The β -oxidation of ω -phenoxyalkylcarboxylic acids in the flax plant in relation to their plant growth-regulating activity

Abstract

Members of the homologous series (C 6 H 5 O(CH 2 ) n COOH) with n = 1 to 10 have been synthesized and their breakdown within flax seedlings, following absorption through the roots, has been investigated by a chemical method. The well washed plants were macerated, steam-distilled and phenol in the distillate was estimated colorimetrically. The results provide evidence that β -oxidation can occur within plant tissue. Those acids with an even number of side chain methylene groups ( n =2, 4, 6, 8, 10) gave rise to appreciable quantities of phenol, some 160μg being found in each experimental group of 200 flax seedlings. In the cases where n was an odd number, however, the acids with n = 1, 3, 5 and 7 yielded only traces (some 10μg) of phenol. 9-Phenoxynonane-1-carboxylic acid ( n = 9) was exceptional yielding about 60μg phenol. This behaviour of the nonane-acid could be explained by side-chain degradation involving ω -oxidation, and correlates with results of animal metabolism studies. All ten acids were examined as plant growth-regulators by six different methods. Uniform inactivity was shown in the tomato leaf epinasty, tomato leaf rooting, tomato parthenocarpy and Avena cylinder tests. In both the Went pea and a bean seedling test, however, an unexpected type of alternation in activity was observed in this series. This is considered in relation to the alternation in growth-regulating activity obtained with other homologous series of aryloxy-acids.