The influence of growth substances upon sulphydryl compounds 



competitive interaction in root growth. Housley et al. (1954) have re- 

 examined the evidence and suggested that this inhibitor was in reaHty non- 

 competitive with auxin. The findings reported here, that the anisole may 

 react with thiol groups whereas auxins do not, would seem to be in agreement 

 with these criticisms. 



Some data on indoleacetic acid and naphthalene acetic acid are also 

 presented in Figure 8. We consider the changes with these reagents to be 

 small. 



0-150 



0-050 



2:9 -Phenol 



2:9 -/In/so/e 



9x10 ^M 



c^. 



-Z 







to 



2 9- e;<10 ^M 



Concn. of growth substances 



Figure 8. Cysteine disappearance with 2-A-dichlorophenol, lAA, NAA, and 2-A-dichIoroanisole. 

 Conditions as in Figure 4. 



Sulphydryl reactions of enzymes and coenzymes 



The evidence presented so far would suggest that some growth substances 

 are able to react with sulphydryl groups and it is implied from this that by so 

 doing they would influence some metabolic processes in a manner which 

 would be reflected in growth. If this is true then the functioning of enzymes 

 which require free sulphydryls for their activity should be inhibited by these 

 growth substances. We selected amylase as being such an enzyme with which 

 we might demonstrate sulphydryl inhibition. 



Elliott and Leopold (1953) utilized the inhibition of amylase as an assay 

 for a naturally occurring growth inhibitor in oats. Evidence was brought 

 forward that this inhibitor might attack sulphydryl groups and apparently 

 through this function it would inhibit growth. Since amylase activity is a 

 function of its free sulphydryl groups, it could be utilized as a handy quantita- 

 tive assay for the inhibitor. In the present experiments essentially the same 

 scheme was used. Amylase was incubated at room temperature with TIBA 

 at various concentrations ranging from 25 to 0-5xlO~^M. After this 

 incubation period, the ability of the enzyme to hydrolyse stai'ch was 



277 



19 



