Biomedical Engineering Reference
In-Depth Information
2.5.5
Biological Function of Lignin
2.5.5.1
The Relationship Between Metabolism of Lignin and Cell
Differentiation
Lignin metabolism in plants has physiological significance, which was mainly
present as the close relationship between changes of its enzyme activity, the
increase of intermediate and lignin contents and cell differentiation, the resistance
to pathogen infection, and other physiological activities in plant development [
37
].
Plant cell differentiation is a core problem in developmental biology. The process
of cell differentiation is essentially the changing process of cell physiology and
morphology; cell differentiation and organ growth have some relation with phenyl-
propanoid metabolism and its products. Since the 1970s, there have been many
reports about the relationship between lignin metabolism and cell differentiation;
Oven found that when the plant was injured, the callus first formed lignified
parenchyma cells, followed by formation of short vessels and traumatic resin canals.
This process required the participation of the phenylpropanoid metabolites. Mala
et al. thought that phenylalanine metabolism had a closer relationship with further
development of an embryo.
The structure of cell walls from outside to inside is as follows: ML, primary
wall, the first secondary wall (S1), the second secondary wall (S2), and the third
secondary wall (S3). The structure of S1 and S2 of the wild-type tobacco cell wall
is dense. However, the structure of the anti-CCR transgenic tobacco cell wall varies
with types of cells. For example, in fiber cells, the fiber framework of S2 becomes
significantly loose, but in vessel cells, the structures of S2 and S3 are changed.
However, in the anti-COMT gene tobacco plants, structural changes of the cell wall
are not detected. In the hybrid generation of these two transgenic plants, only the
S3 structure of the vessel cell wall has slight changes. The immunocytochemistry
analysis of the lignin subunit showed that the G and S units of wild-type plants
concentrated on S2 in the fiber cells, G and S units of wild-type plants decreased
in the hybrid generation, and cell walls became thin. In the vessel cells, G and S
units in wild-type plants were unevenly distributed in the S1, S2, and S3, mostly
in S2. However, G and S units of hybrid generation were distributed in S1 and
S3. Corresponding with this microscopic change, plants with antisense CCR gene
grow shorter and have smaller leaves. But, plants with anti-COMT gene have slight
changes in height and leaf size, the height and leaf features of hybrid generation are
between those of CCR gene plants and anti-COMT gene plants.
Many studies have confirmed that the formation of tracheary elements is accom-
panied by the synthesis of lignin. Therefore, research on the metabolism physiology
of lignin is an important part in research on the differentiation physiology of
tracheary elements. The results for the differentiation of wheat root tip (meristematic
zone, elongation zone, maturation zone) showed that the tracheary element is mainly
formed in the maturation zone. There was only preliminary differentiation and a
small amount of lignin deposition in the elongation zone. Lignin is the basic factor
