Pollination in Lilium longiflorum and Arabidopsis thaliana: The Role of Adhesion Molecules in Pollen Tube Cell Movement in the Style

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0077886LordThe goals of this study of plant reproduction are to describe the interaction between the pollen tube, which carries sperm cells, and the style, which must be traversed by the pollen tube before the sperm can be released in the ovule to the egg cell. Two adhesion molecules have been identified from the style in lily that are responsible for pollen tube cell adhesion and guidance. These are the first adhesion molecules to be described in plants. In lily, the transmitting tract is a secreting epidermis that lines the stylar canal which empties into the ovary. Pollen tubes germinate on the secretory epidermis of the top of this canal, the stigma, and enter the style tracking the epidermal surface. These secretions can be isolated from dissected styles and used to make an in vitro stylar matrix which serves as an adhesion assay. When pollen tubes are added to this assay system, they adhere to each other and to the artificial stylar matrix. This assay was used to isolate two fractions from the stigma/stylar transmitting tract that are necessary for adhesion; one is a small cysteine rich 9kD protein and the other a large pectic polysaccharide (sugar). Neither of these molecules alone is adhesive; the combination of the two is necessary to induce pollen tube adhesion to other pollen tubes and to the stylar matrix.The hypothesis is that the adhesive molecules are involved both in guiding the tube cell to the ovule and in the mechanism of tube cell movement that accompanies this guidance. A multifaceted approach incorporating the tools of developmental, cell and molecular biology is being used to: 1) decipher the mechanism by which the 9kD protein in lily acts with a pectin to induce adhesion of the pollen tube to the stylar matrix. 2) develop an in vivo test for the 9kD protein's role in adhesion using both lily and Arabidopsis. 3) understand the role of the cytoskeleton in tube cell movement and adhesion. 4) study tip growth in both lily and Arabidopsis pollen tubes. The proposed work on adhesion molecules in the lily and Arabidopsis pollination systems addresses two major questions: 1) What is the mechanism of adhesion of the pollen tube cell to the stylar extracellular matrix? 2) How is adhesion related to tube cell movement and what is the role of tip growth? Adhesion molecules, other than the two we have described for pollination, have yet to be described in plants though adhesion is critical for plant development. There are few cases in plants where