ACCUMULATION OF THE COMPATIBLE SOLUTE 3-DIMETHYLSULFONIOPROPIONATE IN SUGARCANE AND ITS RELATIVES, BUT NOT OTHER GRAMINEOUS CROPS

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 mu mol g(-1) fresh wt; other species contained no more than 0.3 mu 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 H-1 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 concentrations above 1 M by osmotically stressed bacterial cells. Because DMSP is the biological precursor of dimethylsulfide, sugarcane fields may be sources of dimethylsulfide emissions.