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 μM of NO donor sodium nitroprusside (SNP) or 200 μM 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.