Fertilization in brown algae. V. Further investigations of lectins as surface probes

The binding of FITC- (fluorescein isothiocyanate), Au- and 125I-labelled lectins (conA, RCA120 (Ricinus communis agglutinin, MW 120 000) and FBP (fucose-binding protein from Lotus tetragonobolus)) to gametes of Fucus serratus and their physiological effects on fertilization have been studied. Results indicate that eggs strongly bind FITC- and Au-labelled conA and RCA120, whilst FITC-FBP binds strongly to sperm. All three iodinated lectins bound to eggs but this was apparently non-specific and similar in magnitude to the binding of iodinated bovine serum albumin. The results suggested the possibility of two distinct types of lectin receptor on egg surfaces: non-specific, highly abundant receptors and less abundant, specific receptors, possibly locally aggregated. All three lectins inhibit fertilization, FBP being the most effective.