ABSTRACT
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.
ABSTRACT
The developmental and morphogenetic process of pistil formation was examined by analysing flowers of wild type and six flower mutants of Arabidopsis thaliana, a small crucifer. The wild type is suggested to originate from two 'pistil-forming units' (carpels) arranged laterally against the axis of the inflorescence at a pistil primordium. Aberrant structures of the pistils of mutants indicate that a set of genes regulate each step of pistil development and morphogenesis, namely arrangement of the units at the pistil primordia, fusion of the units, growth of primordia, formation of the septum in the ovary, and formation of the stigma.
