The bud-inducing effect of the cytokinin N(6)-(Δ(2)-isopentenyl)-adenine (i(6)-Ade) was examined in the moss Physcomitrella patens growing in liquid culture. Under these conditions, buds could be induced on chloronemata as well as on caulonemata. By application of i(6)-Ade, bud-formation was accelerated in both types of tissue. The number of buds, their size and their site of development were dependent on the concentration of the cytokinin in the range of 10(-7) M to 10(-5) M. Moreover, the percentage of caulonema cells increased with a cytokinin concentration of 10(-5) M. These results indicate that chloronema cells may also function as target cells for exogenous cytokinins. The composition of proteins from caulonemata and chloronemata of two different species (P. patens and Funaria hygrometrica), grown on solid medium were compared. No differences could be detected between the protein patterns of caulonemata and chloronemata of the same species while between the two species the differences were obvious.

A wild-type (WT) strain of the moss Physcomitrella patens (Hedw.) B.S.G., two mutants derived from it (PC22 and P24), and a somatic hybrid, PC22(+)P24, were analysed. Staining of metaphases revealed 54 +/- 2 chromosomes in the somatic hybrid and 27 chromosomes in the wild type and the two mutants. Using flow cytometry (FCM), DNA contents were calculated to be 0.6 pg (WT, PC22), 1.2 pg (P24), and 1.6 pg (PC22(+)P24) per nucleus, respectively. Southern hybridization provided evidence for at least one family of highly repetitive DNA and, furthermore, revealed different amounts of repetitive DNA in the four genotypes. However, these sequences cannot account for the 100% increase in the nuclear DNA amount in mutant P24, relative to wild type. In FCM analyses every moss genotype generated just one single peak of fluorescence, indicating an arrest in the cell cycle during the daytime. Thermal denaturation of wild-type DNA revealed a G+C content of 34.6% for total DNA and 38.6% for plastid DNA. A cDNA library of 1.2 x 10(6) independent clones was established, from which sequences homologous to cab and rbcS, respectively, were isolated. These genes show significant homologies to those of higher plants, and, likewise, comprise multigene families. No restriction fragment length polymorphisms could be detected between the four moss genotypes using these cDNA probes.

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We have cloned and sequenced an 8.9-kb mitochondrial-DNA fragment from rapeseed (Brassica napus L.). The nucleotide sequence indicates a gene cluster that encodes four ribosomal proteins (S3, L16, L5, S14), two tRNA genes (trnD, trnK), and the 5' region of the cob gene. The arrangement of these seven genes is trnD-trnK-rps3-rpl16-rpl5-rps14-cob. The rps3 and rpl16 frames overlap by 131 bp. The rpl5 and rps14 genes are separated by a 4-bp spacer. A 1474-basepair intron is located in the rps3 gene. The tRNA(Asp) gene (trnD) is very similar to the corresponding gene from chloroplasts (cp-like-tRNA(Asp)). Gene-specific probes for each ribosomal protein gene, and for the cp-like-trnD, trnK and cob genes, hybridized to a common pre-mRNA of an estimated size of 10 kilobases, indicating that these seven genes may be expressed as a single transcription unit. The rps3-rpl16-rpl5-rps14 region of B. napus mtDNA may function as a ribosomal operon, similar to the S10 and SPC operons of Escherichia coli and to the ribosomal protein operon of the chloroplast genome from Euglena gracilis.