Changes in Auxins in Expanding and Senescent Primary Leaves of Dwarf French Bean (Phaseolus vulgaris)

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Abstract
A bound, unextractable auxin, or auxin precursor, in the primary leaves of dwarf French bean was converted to a form, probably indol-3yl-acetic acid, extractable in ethyl acetate, by macerating leaves in pH 7.5 phosphate buffer and incubating them at 37–38° C for 2 days in the presence of toluene or hibitane. Boiling the leaves before macerating and incubating them prevented the release of bound auxin. This bound auxin was also released when macerated leaves were hydrolysed with normal potassium hydroxide at 100° C for 2 hours. The amounts of free auxin and tryptophan in senescent primary leaves increased as their bound auxin and chlorophyll decreased. Removing the apical growing region immediately above the node bearing the primary leaves delayed their senescence and the conversion of their bound to free auxin.