Autoradiographic detection of the uptake of the label from bacterial3H-DNA in relation to the kinetics of the mitotic cycle in barley embryos
Extirped barley embryos were pre-cultivated in aerated liquid nutrient solution for 24 h and then cultivated for 6 h in nutrient solution containing either3H-DNA fromBacillus subtilis or3H-thymidine. After this treatment the embryos were thoroughly washed and transferred to the fresh nutrient medium. Samples were fixed at different intervals up to 24 h. Feulgen squashes were made and covered with autoradiographic emulsion. Microautodiagrams of different parts of the embryos (root meristem, shoot apex plus meristem of the third leaf, second leaf meristem, coleoptile, scutelum) were observed. Labelling of the nuclei after the application of both3H-DNA and3H-thymidine was found in the proliferating parts of the embryos but no label was found in the scutelum. The labelling index values were almost similar in different embryo organs after the treatment with3H-DNA and3H-thymidine. Labelling index and the fraction of labelled mitoses at different intervals after the application of the labelled substances were almost similar after treatment with3H-DNA and3H-thymidine, except some variations due to irrelevant differences in the kinetics of the mitotic cycle. No disappearance of the activity of3H-DNA was observed at different intervals after removal from the labelled solutions during cultivation for other 24 h in non-labelled nutrient medium either containing DNA fromBacillus subtilis or without it. The embryos which were immersed into 0.2% NaCl solution with either one of the labelled compounds did not show any initiation of the S phase nor uptake of3H-DNA. All these results demonstrate that the label from3H-DNA is localized in those cell nuclei which were in the S phase during treatment but they do not yet distinguish unambiguously between the adsorbtion of polymerous DNA or its degradation and reutilization of low-molecular weight products.
KeywordsRoot Meristem Mitotic Cycle Barley Embryo Label Mitosis Fresh Nutrient Medium
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