The lignin structural ramifications of coumarate 3-hydroxylase (C3H) downregulation have not been addressed in hardwoods. Such information is required to accompany an assessment of the digestibility and bioenergy performance characteristics of poplar, in particular. Structurally rich 2D NMR methods were applied to the entire lignin fraction to delineate lignin p-hydroxyphenyl:guaiacyl:syringyl (H:G:S) levels and linkage distribution changes (and to compare with traditional degradative analyses). C3H downregulation reduced lignin levels by half and markedly increased the proportion of H units relative to the normally dominant G and S units. Relative stem H unit levels were up by ∼ 100-fold to ∼ 31 %, almost totally at the expense of G units; differences in the lignin interunit linkage distributions were more subtle. The H level in the most drastically C3H-downregulated transgenic poplar falls well beyond the H:G:S compositional bounds of normal angiosperms. The response observed here, in poplar, differs markedly from that reported for alfalfa where the S:G ratio remained almost constant even at substantial H levels, highlighting the often differing responses among plant species.

中文翻译：

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对杨树香豆酸酯3-羟化酶木质素结构的影响。

硬木中未解决香豆酸酯3-羟化酶（C3H）下调的木质素结构分支。特别是在评估杨树的可消化性和生物能性能特征时需要这些信息。将结构丰富的2D NMR方法应用于整个木质素部分，以描绘木质素p-羟苯基：愈创木基：丁香基（H：G：S）的水平和键分布的变化（并与传统的降解分析进行比较）。C3H下调将木质素水平降低了一半，并且相对于通常占优势的G和S单元，H单元的比例显着增加。相对茎H单位水平提高了约100倍，达到约31％，几乎全部以G单位为代价；木质素单元间连锁分布的差异更细微。C3H下调程度最高的转基因杨树中的H水平远远超出正常被子植物的H：G：S组成范围。在杨树中观察到的响应与苜蓿报道的显着不同，在苜蓿中，即使在高水平的H下，S：G比例也几乎保持恒定，突出了植物物种之间通常不同的响应。