97. Mueller, S. C., Maclachlan, G. A., and R. M. Brown, Jr. 1983. Cellulose microfibril assembly and orientation in higher plant cells. Journal of Applied Polymer Science: Applied Polymer Symposium 37:79-90.

97. Synopsis

Freeze-fractured plasma membranes of seedlings of Zea mays L., Burpee's Snowcross, and Pisum sativum L., variety Alaska, contain terminal complex structures and the impressions of microfibrils from the newest cell wall layer. Terminal complex subunits are on the exoplasmic fracture (EF) face, and rosette subunits are on the protoplasmic fracture (PF) face of the membrane. The association of terminal complexes and rosettes with microfibril tips and their association with newly deposited groups of microfibrils is indirect evidence for their role in microfibril assembly. Microfibril tips associated with terminal complexes have been observed with the tips all pointing in the same direction (S. C. Mueller and R. M. Brown. Jr., Planta, 154, 489 (1982)). This asymmetry in the orientation of microfibril tips was observed when microfibril deposition was very orderly. Asymmetric patterns of microfibrils around pit fields that are flow-like in appearance have also been observed. Unidirectionally oriented microfibril tips and flow-like patterns of microfibrils were still observed in colchicine-treated cells when microtubules were depolymerized. However, bands of microfibrils were no longer observed on the plasma membrane. Microtubules may be responsible for certain orientations of microfibrils, particularly the formation of bands of microfibrils in newly deposited wall layers. However, microfibril orienting mechanisms are more complex, involving factors still present during colchicine treatment. A marker specific for newly formed microfibrils could be used to probe the function of terminal complexes. Since UDP-glucose is thought to be a precursor of cellulose microfibrils in higher plant cells, EM radioautography was used to determine the site of incorporation of glucose. However, under the conditions used, glucose was only incorporated from UDP-glucose at the surface of cut or damaged pea stem cells, i.e., in vitro. Thus, incorporation of glucose from UDP-glucose was not useful for probing the patterns of cellulose microfibril synthesis in vivo.

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Last modified 27 October 2005.
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