RESUMEN
Experimental and newly formed hybrids and polyploids generated by wide crosses usually show varying degrees of cytological instability. The spatial separation of parental genomes and uniparental chromosome elimination in hybrid cells has been reported in many hybrids from plants and animals. Herein, the behavior of parental genomes in intergeneric somatic hybrids between Brassica napus and Orychophragmus violaceus was analyzed using genomic in situ hybridization (GISH). In mitotic and meiotic cells, the chromosomes from O. violaceus were distinguished from B. napus by their larger size and staining patterns. In interphase nuclei of the hybrid, O. violaceus-labeled chromatin appeared as large heterochromatic blocks that were nonrandomly distributed at prophase, typically distributed toward one side of the nucleus. In pollen mother cells at prophase I of meiosis, O. violaceus chromosomes appeared as one or two deeply stained chromatin blocks that resolved into bivalents at a late stage, after bivalents from B. napus were visible. Thereafter, bivalents of O. violaceus congressed to the equatorial plate and segregated at anaphase I after those from B. napus. The different behavior of O. violaceus chromosomes in the hybrids indicates that they have differential condensation states at interphase and progress later through the cell cycle and meiosis than B. napus chromosomes. This difference in behavior may restrict or prevent the formation of bivalents of mixed genome origin. Differential gene expression of parental alleles including rDNA loci may contribute to their distinct cytological behavior and to the phenotype of hybrids.
Asunto(s)
Brassica napus/genética , Cromosomas de las Plantas/genética , Hibridación Genética , Cruzamientos Genéticos , Hibridación in Situ , Meiosis/genética , Mitosis , Polen/genética , PoliploidíaRESUMEN
The wild species Brassica fruticulosa Cyr. (FF, 2n = 16) is closely related to the cultivated Brassica species.Through interspecific reciprocal crosses between B. fruticulosa and three cultivated Brassica allotetraploids (AABB, AACC,and BBCC where A = 10, B = 8, and C = 9), four trigenomic hybrids (F.AC, 2n = 27; F.AB, 2n = 26; F.BC, 2n = 25;BC.F, 2n = 25) were produced. By chromosome doubling of respective hybrids, three allohexaploids (FF.AACC, 2n = 54;FF.AABB, 2n = 52; BBCC.FF, 2n = 50) were synthesized. In pollen mother cells (PMCs) of the trigenomic hybrids, 12 autosyndetic bivalents were detected within A, B, and C genomes but only one within F genome; 13 allosyndetic bivalents between any two genomes were observed, and a closer relationship of F and B genomes than F and A genomes or F and C genomes was revealed. The all ohexaploids showed a generally low but different pollen fertilities. The chromosomes in PMCs were predominantly paired as bivalents but some univalents and multivalents at variable frequencies were observed.The bivalents of homologous pairing for each genome prevailed, but all osyndetic quadrivalents and hexavalents involving any two genomes were observed, together with autosyndetic quadrivalents for A, B, and C genomes but not the F genome.The nondiploidized cytological behaviour of these allohexaploids contributed to their low fertility. The relationships between the genome affinity and meiotic behavior in these allohexaploids were discussed.
Asunto(s)
Brassica/genética , Genoma de Planta , Meiosis/genética , Polen/genética , Polinización/genética , Tetraploidía , Quimera/genética , Emparejamiento Cromosómico/genética , Segregación Cromosómica/genética , Cruzamientos Genéticos , Fertilidad/genéticaRESUMEN
With the dye and medicinal plant Isatis indigotica (2n = 14) as pollen parent, intertribal sexual hybrids with Brassica napus (2n = 38, AACC) were obtained and characterized. Among a lot of F1 plants produced, only five hybrids (H1-H5) were distinguished morphologically from female B. napus parents by showing low fertility and some characters of I. indigotica, and also by having different chromosome numbers. H1-H4 had similar but variable chromosome numbers in their somatic and meiotic cells (2n = 25-30), and H5 had 2n = 19, the same number as the haploid of B. napus. GISH analysis of the cells from H1 and H5 detected one I. indigotica chromosome and one or two chromosome terminal fragments. New B. napus types with phenotypic and genomic alterations were produced by H1 after pollination by B. napus and selfing for several generations, and by H5 after selfing. A progeny plant (2n = 20) was derived from H1 after pollination by I. indigotica twice and had a phenotype similar to a certain type of B. rapa, showing that hybrid H1 likely retained all chromosomes of the A genome and lost some of the C genome in parental B. napus. The reasons for the formation of the partial hybrids with unexpected chromosomal complements and for the chromosome elimination are discussed.