Selection for diploid cells in suspension cultures of Haplopappus gracilis

Abstract

CHANGES in the number and structure of chromosomes of plant cells cultured in vitro are of common occurrence¹, and cell populations devoid of diploid karyotype have been reported^2–4. The chromosome number is known to become variable even in clones derived from single cells^5,6. In the case of Picea glauca Voss. (n = 21) callus cultures, a positive correlation between growth rate and chromosome number was observed⁷, which indicates a selection for polyploid cells. Only diploid cells were, however, observed in mitosis in suspension cultures of Haplopappus gracilis (Nutt.) Gray (n = 2) (ref. 2), Medicago sativa L. (n = 16) (ref. 8) and Crepis capillaris L. Wallr. (n = 3) (ref. 9). This could result from polyploid cells dividing less frequently than diploid cells, as diploid and polyploid cells differ physiologically. A strong selection for diploid cells was observed¹⁰ in Vicia hajastana Grossh. (n = 5) suspension cultures initiated from mature seeds. It therefore seemed likely that cell cultures of other plant species with a low chromosome number, n = 7 or less, would show a selection for diploid cells.