Colchicine-induced paracrystals in the tapetum of wheat anthers.
Prolonged colchicine treatment induced the formation of numerous cytoplasmic para-crystals in tapetal cells of wheat anthers containing germ line cells at pre-meiotic mitosis or early pre-meiotic interphase. Such paracrystals were up to 8 microns long and 0.7 microns in diameter, and filled up to about 8% of the volume of the cytoplasm. Paracrystals were not bounded by a membrane. A paracrystal consisted of tubules running in parallel with its long axis. Paracrystals cut at right angles to their long axes revealed hexagonal arrays of circles with a maximum diameter of about 35 nm and electron-dense walls 6--7 nm in thickness. Similar paracrystals were not seen in any cell type of untreated anthers, or in germ line cells of treated anthers, containing stages between pre-meiotic mitosis and first metaphase of meiosis inclusive. The possible significance of the paracrystals in relation to the function of the tapetum is discussed.