ZINK UPTAKE BY NEUROSPORA 



911 



the specific activities of the zinc present in the culture solution and in tlic mould 

 and the amount of zinc added to the culture solution, the zinc content of Neuro- 

 spora crassa was calculated. We are mueli indebted to the Atomic Energy Com- 

 mission of theU.S.Aand the Chief of the Isotope Branch, Dr. Paul Aebersold, 

 for supplying the zinc containing the radioactive isotope ^^Zn. 



The activity of the «5Zn taken up by Neurospora was less than 1 //curie, and 

 thus the radiation emitted could hardly produce any noxious action on the mould. 



After centrifuging and thorough washing the Neurospora was dried at 105°, 

 brought into solution by wet ashing, 5 mgm. zinc as sulphate added as carrier 

 and the zinc precipitated with 8-hydroxyquinoline. The precipitate was filtered 

 through a perforated aluminium dish covered by a layer of filter paper, and the 

 dish placed under a Geiger— Miiller counter of the type described by Madsen 

 (1945). A sample of the active ZnClg solution was treated in the same way. By 

 comparing the activities of this 'standard' precipitate of known zinc content 

 and that of the above-mentioned precipitates, the percentage of the zinc originally 

 present in the culture solution which accumulated in the mould was calculated. 



RESULTS 



The results of some of our experiments, in which each Neurospora 

 was grown in 150 ml. culture solution of varying zinc content for 5 days 

 at 25°, are given in Table 1. This table and Fig. 1 show that the presence 

 of 1 part of zinc in about 30,000 parts of dry mould is sufficient for an 

 almost maximal growth, and the presence of 12.5 /ugm. zinc in 150 ml. 

 culture solution suffices to give that zinc content. It is advisable to 

 add a somewhat larger amount of zinc to the culture solution, e.g. 



200 



180- 

 □ 



gl60-| 



If) 



o 



-z. 

 ^120 



.§100 -P 



gi 80- 



s 



>, 60- 



Q 



40- 



20- 



n — I I I ! I 1 — rn rn i 



1030507090 130 170 210 250 

 no 150 190 230 

 Zinc (ixg.)added to 150ml culture solution 



0,35 e 

 o 



■0,31 I 

 -0,272 



-0,23 



hO,19>- 

 o 



-015 g; 

 - 0, 1 1 £ 



c 



-o.oz"-' 



c 



o.os-^ 



Fig. 1. Effect of varying zinc content of the culture solution on the 

 dry weight (Q) and zinc content (x) oi Neurospora after the lapse 



of 5 days. 



