LITHIUM ALTERS MITOTIC PROGRESSION IN STAMEN HAIR-CELLS OF TRADESCANTIA IN A TIME-DEPENDENT AND REVERSIBLE FASHION

  • 1 October 1987
    • journal article
    • research article
    • Vol. 44  (2) , 286-293
Abstract
Stamen hair cells of Tradescantia exhibit remarkable precision in the timing of their mitotic events. This precision is altered dramatically with treatment in 50 .mu.M to 1 mM LiCl, an inhibitor of the polyphosphoinositide cycle. Mitotic progression is altered as a function of the time of treatment with LiCl. If cells as treated during late prophase, greater than 80% fail to enter metaphase. Most of the cells that undergo nuclear envelope breakdown become arrested in metaphase. Treatment with LiCl earlier in prophase also results in metaphase arrest. Metaphase arrest can be reversed by the addition of 10 .mu.M myo-inositol or 100 .mu.M CaCl2 to the extracellular medium. The timing of reversal by myo-inositol takes 10 to 14 min while CaCl2 promotes anaphase onset in 2 to 5 min. The difference in kinetics for reversal between these two treatments suggests that myo-inositol addition overrides a biochemical pathway while Ca2+ addition supplants a phosphoinositide-mediated rise in the cation that may be necessary for anaphase onset. Buffer without myo-inositol or CaCl2 is insufficient for reversal. If the cells are treated with LiCl in mid-late-metaphase, at least 5 min prior to the expected time of anaphase onset, sister chromatids split at the normal time, 33 .+-. 4 min after nuclear envelope breakdown, but further chromosome separation is arrested. Anaphase chromosome movement can be restored by treatment with either 10 .mu.M myo-inositol or 100 .mu.M CaCl2 in the medium. In contrast, if cells are treated with LiCl 0 to 18 min after nuclear envelope breakdown, they enter anaphase precociously; metaphase transit time is reduced from 33 .+-. 4 min in untreated cells to 19 to 26 min in LiCl, depending on the time of Li+ addition, and the cells proceed through anaphase at a rate significantly faster than controls. The rate of chromosome movements is increased slightly, and the extent of chromosome separation is reduced slightly compared to untreated control cells. The time-dependency of Li+ sensitivity suggests that the inhibitor affects a serial sequence of regulatory events and that the activities of some elicitors affected by the Li+ treatment may oscillate under normal conditions during different stages of mitosis. Reversibility by myoinositol suggests that the polyphosphoinositide pathway may be involved in the regulation of mitosis.