Identification and Determination by Fast Atom Bombardment Mass Spectrometry of the Compatible Solute Choline-O-sulfate in Limonium Species and Other Halophytes

Abstract

A sensitive and specific method was developed for determining choline-O-sulfate by fast atom bombardment mass spectrometry, using a deuterium labelled choline-O-sulfate internal standard. This method was used to survey leaves or shoots of 30 native halophytic species from 14 families, collected from temperate and subtropical saline habitats. Twenty-three species had very little choline-O-sulfate (< 1- 2 μmol g^-1 dry wt) but Avicennia germinans contained 8 μmol g^-1 dry wt, and all six members of the family Plumbaginaceae surveyed (Limonium spp. and Armeria maritima) accumulated > 100 μmol g^-1 dry wt. Three cultivated Limonium species were also found to accumulate choline-O-sulfate when salinised with NaCl or with NaCl plus Na₂SO₄ under controlled environmental conditions. The identity of choline-O-sulfate in Limonium species was confirmed by high resolution and tandem mass spectrometry, by ¹H nuclear magnetic resonance, and by analysis of hydrolysis products. Tests with Limonium leaf disks showed that the salt glands of this genus secrete very little sulfate. Possible roles for choline-O-sulfate in osmotic adjustment and sulfate detoxification are discussed.