RECENT RESULTS AT WAOENINGEN 005 



donors, such as riboflavin and naphthaqiiinone, ran easily be reduced and oxi- 

 dized in the absence of any apoenzymes. Therefore, it may be that this is simply a 

 transfer of hj^drogen from one reducing agent to another, without the intervention 

 of a specific catalyst. 



Lumry: In so far as I can determine from a rather casual look at Kok's data, 

 there is a marked qualitative similarity between his results and those obtained 

 by Gilmour from flashing-light studies of chloroplast fragments. Quantitative 

 differences seem explainable if one assumes that the fragments had about one- 

 fourth of the algae's concentration of the enzyme limiting the slow dark step. 

 This is the factor relating the oxygen-liberation rates at light saturation in the 

 two systems. 



We, too, have observed an inhibition by excess light, but only at relatively high 

 pTT values. 



Frenkel: Gaffron earlier mentioned that cells can be grown with "units" of 

 different size, and asked about their chlorophyll content. The relation should be 

 reflected in the photosynthetic saturation rate in continuous light, expressed on 

 chlorophyll basis. We have some data on Scenedestnus, showing the effect of 

 growth conditions on saturation rate which are independent of chlorophyll con- 

 tent. The experiment shown in Fig. 6 was performed in Dr. Arnon's laboratory. 

 Cells were cultured in the presence and absence of vanadium; those grown in 

 vanadium-deficient medium for 2 or 3 days showed a marked depression of 

 their light saturated rates. At low intensity little or no difference was apparent. 

 Thus, vanadium deficiency appears to affect primarily one (or several) dark re- 

 actions. It would be of interest to get flashing-light data of the kind Rieke and 

 Gaffron had obtained (with grouped flashes), in order to localize further the action 

 of vanadium. 



Bassham: There seems to be a real deficiency in these algae; the chlorophyll 

 content is lower. 



Amon: Under conditions of vanadium deficiency, Scenedes7nus shows a growth 

 deficiency, while Chlorella does not; yet both show an effect of the lack of vana- 

 dium on photosynthesis. (Compare Warburg's recent work on Chlorella.) 



References 



1. Kok, B., and Spruit, C. J. P., Biochim. et Biophys. Acta, 19, 212 (1956). 

 la. Spruit, C. J. P., and Kok, B., Biochim. et Biophys. Acta, 19, 417 (1956). 



2. Burk, D., and Warburg, O., Z. Naturforsch., 6\ 12 (1951). 



3. Kok, B., Biochim. et Biophys. Acta, 21, 245 (1956). 

 3a. Kok, B., and Businger, J. A., Nature, 177, 135 (1956). 



4. Emerson, R., and Arnold, W., /. Gen. Physiol, 16, 191 (1932). 



5. Myers, J., and Burr, G. O., J. Gen. Physiol., S4, 45 (1940). 



6. Kok, B., Biochim. et Biophys. Acta, SI, 234 (1956). 



7. Arnon, D. I., Ichioka, P., and Frenkel, A. W., Program for the 29th Annual 



Meeting, American Society of Plant Physiologists, September 1954, p. 27. 



