Localization of benzoxazinones that occur constitutively in wheat seedlings

Occurrence and localization of novel antimicrobial and antifeeding compounds in wheat, 2,4-dihydroxy-1,4-benzoxazin-3-one (DIBOA) and 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA), and their glucosides, were examined by staining wheat plants (Triticum aestivum L.) in the juvenile stage of growth by ferric chloride. The methanol extracts of the stained plant tissues gave a characteristic blue color, which was shown by spectroscopic and chromatographic analyses to be exclusively due to benzoxazinones. When ferric chloride was applied to the root in the seedlings, the blue color immediately developed, the staining being strongest at the tip region and becoming lighten towards the basal part. The staining pattern of the radicle in the pre-emerging seed was similar to that in the root, but the coleorhiza was not stained. Little staining was observed in the epidermal layer of the leaf sheath in the shoot but the underlying tissue was stained strongly. The foliage leaf folded in the sheath was also stained, but less intense than the shealth tissue. It is suggested that the DIBOA and DIMBOA 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 compounds during this vulnerable plant stage.