PLOIDY INSTABILITY OF EMBRYOGENIC CUCUMBER (CUCUMIS-SATIVUS L) CALLUS-CULTURE

Embryogenic callus cultures were established from immature cucumber (C ucumis sativus L.) embryos on E20A (Dumas de Vaulx et al. 1981) or MS (Murashige and Skoog 1962) media supplemented with 6-benzylaminopurine (BAP), alpha-naphthylacetic acid (NAA) and/or 2,4-dichlorophenoxyacet ic acid (2,4-D). Regeneration of plants was observed after a transfer to culture media either without growth regulators or supplemented with kinetin and NAA. Flow cytometry was employed to estimate DNA ploidy l evels. Most of cell nuclei in young leaf tissues were found in G(1) ph ase with 2C DNA content. Callus cultures were mixoploid with DNA conte nt ranging from 2C to 32C. The frequency of polyploid cells was increa sing with the age of culture and the polyploidization was accompanied by a gradual loss of regeneration ability. Plants regenerated from cal lus cultures were classified as diploid (57 %), tetraploid (18 %), oct oploid (4 %) and mixoploid (2n/4n, 4 %) and (4n/8n, 17 %). The results of this study confirmed a close link between the polyploidization and the loss of totipotency in vitro. Tetraploid plants obtained in this study have a potential to be used in interspecific crosses where their tetraploid status could help in overcoming existing breeding barriers due to differences in chromosome number.