Fig. 6

Longitudinal section of HPF PTs outside the pistil showing different regions of the cytoplasm. The cyto-architecture across the pollen tube apical region (a, b), the male germ unit region (c, d) and the large vacuolar region (e, f). (a) and (b) show two longitudinal sections of the same PT about 200–250 μm apart, providing a glimpse into the 3D ultrastructure. The cell wall in the apical region has different thicknesses across the length. An apical cytoplasmic-clear region within 4–5 μm of the apex is full of small vesicles; large organelles are only present distally. In (c) a sperm cell is distinguished from the tube nucleus by the inclusion of their nucleus within membrane delimited cytoplasm. d is a close-up view of the marked area in (c) showing a cytoplasmic extension of sperm cell I (sc1) connecting to the tube nucleus (tn); microtubule arrays (arrowheads) can also be seen in this region. In (e) and (f), the large central vacuole is shown. f is a close-up view of the marked area in (e) showing the sites of vacuole integration (arrows); equally the inner callose, the transition zone, and outer fibrous layers of the cell wall are visible. m = mitochondria, g = Golgi apparatus, er = endoplasmic reticulum, cw = cell wall, v = vacuole, scn = sperm cell nucleus, sc1 = sperm cell 1, sc2 = sperm cell 2, tn = tube nucleus. Scale bars = 1 μm