Late labelled regions in relation to Q- and C-bands in chromosomes of Lilium longiflorum and L. pardalinum

Root tips were pulse-labelled with tritiated thymidine. Late-labelled regions were mapped by quantitative autoradiography of metaphase chromosomes collected 11 h after the pulse for longiflorum (mean G₂=14 h), and 13 h for pardalinum (mean G₂=18 h). Late label in both species was preferentially located in sub-distal regions of the longer chromosome arms. Minimal labelling occurred in centromeric areas. - Some brightly Q-banded regions were late labelled, and some dull areas were not. However, late patterns were considerably more localised than bright Q-bands, and late regions were closely similar between species whereas Q-band patterns are not. Therefore bright Q-bands are apparently not consistently late replicating in Lilium, as they are in mammals, and they may therefore represent a different category of chromosomal substructure. - Centromeric C-bands and those at most nucleolar organisers were not late labelled. Only the more distal intercalary C-bands replicated late, and they were not significantly later than the chromatin surrounding them.