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D. D. HENDLEY 



from the cell. This remains a possibility, however, for the bacterial 

 acid giish, since our measurements were restricted to a pH above 

 6 owing to the sensitivity of the bacteria to acid conditions. 



That the acid gush may attain the equivalent of 0.2 voliune of 

 carbon dioxide suggests, under those conditions, an intermediate 

 change in intracellular concentration to the extent of 0.009 A''. If 

 the intermediate were stable, such a concentration change should be 

 detectable by the tracer technique used by Calvin and Massini (6) 

 for measuring pool sizes of intermediates. We are at present making 

 a quantitative comparison of C^Mabeled intermediate pool changes 

 during the acid gush with the pH changes in the suspension being 

 measured simultaneously. 



12 3 

 MINUTES 



Fig. 3. 



The initial uptake. When short dark periods follow a longer 

 period of photoreduction in H2 an initial increase in pH rather than 

 an acid gush usually occurs on reillumination, clearly distinguished 

 from steady-state photoreduction by its greater slope. The rate of 

 acid uptake at low light intensity is approximately two times higher 

 than photoreduction with H2 as H-donor. In magnitude the initial 

 uptake may exceed the equivalent of 0.05 volume of CO2 per volume 

 of cells, suggesting a change in the intracellular concentration of some 

 intermediate of about 0.002 A^. 



The initial uptake is followed in the dark by a reverse reaction of 

 approximately equal size, the "dark gush." The connection between 

 the initial uptake and dark gush is best sho\vn in Fig. 3, which is a 

 record of pH changes in a suspension which was subjected to a series 

 of short light and dark periods. Initial uptakes followed by dark 

 gushes of the same size have also been seen in heat-treated leaves by 

 van der Veen (7) . The quantum yield of the initial uptake in green 

 plants has not been determined. 



