MANGANESE IN OXYGEN EVOLUTION 247 



form water; under these conditions only a comparatively small frac- 

 tion of the YOH goes via Z(0H)2 to O2 (13). With increasing light 

 intensity, more Z(0H)2 is formed, which eventually oxidizes the hy- 

 drogenase and thereby causes deadaptation to normal photosynthesis 

 with evolution of oxygen. In the case of manganese deficiency, the 

 formation of Z(0H)2 is inhibited; thus deadaptation of photoreduc- 

 tion is prevented or at least considerably delayed, and all the YOH 

 formed will be disposed of by the hydrogenase reaction, thereby 

 avoiding the step requirijig manganese in the evolution of oxygen. In 

 unadapted algae, how^ever, this possibility does not exist. Therefore, 

 the YOH may react back causing chemiluminescence (14) or oxidize 

 cellular substances. This latter reaction may lead to the formation of 

 a "narcotic" (15), which, in turn, will inhibit the photochemical reac- 

 tion, thus reducing the rate of photosynthesis at all light intensities. 



Discussion 



Aronoff: How many generations occur after starting a manganese-deficient 

 culture? 



Kessler : Growth is not completely inhibited by manganese deficiency. It is 

 only retarded, but I don't know how many generations there are. 



Jacobs : Can the inhibition of photosynthesis be relieved by the addition of 

 manganese? 



Kessler : Yes. If one adds manganese to deficient cells, the rate of photosyn- 

 thesis will go up to the normal level. The speed of recovery depends upon the age 

 of the deficient culture. In the beginning it goes very fast. With strong deficiency, 

 however, the rate of photosynthesis goes up to the normal level within about 10 

 hours or so. But if one adds manganese in photoreduction, then the addition of 

 manganese will inhibit photoreduction and will accelerate deadaptation. 



Amon: On this point of time that Dr. Kessler has answered, I would like to 

 say that we are able to confirm that under certain conditions the minus manganese 

 ceils can restore their full photosynthetic rate equal to that of the plus-manganese 

 cells within 20 minutes after the addition of manganese. This is far less time than 

 required for any new cell division or even formation of a protein. 



Rosenberg : I wonder if you have any data on the concentration of manganese in 

 chloroplasts in normal cells and in deficient cells. 



Kessler : No, I don't have any analytical data on the manganese content of the 

 cells. I also haven't done any experiments on the Hill reaction, but I know from 

 unpubhshed work of Clendenning that the Hill reaction is also inhibited by lack of 

 manganese, and that its rate can be increased by the addition of manganese. 



Also Gerretsen has shown that manganese is somehow involved in peroxide 

 formation in isolated chloroplasts. However, it is not quite clear from his data 

 what his results have to do with normal photosj'nthesis. He worked with isolated 

 chloroplasts in the absence of Hill reagents, measured the oxidation-reduction 



