INORGANIC IONS 951 



Chi • Z, may be accumulated in strong light. Each of the four forms should 

 have its own characteristic yield of fluorescence, limited by the rate of 

 internal energy dissipation and, in the case of the normal form X- Chi -HZ, 

 also by the competition of fluorescence with the primary photoprocess 

 (X • Chi -UYj -\- hv-* HX • Chi ■ Z) . The conditions under which the three 

 forms can be expected to predominate in strong light, are summarized in 

 the following table. 



Conditions of accumulation 

 Form Formula Oxidant (CO2) Reductant 



Tautomeric HXChlZ 



Reduced HX-ChlHZ - + 



Oxidized X-Chl-Z + - 



Which form will be accumulated in the presence of very strong light 

 when both the oxidant and the reductant are in good supply (case ++) 

 cannot be predicted a priori, since this will depend on which of the supply 

 processes first fails to keep pace with the primary photoprocess. 



If the influence of carbon dioxide deprivation on fluorescence is due to 

 the accumulation of the form HX-Chl-HZ, while the effect of "RH starva- 

 tion" is caused by accumulation of the form X-Chl-Z, the absence of an 

 effect of carbon dioxide in RH-starved cells can be interpreted as evidence 

 of a similarity in the fluorescent capacity of the forms HX-Chl-Z and X-- 

 Chi • Z (or, perhaps as indication that in the absence of both carbon dioxide 

 and reductant, the complex accumulates in the same form X-Chl-Z, as in 

 the absence of reductants alone). 



As mentioned on page 943, Franck's hypothesis, that all strong in- 

 creases of fluorescence are evidence of narcotization of the chlorophyll com- 

 plex, is not incompatible with the interpretation of the primary photo- 

 chemical process as hydrogen transfer in the complex, X . Chi . HZ ; it only 

 implies that the differences in the capacity for fluorescence of the various 

 forms of this complex (X- Chi -HZ, HX-Chl-Z, X-Chl-Z, and HX-Chl-- 

 HZ) are less significant than that between all of them and the "narcotized" 

 form. 



D. Concentration of Inhibitors* 



1. Inorganic Ions 



The effect of the hydrogen ion concentration on photosynthesis was dis- 

 cussed in chapter 8 (Vol. I), and also in the first part of the present chapter, 

 from the point of view of the correlated shifts of the carbonate-bicarbonate - 



* Bibliography, page 963. 



