50 Fundamentals of Auxin Action 



2,4-D ranging from 1 to 20 mg./liter, as shown in figure 25. Similar 

 color reactions are obtained with each of the several phenoxyacetic 

 acid derivatives tested (Le Tourneau and Krog, 1952). 



A spectrographic technique for measuring phenoxyacetic acid 

 compounds has been worked out by Bandurski (1946). By measuring 

 changes in the absorption characteristics at 325 m^, changes in 2,4-D 

 content can be followed in clear solutions. 



A very simple method of following changes of auxin concentra- 

 tions in quite pure solutions is by measurement of pH changes (Brau- 

 ner, 1952). The changes in acidity in relation to concentration of 

 indoleacetic acid (lAA) are shown in figure 2G. This method has 

 proved to be effective for following the photo-destruction of auxin 

 in vitro, especially when used in conjunction with other tests such 

 as the ferric chloride test for the entire lAA molecule and the Hopkins- 

 Cole test for the indole ring (Brauner 1953). 



CHROMATOGRAPHIC SEPARATION OF AUXINS 



The recent development of chromatographic techniques for sep- 

 aration and identification of compounds has provided a new and 

 valuable means for separation and identification of growth hormones, 

 their precursors and breakdown products in plants. 



The technique of paper chromatography, first introduced by 

 Consden et al (1944), has only recently been extensively applied to 

 the investigations of plant growth regulators. This technique utilizes 

 the principle of separation of substances by partition between two 

 liquid phases, one stationary and the other mobile, cellulose acting 

 as an inert support. Different substances move at different rates, de- 

 pending on their distribution ratios between the solvents, and by this 

 means separation is effected. Though the phenomenon is primarily a 

 case of partition, adsorption has also an important role — a role which 

 becomes a major one in certain cases (Burma, 1953). 



Detailed descriptions of the procedures involved in paper chroma- 

 tography are available in the book by Block et al (1952). Compre- 

 hensive surveys of the Rf values and color detection methods for indole 

 derivatives and auxins have been carried out by Sen and Leopold 

 (1954), Weller et al (1954) and Stowe and Thimann (1954). 



Jerchel and Miiller (1951) were possibly the first to chromato- 

 graph indoleacetic acid on paper. The Rf values (the ratios of the 

 distance moved by a substance to that moved by the solvent front) of 

 indole, indoleacetic acid, isatin and tryptamine were also reported by 

 Berry et al (1951). Since then indoleacetic acid and allied substances 



