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 TST2.1 or by generation of mutants with decreased vacuolar invertase activity (). Surprisingly, 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 TST2.1 and the invertase inhibitor VIF. However, we observed strongly increased sucrose levels in leaf extracts from independent lines and non-aqueous fractionations confirmed that sucrose accumulation in corresponding vacuoles. 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 genes, while frost tolerance of mutants was similar to WT indicating that increased vacuolar sucrose levels fully compensate for low monosaccharide concentrations.