important signal molecules involved in plant development and other physiological processes. Marigold (Tagetes erecta L. 'Marvel') was used to understand the role and relationship of NO and H2O2 in adventitious root development of plants. The results showed that the effects of H2O2 or NO on adventitious root organogenesis of explants were dose dependent, with maximal biological responses at 200 mu M H2O2 or 50 mu M NO donor sodium nitroprusside (SNP). The results also indicated the importance of both putative NO synthase (NOS)-like and nitrate reductase (NR) enzymes, which might be responsible for the production of NO in explants during rooting. Additionally, guanosine 3', 5' -cyclic monophosphate (cGMP) was involved in NO- induced root formation of marigold, but it was not involved in H2O2- mediated rooting process. The root number and length of explants treated with NO and H2O2 simultaneously were significantly higher than those of explants treated with H2O2 or NO alone. Moreover, NO treatments enhanced endogenous H2O2 levels in hypocotyls. Together, these results indicate that NO and H2O2 play crucial roles in the adventitious root development of marigold explants both synergistically and independently.