Effects of host-selective SV-toxin from Stemphylium vesicarium, the cause of brown spot of European pear plants, on ultrastructure of leaf cells

• Published in: Journal of phytopathology Vol. 148; no. 2; pp. 87 - 93
• Main Authors: Singh, P, Park, P, Bugiani, R, Cavanni, P, Nakajima, H, Kodama, M, Otani, H, Kohmoto, K
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Science, Ltd 01-02-2000
• Subjects: cell ultrastructure; culture filtrates; cytoplasm; Golgi apparatus; host plants; host range; host-specific toxin; leaves; mesophyll; mycotoxins; organelles; phloem; plant diseases and disorders; plant vascular system; plasma membrane; plasma membranes; plasmodesmata; Pyrus communis; Stemphylium vesicarium; SV-toxin; ultrastructural studies
• ISSN: 0031-9481; 0931-1785; 1439-0434
• DOI: 10.1046/j.1439-0434.2000.00474.x

Brown spot of European pear (Pyrus communis L.) caused by Stemphylium vesicarium (Wallr.) E. Simmons is a disease of economic importance in fruit-growing areas of southern Europe. The pathogen produces two host-specific SV-toxins (SV-toxin I and II) in culture filtrates, which selectively induce veinal necrosis only on susceptible cultivars. Ultrastructural changes in leaf cells treated with SV-toxin were observed by transmission electron microscopy. Plasma membrane modification specifically occurred at the plasmodesmata of susceptible leaf cells. The plasmalemmal invaginations appeared at both ends of the plasmodesmata 3 h after toxin treatment. Many Golgi vesicles were found in the cytoplasm close to or fused to the invaginated plasma membranes. Polysaccharide-like materials were released from the fused vesicles to extracellular spaces between cell walls and invaginated plasma membranes. Membrane fragments from modified plasma membranes and extended desmotubules from plasmodesmata were also observed at invaginated sites. No changes in ultrastructure were detected in other organelles. These results suggest that the target site of SV-toxin action may be on the plasma membranes of susceptible cells.