Response of Tonoplast and Plasma Membrane ATPases in Chilling-Sensitive and -Insensitive Rice (Oryza sativaL.) Culture Cells to Low Temperature

摘要

Tonoplast and plasma membrane vesicles were prepared from chilling-sensitive (CS) and chilling-insensitive (CI) cultured cells of rice (Oryza sativaL.) to examine how they would respond to low temperature. With CS cells, the specific activity of ATPase in tonoplast vesicles was relatively higher than that of plasma membrane ATPase. Tonoplast ATPase activity was decreased by low temperature treatment, and a slight decrease in plasma membrane ATPase activity was also observed. The decrease in the specific activity of the tonoplast ATPase by low temperature may reflect a decrease in Vmax. However, no change was noted inKm. The break point of the Arrhenius plots of the tonoplast ATPase was ca. 32°C, this value being ca. 9°C higher than that of the plasma membrane ATPase. With CI cells, the specific activity of tonoplast ATPase was somewhat less than that of the plasma membrane ATPase. Tonoplast ATPase activity was decreased by low temperature at 5°C, whereas an increase in plasma membrane ATPase activity was observed. The break point of the tonoplast ATPase activity was ca. 22°C, which was 3°C higher than that of the plasma membrane ATPase. Using ATPase solubilized from the plasma membrane or tonoplast, the Arrhenius plots of log ATPase activity against the reciprocal of absolute temperature gave a straight line fit from 5°C to 45°C with no obvious break point. The break point appeared on adding a phospholipid mixture (asolectin) to a reaction mixture containing solubilized enzyme. The slope of the curve of the Arrhenius plot was very different between the CS and CI cells. The plasma membrane and tonoplast ATPases from the CS cells had a higher Eaabove 20°C, whereas that from the CI cells had a lower one.These findings indicate that the tonoplast ATPase in a rice plant is more sensitive to low temperature than the plasma membrane ATPase, with this response possibly being due to interactions between the proteins and phosph