Natural auxins 



used for auxin determinations, the inhibitors may have had no direct effect 

 on auxin but instead may have been inhibitory in themselves to the growth 

 of Avena sections. Paper chromatography, however, permits a study of the 

 effect of boiling directly on the stability of I AA. The results of experiments 

 involving boiling tissue and added lAA are given in Table 6. 



Table 6 



Stability of lAA to heat in the presence and absence of plant 



tissue as determined by paper chromatography 



t Theoretical value for total recovery of lAA is 0-33. 



There is no discernible release of inhibitors of lAA from plant tissue which 

 is boiled. The results suggest that boiling plant tissue for short periods may 

 be used to inactivate the enzymes which catalyse the conversion of tryptophan 

 to lAA, providing that lAA content is determined chemically and not by 

 means of biological assays. 



FREE INDOLE ACIDS IN SHORT-DAY PLANTS GROWN UNDER 

 PHOTOINDUCTIVE AND NON-PHOTOINDUCTIVE DAYLENGTHS 



The development of the extraction procedure and the quantitative paper 

 chromatographic technique was a pre-requisite to assays of indole compounds 

 in photoperiodically sensitive plants (Vlitos and Meudt, 1954b). The above 

 techniques were applied to answer the question : are free I AA levels decreased 

 in short-day plants as a result of photoinduction? Such information is 

 essential if plant physiologists are to examine the validity of the hypotheses 

 which have been proposed to account for the influence of auxin in the 

 flowering process (Bonner and Liverman, 1953; Fisher and Loomis, 1954). 

 Soybean {Glycine max Mer. varieties Biloxi and Lincoln) and tobacco 

 {Micotiana tabacum L. var. Maryland Mammoth) were the short-day plants 

 used in the study. One group of plants was grown under greenhouse 

 conditions in an environment providing a total of 18 hours light in a 24-hour 

 cycle. The prevailing natural daylength was extended by light emanating 

 from 500-watt Mazda tungsten lamps. The second group of plants was 

 grown under short-day conditions (8-hour daylengths) attained by covering 

 the plants with light-proof, aluminium-foil shields. The number of photo- 

 inductive cycles necessary for floral initiation was determined from previous 

 experiments under similar conditions. In every case the plants which were 

 harvested for extraction were photoinduced or were completely vegetative. 

 Photoinduced plants were harvested before macroscopic flower parts had 

 formed. Vegetadve plants were of the same age as photoinduced ones at 



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