Factors influencing changes in ploidy and nuclear DNA levels in cells from normal,crown-gall and habituated cultures ofHelianthus annuus L.

Summary Normal and crown-gall tissue cultures ofHelianthus annuus were initiated from diploid cells of the stem and diploid tumour cells respectively. For the first 16 months both normal and tumour isolates remained predominantly diploid, but subsequently many isolates showed varying degrees of polyploidy. It was concluded that cultures fromH. annuus were initially stable, but that this stability was lost during prolonged culture. There was no evidence that tumour or habituated isolates had any greater tendency to become polyploid than normal isolates grown in similar conditions. Furthermore normal isolates initiated and maintained on media supplemented with different auxins (2,4-dichlorophenoxyacetic acid, 1-naphthaleneacetic acid, 3-indoleacetic acid and 4-chloro-2-oxobenzothiazolin-3-yl acetic acid) remained chiefly diploid during the first 13 months in culture, but subsequently became polyploid. In addition, increasing the concentration of kinetin in the medium had no obvious effects on the occurrence of polyploid nuclei.