Poster: Pollination Biology

Abs # 373: Lily Pollen Tube Guidance by SCA (Stigma/stylar Cysteine-rich Adhesin), on the Stigma (Chemotropism) and in the Style (Adhesion)

Presenter:	Kim, Sunran , sunran@ucrac1.ucr.edu
Additional Authors	Park, Sang-Youl  (A)   Mollet, Jean-Claude  (A)   Lord, Elizabeth M (A)
Affiliations:	(A): Department of Botany and Plant Sciences, University of California, Riverside CA 92521

Pollen grains landing on the stigma produce pollen tubes which grow through a specialized extracellular matrix (ECM), the transmitting tract, to the ovule. The specific mechanism of guidance for pollen tubes through the ECM of the pistil is not known though many factors have been implicated. The growth of pollen tubes in the lily (Lilium longiflorum) style involves tube cell adhesion to transmitting tract cells (1, 2). Stigma/stylar cysteine-rich adhesin (SCA) is a peptide (~9 KD) isolated from the lily pistil (1) which functions with a pectic polysaccharide (2) in adhesion and guidance of pollen tubes in the stylar canal. SCA is expressed in abundance as well in the stigma. In lily, significant directional cues are essential on the stigma to facilitate pollen tube entrance into the hollow stylar canal. In a recent study, we confirm the existence of a diffusable chemotropic factor in the lily stigma and identify it as SCA. Our work demonstrates the chemotropic activity of SCA in two types of in vitro assay. In a reorientation assay, lily pollen tubes growing in random directions reorient their growth toward a gradient of SCA. In an in vivo mimic assay, pollen tube germination and growth is oriented toward a central source of SCA. SCA is the first chemotropic peptide to be identified in plants. (1) Park, S.-Y. et al. A lipid transfer-like protein is necessary for lily pollen tube adhesion to an in vitro stylar matrix. Plant Cell 12, 151-163 (2000). (2) Mollet, J.-C. et al. A lily stylar pectin is necessary for pollen tube adhesion to an in vitro stylar matrix. Plant Cell 12, 1737-1749 (2000).