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PLANT PHYSIOLOGY , Vol 107, Issue 1 77-85, Copyright © 1995 by American Society of Plant Biologists
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DEVELOPMENT AND GROWTH REGULATION |
Selection and Characterization of [alpha]-Methyltryptophan-Resistant Lines of Lemna gibba Showing a Rapid Rate of Indole-3-Acetic Acid Turnover
Y. Y. Tam, J. P. Slovin and J. D. Cohen
Department of Botany, University of Maryland, College Park, Maryland 20742 (Y.Y.T.)
Turnover rate is an important aspect of the regulation of plant processes
by plant growth substances. To study turnover of indole-3-acetic acid
(IAA), two [alpha]-methyltryptophan-resistant lines (MTR1 and MTR2) of
Lemna gibba were generated by nitrosomethyl urea treatment of an inbred
line derived from L. gibba G-3. In this report we describe: (a) the
development of a selection system using this near isogenic line of L.
gibba; (b) techniques for chemical mutation of the lines and selection for
[alpha]-methyltryptophan resistance; and (c) the partial characterization
of the selected lines. MTR lines contained 3-fold higher levels of
anthranilate synthase activity. The enzyme in the MTR lines required higher
levels of tryptophan for feedback inhibition. MTR lines also contained
8-fold higher levels of tryptophan, 3-fold higher levels of free IAA, and
similar levels of total IAA compared to the inbred line. Turnover rates in
the inbred and selected lines were calculated, using the first-order rate
equation, based on the decrease over time in isotopic enrichment of
I3C6-IAA introduced into L. gibba during a 1-h pulse period. Isotope
enrichment in IAA was determined by using gas chromatography-mass
spectrometry. Both MTR lines had an approximately 10-fold higher rate of
IAA turnover than the parent inbred line.
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