EFFECT OF EPIBRASSINOLIDE ON HYPOCOTYL GROWTH OF THE TOMATO MUTANT DIAGEOTROPICA

The effect of epibrassinolide (epiBR) on the growth and gravitropism o f hypocotyls was investigated in diageotropica (dgt), a mutant of toma to (Lycopersicon esculentum Mill.). The elongation of (dgt) hypocotyls , which had been reported to be auxin-insensitive, was promoted by inc reasing concentrations of indole-3-acetic acid (IAA) in the presence o f epiBR. alpha-(p-Chlorophenoxy)isobutyric acid, an inhibitor of auxin action, blocked the enhancement of growth by IAA and epiBR. Time cour se analysis of IAA-induced dgt hypocotyl elongation in the presence of epiBR revealed typical auxin response kinetics. These results suggest that epiBR restores the auxin responsiveness of dgt hypocotyls with r espect to elongation. However, epiBR did not rescue the dgt phenotype with respect to shoot gravitropism. It was therefore concluded that br assino-steroid insensitivity or deficiency is not the primary defect o f the dgt mutation.