IV 



CHEMISTRY OF THE GROWTH SUBSTANCES 



761 



TABLE 3 



AUXIN CONTENT OF TISSUE CULTURES, EXPRESSED AS EQUIVALENT PARTS 

 OF INDOLEACETIC ACID PER I O^ PARTS OF FRESH WEIGHT 



Data of Kulescha, 1951 



Artichoke Grape '' Vigne-vierge'' 



{Helianthus ( Vitis vinifera) Scorzonera [Parthenocissiis 



tuberosus) stem hispanica tricuspidata) 



tuber root stem 



Probably due to buds formed 



and the well known instability to hot acid. However, a number of the assumed 

 identifications are less thorough and may require revision. Nevertheless, the reac- 

 tions of indoleacetic acid are fairly characteristic, and there can be little doubt 

 about its very widespread occurrence as a natural auxin. 



In some plants a neutral material occurs which has little or no growth-promoting 

 activity when freshly extracted but is rapidly converted by enzymes present 

 in soil, milk or (in some cases) in test plants themselves, to an active auxin, which 

 is an acid. This neutral material was first found in etiolated seedlings and therein 

 tentatively identified by Larsen (1944, 1951b) as indoleacetaldehyde, II. The 

 enzyme converting it to the acid, which of course is indoleacetic acid, I, is aldehyde 

 dehydrogenase or Schardinger enzyme. The aldehyde occurs in pea and sunflower 

 seedlings, in potato tubers, corn embryos and pineapple leaves. Probably, then, 

 it is widespread, and this fact indirectly supports the importance of lAA as a 

 general plant hormone. Aldehyde oxidases or dehydrogenases are, of course, 

 universal and there is no reason to believe, at least as far as present evidence goes, 

 that indoleacetaldehyde requires a specific dehydrogenase. 



A third indole compound, indoleacetonitrile, III, has been isolated from cab- 



-CHjCOOH 



Indoleacetic acid 

 I 



-CH2CH0 



Indoleacetaldehyde 

 II 



-CHaCN 



Indoleacetonitrile 

 III 



bage (Henbest et al., 1953) and its presence is virtually certain in several closely 

 related vegetables. It has also been tentatively identified in several unrelated plants 

 including tissue cultures. Unfortunately, the chromatographic behavior of this 

 and other neutral compounds in most procedures is not highly characteristic, so 

 that many of the identifications are as yet by no means certain. A remarkable 

 characteristic of the nitrile is that, although more active then lAA on Avena cole- 



Literature p. 8i6 



