Effects of Nuclear Genomes on Anther Development in Cytoplasmic Male Sterile Chicories (Cichorium intybus L.): Morphological Analysis

Figure 4

Anther wall and pollen development. (a) Stage 4: round stamen with three germ layers (L1, L2, and L3). (b)-(c) Stage 5: oval shaped anther. The four-locule anther structure established by division of archesporial cells in the four corners (arrow heads). Connectivum differentiation (). (d) Stage 6: under epidermis (ep) the primary sporogenous (psc) and primary parietal cells (ppc) are formed. (e) Stage 7: early pollen mother cell (pmc). Two layers form the secondary parietal cells (spc). (f) Stage 8: late pollen mother cells. Four distinguishable anther layers: epidermis, endothecium (en), middle layer (ml), and tapetum (ta). Inset: row of microsporocytes in a longitudinal section at this stage. (g) Stage 9: meiocytes enter meiosis and tapetum enlarges and becomes vacuolated (). (h) Stage 10: tetrads of microspores (te). In some tapetal cells two nuclei are visible () (i) Stage 11: release of microspores and tapetal protoplasms intrusion in the locule (). (j) Stage 12: uninucleate vacuolate pollen grain. The septum starts to disintegrate (arrow). (k) Stage 13: binucleate pollen grain (gn: generative nucleus and vn: vegetative nucleus). Endothecium expansion and cell wall thickening (arrow heads). The tapetal cell remains are still visible individually in the locule wall (). (l) Stage 14: bicellular pollen. (gc: generative cell and vc: vegetative cell). The septum is almost fully disrupted (). (m) Magnification of the connectivum region at stage 14 showing U-shaped secondary thickenings (arrows). (n) Magnification of the locule wall showing expanded endothecium cells and their thickened cell walls (arrow heads). Inset: starch grains in the pollen stained by PAS. (o) Stage 15: tricellular pollen. Anther walls have completely opened. Inset 1 shows carbohydrates in the pollen grain stained with PAS and in inset 2 the mature pollen grain with the three nuclei (arrow heads) colored with DAPI. Bars 20 μm.

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