Genetic Variation and the Reproduction of Cordylanthus maritimus ssp. maritimus to Sweetwater Marsh, California

This study evaluated the genetic consequences of a reintroduction of the endangered annual plant Cordylanthus maritimus ssp. maritimus to Sweetwater Marsh (San Diego County, California). A survey of 21 enzyme loci in natural populations revealed that genetic diversity is very low and is primarily found as rare alleles at a few loci, making this species especially susceptible to the loss of alleles and heterozygosity through genetic drift. The reintroduction was performed in 1991 and 1992 by sowing seeds (collected from Tijuana Estuary) in numerous small patches of suitable habitat. For this study, leaf tissue was collected from all plants in all patches during flowering in 1995 and surveyed for genotype at the three enzyme loci that are polymorphic at Tijuana Estuary. Rare alleles were absent in 27 out of 30 patches for Pgm-1, in 17 out of 30 patches for Pgm-2, and in 10 out of 11 patches for Mdh-1. In all, half of the patches lacked any rare allele. Rare alleles tended to occur in patches with few individuals. Overall rare allele frequency was lower than in the colonies from which seeds were collected at two of the three loci, and heterozygosity was reduced. The Sweetwater Marsh population is at risk of losing most of its genetic variation at enzyme loci through the extinction of patches with few individuals. Future reintroduction attempts should attempt to create contiguous sets of patches or to periodically reseed existing patches to reduce the loss of genetic variation.     

What are mycoplasmas: the relationship of tempo and mode in bacterial evolution

In phenotype the mycoplasmas are very different from ordinary bacteria. However, genotypically (i.e., phylogenetically) they are not. On the basis of ribosomal RNA homologies the mycoplasmas belong with the clostridia, and indeed have specific clostridial relatives. Mycoplasmas are, however, unlike almost all other bacteria in the evolutionary characteristics of their ribosomal RNAs. These RNAs contain relatively few of the highly conserved oligonucleotide sequences characteristic of normal eubacterial ribosomal RNAs. This is interpreted to be a reflection of an elevated mutation rate in mycoplasma lines of descent. A general consequence of this would be that the variation associated with a mycoplasma population is augmented both in number and kind, which in turn would lead to an unusual evolutionary course, one unique in all respects. Mycoplasmas, then, are actually tachytelic bacteria. The unusual evolutionary characteristics of their ribosomal RNAs are the imprints of their rapid evolution.     

Quantitative Untersuchungen zur Brut des Teichrohrs?ngers (Acrocephalus scirpaceus Hermann)

Ohne Zusammenfassung     

Changes in viscoelastic properties of rat lung parenchymal strips with maturation.

The lung extracellular matrix changes rapidly with maturation. To further our understanding of the mechanisms underlying lung tissue mechanics, we studied age-related changes in mechanical properties in lung parenchymal strips from baby (10-15 days old), young ( approximately 3 wk old), and adult ( approximately 8 wk old) rats. Subpleural strips were cut and suspended in a fluid-filled organ bath. One end of the strip was attached to a force transducer and the other to a servo-controlled lever arm. Measurements of force (F) and length (L) were recorded during sinusoidal oscillations of various amplitudes and frequencies. Resistance modulus (R) and elastance modulus (E) were estimated by fitting the equation of motion to changes in stress (T) and stretch ratio (lambda). Hysteresivity (eta) was calculated as follows: eta = (R/E)2pif, where f is frequency. Slow-cycling T-lambda curves were measured by applying a constant slow length change. Finally, quasi-static T-lambda curves were measured as stress was increased from 0 to 6 kPa and back to 0 kPa in stepwise increments. Our results showed that lung tissue from immature rats was stiffer and less hysteretic than tissue from more mature animals. In addition, tissue from baby animals behaved in a manner compatible with an increased vulnerability to plastic change.     

[14C]-Glucose Metabolism during Shoot Bud Development in Cultured Cotyledon Explants of Pinus radiata

Excised cotyledons of Pinus radiata D. Don cultured under shoot-forming(plus benzyladenine) and non shoot-forming (minus benzyladenine)conditions for 10 and 21 days were fed U-[¹⁴C]-glucose for 3h in the light followed by a 3 h chase period. The labellingof individual metabolites as well as ¹⁴C incorporation intoprotein was assessed. It was found that the general metabolicpatterns were qualitatively the same in shoot-forming and nonshoot-forming conditions, however, metabolism leading to respirationas well as to the synthesis of some amino acids and proteinsynthesis was enhanced in the shoot-forming cultures. (Received February 16, 1987; Accepted July 8, 1987)     

Subunit II of cytochrome c oxidase from Paracoccus denitrificans. DNA sequence, gene expression and the protein

Cytochrome c oxidase from the bacterium Paracoccus denitrificans, while being related to the mitochondrial enzyme in many ways, consists of only two to three different subunits. For the identification of its genes, a Paracoccus DNA library was constructed and screened with specific antibodies for expression of cloned inserts in E. coli. A positive clone expressing immunoreactive products in the molecular mass region of authentic subunit II revealed a high homology of its DNA-deduced amino acid sequence with subunit II sequences of the mitochondrial oxidases; several typical features, such as the transmembrane folding pattern and the presumed copper-binding site, are highly conserved between prokaryotic and mitochondrial polypeptides. A comparison with peptide sequencing data of the purified subunit established the presence of a characteristic N-terminal extension as well as a longer C terminus in the initial translation product of the Paracoccus subunit; by mass spectroscopy, the first N-terminally blocked residue of the mature polypeptide was identified as a pyroglutamate. No code abnormalities, but a highly specific codon usage were observed; no evidence for a localization of the subunit I gene directly adjacent to this gene has been obtained.     

The genes of the Paracoccus denitrificans bc1 complex. Nucleotide sequence and homologies between bacterial and mitochondrial subunits

The genes for the three subunits of the cytochrome bc1 complex from the bacterium Paracoccus denitrificans were identified by screening a gene library constructed in pBR 322 for expression using a cytochrome c1-specific antibody. These three genes coding for the FeS subunit, cytochrome b, and cytochrome c1 were located on contiguous sites on the genome in a presumed operon arrangement. The DNA-deduced amino acid sequence shows that all three subunits are homologous to corresponding polypeptides of the mitochondrial cytochrome bc1 complex. Cytochrome c1 of Paracoccus is much larger than its mitochondrial counterpart due to an extra 150 amino acids of unique, highly acidic composition; in addition, it is most likely synthesized as a precursor polypeptide.