Transgenic sugarcane (Saccharum officinarum L.) lines
were created to express altered invertase isoform activity to elucidate the
role(s) of invertase in the sucrose accumulation process. A sugarcane soluble
acid invertase cDNA (SCINVm, AF062734) in the antisense
orientation was used to decrease invertase activity. The
Saccharomyces cerevisiae invertase gene
(SUC2), fused with appropriate targeting elements, was
used to increase invertase activity in the apoplast, cytoplasm and vacuole. A
callus/liquid culture system was established to evaluate change in
invertase activity and sugar concentration in the transgenic lines. Increased
invertase activity in the apoplast led to rapid hydrolysis of sucrose and
rapid increase of hexose in the medium. The cellular hexose content increased
dramatically and the sucrose level decreased. Cells with higher cytoplasmic
invertase activity did not show a significant change in the sugar composition
in the medium, but did significantly reduce the sucrose content in the cells.
Transformation with the sugarcane antisense acid invertase gene produced a
cell line with moderate inhibition of soluble acid invertase activity and a
2-fold increase in sucrose accumulation. Overall, intracellular and
extracellular sugar composition was very sensitive to the change in invertase
activities. Lowering acid invertase activity increased sucrose accumulation.
Antisense Acid Invertase (TIV1) Gene Alters Soluble Sugar Composition and Size in Transgenic Tomato Fruit
