Biology Reference
In-Depth Information
isolation from the cell wall (
Kim et al., 2008
). This technique produces
minimal structural modification in the cell wall (mainly due to the
requirement for fine milling), revealing structure and composition not
only of lignin, but also of polysaccharide components of the wall (
Kim
and Ralph, 2010
).
.
Degradative methods: acidolysis, nitrobenzene oxidation and especially:
Thioacidolysis is an acid depolymerization procedure, which acts
through the cleavage of
b
-O-4 linkages. Only aryl-glycerol-
b
-aryl
ether linked units produce C
6
C
3
phenylpropanoid monomers with
thioethylated chains. Thioacidolysis analysis allows the study of
both the composition and structure of the lignin polymer on whole
cell wall samples, that is, without requiring isolation of the lignin. The
most important limitation of this technique is the application to
samples with low contents of
b
-O-4 linkages. However, thioacidolysis
has been the most diagnostic method for lignin characterization
(
Lapierre, 1993; Rolando et al., 1992
).
Derivatization followed by reductive cleavage (DFRC) is a degradative
method that efficiently cleaves the
a
-ether and
b
-ether linkages in
lignins, releasing analysable monomers for quantification. The method
also provides some information on carbon-carbon-linked lignin (
Lu
and Ralph, 1997
). In the DFRC procedure, acetyl bromide produces
the derivatization and cell wall solubilization, in a similar way to lignin
determination based on acetyl bromide (
Johnson et al., 1961
). Reduc-
tive cleavage is performed in acidic medium and, following acetylation,
4-acetoxycinnamyl acetate monomers are quantified by GC. This tech-
nique provides data analogous to thioacidolysis, and offers an advan-
tage that it leaves native lignin esters intact (
Lu and Ralph, 1997
).
The application of these techniques to different plant groups has provided
important new findings and data, which make necessary an updated overview
of the occurrence and composition of lignins in the phylogenetic groups.
Here, we review the characteristics of lignins in the different plant groups,
with particular attention to the new contributions and the occurrence and
evolution of S lignins.
A. ALGAE
Green algae and bryophytes are paraphyletic groups, and some of the
characteristics that presented bryophytes with adaptations to life on land
have their precursors in Coloechaetales and Charales, which appear to be
preadapted to make the transition to land (
Graham, 1993
).
