Somatic nuclear division in the sporidia of Ustilago violacea. II. Observations on living cells with phase-contrast and fluorescence microscopy.

Abstract

Somatic nuclear division in living cells is described under both phase-contrast and acridine orange fluorescence microscopy. The observations confirm a previous description of the division in fixed cells stained with acetic orcein. Acridine orange at the optimum concentration of 75–250 mg/liter complete medium clearly differentiated the nucleolus, chromatinic granules, nucleoplasm, and spindle pole body, as well as indicating changes in RNA content in the cytoplasm during budding. Acridine orange fluorescence was identical in both living and fixed cells. The fluorescence of the spindle pole body indicated that it contains DNA, which may initiate RNA synthesis. Time-lapse phase-contrast observations confirmed that neither the fixation technique nor acridine orange or acetic orcein staining caused noticeable artefacts during division, and provided indisputable evidence for the sequencing of stages. Estimates from the time-lapse observations indicated that the division is quite slow (about 45 min) and that 'prophase' takes about 12 min, 'metaphase' 5 min, and 'anaphase–telophase' about 28 min.