Journal of Experimental Botany, Vol 50, 777-783, Copyright © 1999 by Oxford University Press
V Cotelle, J Pierre and A Vavasseur
In plants, water availability and CO2 partial pressure modulate stomatal
aperture. Phosphoenolpyruvate carboxylase (PEPCase) is
a major enzyme in the pathway leading to malate synthesis which is, with
chloride, the main counterion for potassium accumulated in the guard cell
vacuole during stomatal opening. Whether phosphorylation of PEPCase could
be a major event in guard cell regulation was investigated. Antibodies
(APS-IgGs) raised to a synthetic polypeptide of 23 amino acids containing
the phosphorylation site (ser-8) of the Sorghum
PEPCase recognized the guard PEPCase from Commelina
communis L. at 110 and 120 kDa. The in
vitro phosphorylation of the 110 kDa isoform by PKA was 50%
inhibited by APS-IgGs demonstrating that the regulatory phosphorylation
site was present and functional in the guard cell enzyme. Phosphorylation
by PKA resulted in a 50% increase in the Vmax of the
enzyme (4.2
ARTICLES
Potential strong regulation of guard cell phosphoenolpyruvate carboxylase through phosphorylation
CEA, Département d'Ecophysiologie Végé et Microbiologie, CEN Cadarache, BP1, St Paul-lez, Durance, F-13108, France; Institut de Biotechnologie des Plantes, UA CNRS D1128, Universityé de Paris-Sud, Bât. 630, 91405 Orsay Cedex, France; Corresponding author; Fax: +33 4 42 25 46 56; E-mail: vavasseur@dsvcad.cea.fr
0.3 compared to 2.80.4 pmol h-1
GCP-1, pH 7.3 and 200 
M PEP) and a reduction in
L-malate inhibition (64% compared to 82% inhibition
by 1 mM L-malate). In the presence of 1 mM
L-malate (pH 7.3) phosphorylation of the enzyme by
PKA resulted in a 3-fold increase in the Vmax. Binding
of APS-IgGs to the phosphorylation site of the enzyme led to the highest
activity (10.9±2.6 pmol h-1
GCP-1) and to an absence of inhibition by 1 mM
L-malate at pH 7.3 and 8.0. These changes in the
kinetic properties of the enzyme after phosphorylation should have
important consequences in terms of stomatal regulation.Keywords:
Commelina communis L., guard cell,
phosphoenolpyruvate carboxylase, protein
phosphorylation, stomata.
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