A Light-Reversible Carbon Monoxide Inhibition of 

 Isotopic Phosphate Uptake by Photosynthesizing 



Barley Leaves* 



ALBERT R. KRALL,t Biology Division, Oak Ridge National Laboratory, 



Oak Ridge, Tennessee 



The relationship between the respiratory process as it occurs in 

 the darkened plant and the photosynthetic process in that same 

 plant when illuminated is a matter of perennial experimental interest. 



The conclusion that oxidative action is probably necessary at least 

 for prevention of induction effects has been drawn by Hill and 

 Whittingham (1) measuring oxygen evolution in Chlorella and by 

 Krall and Burris (2) and Krall (3) measuring ^"02 uptake. The 

 latter authors on the basis of inhibition by carbon monoxide sug- 

 gested that cytochrome oxidase mediated the oxidative reaction in- 

 volved. 



The first work that indicated the existence of carbon monoxide 

 effects on photosynthesis was that of Padoa and Vita (4) where 

 assimilation was inhibited while respiration was stimulated. Gaffron 

 (5) did the first systematic study of the effects of CO on Chlorella. 

 He found that fairly long exposures to CO in darkness produced an 

 induction effect more pronounced than that caused by exposure to 

 nitrogen for the same length of time. He observed rates of pressure 

 change following the induction period which were lower in the CO- 

 treated cells than in the nitrogen controls. In some cases the CO 

 effect was completely reversible by exposure to air but in others 

 where exposure to CO in darkness was longer it was irreversible. 

 Gaffron considered mainly two different explanations for the effects 

 he observed: {!) inhibition of a photo-catalase, after establishment 

 of rigid anaerobiosis, by CO, which inhibition was reversible by 

 oxygen, or {2) formation of inhibitory fermentative products in 



* Work performed under U.S. Atomic Energy Commission Contract No. \V- 

 7405-eng-26. 



t Present address: RIAS, Inc., Baltimore, Md. 



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