Role of Sucrose Synthase and Other Related Enzymes in Sucrose Accumulation in Peach Fruit.

Abstract

Four peach cultivars differing in their maturation time and sugar composition were analyzed for the detection of seasonal changes in the content of sugars in the flesh and peduncle, and in the activity of sucrose-metabolizing enzymes. Besides the accumulation of sucrose as a major sugar at the mature stage in all the cultivars, the fructose content was similar to glucose content in 'Akatsuki' and 'Yuzora'. While in 'Naganoyaseito-early' and 'Hokimomo' the fructose content was low. Of the enzymes assayed, there were no clear differences in the activity among the peach cultivars. In all the cultivars, the sucrose synthase (SS) activity increased with sucrose accumulation, suggesting the importance of its role in sucrose accumulation in peach fruit. On the contrary, the sucrose-phosphate synthase (SPS) activity did not increase with sucrose accumulation. The acid invertase activity decreased with fruit development. The decrease in the acid invertase activity appeared to reflect fruit maturation, during which sucrose accumulated. The UDPglucose pyrophosphorylase activity was also assayed in these peaches throughout the development of fruit. However, typical seasonal fluctuations of the activity were not observed among the four cultivars. Kinetic parameters of SS from immature and mature peach fruit suggested that SS tended to be involved in sucrose synthesis in the mature peach fruit compared with the immature one. The differences in sucrose synthesis between peach and other fruits were also discussed, based on the activities and properties of these enzymes.