Introduction: Fucus as a model system

Our understanding of the molecular basis of recognition and signalling systems in plant cells is very poor, and information and concepts are often uncritically extrapolated from studies on animal cell systems. Most higher plant systems suffer from disadvantages such as limited accessibility to plasma membrane-based receptors because of intervening cell walls, thus necessitating protoplasting, with potentially undesirable side effects. Responses to stimuli are often slow, rendering experimentation more difficult. The analysis of the molecular organisation of plant plasma membranes has in itself been fraught with considerable difficulty because of problems in obtaining sufficient quantities of pure material and the lack of truly unequivocal criteria for purity.

In studies on higher plant reproductive systems, interactions between egg and sperm cells are particularly difficult to follow because the events are embedded within tissues, and although male and female gametes can now be isolated from angiosperms (for a recent review, see Theunis et al., 1991), this is still fraught with considerable technical difficulty. In this context then, ‘simpler’ recognition systems presented by oogamous lower plants such as Fucus have much to offer. Naked gametes of these algae are released in large enough quantities to permit detailed biochemical studies. The interaction provides a rapid and simple bioassay permitting direct analysis of the activity of blocking agents such as antibodies, oligosaccharides, putative receptor fractions, etc. Reproductive mechanisms apart, studies on Fucus gametes provide information on the molecular architecture of natural protoplast surfaces (e.g. the existence of discrete subsets (glycoforms) of glycoproteins, types of oligosaccharide structure and presence of topographical domains) that will be of value in exploring the organisation and complexity of plant plasma membranes in general.