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Physiology and Biochemistry

Interaction of Rhizoctonia spp. with Peanut Lectin. Jane R. Leatherman, Former graduate assistant, Department of Plant Pathology, University of Florida, Gainesville 32611, Present address: Department of Plant Pathology, University of Missouri, Columbia 65211; Steven G. Pueppke, former associate professor, Department of Plant Pathology, University of Florida, Gainesville 32611. Phytopathology 75:598-602. Accepted for publication 19 December 1984. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/Phyto-75-598.

Cotyledons of 9-day-old peanut seedlings were inoculated with Rhizoctonia solani and harvested at 3-day intervals until 18 days postinoculation. Protein was extracted from infected and control cotyledons in phosphate-buffered saline (PBS). Peanut lectin (PNL) subsequently was purified from the protein extracts by affinity chromatography. Each cotyledon contained about 18.7 mg of PBS-soluble protein and 145 μg of PNL at inoculation. Protein and PNL concentrations decreased at similar rates in infected and control cotyledons, such that by 18 days postinoculation, each cotyledon contained 4- 5 mg of protein and 3- 4 μg of PNL. The PNL preparations were subjected to polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate, and isolectins were resolved by isoelectric focusing in polyacrylamide gels. Although basic isolectins disappeared most rapidly, infection did not substantially alter the subunit molecular weight of the lectin or isolectin profiles. Fluorescent-labeled PNL bound hapten-specifically to young hyphae of R. solani and R. zeae (nonpathogenic to peanut), but physiological concentrations of the lectin did not inhibit the in vitro radial growth or dry weight increase of either fungus. A new acidic isolectin appeared in liquid cultures of R. solani that had been amended with PNL, and the amount of basic isolectin 6 decreased. Alteration of PNL isolectins by liquid cultures of R. zeae was much less pronounced. After 6 days, recovery of PNL from liquid cultures was 40% (uninoculated controls), 5% (inoculated with R. solani), and 0.2% (inoculated with R. zeae) of the amount recovered at time 0. We conclude that PNL is of questionable significance in the interaction of Rhizoctonia spp. with peanut cotyledons.

Additional keywords: Arachis hypogaea.