[[(3)H]thymidine incorporation and DNA-synthesis in Funaria hygrometrica]

Incubation of caulonema filaments of the moss Funaria hygrometrica with [(3)H]methylthymidine followed by autoradiography fails to show the real amount of DNA-synthesis. Especially nuclei of steadily growing tip cells remain unlabelled, whereas basic cells become radioactive. This effect is not based on different permeabilities. Autoradiographic results of experiments with 5-fluordesoxyuridine and cycloheximide lead to the conclusion that there exists a marked thymidine-kinase gradient along the filament which depends on age and position of the cells.