Applications of kinetics to auxin-induced growth 



workers find that initial extension rates in high auxin concentrations are not 

 reduced by the presence of other solutes, sugars, maleate, etc. (cf. Bonner and 

 Foster, 1955, Figure 4. In our experiments, using unbuffered auxin, auxin 

 adjusted to pH 4-5 or 5-5 by NaOH, and similar solutions buffered either with 

 maleate or citrate or with other additives, we invariably find that addition of 

 buffer or other osmotica depresses initial extension rate and tends to flatten out 

 the extension-time curve from concave to the horizontal axis towards linearity 

 as shown in Figure 2. 



Consequently, our view is that the inhibitions which develop at high auxin 

 concentration are due to secondary destruction of part of the cell mechanism 

 rather than to a competitive attachment to one of the postulated pair of auxin 

 attracting centres. The lack of reversibihty following injury due to high 

 auxin concentration is consistent with this view, 



REFERENCES 



Bennet-Clark, T. a., and Kefford, N. P. (1954). The extension growth time 

 relationship for Avena coleoptile sections. J. exp. Bot. 5, 293-304. 



Bonner, J., and Foster, R. J. (1955). The growth time relationships of the auxin- 

 induced growth in Avena coleoptile sections. J. exp. Bot. 6, 293-302. 



Housley, S., Bentley, J. A., and Bickle, A. S. (1954). Studies on plant growth 

 hormones. III. J. exp. Bot. 5, 373-388. 



Marinos, N. G. (1955). Studies on cell elongation. Ph.D. Thesis, University of 

 Adelaide, S. Australia. 



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