Abstract: ‘Robertson Navel’orange fruits from five representative areas of three ecotypes in Sichuan province were used to study soluble sugar accumulation and their related enzymes during the fruit development , especially the changes in activities of sucrose phosphate synthase (SPS) and sucrose synthase (SS) . The results showed that SPS played an important role in sugar accumulation in fruit during the fruit inflating stage , while SS in
the synthetic direction was the key enzyme during the fruit ripening stage. The activities of SPS and SS in the cleavage direction in fruit were similar between different habitats , whereas SS activity in the synthetic direction changed significantly in the different habitats. It was suggested that although SS in the cleavage and synthetic direction regulated the sugar transport and accumulation though fruit sink strength , SS in the synthetic direction was the dominant enzyme which led sugar different accumulation in different habitats.

Key words: Citrus, Navel orange fruit, Habitat, Sugar accumulation, Sucrose synthase ( SS), Sucrose phosphate synthase (SPS)