The Journal of Cell Biology, Vol 80, 141-149, Copyright © 1979 by The Rockefeller University Press
Membrane movements and fluidity during rotational motility of a termite flagellate. A freeze-fracture study
SL Tamm
Freeze-fracture electron microscopy was used to examine the structure of a
region of plasma membrane that undergoes continual, unidirectional shear.
Membrane shear arises from the continual clockwise rotation of one part
(head) of a termite flagellate relative to the rest of the cell.
Freeze-fracture replicas show that the lipid bilayer is continuous across
the shear zone. Thus, the relative movements of adjacent membrane regions
are visible evidence of membrane fluidity. The distribution and density of
intramembrane particles within the membrane of the shear zone is not
different from that in other regions of the cell membrane. Also, an
additional membrane shear zone arises when body membrane becomes closely
applied to the rotating axostyle as cells change shape in vitro. This
suggests that the entire membrane is potentially as fluid as the membrane
between head and body but that this fluidity is only expressed at certain
locations for geometrical and/or mechanical reasons. Membrane movements may
be explained solely by cell shape and proximity to rotating structures,
although specific membrane-cytoskeletal connections cannot be ruled out.
The membrane of this cell may thus be viewed as a fluid which adheres to
the underlying cytoplasm/cytoskeleton and passively follows its movements.
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