SELECTIVE ACCUMULATION 



451 



that spores of Monilinia fructicola exposed to copper accumulate the 

 metal to a concentration 2000-4000 times its external concentration. 

 Even more striking results are reported by Miller, McCallan, and 

 Weed (290, 291), using different fungi and such diverse materials as 

 silver, cerium, 2-heptadecyl-2-imidazoline, and ferric dimethyldithio- 

 carbamate. Several features of these data warrant emphasis: 



1. Uptake is extremely rapid; spores of Neurospora sitophila take 

 up their limit of the imidazoline within 15 seconds from a dilute solu- 

 tion, within 5 minutes from a more concentrated solution. Uptake of 

 dithiocarbamates by yeast is similarly rapid (127). 



2. Fungicidal action is a linear function of the amount of toxicant 

 taken up. 



3. Some toxicants are concentrated as much as 10,000-fold. 



4. A material which has low inherent toxicity on a spore weight 

 basis may be so extensively concentrated by spores as to be an effective 

 inhibitor. The application to bioassay is obvious — external concen- 

 tration is not necessarily a measure of effective dose. Valko (419) dis- 

 tinguishes "apparent toxicity," a function of external concentration, 

 from "specific toxicity," a function of the amount of toxicant absorbed 

 by the cell. 



5. Species differ in the amount taken up of a given toxicant. 



6. Unrelated toxicants are taken up independently, i.e., previous ex- 



Figure 5. The relation between 

 uptake and antifungal activity 

 (test organism Neurospora sito- 

 phila) in chlorine derivatives 

 of 2,4dichloro-6-anilino-5-tria- 

 zine. Curve 1, fungicidal ac- 

 tion; curve 2, fungistatic action. 

 Compounds: u = unsubstituted, 

 o — ortho-chloro, rn = meta- 

 chloro, p = para-chloro deriva- 

 tive. Drawn from data of 

 Burchfield and Storrs 51). 



1.0 1.5 2.0 2.5 



Relative uptake by spores 



