Isolation of a Plant Glycoprotein Involved with Control of Intercellular Recognition

A recognition molecule was isolated from stigmas of S-allele genotype S(2)S(2) of Brassica oleracea var. capitata L. After Sephadex chromatography, it eluted as a single symmetrical peak during diethylaminoethane-cellulose chromatography. A high degree of purity was affirmed by: sedimentation as a single peak during ultracentrifugation through 5 to 20% sucrose gradients; elution as a single peak from Sephadex G-100; visualization as a single band which stains with Coomassie blue and periodic acid Schiff reagent after electrophoresis on polyacrylamide gels. Other criteria supporting the conclusion that it is a glycoprotein are: (a) the highly purified preparation is anthrone-positive and has a Lowry protein to anthrone-positive carbohydrate ratio of 1.3; (b) the preparation contains arabinose, galactose, glucose, and mannose, although it is not precipitated by concanavalin A; (c) the immunological properties of the molecule are lost following protease treatment, and it has a molecular weight of 90,000 by Sephadex gel-filtration analysis and 54,500 by velocity sedimentation analysis.In vitro pretreatment of S(2)S(2) pollen with the post-diethylaminoethane-purified S(2) glycoprotein prevented the S(2)S(2) pollen from germinating on three classes of compatible stigmas: (a) mature stigmas of genotypes S(3)S(3) and S(8)S(8), which are non-self genotypes; (b) immature stigmas of genotype S(2)S(2), where incompatibility is not expressed; and (c) mature stigmas with a recessive S(2) allele. Pretreatment of S(3)S(3) and S(8)S(8) pollen with the S(2) glycoprotein did not interfere with their germination.