1682 



CHEMICAL PATH OF CARBON DIOXIDE REDUCTION 



CHAP. 36 



end of illumination, described in chapters 8 and 33. Changes in the cell 

 composition, observed by radiography, undoubtedly are correlated with the 

 liberation of CO2 or O2 into the medium (or their uptake from the medium) . 

 Figure 36.24 summarizes the results of another experiment in which 0.2 

 ml. of wet Chlorella cells were exposed to 1 min. strong light (160 kerg/cm.^ 

 sec, infrared-free) + 1 min. dark sequence. Controls were exposed to 

 light for 1 or 2 min. This figure again illustrates the appearance of C* in 

 citric and glutamic acids after the light had been switched off. 



80 



70 



60 



> 



P 50 



o 



< 



< 40- 



K 

 O 



I- 



u. 



o 30 



20 



10- 



"1 r 



-1 1 1 r 



PGA 



o ^_^ — o 



TOTAL SUGAR PHOSPHATES 



16 



18 



2 4 6 8 10 12 14 



TIME (SECONDS) 



Fig. 36.25. Extrapolation of tagging in Scenedesnius to zero time 



(after Bassham et at. 1954). 



Benson (1952) described an independent determination of the photo- 

 stationary concentration of various phosphate esters in steadily photo- 

 synthesizing Scenedesmus. It consisted in ''saturating" the plants with 

 radiophosphorus by 20 hours photosynthesis at 30 klux, in a nutrient solu- 

 tion containing 2 mc. P(32), in 4% CO2, killing them with boiling ethanol 

 in light, extracting with hot ethanol and water, chromatographing, and 

 counting the several radioactive spots. Table 36. VIII showed the results 

 in the last column. Considering the difference in conditions between the 

 two experiments, the agreement with the data obtained by C(14) saturation 

 is satisfying. 



Bassham, Benson et al. (1954) gave some additional kinetic data perti- 



