II. 28 Aneuploidy and chromosome breakage in root tip cells of plants regenerated from microspore callus.
G. Mix and B. Foroughi-Wehr, Department of Plant Genetics, Gesellschaft für Strahlen- und Umweltforschung, mbH, 8059 Grünbach 1, West Germany
This report gives a brief review of the cytological abnormalities observed in root tip cells of regenerated plants from microspore-callus of Hordeum vulgare. A total of 240 plants with different phenotypes (Mix et al., 1978) were studied. For cytological studies, root tips were fixed and prepared as described previously (Foroughi-Wehr et al., 1976). The chromosome counts were carried out several times during the growth period and it turned out that in the individuals studied the proportion of the various chromosome numbers did not change throughout the lifetime (Mix et al., 1978).
About 30 percent of the plants showed abnormalities in their root tip cells, such as aneuploid cells and chromosome breaks. The chromosome numbers in aneuploid root tip cells ranged from 3 to 26. The frequencies of different aneuploid cells are shown in Fig. 1. Most of the cells had chromosome numbers in the range of 8 to 13 whereas cells with 15 to 26 relatively rare. One of the reasons for the high percentage of aneuploid cells obviously is the frequent occurrence of multipolar mitosis, producing daughter nuclei with aneuploid chromosome numbers (Fig. 2c).
Fig. 1. Frequency of aneuploid root tip cells with different chromosome numbers
Further observations indicated that the occurrence of aneuploid chromosome numbers is obviously closely related to the occurrence of chromosome fragments (Fig, 2a). The chromosome breakage causes a number of structural alterations.
In general, chromosome breaks and their cytological consequences such as di- and tricentric chromosomes (Fig. 2b), ring chromosomes, anaphase bridges and chromosome fragments (Mix et al., 1978) occurred frequently.
The observations described indicate that a plant regenerated from microspores via callus does not necessarily need to be stable haploid This means that new cytological problems arise and it is important to find out the reason for the abnormalities described.
References:
Foroughi-Wehr,B., G. Mix, H. Gaul, H.M. Wilson. 1976. Plant production from cultured anthers of Hordeum vulgare L. Z. Pflanzenzüchtung 77, 198-204.
Mix, G., H.M. Wilson, B. Foroughi-Wehr. 1978. The cytological status of plants of Hordeum vulgare L. regenerated from microspore callus. Z. Pflanzenzüchtung, in press.
