Effect of Nitric Oxide and Hydrogen Peroxide on Adventitious Root Development from Cuttings of Ground-Cover Chrysanthemum and Associated Biochemical Changes

It is well known that plant adventitious root formation can be stimulated by the application of nitric oxide (NO) and hydrogen peroxide (H2O2) exogenously but the mechanism of this physiological response is still unclear. Ground-cover chrysanthemum (Dendranthema morifolium 'Beiguozhicun') was used to understand the effects of NO and H2O2 on the rooting of plant cuttings and the associated biochemical changes of the rooting zone during the rhizogenesis process. The results showed that the effect of NO or H2O2 on rooting of ground-cover chrysanthemum cuttings was dose-dependent, with a maximal biological response at 50 mu M of NO donor sodium nitroprusside (SNP) or 200 mu M H2O2. There was a synergistic effect between NO and H2O2 on mediating rooting. NO and H2O2 treatments at the proper dosage might increase the activities of polyphenol oxidase (PPO) and indoleacetic acid oxidase (IAAO) and the content of water-soluble carbohydrate (WSC) and total nitrogen, while decreasing the total polyphenol content of ground-cover chrysanthemum cuttings. In addition, rooting percentage was significantly correlated with these biochemical constituent activities or contents. Together, these results indicated that NO and H2O2 treatments enhanced adventitious root development synergistically and independently by stimulating the activities of PPO and IAAO enzymes and the content of carbohydrate and nitrogen and simultaneously repressing the production of polyphenol.