DISCUSSION 



387 



cxphiiKition of the I'.mcrson cfTcrt. Kincrson fouiul lli;il illuinination witli 

 two light sources of clilfeient wavelengths, if applied together, gave a higher 

 photosynthetic rate than the sum of the two independent irradiations. Of 

 special interest is Jack Myer's new result tiiat this is still llie case if the 

 irradiations are offered in succession, separated by dark, periods of several 

 seconds. It seems diiTicult to reconcile the.se data with the assumption that 

 light is solely used for photoioni/ation: the indications are rather, that the 

 first irradiation produces a photochemical intermediate stable enough to 

 survive a dark period and to undergo a second photochemical change by 

 the following irradiation with light of shorter wavelengths. 



1 he examples of difficulties encountered by the assumption that light 

 is solely used in photosynthesis for photoionization of chlorophyll make 

 it ecjually difficult to accept any other concept which ascribes specificity to 

 the photochemical acts of photosynthesis. Photochemistry is unspecific and 

 permits all those reactions of substance which come in contact with the 

 excited dye molecule for which the energy stored in the excited state is 

 sufficient. The hypothesis that light energ)' in photosynthesis is specifically 

 used for reduction of TPN implies that the excited chlorophyll encounters 

 TPN as the only photosensitive species. Oxygen present in the cells under 

 aerobic condition in higher ccincentration is known to make during impacts 

 efficient use of excited singlet energy, and of the energy of the metastable 

 triplet state. Why does it in the region of light limitation not interfere 

 with photosynthesis? 



Our conclusion is that the photosynthetic oxidants must be present in 

 substrate concentration rather than in catalytic ones. The final photo- 

 synthetic oxidants PG.A, and probably the short-lived acid formed by 

 addition of CO- to ribulose diphosphate, are present during the steady 

 state of photosynthesis in substrate concentration, and, as we want to 

 mention as last point of this discussion, we have reason to assume that they 

 are able to undergo photochemical changes at the cost of the lowest excited 

 state of chlorophyll-rt, its metastable triplet state. 



Our interpretation of the photochemical acts of photosynthesis may be 

 visualized by a diagram represented by a lantern slide. 



R 



1) (HOH) (Enz) 



H 



O 



HO— C 



^Met. 



O 



H 



I 

 C— CH3 



R 



(HOU)(Enz) 



H 

 O 



I 

 HO— C= 



O 

 H 



-C< — CHs 



O 

 H 



O 

 H 



