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24. Brown, Jr. R. M., Franke, W. W., Kleinig,
H., Falk, H., and P. Sitte. 1970. Scale formation in chrysophycean
algae. I. Cellulosic and non-cellulosic wall components made by
the Golgi apparatus. J. Cell Biol. 45:246-271.
24. Abstract
The cell wall of the marine chrysophycean
alga Pleurochrysis scherfellii is composed of distinct
wall fragments embedded in a gelatinous mass. The latter is a
polysaccharide of pectic character which is rich in galactose
and ribose. These wall fragments are identified as scales. They
have been isolated and purified from the vegetative mother cell
walls after zoospore formation. Their ultrastructure is described
in an electron microscope study combining sectioning, freeze-etch,
and negative staining techniques. The scales consist of a layer
of concentrically arranged microfibrils (ribbons with cross-sections
of 12 to 25 X 25 to 40 A) and underlying radial fibrils of similar
dimensions. Such a network-plate is densely coated with particles
which are assumed to be identical to the pectic component. The
microfibrils are resistant to strong alkaline treatment and have
been identified as cellulose by different methods, including sugar
analysis after total hydrolysis, proton resonance spectroscopical
examination (NMR spectroscopy) of the benzoylated product, and
diverse histochemical tests. The formation and secretion of the
scales can be followed along the maturing Golgi cisternae starting
from a pronounced dilated "polymerization center" as
a completely intra-cisternal process which ends in the exocytotic
extrusion of the scales. The scales reveal the very same ultrastructure
within the Golgi cisternae as they do in the cell wall. The present
finding represents the first evidence on cellulose formation by
the Golgi apparatus and is discussed in relation to a basic scheme
for cellulose synthesis in plant cells in general.
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