RELATIONSHIP BETWEEN SUCROSE ACCUMULATION AND SUCROSE-METABOLIZING ENZYMES IN DEVELOPING GRAPES

The present study examined sugar accumulation and changes in sucrose-m etabolizing enzyme activity (acid invertase, sucrose synthase and sucr ose phosphate synthase) in the skin and flesh tissues of Steuben and M uscat Bailey A (Bailey x Muscat Hamburg) grapes during development. Su crose accounted for 18.6% and 31.3% of total sugars in the flesh and s kin tissues, respectively, in Steuben grapes and 2.0% and 16.2%, respe ctively, in Muscat Bailey A grapes. Sucrose synthase and sucrose phosp hate synthase activity increased with development in both types of gra pes, but this increase was small. The significant enzymic difference b etween Muscat Bailey A and Steuben grapes exists at the level of acid invertase activity; acid invertase activity in Muscat Bailey A increas ed and reached a maximum at the beginning of sugar accumulation and th en decreased, whereas that in Steuben grapes decreased with developmen t and remained much lower than that of Muscat Bailey A. These results suggest that the higher proportion of sucrose in Steuben grapes is ass ociated with a lower acid invertase activity.