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

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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 GA_3. Gibberellin A_3 had no significant effect on the bending of the second leaf lamina, nor did any synergism exist between BR and GA_3 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 a 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.
日本植物生理学会の論文