1410 INDUCTION PHENOMENA CHAP. 33 



of reacting with each of the several reduction substrates. For example, 

 in scheme 7. VA, the reduction rate must be the same for A • CO2, A • HCO2, 

 A -112002 and A-H3002. Furthermore, in this and other schemes (such 

 as 7.V) which postulate photochemical oxidation of water by oxidized 

 chlorophyll in addition to photochemical reduction of carbon dioxide by 

 reduced chlorophyll, the photoxidation must run at the same rate as the 

 photoreduction {i. e., chlorophyll must be distributed about evenly between 

 the oxidized and the reduced forms). 



If, at the end of the dark period, all acceptor molecules are in the state 

 A -002, or all chlorophyll molecules are in the oxidized (or the reduced) 

 state, the induction period required to redistribute the acceptor and the 

 chlorophyll molecules so as to permit equipartition of quanta obviously 

 must be inversely proportional to the intensity of illumination. 



As a strict requirement, the equipartition of energy between the complexes A- CO2, 

 A • HCO2, . . . and between the oxidized and reduced forms of the sensitizer is mandatory- 

 only in the Unear part of the light curves, where practically all the absorbed quanta 

 have to be utiUzed for photosynthesis; this condition gradually loses its vaUdity with ap- 

 proach to light saturation, where more and more Ught quanta are allowed to be wasted. 



It will also be noted that, if, in the dark, all chlorophyll were to accumu- 

 late in the oxidized form, the evolution of oxygen should start at twice its 

 steady rate, and then decrease gradually, while the consumption of carbon 

 dioxide should start at zero, and gradually increase to the steady level. 

 According to scheme 7.VA, the achievement of equipartition with respect 

 to the reduction intermediates A -002, A -11002, A -112002 and A-H3OO2 

 should require four times as many quanta as the achievement of equiparti- 

 tion with respect to oxidation and reduction (X and HX). If at the begin- 

 ning of illumination, all acceptor is in the form A-OO2, and all chlorophyll 

 in the oxidized form, X, the carbon dioxide consumption should require 

 four times longer to rise to its steady rate, than the oxygen production to 

 decline to a steady level. 



Experimentally, the duration of the induction period is either independ- 

 ent of light intensity, or increases slowly with it; and as a general rule, no 

 differences in sign or duration have been noticed between the carbon di- 

 oxide and the oxygen induction curves. This indicates that the building 

 up of photochemical intermediates is not the essential cause of induction. 



It was mentioned once before that Shiau and Franck (1947) have sug- 

 gested an interpretation of the "second wave" of induction by the interplay 

 of catalytic inhibition and redistribution of intermediates. This hypothesis 

 assumes that the plant starts, after a period of darkness, with an equipar- 

 tition of A among the intermediates, A • OO2, A • HOO2, • • - In strong light, 

 however, this equipartition will be disturbed, if the photochemical reduc- 

 tion is not instantaneously compensated by carbon dioxide uptake by 



