Colchicine-induced Paracrystals in Root Cells of Wheat (Triticum aestivum L.)

Tubulin conformations other than microtubules in the meristematiccells of wheat roots grown in the presence of 2 mM colchicinesolution were investigated by immunofluorescence and electronmicroscopy. In the affected cells microtubules disappeared andwere replaced by tubulin fluorescent strands that occurred inthe cortical cytoplasm. With increasing time of exposure tocolchicine the tubulin strands became better organized and occurredalso in the subcortical cytoplasm and finally they were restrictedto the area around the nucleus. In prophase and preprophasecells thick strands occupied the cortical cytoplasmic zone wherein normal cells a preprophase microtubule band (PMB) was expectedto be assembled. In the colchicine-treated cells electron microscopy revealedan accumulation of paracrystalline aggregates, which initiallyoccurred along the cell wall and later deeper in the cytoplasm,in the perinuclear regions and the cytoplasmic invaginationsof the nucleus. In transverse planes the paracrystalline strandsappear to consist of hexagonal subunits in a 'honeycomb' arrangement,while in longitudinal and oblique sections they exhibit variableimages. Since their distribution coincides with that of thetubulin strands visualized by immunofluorescence, they are consideredto be the same structure. Therefore, the paracrystals consistof, or at least contain, tubulin. They are most likely to bepolymers of tubulin-colchicine complexes.Copyright 1995, 1999Academic Press Wheat roots, colchicine, immunofluorescence, electron microscopy, tubulin paracrystals, Triticum aestivum L