Variation in nuclear DNA content of isonicotinic acid hydrazide-resistant cell lines and mutant plants of Nicotiana tabacum.

Isonicotinic acid hydrazide (INH)-resistant lines of Nicotiana tabacum have been maintained in callus culture for six years and mutant plants have been regenerated from a number of these lines. This study examines variations in DNA content in nuclei of several of these callus cultures, regenerated plants, and secondary callus from the regenerated plants. The lines selected for study include three easily regenerated lines (I 21, I 24, and I 9) and two lines of poor regenerating capacity (I 1 and I 18). Two of the regenerating lines eventually led to fertile plants and the third produced only sterile plants. In general, the range of total nuclear variability was not as high as anticipated from other studies of long-term tobacco callus cultures. The majority of nuclei in all the distributions were between 3 and 20 pg, and the most frequently encountered distributions concentrated in the 7-18 pg region corresponding to 2-5C by our estimate of the C value for tobacco. Distributions were not identical for plants regenerated from the same culture simultaneously, and the nuclear DNA content of secondary callus cultures from one of the plants examined did not reflect the quantitative DNA pattern of the plant from which it was derived. The greatest degree of variability and highest DNA content for individual nuclei were observed in the primary callus of the poorly- and non-regenerating lines. The variability in DNA content was not associated with the INH-resistant trait.