PLANT PHYSIOLOGY , Vol 106, Issue 3 1187-1193, Copyright © 1994 by American Society of Plant Biologists
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METABOLISM AND ENZYMOLOGY |
Choline-O-Sulfate Biosynthesis in Plants (Identification and Partial Characterization of a Salinity-Inducible Choline Sulfotransferase from Species of Limonium (Plumbaginaceae)
J. Rivoal and A. D. Hanson
Institut de Recherche en Biologie Vegetale de l'Universite de Montreal, 4101 Rue Sherbrooke Est, Montreal, Quebec, H1X 2B2, Canada
Choline-O-sulfate is a compatible osmolyte accumulated under saline
conditions by members of the halophytic genus Limonium and other
Plumbaginaceae. A choline sulfotransferase (EC 2.8.2.6) responsible for the
formation of choline-O-sulfate was characterized in Limonium species. A
simple radiometric assay was developed in which [14C]choline was used as
substrate, and the h [14C]choline-O-sulfate product was isolated by
ion-exchange chromatography. The choline sulfotransferase activity was
soluble, required 3[prime]-phosphoadenosine-5[prime]-phosphosulfate as the
sulfate donor, and showed a pH optimum at 9.0. Apparent Km values were 25
[mu]M for choline and 5.5 [mu]M for
3[prime]-phosphoadenosine-5[prime]-phosphosulfate. Choline sulfotransferase
activity was detected in various Limonium species but was very low or
absent from species that do not accumulate choline-O-sulfate. In roots and
leaves of Limonium perezii, the activity was increased at least 4-fold by
salinization with 40% (v/v) artificial sea water. Choline sulfotransferase
activity was also induced in cell cultures of L. perezii following salt
shock with 20% (v/v) artificial sea water or osmotic shock with 19% (w/v)
polyethylene glycol 6000. Labeling experiments with [14C]choline confirmed
that the enzyme induced in cell cultures was active in vivo.