HIGH-FREQUENCY REGENERATION OF DIPLOIDS FROM APICAL END OF CULTURED HYPOCOTYL TISSUE IN TOMATO

Chromosome constitution was studied in plants regenerated from culture d hypocotyl tissue of tomato (Lycopersicon esculentum L.). A majority (85.3 %) of the regenerants from the apical end of hypocotyl pieces we re diploids. On the other hand, a high level (67.9 %) of polyploidy an d mixoploidy was found among the regenerants from the basal end. The b asal end contained, on average, 14 pg of IAA per hypocotyl piece, whil e no IAA was detected in the apical end. Only diploids were regenerate d from the basal end on medium supplemented with kinetin. These result s suggest 1) a high amount of endogenous auxin resulted from the basip etal polar transport plays a role in the induction of polyploidy and 2 ) kind of exogenous cytokinin affects the frequency of polyploidizatio n in the presence of auxin. Structural aberrations (deletions) were de tected in satellite chromosomes. Our results suggest the usefulness of hypocotyl tissues for in vitro production of plants with normal chrom osome constitution in tomato.