In situ Raman investigation of single lipid droplets in the water-conducting xylem of four woody plant species

A micro-Raman spectroscopy approach was used for the direct in situ characterization of lipid bodies in the water-conducting branch xylem of an African resurrection plant and three deciduous European tree species. Because of average diameters of at least 1 (mu)m, the lipid bodies of all investigated species proved to be easily accessible by this technique. All vesicle-forming xylem lipids were identified as fatty acid esters, which may correspond to phospholipids. Whereas in the resurrection plant saturated lipids were dominant, the lipid bodies of the European trees consisted of highly unsaturated fatty acids. A comparison of the spectra of lipid droplets of lime obtained in situ and from isloated xylem sap revealed slightly different signatures. This finding suggests that micro-Raman spectroscopy may be used to detect modifications of the chemical composition of biological substances as a result of the extraction mode.