Localization of Benzoxazinones that Occur Constitutively in Wheat Seedlings

O ccurrence and localization of novel antimicrobial and antifeeding com pounds in w heat, 2,4-dihydroxy-l,4-benzoxazin-3-one (D IB O A ) and 2,4-dihydroxy-7-methoxy-l,4-benzoxazin3-one (D IM B O A ), and their glucosides, were examined by staining w heat plants ( Triticum aestivum L.) in the juvenile stage of growth by ferric chloride. The m ethanol extracts of the stained plant tissues gave a characteristic blue color, which was shown by spectroscopic and chrom atographic analyses to be exclusively due to benzoxazinones. W hen ferric chloride was applied to the root in the seedlings, the blue color im mediately developed, the staining being strongest at the tip region and becom ing lighter towards the basal part. The staining pattern of the radicle in the pre-em erging seed was similar to tha t in the root, but the coleorhiza was not stained. Little staining was observed in the epiderm al layer of the leaf sheath in the shoot but the underlying tissue was stained strongly. TTie foliage leaf folded in the sheath was also stained, but less intense than the sheath tissue. It is suggested that the D IB O A and D IM BO A are produced within the stained region of the leaf and root. Together with previous findings that the benzoxazinones appear constitutively in wheat during the juvenile stage of growth, their localized occurrence in the tissues exposed to microbial and insect attacks suggests that they act as defense com pounds during this vulnerable plant stage.