676 



C. P. Whittlngham, et al. 



201 ethanol and the two extracts combined. Subsequent treatment followed the 

 procedure of Bassham and Calvin^ ^> . Radioactivity in the compounds located by 

 radioautography was counted directly on the paper chromatograms using a thin 

 end-window Geiger-Muller tube. 



PHOTOSYNTOETIC GLYCOLLATE PRODUCTION 



The production of glycollate was first determined during photosynthesis at a 

 high light intensity (56,000 lux) and with different concentrations of CO2. 

 These concentrations of CO2 are those in the gas phase bubbling through the 

 suspension; the effective CO2 concentration at the cell surface was estimated 

 to be of the order of one-tenth of this. Ihe results are shown in Fig. 1. 

 The maximum rate of glycollate excretion was reached at a CO2 concentration in 

 the gas phase of 0.1%; above this value the rate declined rapidly, reaching a 

 very low value at 0.4^ CO2. Ihe rate of photosynthesis increased almost 

 linearly over the range of O.O3 to 0.2'4% CO2. Above 0.24% the rate increased 

 less with increase in concentration, but saturation was not reached with the 

 highest concentration used, i.e., 0.4%. At hi^er CO2 concentrations prelimi- 

 nary experiments show that as photosynthesis becomes CO2 saturated the excre- 

 tion of glycollate remains low. A time course of 14c02 incorporation into 

 individual ethanol soluble conpounds during photosynthesis at 0.1% (="low CO2") 

 the point of maximum glycollate excretion, and 0.4% CO2 (="high CO2") is shown 

 in Fig. 2. At "low CO2" there is more activity in glycollate and glycine 

 despite a lower rate of CO2 fixation. At "high CO2", activity in the two 

 carbon conpounds is suppressed while that in PGA and sucrose increased sharply. 



t 



I 



0-2 

 CO, concn. {%) 



& 5 1 



TIME IN MNUTES 



Fig. 1. The effect of carbon dioxide concentration on glycollic 

 acid excretion and the rate of carbon dioxide uptake in the 

 presence and absence of isoniazid. In the absence of isoniazid: 

 9, glycollic acid excretion; A., carbon dioxide uptake. In the 



