. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. RHYTHMS IN ACETABULARIA. I 663 producing the curve were grown in an 8L-16D regime and subjected to experi- mentation in the latter half of a light period. The physiological state of the cells was therefore that of late stage 2 when the diurnal photosynthetic cycle is at its maximum. Before each exposure to light the algae were allowed to reach a steady- state of oxygen exchange in the dark. The rate of photosynthesis at each in- tensity was then taken as the increase in the rate of oxygen production that took place during 30
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. RHYTHMS IN ACETABULARIA. I 663 producing the curve were grown in an 8L-16D regime and subjected to experi- mentation in the latter half of a light period. The physiological state of the cells was therefore that of late stage 2 when the diurnal photosynthetic cycle is at its maximum. Before each exposure to light the algae were allowed to reach a steady- state of oxygen exchange in the dark. The rate of photosynthesis at each in- tensity was then taken as the increase in the rate of oxygen production that took place during 30 seconds of illumination. Since we observed stage 1 responses only following dark periods of at least several hours' duration, the light curve in Figure 2 is attributable to stage 2 photosynthesis. The light curve obtained in this manner has an Ik somewhat below 300 whereas saturation required intensities in excess of 1000 Ik is the intensity at which the extrapolated initial slope of a light curve intersects a horizontal line through the maximum rate of photosynthesis. Curves of this form are produced even by single Acetabularia cells (unpublished results), eliminating the possibility that mutual shading was responsible for the unusually slow approach to saturation. Consequently, the rate of photosynthesis of Acetabularia over a wide range of intermediate light intensities is not limited solely by a light reaction or a dark reaction, sensu strictu. 2 O I- 3 _J O LU X o. 1000 FT-C 250 FT-C 45 FT-C i — I - ' — | NOON MN 1 - 1 - 1 - 1 - 1 - 1 - 1 NOON MN NOON MN I - i — I - i - 1 — NOON MN NOON FIGURE 3. The free-running rhythm of oxygen production in continuous light at three intensities. Scale of ordinate is non-uniform. Prior to experiments the cells received 8 hours of illumination at 300 ft-c. daily from 9 to 17 o' Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - colorati
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
