Effects of water soluble oncostatic fraction from Rheum officinale Baill. rhizomes on Allium cepa root meristem. II. Meristem length and mitotic activity distribution

Incubation in 5 and 12.5 per cent extract from Rheum officinale rhizomes causes disturbance of the dynamic equilibrium between the number of dividing cells and the number of those passing to the elongation zone. The zone of meristematic cells is shortened to 2/3 and the zone of mitoses to 1/2 after 24-h incubation in 5 per cent extract. 12-h incubation in 12.5 per cent extract does not reduce the zone of meristematic cells, although it shortens the mitosis zone to 1/5. This suggests that a high concentration of the inhibitor arrests elongation. growth. Mitotic activation of the meristem in the beginning of postincubation period occurs on a wide area since the last mitotic cycle runs in the cells of the basal part of the meristem. During further postincubation (48 and 72 h after 5% and 72 h after 12.5% extract) the meristematic zone is greatly shortened and the zone of highest mitosis frequency shifts in apical direction. The mitotic activity in the apical sector much higher than in the control suggests, that the quiscent centre takes part in the reconstruction of the meristem