76. Montezinos, D. and R. M. Brown, Jr.
1979. Cell wall biogenesis in Oocystis: experimental alteration
of microfibril assembly and orientation. Cytobios 23:119-139.
76. Abstract
Cell wall biogenesis in the unicellular
green alga Oocystis apiculata has been studied. Under
normal growth conditions, a cell wall with ordered microfibrils
is synthesized. In each layer there are rows of parallel microfibrils.
Layers are nearly perpendicular to each other. Terminal linear
synthesizing complexes are located in the plasma membrane, and
they are capable of bi-directional synthesis of cellulose microfibrils.
Granule bands associated with the inner leaflet of the plasma
membrane appear to control the orientation of newly synthesized
microfibrils. Sub-cortical microtubules also are present during
wall synthesis. Patterns of cell wall synthesis were studied
after treatment with EDTA and EGTA as well as divalent cations
(MgSO4, CaSO4, CaCl2). 0.1 M
EDTA treatment for 15 min results in the disassociation of the
terminal complexes from the ends of microfibrils. EDTA-treated
cells followed by 15 min treatment with MgSO4, results
in reaggregation of the linear complexes into a paired state,
remote from the original ends to which they were associated.
After 90 min treatment with MgSO4,normal synthesis
resumes. EGTA and calcium salts do not affect the linear complexes
or microfibril orientation. Treatments with colchicine and vinblastine
sulphate do not depolymerize the microtubules, but the wall microfibril
orientation is altered. With colchicine or vinblastine, the change
in orientation from layer to layer is inhibited. The process
is reversible upon removal of the drugs. Lumi-colchicine has
no effect upon microfibril orientation, but granule bands are
disorganized. Treatment with coumarin, a known inhibitor of cellulose
synthesis causes the loss of visualization of subunits of the
terminal complexes. The possibility of the existence, of a membrane-associated
colchicine-sensitive orientation protein for cellulose microfibrils
is discussed. Transmembrane modulation of microfibril synthesis
and orientation is presented.