[The effect of FdUrd on nucleic acid metabolism of cells in isolated tissue fragments from the thallus of Riella helicophylla].

In isolated thallus fragments of Riella dedifferentiation of mature cells takes place in a polar region. RNA-synthesis is stimulated first and then DNA-synthesis as well as nuclear and cell divisions in some of the cells. DNA-synthesis is blocked by 10(-5) M FdUrd while polarity of dedifferentiation disappears due to activation of RNA-synthesis in an increasing number of cells.The influence of FdUrd on RNA-synthesis in regenerating fragments has been investigated by determining incorporation of [(14)C8]adenine-sulfate into nucleic acids and measuring the rate of turn-over of the latter. The nucleic acids were fractionated on columns of Sephadex G-150 and G-200 and subjected to electrophoresis on polyacrylamide gels.No differences in the rate of synthesis of the single species of RNA were found. Apparently, the synthetic capacity of the whole fragment is unchanged after treatment with FdUrd but the intercellular correlations which control the formation of meristematic centres are not evolved.After precipitation of the nucleic acids with ethanol the low molecular weight precursors in the supernatant were fractionated on Sephadex G-10 columns. After treatment with FdUrd the fraction of nucleotides has a higher rate of incorporation of [(14)C]adenine and a higher turn-over. It is assumed that the energy metabolism is changed when the cells are blocked at the beginning of the S-phase.