Endoreduplication in leaf protoplasts of haploid Nicotiana plumbaginifolia cultured in vitro

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Abstract
When protoplasts isolated from the leaves of haploid plants of Nicotiana plumbaginifolia Viviani were examined cytologically during in vitro culture, a small fraction was found to contain diplochromosomes at the first mitosis. DNA measurements of freshly isolated protoplasts revealed that 92% contained G1 and 8% contained G2 haploid nuclei. The origin of the diplochromosomes was investigated by a simplified sister chromatid differential staining technique and autoradiography. Our results showed that nuclear division in the G1 protoplasts was normal, with each round of DNA replication being followed by mitosis. In the G2 protoplasts, however, one extra round of DNA replication often took place before the nucleus entered mitosis.Key words: Nicotiana plumbaginifolia, protoplast culture, endoreduplication, sister chromatid differentiation.