The Effect of Colchicine on Meiosis in Aloinae

抄録

1) The present study has been made on the chromosome ehaviour during meiosis in Aloinae (n=7) after treatment with colchicine. In addition to the special effect of colchicine on the spindle mechanism, an effect on chiasma formation, chromosome spiralisation and cell-membrane formation were also observed, in contrast to the effects induced by acenaphthene and other chemicals. In the premeiotic division, the second meiotic division and microspore division, ski-like pairs of chromosomes (cf. c-pairing of LEVAN) are clearly seen after treatment with colchicine, as in the somatic divisions of root-tips.
2) PMC's derived from the affected premeiotic tissue are found to be tetra- and octoploid and they may form 2n, 4n, 8n or 16n pollen grains after the formation of the tetrad, diad or monad. Multivalent, especially tetravalent formation in doubled PMC's is observed during metaphase I and irregularities due to the after-effect of colchicine are noted frequently. The chromatid bridges in 4n PMC's suggest that unusual crossing-over occurred between tetravalent chromosomes. Colchicine may induce and at least does not decrease other karyotype alterations besides the polyploidy which has been chosen most often for study by cytogenetists. Experiments on increasing stability or fertility by chromosome doubling may come up against an unexpected difficulty as in the present case, but such unstable polyploids as these amphidiploids may be rather more valuable for further breeding than the stable ones.
3) In the case of treatment from the prophase, 7 bivalents aggregate at one side of a cell without spindle formation and divide there and later form a monad. At the beginning of colchicine treatment and in the process of recovery a multipolar division is induced, the chromosomes remain scattered all over the cell and polynucleate cells or asymmetric polyads are formed. Consequently heteroploid pollen grains are derived from asymmetric polyads.