Auxins and tropisms

J Plant Growth Regul. 2001 Sep;20(3):226-43. doi: 10.1007/s003440010027.


Differential growth of plants in response to the changes in the light and gravity vectors requires a complex signal transduction cascade. Although many of the details of the mechanisms by which these differential growth responses are induced are as yet unknown, auxin has been implicated in both gravitropism and phototropism. Specifically, the redistribution of auxin across gravity or light-stimulated tissues has been detected and shown to be required for this process. The approaches by which auxin has been implicated in tropisms include isolation of mutants altered in auxin transport or response with altered gravitropic or phototropic response, identification of auxin gradients with radiolabeled auxin and auxin-inducible gene reporter systems, and by use of inhibitors of auxin transport that block gravitropism and phototropism. Proteins that transport auxin have been identified and the mechanisms which determine auxin transport polarity have been explored. In addition, recent evidence that reversible protein phosphorylation controls this process is summarized. Finally, the data in support of several hypotheses for mechanisms by which auxin transport could be differentially regulated during gravitropism are examined. Although many details of the mechanisms by which plants respond to gravity and light are not yet clear, numerous recent studies demonstrate the role of auxin in these processes.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.
  • Review

MeSH terms

  • Biological Transport
  • Cytoskeleton / physiology
  • Gene Expression Regulation, Plant
  • Genes, Plant
  • Gravitropism / genetics
  • Gravitropism / physiology*
  • Indoleacetic Acids / metabolism*
  • Indoleacetic Acids / physiology
  • Phosphorylation
  • Phototropism / genetics
  • Phototropism / physiology*
  • Plant Development*
  • Plant Growth Regulators / metabolism
  • Plant Growth Regulators / physiology*
  • Plants / genetics
  • Plants / metabolism
  • Signal Transduction / physiology*


  • Indoleacetic Acids
  • Plant Growth Regulators
  • indoleacetic acid