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PLANT PHYSIOLOGY , Vol 102, Issue 3 983-989, Copyright © 1993 by American Society of Plant Biologists
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DEVELOPMENT AND GROWTH REGULATION |
Ammonium Inhibition of Arabidopsis Root Growth Can Be Reversed by Potassium and by Auxin Resistance Mutations aux1, axr1, and axr2
Y. Cao, ADM. Glass and N. M. Crawford
Department of Biology and Center for Molecular Genetics, University of California at San Diego, La Jolla, CA 92093-0116 (Y.C., N.M.C.)
A novel effect of ammonium ions on root growth was investigated to
understand how environmental signals affect organ development. Ammonium
ions (3-12 mM) were found to dramatically inhibit Arabidopsis thaliana
seedling root growth in the absence of potassium even if nitrate was
present. This inhibition could be reversed by including in the growth
medium low levels (20-100 [mu]M) of potassium or alkali ions Rb+ and Cs+
but not alkali ions Na+ and Li+. The protective effect of low
concentrations of potassium is not due to an inhibition of ammonium uptake.
Ammonium inhibition is reversible, because root growth was restored in
ammonium-treated seedlings if they were subsequently transferred to medium
containing potassium. It is known that plant hormones can inhibit root
growth. We found that mutants of Arabidopsis resistant to high levels of
auxin and other hormones (aux1, axr1, and axr2) are also resistant to the
ammonium inhibition and produce roots in the absence of potassium. Thus,
the mechanisms that mediate the ammonium inhibition of root development are
linked to hormone metabolic or signaling pathways. These findings have
important implications for understanding how environmental signals,
especially mineral nutrients, affect plant root development.
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