Neiu Auxins Fiuin 'Maryland MammoUi Tobacco 67 



DISCUSSION 



Dr. Stowe: I am interested in this rejjort because we obtained 

 much the same results in pea straight-growth assays, testing a number 

 of higher alkyl lipide compounds. In the pea section-growth assay, 

 it is necessary for auxin to be present if growth acceleration is to be 

 found. May I ask if lAA or other auxins were introduced in your 

 assay? 



Dr. Crosby: No exogenous lAA was ever introduced. 



Dr. Wain: Reference has been made to the occurrence of plant 

 waxes. We all know that these are in the main esters of long-chain 

 fatty acids and long-chain monohydric alcohols. Obviously, with 

 this large amount of material a good deal of wax would be extracted 

 from the tobacco. It is rather significant that one gets here not only 

 an alcohol but an acid. Does the possibility exist that these two com- 

 pounds have arisen from the cuticular wax? 



Dr. Crosby: From its configuration, our long-chain fatty acid must 

 be an extremely unstable one. It is possible, but I would be sur- 

 prised if this were the case. We would never say that these materials 

 positively had an importance to the plant, but they are of interest to 

 us in that they stimulate growth. 



Dr. Kefford: My particular interest in the auxins of 'Maryland 

 Mammoth' tobacco is the presence or absence of lAA. The most spe- 

 cific auxin test is the Avena curvature test and, to date, of the natu- 

 rally occurring auxins only lAA has been found to give this test. I 

 have been able to detect activity with this test in extracts of 'Mary- 

 land Mammoth' tobacco following repeated chromatography. But the 

 activity is very small - about 1/40 of the activity found in other to- 

 bacco varieties. 



Dr. Vlitos: I would like to say that we have not tested the fatty 

 alcohols in the Avena curvature test, although Dr. Kefford, through 

 correspondence, has many times urged us to do so. I feel that w'e 

 have used the most rigorous type of chemical evidence to identify a 

 naturally occurring auxin, and I have not felt it necessary to rely on 

 what is perhaps a nonspecific biological assay. Since we were using 

 the Avena first internode test which seemed to be responsive to the 

 alcohols, and it looked as though we were getting a classical growth 

 dosage response in that particular assay, we relied entirely on chemi- 

 cal identification. I would say I feel that there are very few instances 

 where growth substances have been isolated in crystalline form and 

 shown by a series of rigorous chemical methods to be a particular 

 substance. We relied neither on a bioassay nor on a colorimetric 

 test. 



