Chemical structure and biological activity 



Reliance has to be placed on the known structure of certain related com- 

 pounds to assign the substituent groups to appropriate positions, but with 

 this latitude one can say definitely that the chemical analysis of the product 

 as isolated, the presence of the monoglucoside group, and the analysis of the 

 pigment which results when the glucose is split off and the cyanidin-like 

 pigment is produced in the form of its oxonium chloride, are all consistent 

 with this type of structure [Figure 9). 



This general discovery seems to open a new door in the study of the 

 chemical induction of growth. Hitherto, the physiological role of these 

 complex biochemical constituents, the anthocyanins and their precursors the 

 leucoanthocyanins, has been somewhat obscure. When such a function as 

 the ability to induce growth by cell division when added to otherwise complete 

 nutrient media to which mature cells are exposed is attributed to a type of 

 compound such as this, it is obvious that they may have important roles to 

 play. Examinations have therefore been made of a number of other extracted 

 materials (such as anthocyanins and flavanol glucosides) furnished to us by 

 various investigators but having chemical properties somewhat similar to 

 the structural formulae indicated above. Sufficient activity has been detected 

 in compounds of this kind to indicate that we are proceeding along the 

 right general track. 



The conclusion of this general account must therefore be as follows : 



To undergo growth by cell division and cell enlargement, plant cells 

 obviously require a variety of chemical substances that perform quite 

 different roles: water itself for enlargement, nutrients both inorganic and 

 organic, vitamins and the essential co-factors of vitamin-like systems. Many 

 or all of these may be specified. In addition, however, there still seem to be 

 requirements for additional substances which determine whether the cell can 

 fully exploit its ability to enlarge without division or to divide without 

 enlargement. In balanced degree both processes may occur simultaneously. 

 The presence of one substance may induce one type of growth to the exclu- 

 sion of another, as for example the predominant effect of indoleacetic acid on 

 cell enlargement. The effect of other types of substances, such as those found 

 in coco-nut milk, may induce cell division to the exclusion of cell enlargement. 

 Almost certainly both types of growth-promoting materials, the auxin-like 

 substances of which indoleacetic acid is the predominant natural example, or 

 the cell division-promoting substances such as those found in coco-nut milk 

 and related materials, represent a group or family of substances rather than 

 single unique individuals. The baffling thing is that the chemical properties 

 which determine the ability of the substance to promote growth by cell 

 division are so obscure that it is difficult to see what substances like diphenyl- 

 urea, the quite different molecules of Compounds B, C, and F from coco-nut 

 milk, and 2-benzthiazolyloxyacetic acid, with the further addition of the 

 substance kinetin, all may have in common. This becomes even more 

 difficult, however, when this activity is extended in its range by the fact that 

 leucoanthocyanin-like substances, nitrogen-free, are found to be active and 

 even very potent. 



It is obviously too soon to state what any or all of these molecules may have 

 in common. The only idea that has already occurred is that, in greater or 

 lesser degree, many of these substances might exert their activity by their 



184 



