1364 - INDUCTION PHENOMENA CHAP. 33 



volved in the utilization of bicarbonate in photosynthesis — either in the 

 transport of bicarbonate through the cell wall, or in its chemical transfor- 

 mation (in the latter case, this factor may be the enzyme, carbonic anhy- 

 drate). Similar observations were made by Briggs and Whittingham 

 (1952) with ChloreJla. They found, however, that induction continued if 

 the illuminated algae were transferred from bicarbonate back into carbon 

 dioxide solution, and therefore suggested a different explanation: that 

 cells grown in a carbon dioxide-rich medium and therefore full of metabo- 

 lites, suffer, when exposed to light in a solution that is low in carbon 

 dioxide, "self-poisoning" by the formation of "narcotics" which cover the 

 surface of chlorophyll, and that this causes a prolonged induction. This 

 would place the observed phenomenon alongside certain other forms of 

 "long" inductions, such as that after anaerobic incubation (c/. next sec- 

 tion). OsterHnd (1952) could not confirm with his plant material the 

 above-mentioned findings of Whittingham and Briggs with Chlorella. 

 The long induction Scenedesmus quadricauda shows after transfer into bi- 

 carbonate solution may therefore have a different origin from that observed 

 under the same conditions in ChlorcUa. This is not implausible, because 

 (as we will see in chapter 37D), Scenedesmus quadricauda appears to be 

 much better adapted to utiUze bicarbonate for photosynthesis than Chlo- 

 rella pyrenoidosa. 



6. Influence of Anaerobiosis on Induction 



In chapter 13, we discussed the question whether small ciuantities of 

 oxygen are necessary for photosynthesis, and answered it in the negative. 

 (The question has been revived more recently by Warburg; but new experi- 

 ments seem to confirm the above conclusion, cf. chapter 37D, section 2b). 

 Nevertheless, there is no doubt that green plants deprived of oxygen 

 during a prolonged period of darkness, and then exposed to light, often show 

 considerable initial inhibition. Boussingault (18G5), Pringsheim (1887) 

 and Willstatter and Stoll (1918) found that, after several hours of anaerobic 

 incubation in the dark, the photosynthesis of higher land plants was prac- 

 tically completely inhibited, and required a considerable time for recovery. 

 Green algae were found to suffer, too, but usually to a lesser degree. 



From experiments of Franck, Pringsheim and Lad (1945) it appears 

 that the maximum capacity of algae for photosynthesis is reduced by an- 

 aerobic incubation, not to zero, but to a low, finite level, which may be two. 

 ten or several hundred times lower than the saturation rate in the aerobic 

 state. The level of inhibition depends on the nature of the plant and the 

 duration and specific conditions of the anaerobic treatment. The speed of 

 recovery in light depends — in continued absence of external oxygen supply 



