The existence and formation of covalent lignin–carbohydrate (LC) linkages in plant cell walls has long been a matter of debate in terms of their roles in cell wall development and biomass use. Of the various putative LC linkages proposed to date, evidence of the native existence and formation mechanism of phenyl glycoside (PG)‐type LC linkages in planta is particularly scarce. The present study aimed to explore previously overlooked mechanisms for the formation of PG‐type LC linkages through the incorporation of monolignol glucosides, which are possible lignin precursors, into lignin polymers during lignification. Peroxidase‐catalyzed lignin polymerization of coniferyl alcohol in the presence of coniferin and syringin in vitro resulted in the generation of PG‐type LC linkages in synthetic lignin polymers, possibly via nucleophilic addition onto quinone methide (QM) intermediates formed during polymerization. Biomimetic lignin polymerization of coniferin via the β‐glucosidase/peroxidase system also resulted in the generation of PG‐type as well as alkyl glycoside‐type LC linkages. This occurred via non‐enzymatic QM‐involving reactions and also via enzymatic transglycosylations involving β‐glucosidase, which was demonstrated by in‐depth structural analysis of the synthetic lignins by two‐dimensional NMR. We collected heteronuclear single‐quantum coherence (HSQC) NMR for native cell wall fractions prepared from pine (Pinus taeda), eucalyptus (Eucalyptus camaldulensis), acacia (Acacia mangium), poplar (Populus × eurarnericana) and bamboo (Phyllostachys edulis) wood samples, which exhibited correlations, albeit at low levels, that were well matched with those of the PG‐type LC linkages in synthetic lignins incorporating monolignol glucosides. Overall, our results provide a molecular basis for feasible mechanisms for the generation of PG‐type LC linkages from monolignol glucosides and further substantiates their existence in planta.

中文翻译：

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在用单木酚糖苷木质化中产生苯基糖苷型木质素-碳水化合物键的可能机制。

就其在细胞壁发育和生物质利用中的作用而言，植物细胞壁中共价木质素-碳水化合物（LC）键的存在和形成一直是一个争论的问题。迄今提出的各种推定LC联系，苯基糖苷的天然存在和形成机制的证据（PG）型LC连接在植物中特别少。本研究旨在探讨在木质化过程中通过将单木酚糖苷（可能是木质素的前体）掺入木质素聚合物中来探索PG型LC键形成过程的先前被忽视的机制。过氧化物酶-催化木质素松柏醇的聚合反应中的松柏存在和丁香体外导致合成木质素聚合物中PG型LC键的生成，可能是通过亲核加成到聚合过程中形成的甲基苯醌（QM）中间体上。针叶树素通过β-葡萄糖苷酶/过氧化物酶系统的仿生木质素聚合也导致生成了PG型以及烷基糖苷型LC键。这是通过涉及非酶QM的反应以及涉及β-葡萄糖苷酶的酶转糖基化发生的，这通过二维NMR对合成木质素的深入结构分析证明。我们收集了从松树（Taeda taed），桉树（Eucalyptus camaldulensis），阿拉伯树胶（Acacia mangium）制备的天然细胞壁级分的异核单量子相干（HSQC）NMR），杨木（Populus  ×  eurarnericana）和竹木（Phyllostachys edulis）木材样品，尽管含量很低，但仍显示出相关性，它们与掺入单木酚苷的合成木质素中的PG型LC键很好地匹配。总体而言，我们的结果为从单木酚糖苷生成PG型LC键的可行机制提供了分子基础，并进一步证实了它们在植物中的存在。