The content of cellulose in pollen tubes is remarkably low and the subcellular localization varies depending on the species ( Schlüpmann et al., 1994). This primary wall forms the outer layer of the cell wall in the pollen tube shank, where a secondary callose wall is deposited adjacent to the plasma membrane ( Geitmann and Steer, 2006). At the tip, the pollen tube wall is formed by a primary wall, mainly composed of newly synthesized pectins.
Pollen tube cell walls differ in both structure and function from those of somatic plant cells ( Geitmann and Steer, 2006). Pollen tube growth is driven by the rapid and continuous secretion of Golgi-derived vesicles, which dock and fuse with the plasma membrane at the pollen tube tip, providing new plasma membrane and cell wall precursors. Pollen tubes are fast-growing cells exhibiting polar growth at their apex ( Hepler et al., 2001). Within the ovary, the pollen tube enters a receptive ovule through the micropyle, and delivers the male gametes within the embryo sac (female gametophyte) to carry out fertilization.
Then, a pollen tube emerges through the pollen aperture, which is guided through the style by chemical clues from the female tissue to the ovary ( Johnson and Lord, 2006).
Sexual reproduction in seed plants begins when the pollen grain (male gametophyte) lands on the surface of a compatible stigma, where it hydrates and resumes its metabolism.
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