The Class III Pistil-Specific Extensin-Like Proteins of Nicotiana tabacum Show Arabinogalactan-Protein-Like Characteristics and are Non-Specifically Translocated Through Pollen Tube Walls In Vivo

Sexual plant reproduction initially involves a unique interaction between fast-growing pollen tubes and the complex fluid matrixes produced by the female reproductive organ during flower development. After pollen lands on a compatible stigma, pollen grains rapidly hydrate, germinate and form a pollen tube that grows by polarized tip extension. The secretory cells and intercellular matrix of the stigma are in continuum with the cells and intercellular matrix of the transmitting tissue present in the center of the style. Both the architecture of these tissues and the presence of specific components in the intercellular matrixes are thought to be directly involved in promoting an optimal and directional pollen tube growth during the progamic phase of compatible matings. The most abundant proteins present in the intercellular matrix are glycoproteins that share similarities with one or more classes of the traditional Hyp-rich glycoproteins (HRGPs) (Sommer-Knudsen et al 1998).