No abstract

Percentage of crude fiber, hull proportion, 1000‐seed weight, as well as oil and protein content of seeds were studied for the first time in genotypes of Brassica napus L. differing in seed color. Yellow and brown seeds exhibited a 3 % reduction in fiber and hull contents as compared to the commonly occurring black seeded forms. In addition, an average of 2.6 % higher oil and protein content was determined in brown vs. black seeds indicating that breeding for light seeded cultivars of rapeseed has great impacts on the chemical properties of the seed. As a rapid procedure of selection for low crude fiber content in rapeseed, the simple determination of hull proportions proved to be more adequate than the direct chemical analysis of the fiber which is commonly practised.

We compared Brassica campestris mitochondrial and chloroplast DNAs from whole plants and from a 2-year-old cell culture. No differences were observed in the chloroplast DNAs (cpDNAs), whereas the culture mitochondrial DNA (mtDNA) was extensively altered. Hybridization analysis revealed that the alterations are due entirely to rearrangement. At least two inversions and one large duplication are found in the culture mtDNA. The duplication element is shown to have the usual properties of a plant mtDNA high frequency "recombination repeat". The culture mtDNA exists as a complex heterogeneous population of rearranged and unrearranged molecules. Some of the culture-associated rearranged molecules are present in low levels in native plant tissue and appear to have sorted out and amplified in the culture. Other mtDNA rearrangements may have occurred de novo. In addition to alterations of the main mitochondrial genome, an 11.3 kb linear mtDNA plasmid present in whole plants is absent from the culture. Contrary to findings in cultured cells of other plants, small circular mtDNA molecules were not detected in the B. campestris cell culture.

We previously showed that the mitochondrial DNA (mtDNA) of a Brassica campestris callus culture had undergone extensive rearrangements (i.e. large inversions and a duplication) relative to DNA of the control plant [54]. In this study we observed that after continued growth, the mtDNA of this culture continues to change, with rearranged forms amplifying and diminishing to varying proportions. Strikingly similar changes were detected in the mtDNA profiles of a variety of other long- and short-term callus and cell suspension lines. However, the proportions of parental ('unrearranged') and novel ('rearranged') forms varied in different cultured cell mtDNAs. To address the source of this heterogeneity, we compared the mtDNA organization of 28 individual plants from the parental seed stock. With the exception of one plant containing high levels of a novel plasmid-like mtDNA molecule, no significant variation was detected among individual plants and therefore source plant variation is unlikely to have contributed to the diversity of mitochondrial genomes observed in cultured cells. The source of this culture-induced heterogeneity was also investigated in 16 clones derived from single protoplasts. A mixed population of unrearranged and rearranged mtDNA molecules was apparent in each protoclone, suggesting that the observed heterogeneity in various cultures might reflect the genomic composition of each individual cell; however, the induction of an intercellular heterogeneity subsequent to the protoplast isolation was not tested and therefore cannot be ruled out. The results of this study support our earlier model that the rapid structural alteration of B. campestris mtDNA in vitro results from preferential amplification and reassortment of minor pre-existing forms of the genome rather than de novo rearrangement. Infrequent recombination between short dispersed repeated elements is proposed as the underlying mechanism for the formation of these minor mtDNA molecules.

We have cloned several genes that were continuously induced by salt in our salt‐tolerant alfalfa (Medicago sativa L.) callus. These genes were not induced by 24 h salt stress in the parent salt‐sensitive cell line. To investigate the extent to which salt‐stress regulation of these genes is influenced by a program of tissue specific regulation we have characterized another one of the cloned cDNAs, pA18, determined the expression of the transcript it encodes and compared its salt‐inducible tissue‐specific expression in plants with MsPRP2, another single or low copy gene induced in the salt‐tolerant cells. While pA18 and MsPRP2 transcripts are similarly salt‐induced in callus, comparisons of tissue specific expression between these two genes demonstrate that regulated tissue specific expression can override salt inducibility of mRNA accumulation for individual genes.