Tricin, a Flavonoid Monomer in Monocot Lignification
Tricin, a Flavonoid Monomer in Monocot Lignification
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DOI：
10.1104/pp.114.253757
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发表时间：
2015-04-01
期刊：
影响因子：
7.4
通讯作者：
Ralph, John
中科院分区：
文献类型：
--
作者：
Lan, Wu;Lu, Fachuang;Ralph, John
麦黄酮是最近发现的木质素制剂从小麦（小麦）秸秆，随后在所有单子叶植物样品检查。为了证明麦黄酮参与木质化并建立其掺入木质素聚合物的机制，合成了麦黄酮与单木质素醇（对香豆醇、松柏醇和芥子醇）的4 '-O-β-偶联产物以及由其与芥子醇、然后与松柏醇的4'-O-β-偶联产生的三聚体沿着。还发现，在使用过氧化物酶/过氧化氢或银（I）氧化的仿生氧化中，麦黄酮与单木质醇交叉偶联以形成麦黄酮-（4 '-O-β）-连接的二聚体。凝胶渗透色谱法分级乙酰化玉米（Zeamays）木质素的核磁共振表征表明，麦黄酮部分被发现在甚至最高分子量的馏分，醚连接到木质素单元，表明麦黄酮确实被纳入到木质素聚合物。这些研究结果表明，麦黄酮是完全兼容的木质化反应，是一个真正的木质素单体，并且，因为它只能启动一个木质素链，功能作为一个成核位点的木质化在单子叶植物。这种引发作用有助于解决一个长期存在的困境，即单子叶植物木质素链似乎不像双子叶植物中具有相似的胡萝卜基-愈创木基组合物那样由单纤维素同源脱氢二聚化引发。术语黄酮木脂素被推荐用于从细胞壁中的麦黄酮（或掺入其他类黄酮）开始的单木脂素的外消旋低聚物和聚合物，类似于用于由类黄酮和木脂素部分组成的低分子量化合物的现有术语黄酮木脂素。
Tricin was recently discovered in lignin preparations from wheat (Triticum aestivum) straw and subsequently in all monocot samples examined. To provide proof that tricin is involved in lignification and establish the mechanism by which it incorporates into the lignin polymer, the 4'-O- beta-coupling products of tricin with the monolignols (p-coumaryl, coniferyl, and sinapyl alcohols) were synthesized along with the trimer that would result from its 4'-O-beta-couplingwith sinapyl alcohol and then coniferyl alcohol. Tricin was also found to cross couple with monolignols to form tricin-(4'-O-beta)-linked dimers in biomimetic oxidations using peroxidase/hydrogen peroxide or silver (I) oxide. Nuclear magnetic resonance characterization of gel permeation chromatography-fractionated acetylated maize (Zeamays) lignin revealed that the tricin moieties are found in even the highest molecular weight fractions, ether linked to lignin units, demonstrating that tricin is indeed incorporated into the lignin polymer. These findings suggest that tricin is fully compatible with lignification reactions, is an authentic lignin monomer, and, because it can only start a lignin chain, functions as a nucleation site for lignification in monocots. This initiation role helps resolve a long-standing dilemma that monocot lignin chains do not appear to be initiated by monolignol homodehydrodimerization as they are in dicots that have similar syringyl-guaiacyl compositions. The term flavonolignin is recommended for the racemic oligomers and polymers of monolignols that start from tricin (or incorporate other flavonoids) in the cell wall, in analogy with the existing term flavonolignan that is used for the low-molecular mass compounds composed of flavonoid and lignan moieties.