BRASSINOSTEROID-INDUCED RICE LAMINA JOINT INCLINATION AND ITS RELATION TO INDOLE-3-ACETIC-ACID AND ETHYLENE

Brassinosteroid (BR)-induced rice (Oriza sativa L,.) lamina joint (RLJ ) inclination and its relationship to indole-3-acetic acid (IAA) and e thylene were investigated using BR isolated from beeswax. The effect o f BR on RLJ inclination was time- and concentration-dependent. Etiolat ed lamina were more sensitive to BR than green lamina. The BR-induced inclination was accompanied by increased lamina fresh weight, total wa ter content, free-water content, proton extrusion and ethylene product ion, and decreased bound-water content. Lamina dry weight was not chan ged. The inclination was due to greater expansion of the adaxial cells relative to the dorsal cells in the lamina joint. This response was c aused by BR and/or BR-induced signal(s) that were transported from the leaf sheath to the leaf blade. Both BR-induced RLJ inclination and et hylene production were inhibited by cobalt chloride (CoCl2), an inhibi tor of ACC oxidase. BR-induced inclination was much higher than that o f IAA, and was inhibited by high concentration of 2,3,5-triiodobenzoic acid (TIBA), an inhibitor of IAA transport. A synergistic effect was observed between BR and IAA. These results suggest that the effects of BR on RLJ inclination and pulvinus cell expansion may be resulted fro m BR-increased water potential and proton extrusion in the lamina. The BR-induced RLJ inclination may involve the action of ethylene but may be independent of IAA.