Ultrastructure of wilt syndrome caused by Verticillium dahliae. V. Attempted localization of phenolic compounds in the vascular region

Abstract

Ferric chloride has been used in an attempt to detect phenolic compounds at the ultrastructure level in the petioles of chrysanthemums and sunflowers infected with Verticillium dahliae. The fungus contains two types of cytoplasmic structures which stain very densely with ferric chloride; one is similar to a multivesicular body, the other solid and apparently spherical. In treated chrysanthemums, the ferric ion accumulates mainly in vessel plugs, in laminar arrays or localized diffuse deposits in the secondary walls of vessels, in vasicentric parenchyma cells, and the protective layer of parenchyma cells immediately adjacent to the vessels. In treated sunflowers the ferric ion accumulates mainly in vessel plugs, in the pectinaceous layers of the cell wall (i.e. middle lamella and primary cell walls), and in the vasicentric parenchyma cells. Differences in the pattern of phenolic deposition in the two hosts could account wholly or in part for differences in symptom expression.