Mitotic cycle kinetics of root meristems of isolated barley embryos and intact seedlings. Labelling of nuclei by tetraploidy

The minimum length of the mitotic cycle of root meristems of cultivated barley embryos and intact seedlings was longer than that measured by the construction of the labelled mitoses curve; it was 10–12 h for intact seedlings and 16 h for cultivated barley embryos. Action of colchicine on interphase was detected. Colchicine induces the increase of the frequency of prophases starting from the fourth hour. The most probable explanation is shortening of the S-phase. As the whole mitotic cycle duration is increased in comparison with that after³H-thymidine, it is most probable that G₁ phase duration is increased by colchicine treatment. Different cytogenetic effects of colchicine were analysed in detail. A basic difference between the response of root meristems of isolated embryos and of intact seedlings was found. In isolated embryos, the effect of 0.1% and 0.4% colchicine (i.e. blockage of anaphase movement, metaphase arrest and contraction of chromosomes) disappears within 2–5 h after removing the colchicine. In intact seedlings, the effect of colchicine is maintained for a considerably longer time. It leads to gradual accumulation of metaphases over 9 h after pulse treatment and this accumulation of metaphases leads to a gradual increase of the incidence of tetraploid mitoses starting from 10th – 12th till 22nd hour after the pulse. This is the reason why maximum frequency of tetraploid cells in root meristems of cultivated isolated embryos was 16 h after the pulse (i.e. at the beginning of their incidence) and it reached the value 5.4% while in seedlings the maximum was 22 h after colchicine treatment and it reached the value 38%.