Utilization of the label from bacterial [3H] DNA by isolated barley roots and embryos under different conditions

³H] DNA fromEscherichia coli and ³H] thymidine were applied, in sterile conditions, on isolated barley embryos and on roots excised from these embryos, both cultivated in the liquid medium and on halves of barley seeds, through the endosperm bridge. In embryos and roots, the labelled compounds were applied in 1.5% sucrose + 0.2 SSC alone, or together with either unlabelled thymidine or DEAE-dextran. Similar labelling indices were found after ³H] thymidine and ³H] DNA treatment which shows that the activity of ³H] DNA is utilized during the S phase. After application of ³H] thymidine, only cell nuclei in S phase were labelled. After the application of ³H] DNA an extranuclear label, in addition to the labelling of nuclei in the S phase, was observed in some experimental variants. The density of label above labelled nuclei after ³H] DNA treatment sharply decreased when unlabelled thymidine or DEAE-dextran was added, while the density of label above nuclei labelled by ³H] thymidine decreased when unlabelled thymidine but not DEAE-dextran was added. The labelling of nuclei with the label from ³H] DNA is the result of degradation of exogenous DNA reutilization of low molecular weight products. Extranuclear labelling is most probably due to the polymerous or partly degraded DNA.