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Physiology and Biochemistry

Purification and Partial Characterization of a Host-Specific Pathotoxin from Culture Filtrates of Septoria glycines. H. S. Song, Graduate research assistant, Department of Plant Pathology, University of Illinois, Urbana 61801; S. M. Lim(2), and J. M. Clark, Jr.(3). (2)Plant pathologist and professor, Crop Protection Unit, Agricultural Research Service, U. S. Department of Agriculture, and Department of Plant Pathology, University of Illinois, Urbana 61801, Present address: Department of Plant Pathology, University of Arkansas, Fayetteville 72701; (3)professor, Department of Biochemistry, University of Illinois, Urbana 61801. Phytopathology 83:659-661. Accepted for publication 17 February 1993. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1993. DOI: 10.1094/Phyto-83-659.

A host-specific pathotoxin isolated from culture filtrate of Septoria glycines caused typical symptoms of brown spot disease on cotyledons and leaves of soybean. This toxin was stable until autoclaving, but drying the toxin under flash-evaporation at 46 C in vacuo destroyed over 99% of the toxin activity. The toxin was purified approximately 16,000-fold by sequential carboxymethyl (CM)-cellulose treatment, diethylaminoethyl (DEAE)-cellulose chromatography, dialysis, gel filtration, and 5% charcoal treatment. The purified toxin appeared to be a polysaccharide because it was resistant to proteinase K, but oxidation with 35 mM IO₄^– and incubation with α-mannosidase, β-galactosidase, or ?-glucosidase markedly reduced toxin activity. The partial characterization of the purified toxin as a polysaccharide was supported by positive results with phenol-H₂SO₄ and carbazole tests and increased generation of reducing center analysis (detected by reduction with NaB³H₄) after acid hydrolysis. The combined results indicated that the toxin is an approximately 20,000-Da polysaccharide with a high content of uronic acids and perhaps low levels of mannose, galactose, and glucose.