Gamete recognition in angiosperms: model and strategy for analysis

Summary

Summary

Double fertilisation in angiosperms remains an enigma. The two male gametes from the pollen grain or tube fuse with the two female gametes in the embryo sac included in female tissues. Structural data in Plumbago showed that the plastid-rich male gamete preferentially fuses with the egg cell leading to the embryo (Russell, 1985). In maize BMS line, the male gamete bearing the non-disjointed B-chromosome preferentially fuses with the egg cell (Roman, 1948). Is this preferential fusion the result of recognition events at the gamete level? In order to answer this question, one needs to work with male and female gametes isolated from their gametophytes. For this purpose, we chose Zea mays (maize) as a plant model, because it offers large amounts of pollen and female flowers. We succeeded in isolating intact, viable and functional gametes (Dupuis et al., 1987; Wagner et al., 1989b; Roeckel, 1990). What, then, is the best strategy for intergametic recognition studies? We decided to construct a library of monoclonal antibodies directed against cell surface determinants of isolated male gametes. These immunological probes will be used to assess membrane dimorphism of the two male gametes of one pollen grain. We also attempted to develop an in vitro model of intergametic fusion. Experiments of fusion inhibition by monoclonal antibodies in this in vitro model would allow us to sort specific cell surface determinants involved in gametic recognition.