The role of genes influencing the corolla in pollination of Antirrhinum majus

Studies of pollination ecology have been hindered by an absence of biochemi cal information about the basis of polymorphism. Using model plants and mut ant lines described by molecular genetics may circumvent this difficulty. M utation of genes controlling petal colour and petal epidermal cell shape in Antirrhinum majus was previously shown to influence fruit set. White flowe rs set less fruit than magenta flowers and mutants with flat petal epiderma l cells set less fruit than flowers with conical cells. Here we analyse the causal pathway underlying this phenomenon through a study of floral charac teristics and bee behaviour. Results indicate that bees recognized plants w ith magenta conical-celled flowers at a distance and did not approach white flowers or magenta flat-celled flowers so frequently. Petal cell shape int eracted with colour in determining whether an approaching bee landed on a f lower within a plot and whether a bee landing on a flower would probe it. T he intrafloral temperature of flowers with conical petal cells was shown to increase with solar irradiance, unlike the intrafloral temperature of flow ers with flat petal cells. The difference in fruit set may reflect pollinat or discrimination between genotypes as a consequence of the effect of intra floral temperature on nectar quality and quantity.