THE PLANT CELL, Vol 1, Issue 2 241-248, Copyright © 1989 by American Society of Plant Biologists
Photorespiration and Light Act in Concert to Regulate the Expression of the Nuclear Gene for Chloroplast Glutamine Synthetase
J. W. Edwards and G. M. Coruzzi
The Laboratory of Plant Molecular Biology, The Rockefeller University, New York, New York 10021-6399
In Pisum sativum, distinct chloroplast and cytosolic forms of glutamine
synthetase (GS) are encoded by homologous nuclear genes that are
differentially expressed in vivo (Tingey, S.V., Tsai, F.-Y., Edwards, J.W.,
Walker, E.L., and Coruzzi, G.M. [1988]. J. Biol. Chem. 263, 9651-9657). In
leaves, light selectively affects the expression of the nuclear gene for
chloroplast GS2. Differences in the maximal levels of GS2 mRNA in etiolated
plants treated with red or white light indicate that only part of the
white-light-induced accumulation of GS2 mRNA is due to a
phytochrome-mediated response. The kinetics of GS2 mRNA accumulation in
response to white-light illumination of etiolated or dark-adapted green
plants indicates that GS2 mRNA accumulates more rapidly in plants
containing mature, photosynthetically competent chloroplasts. Other
evidence that GS2 mRNA levels are affected by the metabolic status of
chloroplasts concerns the selective induction of GS2 mRNA in plants grown
under conditions that result in the production of photorespiratory ammonia.
These results indicate that the light-induced accumulation of GS2 mRNA in
leaves results from the action of phytochrome as well as light-induced
changes in chloroplast metabolism.
