Many mature peach fruits accumulate more than 80%
of sugars as sucrose. This accumulation of sucrose was
produced by an increase in SuSy activity with fruit
maturation, but SPS activity did not increase (Moriguchi
et al., 1990). In the sucrose-accumulating type of Asian
pear fruit, sucrose accumulated because of an increase
in both SuSy and SPS activities, especially SuSy, with
fruit maturation (Moriguchi et al., 1992). Generally,
SuSy catalyzes the reaction of sucrose degradation,
rather than of sucrose generation, to have ADPglucose
as a precursor of starch synthesis. However, the SuSy
isozyme, whose reaction inclines toward sucrose
synthesis, was present in pear fruit (Tanase and Yamaki,
2000b). Thus, sucrose accumulates in fruit by using
various sucrose-metabolic pathways.