Effects of bleeding on stem physiology of Actinidia arguta (Sieb. & Zucc) Planch. ex miq. and metabolomics analysis of bleeding sap.

In early spring, bleeding is a common occurrence in A. arguta when local temperatures reach 8 °C-10 °C. In this study, changes in the composition of bleeding sap and effect of bleeding on A. arguta were determined by analyzing the variation in the composition of bleeding sap from different periods. Accordingly, the bleeding sap was analyzed by gas chromatography-mass spectrometry (GC-MS), and the related physiological indexes in the stem were measured. The results revealed that in annual early spring, bleeding seriously affected A. arguta. In addition, annual branches had a stronger capacity for scavenging free radicals than biennial or barren branches. The metabolomics analysis identified a total of 153 differential metabolites, mainly involved in glycolysis and the tricarboxylic acid cycle. Bleeding decreased the number and length of new shoots and basal stems, as well as the size of the phloem, phloem fibers, and xylem. In contrast, the proline, soluble protein, soluble sugar, and malondialdehyde contents, as well as the activities of superoxide dismutase, catalase, and peroxidase, increased in treated stems compared with untreated controls. This study was the first to analyze the metabolomic profile of bleeding sap in A. arguta and investigate the effects of bleeding on its growth and development. The results will provide a theoretical basis for explaining the physiological changes occurring in stems after bleeding and lay a foundation for further research on understanding the underlying mechanism and repairing bleeding.