Root-derived cytokinins as long-distance signals for NO3--induced stimulation of leaf growth

J Exp Bot. 2005 Apr;56(414):1143-52. doi: 10.1093/jxb/eri107. Epub 2005 Feb 14.


Leaf growth of many plant species shows rapid changes in response to alterations of the form and the level of N supply. In hydroponically-grown tomato (Lycopersicon esculentum L.), leaf growth was rapidly stimulated by NO(3)(-) application to NH(4)(+) precultured plants, while NH(4)(+) supply or complete N deprivation to NO(3)(-) precultured plants resulted in a rapid inhibition of leaf growth. Just 10 microM NO(3)(-) supply was sufficient to stimulate leaf growth to the same extent as 2 mM. Furthermore, continuous NO(3)(-) supply induced an oscillation of leaf growth rate with a 48 h interval. Since changes in NO(3)(-) levels in the xylem exudate and leaves did not correlate with NO(3)(-)-induced alterations of leaf growth rate, additional signals such as phytohormones may be involved. Levels of a known inhibitor of leaf growth, abscisic acid (ABA), did not consistently correspond to leaf growth rates in wild-type plants. Moreover, leaf growth of the ABA-deficient tomato mutant flacca was inhibited by NH(4)(+) without an increase in ABA concentration and was stimulated by NO(3)(-) despite its excessive ethylene production. These findings suggest that neither ABA nor ethylene are directly involved in the effects of N form on leaf growth. However, under all experimental conditions, stimulation of leaf growth by NO(3)(-) was consistently associated with increased concentration of the physiologically active forms of cytokinins, zeatin and zeatin riboside, in the xylem exudate. This indicates a major role for cytokinins as long-distance signals mediating the shoot response to NO(3)(-) perception in roots.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Abscisic Acid / pharmacology
  • Cytokinins / pharmacology
  • Cytokinins / physiology*
  • Hydroponics
  • Nitrates / pharmacology*
  • Plant Growth Regulators / pharmacology
  • Plant Growth Regulators / physiology
  • Plant Leaves / drug effects
  • Plant Leaves / growth & development*
  • Plant Roots / physiology*
  • Signal Transduction / physiology*
  • Solanum lycopersicum / drug effects
  • Solanum lycopersicum / growth & development
  • Solanum lycopersicum / physiology*
  • Zeatin / pharmacology


  • Cytokinins
  • Nitrates
  • Plant Growth Regulators
  • Abscisic Acid
  • Zeatin