Endogenous hormone levels and activities of IAA-modifying enzymes during adventitious rooting of tree peony cuttings and grafted scions

During rooting of both cuttings and grafted scions of tree peony (Paeonia suffruticosa Andr.) cultivar ‘Fengdanbai’, the anatomical structure, the contents of endogenous hormones (indole acetic acid, IAA; zeatin, ZT; gibberellin, GA3; and abscisic acid, ABA), and the activities of IAA oxidase (IAAO), peroxidase (POD), and polyphenol oxidase (PPO) were observed. The results showed that the rooting processes in cuttings and grafted scions were similar, but that the critical period of rooting in cuttings was earlier than in grafts (cuttings: 18–20 days; scions: 38–40 days). IAA content showed a direct correlation with rooting, with the peak value appearing as the adventitious roots were breaking through the epidermis in both cuttings and grafts (cuttings: 20 days; scions: 38 days). ZT and GA3 promoted adventitious rooting, and ABA inhibited it. The peak values of the IAA:ABA and IAA:ZT ratios appeared at the same time as the IAA peak (cuttings: 20 days; scions: 38 days), which indicated that these values were closely related to the occurrence of adventitious roots. Changes in the activities of IAAO, POD, and PPO, which modify IAA levels, indicated that there were no direct relationships between these three enzymes and adventitious root formation in cuttings or grafts. These results provide a basis for further study of adventitious root formation in the ornamental tree peony.