244 



E. KESSLER 



CO2. The light metabolism of this alga, grown with and without man- 

 ganese, is shown in Fig. 1. Photosynthesis is inhibited to about one- 

 fourth of the normal rate in manganese-deficient cells, the degree of 

 inhibition being independent of light intensity. By contrast, photo- 

 reduction is not at all inhibited by manganese deficiency; its rate in 



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LJ 

 CC 



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1000 2000 3000 



LIGHT INTENSITY (LUX) 



4000 



Fig. 1. Rates of photosynthesis and photoreduction at various Hght intensities 

 in normal and in manganese-deficient Anki^trodesmus braunii. Manometric 

 readings correspond to evolution of oxygen (corrected for respiration) in photo- 

 synthesis and to absorption of hydrogen and caibon dioxide in photoreduction. 

 Experimental conditions: Warburg No. 9 buffer, pH 9, gas phase air, for photo- 

 synthesis; 0.02 M phosphate buffer, pH 6.5, gas phase 96% H2 + 4% CO2, puri- 

 fied by means of a "Deoxo" cartridge, for photoreduction; temperature 25°C., 

 10 mm.' cells (3 mg. dry weight) per vessel. Preceding dark period: 4 hours; 

 periods of 15 minutes for each light intensity. 



the light-limited range is even somewhat higher in the deficient 

 cells {cf. 8). At higher light intensities extremely high rates of photo- 

 reduction are observed with the deficient algae, whereas in normal 

 organisms deadaptation and evolution of oxygen occur. Thus the 

 action of manganese deficiency strongly resembles the effect of hy- 

 droxylamine, o-phenanthroline, and phthiocol (4,7). At high con- 

 centrations these poisons, however, are more efficient in stabilizing 



