The inability of Septoria nodorum Berk, to penetrate barley leaves was associated with the development of papillae beneath penetration sites and a modification to the structure of the cell wall surrounding papillae. Penetration hyphae did not progress further than the outer cellulose layers of the wall.
Reaction sites (papillae and modified cell walls) were isolated using cellulase. Modified cell walls were resistant to cellulase and did not react with zinc chlor-iodide, indicating that the cellulose microfibrils were protected from both the enzyme and the stain. Material deposited in the interfibrillar spaces appeared to be responsible for this protection. Callose could not be detected in papillae; however, this may have also been due to encrusting substances which prevented callose reacting with aniline blue. The material deposited within papillae appeared to be similar to that deposited in cell walls. Lignin could not be detected in reaction sites. Intense staining with Coomassie brilliant blue R250 and periodic acid Schiff's reagent suggested that both proteins and carbohydrates were deposited in these structures. The possibility that these deposits were glycoproteins is discussed.