Vacuolar sucrose homeostasis is critical for development, seed properties and survival of dark phases of Arabidopsis

Although we know that most of the cellular sucrose is present in the
cytosol and vacuole, our knowledge on the impact of this sucrose
compartmentation on plant properties is still fragmentary. Here we
attempted to alter the intracellular sucrose compartmentation of
Arabidopsis mesophyll cells by either, overexpression of the vacuolar
sucrose loader BvTST2.1 or by generation of mutants with decreased
vacuolar invertase activity (amiR vi1-2). Surprisingly, BvTST2.1
overexpression led to increased monosaccharide levels in leaves, while
sucrose remained constant. Latter observation allows the conclusion, that
vacuolar invertase activity in mesophyll vacuoles exceeds sucrose uptake
in Arabidopsis, which gained independent support by analyses on tobacco
leaves transiently overexpressing BvTST2.1 and the invertase inhibitor
NbVIF. However, we observed strongly increased sucrose levels in leaf
extracts from independent amiR vi1-2 lines and non‑aqueous fractionations
confirmed that sucrose accumulation in corresponding vacuoles. amiR vi1-2
lines exhibited impaired early development and decreased weight of seeds.
When germinated in the dark, mutant seedlings showed problems to convert
sucrose into monosaccharides. Cold temperatures induced marked
downregulation of the expression of both VI genes, while frost tolerance
of amiR vi1-2 mutants was similar to WT indicating that increased
vacuolar sucrose levels fully compensate for low monosaccharide
concentrations.