英语翻译Forexample,Klason lignin analyses of driedpine needles i

英语翻译
For
example,Klason lignin analyses of dried
pine needles indicate that they contain up
to 30% lignin by weight (Theander,1978),
but this value exceeds that found even in
many woods and is probably too high.On
the other hand,the Klason procedure tends
to underestimate the amount of lignin in
annual plants,because some of the polymer
is acid-soluble and consequently lost during
the hydrolysis of polysaccharides.
The fungal delignification of woody
material can be monitored by electron
microscopy (Blanchette,1991) or light
microscopy.with selective staining
(Srebotnik and Messner,1994),although
these procedures are relatively complex
and only semiquantitative.Microscopy is,
of course,useful only when the substrate
being investigated still contains lignified
cell walls,but these techniques might be
used with advantage to assess ligninolysis
in relatively intact twigs or conifer needles.
Several chemical procedures have also
been introduced for the estimation of
lignin content.For example,pulverized
wood samples can be treated with acetyl
bromide in acetic acid,and the absorbance
of the resulting solution at 280 nm can be
compared with the absorbance obtained
from known lignin standards.Methods of
this type are subject to interference from
other components,but can be useful for
the comparison of closely related lignocellulosic
samples (Theander and Westerlund,
1993).
A less direct but very flexible approach
to the study of fungal ligninolysis is to
assess not whether the growth substrate
itself is being delignified,but rather
whether the fungus degrades a simpler target
molecule whose breakdown indicates
that ligninolytic systems must be functioning.
Model substrates of this type can be
infiltrated into the organism’s natural
lignocellulosic growth medium,e.g.wood
or litter,or they can be used as probes in
defined liquid growth media (Kirk et al.,
1975,1978; Srebotnik et al.,1994).The
most frequently used probes are 14C -
labelled synthetic lignins,which can be
prepared by polymerizing 14C-labelled phydroxycinnamyl
alcohols (e.g.labelled
coniferyl alcohol,see inset to Fig.2.1) with
horseradish peroxidase (Kirk and Brunow,
1988).

例如,干松针的克拉松木质素分析表明,其木质素含量为30%（西恩德,1987年）,但这个比例比在很多木材中测得的含量都要高,可能有夸张成分.另一方面,克拉松分析常常低估一年生植物中的木质素含量,因为有些聚合体是酸溶的,可能在多糖的水解过程中流失.
木质材料的真菌去木质过程经过染色后（斯莱伯尼克和梅斯纳尔,1994年）可以通过电子显微镜（布兰切特,1991年）或光学显微镜观察,尽管这一过程相对较复杂,且属于半定量反应.显微镜只有在基片中仍含有木质化细胞壁时有效,但这种手段可以被用于对相对完整的树枝或针叶进行木质素降解研究.
一些化学手段也被用于测量木质素的含量.例如,将木屑样品在乙酸环境下与乙酰溴进行反应,再将280纳摩尔所得溶液的吸收率与已知的木质素标准吸收率进行比较.此类方法易受其它成分的影响,但在对若干相似木质纤维素样品进行比较时很管用（西恩德和韦斯特伦德,1993年）.
另一个研究真菌木质素降解的方法较为间接,但更灵活,即不要去观察基片的生长是否被去木质化了,而是转而研究真菌能否降解更简单的目标分子,如果能降解,就说明木质素降解系统在作用.
这类基片模型可以被植入生物的自然木质纤维素培养基,例如木材或落物,或者将它们作为特定液体培养基的探测器（柯克等,1975,1978；斯雷波特尼克等,1994年）.最常用的探测器是14碳人造木质素,可以通过合成14碳phydroxycinnamyl醇（例如,标记的松柏醇,见图2.1）和辣根过氧化酶得到（柯克和布鲁诺,1988年）.