Plant Science Letters, 9 (1977) 121--128 121 © Elsevier/North-Holland Scientific Publishers, Ltd. THE MYCOTOXIN PATULIN INHIBITS RESPIRATION OF HIGHER PLANT CELLS JOSEPH CARMINE POLACCO and DAVID C. SANDS* Genetics Department and Department of Plant Pathology, Connecticut Agricultural Experiment Station, New Haven, Conrt 06504 (U.S.A.) (Received October 18th, 1976) (Revision received and accepted December 8th, 1976) SUMMARY The mycotoxin patulin inhibits germination of apple pollen in vitro, and the growth of cultured soybean cell suspensions. Patulin inhibits pollen respiration by 50%. In soybean cultures both salicylhydroxamic acid (SHAM), an inhibitor of the cyanide-insensitive mitochondrial electron transport which is alternative to cytochrome electron transport, and patulin inhibit respiration 50--60%. In contrast KCN stimulates soybean cell respiration. Patulin and SHAM appear to compete for the same site(s) of inhibition since patulin is not as inhibitory when respiration is previously inhibited by SHAM. Patulin inhibits the entry of phenylalanine and threonine into soybean cells. Phenylalanine transport appears to be energy coupled since it is inhibited by the uncoupler 2,4-dinitrophenol (DNP) and by a combination of the respiratory inhibitors KCN plus SHAM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . INTRODUCTION Patulin, an unsaturated lactone (4-hydroxy-4H-furo-[3,2C] pyran-2(6H)-one), is a mycotoxin which has antibiotic, carcinogenic and mutagenic properties [1] and is produced by several species of Aspergillus [2,3], Penicillium [4] and by Bysochlamys nivea [5]. Patulin has been implicated as a toxic product of wheat~straw decomposition and as contributing to poor germination when wheat is sown in soil containing wheat straw debris [6]. Because of its possible agronomic significance we have sought evidence for the site(s) of * Present address: Department of Plant Pathology, Montana State University, Bozeman, Mont. 59715 (U.S.A.). Abbreviations: 2,4-D, 2,4-dichlorophenoxyacetic acid; DNP, 2,4-dinitrophenol; IAA, indoleacetic acid; 2-IP, N6-(~ '-isopentenyl) adenine; MES, 2-(N-morpholino)-ethane- suifonic acid; SHAM, salicylhydroxamic acid.