The effect of age on the structure and composition of isolated
and purified cell walls from cultures of Choanephora cucurbitarum
was investigated by microchemical analyses, visible and infrared
spectrophotometry, x-ray diffractometry and electron microscopy.
Qualitative evaluation revealed the presence of lipids, proteins,
neutral sugars, strong alkali soluble sugars, chitin, chitosan and
uronic acids in the cell walls of both the 1 and 7 day old cultures.
As the mycelium aged, there was a slight but statistically significant
increase in the protein content, and a pronounced rise in the chitin
and neutral sugar constituents of the cell walls. Conversely, the
decrease in the chitosan content during this period had the net
effect of altering the chitin: chitosan ratio from near unity in the
younger cultures, to a 2:1 ratio in the 7 day old cell wall samples.
Glutaraldehyde-osmium fixed thin sections of the 1 day old vegetative
hyphae of £. curbitarum revealed the presence of a monolayered
cell wall, which upon aging became bilayered. Replicas of acid
hydrolysed cell walls demonstrated that both the 1 and 7 day old
samples possessed an outer layer which was composed of finely granular
amorphous material and randomly distributed microfibrils. The deposition
of an inner secondary layer composed of parallel oriented microfibrils
in the older hypha was correlated with an increase in the
chitin content in the cell wall.
The significance of these results with respect to the intimate
relationship between composition and structure is discussed.
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