Characterization and Localization of New Antifungal Cysteine-Rich Proteins from Beta vulgaris. Karsten M. Kragh. Danisco Biotechnology, Langebrogade 1, P.O. Box 17, DK-1001 Copenhagen, Denmark. John E. Nielsen, Klaus K. Nielsen, Susanne Dreboldt, and Jorn D. Mikkelsen. Danisco Biotechnology, Langebrogade 1, P.O. Box 17, DK-1001 Copenhagen, Denmark. MPMI 8: 424-434. Accepted 8 February 1995. Copyright 1995 The American Phytopathological Society.

Two novel antifungal proteins, AX1 and AX2, were isolated From leaves of sugar beet infected with Cercospora beticola. AX1 (MW = 5078 ± 3D) and AX2 (MW = 5193 ± 3D) were N-terminally sequenced and identified as monomeric, basic proteins consisting of 46 amino acid residues, of which eight are cysteines. Both AX proteins strongly inhibit growth of C. beticola and other filamentous fungi, but have little or no effect against bacteria. Based on primary sequence homology (24 to 46% identity), they are related to the superfamily of y-thionins, which have been isolated recently from seeds of monocotyledons and Brassicaceae. Specific antibodies were raised against the AX proteins after conjugation to diphtheria toxoid. Using immunoblotling and immunohistology, we detected high concentrations of AX proteins extracellu-larly in cell walls and in globular bodies around necrotic lesions in sugar beet leaves infected with C. beticola, suggesting that AX proteins are involved in anlifungal defense. Furthermore, AX proteins or serologically related proteins were delected in xylem, stomata, and stomatal cells as well as in sugar beet styles.