The tertiary sulfonium compound 3-dimethylsulfoniopropionate (DMSP) is found at high levels in many marine algae, but among higher plants it has been reported to accumulate only in Spartina (Gramineae) and one other genus. Cultivated and wild species from 23 genera of Gramineae were tested for DMSP accumulation in leaves of non-stressed plants, using an indirect gas chromatographic assay. Sugarcanes and closely related species accumulated up to 6 μmol g-1 fresh wt; other species contained no more than 0.3 #956;mol g-1 fresh wt. In sugarcanes, mature leaves had higher levels of DMSP than expanding leaves, immature internodes and mature internodes. The identity of DMSP was confirmed by a novel gas chromatography-mass spectrometry method, by fast atom bombardment mass spectrometry and by 1H nuclear magnetic resonance. Mass spectral evidence indicated that DMSP levels in leaves were at least ten-fold higher than glycine betaine levels, suggesting that DMSP may have replaced glycine betaine as a compatible osmolyte in sugarcane. Consistent with this possibility, DMSP was as effective as glycine betaine in relieving osmotic inhibition of bacterial growth, and was accumulated to concen- trations above 1 M by osmotically stressed bacterial cells. Because DMSP is the biological precursor of dimethylsulfide, sugarcane fields may be sources of dimethylsulfide emissions.

A sensitive and specific method was developed for determining choline-0-sulfate by fast atom bombardment mass spectrometry, using a deuterium labelled choline-0-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-0-sulfate (< 1-2 pmol g-' dry wt) but Avicennia germinans contained 8 pmol g-' dry wt, and all six members of the family Plumbaginaceae surveyed (Limonium spp. and Armeria maritima) accumulated > 100 pmol g-' dry wt. Three cultivated Limonium species were also found to accumulate choline-0-sulfate when salinised with NaCl or with NaCl plus Na2S04 under controlled environmental conditions. The identity of choline-0-sulfate in Limonium species was confirmed by high resolution and tandem mass spectrometry, by 'H 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-0-sulfate in osmotic adjustment and sulfate detoxification are discussed.O3lO-7841/9l/O4O3 l7$OS. OO

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