Structure and function of wall appositions. 1. General histochemistry of papillae in barley coleoptiles attacked by Erysiphe graminis f. sp. hordei

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Abstract
Penetration pegs of Erysiphe graminis D.C. f. sp. hordei Em. Marchal are usually not impeded by normal papillae of barley coleoptiles, whereas oversize papillae are impenetrable to appressoria of the pathogen. We investigated the chemical composition of these papillae and the cell walls by classical histochemistry, in part to extend the fragmented knowledge of these structures and in part to find out if there are differences between normal and oversize papillae which would account for their different efficacies in resisting penetration. These papillae were indistinguishable from one another histochemically and contained protein, carbohydrate other than pectin, and a phenolic which was not lignin. We report also a definitive proof of callose in papillae. They do not contain cutin or suberin. The cell wall did not contain callose or cutin–suberin but did contain protein, pectin, and a phenolic (also not lignin). The results imply that different linkages between molecules in oversize papillae, or some other differences not revealed in this study, are responsible for their ability to prevent fungal penetration.