Rice chromosomes were observed in protoplast-derived calli of two cultivars (japonica), and in plants regenerated from the calli of five cultivars (japonica). The chromosomal behavior was different between the two cultivars. In cv ‘Nipponbare’, most cells observed were stable in a diploid state (2n=24) during protoplast culture. In cv ‘Iwaimochi’, on the contrary, diploid, tetraploid, aneuploid and octoploid cells were present chimerically in calli. It is suggested that the appearance of polyploid cells in cv ‘Iwaimochi’, might have resulted in endopolyploidy during protoplast culture. In the forty-three regenerants observed in the four cultivars including ‘Nipponbare’ forty-two were diploids, while in cv ‘Iwaimochi’ tetraploid plants were regenerated at a higher frequency (6/11 plants), compared to the other four cultivars (1/43 plant). Therefore, the high frequency of tetraploid regenerants seems to correlate with the chimeric presence of diploid and tetraploid cells in calli.
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