Study On The Chemical Association Between Lignin And Mannose In Plant Cellwall By Isotopic Tracer

In pulping and paper making industry, one of the most important technology is toremove lignin from plant raw materials efficiently, and to retain composition thecellulose and hemicelluloses as more as possible; But the pulping yield and bleachingefficiency is affected by the presence of lignin-carbohydrate complexes (LCC) inplants, not only wastes chemicals, but also increases the duty on the environment.Previous studies comfirmed that there are chemical connections between hemicellulosesand lignin, such as benzyl ether linkage, ketal linkage, benzyl ester linkage.In order to elucidate the chemical connections between carbohydrates and lignin ingymnosperms tree, the linkage between sugar units in hemicelluloses andphenylpropane sunstructure was analyzed based on the perspectives of mannose. Thefull13C labelled mannan precursor, i.e. D-13C6-mannose and the inhibitor ofphenylalanine ammonia-lyase was injected into a living ginkgo tree with exogenouslignin precursors to label the cell wall mannose in growing ginkgo plant (Ginkgo bilobaL) by carbon-13. The converting to lignin was inhibited by administration of AOPP.After cuture in climatic chamber for30days, if was found that there was no obviousinfluence on the normal metabolism of ginkgo trees. The result from the13C abundanceof the newly-formed xylem of ginkgo shoots detected by the Vario PYRO cube elementanalyzer indicates that ginkgo trees had been marked succefully, and theD-13C6-mannose can be polymerize into hemicelluloses. With the detection of thenewly-formed xylem of ginkgo shoots by high resolution solid state nuclear magnetic13C NMR, the signals from the1-6C of mannose units labeled by carbon13isotopewere enhanced significantly. This indicates that the bonds between C6position ofmannose units in hemicelluloses and α-carbons of lignin side chain is benzyl etherlinkage. Hemicelluloses and lignin were isolated from13C labeled xylem of ginkgo treesand the results from the13C abundance detections indicated that the inhibitor stoppedthe converting from mannnose to lignin. Therefore, hemicelluloses labelled by carbon13isotope succefully. Hemicelluloses were isolated respectively from differentthickness. By detection of13C abundance, the deposition of glucomannanhemicelluloses in the newly-formed xylem was very fast and effective in the primarywall and s1wall.The specifically LCC were isolated from the newly formed-xylem of ginkgoshoots by the method of Bj rkman, The results of determination of FT-IR and13C-NMR,indicates that the bonds between C6position of mannose units in hemicelluloses andα-carbons of lignin side chain is benzyl ether linkage.In order to remove the sugar unitswhich have no chemical bonds connection with lignin, The specifically13C-enrichedLCC were degraded by cellulase and hemicellulase. Lignin-rich fractions, so calledenzyme-degraded LCCs (EDLCCs) were abtained. The determination of FT-IR and13CNMR, indicates that the bonds between C6position of mannose units in hemicelluloses and α-carbons of lignin side chain is benzyl ether linkage.In order to confirm the correction of the conclusion above, DHPs were preparedwith the existence of mannose in vitro. Mannose-DHP complex was finally obtained.The determination of FT-IR and13C NMR, proves the above experimental results.