CHROMOSOME NUMBERS IN CULTURED PITH TISSUE OF TOBACCO

抄録

Excised pith tissues of tobacco (Nicotiana tabacum, 2n=48) were cultured on the Skoog's nutrient-agar medium containing 2.0 mg/l of indoleacetic acid (IAA) and 0.2 mg/l of kinetin. The first mitosis in parenchymatous cells of the cultured pith took place after 5-7 days of the culture. Chromosome number was already varied between 40 and 215. Frequencies of di- and tetraploid cells were only 12.5% and 17.5%, respectively. About 50% of the cells had more than 100 chromosomes. The in vivo pith tissue of tobacco seems to consist of cells with variable chromosome numbers. At the second mitosis taking place 1-2 days after the first mitosis a similar variation in chromosome numbers was observed, but the frequency of cells with more than 100 chromosomes was greatly reduced (22.7%).
Callus tissues, that were derived from a pith segment and subcultured for about one and a half years, grew vigorously on the medium supplemented with 3.0g/l casein hydrolysate. Nearly 70% of their cells had chromosome numbers between 77 and 96. Karyotype of the callus cell also differed from that of the normal root-tip cell. As to chromosome number, the cell population became much more uniform after a long period of subculture.