PLANT PHYSIOLOGY , Vol 102, Issue 1 101-105, Copyright © 1993 by American Society of Plant Biologists
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CELL BIOLOGY AND SIGNAL TRANSDUCTION |
Inositol Trisphosphate Metabolism in Subcellular Fractions of Barley (Hordeum vulgare L.) Mesophyll Cells
E. Martinoia, R. Locher and E. Vogt
Institute of Plant Sciences, Swiss Federal Institute of Technology, Zurich Sonneggstrasse 5, ETH-Z, CH-8092 Zurich, Switzerland (E.M., E.V.)
Phosphatases in cytosolic fractions, vacuoles, and vacuolar membranes from
barley (Hordeum vulgare L.) leaves were found to dephosphorylate inositol
1,4,5-trisphosphate (IP3). 1,4-inositol bisphosphate (1,4-IP2) is the main
product of IP3 dephosphorylation by the cytosolic fraction. The activity
was strictly Mg2+ dependent. In contrast, IP3 dephosphorylation activity of
both the soluble vacuolar and the tonoplast fractions was inhibited up to
50% by Mg2+. When vacuolar membranes were incubated with IP3, 1,4-IP2 was
produced only under neutral and slightly alkaline conditions. Under acidic
conditions, however, dephosphorylation yielded putative 4,5-inositol
bisphosphate. Li+ (20 mM) and Ca2+ (100 [mu]M) strongly inhibited activity
in the soluble vacuolar fraction but had only a slight effect on the
activities of the cytosolic and tonoplast fractions.