Cellulose microfibril biosynthesis, assembly,
and orientation in the unicellular green alga, Oocystis,
is visualized in association with a linear enzyme complex embedded
in the B face of the plasma membrane. Granule bands of the A
face and complementary ridges of the B face are postulated to
assist in the orientation of recently synthesized microfibrils.
A model for microfibril synthesis and orientation is proposed
and correlated with current hypotheses regarding cellulose biosynthesis
in higher plants.