Endogenous metabolic content of the cutting positions and ndole-3-butyric acid influence rooting of Toona ciliata var. pubescens stem cuttings

Abstract

Toona ciliata var. pubescens (family Meliaceae) is an endangered species of mahogany endemic to China. It is now under Class II protection, and stem cuttings are an important means for its clonal propagation. However, the metabolic changes that occur in the cuttings during adventitious root formation and how these are influenced by indole-3-butyric acid (IBA) are still unclear. This study investigated the influence of cutting positions (top, middle and base) on the rooting ability and the associated metabolic changes during adventitious root formation. We compared treatment with 800 mg l−1 IBA with controls. The results showed that the rooting percentage, taproots per cutting, and longest root length differed significantly depending on the cutting position. Base cuttings had the best rooting ability and exhibited the highest average rooting percentage, the longest roots, and most taproots per cutting. The contents of soluble sugar, starch, non-structural carbohydrates (NSCs) and soluble proteins, and the peroxidase (POD) activity, were significantly higher in base cuttings than in middle and top cuttings; however, polyphenol oxidase (PPO) activity did not differ significantly among the positions. Metabolic changes occurred during the cutting process. The levels of POD and PPO activities increased significantly until 20 days after planting, suggesting that this period is key for the induction of adventitious rooting in this species. In the rooting process, IBA promoted an increase in the contents of soluble sugar, starch, NSCs and soluble proteins in the stem cuttings and it also increased the activities of POD and PPO. Bark-water extract from the stem cuttings inhibited the germination of Chinese cabbage seeds in a concentration-dependent manner, irrespective of the cutting position.