Auxin controls local cytokinin biosynthesis in the nodal stem in apical dominance

Plant J. 2006 Mar;45(6):1028-36. doi: 10.1111/j.1365-313X.2006.02656.x.

Abstract

In intact plants, the shoot apex grows predominantly and inhibits outgrowth of axillary buds. After decapitation of the shoot apex, outgrowth of axillary buds begins. This phenomenon is called an apical dominance. Although the involvement of auxin, which represses outgrowth of axillary buds, and cytokinin (CK), which promotes outgrowth of axillary buds, has been proposed, little is known about the underlying molecular mechanisms. In the present study, we demonstrated that auxin negatively regulates local CK biosynthesis in the nodal stem by controlling the expression level of the pea (Pisum sativum L.) gene adenosine phosphate-isopentenyltransferase (PsIPT), which encodes a key enzyme in CK biosynthesis. Before decapitation, PsIPT1 and PsIPT2 transcripts were undetectable; after decapitation, they were markedly induced in the nodal stem along with accumulation of CK. Expression of PsIPT was repressed by the application of indole-3-acetic acid (IAA). In excised nodal stem, PsIPT expression and CK levels also increased under IAA-free conditions. Furthermore, beta-glucuronidase expression, under the control of the PsIPT2 promoter region in transgenic Arabidopsis, was repressed by an IAA. Our results indicate that in apical dominance one role of auxin is to repress local biosynthesis of CK in the nodal stem and that, after decapitation, CKs, which are thought to be derived from the roots, are locally biosynthesized in the nodal stem rather than in the roots.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alkyl and Aryl Transferases / genetics
  • Alkyl and Aryl Transferases / metabolism
  • Arabidopsis / genetics
  • Cytokinins / biosynthesis*
  • Gene Expression Regulation, Plant / drug effects
  • Indoleacetic Acids / pharmacology*
  • Peas / drug effects
  • Peas / genetics
  • Peas / metabolism*
  • Plant Proteins / genetics
  • Plant Proteins / metabolism
  • Plant Roots / genetics
  • Plant Roots / metabolism
  • Plant Shoots / genetics
  • Plant Shoots / metabolism
  • Plant Stems / genetics
  • Plant Stems / metabolism
  • Plants, Genetically Modified / drug effects
  • Plants, Genetically Modified / genetics
  • Plants, Genetically Modified / metabolism
  • Promoter Regions, Genetic
  • Triiodobenzoic Acids / pharmacology

Substances

  • Cytokinins
  • Indoleacetic Acids
  • Plant Proteins
  • Triiodobenzoic Acids
  • indoleacetic acid
  • Alkyl and Aryl Transferases
  • adenylate isopentenyltransferase
  • 2,3,5-triiodobenzoic acid