Modulation of Vacuolar H⁺-Pumps and Aquaporin by Phytohormones in Rice Seedling Leaf Sheaths

Abstract

The effects of exogenously applied gibberellic acid (GA₃) 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 GA₃, although the level gradually decreased without phytohormones, indicating that GA₃ 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 GA₃ 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 GA₃ and BL might be involved in the regulation of the quantity and activities of plant vacuolar H⁺-pumps.