Abstract
In acidic soils, aluminum ion causes root growth inhibition, which is due to the inhibition of cell elongation at root apical meristem by aluminum ion. Furthermore, cell elongation inhibition by aluminum accompanies an increase in the production of reactive oxygen species. These responses to aluminum are also observed in actively growing cultured tobacco cells. For cell elongation, water uptake is necessary, and a motive force of water uptake is an increase in osmolality by increases in solutes such as free sugars, inorganic ions and amino acids in vacuole. Invertase localized in vacuole contributes to an increase in osmolality by hydrolysis of sucrose to glucose and fructose. In this study, we examined a possibility that aluminum ion might inhibit invertase activity in vacuole, in cultured cells and roots of tobacco, by measuring invertase activity in cell-free extracts and histochemical staining of invertase activity, respectively. On the contrary, we found that invertase activity in vacuole was enhanced by aluminum in both systems, suggesting that an increase in invertase activity in vacuole may contribute to alleviate the cell elongation inhibition under aluminum stress.
