Amthor Jeffrey S
SC-74/Germantown Building, U.S. Department of Energy, 1000 Independence Avenue SW, Washington DC 20585-1290, USA.
Ann Bot. 2003 May;91(6):673-95. doi: 10.1093/aob/mcg073.
Lignin is derived mainly from three alcohol monomers: p-coumaryl alcohol, coniferyl alcohol and sinapyl alcohol. Biochemical reactions probably responsible for synthesizing these three monomers from sucrose, and then polymerizing the monomers into lignin, were analysed to estimate the amount of sucrose required to produce a unit of lignin. Included in the calculations were amounts of respiration required to provide NADPH (from NADP(+)) and ATP (from ADP) for lignin biosynthesis. Two pathways in the middle stage of monomer biosynthesis were considered: one via tyrosine (found in monocots) and the other via phenylalanine (found in all plants). If lignin biosynthesis proceeds with high efficiency via tyrosine, 76.9, 70.4 and 64.3 % of the carbon in sucrose can be retained in the fraction of lignin derived from p-coumaryl alcohol, coniferyl alcohol and sinapyl alcohol, respectively. The corresponding carbon retention values for lignin biosynthesis via phenylalanine are less, at 73.2, 65.7 and 60.7 %, respectively. Energy (i.e. heat of combustion) retention during lignin biosynthesis via tyrosine could be as high as 81.6, 74.5 and 67.8 % for lignin derived from p-coumaryl alcohol, coniferyl alcohol and sinapyl alcohol, respectively, with the corresponding potential energy retention values for lignin biosynthesis via phenylalanine being less, at 77.7, 69.5 and 63.9 %, respectively. Whether maximum efficiency occurs in situ is unclear, but these values are targets that can be considered in: (1) plant breeding programmes aimed at maximizing carbon or energy retention from photosynthate; (2) analyses of (minimum) metabolic costs of responding to environmental change or pest attack involving increased lignin biosynthesis; (3) understanding costs of lignification in older tissues; and (4) interpreting carbon balance measurements of organs and plants with large lignin concentrations.
对香豆醇、松柏醇和芥子醇。分析了可能负责从蔗糖合成这三种单体，然后将单体聚合成木质素的生化反应，以估算生产单位木质素所需的蔗糖量。计算中包括为木质素生物合成提供NADPH（来自NADP(+)）和ATP（来自ADP）所需的呼吸量。考虑了单体生物合成中期的两条途径：一条通过酪氨酸（存在于单子叶植物中），另一条通过苯丙氨酸（存在于所有植物中）。如果木质素生物合成通过酪氨酸高效进行，蔗糖中分别有76.9%、70.4%和64.3%的碳可保留在源自对香豆醇、松柏醇和芥子醇的木质素部分中。通过苯丙氨酸进行木质素生物合成时，相应的碳保留值较低，分别为73.2%、65.7%和60.7%。通过酪氨酸进行木质素生物合成时，源自对香豆醇、松柏醇和芥子醇的木质素的能量（即燃烧热）保留率分别高达81.6%、74.5%和67.8%，而通过苯丙氨酸进行木质素生物合成时，相应的势能保留值较低，分别为77.7%、69.5%和63.9%。原位是否能达到最大效率尚不清楚，但这些值可作为以下方面的参考目标：（1）旨在使光合产物的碳或能量保留最大化的植物育种计划；（2）分析应对环境变化或害虫侵袭（涉及木质素生物合成增加）的（最低）代谢成本；（3）了解老组织中木质化的成本；（4）解释木质素浓度高的器官和植物的碳平衡测量结果。
