On the mercaptoethanol-induced polyploidization inAllium cepa

Abstract

Root tips ofAllium cepa were treated with 2-mercaptoethanol at concentrations from 1 M to 1.3×10−5 M, and for a duration of 10 minutes to 144 hours. The effect of the SH-compound on mitosis and chromosomes was studied both directly after treatment and after a recovery period of 4 hours to 6 days. The following results were obtained. 1. DNA synthesis was not inhibited, but the mitotic index decreased. When the mitotic index was zero (only in one experiment), most nuclei were arrested in G2 (DNA content 4 C). 2. Under specific conditions, promotion of mitotic activity occurred in diploid and spontaneously formed endopolyploid cells. A partial synchronization of mitosis was recognized after recovery. 3. Metaphase chromosomes were always over-contracted, prophase chromosomes partly showed swelling, partly over-condensation. 4. Anaphase was delayed, and sometimes blocked causing tetraploid restitution nuclei and other aberrations. No endoreduplication and no endomitosis could be induced. 5. The appearance of tetraploid mitoses showing diplochromosome-like chromosome arrangement was caused by the formation of restitution nuclei before completion of chromatid segregation, and by the mitotic stimulation of spontaneously formed endotetraploid nuclei.