Plant Physiology 83:195-198 (1987)
© 1987 American Society of Plant Biologists
Development and Growth Regulation
Investigations on the Mechanism of the Brassinosteroid Response
VI. Effect of Brassinolide on Gravitropism of Bean Hypocotyls
Werner J. Meudt
United States Department of Agriculture, Agricultural Research Service, Agricultural Research Center-West, Beltsville, Maryland 20705,
Plant Hormone Laboratory, Beltsville, Maryland 20705
Brassinosteroids are steroidal lactones of plant origin that promote growth of a number of plant systems, and particularly the growth induced by auxins. Biologically active brassinosteroids (BR) also promote the growth of gravisensitive hypocotyls of 7-day-old light grown Phaseolus vulgaris when gravistimulated. Brassinolide-mediated promotion of curvature of gravistimulated internodes occurs in the absence of exogenously supplied indole-3-acetic acid (IAA). This is in contrast to the BR-promoted bending of vertically positioned bean hypocotyls, which is dependent upon exogenous IAA. Brassinosteroid treatment increased the graviperception of young internode tissues and the bending of the gravistimulated sections as well as the subsequent reversal of bending after the sections were placed vertically. These results indicate that BR sensitizes bean hypocotyls to gravistimulation and potentiates the action of a growth factor that induces gravitropic growth.
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