Dynamic analysis of lignin biosynthesis by stable-isotope tracer method

虽然最近的分子生物学研究已经导致了木质素生物合成的“代谢网格”的一般想法，导致木质素研究的新发现，许多问题仍然存在。其中一个问题是单分子供给机制。为了研究木质化木质部组织中单脂素的储存和供应，我们重点研究了针叶素（针叶醇糖苷）和针叶醛糖苷。用标记的葡萄糖苷进行的示踪实验表明，两种葡萄糖苷都能有效地结合到木质素中，并且部分松柏素在聚合成木质素之前通过醛形式。这表明，除了由β-葡萄糖苷酶催化的去糖基化途径外，针叶素还通过另一条途径加入到单木质素生物合成途径中。有趣的是，很少通过肉桂醇阶段从针叶素合成丁香基单位，而许多丁香基单位是由针叶醛葡萄糖苷合成的。基于这些结果，我们提出了一种可能的途径，其中一些储存的针叶树素被氧化成针叶树醛糖苷，脱糖基化产生针叶树醛，并流入单素途径。

Although recent molecular biological studies have led to the general idea of a "metabolic grid" for lignin biosynthesis, leading to novel findings in the study of lignin, many problems remain. One of these problems is the monolignol supply mechanism. To examine the storage and supply of monolignol in lignifying xylem tissue, we focused on coniferin (coniferyl alcohol glucoside) and coniferaldehyde glucoside. Tracer experiments using labeled glucosides showed that both glucosides were efficiently incorporated into lignin, and that a portion of the coniferin administered passed through an aldehyde form before polymerization into lignin. This suggests that there is another pathway by which coniferin joins the monolignol biosynthesis pathway, in addition to the pathway consisting of de-glucosylation catalyzed by β-glucosidase. Interestingly, syringyl units were rarely synthesized from coniferin via the cinnamyl alcohol stage, whereas numerous syringyl units were synthesized from coniferaldehyde glucoside. Based on these results, we propose a possible pathway in which some of the stored coniferin is oxidized to coniferaldehyde glucoside and de-glucosylation generates coniferaldehyde, which flows into the monolignol pathway.