CHANGES OF SORBITOL CONTENT AND RELATED ENZYMES DURING FRUIT DEVELOPMENT IN TWO LOQUAT CULTIVARS

The changes of sorbitol, fructose and glucose contents and the activities of sorbitol-metabolizing enzymes, including sorbitol dehydrogenase (SDH) and sorbitol oxidase (SOX), were studied during the fruit development of ‘Baili’ and ‘Jiefangzhong’ loquat (Eriobotrya japonica Lindl.). This study was carried out to explore the relationships between sorbitol metabolism and the growth, development and quality formation of loquat fruits. The results showed that sorbitol content in the two cultivars generally decreased during fruit development, and that sorbitol content was generally higher in ‘Baili’ than in ‘Jiefangzhong’. In the two cultivars, young loquat fruits from 35 to 80 days after anthesis exhibited low and relatively stable contents of fructose and glucose; their contents increased gradually from 95 to 140 days after anthesis, reaching a peak from 125 to 140 days after bloom. The glucose contents in the developing loquat fruits were similar in the two cultivars (P>0.05). The fructose content of ‘Baili’ fruit was significantly higher than that of ‘Jiefangzhong’ during fruit maturation (P<0.05). In both cultivars, the activities of SDH and SOX decreased at first, and then rose during loquat fruit development. Trends of sorbitol, fructose, and glucose contents and SDH, SOX activities were similar in the two cultivars, except for sorbitol content, SDH, and SOX activities at the stage of loquat fruit enlargement (P<0.05). This may be the key period for the formation of fruit size and quality in the two loquat cultivar with yellow and white pulp, respectively.