437 



H. Gaffron, W. Wiessner and P. Homann 



After adaptation in hydrogen the state of affairs is reversed, i.e. , 

 the efficiency in the shorter wavelength region is dften much 

 less than before and the far-red light has become surprisingly 

 efficient. (Exact quantum yields have still to be determined. ) 

 The combined illumination does not produce the enhancement 

 seen under aerobic conditions. Instead we often observed that 

 mixing short and long wavelength lights seemed to lower the 

 efficiency. Data published elsewhere by Bishop and Gaffron 

 show that any conditions which aerobically diminish oxygen 

 evolution, such as poisons, Mn deficiency, or genetic changes, 

 leave the photoreductive COn fixation as efficient in the infrared 

 as it is in visible light. It follows that complete carbon dioxide 

 assimilation into the usual reduced products is possible with 

 near infrared light, provided that there is no need to eliminate 

 the equivalent amount of oxygen as free gas. 



ASSIMILATION OF ACETATE IN THE NEAR INFRARED 



The alga Chlamydobotrys needs acetate and light for growth. 

 Its respiration in the dark cannot replace the action of light. 

 This organism, first described by Pringsheim and Wiessner and 

 studied intensively by Wiessner, was subjected to the same 

 tests as the Scenedesmus described above. But in contrast to 

 the behavior of the adaptable algae there was no need for 

 anaerobic treatment. Comparing the efficiency of acetate assimi- 

 lation at various points in the shorter wavelength region {\ 680, 

 660, 620, 547 and 450 m[i) and at X 705, 723 and 740 m^L, we 

 found that in the region where in the better known green plants 

 the efficiency of photosynthesis is high, that of acetate assimi- 

 lation in this peculiar organism is low. It rises steeply, 

 however, in the far-red when the chlorophyll a peak at X 685 mfx 

 has been passed. 



Wiessner found earlier that in presence of carbon dioxide 

 (which normally is not needed when the algae are grown in air) 

 Chlamydobotrys can do some orthodox photosynthesis, just 

 enough to keep it alive when it lacks acetate. We observed that 

 the acetate assimilation in the infrared stops immediately when 

 air is replaced by nitrogen. But half a per cent of carbon dioxide 

 relieves the anaerobic inhibition. This relief occurs only when 

 visible light of shorter wavelength is superimposed on the far- 

 red light. Thus anaerobically we see a reversed Emerson effect. 

 Under these conditions acetate assimilation remains poor with 

 \ 723 m^. alone. Light absorbed in this region apparently does 

 not produce the oxidative power needed to promote continuous 



