Modulation of vacuolar H+ -pumps and aquaporin by phytohormones in rice seedling leaf sheaths.

The effects of exogenously applied gibberellic acid (GA(3)) or brassinolide (BL) on the H(+)-pumps and aquaporin in the vacuolar membrane of rice seedling leaf sheath were investigated. Antibodies against mung bean H(+)-PPase, the B subunit of V-ATPase, and radish tonoplast intrinsic protein (TIP) cross-reacted with the vacuolar membrane proteins of rice seedling leaf sheath. The results of immunoblot analysis showed that the amounts of H(+)-PPase and V-ATPase were retained at a high level for two days in the presence of GA(3), although the level gradually decreased without phytohormones, indicating that GA(3) has a promotive effect on the activities of vacuolar H(+)-pumps. However, the levels of V-ATPase and H(+)-PPase were increased on day 2 and then decreased when treated with BL. There were no visible differences in the level of TIP upon treatment with GA(3) and BL. In comparison with the water control, the activity of H(+)-PPase treated with BL was also retained at a relatively high level, suggesting that BL has a stimulative effect on the activities of H(+)-PPase. These results indicate that GA(3) and BL might be involved in the regulation of the quantity and activities of plant vacuolar H(+)-pumps.