Etxeberria et al. (2005a) and Baroja-Fernandez et al.
(2006) reported the uptake system of sucrose, in which
vesicles containing sucrose are generated in apoplasts
and are taken up into the cytoplasm by endocytosis.
Vesicles containing sucrose were carried directly into
vacuoles by endocytosis in sycamore suspension cells,
and the endocytosis of sucrose was induced by sucrose.
In citrus fruit, sucrose in apoplasts is transported directly
into vacuoles by the same endocytosis as for sycamore
cells (Etxeberria et al., 2005b). Although this kind of
sugar uptake system is very efficient for accumulation
of a lot of sugar in vacuoles, further study is needed.