Chemical Composition and Structure of Natural Lignocellulose - Biotechnology of Lignocellulose - page 37

mechanical energy, causing changes of morphology and microstructure; these
changes are shown as decreased DP and crystallinity and significantly increased
accessibility [ 10 ].

2.3.4 Biosynthesis of Cellulose

2.3.4.1 Cellulose Synthesizing Site

Some research has already forecast that assembling of cellulose microfilaments is
finished in the enzyme complex located in the extending top of the cellulose. Then,
scientists hypothesized that a cellulose synthase complex was made up of many
subunits, and each subunit synthesized single-chain glucose, then polymerized it
to the ordered particles of cellulose. But, until 1976, through the freeze-etching
technique, the complex located in the end of the cellulose microfilament was first
observed in green algae. This verified the hypothesis that assembling of cellulose
microfilaments is finished in the enzyme complex located in the extending top of
the cellulose. The subunits of the complex are arranged linearly in three lines and
form the linear enzyme complex where cellulose is synthesized [ 11 ]. The alternating
self-aggregation and dispersion of the complex determine that the microfilament
arrangement direction changes periodically, resulting in different levels of micro-
filaments arranged perpendicular to each other. Later, similar terminal complexes
were observed in bacteria, mosses, ferns, green algae, and microtubule plants, but
in corns, spherical complexes were found [ 12 ].
A terminal complex like a rosette has been observed in higher plants and
concentrates in the cellulose gathering place. Each six cellulose synthase sub-
units of rosette synthesizes 6 glucose chains and then forms microfilaments
with 36 chains. The microfilament directions are mutually different in the dif-
ferent levels of the cell wall, which makes the cell wall in any direction have
high mechanical strength [ 13 ]. The rosette complex not only has the function
of synthase but also can bring glucose chains to the surface of cytoplasm. A
complete rosette complex is essential for the synthesis of crystalline cellulose.
The terminal complex would disappear or be changed when EDTA (ethylenedi-
aminetetraacetic acid) is used to handle oysters or Congo red is used to han-
dle banana cells, further causing the interruption or disturbance of cellulose
biosynthesis. Once the cellulose synthesis recovers, the terminal complex reap-
pears. The mutation of the Ces AI gene in Arabidopsis heat-sensitive mutants
(RSWL) will lead to the reduction of the cellulose content, the content of antacid
“

-glucan, and the number of rosette complexes in the cell membrane, perhaps
because the mutation of this enzyme disrupts the structure of the rosette complex.
This indicates that the RSW1 (a radial swelling phenotype) maybe one component
constituting the rosette complex [ 14 ]. Kimura et al. [ 15 ] used the polyclonal
antibody technique on the central area in cotton CesA protein to verify that the
plasma membrane has a rose-like structure, which was the complex of cellulose
synthase, and was Ces A protein located in rosettes. This finding demonstrated that