Incorporation of 3H-deoxynucleosides: changes in labelling indices during root development

Abstract

Whole root systems of Vicia faba were treated with 3H-TdR (tritiated deoxythymidine), 3H-AdR (tritiated deoxyadenosine), or 3H-CdR (tritiated deoxycytidine) solutions for 1 h. Labelling indices were determined immediately after treatment or up to 15 h later. Cells of lateral root meristems labelled immediately and most effectively with 3H-TdR. Lower levels of labelling were found in roots treated with 3H-AdR or 3H-CdR; these precursors, in particular 3H-CdR, appear to be unsuitable for the determination of any parameter of DNA synthesis. Cells of small primordia showed poor incorporation of labelled precursors immediately after a 1-h treatment but their labelling indices increased subsequently. It is suggested that pools of 3H-TdR and 3H-AdR are maintained and drawn upon by small primordia. Large primordia showed little or no incorporation of labelled precursors. The different responses of mitotically active cells taken from various developmental stages of a lateral root suggest that alternative pathways for the synthesis of DNA precursors are used to different extents during morphogenesis; the interesting aspect is that such changes can occur over a small number of cell cycles in a population of actively dividing cells.