Spectral changes of the fluorescent acriflavine--(Feulgen) DNA dye complex at different temperatures: application of a new cryostat for measurements in reflected and transmitted light.

The fluorometric behaviour of cellular objects is influenced during excitation by two nearly independent phenomena: (1) by the photochemical reaction of the DNA/AF dye complex, and (2) by the energy transfer among several DNA/AF dye complexes. Both processes show a distinct temperature-dependent behaviour and can therefore be characterized by the analysis of the fluorescence spectra at different temperatures. All microfluorometric measurements were performed with a self-constructed cooling device. The cryostat permits measurements of the cellular fluorescence within a range of temperatures between 4 K and 300 K. The cooling unit operates in accordance with the 'Continuous Flow Principle' and allows the application of objectives up to a numerical aperture of 0.6.