Differentiation of algal chemoreceptors. A comparative receptor study with two seaweed pairs: Cutleria multifida/Syringoderma phinneyi and Desmarestia aculeata/Ectocarpus siliculosus (Phacophyceae).

Gamete encounter in the reproduction of brown algae is supported by lures produced by the female cells. These signals are low-molecular-mass, volatile, olefinic hydrocarbons. Specific receptors on the motile male gametes recognize the pheromones at threshold concentrations as low as 6.5 pmol/l. The pheromones are possibly bound by dispersion and dipolar interactions. Tight fitting has to compensate for these weak contact forces. This causes strong chiral discrimination (relative affinities to enantiomeric lures 1:100). Structurally related messengers with identical substitution patterns and overall space filling are mutually distinguished in several species by means of altered topologies in their receptor mould. Responses to systematically varied synthetic bis-alkenyl-cyclopentene pheromones showed that the sensors of Syringoderma and Cutleria androgametes consist of a mosaic of attachment sites individually adapted to specific structural elements in the messenger molecule. They may be permutated to afford optimal binding. An alternative strategy: distinct reading of electron density combined with variation of sensitivity, brings about 'fidelity' in signal transmission by the alkylated cycloheptadiene pheromones in two species of Desmarestia and Ectocarpus. Inhibition of chemotaxis by ectocarpene is observed in Ectocarpus males in the presence of desmarestene, the lure of Desmarestia, and related parapheromones. This indicates complex interactions between different species of algae sharing a common habitat, in their defense of living space.