The Circadian Rhythm in Photosynthesis in Acetabularia in the Presence of Actinomycin D, Puromycin, and Chloramphenicol

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Abstract
AnucleateAcetabularia crenulata shows a circadian rhythm in photosynthesis. In this study, an oxygen electrode was employed to measure this photosynthetic rhythm in thepresenceandabsence of the inhibitors, actinomycin D, chloramphenicol, and puromycin. High concentrations of the inhibitors were used: actinomycinD, 20-40 [mu]g ml-1; puromycin, 30 and 100 [mu]g ml-1 and chloramphenicol, 250 [mu]g ml -1 The effectiveness of these inhibitors on protein synthesis was also measured underthesameconditionsusedfor the determination of rhythmicity. In spite of large effects of all 3 inhibitors on the incorporation of C14 leucine, no effect on the period on the period or the phase of the photosynthetic rhythm was observed. The higher concentration of puromycin and chloramphenicol produced toxic effects which were expressed as a reduction in the amount of photosynthesis, but rhythmicity was still apparent. After 3 or 4 days'' exposure to actinomycin, Acetabularia became resistant to its effect. Recovery was also observedliTthe ability to incorporate leucine. The implications of these results for theories of the basic oscillator responsible for circadian rhythmicity are discussed.