Differentiation of cell organelles during pollen formation?maturation and pollen tube elongation-focusing on the vacuolar system-

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Summary: The ultra-structural changes and behavior of vacuoles and related organelles(rER and Golgi bodies)during pollen development and maturation of Arabidopsis thaliana, and pollen tube elongation of Tradescantia reflexa will be described. In microspores just before generative cell formation, a large vacuole appeared which was made by fusion of pre-existing vacuoles and probably absorption of solutions. In the young pollen grain after the first mitosis, a large vacuole was divided into small vacuoles. The manner of division was not by binary fission and centripetally, but by the invagination of tonoplasts from one side to the opposite side of a vacuole. After the second mitosis, somatic typed vacuoles disappeared. In mature pollen grains just before germination, membrane-bound structures containing fine fibrillar substances(MBFs)appeared.Because of the expression of the pB vacuolar processing enzyme gene in these mature pollen grains, the MBFs were considered as storage vacuoles. In pollen grains from flowers in bloom, MBFschanged to lysosomal structures with acid phosphatases(lytic vacuole). They gradually increased in number andvolume, and decomposed the cytoplasm. A large vacuole at the base of elongating pollen tube may develope by membrane supply controlled with the ER and lipid granules, in addition to the absorption of water.
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