Key enzymes of sucrose metabolism play an important role in source–sink regulation of walnut fruit growth and development

Abstract

ABSTRACT Carbohydrate content and metabolism-related enzyme activities were analysed in walnut fruits during fruit growth by artificial manipulation of the leaf-to-fruit ratio (LFR) to investigate the relationship between carbohydrate utilisation and LFR. LFR significantly affected glucose and sucrose content, and sucrose synthetase (SS) activity in the pericarp or kernel. When the leaf number was the same, sucrose content and SS activity in the pericarp and kernel decreased with increasing fruit load, while glucose and fructose content and acid invertase (AI) activity in the pericarp increased gradually. When the fruit number was the same, glucose and sucrose content and SS activity in the pericarp and kernel increased gradually as the number of leaves increased, while fructose content and AI and sucrose phosphate synthetase (SPS) activity in the pericarp increased, thereby indicating that enhanced AI activity in the pericarp improved the competitive ability of the sink when LFR was low during the fast fruit-growing period, while, high AI activity rapidly decomposed sucrose into hexose to supply the energy required for cell multiplication and growth during the fruit fast-growing period, when LFR was high. During the oil transformation period, the increase in sucrose content in the pericarp resulted from SS and SPS activities.