85. Summary

The electron-microscopical evidence for the existence of 'nascent cellulose fibrils in green plants' (Leppard, G.G. & Colvin, J.R., J. Microsc. 113 (1978), 181) is examined critically. It is concluded that images of pre-shadowed carbon replicas which appear to show cell wall microfibrils having a sheath enclosing a core are unavoidable technical artifacts in which the sheath consists of the replicating carbon. This interpretation is supported by the finding of similar apparent sheaths around air-dried microfibrils which were suspended above the main plane of the substrate surface at the time of replica-making. It is shown that the impressions of microfibrils in fractured plasma membranes have greater cross-sectional dimensions than the microfibrils themselves as a result of the relationship between the microfibrils and the plasma membrane, and that such impressions are not evidence of 'nascent fibrils'. Furthermore, it is argued that there is no evidence at present which supports the hypothesis that a swollen, sheathed 'nascent fibril' of cellulose is produced by prokaryotic Acetobacter xylinum. A light core is demonstrated in images of unshadowed replicas of microfibrils and it is proposed that radiation damage may play a role in the formation of this image. It is demonstrated that the coincidence of Fresnel fringes around unshadowed defocused replicas of microfibrils can also lead to the formation of an apparent core. Problems associated with obtaining measurements from replicas of cell wall microfibrils are discussed and some recommendations are made.

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Last modified 27 October 2005.
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