A "Microtubule" in Plant Cell Fine Structure

Abstract

This paper reports an electron microscope examination of the cortices of some plant cells engaged in wall formation. Previous studies of similar material fixed in OSO4 alone have disclosed discontinuities in the plasma membrane and other evidence of inadequate fixation. After glutaraldehyde, used as a fixative in this present study, the general preservation of cortical fine structure is greatly improved. This is shown, for example, by the first evidence of slender tubules, 230 to 270 A in diameter and of indeterminate length, in plant cells of this type. They have been found in the cortical regions of cells of two angiosperms and one gymnosperm, representing all the material so far studied following this method of fixation. The tubules are identical in morphology to those also observed here in the mitotic spindles of plant cells, except that the latter have a somewhat smaller diameter. It is noted that the cortical tubules are in a favored position to govern cytoplasmic streaming and to exert an influence over the disposition of cell wall materials. In this regard it may be of some significance that the tubules just beneath the surface of the protoplast mirror the orientation of the cellulose microfibrils of the adjacent cell walls.

The frequency of plasmodesmata increases early in the whole shoot apical meristem of Sinapis alba L. during floral transition

“…Ten rapidly defoliated SAMs of both SD-control and LD-induced plants were collected at di erent time intervals after start of the LD (28, 32, 36 and 48 h). Five di erent kinds of ®xation were tested: (i) the classical double ®xation with glutaraldehyde and osmium tetroxide (Ledbetter and Porter 1963), (ii) the same ®xation plus tannic acid (Olesen 1979), (iii) osmium tetroxide-potassium ferricyanide ®xation (Hepler 1981), (iv) double ®xation with formaldehyde-calcium followed by potassium dichromate (Glauert 1965), and (v) potassium permanganate ®xation (Luft 1956). Since our aim was not to describe the ultrastructure of the Pd but only to count them unequivocally, we chose the last ®xation method which produced high-contrast membranes (as the appressed ER passed through the Pd), and was rapid and easily utilized.…”

Freeze-Fracture of Microtubules and Bridges in Motile Axostyles

“…Indeed, it is possible that each microtubule has a layer of material associated with its surface analogous with the surface coat or "glycocalyx" found on many cell surfaces, and that dehydration may remove this material. A 40-80-A clear zone or exclusion zone devoid of recognizable structure has been observed around microtubules in thin sections (Ledbetter and Porter, 1963;Porter, 1966;Silver and McKinstry, 1967;Lane and Treherne, 1970;Macgregor and Stebbings, 1970) and freeze-etch replicas (Stebbings and Willison, 1973). It may be normally unstained surface material that is being visualized when microtubules are observed in negative contrast after treatment with lanthanum (Lane and Treherne, 1970;Bannister, 1972;Burton and Fernandez, 1973), ruthenium red (Tani and Ametani, 1970), thiourea (Warner and Satir, 1973), or tannic acid (Mizuhira and Futaesaku, 1971;Tilney et al, 1973), or even without specific treatment (Ledbetter and Porter, 1964).…”

Aging of the Shoulder Joint of Guinea Pigs. Electron Microscopic and Quantitative Histochemical Aspects

“…Apparently cell renewal took place in the replacement of dead cells, keeping the number of cells more or less constant. The presence of large numbers of microfilaments and microtubules in these chondrocytes is difficult to explain: These structures are believed to be related to movement of intracellular material (Ledbetter & Porter, 1963;Slautterback, 1963) or to contractility of cells or cell parts (Allison, Davies, & Petris, 1971;Ishikawa, Bischoff, & Holtzer, 1969;Ledbetter & Porter, 1963). Neither of these functions is likely to be significantly enhanced in the comparatively inactive chondrocytes, in which microtubules and filaments are most prominent.…”