APOPLASTIC SUGAR CONCENTRATION AND PH IN BARLEY LEAVES INFECTED WITH BROWN RUST

Soluble sugars were extracted by low speed centrifugation from the apoplast of leaves of barley (Hordeum distichum L.) infiltrated with water. Infection of the leaf with the brown rust fungus (Puccinia hordeii) resulted in a reduction in the concentration of sucrose, glucose and fructose in the apoplast. Sugars were present in an apoplastic space occupying 12 and 17 cm3 M-2 of leaf area in healthy and infected tissue, respectively. Uptake of hexoses by intercellular hyphae is suggested as a cause of this reduction. The pH of apoplastic sap extracted from rust-infected leaves was increased to pH 7.3 from pH 6.6 in controls. The effect of a reduced apoplastic sugar pool and increased pH on export from infected leaves is discussed.