Fig. 3

The transverse sections of ChF, PF and HPF PTs outside the pistil at similar distance from the tip showing the cell wall and cytoplasmic structures. a-d are entire transverse sections of PTs at about 40 μm from the apex showing the cell wall, and cytoplasmic features, including the sperm cell and sperm cell nucleus (a, c). The resolution of ChF/Epon section (a) is higher than ChF/LR white section (b). (e–j) are close-up views showing the cell wall layers: the inner (whitish/light grey) and outer (dark striated and fluffy) layers. A distinguishable transition layer (dark grey region) is seen between the outer and the inner layer in the HPF sections (h–j). The development of the cell wall layers is presented from the apical region (h) through sub-distal (about 25–35 μm from apex: [i]) to the distal about 40 μm toward the shank (j). The HPF section (h) of the apical cell wall where the callose layer (secondary/inner wall) is absent reveals that the primary cell wall of Arabidopsis PTs has two layers: an outer dark fluffy/hairy and an inner grey layer. In the shank where the secondary callose layer is formed (i and j), the three different wall layers are clearly visible. The bilayer of the plasma membrane is visible only in HPF sections. m = mitochondria, g = Golgi apparatus, er = endoplasmic reticulum, cw = cell wall, p = plasma membrane, icw = inner cell wall, ocw = outer cell wall, v = vacuole, sc = sperm cell, scn = sperm cell nucleus, tr = transition layer. Scale bar: (a–d) = 500 nm; (e–j) = 200 nm