Coleoptile surface cuticle of barley is involved in survival and penetration of Blumeria graminis

Abstract

When portions of the cuticle of barley coleoptile surfaces were removed mechanically, prior to inoculation with Blumeria graminis, the tip cells of appressoria prematurely collapsed prior to attempted penetration. Mild chemical removal of the cuticle by ether also caused premature appressorial tip collapse. Recoating the cuticleless surface with exogenous cuticle decreased the frequency of collapse. By removing the cuticle mechanically or chemically, the available moisture on the coleoptile surface increased greatly, and exposure to this moist condition before attempted penetration was linked to premature appressorial tip collapse. However, when the cuticle of the coleoptile surface was removed thoroughly by rinsing in ether thrice for 5 min each, subsequent inoculation revealed no premature appressorial collapse, although moisture at the coleoptile surface was abundant. After removing the cuticle from the coleoptile surface mechanically, treatment of coleoptiles with 0.3 M mannitol greatly decreased the penetration attempts and the frequency of premature appressorial collapse, despite the abundant available moisture on the coleoptile surface. These results suggest that cuticle components of coleoptiles are needed for fungal penetration, and also protect the appressoria against excessive surface moisture when attempting penetration. © 2002 Elsevier Science Ltd.