Pollen from three S-genotypes of Nicotiana alata was grown in vitro in the presence of S-glycoproteins isolated from styles of the same three genotypes. Pollen germination was not affected by the presence of the S-glycoproteins, but pollen tube growth of all genotypes was inhibited. S2 pollen was preferentially inhibited by the S,-glycoprotein and S, pollen by the S3-glycoprotein. The S6-glycoprotein preferentially inhibited growth of both S2 and s 6 pollen over S3 pollen. Heat treatment

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... cally increased the inhibitory activity of the S-glycoproteins as inhibitors both of pollen germination and tube growth; after heat treatment, S-allele specificity of pollen tube inhibition was not detected.