Choline-O-sulfate biosynthesis in plants: Identification and partial characterization of a salinity-inducible choline sulfotransferase from species of Limonium (Plumbaginaceae)

Abstract

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′-phosphoadenosine-5′-phosphosulfate as the sulfate donor, and showed a pH optimum at 9.0. Apparent Km values were 25 μM for choline and 5.5 μM for 3′-phosphoadenosine-5′-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.