19:	A lipid transfer protein (LTP) is required for adhesion in lily pollination.

Authors:	Park, Sang-Youl(A)Jauh, Guang-Yuh(B)Mollet, Jean-Claude(A)Eckard, Kathleen , J.(A)Nothnagel, Eugene , A.(A)Walling, Linda , L.(A)Lord, Elizabeth, M.(A)
Affiliations:	(A): Department of Botany and Plant Sciences, University of California, Riverside, CA 92521 (B): Institute of Biological Chemistry, Washington State University, Pullman, WA 99164
Presenter:	Park, Sang-Youl , sypark@citrus.ucr.edu

Flowering plants possess specialized extracellular matrices (ECMs) in the female organs of the flower. The pollen tube, carrying the sperm cells, grows into the style and toward the ovary via these ECMS, collectively referred to as a transmitting tract. The transport of the pollen tube cell and the sperm cells involves a cell adhesion and migration event in species like lily that possess a transmitting tract epidermis in the stigma, style and ovary. Molecules involved in adhesion of the pollen tube to the transmitting tract cells in lily have been studied. There are at least two molecules in the stylar extracellular matrix (ECM) involved in pollen tube adhesion; one a small molecule (<30 kD) and another a large molecule (>100 kD). The small molecule has been purified from the lily stigma/style using an in vitro adhesion assay and the cDNA corresponding to the protein has been cloned. The small molecule is highly homologous to plant nonspecific lipid transfer proteins (nsLTPs). By using an immunogold labeling method, the nsLTP has been localized to the transmitting tract epidermis of the style, where pollen tubes adhere in the stylar ECM, and to the walls of in vivo grown pollen tubes. Plants nsLTPs are so named because of their ability to transfer lipids from one organellar membrane to another in vitro, but the fact that they are secreted molecules localized to the ECM and not cytoplasmic, as initially expected, means their function is as yet unknown in plants. Our bioassay system for lily pollen tube adhesion to an artificial stylar ECM shows that a nsLTP in the lily stigma/stylar ECM functions in cell adhesion.