Biomedical Engineering Reference
In-Depth Information
the
Ces
A gene has an important role in cellulose synthesis and provided direct
evidence for the hypothesis that cellulose biosynthesis takes place in the terminal
complex of the rosette [
11
].
It is uncertain whether the rosette complex is composed of identical subunits or
different subunits. Key information on assembly also still cannot be clarified. The
bacteria linear terminal complex goes through the cell membrane and lipopolysac-
charide layer and mainly synthesizes the 1
types of cellulose I, which is the
metastable monoclinic system. But, the rosette terminal complex in plants is part
of the cell membrane, which mainly synthesizes the 1
'
type of cellulose I, which is
a stable monoclinic form. Therefore, it is generally believed that cellulose synthesis
in cotton also occurs in the cellulose synthase complex connected with the plasma
membrane.
In the process of cellulose biosynthesis, in addition to the terminal complex,
another polypeptide with a molecular mass of 18 kDa also plays an important role.
This polypeptide does not exist in the plasma membrane but is loosely connected
with the plasma membrane. So, it is unlikely to be the component with catalytic
activity in the cellulose synthase complexes. However, it may have regulating effect
because it can combine with 2,6-dichloro-phenyl nitrile, which is the inhibitor of
cellulose synthesis.
“
2.3.4.2
Substrate for Cellulose Synthesis
Identifying the substrate of cellulose synthesis has been difficult. Previous studies
reported that callosum generated in the translating period was the substrate of cel-
lulose synthesis. This result was derived from the fact that, with in vivo conditions,
the speed of synthesizing callosum from the substrate that can supply a radioactive
label is higher than the predictable accumulation level, and the conversion of callose
radioactivity is consistent with the change of cellulose. The conversion may occur
because of the transglycosylation of
“
-l,3-glucose polymerase; the discovery that the
cell wall had the activity of
-l,3-glucose polymerase also supports the hypothesis
mentioned. Callose is a homopolymer of
“
-1,3-linked glucoses. It plays an important
role in the regulation of vital processes, such as metabolism of the sieve tube, the
development of the gametophyte, and so on. The composition and resolution of
callose are directly related to the normal growth of plant metabolic processes [
16
].
The precursor for the biosynthesis of cellulose is uridinediphosphate-
D
-glucose
(UDPG). However, in the past, UDPG was thought to be obtained by the catalysis
of UDPG pyrophosphorylase. Now, with research on cotton fiber development, it
has been found that the catalytic reaction by the sucrose synthase could also provide
UDPG. In the formation stage of the secondary wall of the cotton fibers, sucrose
synthase is connected with cellulose synthase, which may be used as carbon path.
Two sets of evidence support this view. It has been proved that in vitro biosynthesis
of cellulose takes cellulose synthase from the cell membrane of cotton fiber as the
enzyme source and UDPG as a substrate. The products are always
“
“
-1,3-glucan and
