A cryostat was constructed, which permits measurements of the intracellular fluorescence within a range of temperature between 3.5 to 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. It results from measurement of BAO Feulgen stained nuclear DNA, that a decrease of fluorescence intensity is caused by two different mechanisms: (1) There is a highly temperature dependent effect, originating from phenomena of solid physics, and (2) a second effect, which is almost temperature independent, and can be explained as a photochemical reaction.

No abstract

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.