II. 20. Nuclear DNA content in root and callus cells of haploid and diploid barley.
J. Maluszynska, E. Kurczynska, M. Gaj and M. Gaj, Department of Biophysics and Cell Biology, Department of Genetics, Silesian University, Katowice, Poland.
Cytophotometric measurements of the DNA content (Feulgen's procedure) were carried out in the root and callus cells of diploid (H. vulgare) and haploid barley obtained by crossing H. vulgare and H. bulbosum. From the comparison of nuclear DNA content in the meristematic cells of haploid and diploid roots it was found that in contrast to diploids, the range of DNA content in the haploid cells is very narrow and reaches only 2C value (Fig. 1). Nevertheless, the number of cells in different phases of the cell cycle is very similar.
Fig. 1. DNA content in root and callus cells of haploid and diploid barley.
On the other hand the callus obtained from the haploid embryo showed a very wide range of the DNA content in the cell nuclei. The number of G1 cells was very small in both types of callus. Another interesting difference between the DNA content in root and callus cells is the occurrence of the cells with a content of the DNA over 4C and even over 8C, particularly in the older callus cells. In our investigations, the polyploidy degree is much greater in the callus obtained from the haploid embryo than in the diploid one. Also, the process of endoreduplication in the callus cells from haploid tissues was much faster than in the cells of diploid callus. Twenty percent of cells had an increased level of DNA already after 25 days of the haploid callus culture. By contrast in the 12 weeks old diploid callus only 10% of cells had a DNA content over 4C. Polyploidization occurs not only in non-dividing cells, i.e. as a result of the endoreduplication, but an increase of the number of chromosomes was also observed in mitotic cells.
It should be emphasized that the number of chromosomes in the callus cells was not always a multiple of 7. It may be a result of irregular disjunction of the chromosomes in some anaphase cells.
The increase of DNA content or polyploidy of callus cells together with its age is a common phenomenon. Simultaneous cytological and cytophotometrical studies made it possible to investigate changes taking place in nuclei during the development from the primary explant to several week old callus of such species as Pelargonium (Bennici et al., 1968) or Hedera helix (Banks-Izes and Polito, 1980); yet they have not explained the reasons of the increasing of DNA content in the nuclei.
References:
Banks-Izeh, M.S., W.B. Polito. 1980. Changes in ploidy level in calluses
derived from two growth phases of Hedera helix L., the English ivy.
P1. Sci. Letters 18:161-167.
Bennici, A., M. Buotti and F. D'Amato. 1968. Nuclear conditions in haploid Pelargonium in vivo and in vitro. Chromosoma 24:194-201.
