The influence of 5-aminouracil on the mitotic index of barley root meristems

Isolated barley embryos were cultivated in the complete liquid medium for 24 h and then treated with 200 ppm or 750 ppm 5-AU for 2 h, 8 h or 24 h. During the 24 h treatment, MI decreased from 5–12% to 2–5%. After putting the embryos into the fresh medium without 5-AU, the original decrease of MI was followed by slight increase which was manifested only in part of the roots of some experimental variants. The time of the occurrence of MI maxima varied with the duration of treatment and concentration of 5-AU. After treatment with 750 ppm, the increase of MI occurred later but it was more pronounced than after cessation of the treatment with 200 ppm. In the former case, frequencies exceeding the controls appeared 12 h–16 h after treatment and they were manifested especially after treatments of shorter durations (2 h and 8 h). In the latter case, the increase of MI occurred mainly 6 h after cessation of the 24 h treatment. A slight chromosome breaking ability of this drug was found.