Influence of brassinosteroids on initiation of the root gravitropic response in Pisum sativum seedlings

In roots of Pisum sativum seedlings, the average lag-time required for initiation of the gravitropic response was reduced proportionally to the concentration of 24-epibrassinolide (EBL) added to the root solution (range of 10(-13) to 10(-8) M concentrations). A treatment with clotrimazole, a compound inhibiting steroid synthesis, prevents initiation of the gravitropic response. This effect was partly reverted by addition of EBL. From analysis of variability in the populations, it is suggested that BR conditions the root curvature through a gravitropic-induced change in sensitivity to the PGRs regulating cell elongation.