Indole compounds in photoinduced plants 



harvest. Employing the extraction method and quantitative paper chromato- 

 graphy as described above the types and amounts of indole compounds 

 recovered from extracts were recorded. Results of a typical experiment 

 appear in Table 7. 



Table 7 

 Amounts of Z-indoleacetic add {lAA), 3-indolepyruvic acid (IPA), and tryptophan {Tryp) in short-day 

 plants grown under 8- and \8-hour photoperiods as determined by quantitative paper chromatography 



t It was not possible to express the amounts of 3-indolepyruvic acid quantitatively since synthetic samples of the 

 compound were too unstable to chromatograph quantitatively. 



J Tryptophan was contained in the aqueous fractions of tobacco extracts. Soybean extracts were not assayed 

 for tryptophan content. 



A compound possessing an R^ value identical to 3-indolepyruvic acid (IPA) 

 was detected in the three short-day plants which were studied. Strongly 

 coloured spots were obtained on chromatograms for this compound in 

 extracts from tissues grown under photoinductive cycles. Free lAA was 

 present in highest concentration in extracts of tissues of Biloxi soybean plants 

 grown under short-day conditions. Lincoln soybeans which were grown 

 under these short-day conditions also contained more lAA than comparable 

 plants grown under long-day cycles. 



The results of this study indicate that free lAA and IPA levels are increased 

 under light conditions which favour the flowering of short-day plants, 

 Biloxi and Lincoln soybean. IPA levels in Maryland Mammoth tobacco 

 leaves are highest in photoinduced tissue. These results are at variance with 

 the hypothesis that photoinduction and reduction in endogenous lAA levels 

 are related processes. 



The recent work of Cooke (1954) substantiates most of the findings 

 outlined above. Cooke found changes in auxin content in vegetative 

 Maryland Mammoth tobacco {Nicotiana tahaatm L.) and Biloxi soybean to be 

 correlated with the daylength in which the plants were growing. In contrast 

 to our work he found more auxin in plants growing under long-day than in 

 plants growing under short-day conditions. Plants which were suddenly 

 shifted from long-day to short-day conditions showed a rise in auxin content 

 for the next few days. Similar increases in auxin content have been noted in 

 plants which are transferred to total darkness (Gustafson, 1946). According 

 to Cooke (1954) increased auxin concentration occurs during the period of 

 floral induction and it is not until several days later that the concentration 

 of auxin begins to decrease. A decrease in auxin is not the cause of flowering 

 as this decrease does not occur until after the induction period. Cooke in his 



63 



