178 P. E. Pilet 



25. Pilet, P. E., and Collet, G. fitude de rallongcment de sections d'epicotyles 

 (comparaison de tests auxiniques). Bui. Soc. Bot. Suisse. 69: 47-57. 1959. 



26. , and Galston, A. W. Auxin destruction, peroxidase activity and per- 

 oxide genesis in the roots of Lens culinaris. Physiol. Plant. 8: 888-898. 1955. 



27. , and Lerch, P. Utilisation d'auxines marquees par du C". Methodes 



et premiers resultats (auxines-oxydases). Mem. Soc. Vaud. Sci. Nat. (In 

 preparation.) 



28. , and Siegenthaler, P. A. Gradients biochimiques radiculaires. I. 



Auxines et reserves azotces. Bui. Soc. Bot. Suisse. 69: 58-74. 1959. 



29. , and Went, F. W. Control of growth of Lens culinaris by temperature 



and light. Amer. Jour. Bot. 43: 190-198. 1956. 



30. Ray, P. M. Destruction of auxin. Ann. Rev. Plant Physiol. 9: 81-118. 1958. 

 31. , and Thimann, K. V. The destruction of indoleacetic acid. I. Action 



of an enzyme from Oniphalia fJavida. Arch. Biochera. Biophys. 64: 175-192. 

 1956. 

 32. Torrey, J. G. Physiology of root elongation. Ann. Rev. Plant Physiol. 7: 

 237-266. 1956. 



DISCUSSION 



Dr. Andreae: In our studies on lAA metabolism, we became 

 particularly interested in the fate of lAA applied to intact tissues. 

 Studies during the past few years have shown that part of the applied 

 lAA accumulates in the tissues as indoleacetylaspartic acid; this has 

 been confirmed by other workers (Fang et ah. Plant Physiol. 34: 26. 

 1959). Fawcett et al. (Nature 181: 1387. 1958) were unable to find any 

 evidence for this reaction. The failure of the latter workers can be 

 ascribed to the inadequate extraction procedure used in their studies. 



Conjugation of lAA with aspartic acid has only so far been ob- 

 served in intact tissues. Cell-free breis entirely lose their ability to 

 conjugate JAA with aspartic acid although such breis may retain 

 lAA-oxidase activity. 



We found that indoleacetylaspartic acid accumulates in pea tis- 

 sues as the major Salkowski-reactive lAA metabolite, but could find 

 no evidence of a metabolically produced, Salkowski-reactive, lAA- 

 protein complex reported by Siegel and Galston (Proc. Nat. Acad. 

 Sci. 39: 1111. 1953). These workers found that dining the initial 

 hours of incubation, lAA is rapidly bound to the pea root proteins 

 and precipitated by trichloroacetic acid. \n oin- studies, the Salkow- 

 ski-reactive material in pea roots can be extracted with ethanol and 

 consits entirely of lAA and indoleacetylaspartic acid (Figure 1). We 

 therefore believe that the lAA-protein complex of Siegel and Galston 

 is not a product of plant metabolism, but an ariifad of the iri- 

 chloroacetic acid precipitation procedine. 



The time course of lAA conjugation with aspartic acid in pea 

 roots is shown in Figure 1. Roots were removed from solution, 

 washed, homogenized, and extracted with ethanol. The entire extract 



