Investigations on the mechanism of the brassinosteroid response

A brassinosteroid treatment of light-grown first internode sections of Phaseolws vulgaris results in an increased bending response foliowing unilateral indole-3-acetic acid (IAA) application. Reverse isotope dilution analysis shows that this increased response is not due to an increase in the concentration of applied IAA in the tissue or a change in the amount of IAA conjugated. Treatment with the brassinosteroid also does not affect the rate of IAA transport as measured using the agar block method. These results indicate that even though brassinosteroid potentiates auxin action, it does not have a direct effect on IAA uptake, metabolism, or celi to celi transport.