The dependence of the ATP level of the blue-green alga Anacystis nidulans on light intensity (300-20000 erg·cm(-2)·s(-1) white light) and on temperature (0-50°), pH (6.5-9.0), and phosphate concentration (up to 10(-1) M) in light (20000 lx) and dark was measured. In contrast to a low ATP level in darkness the level in light remains high and constant with each treatment in a broad range of the respective scales. DCMU [3-(3',4'-dichlorophenyl)-l,1-dimethyl-urea)] (5×10(-6) M) has no effect on the ATP pool in light, supporting the view that the ATP level is maintained by cyclic photophosphorylation. Dio-9, an inhibitor of energy transfer, lowers the ATP level according to concentration in light and dark. The unchanged ATP level after transitions from N2 to N2+CO2 under different conditions indicates an intensive regulation of the ATP pool. The ADP level, where measured, was found to be inverse to the ATP level. These results are discussed in comparison with data collected by other authors using different organisms.

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