Ultrastructural characteristics ofBetula pendulatapetum and pollen grains after rapid freezing and freeze-substitution

Using rapid fixation and freeze substitution method, the ultrastructure of the cytoplasm, including the membrane system, of Betula pendula pollen is well preserved. The cytoplasm of Betula pollen appears compact and organelles such as Golgi and RER are not yet demonstrating any secretory activities. The cytoplasm streaming is not established because the pollen grains are not completely hydrated and the microfilaments are still polymerized in bundless. The cytoplasm of the generative cell is well preserved including the cell wall like structure and cytoskeletal complexes present in the cell. Moreover the application of rapid freeze fixation of microspores and pollen grains of Betula showed clear details of ultrastructure of the Zwischenkorper (Z) at the aperture sites and the Z-layer (ZL) between the apertures. They are mainly composed of dense helical units that extend from the plasmalemma. Rapid freezing improves to a great extent the fixation of the delicate cell structure of the tapetum. After freeze f...