GEORGE T. SCOTT AND HUGH R. HAYWOOD 



43 



the pn of the medium caused by photosynthesis and hence an increase in the 

 activity product (K)(OH) outside the cell. In the above experiments the 

 samples were maintained in freely running sea water so that changes in external 

 pH would be insignificant. 



Influence of lodoacetate in the Light and the Dark: Ulva. The relationship 

 of carbohydrate metabolism to cation regulation was further explored by use 

 of the glycolytic inhibitor monoiodoacetate. 



Fig. 3. Influence of o.ooi m/1. lodoacetate on the potassium content of Ulva lactuca in 

 the light and in the dark. Potassium is expressed in terms of cell water. 



The presence of the inhibitor in a concentration of o.ooi m/1. results in a 

 marked loss of potassium from the cells over a period of 24 hours in the dark. 

 Control samples taken at the beginning and end of this period were essentially 

 constant in potassium content (fig. 3). In the presence of light the inhibitor is 

 completely ineffective in causing the loss of potassium. Rather, the potassium 

 content of the experimentals temporarily increases over that of the controls. 



To evaluate further the influence of light on the prevention of the iodo- 

 acetate effect, the concentration of the inhibitor was raised to 0.005 '^/^- Again 

 light prevented the loss of potassium. 



Concomitant with the potassium loss caused by the o.ooi m/1. iodoacetate 

 in the dark, the cellular sodium increases over that of the controls although the 

 condition of darkness alone is sufficient to cause some sodium increase. Illumina- 

 tion again prevents this action of the inhibitor, and sodium is actually some- 



