360 



A. W. Galston and R. Kaur 



Table 5. The effect of various concentrations of 2,4-D on the growth and protein 

 coagulability of green and etiolated pea stem sections. 



triiuging down the precipitate, transferring it quantitatively to a 

 tared weighing pan, drying overnight at 90° C, cooling in a desic- 

 cator, and weighing to the nearest 0.1 mg. Alternatively, in those in- 

 stances where flocculent precipitates failed to form, the quantity of 

 suspended material could be estimated turbidimetrically in a Klett- 

 Summerson photoelectric colorimeter equipped with a #42 blue 

 filter. Sample data from such measurements are presented in Table 

 5. It is clear that increasing concentrations of 2,4-D sharply reduce 

 the quantity of heat coagulable proteins, whether measured gravi- 

 metrically or turbidimetrically. 



Other experiments (1) have revealed that indole-3-acetic acid 

 (lAA) is approximately as active as 2,4-D in decreasing the heat co- 

 agulability of the proteins; the weak auxins phenylacetic acid and 

 2,3,5-triiodobenzoic acid are slightly active, and the antiauxin p- 

 chlorophenoxyisobutyric acid is completely inactive. The effect ap- 

 pears not to be produced in vitro by a mixing of control protein with 

 the auxin. There also appears to be no effect of auxin on total pro- 

 tein, since the precipitates deposited in 0.5Af trichloroacetic acid are 

 equal in control and auxin-treated fractions. The effect is thus prob- 

 ably to be interpreted as an auxin-induced alteration of the physical 

 state of the cytoplasmic proteins. 



DISCUSSION 



While the auxin effect we have described in this paper is new to 

 plant physiology, there are certain previous references in the liter- 

 ature which appear to be closely related to it. For example, Thimann 

 and Sweeney (8), in an elegant series of papers, showed that lAA ap- 

 plied to Avcna coleoptile cells markedly increased the rate of cyto- 

 plasmic streaming. The effect was apparent within minutes, and the 

 dose response relationships and the inhibition by various agents par- 



