Morreel Kris, Ralph John, Kim Hoon, Lu Fachuang, Goeminne Geert, Ralph Sally, Messens Eric, Boerjan Wout
Department of Plant Systems Biology, Flanders Interuniversity Institute for Biotechnology, Ghent University, B-9052 Ghent, Belgium.
Plant Physiol. 2004 Nov;136(3):3537-49. doi: 10.1104/pp.104.049304. Epub 2004 Oct 29.
Lignin is an aromatic heteropolymer, abundantly present in the walls of secondary thickened cells. Although much research has been devoted to the structure and composition of the polymer to obtain insight into lignin polymerization, the low-molecular weight oligolignol fraction has escaped a detailed characterization. This fraction, in contrast to the rather inaccessible polymer, is a simple and accessible model that reveals details about the coupling of monolignols, an issue that has raised considerable controversy over the past years. We have profiled the methanol-soluble oligolignol fraction of poplar (Populus spp.) xylem, a tissue with extensive lignification. Using liquid chromatography-mass spectrometry, chemical synthesis, and nuclear magnetic resonance, we have elucidated the structures of 38 compounds, most of which were dimers, trimers, and tetramers derived from coniferyl alcohol, sinapyl alcohol, their aldehyde analogs, or vanillin. All structures support the recently challenged random chemical coupling hypothesis for lignin polymerization. Importantly, the structures of two oligomers, each containing a gamma-p-hydroxybenzoylated syringyl unit, strongly suggest that sinapyl p-hydroxybenzoate is an authentic precursor for lignin polymerization in poplar.
木质素是一种芳香族杂聚物，大量存在于次生加厚细胞的细胞壁中。尽管已经开展了许多关于该聚合物结构和组成的研究以深入了解木质素聚合反应，但低分子量的寡聚木酚组分却未得到详细表征。与相对难以研究的聚合物不同，该组分是一个简单且易于研究的模型，能够揭示有关单木质醇偶联的细节，而这一问题在过去几年中引发了相当大的争议。我们对杨树（Populus spp.）木质部中甲醇可溶的寡聚木酚组分进行了分析，木质部是一个具有广泛木质化的组织。通过液相色谱 - 质谱联用、化学合成和核磁共振技术，我们阐明了38种化合物的结构，其中大多数是源自松柏醇、芥子醇、它们的醛类似物或香草醛的二聚体、三聚体和四聚体。所有结构都支持了最近受到质疑的木质素聚合反应的随机化学偶联假说。重要的是，两种寡聚物的结构，每种都含有一个γ - 对羟基苯甲酰化的紫丁香基单元，强烈表明对羟基苯甲酸芥子酯是杨树中木质素聚合反应的一种真实前体。
