Construction of Brassica B genome synteny groups based on chromosomes extracted from three different sources by phenotypic, isozyme and molecular markers.

The three B genomes of Brassica contained in B. nigra, B. carinata and B. juncea were dissected by addition in B. napus. Using phenotypic, isozyme and molecular markers we characterized 8 alien B-genome chromosomes from B. nigra and B. carinata and 7 from B. juncea by constructing synteney groups. The alien chromosomes of the three different sources showed extensive intragenomic recombinations that were detected by the presence of the same loci in more than one synteny group but flanked by different markers. In addition, intergenomic recombinations were observed. These were evident in euploid AACC plants of the rapeseed phenotype derived from the addition lines carrying a few markers from the B genome due to translocations and recombinations between non-homoeologous chromosomes. The high plasticity of the Brassica genomes may have been an powerful factor in directing their evolution by hybridization and amphiploidy.

Mapping the genome of rapeseed (Brassica napus L.). I. Construction of an RFLP linkage map and localization of QTLs for seed glucosinolate content.

A linkage map of the rapeseed genome comprising 204 RFLP markers, 2 RAPD markers, and 1 phenotypic marker was constructed using a F1 derived doubled haploid population obtained from a cross between the winter rapeseed varieties 'Mansholt's Hamburger Raps' and 'Samourai'. The mapped markers were distributed on 19 linkage groups covering 1441 cM. About 43% of these markers proved to be of dominant nature; 36% of the mapped marker loci were duplicated, and conserved linkage arrangements indicated duplicated regions in the rapeseed genome. Deviation from Mendelian segregation ratios was observed for 27.8% of the markers. Most of these markers were clustered in 7 large blocks on 7 linkage groups, indicating an equal number of effective factors responsible for the skewed segregations. Using cDNA probes for the genes of acyl-carrier-protein (ACP) and ß-ketoacyl-ACP-synthase I (KASI) we were able to map three and two loci, respectively, for these genes. The linkage map was used to localize QTLs for seed glucosinolate content by interval mapping. Four QTLs could be mapped on four linkage groups, giving a minimum number of factors involved in the genetic control of this trait. The estimated effects of the mapped QTLs explain about 74% of the difference between both parental lines and about 61.7 % of the phenotypic variance observed in the doubled haploid mapping population.

Mapping of a gene determining linolenic acid concentration in rapeseed with DNA-based markers.

Rapeseed ranks third in world oil production. An important breeding objective to improve oil quality in this crop is to lower linolenic acid concentration in the seeds. Previous reports indicate that the concentration of this acid in Brassica napus is determined by two or three nuclear genes. Using DNA-based markers, we have successfully mapped a gene determining linolenic acid concentration in an F2 population derived from crossing the cultivar 'Duplo' and alow linolenic acid line, 3637-1. Linolenic acid concentration in this population ranged from 2.1% to 10.5% with-amean of 6.2%. A RAPD marker, K01-1100, displayed significantly different frequencies between two subpopulations consisting of either high or low linolenic acid concentration individuals sampled from the two extremes of the F2 distribution. Marker K01-1100 segregated in a codominant fashion when used as an RFLP probe on DNA from individuals of this F2 population. The linolenic acid concentration means for the three resulting RFLP genotypes in the F2 population were 4.8% (homozygous 3637-1 allele), 6.4% (heterozygous), and 7.5% (homozygous 'Duplo' allele), respectively. It is estimated that this marker accounts for 26.5% of the genetic variation of linolenic acid concentration in this population.

Genetic interactions between wheat and rye genomes in triticale : 1. Cytological results.

Six primary triticale lines were produced from two advanced breeding lines of Triticum durum and three inbred genotypes of Secale cereale. The wheat and rye parents and the triticale derivatives were crossed in all possible combinations within each species group. Chiasma and univalent frequency of parents and hybrids were determined. The primary triticale lines had more univalents and less chiasmata per pollen mother cell than the corresponding wheat and rye parents together. The parental wheat F1 exhibited negative heterosis for chiasma frequency whereas all rye hybrids had much higher chiasma frequencies than their inbred parents. Triticale F1s generally showed lower chiasma frequencies and more univalents than their parents, but the degree of pairing failure was dependent upon which of the parental species within the triticale, wheat or rye, was in the heterozygous state. F1s with heterozygous wheat genome only showed the least reduction in chiasma number (presumably caused by gene actions within the wheat genome), while F1s with heterozygous rye genome showed high reduction in chiasma frequency and an increase in pairing failure (induced by negative interactions between the heterozygous rye and the wheat genome in triticale). A high correlation was found between the frequency of undisturbed pollen mother cells and the frequency of aneuploids in the subsequent generation. A higher number of aneuploids occurred in those populations which were heterozygous for the rye genome.

[Relations between chlorophyll content and chloroplast fine structure in a Chlorina mutant of Arabidopsis thaliana (L.) Heynh]. / Beziehungen Zwischen Chlorophyllgehalt und Chloroplastenstruktur in Einer Chlorina-Mutante von Arabidopsis Thaliana (L.) HEYNH.

In a chlorina mutant (ch 3) of Arabidopsis thaliana the total chlorophyll content was reduced to about 1/10 the amount of the green wild-type. At the same time the ratio of chlorophyll a/b was markedly increased. The electron microscopic analysis of the chloroplasts showed a considerable reduction in the membrane formation. Especially an inhibition of the grana differentiation was apparent, leading in some stages to an entirely abnormal thylakoid stacking. Depending on developmental as well as environmental conditions, chlorophyll content and chloroplast structure varied in the mutant in a different manner. These changes induced by endogenous and exogenous factors were comparatively investigated in order to reveal the relations between pigment deficiency and structural disturbances in the chloroplasts.The characteristically deviating a/b-ratio (i.e. the relative chlorophyll b deficiency) in the mutant was "normalized" under particular experimental conditions in two different ways: 1. Under the influence of continous illumination the relative chlorophyll b content increased together with the total amount of chlorophyll, obviously because a threshold of concentration of chlorophyll a was exceeded and thus a normal synthesis of chlorophyll b (from chlorophyll a?) became possible. 2. In cultures of seedlings under an 8:16 hr light-dark-succession as well as in old bleaching rosette leaves the "normalization" of the a/b-ratio was due to a relatively more rapid destruction of chlorophyll a.In electron microscopic cross sections the number, differentiation, and stacking of the thylakoids increased with an increasing total amount of the chlorophylls, while with decreasing chlorophyll content the membranes evidently disintegrated. However, no relation between chloroplast differentiation and absolute or relative chlorophyll b content could be established. Indeed, the proof that chlorophyll b is actually not necessary for the formation of a normal chloroplast structure was furnished by the electron microscopic analysis of another, chlorophyll b-less mutant (ch (1)), in the chloroplasts of which a membrane differentiation with typical grana piles could be demonstrated.