Abstract:Numerous starch granules and lipid bodies stored in cotton ( Gossypium hirsutum L. ) pollen grain are mobilized at the time from pollen hydration to germination after pollination. The ultrastructural events during these processes were investigated. The starch granules were decomposed prior to the lipid bodies. From pollen hydration to gennination, the rough endoplasmie retieulum (RER) and dietyosomes with functional activities were mainly involved in its vegetative cytoplasm, in which large number of coated vesicles were contained. The most conspicuous feature occurred in the vegetative cytoplasm was the remarkable consecutive changes in the configuration of RER. As the pollen just hydrated, the RER eistemae became highly distended in various degree to form a net-work system and were further folded into large amount of RER pocket-like units, containing amyloplasts, lipid bodies and groups of coated vesicles. As the pollen continued to hydrate, the previously formed ER pockets disappeared and the ER eistemae were linked together to form a branched communicat- ing system. When the pollen started to germinate, the ER cisternae became shghtly dilated. Some of them were associated with each other to form a simple net-work system, and others remained as free vesicles. During the whole process, the coated vesicles, which always distributed in groups, were linked closely with the lipid bodies. As the lipid bodies decomposed, some of the coated vesicles lost their membranes and coalesced with the decomposed hpid bodies. Based on the close relationship between the dynamic changes of the pollen ultrastructures and the stages for pollen hydration to the initiation of germinate, the possible functions of the ER and coated vesicles are discussed.