PLANT PHYSIOLOGY , Vol 112, Issue 2 641-649, Copyright © 1996 by American Society of Plant Biologists
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WHOLE PLANT, ENVIRONMENTAL, AND STRESS PHYSIOLOGY |
Coarse and Fine Control and Annual Changes of Sucrose-Phosphate Synthase in Norway Spruce Needles
A. Loewe, W. Einig and R. Hampp
Lehrstuhl fur Physiologische Okologie der Pflanzen, Universitat Tubingen, Auf der Morgenstelle 1, D-72076 Tubingen, Germany
Annual changes of activity of sucrose-phosphate synthase (SPS) from spruce
(Picea abies [L.] Karst.) needles were studied with respect to three
regulatory levels: metabolic fine control, covalent modification
(phosphorylation), and protein amount. Glucose-6-phosphate served as an
allosteric activator of spruce SPS by shifting the Michaelis constant for
the substrate fructose-6-phosphate from 4.2 to 0.59 mM, whereas inorganic
phosphate competitively inhibited this activation. The affinity for the
other substrate, UDP-glucose, was unaffected. Incubation of the crude
extract with ATP resulted in a time- and concentration-dependent decrease
of the maximal velocity of SPS. This inactivation was sensitive to
staurosporine, a potent protein kinase inhibitor, indicating the
participation of a protein kinase. Probing SPS protein with heterologous
antibodies showed that the subunit of spruce SPS is an approximately 139-kD
protein and that changes in the extractable activity during the course of a
year were correlated with the amount of SPS protein. High SPS activities in
winter were paralleled by increased levels of the activator
glucose-6-phosphate and the substrate fructose-6-phosphate, indicating a
high capacity for sucrose synthesis that may be necessary to maintain
photosynthetic CO2 fixation in cold-hardened spruce needles.
