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Two types with regard to adaptation to different light intensities are described: The Chlorella type and the Cyclotella type. The Chlorella type is mostly found among the green algae, the Cyclotella type among the diatoms. The Chlorella type adapts to a new light intensity mainly by changing the pigment content. Therefore the cells adapted to a high light intensity have a lower chlorophyll a content per cell than cells adapted to a low light intensity. Light saturation is mostly rather low for cells adapted to low light intensities. The light-saturated rate of photosynthesis ist mostly lower for cells adapted to a high light intensity than for cells adapted to a low light intensity. The actual photosynthesis is not much higher at a high light intensity than at a low one. The actual photosynthesis is the photosynthesis at the light intensity where the cells are grown. — The Cyclotella type adapts only by changing the light-saturated rate. The chlorophyll content is the same in cells grown at low and high light intensities. Light saturation for cells grown at a low light intensity is rather high. The light-saturated rate is much higher in the case examined at the high light intensity than at the low one. The actual photosynthesis is considerably higher for cells grown at high light intensities than for cells grown at low light intensities. — The two adaptation types are not sharply separated since transition types occur. [ABSTRACT FROM AUTHOR]

A culture of Skeletonema costatum grown at a light intensity of 3 klux and at 20°C was synchronized in diurnally intermittent illumination of 12 hour light and 12 hour dark. The culture was hardly fully synchronous as the cell division period lasted about 9 hours. The cell division started in the middle of the light period. The concentration of the pigments: chlorophyll a, chlorophyll c and fucoxanthin and the rate of light-saturated photosynthesis were followed every hour during the 24 hour period. Both the concentration of pigments and the photosynthetic activity showed a rhythmical variation. The concentration per cell of all three pigments examined increased during the development of the cells and decreased automatically during the period of cell division. An increase in the pigment concentration was found only in the light period. The rate of light-saturated photosynthesis calculated per unit of cell number increased during the cell development and decreased during (tie division period. The increase in the photosynthetic activity at light-saturation started about 4 hours after the end of cell division, which was 4 hours before the light was turned on while the increase in the concentration of chlorophyll a first started 1-2 hours after this moment. The variation in photosynthetic activity was compared with that found by other workers. The results found with Chlorella ellipsoidea by Japanese scientists (Nihei et al.) was explained as an inhibition phenomenon because the cells were not adapted to the experimental conditions. [ABSTRACT FROM AUTHOR]

In a culture of the fresh water diatom Cyclotella Meneghiniana the average cell volume decreased with time due to reduction of the diameter of the valves. The rate of photosynthesis as a function of light intensity was determined for cells with different average cell volume and the chlorophyll a concentration in the cells was measured at the same time. It was found that the concentration of chlorophyll a in the different cells was approximately constant and independent of the cell volume. The rate of photosynthesis per number of cells at a light intensity of 1 Klux was nearly constant and this was also the case for the rate of photosynthesis calculated per unit of chlorophyll a at 1 Klux. The light saturated rate of photosynthesis per number of cells decreased with decreasing cell volume, but only slightly compared to the reduction in cell volume. The rate of photosynthesis per chlorophyll a and hour at a light intensity of 1 Klux varied in the experiments with Cyclotella between 0.28 and 0.41 mg C. The values are in good agreement with the determinations in green leaves deficient in chlorophyll and with determinations on Chlorella vulgaris carried out by other authors. It is suggested that the invariability of the chlorophyll a content in the cells with varying cell volume is due to a decrease in the cell vacuole with decreasing cell volume while the volume of cytoplasma in the cells is nearly unchanged. [ABSTRACT FROM AUTHOR]

Light-photosynthesis curves for cells adapted to 3 Klux and 30 Klux respectively, were studied using the freshwater diatom Cyclotella Meneghiniana. The initial slope of the curves for the two light intensities was the same which is due to the same concentration of chlorophyll in cells grown at 3 and 30 Klux. The light saturated rate per cell was about 40 per cent higher in 30 Klux-cells than in 3 Klux-cells. The amplitude in light adaptation was found to be rather small in Cyclotella. Ik for the light-photosynthesis curves for 3 Klux- and for 30 Klux-cells was 9 Klux and 12 Klux, respectively. In Chlorella vulgaris a much wider amplitude is found. The corresponding IK-values are 4 Klux and 13 Klux. The light adaptation from one light intensity (3 Klux) to another (30 Klux) or back again was found to be a rather rapid process. Already after 24 hours the adaptation to the new light intensity was complete. Cells of Cyclotella were found to be able to withstand light of very high intensity. Cells adapted to 3 Klux and placed at 30 Klux for three hours did not exhibit any of the inhibition of the rate of photosynthesis shown by cells of Chlorella vulgaris. On the contrary the light saturated rate goes up to a level about 30 per cent higher than that for the 3 Klux and place at 30 Klux for three hours did not exhibit any of the inhibition of the rate of photosynthesis shown by cells of Chlorella vulgaris. On the contrary the light saturated rate goes up to a level about 30 per cent higher than that for the 3 Klux-cells. Towards light intensities of 60 or 100 Klux cells of Cyclotella react in a similar way. No inhibition of the rate of the photosynthesis was found at these very high light intensities either. [ABSTRACT FROM AUTHOR]

Curves showing the rate of photosynthesis as a function of light intensity are presented for Chlorella vulgaris growing at a constant light intensity of either 3 or 30 Klux. The rate is given a) per number of cells, b) per unit of weight of chlorophyll (a + b), and c) per unit of wet volume or unit of weight of dry matter. At an illumination of about 3 Klux the average cell size is at its maximum. At the same time the content of chlorophyll per cell is maximal and the content of enzymes active in photosynthesis is very nearly maximal. If we increase the illumination the cell size decreases. At the same time the content of active enzymes per cell increases slightly, but the content of chlorophyll per cell decreases. If we decrease the illumination (from 3 Klux) cells are produced with the maximum content of chlorophyll but decreasing content of enzymes active In photosynthesis. At the same time the cell size decreases. Growth rates at the two light intensities are computed by means of the measured rates of photosynthesis and respiration. They are identical with the growth rates measured by means of the increase in number of cells. After a shift from 3 Klux to 30 Klux it takes only 24 hours before the ratio chlorophyll a+b: dry weight has changed to that normally found at the high light intensity. The same is true concerning the cell size. When shifting from 30 Klux to 3 Klux it takes a little longer. However, a chlorophyll concentration nearly as high as that ordinarily found at 3 Klux was measured. About 36 hours after the shift from 30 Klux to 3 Klux, or vice versa, the shape of the curve giving the rate of photosynthesis as a function of light intensity approaches that characteristic of algae grown constantly at the new light intensity. If Chlorella grown constantly at 30 Klux are transferred to the dark for 22 hours the shape of the tight photosynthesis curve is only moderately changed. IK decreases from 13 to 9 Klux. If instead the algae are transferred to 3 Klux, IK is decreased to 5 Klux after 22 hours. The importance is stressed of using such dilute concentrations of algae in experiments of both growth and photosynthesis that no self shading takes place. [ABSTRACT FROM AUTHOR]