Requirement of the Auxin Polar Transport System in Early Stages of Arabidopsis Floral Bud Formation.

TLDR

The pin‑1 mutants display severe floral and inflorescence defects that mirror those caused by auxin polar‑transport inhibitors, indicating a role for auxin transport in flower development. The authors measured indole‑3‑acetic acid polar transport and endogenous free IAA levels in the inflorescence axes of pin‑1 mutants and wild type. They found that pin‑1 mutants exhibit only 14 % and 7 % of wild‑type polar transport activity, demonstrating that adequate auxin polar transport in the inflorescence axis is essential for early floral bud formation and that pin‑1’s primary role is auxin transport.

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.