PLANT PHYSIOLOGY , Vol 114, Issue 4 1177-1185, Copyright © 1997 by American Society of Plant Biologists
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DEVELOPMENT AND GROWTH REGULATION |
ZEA3: A Negative Modulator of Cytokinin Responses in Plant Seedlings
T. Martin, B. Sotta, M. Jullien, M. Caboche and J. D. Faure
Laboratoire de Biologie Cellulaire, Institut National de la Recherche Agronomique, route de St. Cyr, 78026 Versailles cedex, France (T.M., M.J., M.C., J.-D.F.)
In Nicotiana plumbaginifolia cytokinins affect seedling development by
inhibiting root growth and hypocotyl elongation and by stimulating
cotyledon expansion. The zea3.1 mutant was selected for its inability to
grow in conditions of low nitrogen and for its ability to grow
independently on inhibitory concentrations of zeatin (J.D. Faure, M.
Jullien, M. Caboche [1994] Plant J 5: 481-491). The zea3.1 growth response
to cytokinins is reflected by an increase in cotyledon expansion due to
cell division and by a swelling of the hypocotyl due to cell enlargement.
An analysis of the seedling's root length and fresh weight over a wide
range of benzyladenine concentrations showed that zea3.1 plants exhibit a
higher sensitivity and an amplified response to cytokinins. A similar
response of zea3.1 to benzyladenine was also seen in the expression of
msr1, a cytokinin-regulated gene. Regulation of msr1 expression by protein
phosphorylation was unaffected by the zea3.1 mutation. No significant
differences in cytokinin and auxin levels were found between zea3.1 and
wild-type seedlings, suggesting that the mutant phenotype is not caused by
an alteration of these hormone levels. The data presented suggest that ZEA3
negatively modulates cytokinin responses and may function as a broad
regulator of seedling development.
