Elucidation of new structures in lignins of CAD- and COMT-deficient plants by NMR
Elucidation of new structures in lignins of CAD- and COMT-deficient plants by NMR
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DOI：
10.1016/s0031-9422(01)00109-1
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发表时间：
2001-07-01
期刊：
影响因子：
3.8
通讯作者：
Boerjan, W
中科院分区：
文献类型：
--
作者：
Ralph, J;Lapierre, C;Boerjan, W
研究木质素-生物合成途径突变体和转基因提供了深入了解植物对木质素系统扰动的反应，并增强了我们对正常木质素的理解。当通路后期的酶下调时，木质素的组成和结构可能发生显著变化，核磁共振波谱为阐明难降解木质素聚合物的结构提供了强大的诊断工具，提示已经发生的化学和生化变化。杨树咖啡酸o -甲基转移酶（COMT）下调导致5-羟基松柏醇通过典型的自由基偶联反应进入木质素中，而偶联后的醌甲基内部捕获反应在木质素中产生新的苯二氧嘧啶单位。CAD（肉桂醇脱氢酶）下调导致羟基肉桂醛单脂醇前体紧密结合到聚合物中。在生长的聚合物中，新萘基醛与愈创木酰基和丁香基单元交叉偶联8-O-4。而针叶醛只与丁香基单位8-O-4交叉偶联，反映了简单的化学交叉偶联倾向。羟基肉桂醛和5-羟基松柏醇单体的掺入表明这些单脂醇中间体分泌到细胞壁进行木质素化。认识到新的单位可以纳入木质素预示着显著扩大的机会，工程组成和木质素的后续性质，以提高有价值的植物资源的利用。2001爱思唯尔科学有限公司版权所有。
Studying lignin-biosynthetic-pathway mutants and transgenics provides insights into plant responses to perturbations of the lignification system, and enhances our understanding of normal lignification. When enzymes late in the pathway are downregulated, significant changes in the composition and structure of lignin may result, NMR spectroscopy provides powerful diagnostic tools for elucidating structures in the difficult lignin polymer, hinting at the chemical and biochemical changes that have occurred. COMT (caffeic acid O-methyl transferase) downregulation in poplar results in the incorporation of 5-hydroxyconiferyl alcohol into lignins via typical radical coupling reactions, but post-coupling quinone methide internal trapping reactions produce novel benzodioxane units in the lignin. CAD (cinnamyl alcohol dehydrogenase) downregulation results in the incorporation of the hydroxycinnamyl aldehyde monolignol precursors intimately into the polymer. Sinapyl aldehyde cross-couples 8-O-4 with both guaiacyl and syringyl units in the growing polymer. whereas coniferyl aldehyde cross-couples 8-O-4 only with syringyl units, reflecting simple chemical cross-coupling propensities. The incorporation of hydroxycinnamyl aldehyde and 5-hydroxyconiferyl alcohol monomers indicates that these monolignol intermediates are secreted to the cell wall for lignification. The recognition that novel units can incorporate into lignins portends significantly expanded opportunities for engineering the composition and consequent properties of lignin for improved utilization of valuable plant resources. (C) 2001 Elsevier Science Ltd. All rights reserved.