Effects of Root Pruning on Adventitious Root Formation, Enzyme Activities, and Hormone Levels in Paeonia suffruticosa ‘Fengdanbai’ Seedlings
Zheng Wang, Gege Su, HE Song-lin, Liyun Shi, Dan He, Wenqian Shang, Dajuan Yang
Abstract
Root pruning during early root development can optimize the root structure of woody plants. To determine the effects of root pruning on tree peony (Paeonia suffruticosa), seedlings of the tree peony cultivar 'Fengdanbai' were subjected to varying degrees or different styles of root pruning. Various indexes were analyzed, including the anatomical structure of the root, root vitality, the activity levels of antioxidant enzymes, and the contents of endogenous hormones and their ratios. Comprehensive morphological observation showed that pruning freshly germinated roots that are 3 cm long by 1/3 (i.e., removing 1 cm) yielded the greatest rooting rate (90%), lateral root initiation (2.34 per seedling), and subsequent growth. Analysis of physiological and biochemical indicators during the critical rooting period (3-5 days after root pruning) showed that the levels of superoxide dismutase and abscisic acid (ABA) were decreased, while the oxidase activities of peroxidase, polyphenol oxidase, and indole acetate oxidase and the contents of the endogenous hormones indole acetic acid (IAA), gibberellin (GA3), and zeatin (ZT) were increased. IAA plays a key role in the process of adventitious root formation and the ratios of IAA/GA3, IAA/ABA, and IAA/ZT reflect endogenous hormone homeostasis during adventitious root formation. IAA/ABA and IAA/ZT showed higher values in the pruned roots compared to the control roots, which favor adventitious root induction and elongation. These results provide a basis for the study of adventitious root formation in tree peony.