Investigation of natural auxins and growth inhibitors 



first internodes. When wopropanol (80) -|- water (20) was used as a solvent, a 

 very interesting picture was obtained (^Figure 22). The normal tissues, which 

 require added lAA to grow, did not contain appreciable quantities of lAA, 

 whereas a growth peak coidd be detected at the lAA position in the extracts 

 of the two other types of tissues. On the other hand, a very large growth 

 promotion was detected in the zone of neutral auxins such as IAN and I AE in 

 all cases. Thus the hypothesis was formed, that perhaps the normal tissues 

 manufacture appreciable amounts of a substance like IAN, but are unable to 

 convert it into lAA, whereas the other tissues can. 



Other tissues grown in vitro, such as the vascular parenchyma of the tuber 

 of Jerusalem artichoke, are incapable of transforming IAN into lAA, as 



Figure 23. Effect of various concentrations of 

 lAA, IAN, and lAE on the growth of small 

 cylinders of the tuber of Jerusalem artichoke, 

 var. Pi^dallu 17. The initial explants each 

 weighed 22 rng {fresh weight); they were 

 harvested after 2 1 days of growth on media 

 containing sucrose, mineral salts, and the 

 added auxin {sterilized by filtration). Note 

 that concentrations are given on a molar basis. 



70-'' 10'^ 10- 

 Concenfration, M 



shown in Figure 23. Nevertheless, from the results of Figure 22 alone we 

 cannot be certain that the growth peaks found in all cases in the IAN 

 region are actually due to IAN, for the solvent used cannot separate IAN 

 from other auxins such as lAE. Another set of chroma tograms was developed, 

 therefore, in the hexane-water solvent {Figure 24), but unfortunately from 

 a different batch of cultures. In all three cases, a marked growth promo- 

 tion was detected in the IAN region, but in addition, another growth peak in 

 the lAE region was also apparent. Thus, at this point, it is difficult to say 

 if the hypothesis presented above is correct, for lAE is roughly as active, on 

 a molar basis, as lAA in tissue culture, at least in the case of Jerusalem 

 artichoke tissues. 



A last example will illustrate even better the usefulness of the first internode 

 assay technique. It concerns the examination of a chromatogram obtained 

 with the extract of about 150 apices of rhizomes of the fern Adiantum pedatum 

 dissected under the binocular microscope by Professor Wetmore, so that only 

 the top millimetre or less of tissue was cut off. Altogether, these meristems 

 weighed about 300 mg (fresh weight). Upon dissection, each of them was 

 immediately plunged into a mixture of 2/3 ether and 1/3 absolute ethanol 

 (v/v) kept cold in brine. The total extract was chromatographed in 

 uopropanol-ammonia-water (80; 10; 10) (v/v) and assayed with first 



27 



