The Effect of 5-Fluorouracil on the Growth and Nucleolus of Wheat Coleoptiles

Abstract

Intact etiolated wheat coleoptiles grown from the beginning of imbibition III 5-fluorouracil (5-FU) show normal cell elongation, but division is inhibited. 5-FU-treated coleoptiles, 48 hr after imbibition, have enlarged nucleoli (165% increase in volume) in which the RNA is mostly confined to the periphery. Untreated and treated nucleoli were studied by light and electron microscopy. The 5-FU effects on the nucleolus, which occur at the time cell division usually occurs if 5-FU is not present, are of interest in relation to ribosome synthesis. Uracil or thymidine did not reverse the nucleolar effects, but uracil further inhibited growth, while thymidine partly reversed the cell division inhibition. Results with 5-FU and thymidine suggest that the coleoptile cells can divide at least once when they have abnormal nucleoli, but normal nucleolar metabolism is essential for the complete growth of the etiolated wheat coleoptile.