304 Freed, Reitlicl, and Remmert 



placed on a physical mode of primary action. I can imagine that the 

 effect of 2,4-D on mitochondria could be due to swelling of the mito- 

 chondrial membranes. I would like to ask how 2,6-D and the other 

 homologues behave. 



Dr. Freed: We have measured the effect of 2,6-D, 2,4,6-T, and a 

 nimiber of other compounds on the oxygen uptake of mitochondria. 

 We do find that many of these compounds have an effect. This is as 

 would be postulated since most of them are capable of being adsorbed 

 to a greater or lesser degree. This has a parallel in that as a homolo- 

 gous series is examined for biological activity or activity on mitochon- 

 dria, a few members may be found that are innocuous at quite a 

 range of concentrations, but most of them will have measurable ac- 

 tivity with a few having outstanding activity. This suggests that the 

 structural requirement for activity is not absolute, which is consonant 

 with an adsorption phenomena. Hence the moderate activity of 2,4,6-T 

 is not unexpected. 



Dr. AVain, we are fully aware of the possible implication of the 

 carboxyl group in the absorption phenomenon. "When I say absorp- 

 tion I'm thinking in rather broad terms. The ultraviolet spectra, of 

 course, also implicate electron density because of the electronic con- 

 figuration of the ring that has been modified both by the carboxyl 

 group and the chlorine substituents. 



Dr. van Overbeek: That's why I asked the question, because ab- 

 sorption is necessary but not the timely point. 



Dr. Freed: It appears from these studies that adsorption is the 

 first event in the action of these compounds, but the subsequent effect 

 may well be the crucial mechanism in their action. 



Dr. Bonner: Well, I know it's very attractive to think about how 

 auxin molecules can be adsorbed, presumably by 2-point attachment, 

 to enzyme molecules and cause them to be changed and to do some- 

 thing different than they otherwise would do. It's attractive to think 

 that auxins might do their work by affecting, for example, the mito- 

 chondria which we know are very important, and the powerhouses 

 of the cell, and I yield to no one in my admiration for mitochondria. 

 One of the most fascinating and indeed useful aspects of auxins is, 

 however, that they don't work on all kinds of organisms. We saw, for 

 example, that auxins bind to bovine serum albumen, but it is a well- 

 known fact that auxins do not work on cows. Now, it is a very remark- 

 able fact, I think, that auxins work on sudi a small part of the spec- 

 trum of living organisms. They work on higher plants and a few 

 algae but they don't work on all organisms. It seems to me quite clear, 

 therefore, that when we try to find out how auxin does its work we 

 have to think about processes that go on in and arc unique to plants 



