Fluxes and accumulation of ethirimol in haustoria of Erysiphe pisi and protoplasts of Pisum sativum

Abstract

SUMMARYIsolated purified fractions containing haustorial complexes and mesophyll protoplasts were used to investigate the relative affinities in vitro of the host‐parasite interface and host for the mildew specific fungicide, ethirimol. Compounds labelled with [14C] were used throughout this study.Isolated haustorial complexes accumulated fungicide against a concentration gradient and, in 15 min, to much higher concentrations than they accumulated glucose, sucrose, uracil, glycine, ethanolamine hydrochloride, inulin carboxylic acid, thiocyanate ions or uridine diphosphate glucose. Accumulation of ethirimol ceased after 30 min when the internal concentration was over twenty times greater than in the ambient medium. Similar quantities were absorbed in 15 min at pH 4.2 and 6–2. The quantities absorbed during 1 h incubation were directly related to the ambient concentration (4–400 μm). Ethirimol introduced into haustorial complexes was easily removed by washing; one third was removed in the first 5 min and only one sixth of the original remained after 3 h. Analysis of the kinetics of ethirimol efflux showed that it was located in two compartments within the complexes; thus it most probably entered the fungal cytoplasam.Ethirimol entered pea mesophyll protoplasts showing biphasic kinetics with considerable uptake in the first 30 min and a more gradual influx during the following 18 h. It was not accumulated against a concentration gradient until 6 h and after 18 h the internal concentration exceeded that of the ambient by only 1.74 fold.Extraction and chromatography showed that only small proportions of the ethirimol were degraded by haustorial complexes and protoplasts during the experimental periods.These in vitro experiments indicate competitive accumulation of ethirimol by the host‐parasite interface in vivo.