ELSEVIER Plant Science 118 (1996) II-23 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFE CiENCE Antifungal activity of tobacco osmotin has specificity and involves plasma membrane permeabilization Laura R. Abada, Matilde Paino D’Urzo”, Dong Liua, Meena L. Narasimhan”, Moshe Reuveni”, Jian Kang Zhua, Xiaomu Niua, Narendra K. Singhb, Paul M. Hasegawaa, Ray A. Bressan*a zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQ ‘Center for Pbmt Environmental Stress Physiology, Purdue University. II65 Horticulture Building, West Lofayette, IN 47907-1165, USA bDepartment of Botany and Microbiology, Auburn University, Auburn, AL 36849-5407. USA Received 12 December 1995; revised 9 April 1995; accepted 9 April 1995 zyxwvutsrqponmlkjihgfedcbaZYXW Abstract Osmotin protein is able to inhibit in vitro the growth of a number of unrelated pathogens. A survey of 31 isolates representing 18 fungal genera indicated that sensitivity may be determined at the genus level. Hyphal growth of Aspergillus flavus, Aspergillus parasitica, Rhizoctonia solani and Macrophomina phaseolina was highly resistant to osmotin whereas the growth of Bipolaris, Fusarium and Phytophthora species was very sensitive. Of all fungi tested Trichoderma lortgihrachiatum hyphal growth was most inhibited by osmotin treatment. Osmotin either induced spore lysis, inhibited spore germination or reduced germling viability in seven fungal species that exhibited some degree of sensitivity in hyphal growth inhibition tests. The species-specific growth inhibition was correlated with the ability of osmotin to dissipate the fimgal membrane pH gradient. Both growth inhibition and pH gradient dissipation by osmotin were sensitive to NaCl and other inorganic cations. Cells of T. longibrachiatum were insensitive to osmotin after plasmolysis, suggesting that the cell wall may be a component of the mechanism by which osmotin permeabilizes the plasma membrane and kills fungal cells. Keywords: Antifungal protein; Fusarium sp.; Osmotin; Pathogenesis-related protein; Phytophthora sp.; Trichoderma longibrachiatum Abbreviations: BSA, bovine serum albumin; DMO, 5,5- diiethyl-[2-‘*CJoxaxolidine-2,4ione; FCCP, carbonyl cyanide ptrifluoromethoxyphenylhydraxone; FDA, fluores- cein diacetate; PDA, potato dextrose agar; PDB, potato dex- trose broth; PR, pathogenesis-related. l Corresponding author. Tel.: +I 317 494 7858; fax: +l 317 494 0391; e-mail: becky_fagan@hort.purdue.edu zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA 1. htroduction Plants accumulate a number of antifungal pro- teins. Among these proteins are included the thionins, the ribosome-inactivating proteins, lipid- transfer proteins, 2S storage albumins, non- 0168~9452/96/$15.00 0 1996 Elsevier Science Ireland Ltd. All rights reserved PII: SO I68-9452(96)04420-2