A. W. GALSTON 



and 

 RAVINDAR KAUR 



Yale University 



The Intracellular Locale of Auxin Action: 

 An Effect of Auxin on the Physical State 



of Cytoplasmic Proteins' 



Modern theories of the mechanism of auxin action emphasize the 

 demonstrable effects of auxin in increasing the plastic extensibility 

 of the cell wall (4). These effects, first noted by Heyn more than 25 

 years ago, are attractive in explaining the cell elongational aspects of 

 auxin action, since it is clear that the wall must be plasticized if 

 elongation is to occur. This type of theory is not completely satis- 

 factory in explaining auxin action, however, in that auxin is also 

 known to produce marked changes in the cytoplasm (5, 8), and to 

 initiate mitotic activity in certain cells (7). These latter effects are 

 difficult to account for in terms of changes in cell walls mediated by 

 auxin. 



In the course of investigations on the intracellular location of 

 Ci^-carboxyl-labeled 2,4-dichlorophenoxyacetic acid (2,4-D) fed to 

 green and etiolated pea stem segments, we discovered fortuitously a 

 marked effect of this compound and of other auxins on the physical 

 state of the proteins in a centrifugal supernatant devoid of all cellular 

 particulates. The effect noted was a marked decrease in the heat 

 coagulability of the proteins in the auxin-treated tissues as compared 

 with the control tissues. The magnitude of the effect is as great as 

 the often cited eflEects of auxin on the cell wall, and is therefore to be 

 considered as of possible significance in the growth reaction initiated 

 by auxin. We wish to emphasize that the altered heat coagulability 

 of the cytoplasmic proteins is probably not, per se, the important 

 physical property possibly related to growth; it is, however, a possible 



•Aided by grants from the National Science Foundation and the U.S. Public 

 Health Service. We are indebted to Mary Lyons and Drs. S. Maheshwari and N. 

 Maheshwari for assistance with the experiments on heat coagulability of the 

 proteins. 



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