Incorporation of 3H-arginine in chromosomes of Vicia faba

3H-arginine was used in an effort to label the nuclear protein of Vicia faba root meristem cells. Prior to labeling, the root tips were treated for 24 hr with 5-aminouracil in order to synchronize cell divisions and obtain a large proportion of mitolic figures. Autoradiographs of chromosomes from the first and second division after labeling were examined. Almost 100 per cent of the chromosomes in the first division were labeled. The marked absence of label in metaphase chromosomes at second division suggests turnover of a major fraction of nuclear protein during one cell division cycle.