16 Fundamentals of Auxin Action 



sodium diethyl dithiocarbamate (100 p. p.m.). Combination of several 

 solvents for complete auxin extraction has been effectively employed 

 l)y Avery et al (1941). 



The relative solubility in ether of indoleacetic acid, with chang- 

 ing pH, has been worked out by Gordon and Nieva (1949). It is 

 evident from figure 3 that most efficient extraction of this auxin from 

 wet plant material into ether can be carried out at pH 2.8. It can also 

 be seen that in slightly alkaline solutions the auxin will move out of 

 the ether and into the water partition, a feature which can be utilized 

 when one wants to take the auxin back into water. A saturated solu- 

 tion of sodium bicarbonate is very effective for this alkaline sepa- 

 ration into water. 



If the extraction procedure is preliminary to measurement of the 

 free auxin in the plant tissues, the formation of auxin during extrac- 

 tion may be a large source of error. The formation of auxin during 

 extraction has been shown by Skoog and Thimann (1940) to be en- 

 zymatic in nature. 



To avoid the excessive formation of new auxin during extraction, 

 Gustafson (1941) has established a technique for boiling the plant 

 material a short time prior to solvent extraction. His technique is: 



1. Freeze the tissue rapidly on carbon dioxide ice. 



2. Grind the tissue with mortar and pestle, or dice. 



3. Drop into boiling water and allow one minute of active boil- 

 ing. 



4. Collect plant material on a filter and extract with ether for 

 16 hours, using 3 changes of ether. 



This technique has been used successfully with pineapple, tobacco, and 

 tomato. The main limitation of Gustafson's technique lies in the fact 

 that a certain amount of the free auxin must be destroyed by the 

 heating (Thimann, Skoog and Byer, 1942). And in some green tissues 

 heating causes the release of inhibitors which interfere with auxin 

 assay (van Overbeek et al, 1945). 



Another means of preventing formation of new auxin during ex- 

 traction is by the use of a freezing and lyophilization technique first 

 described by Wildman and Muir in 1949. These workers demonstrated 

 that the formation of auxin during extraction could be effectively 

 limited by carrying out the operation at 0° C. Their observations of 

 the effect of temperatures upon auxin yields are shown in figure 4. The 

 apparatus required for the lyophilization may be of several types. A 

 simple apparatus has been described by Campbell and Pressman (1944) 

 and another by Thomas and Prier (1952). By use of such a mechanism 



