Brassinosteroid-Induced Bending of the Leaf Lamina of Dwarf Rice Seedlings: An Auxin-Mediated Phenomenon

Publisher Website
Google Scholar
Abstract
A synthetic brassinosteroid (BR), 2α,3α,22β,23β-tetrahydroxy-24β-methyl-B-homo 7-oxa-5α-cholestan-6-one, an isomer of the growth promoter brassinolide, when applied to seedlings of dwarf rice Oryza sativa var. Tan-ginbozu and Waito-C, induced a significant bending of the second leaf lamina at 100 ng/plant and higher dosages. Promotion of the second leaf sheath elongation, the characteristic response of dwarf rice varieties to gibberellins, was significantly but modestly enhanced by BR at a dosage of 10,000 ng/plant, five orders of magnitude higher than the minimal dosage response to GA3. Gibberellin A3 had no significant effect on the bending of the second leaf lamina, nor did any synergism exist between BR and GA3 in leaf lamina bending or leaf sheath elongation. Neither ethylene nor (2-chloroethyl)phosphonic acid (ethephon) caused the bending of the second leaf lamina, and neither synergized the BR effect. However, IAA and α-naphthaleneacetic acid caused significant bending at 5,000 ng/plant, and both auxins significantly synergized the effect of BR on the bending, IAA being effective at 500 ng/ plant in this regard. The antiauxins, 2,3,5-triiodobenzoic acid (TIBA) and α-(p-chlorophenoxy)isobutyric acid (PCIB) completely nullified both the BR-induced bending and the BR$IAA-synergized bending. The BR-induced bending response may thus be mediated through endogenous auxin.