Prevention of a plant disease by specific inhibition of fungal polyamine biosynthesis

La DFMO (DL-alfa-difluoremetilornitina) puede proteger plantas de frijol cv. Pinto contra la infeccion por uredosporas del hongo de la roya, Uromyces phaseoli raza O. Se asperjaron hojas unifolioladas de plantulas de 10 dias de edad cultivadas en invernadero, con 400 microlitros de DFMO/hoja a varias concn. en Tween 20 al 0.01 por ciento a pH 7.0 antes o despues de la inoculacion con uredosporas de Uromyces. Despues de 16 h en la oscuridad en camara humeda para facilitar la germinacion de esporas, las plantas se trasladaron al invernadero, se distribuyeron al azar y se examinaron por lesiones locales 7 dias despues. Todas las concn. de DFMO de 0.50 milimolar o mayores dieron proteccion total contra el patogeno; a concn. menores, los tratamientos con DFMO en posinoculacion generalmente fueron mas efectivos que en preinoculacion. La aparicion de lesiones en plantas tratadas con menores concn. de DFMO se retraso 2-6 dias. La DFMO tambien confiere proteccion a partes no asperjadas de plantas tratadas, lo cual indica la translocacion de algun efecto protector desde las areas asperjadas. La DL-alfa- difluorometilarginina, un inhibidor analogo de la descarboxilasa de arginina, enzima retardatriz en una via alternativa de la biosintesis de poliamina en plantas superiores, no confiere proteccion incluso a 5 milimolar. Esto enfatiza que la descarboxilasa de ornitina es el locus bioquimico de escogencia para la prevencion de enfermedades vegetales mediante la inhibicion del metabolismo de la poliamina. (RA-CIAT) spa

The DFMO (DL-alpha-difluoromethylornithine) can protect plants of bean cv. Pinto against infection by uredospores of the bean rust fungus, Uromyces phaseoli race O. Unifoliolate leaves of 10-day-old greenhouse-grown seedlings were sprayed with 400 microliters DFMO/leaf at various concn. in 0.01 percent Tween 20 at pH 7.0 before or after inoculation with uredospores of Uromyces. After 16 h in darkness in dew chambers to facilitate spore germination, plants were transferred to the greenhouse, arranged randomly, and examined for local lesions 7 days later. All concn. of DFMO 0.50 millimolar or higher gave complete protection against the pathogen; at lower concn., postinoculation treatments with DFMO were generally more effective than preinoculation. The appearance of lesions on plants treated with lower concn. of DFMO was retarded 2- 6 days. DFMO also confers protection on unsprayed parts of treated plants, indicating the translocation of some protective effect from sprayed areas. DL-alpha- difluoromethylarginine, an analogous inhibitor of arginine decarboxylase, which is the rate-limiting enzyme in an alternative pathway for polyamine biosynthesis in higher plants, confers no protection even at 5 millimolar. This emphasizes ornithine decarboxylase as the biochemical locus of choice for the prevention of plant diseases by inhibiting polyamine metabolism. (AS) eng