杉木、I-72杨主要化学组成的株内纵向变异研究

对杉木和I 72杨的心、边材的主要化学组成沿树高方向的株内纵向变异进行了研究。主要研究内容为综纤维素、α 纤维素、半纤维素、木质素、酸溶木质素的含量及综纤维素与木质素的比值变化等。研究结果揭示了这两个树种的心、边材的主要化学成分在纵向上的变异规律:杉木和I 72杨的心、边材综纤维素和α 纤维素的含量均为边材高于心材,但在沿树高方向的纵向变化规律各异;杉木、I 72杨心、边材的半纤维素含量沿着树高方向表现出不同的变化规律;杉木木质素在各个树高部位均为边材高于心材,边材木质素含量随着树高的增加逐步降低,而心材木质素含量则沿树高方向先增加然后逐步降低。I 72杨心、边材木质素含量的变化表现各异,心材含量随着树高的增加逐步增加,边材则表现为无规律变化;杉木、I 72杨心、边材的酸溶木质素含量均沿树高方向逐渐降低,但杉木边材的酸溶木质素含量高于心材,而I 72杨却是心材高于边材;综纤维素与木质素的比值在沿树高方向具有不同的纵向变化规律。

山杨和速生杨硫酸盐浆多相水解动力学的研究

研究了木质素含量为０．２３％的山杨漂白浆和１．０５％的速生杨未漂浆稀酸低温多相水解降解反应动力学特性。结果表明，该过程与棉浆、桦木和针叶材浆具有相类似的特点，即纤维素多相水解降解过程分为两个明显阶段（快速降解和缓慢降解），而最终降至极限聚合度（山杨漂白浆为１８０；速生杨未漂浆为２０６）。两个阶段的纤维素水解降解动力学以其不同反应速度为特征，根据试验数据计算出反应速度常数：山杨漂白浆为Ｋ＝２．５×１０￣（－４）／ｍｉｎ；速生杨未漂浆为Ｋ＝１．６×１０￣（－４）／ｍｉｎ，前者明显地高于后者。随着水解时间的增加，水解残渣得率下降，最终结果达到８３％～８４％。测定了各水解试样的木质素含量，结果表明，水解前期（１０～４０ｍｉｎ）木质素变化较大，山杨漂白浆下降４８％，速生杨未漂浆下降３８％；水解后期，木质素含量变化不大。木质素的存在对于多相（固－液）水解降解反应起着阻碍作用并降低其反应速度常数。木质素含量越高水解液渗透至纤维素大分子链之β－Ｄ－葡糖键的速度越慢。

Molecular studies of cellulose synthase supercomplex from cotton fiber reveal its unique biochemical properties

Cotton fiber is a highly elongated and thickened single cell that produces large quantities of cellulose,which is synthesized and assembled into cell wall microfibrils by the cellulose synthase complex(CSC).In this study,we report that in cotton(Gossypium hirsutum)fibers harvested during secondary cell wall(SCW)synthesis,GhCesA 4,7,and 8 assembled into heteromers in a previously uncharacterized 36-mer-like cellulose synthase supercomplex(CSS).This super CSC was observed in samples prepared using cotton fiber cells harvested during the SCW synthesis period but not from cotton stem tissue or any samples obtained from Arabidopsis.Knock-out of any of GhCesA 4,7,and 8 resulted in the disappearance of the CSS and the production of fiber cells with no SCW thickening.Cotton fiber CSS showed significantly higher enzyme activity than samples prepared from knock-out cotton lines.We found that the microfibrils from the SCW of wild-type cotton fibers may contain 72 glucan chains in a bundle,unlike other plant materials studied.GhCesA4,7,and 8 restored both the dwarf and reduced vascular bundle phenotypes of their orthologous Arabidopsis mutants,potentially by reforming the CSC hexamers.Genetic complementation was not observed when non-orthologous CesA genes were used,indicating that each of the three subunits is indispensable for CSC formation and for full cellulose synthase function.Characterization of cotton CSS will increase our understanding of the regulation of SCW biosynthesis.