DNA Replication Pattern in Somatic Chromosomes of <i>Crepis capillaris</i>

Replication in the Marker Chromosomes of a Hypertriploid Mouse Ascites Tumour

“…There is no ordered sequence in the replication of this chromosome, Lima-de -Faria and col. (1967) and Kuroiwa and Tanaka (1970) do not find it either in the chromosomes they examine. The maximum number of marked chromosomes, and the maximum intensity of silver grains per chromosome appears during the early replication periods.…”

Fine Structures of Interphase Nuclei

“…acetic orcein staining and radioautography, it has been shown that heterochromatic segments in mitotic chromosomes of Crepis capillaris corresponded to the late replicating region (6) . Accordingly, the appearance of the silver grains over the electron-transparent region of nuclei fixed immediately after thymidine-3 H treatment suggests that the late replicating heterochromatic segments of mitotic chromosomes are decondensed to dispersed chromatin and are replicated during a late portion of the S period .…”

“…Seeds of Crepis capillaris were germinated on wet filter paper in Petri dishes according to the method described previously (6) . When the primary roots were approximately 4 mm in length, the seedlings were transferred to dishes which contained a thymidine?H aqueous solution .…”

Fine Structures of Interphase Nuclei

“…And average time for component periods were: the synthetic period (S) 5.14 hours, postsynthetic period (G2) 2.20 hours, mitotic period (M) 1.48 hours, presynthetic period (G1) 1 .60 hours (Kuroiwa and Tanaka 1970a). Since one half or more number of nuclei labeled in S period must proceed to G2 period in 2.5 hours and into G1 period in 5 hours from the pulse labeling; therefore, the nuclei of class 3 (open circle) and class 1 (solid triangle) may represent nuclei of G2 period and of G1 period , respectively.…”

“…As material we used root tip cell of Creris capillaris , because it has several advantages for studies of chromosomes, as has it been reported previ ously (Kuroiwa and Tanaka 1970a For electron microscopical study, after 4 hours' fixation in glutaraldehyde fixative, the seedlings were washed in distilled water and post-fixed in 1 or 4 per cent OsO4 solution buffered with phosphate to a pH 6.8, for 10 hours. This post-fixation is needed always to make preparation for electron microscope.…”