Root-derived cytokinins as long-distance signals for NO3--induced stimulation of leaf growth.
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.
Rahayu
Yuni Sri
YS
Institut für Pflanzenernährung (330), Universität Hohenheim, D-70593 Stuttgart, Germany.
Walch-Liu
Pia
P
Neumann
Günter
G
Römheld
Volker
V
von Wirén
Nikolaus
N
Bangerth
Fritz
F
D000040:Abscisic Acid / Q000494:pharmacology; D003583:Cytokinins / Q000494:pharmacology / Q000502:physiology*; D018527:Hydroponics; D018551:Solanum lycopersicum / Q000187:drug effects / Q000254:growth & development / Q000502:physiology*; D009566:Nitrates / Q000494:pharmacology*; D010937:Plant Growth Regulators / Q000494:pharmacology / Q000502:physiology; D018515:Plant Leaves / Q000187:drug effects / Q000254:growth & development*; D018517:Plant Roots / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*; D015026:Zeatin / Q000494:pharmacology
D003583:Cytokinins; D009566:Nitrates; D010937:Plant Growth Regulators; D000040:Abscisic Acid; D015026:Zeatin