CARBON MONOXIDE INHIBITORS 317 



ditions of illumination. The darkened leaves (Expt. 9) showed a P*'^ 

 distribution almost identical with that found if the leaves take up 

 P'^ in air in darkness, indicating that CO does not interfere with the 

 dark exchange process. These leaves are about the same age (7 to 9 

 days) as those in which Daly and BrowTi (7) found no inhibition of 

 lespiration by carbon monoxide. 



Under red light (Expt. 6), about twice as much P^^ ^y^s incor- 

 porated into sugar phosphates and phosphoglycerate as in the same 

 experiments (3 and 4) done under 1% oxygen or less, but the ATP 

 was not labeled as heavily as in the experiments at low PO2. Under 

 yellow illumination (Expt. 7) the ATP*^ level approached that found 

 in photosynthesis in air, but the P^^ in sugar phosphates was still low. 

 The tissue illuminated wdth both red and yellow light (Expt. 8) 

 showed the most striking changes. All fractions contained more P^^ 

 than corresponding fractions from leaves exposed to any other con- 

 dition than air in light. That this increase was not caused simply by 

 greater translocation of P^^ into the leaf is shown by comparison 

 with Expt. 3 under red illumination at 1% oxygen where almost as 

 much P^2 was accumulated by the leaf as in air while illuminated 

 with white light, whereas no more was esterified than in other ex- 

 periments in that series (Expts. 4 and 5) where much less inorganic 

 P^- was taken into the leaf. 



Probably the best measure of the extent to which yellow and red 

 illumination together were able to stimulate phosphate exchange 

 under CO was found in the total counts P^^ esterified, a figure which 

 was from five to ten times as high under this combination as under 

 other illumination used in these experiments. The pattern was still 

 not identical with that found in air. The outstanding difference be- 

 tween Expts. 1 and 8 was in the very much higher P" content of the 

 phosphoglyceric acid-triose phosphate fraction in Expt. 1. The ratio 

 of inorganic P04/organic PO4 in Expt. 8 was still twice that found in 

 Expt. 1. Whether this difference was caused by the presence of CO 

 or by the lower than normal oxygen tension as suggested by results of 

 Daly and Brown (7), w^ho found a 50% inhibition of respiration in 8- 

 day barley leaves under 5% oxygen in nitrogen, has not yet been de- 

 termined. 



The last column in Table I compares the P^- content of the sugar 

 monophosphates in the leaves in the experiments reported here. 

 As was stated earlier the organic phosphates in Expt. 1 were thought 



