68 Fundamentals of Auxin Action 



observed that jirotein-hydrolyzing enzymes were capable of producing 

 auxins from various protein materials. It seems evident that any 

 protein containing tryptophan, a recognized precursor of auxin, could 

 produce auxin upon hydrolysis and oxidation. Certain reservations 

 must be made, however, about the importance of this source in the 

 production of auxins for growth. Although structural protein mate- 

 rials may conceivably serve as an auxin source, auxin production has 

 not been generally associated with protein breakdown in the plant. In 

 fact, auxin production in growing tissues may instead be more logically 

 associated with protein synthesis. Therefore, it seems unlikely that 

 structinal proteins serve to any appreciable extent as bound auxin or 

 precursor of auxin in the normal growing plant. It is curious to ob- 

 serve that some proteins which do not contain perceptible amounts of 

 tryptophan have been reported to produce auxin with enzymatic 

 hydrolysis (Kulescha, 1948). 



IDENTITY OF GROWTH HORMONES 



Before discussing the actual identity of known auxins it might be 

 well to speak of the methods generally used for identifying these 

 plant materials. All of the methods must be usable with minute 

 amounts of auxin, for the growth hormone occurs in most plant parts 

 in fantastically small amounts. A striking illustration of this is the 

 fact that one Avena coleoptile tip will generally contain only 1/50,- 

 000,000 of a milligram of auxin (Haagen-Smit, 1951). 



Because of the minute amounts of auxins in plant parts, the actual 

 purification of the growth hormone and preparation of a derivative 

 for identification is seldom carried out. 



When it is separated and purified, indoleacetic acid can be identi- 

 fied by the picrate salts (Kogl and Kostermans, 1935), by its addition 

 product obtained with 1,3,5-trinitrobenzene (Redemann et al, 1951), 

 or more simply by its melting point and infrared spectrum (Berger 

 and Avery, 1944). 



A more common means of identifying growth hormones is by 

 determining the molecular weight, using the diffusion experiments 

 described in chapter II. Molecular weight determinations have un- 

 doubtedly given some confusing information, however, because auxins 

 diffused from plant parts will sometimes show apparent gross reduc- 

 tions in molecular weight when purified by separation into ether 

 (Wildman and Bonner, 1948). Molecular weight determinations by 

 the agar diffusion technique are valid only for pme preparations, and 

 the presence of other compounds, which may be expected to diffuse 

 out of plant parts at the same time, can greatly alter the results ob- 



