Somatic cell cytology of the chromosome-eliminating, intergeneric hybrid Hordeum vulgare × Psathyrostachys fragilis

Abstract

In the hybrid H. vulgare .times. P. fragilis the 2 genomes were differentiated by length, the P. fragilis chromosomes being 31% longer by a difference in staining intensity of C-banded chromosomes (of possible use for exact localization of breakpoints), the H. vulgare chromosomes being the more heavily stained; by widely different C-banding patterns; and by the difference between N-banded H. vulgare and non-N-banded P. fragilis chromosomes. Only C-banding patterns identified each chromosome. Aneuploid cells had lost between 1 and 5 P. fragilis chromosomes. Loss of H. vulgare chromosomes is ascbribed to squashing. No haploid H. vulgare cell was observed. The P. fragilis chromosomes were characterized by diminished centric constrictions, suppression of nucleolar constrictions, and nucleolus activity, i.e., differential amphiplasty, and generally a peripheral location on the metaphase plate. The same characteristics are normally observed in hybrids producing haploids of H. vulgare, suggesting a common mechanism of chromosome elimination. Some cells had a side-by-side arrangement of genomes. The only effect of the hybrid condition on H. vulgare chromosomes was the formation of wider nucleolar constrictions and larger nucleolus organizer regions (NOR) than in parental H. vulgare, suggesting a compensational mechanism for nucleolus activity. The passage of H. vulgare chromosomes through the hybrid to the dihaploid did not influence chromosomal characteristics.