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

Abstract

The pin-formed mutant pinl-1, one of the Arabidopsis flower mutants, has several structural abnormalities in inflorescence axes, flowers, and leaves. In some cases, pinl-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 (pinl-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-naphthy1)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 pinl mutants and wild type. The polar transport activity in the pinl-1 mutant and in the p i n l -2 mutant was decreased to 14% and 7% of wild type, respectively. These observations strongly suggest that the normal leve1 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 pinl gene is auxin polar transport in the inflorescence axis.

Endocytic Trafficking of PIN Proteins and Auxin Transport

“…The auxin transport capacity of PINs was tested both in plant and heterologous systems (Petrášek et al 2006;Yang and Murphy 2009). These results are also supported by the fact that genetic interference with PIN proteins led to reduced auxin transport and diverse developmental phenotypes (Okada et al 1991;Gälweiler et al 1998) similar to the ones observed after application of auxin transport inhibitors (Okada et al 1991;Vieten et al 2007). …”

Isolation and identification of polar auxin transport inhibitors from Saussurea costus and Atractylodes japonica

“…Almost no auxin transport was observed when IAA was applied at the basal side of the segments in the same manner. Therefore, the 14 C-labeled IAA applied to the apical side was transported to the physiological apical-basal direction in this assay system as well as found in our previous results from a Fujix image analyzer of BAS 2000 (Fuji Photo Film Co., Ltd., Japan) [8] and from a liquid scintillation counter [13]. After incubation at 23.5°C for 18 h, a 2-mm piece of the opposite side of the segment was cut; it was placed directly into a vial containing the liquid scintillation cocktails, and then its radioactivity was determined using a liquid scintillation counter.…”

“…Following the method reported previously [8,13] with minor modifications, the system consisting of an 14 C-labeled IAA solution in the presence or absence of the test compounds in the bottom of 1.5-mL Eppendorf plastic tubes was introduced for the detection of the bioassay-derived PAT regulators. The plant extracts were placed into the bottom of the Eppendorf plastic tubes, dried in vacuo, and then dissolved with 25 μL of 1000-fold diluted 14 C-labeled IAA [ (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14) C)IAA with a specific activity of 55 mCi/ mmol, 0.1 mCi/mL; American Radiolabeled Chemicals, Inc., USA].…”

“…The plant extracts were placed into the bottom of the Eppendorf plastic tubes, dried in vacuo, and then dissolved with 25 μL of 1000-fold diluted 14 C-labeled IAA [ (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14) C)IAA with a specific activity of 55 mCi/ mmol, 0.1 mCi/mL; American Radiolabeled Chemicals, Inc., USA]. Radish hypocotyl segments (each 20 mm in length), excised from 5 mm below the apical side of 6-day-old light-grown seedlings, were placed in the Eppendorf plastic tubes in down orientation of the apical side.…”

“…Auxin mediates different cellular responses based on its graded distribution between cells, local auxin biosynthesis, and directional cell-to-cell transport via carrier-mediated transport, being required for the establishment and maintenance of these auxin gradients in the plant axis. This unique transport system, called polar auxin transport (PAT), is considered to depend mainly on PIN-FORMED (PIN) auxin efflux carriers having a polar, plasma membrane localization [1][2][3][4][5][6][7][8]. It has also been demonstrated that PIN-dependent auxin efflux and local auxin response result in the apical-basal formation of the embryo and thus determine the axiality of the adult plant [9].…”