Studies of fluorophenylalanine induced Avena coleoptile elongation: Possible modulation of auxin oxidase activity

Abstract

Previous studies have established that the amino acid analogue p-fluorophenylalanine promotes the elongation of etiolated Avena coleoptile segments and lead us to suggest that the elongation response induced by this isostere is due to a depression of L-phenylalanine ammonia-lyase activity resulting in a decreased level of low molecular weight phenols which, directly or indirectly, modify Avena auxin oxidase activity and result in altered levels of growth substance in coleoptile segments. Further elucidation of the nature of the growth response necessitated additional studies on analogue specificity. To date only fluorinated analogues have been used to modify L-phenylalanine ammonia-lyase activity, therefore, data on the effects of other halide substituted phenylalanines are presented and comapred to the results of fluorophenylalanine treatment. Data indicate that the p-tluorophenylalanine response is isomer and substituent specific for no other halide substituted analogue elicits a positive elongation response. Treatment of Avena coleoptiles with p-fluorophenylalanine results in a modified auxin oxidase activity. A decrease in oxidase specific activity has been observed throughout a series of temperature and pH studies performed in this laboratory.