PLANT PHYSIOLOGY , Vol 102, Issue 4 1211-1218, Copyright © 1993 by American Society of Plant Biologists
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CELL BIOLOGY AND SIGNAL TRANSDUCTION |
Blue Light-Induced Phosphorylation of a Plasma Membrane-Associated Protein in Zea mays L
J. M. Palmer, T. W. Short, S. Gallagher and W. R. Briggs
Department of Plant Biology, Carnegie Institution of Washington, Stanford, California 94305
Blue light induces a variety of photomorphogenic responses in higher
plants, among them phototropic curvature, the bending of seedlings toward a
unidirectional light source. In dark-grown coleoptiles of maize (Zea mays
L.) seedlings, blue light induces rapid phosphorylation of a 114-kD protein
at fluence levels that are sufficient to stimulate phototropic curvature.
Phosphorylation in response to blue light can be detected in vivo in
coleoptile tips preincubated in 32Pi or in vitro in isolated membranes
supplemented with [[gamma]-32P]ATP. Phosphorylation reaches a maximum level
in vitro within 2 min following an inductive light pulse, but substantial
labeling occurs within the first 15 s. Isolated membranes remain activated
for several minutes following an in vitro blue light stimulus, even in the
absence of exogenous ATP. Phosphoamino acid analysis of the 114-kD protein
detected phosphoserine and a trace of phosphothreonine. The kinase involved
in phosphorylating the protein in vitro is not dependent on calcium. The
114-kD protein itself has an apparent binding site for ATP, detected by
incubating with the nonhydrolyzable analog,
5[prime]-p-fluorosulfonyl-benzoyladenosine. This result suggests that the
114-kD protein, which becomes phosphorylated in response to blue light, may
also be capable of kinase activity.
