Changes in Intensity and Spectral Distribution of Fluorescence Effect of Light Treatment on Normal and DCMU-Poisoned Anacystis nidulans

The intensity of the “steady-state” fluorescence of “aerobic”Anacystis nidulans is variable under prolonged illumination with orange (590 mμ) or blue (440 mμ) light for both normally photosynthesizing and DCMU-poisoned cells. In general, orange light illumination causes an increase of the fluorescence intensity followed by a decrease, while blue light causes an increase until a steady level is reached. Poisoned Anacystis cells show four to eight times larger changes in fluorescence intensity than the normal cells; the detailed time course of fluorescence changes is also different in poisoned and normal cells. When algae are cooled to -196°C in light, the light-induced changes in the “steady-state” fluorescence disappear in both types of cells. Difference fluorescence spectra, constructed by subtracting the fluorescence spectra taken after 5–15min of illumination from those after 60–90min of illumination, show a doublet structure of the difference band with a major peak coinciding with the Anacystis emission maximum (685 mμ) and a minor peak located at about 693 mμ