CHARACTERISTICS OF THE INDUCTION OF THE ACCUMULATION OF PROLINE BY ABSCISIC-ACID AND ISOBUTYRIC ACID IN DETACHED RICE LEAVES

The effects of abscisic acid and isobutyric acid on levels of proline in detached rice leaves were compared. The lowest concentration of abscisic acid that induces accumulation of proline in detached rice leaves was much lower than that of isobutyric acid. The accumulation of porline induced by isobutyric acid was associated with acidification of the cell sap, whereas abscisic acid increased levels of proline without decreasing the pH of the cell sap. Potassium chloride enhanced the accumulation of proline that was induced by abscisic acid, but it did not stimulate that induced by isobutyric acid. Of particular interest is the finding that detached rice leaves treated with fusicoccin showed an increase in levels of proline and a decrease in the pH of the cell sap. A synergistic increase in levels of proline was observed when fusicoccin and abscisic acid applied simultaneously. However, fusicoccin had no effect on the induction of the accumulation of proline by isobutyric acid. Benzyladenine inhibited the induction by abscisic acid of the accumulation of proline, but it did not inhibit the induction by isobutyric acid. It is concluded that the mode of action of abscisic acid in inducing the accumulation of proline differs from that of isobutyric acid. Our results also indicate that factors other than acidification of the cell sap are involved in regulation of the accumulation of proline.