Abstract: The shoot-tips of papaya was used to study ultrastructural changes during cryopreservation by vitrification. Ultrastructure of cryopreserved cells was observed by using the transmission electron microscopy (TEM). The results showed that the plasmolysis became more and more severe during the pretreatment and dehydration after the shoot-tips were precultured. Meanwhile, it was able to improve the desiccation and freeze tolerance. Cellswere mainly damaged during the freezing and thawing process. Some cells were extensively damaged, including cell walls, cellmembranes and nucleus envelopeswere lethally injured during cryop reservation period, which may account for the death of some cells after cryop reservation. On the other hand, there were also many cells, which were basically similar to that of control material. The cells were able to repair such damage and regain their normal ultrastructure within three days in culture. They could survive and regenerate plantlets after cryopreservation.

Key words: Papaya (Carica papaya L), Cryopreservation, Vitrification, Ultrastructure