Photosynthesis in Chlorella during Intermittent Illumination of Long Periodicity

Abstract

Subsequent to a dark period of several minutes the rate of photosynthesis during the first seconds of illumination is generally less than that in the subsequent steady state. This phenomenon has been described by the general term "induction." Recently, Burk and Warburg (1), using a manometric method, determined pressure changes during light and dark for a suspension of Chlorella which was illuminated for periods of three minutes or less alternated with equal dark periods. The pressure changes were interpreted as demonstrating that under these conditions the rate of oxygen production and carbon dioxide consumption during the light periods exceeded that of photosynthesis during the steady state; similarly the oxygen consumption and carbon dioxide production in the dark were greater than the steady state rate of respiration. These experiments are subject to criticism because it appears improbable that during periods as short as one minute the manometer can respond sufficiently rapidly so that the observed pressure changes represent the metabolic rates without the complication of physical lag. Subsequently Damaschke, T6dt, Burk and Warburg (2) determined the consumption and production of oxygen using an electrochemical method. Few results have yet been published; these show that after a period of illumination from 5 to 30 seconds the oxygen consumption immediately following the cessation of illumination was greater than in the preceding or subsequent steady state. The effect was considerably smaller than that observed in the earlier manometric studies. The production of oxygen during the period of illumination corresponded to a quantum efficiency of 0.69 mole/mole quantum whereas measurements in the steady state gave a value of approximately 0.3. On the basis of these observations Warburg, Geleick and Briese (3) formulated a mechanism for photosynthesis which postulated that during illumination the photochemical process was accompanied by an accelerated combustion process. During the steady state the net effect of the combined processes is observed; the two can only be observed independently as transitory phenomena during periods of alternate light and dark.Brackett, Olson and Crickard (4), who also used a polarographic method to determine the time course of oxygen consumption and production by Chlorella, were unable to observe transient phenomena of the type described by Burk, Warburg and collaborators.

Energy Transformation in Photosynthesis and the Relation of Photosynthesis to Respiration

“…Hence other workers chose to investigate this problem using a variety of methods. Further studies have been made by Brackett et al (1953) using a polarographic method, by Hill & Whittingham( 1953) and Whittingham( 1954) showed a marked increase in rate of oxygen consumption during the first 10-20 sec. darkness, as compared to the rate in the steady state, whether the dark period followed a light period of 3 or 6 min.…”

“…The experiments of Hill et al and the majority of those of Damaschke et al were confined to Observations in the presence of an oxygen concentration of between 0.1 and 3.0%. Whittingham (1954) found that after periods of one minute illumination the initial rate of oxygen consumption was sometimes greater than the subsequent steady dark rate; when present the effect could be repeated for a number of cycles of light and dark. T h e half-time of decay was of the order of 2 min.…”

“…They claim that maximum efficiencies can only be observed in the presence of concentrations of carbon dioxide as high as 5 % . This is in marked contrast to the 'saturation ' of photosynthesis at high intensities of illumination with very much lower concentrations of carbon dioxide, when that for half maximal rate is of the order of 0*002+3*02% (Warburg, 1919;Whittingham, 1952~). From kinetic principles it follows that at low light intensities, such as used for the determination of efficiency, a yet smaller concentration should be required for 'satura-CO, + 2H20 -& C,H,,O, + H20 + 0, + I I 5,000 cal.…”

“…This value is the same whether measurements are made in acid or alkaline solution and is thus independent of the presence of bicarbonate ions (Whittingham, 1952~). Assuming reversibility, the free energy of formation of the carboxyl group in vivo will be about -8000 to -9000 cal.…”

“…Inhibition of photosynthesis in Chlorella by cyanide is greater the lower the concentration of carbon dioxide (Whittingham, 1952b). Experiments with tracer carbon in which the uptake of tracer immediately after illumination was determined showed that this uptake was inhibited by addition of cyanide (Gaffron, Fager & Rosenberg, I 95 I).…”