A lipid transfer-like protein is necessary for lily pollen tube adhesion to an in vitro stylar matrix

Flowering plants possess specialized extracellular matrices in the female o rgans of the flower that support pollen tube growth and sperm cell transfer along the transmitting tract of the gynoecium. Transport of the pollen tub e cell and the sperm cells involves a cell adhesion and migration event in species such as lily that possess a transmitting tract epidermis in the sti gma, style, and ovary. A bioassay for adhesion was used to isolate from the lily stigma/stylar exudate the components that are responsible for in vivo pollen tube adhesion. At least two stylar components are necessary for adh esion: a large molecule and a small (9 kD) protein. In combination, the two molecules induced adhesion of pollen tubes to an artificial stylar matrix in vitro. The 9-kD protein was purified, and its corresponding cDNA was clo ned. This molecule shares some similarity with plant lipid transfer protein s. Immunolocalization data support its role in facilitating adhesion of pol len tubes to the stylar transmitting tract epidermis.