PLANT PHYSIOLOGY , Vol 113, Issue 1 219-226, Copyright © 1997 by American Society of Plant Biologists
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CELL BIOLOGY AND SIGNAL TRANSDUCTION |
Water Deficit Rapidly Stimulates the Activity of a Protein Kinase in the Elongation Zone of the Maize Primary Root
T. R. Conley, R. E. Sharp and J. C. Walker
Maize Biology Training Program (T.R.C.), Department of Agronomy, Plant Science Unit (R.E.S.), and Division of Biological Sciences (J.C.W.), Universtiy of Missouri, Columbia, Missouri 65211
The mechanisms by which plants detect water deficit and transduce that
signal into adaptive responses is unknown. In maize (Zea mays L.)
seedlings, primary roots adapt to low water potentials such that
substantial rates of elongation continue when shoot growth is completely
inhibited. In this study, in-gel protein kinase assays were used to
determine whether protein kinases in the elongation zone of the primary
root undergo activation or inactivation in response to water deficit.
Multiple differences were detected in the phosphoprotein content of root
tips of water-stressed compared with well-watered seedlings. Protein kinase
assays identified water-deficit-activated protein kinases, including a
45-kD, Ca2+-independent serine/threonine protein kinase. Water-deficit
activation of this kinase occurred within 30 min after transplanting
seedlings to conditions of low water potential and was localized to the
elongation zone, was independent of ABA accumulation, and was unaffected by
cycloheximide-mediated inhibition of protein translation. These results
provide evidence that the 45-kD protein kinase acts at an early step in the
response of maize primary roots to water deficit and is possibly involved
in regulating the adaptation of root growth to low water potential.
