Stems of the Arabidopsis pin1-1 mutant are not deficient in free indole-3-acetic acid
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The pin1-1 mutant of Arabidopsis thaliana has been pivotal for studies on auxin transport and on the role of auxin in plant development. It was reported previously that when whole shoots were analysed, levels of the major auxin, indole-3-acetic acid (IAA) were dramatically reduced in the mutant, compared with the WT (Okada et al. 1991). The cloning of PIN1, however, provided evidence that this gene encodes a facilitator of auxin efflux, raising the question of how the pin1-1 mutation might reduce overall IAA levels as well as IAA transport. We therefore re-examined IAA levels in individual parts of pin1-1 and WT plants, focusing on inflorescence stems. Our data show that there is in fact no systemic IAA deficiency in the mutant. The previously reported difference between mutant and WT may have been due to the inclusion of reproductive structures in the WT harvest: we show here that the inflorescence itself contains high levels of IAA. We reconcile the normal IAA levels of pin1-1 inflorescence stems with their (previously-reported) reduced ability to transport IAA by presenting evidence that the auxin in mutant stems is not imported from their apical portion. Our data also indicate that levels of another auxin, indole-3-butyric acid (IBA), are very low in stems of the genotypes used in this study.
KeywordsArabidopsis Auxin content Auxin transport GC-MS-MS pin1-1 mutant
Gas chromatography/mass spectrometry/mass spectrometry
We thank Ian Cummings and Tracey Winterbottom for technical assistance, Jennifer Smith for assistance with the figures, Gregory Symons and James Reid for comments on the manuscript, and David Smyth (Monash University, Victoria, Australia) for the gift of the pin1-1 mutant.
- Aloni R, Schwalm K, Langhans M, Ullrich CI (2003) Gradual shifts in sites of free-auxin production during leaf-primordium development and their role in vascular differentiation and leaf morphogenesis in Arabidopsis. Planta 216:841–853Google Scholar
- Davies PJ (2004) Plant hormones—biosynthesis, signal transduction, action! Davies PJ (ed) Kluwer Academic Publishers, DordrechtGoogle Scholar
- Friml J (2003) Auxin transport—shaping the plant. Curr Opin Plant Biol 6:7–12Google Scholar
- Friml J, Palme K (2002) Polar auxin transport—old questions and new concepts? Plant Mol Biol 49:273–284Google Scholar
- Ljung K, Bhalerao RP, Sandberg G (2001) Sites and homeostatic control of auxin biosynthesis in Arabidopsis during vegetative growth. Plant J 28:465–474Google Scholar
- Palme K, Gälweiler L (1999) PIN-pointing the molecular basis of auxin transport. Curr Opin Plant Biol 2:375–381Google Scholar
- Reinhardt D, Mandel T, Kuhlemeier C (2000) Auxin regulates the initiation and radial position of plant lateral organs. Plant Cell 12:507–518Google Scholar
- Ross JJ, O’Neill DP, Smith JJ, Kerckhoffs LHJ, Elliott RC (2000) Evidence that auxin promotes gibberellin A1 biosynthesis in pea. Plant J 21:547–552Google Scholar