Synthesis of Nucleoprotein in Bean Root Cells

Abstract

THE autoradiograph technique permits the presence of a radioactive isotope to be detected in individual cells and cell parts. It thus becomes possible to study the time of synthesis of a compound by providing the cell with an isotope of a suitable element, and, after fixation, dissolving out all other compounds which contain this element. This method has been applied¹ to the uptake of phosphorus-32 by nuclei of Vicia faba root cells, by growing roots in a solution of sodium dihydrogen phosphate and treating the fixed tissue with acetic acid - alcohol, water and N hydrochloric acid at 60° C. Squash preparations then show nuclear autoradiographs above some cells; that is, cell nuclei contain phosphorus-32 in the form of a compound which is not removed by these reagents. From a study of the percentage of resting nuclei which show autoradiographs after different periods of growth with phosphorus-32, and their distribution in the length of the root, and from the delay in the appearance of an autoradiograph over dividing nuclei, it was concluded that: (1) the phosphorus compound is not synthesized during cell division, nor during the period immediately preceding it, but during some part of interphase; (2) it is synthesized in cells which are preparing for division, but not in cells which will differentiate without further division; (3) phosphorus-32 in the form of this compound remains in nuclei for considerable periods of time and is transmitted to daughter nuclei.