SUTURE SOFTENING AND SUGAR METABOLISM IN PEACH (PRUNUS PERSICA L. BATCH 'OKUBO')

Ventral suture softening of peach reduces fruit quality and shortens the post- harvest period. We measured sucrose, glucose, fructose and sorbitol contents, and activity of sugar metabolism enzymes in suture site of softening and normal fruit at different developmental stages of Dajiubao peach (Prunus persica L. Batch ‘Okubo’). Enzyme activities measured included acid invertase, neutral invertase, sucrose synthase, sucrose phosphate synthetase, and sorbitol dehydrogenase (SDH) and sorbitol oxidase (SOX). At the same time, we also analyzed the relationship of sugar accumulation and enzyme activity between the softening fruit and normal fruit. Sugar metabolism and related enzyme activity were much higher in soft suture fruit than in normal fruit. This observation is consistent with the fact that the suture of softening fruit was growing faster at the hard-core stage. The metabolism of monosaccharides plays a key role at this stage mainly through high activity of neutral invertase. At stage III of fruit development, sugar metabolism is much faster in softening fruit than in normal fruit. In addition, at early stage III, sugar metabolism in soft suture fruit is very active with abundant synthesis of sucrose. At late stage III, the sugar accumulation rate declined resulting in a drop of sugar content, coinciding with the initiation of suture softening. Our results therefore show that suture softening starts when fruit is immature and that sugar metabolism is one of the important factors that affects peach suture softening.