Abstract
One specific action of brassinosteroids is the induction of leaf-bending in rice, which occurs as a result of preferential elongation of cells on the adaxial side of the lamina joint. Since leaf-bending in etiolated seedlings of rice has been reported to be induced by the continuous irradiation with blue-light, we hypothesized that blue-light induces leaf-bending by stimulating brassinosteroid-biosynthesis at the lamina joint. To confirm this hypothesis, we examined changes in the expression of brassinosteroid-biosynthesis genes in the lamina-joint part of the second leaves by RT-PCR. Continuous irradiation with blue-light enhanced the expression of all the genes examined by 1 h, and the expression level was kept high at least up to 12 to 24 h. On the contrary, irradiation with red-light, which is known to inhibit leaf-bending, suppressed the expression to the levels below those kept in the continuous dark control. These results are consistent with our hypothesis.
