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

树脂素是木本植物外皮中的主要成分之一。该不溶性生物聚合物由脂肪族结构域和芳香族结构域组成。虽然脂肪族结构域的结构和组成已经得到了很好的研究，但芳香族结构域的结构和组成还不清楚。此外，还没有关于Suberin芳香族结构域的生物合成的研究。本研究首先对栓皮栎和银杏树皮中的对羟基肉桂酸烷基酯进行了分析，预测了松香的芳香族结构域的前体。咖啡酸烷基酯和阿魏酸酯仅存在于栓皮栎的外皮中，而阿魏酸烷基酯则专有地存在于银杏的外皮中。其次，在过氧化氢存在下，阿魏酸丁酯和咖啡酸丁酯与两种外皮粗酶进行脱氢聚合反应。阿魏酸丁酯…的聚合β-O-4‘-烯醇醚、β-5’、二氢萘、萘和β-β‘对称型二聚体较多，咖啡酸丁酯二聚体有二氢萘、萘和β-6’型二聚体。第三，对这两种树种的无萃取物树皮粉末进行了甲醇分解。从栓皮栎中分离鉴定了β-O-4‘-烯醇醚和β-5’型阿魏酸甲酯二聚体、阿魏酸甲酯、香草醛和针叶醛。从银杏中分离得到β-O-4‘二聚体和阿魏酸酯类化合物。第四，用L-苯丙氨酸和对羟基肉桂酸对栓皮栎的切取枝条进行了单独给药，然后对给药树皮进行了甲醇分解。放射性被并入含有β-O-4‘二聚体和针叶醛的级分中。最后，为了从两种树皮中分离出具有芳香结构域/木质素的聚合物，并用FT-IR和固体核磁共振分析其结构，制备了无抽提物的树皮微粉，分别用纤维素酶、半纤维素酶和果胶酶处理，然后进行甲醇分解。这表明树皮外层的多糖与Suberin脂肪族结构域有化学键，而与芳香族结构域没有化学键。这些结果表明，在栓皮栎和银杏的外皮中，阿魏酸的衍生物被过氧化物酶脱氢聚合，得到了松脂素的芳香区。较少

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