Conversion of tryptophan to auxin by phenolic esters from leaves of dwarf french bean ( Phaseolus vulgaris L.)

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Macerated bean leaves ( Phaseolus vulgaris) produced more auxin when incubated at pH 7·5 in the presence of toluene for 2 days with tryptophan than without. Boiled or autoclaved leaves did not produce auxin when incubated alone, but did so after adding tryptophan. Conversion of tryptophan to auxin during incubation of macerated leaves was attributed to phenols, later identified as esters of caffeic, ferulic and p-coumaric acids. The phenolic esters extracted from bean leaves promoted growth of wheat coleoptile sections only when assayed with tryptophan, and produced auxin only when incubated or hydrolysed with tryptophan. Caffeic acid reacted with tryptophan like the bean phenols but ferulic and p-coumaric acids were less effective. Phosphate buffer, pH 7·5, removed phenolic esters, but not auxins, from the surface of bean leaves, and like the extracted bean phenols they produced auxin when incubated with tryptophan.