PLANT PHYSIOLOGY , Vol 101, Issue 2 429-434, Copyright © 1993 by American Society of Plant Biologists
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METABOLISM AND ENZYMOLOGY |
Arabidopsis Chloroplasts Dissimilate L-Arginine and L-Citrulline for Use as N Source
R. A. Ludwig
Department of Biology, Sinsheimer Laboratories, University of California, Santa Cruz, California 95064
When aseptically grown on defined medium with either L-arginine,
L-citrulline, or nitrate as the sole N source, Arabidopsis plants grew and
developed normally. Three catabolic activities, L-arginine iminohydrolase,
L-ornithine carbamoyltransferase, and carbamate kinase, were found in
stromal fractions of purified Arabidopsis chloroplasts. These activities
dissimilate L-arginine and/or L-citrulline into L-ornithine, ammonium,
bicarbonate, and ATP. In physiological tests with purified, intact
Arabidopsis chloroplasts, L-[guanido-14C]arginine was rapidly taken up and
about 10% was decomposed, releasing 14CO2. Therefore, chloroplasts can take
up and dissimilate L-arginine. In principle, chloroplast arginine
dissimilation allows Arabidopsis to use L-arginine and/or L-citrulline as
general N sources for growth. However, plants rarely encounter exogenous
L-arginine and/or L-citrulline in amounts exceeding their biosynthetic
needs. Therefore, L-arginine and L-citrulline might serve as endogenous N
sources.
