Suppression of Acid Invertase Activity by Antisense RNA Modifies the Sugar Composition of Tomato Fruit

cDNA for an acid invertase (EC 3.2.1.26) of tomato (Lycopersicon esculentum Mill.) fruit was introduced into tomato plants under the control of the cauliflower mosaic virus 35S promoter in the antisense orientation. The antisense gene effectively suppressed the invertase activity in soluble and cell wall fractions from ripening fruits. The sucrose content of fruits of the transformants was markedly increased, while the hexose content was reduced. These results indicate that acid invertase is one of main determinants of the sugar composition of tomato fruit. The invertase activity in the cell wall fraction of the leaf tissues of the transformants was not suppressed to the same extent as that in the soluble fraction. Wounding of the control leaf tissues induced invertase activity in both soluble and cell wall fractions. The induction of activity in the soluble fraction was suppressed by the antisense gene, while that in the cell wall fraction was unaffected. These findings suggest that mRNA for some other invertase, in particular, the mRNA for a cell wall-bound invertase, was present in leaves.