248 E. KESSLEK 



potential, and found that it changed in a very marked way upon the addition of 

 manganese, suggesting that peroxide is formed in the presence of manganese but 

 not in its absence. 



Spikes: In isolated, well-washed chloroplasts we can find practically no manga- 

 nese. 



Kessler : Probably the chloroplasts of nondeficient plants contain an amount 

 of manganese sufficient for the maximum rate of the Hill reaction. 



Spikes : If it is there, it must be in a very tightly bound form, because 20 or 30 

 washings of isolated chloroplasts do not result in any marked decrease in the rate of 

 the Hill reaction. 



Amon : I think that the evidence in support of the role of manganese in oxygen 

 evolution is quite substantial. However, this would not necessarily exclude the 

 participation of manganese in CO2 fixation. Aren't we assuming that the COj 

 metabolism in photoreduction is similar to that in photosynthesis. I take it that 

 there are no chemical data to tell us that they are in fact similar. 



James Smith : Long ago, when we treated sunflower leaves with carbon dioxide 

 we could demonstrate that manganese was one of the carbon dioxide acceptors. 

 When we treated leaves with carbon dioxide in order to see what compounds were 

 soluble we could extract manganese, magnesium, and calcium, and we could 

 demonstrate b}^ radiocarbon experiments that the manganese certainly entered 

 into this and was part of the reservoir for the carbon dioxide uptake. I don't 

 know how this fits into your picture, but it may have something to do with it. 



Amon : The conclusion I was leading up to was this and this again is an assump- 

 tion: If the CO2 fixation pattern during photoreduction were altered bj^ manga- 

 nese deficiency in such a way that light would not be able to accomplish deadapta- 

 tion, this would still be compatible with the results that you presented. 



Now let me add, as I stated earlier, that we ourselves have also found that oxy- 

 gen evolution is influenced by manganese deficiency and that the effect is reversi- 

 ble, but at the moment the other possibility should be kept open at least as a sub- 

 sidiary point. 



Jacobs: Can the requirement for manganese be replaced by higher levels of 

 magnesium, cobalt, or nickel? 



Kessler: Cobalt and nickel are not present in our culture medium except for 

 those impurities which are always introduced with iron and zinc, and the other 

 nutrient components, but quite a high concentration of magnesium is present in 

 both the normal and the deficient medium. 



References 



1. Pirson, A., Z. Botan., SI, 193 (1937). 



2. Pirson, A., Tichy, C, and Wilhelmi, G., Planta, Jfi, 199 (1952). 



3. Arnon, D. I., Vlll' Congr. intern. Botan., Paris, Sect. 1 1, 73 (1954). 



4. Gaffron, H., J. Gen. Physiol., 26, 195 (1942). 



5. Weller, S., and Franck, J., J. Phys. Chem., 45, 1359 (1941). 



6. Gaffron, H., Biol. Revs. Cambridge Phil. Soc, 19, 1 (1944). 



7. Gaffron, H., J. Gen. Physiol, 28, 269 (1945). 



8. Kessler, E., Arch. Biochem. and Biophys., 59, 527 (1955). 



