K.S 



CHEMICAL AGENTS 



Figure 9. The effect of pH on the toxicity of copper chloride to spores of 

 Alternaria tenuis. Curve 1 (solid line), control; curve 2 (broken line), 0.0001 M CucL. 

 Drawn from data of Biedermann and Midler (28). 



Divalent cations generally reduce both uptake and toxicity of the 

 heavy metals (1, 28, 150, 226, 232, 273, 308). The uptake of silver by 

 spores is reduced by copper and, more completely, by mercury (288). 

 Competition by hydrogen ion is equally important; this is shown in 

 Figure 9 and also by the fact that absorbed copper is removed from 

 spores by acid (3, 34, 174, 291). 



There are at present two ways in which to interpret the data on up- 

 take of metals by spores. First, we may assume that the entire volume 

 of the spore protoplasm accumulates the metal. This assumption re- 

 quires, in view of the rapidity of the uptake, that the metal move rela- 

 tively freely across the semi-permeable membrane; such a rapid move- 

 ment is suggested by the speed with which cellular zinc of Aspergillus 

 niger exchanges with extracellular zinc (288), and by some data on the 

 loss of potassium from bacteria (209). Staining methods show that 

 copper does enter spores (129, 418), but this approach has not been 

 developed sufficiently to be of critical importance. 



The second mode of interpretation is to consider metal uptake as 

 an adsorption, defined as a process that concentrates one component 

 of a system at an interface, and to limit the locus of this adsorption to 

 peripheral regions of the cell, i.e., outside the permeability barrier. 



