BIOSYNTHESIS OF AVENIC-ACID-A IN OAT CV ONWARD - STUDIES WITH C-14 ORN-15 LABELED COMPOUNDS

The precursory role of avenic acid A (AVA) in the biosynthesis of the mugineic acid family (MAs) of phytosiderophores was studied by feeding C-14 or N-15 labeled compounds into iron-deficient oat roots (Avena s ativa L. cv. Onward). Carbon-14 of methionine was incorporated into AV A and 2'-deoxymugineic acid (DMA) in the oat roots, while C-14 Of homo serine was not incorporated into either AVA or DMA. The molar radioact ivity of DMA was higher than that of AVA. Incorporation of N-15 into M As was examined by feeding N-15-ammonium sulfate into oat roots. The v alue of N-15 atom-% excess of DMA was higher than that of AVA. These r esults indicate that methionine, rather than homoserine, is the direct precursor of MAs in oat, which is similar to that in barley, and that AVA is not the precursor of the other MAs.