CHAPTER II 



Auxin Extraction and 

 Measurement Techniques 



The majority of studies involving auxins either requires measure- 

 ments of auxin activity or would be greatly benefited by the inclusion 

 of such measurements. By the carefully worked out techniques of Went 

 and other more recent workers, such measurements are quite easy to 

 make. Techniques are available for which practically no elaborate 

 equipment is needed and the time involved is quite small indeed. 



It should be clearly understood that all procedures for the deter- 

 mination of auxin content of plant materials do not measure the same 

 constituents. There are many forms of auxin in the plant. The diffu- 

 sion technique yields a readily available auxin. Extraction of plant 

 material with cold solvents for a short period of time is thought to 

 yield the same auxin, and in some cases the diffusible auxin has been 

 shown to be quantitatively similar to that obtained by short time ex- 

 traction. This supply of auxin is commonly termed "free auxin." 

 When extraction is continued over a long period of time there is 

 clearly a production of additional auxin by the plant tissue during 

 extraction and this production can continue over a period of several 

 months of extraction (Thimann and Skoog, 1940). It is assumed that 

 forms of the hormone which are not extractable in a short time are 

 largely unavailable immediately for plant growth, and these forms are 

 spoken of as "bound auxin." 



The concepts of free and bound auxin, however, are not entirely 

 simple. For instance, Thimann and Skoog (1940) have shown that pure 

 indoleacetic acid added to plant material is not entirely recoverable 

 by short time extraction. Some of it is retained by the plant material 

 and appears in the solvent only after several horns of extraction, in a 

 manner more characteristic of bound auxin than of free auxin. More 

 recently Siegel and Galston (1953) have been able to follow the bind- 

 ing of free auxin onto a protein in vitro. There are many examples of 

 bound auxin being released in the free form during extraction, as men- 

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