Dry mass distribution among interphase nuclei of Tradescantia as determined by X-ray microradiography and microinterferometry.

Abstract

The interphase nuclei of petal cells of Tradescantia paludosa, which showed an active protein and ribonucleic acid (RNA) turnover but no detectable deoxyribonucleic acid (DNA) turnover, were assumed to be in metabolic interphase. These nuclei were estimated to have a dry mass of 0.25±0.03 ng (mean and standard deviation) by X-ray microradiography, and 0.25 ±0.04 ng by microinterferometry.The nuclear dry mass in this stage diverged wider (12.0-16.0%) than that in the interphase preceding meiosis (7.5%) and that in the zygotene stage of meiosis (3.4%). This divergency in dry mass is due mainly to an active turnover of nuclear acidic proteins, and may be an expression of divergent states in nuclear activity at the beginning of the differentiation period.Recent advances in cytochemistry have permitted us to quantificate cellular events. In order to get some insight into the events occuring in the metabolic interphase nuclei at the onset of differentiation, comparative attempts to determine the dry mass of individual nuclei were carried out by X-ray microradiographic and microinterferometric means. Autoradiographic examinations were also made to ascertain the turnover level of these nuclei. The results obtained will be reported below. MATERIAL AND METHODSThe petal tissues of Tradescantia paludosa were used as the material, because they show two distinct periods in development-a dividing period and a differentiating one. The tissues at the beginning of the latter period were chosen exclusively.X-ray microradiography of sectioned petal nuclei: Floral buds, 3.5 mm in length, were fixed with formol-acetic acid-alcohol fixative (FAA), dehydrated with a graded series of ethanol, infiltrated with chloroform, then with paraffin, and finally sectioned at 4 micra (Spencer, Type 820, American Optical Co.). After being stretched on a water surface at 52°C, a selected section was picked up on parlodion film which had been mounted over a ring of aluminum foil. The section