Biosynthesis of Indol-3-yl-acetyl-myo-inositol Arabinoside in Kernels of Zea mays L.

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Abstract
Extracts of immature kernels of Z. mays L. catalyzed the synthesis of IAA-myo-inositol arabinoside from IAA-myo-inositol and UDP-[U-14C]xlose. The product contained radioactivity which upon hydrolysis with trifluoroacetic acid cochromatographed with arabinose and not xylose. The amount of product from the reaction was proportional to the amount of IAA-myo-inositol added and the product was positive to Ehmann''s reagent for indoles. The product and authentic IAA-myo-inositol arabinoside had the same RF or retention time in 3 chromatographic systems. By analogy to the wheat germ system, a UDP-D-xylose 4-epimerase may be present in immature kernels of maize and this enzyme may catalyze the conversion of UDP-D-xylose to UDP-L-arabinose, the probable sugar donor to indol-3-yl-acetyl-myo-inositol. A previously undescribed enzyme, UDP-arabinose:indol-3-yl-acetyl-myo-inositol arabinosyl transferase was present in maize kernels. A pathway for the biosynthesis of all the low MW esters of IAA in maize kernels is provided.