Intracellular Locale of Auxin Action 361 



alleled closely the results obtained in growth experiments. In a some- 

 what similar series of experiments, Northen (5) applied auxins in 

 lanolin paste to one side of 'Navy' bean petioles, and after a 

 suitable incubation period, centrifuged the petioles at right angles 

 to their long axis. Cells on the auxin-treated side showed predom- 

 inantly displaced contents, while those on the control side did not. 

 Northen interpreted these results as indicating an auxin-mediated 

 decrease in cytoplasmic viscosity. This interpretation would har- 

 monize well with the Thimann-Sweeney experiments, since the rate 

 of cytoplasmic streaming must be assumed to be inversely propor- 

 tional to the viscosity of the cell contents. Similarly, our results can 

 best be interpreted as an alteration of the physical state of the cyto- 

 plasmic proteins, which could be reflected in altered heat coagulabil- 

 ity patterns, as well as in viscosity and other physical properties. 



Various workers, on the basis of structure-activity studies with 

 various auxin analogues, have proposed attachment of auxin to a sur- 

 face of some colloidal or polyphasic system, with a resultant swelling 

 (hydrophily) of this system (9). Our results are also consistent with 

 these observations. 



The significance of these findings is as yet difficult to assess. At 

 most, they may provide an explanation of how auxin acts in promot- 

 ing cell growth; at the least, they provide an alternative to the cur- 

 rent cell-wall theories of auxin action which, it seems to us, are in- 

 herently incapable of accounting for all aspects of auxin action. 



SUMMARY 



C"-carboxyl-labeled 2,4-D was applied to etiolated and green pea 

 epicotyl sections at concentrations promoting growth. The sections 

 were subsequently homogenized in 0.25M sucrose + .00 IM EDTA 

 and the various particulates separated by centrifugation and counted 

 for C^*. No evidence could be found for the attachment of the 2,4-D 

 to anything in the cell, the great preponderance of it remaining in 

 the final centrifugal supernatant fraction. Attempts at heat coagu- 

 lation of the proteins of this fraction revealed that 2,4-D greatly de- 

 creased the amount of protein so deposited without affecting total 

 protein content. This effect of auxin on the physical state of the 

 cytoplasmic proteins appears to be correlated with auxin-induced 

 growth. 



LITERATURE CITED 



1. Galston, A. W., and Kaur, R. An effect of auxins on the heat coagulability 

 of the protein of growing plant cells. Proc. Nat. Acad. Sci. U. S. 45: 1587-1590. 

 1959. 



2. , and McCune, D. C. An analysis of gibberellin-auxin interaction and 



its possible metabolic basis. This volume, pp. 611-625. 



