A LIGNIN-LIKE POLYMER IN THE CUTICLE OF SPRUCE NEEDLES - IMPLICATIONSFOR THE HUMIFICATION OF SPRUCE LITTER

Information on the type and amount of refractory biopolymers produced by plants is still insufficient. The aim of the present work was to de termine the chemical (structural) composition of spruce cuticles as a source material for humification. Intact cuticles were isolated by con ventional techniques from fully developed needles of Norway spruce (Pi cea abies (L.) Karst.). The cuticles were subjected to a series of sel ective treatments to remove different types of polymers. Extraction wi th organic solvents, to remove lipids and waxes, was followed by sapon ification to remove the cutin polyester. Finally, the cuticle residues were hydrolyzed to remove polysaccharides. Through investigations com bining CP/MAS C-13-NMR spectroscopy, analytical pyrolysis, and wet che mical methods (CuO oxidation), the chemical composition of the polymer was determined in the cuticle, and in the residues obtained by the se lective chemical treatments. These data show that the isolated spruce cuticles consist of extractable lipids, polysaccharides, and cutin, bi opolymers commonly found in plant cuticles. In addition, a lignin-type polymer was identified, which was selectively isolated after the trea tments described above, from the final residue. In conjunction with re sults from a microscopic survey of the cuticles, these investigations provide evidence for the presence of a lignin-like polymer as a compon ent of intact cuticles of Norway spruce. The consequences of this find ing for the humification process of spruce litter are discussed.