DYNAMICS OF VEGETATIVE CYTOPLASM DURING GENERATIVE CELL-FORMATION ANDPOLLEN MATURATION IN ARABIDOPSIS-THALIANA

Ultrastructural changes of pollen cytoplasm during generative cell for mation and pollen maturation in Arabidopsis thaliana were studied. The pollen cytoplasm develops a complicated ultrastructure and changes dr amatically during these stages. Lipid droplets increase after generati ve cell formation and their organization and distribution change with the developmental stage. Starch grains in amyloplasts increase in numb er and size during generative and sperm cell formation and decrease at pollen maturity. The shape and membrane system of mitochondria change only slightly. Dictyosomes become very prominent, and numerous associ ated vesicles are observed during and after sperm cell formation. Endo plasmic reticulum appears extensively as stacks during sperm cell form ation. Free and polyribosomes are abundant in the cytoplasm at all dev elopmental stages although they appear denser at certain stages and in some areas. In mature pollen, all organelles are randomly distributed throughout the vegetative cytoplasm and numerous small particles appe ar. Organization and distribution of storage substances and appearance of these small particles during generative and sperm cell formation a nd pollen maturation are discussed.