PLANT PHYSIOLOGY , Vol 102, Issue 4 1219-1225, Copyright © 1993 by American Society of Plant Biologists
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CELL BIOLOGY AND SIGNAL TRANSDUCTION |
Correlation of Blue Light-Induced Phosphorylation to Phototropism in Zea mays L
J. M. Palmer, T. W. Short and W. R. Briggs
Department of Plant Biology, Carnegie Institution of Washington, Stanford, California 94305
The physiology of light-induced phototropic curvature has been studied
extensively in coleoptiles of grasses, particularly in Avena and Zea mays
L. In Z. mays L., we have found that, in addition to curvature, blue light
also induces rapid phosphorylation of a 114-kD protein in the tips of
coleoptiles, and, in a previous report, we reported several characteristics
of the phosphorylated substrate protein and kinase (J.M. Palmer, T.W.
Short, S. Gallagher, W.R. Briggs [1993] Plant Physiol 102: 1211-1218).
Here, we compare the phosphorylation response to several known aspects of
phototropism physiology. Blue light-induced phosphorylation occurs only in
the upper portion of the coleoptile and is absent from the node and
mesocotyl. The specific activity of phosphorylation is highest in the
extreme apical portion of the tip, which is also the site of maximal
sensitivity to phototropic stimuli (A. W. Galston [1959] In Physiology of
Movements, Encyclopedia of Plant Physiology, Springer, Berlin).
Fluence-response determinations indicate that light dosage levels that
stimulate curvature also stimulate phosphorylation. However, the threshold
for inducing detectable phosphorylation in maize cannot be matched to the
threshold for curvature induction. The recovery of sensitivity to
phototropic stimuli after exposure to high fluences of light occurs with
kinetics that are very similar to those for recovery of the phosphorylation
response after a previous high-fluence light exposure. In addition,
wavelengths of light in the blue and near-ultraviolet regions of the
spectrum that maximally stimulate phototropic curvature also maximally
stimulate in vitro phosphorylation in maize. The pattern of stimulation
matches the absorption spectra of flavoproteins, which have been proposed
as candidates for blue light photoreceptors.
