Histochemistry of Papillae Formed in Reed Canarygrass Leaves in Response to Noninfecting Pathogenic Fungi

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Abstract
Leafspot fungi nonpathogenic to reed canarygrass [Pharis arundinacea] but pathogenic to other plants, formed appressoria and penetration pegs on reed canarygrass leaves. Papillae usually formed in the outer epidermal walls beneath penetration pegs, and no penetration occurred. The epidermal walls became histochemically modifed in disk-shaped areas, up to 60 .mu.m in diameter, around the sites of attempted penetration. Lateral epidermal walls beneath the disks (disk-shaped areas) became swollen and histochemically modified. Papillae in leaves inoculated with Helminthosporium avenae gave histochemical reactions with toluidine blue O, Cl water-sodium sulfite and phloroglucinol-HCl which indicated that lignified material was a major structural component of the core of the papillae and the altered lateral walls and only a minor component of the disks. Insolubility in 72% H2SO4 and solubility in Cl-sulfite supported these conclusions. Tests with resorcinol blue, lacmoid and aniline blue-fluorescence indicated that callose was present in the papillae, lateral walls and disks. Results from tests with IKI-H2SO4 and toluidine blue O, and for birefringence suggested that cellulose was a significant structural component of the disks, the altered lateral walls and the cover layer of the papillae. Tests for cutin, suberin, tannins, gums and pectin compounds were negative. Callose was more readily demonstrated 10-12 h after inoculation with H. avenae than at later times. Lignification was detected at 10 h, and was strong after 24-48 h. Six clones of reed canarygrass had the same structural and histochemical reactions. Papillae and wall modifications formed at 17, 24 and 29.degree. C in continuous light or dark had similar histochemical reactions. Positive tests for lignified material, callose and cellulose were obtained in papillae, disks, and lateral walls associated with penetration attempts by Botrytis cinerea, Leptosphaerulina trifolii, Stagonospora arenaria, Stemphylium botryosum, H. catenarium and Ascochyta sp.

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