Pollen tube cells adhere to the wall surface of the stylar transmitting tra
ct epidermis in lily. This adhesion has been proposed as essential for the
proper delivery of the sperm cells to the ovule. An in vitro adhesion bioas
say has been used to isolate two stylar molecules required for lily pollen
tube adhesion. The first molecule was determined to be a small, cysteine-ri
ch protein with some sequence similarity to lipid transfer proteins and now
called stigma/stylar cysteine-rich adhesin (SCA). The second, larger, mole
cule has now been purified from style fragments and characterized. Chemical
composition, specific enzyme degradations, and immunolabeling data support
the idea that this molecule required for pollen tube adhesion is a pectic
polysaccharide. In vitro binding assays revealed that this lily stylar adhe
sive pectin and SCA are able to bind to each other in a pH-dependent manner
.