A Comparison of Soybean Agglutinin in Cultivars Resistant and Susceptible to Phytophthora megasperma var. sojae (Race 1)

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Abstract
The amount of soybean agglutinin (SBA) detectable by radioimmunoassay in seeds of resistant cultivars to P. megasperma var. sojae was approximately twice that of susceptible cultivars. SBA was preferentially released at earlier times (6-9 h) and in higher amounts in the imbibate from resistant cultivars as compared to susceptible cultivars. The lectin in the imbibate was immunologically identical to the seed lectin, indicating little or no proteolysis had occurred and was active in hemagglutination. Binding of fluorescein isothiocyanate-labeled SBA to mycelial cell walls could be abolished by adding N-acetylgalactosamine or galactose. Purified SBA at concentrations of 150-300 .mu.g inhibited mycelial growth by 50%, and the imbibate from cv. Govan (resistant) was more inhibitory than the imbibate from cv. Shore (susceptible) cv. Removal of SBA from the imbibate by affinity chromatography abolished the inhibition of mycelial growth, but the inhibition could be recovered from the eluant containing lectin.