Autofluorescent and ultraviolet-absorbing components in cell walls and papillae of barley coleoptiles and their relationship to disease resistance

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Abstract
Earlier studies showed that normal-size papillae induced in barley coleoptile epidermal cells by Erysiphe graminis f. sp. hordei were less effective in resisting fungal penetration attempts than were oversize papillae. To determine if a differential content of phenolic derivatives could account for this difference in resistance, we analyzed normal papillae and oversize papillae by histochemical, epifluorimetric, and ultraviolet-microspectrophotometric methods. Whereas the histochemical tests revealed phenolic derivatives only in oversize papillae, the autofluorescence and ultraviolet-absorption properties indicated that both types of papillae contain phenolics. Ultraviolet-absorption spectra indicated that the phenolics were primarily phenylpropanoid groups. Phenolics in papillae were distinct from both those in the secondary wall thickenings of coleoptile xylem vessel elements and those in the periclinal walls of coleoptile epidermal cells. The deposition of phenolics in oversize papillae long before they were challenged by the fungus, the presence of certain phenolics that, tentatively, were detected histochemically only in the oversize papillae, or both could have rendered them resistant to penetration by the fungus.