Natural auxins 



during the extraction procedure, nor do we want any destruction of these 

 substances. It has been shown by many authors (Thimann et al., 1940, 1942; 

 Gustafson, 1941 ; van Overbeek et al., 1947) that when ether is used, auxin 

 can be generated from plant material over periods as long as a year. 

 Temperature stimvdates this generation (Wildman and Muir, 1949). That 

 boiling stops the production indicates the enzymatic nature of the process. On 

 the other hand, especially when tissues are ground or cut, the destruction of 

 auxins during extraction may be extensive, depending on the kind of 

 material used. This destruction is also an enzymatic phenomenon of the 

 oxidative type (Tang and Bonner, 1947; Wagenknecht and Burris, 1950; 

 Steeves et al., 1953; Briggs et al., 1955a, b). To obtain a reliable picture of 

 the auxins present in the plant at the time of extraction, one has to stop this 

 oxidative destruction of auxins. 



Table 1 gives the results of a series of tests performed on the tuber tissue 

 of Jerusalem artichoke. The extent of browning was taken as an index of the 

 oxidative activity at the cut surfaces. Tissues in ether and ethyl acetate 

 turned dark brown, indicating that these solvents do not stop the activity 



Table 1 

 The prevention of tissue browning during auxin extraction 



Jerusalem artichoke tuber tissues left overnight in the ice-box at about 5°C. 



t The tissues are shrivelled after extraction. 



J Dissolves Vi'hen the fresh tissue is put in the mixture. 



of at least the polyphenoloxidase system. It is not surprising then, that 

 previous workers have found that enzymes which produce auxins also are 

 not inactivated by ether. Unless special precautions are taken, such as short 

 time extraction and low temperatures, ether is not a reliable extracting 

 solvent for auxins. According to Table 1, chloroform is slightly better than 

 ether in preventing browning, but petroleum ether, acetone, and absolute 

 ethanol are even better. The very best solvent, however, seems to be 



4 



