Abstract:

The ultrastructure of pollen development in Beta vulgaris was investigated by transmission electron microscopy. Cytoplasm reorganization occurred during meiosis of microsporocytes and resulted in decreased ribosomes and regular changes of plastids and mitochondria. Telophase shows an organelle band between two nuclei. The function of the organelle band is similar to that of the cell plate that separates the cytoplasm into two parts. The tetrasporophyte wrapped by callose is of simultaneous type. Depositions of wall started at the late tetrad stage, and the exine was fundamentally completed by the late microspore stage. The monokaryotic microspore has a large nucleus and abundant organelles. Development of 2-celled pollen is accompanied by changes in the generative cell wall, which showed no plasmodesmata. Mature trinucleate pollen grains showed a vegetative cell and two sperm cells, each sperm cell separated from the vegetative cytoplasm by two continuous membranes that enclosed the cytoplasm and nucleus. Sperm was a naked cell and had a short caudal. Generative cell and sperm showed no plastids.