GAMETE RECOGNITION DURING FERTILIZATION IN A RED ALGA, ANTITHAMNION-NIPPONICUM

Fertilization in the marine red alga Antithamnion nipponicum is a high ly specific process involving non-motile male gametes, spermatia, and female receptive structures, carpogonia. FITC-lectin and Calcofluor wh ite ST labelling show that the outer cell walls of spermatia differ fr om vegetative cells in carbohydrate composition. Specific binding of t he lectins to spermatial walls was confirmed by lectin-gold labelling on thin sections. Gametic recognition in Antithamnion nipponicum is ba sed on the interaction of a surface carbohydrate on the spermatia with a surface carbohydrate receptor on the trichogynes. Spermatial bindin g to trichogynes is inhibited by pre-incubation with concanavalin A an d trichogyne receptors are blocked by the complementary carbohydrate a lpha-D-methyl mannose. The inhibitory effects of concanavalin A to spe rmatial binding of trichogynes is reversed by preincubation with alpha -D-methyl mannose. The combination of long spermatial appendages and a carbohydrate-carbohydrate receptor-based gamete recognition mechanism make fertilization in this species an efficient process.