Cell-cell recognition during fertilization in the red alga, Aglaothamnion oosumiense (Ceramiaceae, Rhodophyta)

Abstract

The binding of fluorescein isothiocyanate (FITC) conjugated lectins to gametes of Aglaothamnion oosumiense Itono during fertilization was studied by the use of confocal microscopy. The physiological effects of lectins and carbohydrates on gamete binding were also examined. Four different lectins, concanavalin A (ConA), soybean agglutinin (SBA), Dolichos biflorus agglutinin (DBA) and wheat germ agglutinin (WGA) bound to the surface of spermatia, but each lectin labelled a different region of the spermatium. SBA and DBA bound only to the spermatial appendages but ConA bound to all the spermatial surface except the spermatial appendages. WGA labelled a narrow region that connects the spermatial body and appendages. During fertilization, the ConA and WGA specific substances on the spermatial surface moved towards the area contacting the trichogyne and accumulated on the surface of the fertilization canal. Spermatial binding to trichogynes was inhibited by pre-incubation of spermatia with SBA or ConA, while trichogyne receptors were blocked by the complementary carbohydrates, D-glucose or N-acetyl-galactosamine, respectively. WGA and DBA as well as their complementary carbohydrates had little effect on gamete binding. The inhibitory effects of ConA and SBA were increased when the two lectins were applied simultaneously. The inhibitory effects of both lectins were partially reversed (to 80-90% of controls) by addition of complementary carbohydrates at the same time. The results suggested that SBA and ConA receptors on the spermatial surface are involved in gamete recognition in Aglaothamnion oosumiense.