The photosynthetic rhythm of acetabularia crenulata. i. continuous measurements of oxygen exchange in alternating light-dark regimes and in constant light of different intensities

TLDR: Both maxima of the diurnal time course of oxygen evolution as well as the free-running rhythm were expressed at a moderate (250 ft.) and at a high (1000 ft.-c.) light intensity, indicating an unusually loose coupling of the light and dark reactions.

Abstract: 1. Oxygen exchange by Acetabularia crenulata in various light regimes was monitored continuously for as long as 10 days by means of a rate-measuring graphite oxygen electrode.2. The time course for photosynthesis in 8-hour light periods is bimodal, and consists of an initial burst of oxygen production followed by a depression and a subsequent slow rise to a (usually) higher maximum in the latter part of the period. The two maxima show differential sensitivity to the deleterious effects of long-term exposure to the environment of the oxygen electrode.3. The light curve for photosynthesis departs from linearity at the comparatively low intensity of 200 ft.-c. but does not reach saturation below 1300 ft.-c., indicating an unusually loose coupling of the light and dark reactions.4. Both maxima of the diurnal time course of oxygen evolution as well as the free-running rhythm were expressed at a moderate (250 ft.-c.) and at a high (1000 ft.-c.) light intensity. A free-running rhythm was also found at 45 ft.-c. ...