Summary: Extracellular material produced by (the apple scab disease organism) formed a tightly bound complex with silver. The silver complex (in aqueous solution) was taken up by whole detached apple leaves (cultivar MM 109) and was observed in the petiole cytoplasm as ribosome-like particles. Diffuse deposits of silver were observed in the cell walls.

The silver complex was also taken up by a proportion of the particles present in ribosome preparations made from apple-leaf tissues and from bacterial cultures. Such complexed ribosomes were apparently swollen by internal adsorption of the substance, some showing (in the electron microscope) a faint halo round the central core; the cleft between the sub-units was visible. Comparatively few ribosomes from showed strong affinity for the silver complex. The ribosomal particles were similar in most respects to the particles seen in treated leaf petioles. Silver-complexed particles prepared from isolated ribosomes were degraded by ‘Pronase’ to ragged skeletal remnants which were further digested by pancreatic ribonuclease. The latter enzyme did not attack intact particles.

The results support evidence from earlier work that the progress of the disease is partly controlled by the effects of fungal pigments on host solute transport (possibly mediated via the cell-wall membrane system) and on hormone-controlled plant metabolism and photosynthesis (via the protein-synthesizing system).


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