Genome Multiplication in Cultured Protoplasts of Two Nicotiana Species

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Abstract
Chromosome number and nuclear behavior in mesophyll protoplasts isolated from haploid plants of Nicotiana plumbaginifolia and Nicotiana sylvestris were investigated during the process of plant regeneration. At the first mitotic division, a great majority of nuclei had the haploid number of chromosomes. Of these, 10.4% in N. plumbaginifolia and 3.5% in N. sylvestris contained diplochromosomes, indicating that endoreduplication occurred. In subsequent divisions, however, only two-chromatid chromosomes were present. One other abnormality observed during the first few days of culture was the formation of di- and multinucleate cells due to failure of cytokinesis and wall formation. Division of the di- and multinucleates was highly synchronized and fusion occurred as the chromatids of two or more nuclei moved to the same pole at anaphase. As a consequence of the occurrence of these abnormalities, the frequencies of haploids decreased and those of diploids and polyploids increased as culture proceeded. All protoplast-derived plants were diploid or polyploid and none was haploid.