COLCHICINE-INDUCED PARACRYSTALS IN ROOT-CELLS OF WHEAT (TRITICUM-AESTIVUM L)

Tubulin conformations other than microtubules in the meristematic cell s of wheat roots grown in the presence of 2 mM colchicine solution wer e investigated by immunofluorescence and electron microscopy. In the a ffected cells microtubules disappeared and were replaced by tubulin fl uorescent strands that occurred in the cortical cytoplasm. With increa sing time of exposure to colchicine the tubulin strands became better organized and occurred also in the subcortical cytoplasm and finally t hey were restricted to the area around the nucleus. In prophase and pr eprophase cells thick strands occupied the cortical cytoplasmic zone w here in normal cells a preprophase microtubule band (PMB) was expected to be assembled. In the colchicine-treated cells electron microscopy revealed an accumulation of paracrystalline aggregates, which initiall y occurred along the cell wall and later deeper in the cytoplasm, in t he perinuclear regions and the cytoplasmic invaginations of the nucleu s. In transverse planes the paracrystalline strands appear to consist of hexagonal subunits in a 'honeycomb' arrangement, while in longitudi nal and oblique sections they exhibit variable images. Since their dis tribution coincides with that of the tubulin strands visualized by imm unofluorescence, they are considered to be the same structure. Therefo re, the paracrystals consist of, or at least contain, tubulin. They ar e most likely to be polymers of tubulin-colchicine complexes. (C) 1995 Annals of Botany Company