Marita Jane M, Ralph John, Hatfield Ronald D, Guo Dianjing, Chen Fang, Dixon Richard A
US Dairy Forage Research Center, USDA-Agricultural Research Service, 1925 Linden Drive West, Madison, WI 53706-1108, USA.
Phytochemistry. 2003 Jan;62(1):53-65. doi: 10.1016/s0031-9422(02)00434-x.
Isolated lignins from alfalfa deficient in caffeic acid 3-O-methyltransferase contained benzodioxanes resulting from the incorporation of the novel monomer, 5-hydroxyconiferyl alcohol. Due to the high level incorporated into the soluble lignin fraction and the use of sensitive NMR instrumentation, unique structural features were revealed. A new type of end-unit, the 5-hydroxyguaiacyl glycerol unit, was identified. It was possible to establish that coniferyl alcohol, sinapyl alcohol, and the novel 5-hydroxyconiferyl alcohol can cross-couple with the 5-hydroxyguaiacyl units that are formed in the lignin, the latter giving rise to extended chains of benzodioxane units. There is also evidence that 5-hydroxyconiferyl alcohol couples with normal (guaiacyl or syringyl) lignin units. Lignin in the alfalfa deficient in caffeoyl CoA 3-O-methyltransferase was structurally similar to the control lignin but the transgenic exhibited a dramatic decrease in lignin content (approximately 20%) and modest increase in cellulose (approximately 10%) reflecting a 30% increase in cellulose:lignin ratio. The compositional changes in both transgenics potentially allow enhanced utilization of alfalfa as a major forage crop by increasing the digestibility of its stem fraction.
从缺乏咖啡酸3 - O - 甲基转移酶的苜蓿中分离出的木质素含有由新型单体5 - 羟基松柏醇掺入而产生的苯并二恶烷。由于大量掺入可溶性木质素部分并使用了灵敏的核磁共振仪器，揭示了独特的结构特征。鉴定出一种新型的末端单元，即5 - 羟基愈创木基甘油单元。可以确定，松柏醇、芥子醇和新型的5 - 羟基松柏醇能够与木质素中形成的5 - 羟基愈创木基单元发生交叉偶联，后者产生苯并二恶烷单元的延伸链。也有证据表明5 - 羟基松柏醇与正常（愈创木基或紫丁香基）木质素单元偶联。缺乏咖啡酰辅酶A 3 - O - 甲基转移酶的苜蓿中的木质素在结构上与对照木质素相似，但转基因苜蓿的木质素含量显著降低（约20%），纤维素含量适度增加（约10%），这反映出纤维素与木质素的比例增加了30%。两种转基因苜蓿的成分变化可能通过提高其茎部的消化率而增强苜蓿作为主要饲料作物的利用率。
