THE PLANT CELL, Vol 3, Issue 7 677-684, Copyright © 1991 by American Society of Plant Biologists
Requirement of the Auxin Polar Transport System in Early Stages of Arabidopsis Floral Bud Formation
K. Okada, J. Ueda, M. K. Komaki, C. J. Bell and Y. Shimura
Division I of Gene Expression and Regulation, National Institute for Basic Biology, Okazaki 444, Japan
The pin-formed mutant pin 1-1, one of the Arabidopsis flower mutants, has
several structural abnormalities in inflorescence axes, flowers, and
leaves. In some cases, pin1-1 forms a flower with abnormal structure (wide
petals, no stamens, pistil-like structure with no ovules in the ovary) at
the top of inflorescence axes. In other cases, no floral buds are formed on
the axes. An independently isolated allelic mutant (pin1-2) shows similar
phenotypes. These mutant phenotypes are exactly the same in wild-type
plants cultured in the presence of chemical compounds known as auxin polar
transport inhibitors: 9-hydroxyfluorene-9-carboxylic acid or
N-(1-naphthyl)phthalamic acid. We tested the polar transport activity of
indole-3-acetic acid and the endogenous amount of free indole-3-acetic acid
in the tissue of inflorescence axes of the pin1 mutants and wild type. The
polar transport activity in the pin 1-1 mutant and in the pin1-2 mutant was
decreased to 14% and 7% of wild type, respectively. These observations
strongly suggest that the normal level of polar transport activity in the
inflorescence axes is required in early developmental stages of floral bud
formation in Arabidopsis and that the primary function of the pin1 gene is
auxin polar transport in the inflorescence axis.
