JXB Advance Access originally published online on February 14, 2005
Journal of Experimental Botany 2005 56(414):1143-1152; doi:10.1093/jxb/eri107
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RESEARCH PAPER |
Root-derived cytokinins as long-distance signals for NO3–-induced stimulation of leaf growth
1Institut für Pflanzenernährung (330), Universität Hohenheim, D-70593 Stuttgart, Germany
2Institut für Sonderkulturen und Produktionsphysiologie (370), Universität Hohenheim, D-70593 Stuttgart, Germany
Present address and to whom correspondence should be sent: Biological Sciences, Lancaster University, Lancaster LA1 4YQ, UK. Fax: +44 (0)1524 843 854. E-mail: p.walch-liu{at}lancaster.ac.uk
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 
application to 
precultured plants, while supply or complete N deprivation to precultured plants resulted in a rapid inhibition of leaf growth. Just 10 µM supply was sufficient to stimulate leaf growth to the same extent as 2 mM. Furthermore, continuous supply induced an oscillation of leaf growth rate with a 48 h interval. Since changes in levels in the xylem exudate and leaves did not correlate with -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 without an increase in ABA concentration and was stimulated by 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 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 perception in roots.
Key words: ABA, cytokinins, ethylene, flacca mutant, hydroponic culture, leaf growth, Lycopersicon esculentum, NH4+, NO3–, N deprivation
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