Metabolism of Some Indole Auxins in Excised Tomato Roots

Abstract

Indolylacetylaspartic acid (IAAsp) and possibly indolylacetylglutamic acid (IAG) are formed by exposure of excised tomato roots to IAA. Little ‘free’ IAA accumulates in the tissue. An unidentified substance reacting pink with nitricnitrite reagent is also formed. These substances are metabolized when IAA-treated roots are transferred to auxin-free medium. IAAsp and IAA are similarly inhibitory to the growth of excised tomato roots. Excised tomato roots do not interconvert IAA and IAN. IAN-feeding leads to IAN accumulation and the appearance of indolylcarboxylic acid (ICA); transference to auxin-free medium causes a decline in the IAN activity but the ICA spot persists. The inhibitory activity of IAN is not due to its conversion to ICA. Excised tomato and wheat roots respond very differently to external l-tryptophane but in neither case is there evidence of the conversion of tryptophane to ethyl acetate-soluble auxins.