Chemical Structure and Biosynthesis of the Aromatic Domain of Suberin in Bark

木素是木本植物外皮的主要成分之一。该不溶性生物聚合物由脂肪结构域和芳香结构域组成。虽然脂肪结构域的结构和组成已被很好地研究，但芳香结构域的结构和组成尚不清楚。此外，尚无关于木质素芳香结构域的生物合成研究。本研究分析了栓皮栎和银杏树皮中对羟基肉桂酸第一烷基酯作为木质素芳香结构域的预测前体。咖啡酸烷基酯和阿魏酸烷基酯特异性存在于变异栎的外树皮中，阿魏酸烷基酯特异性存在于双叶栎的外树皮中。其次，在过氧化氢的存在下，用两种树皮的粗酶进行阿魏酸丁酯和咖啡酸丁酯的脱氢聚合作为模型体系。阿魏酸丁酯聚合得到β- o -4′烯醇醚、β-5′、二氢萘、萘和β-β′对称型二聚体，咖啡酸丁酯聚合得到二氢萘、萘和β-6′对称型二聚体。第三，对两种树种的无提取物树皮粉进行甲醇分解。分离鉴定了阿魏酸甲酯二聚体β-O-4′烯醇醚型和β-5′型、阿魏酰氧基脂肪酸甲酯型、阿魏酸甲酯型、香兰素型和松木醛型。结果表明，该化合物具有β-O-4'二聚体和阿魏酰氧基脂肪酸酯。第四，将L-[U-^<14>C]苯丙氨酸和对羟基[8-^<14>C]肉桂酸分别施用于变异栎的切除分支，然后对所施用的树皮进行甲醇分解。放射性被纳入含有β-O-4'二聚体和松柏醛的馏分中。最后，为了从两种树皮中分离出聚木质素芳香域/木质素，并通过FT-IR和固态^<13>C NMR分析其结构，制备了无提取物的树皮细粉，分别用纤维素酶、半纤维素酶和果胶酶进行处理，然后进行甲醇水解。结果表明，外皮多糖与木质素脂肪结构域而非芳香结构域具有化学键。这些结果表明，阿魏酸衍生物是由过氧化物酶脱氢聚合而成的，形成了变异栎和双叶栎外树皮中的亚木质素芳香结构域。少

Suberin is one of the main components in the outer bark of woody plants. The insoluble biopolymer is composed of an aliphatic domain and an aromatic domain. Although the structure and composition of the aliphatic domain have been well investigated, those of the aromatic domain are unclear. Furthermore, there have been no study on biosynthesis of the suberin aromatic domain. In this study, first p-hydroxycinnamic acid alkyl esters, as predicted precursors of the aromatic domain of suberin, in the bark of Quercus variabilis and Ginkgo biloba were analyzed. Caffeic acid alkyl esters and ferulic acid alkyl esters were specifically present in the outer bark of Q. variabilis, while ferulic acid alkyl esters were specifically present in the outer bark of G. biloba. Second, dehydrogenative polymerization of butyl ferulate and butyl caffeate with crude enzymes from both of the outer bark in the presence of hydrogen peroxide were carried out as a model system. The polymerization of butyl ferulat … More e gave dimers of β-O-4' enol ether, β-5', dihydronaphthalene, naphthalene, and β-β' symmetry types, and that of butyl caffeate afforded dimers of dihydronaphthalene, naphthalene, and β-6' types. Third, methanolysis of extractive-free bark powder from both tree species was performed. Methyl ferulate dimers of β-O-4' enol ether and β-5' types, feruloyloxy fatty acid methyl esters, methyl ferulate, vanillin, and coniferaldehyde were isolated and identified from Q. variabilis. The β-O-4' dimer and feruloyloxy fatty acid ester were obtained from G. biloba. Fourth, individual administrations of L-[U-^<14>C]phenylalanine and p-hydroxy[8-^<14>C] cinnamic acid to excised branches of Q. variabilis, followed by methanolysis of the bark administered were carried out. The radioactivity was incorporated into fractions that contain β-O-4' dimer and coniferaldehyde. Finally, to isolate polymeric suberin aromatic domain/lignin from both of the outer bark and to analyze the structure by FT-IR and solid-state ^<13>C NMR, extractive-free fine powder of the outer bark was prepared and treated with cellulases, hemicellulases, and pectinases, followed by methanolysis. It was suggested that the polysaccharides in the outer bark have chemical bonds with suberin aliphatic domain rather than with the aromatic domain. These results indicate that ferulic acid derivatives are dehydrogenatively polymerized by peroxidase to give the suberin aromatic domain in the outer bark of Q. variabilis and G. biloba. Less