Relationship of autofluorescent and ultraviolet-absorbing components in cell walls and wall appositions to disease resistance in kohlrabi roots

Abstract

It has been shown that wound plugs induced mechanically by bending of kohlrabi root hairs are more resistant to subsequent penetration attempts by Olpidium brassicae than are papillae induced by the fungus. A histochemical, autofluorescence, and ultraviolet-microspectrophotometric study was undertaken to determine if a differential composition of phenolic derivatives could explain this difference in resistance. Phenolics in the secondary wall thickenings of xylem vessel elements of roots were distinct from those in wound plugs, papillae, and root hair cell walls. But phenolics in wound plugs and papillae could not be distinguished from each other by the methods employed. Thus, the results do not support the hypothesis that wound plugs are more resistant to penetration than are papillae because they contain phenolic derivatives not found in the latter. However, the possibility that an earlier deposition of phenolics in wound plugs accounts for their greater resistance to penetration has not been ruled out.