Chemical structure and biological activity 



EFFECT OF ADDED SUBSTANCES ON GROWTH BY CELL DIVISION AND 



CELL ENLARGEMENT 



It will be recalled that Wain and Wightman (1954) had found that the effect 

 of the length of the aliphatic side-chain in a series of aryloxyalkylcarboxylic 

 acids could be interpreted to mean that those substances that were active in 

 certain growth tests also contained an even number of carbon atoms in the 

 side-chain thus permitting the chain to be degraded by progressive beta- 

 oxidation to a 2 carbon side-chain. In the attempt to determine the best 

 series of substituted aryloxyalkylcarboxylic acids with which to carry out a 

 similar trial on potato tissue in presence of coco-nut milk as an assay system, a 

 considerable number of variously substituted phenoxyacetic acids were 

 tested. The first result, however, was of a different and somewhat unexpected 

 kind. 



Relative increase in: 



Fresh wt. = weight of cukures under treatment divided by weight of coco-nut milk 

 controls. 



Cell No. = Cell No. of cultures under treatment divided by Cell No. of coco-nut milk 

 controls. 



Cell size = Cell size of cultures under treatment divided by cell size of coco-nut milk 

 controls. 



CI 



Treatment : 



Rel. increase in 



fresh wt. x6-9 10-2 5-0 



Rel. increase in 



Cell No. x2-9 2-8 1-8 



Rel. increase in 



cell size x2-3 3-8 2-7 



Weight Cell No. Cell size 



Controls per culture per culture Cells per /tig fig per cell 



Basal medium 2-7 mg l-9xl0« 0-70 1-4 



Basal medium + 



coco-nut milk 5-7 mg 34-6xl0» 6-1 0-16 



Figure 4. The effects of various phenoxyacetic acids on growth of potato tuber tissue in media 

 containing coco-nut milk 



The tissues in question were submitted to the analysis of growth both in 

 terms of fresh weight and in cell number, and this data furnished the first 

 fairly extensive information relating the effect of chemical constitution to 

 the stimulation by the synergist of growth by cell division and/or by cell 

 enlargement. In Figure 4 the effect of the various substances, as used at their 



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