Chemical induction of growth 



The remaining substances, Compounds B, C, and F, still await complete 

 chemical identification. It may, however, be stated that they are all cyclic 

 nitrogen compounds though none of them contain the requisite amount of 

 nitrogen to resemble even remotely the substance kinetin, recently described 

 by Skoog and his associates, and which appears to originate when nucleic 

 acids are autoclaved, or aged (Miller et al., 1955a), The structure of kinetin, 

 now known to be 6-furfurylaminopurine (Miller et al., 1955b) does not 

 remotelv resemble diphenylurea, nor can it remotely resemble the other 

 substances B, C, and F. The substance kinetin is active in causing cell 

 division in tobacco callus tissue at very great dilutions. Direct comparisons 

 of the activity of kinetin! with coco-nut milk and some fractions thereof and 

 with other substances known to stimulate cell division in the tissue culture 

 system are being made. Preliminary results show that kinetin in presence of 

 indoleacetic acid unquestionably has activity toward carrot tissue under our 

 conditions. However, the growth so induced is much less than that caused by 

 coco-nut milk whether this is measured by fresh weight or cell division. 

 The visible effect of kinetin is accentuated by its ability to form small internal 

 cells in the otherwise large cells of tobacco callus. Though definitely active 

 toward carrot tissue in culture, it has proved almost inactive toward a strain 

 of artichoke tuber tissue. These results are shown by the following extract 

 from the data available. 



t Indoleacetic acid and kinetin applied separately do not give this characteristic effect. 



There is obviously, therefore, no single molecule that unlocks the door of 

 cell division for all cells. This is hardly to be expected. Many such molecules 

 have this property. Some may be of natural origin and these are of the 

 greatest interest; many more may be found as a result of tests on synthetic 

 substances. Indeed, by chance, a very potent substance capable of inducing 

 growth by cell division in carrot and artichoke tissue has been found in 

 2-benzthiazolyloxyacetic acid. 



The effects of diphenylurea in stimulating growth by cell division in 

 carrot, artichoke, and potato tissue are illustrated in Tables 1 and 2. The 

 effect of 2-benzthiazolyloxyacetic acid on both carrot and artichoke tissue 

 are shown in Figure 7. It can be seen that the 2-benzthiazolyloxyacetic acid 

 even exceeded the activity of whole coco-nut milk when applied to a given 

 population of artichoke explants grown on agar medium. It is also evident 



t The kinetin was kindly supplied by Dr. F. Skoog and his colleagues at the University of 

 Wisconsin. 



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