Evidence that a New Antibiotic Flavone Glycoside Chemically Defends the Sea Grass Thalassia testudinum against Zoosporic Fungi

Significantly fewer thraustochytrid protists (zoosporic fungi) were observed in association with healthy leaf tissue of the marine angiosperm Thalassia testudinum than in association with sterilized samples that were returned to the collection site for 48 h. In support of the hypothesis that sea grass secondary metabolites were responsible for these differences, extracts of healthy T. testudinum leaf tissues inhibited the growth of the co-occurring thraustochytrid Schizochytrium aggregatum and deterred the attachment of S. aggregatum motile zoospores to an extract-impregnated substrate. By using S. aggregatum for bioassay-guided chemical fractionation, a new flavone glycoside was isolated and structurally characterized as luteolin 7-O-beta-d-glucopyranosyl-2"-sulfate. Whole-leaf tissue concentrations of this metabolite (4 mg/ml of wet leaf tissue) inhibited S. aggregatum attachment, and a significantly lower concentration (270 mug/ml) reduced thraustochytrid growth by 50%, suggesting that natural concentrations are at least 15 times greater than that needed for significant microbiological effects. These results offer the first complete chemical characterization of a sea grass sulfated flavone glycoside and provide evidence that a secondary metabolite chemically defends T. testudinum against fouling microorganisms.     

DNA polymorphism in lycopersicon and crossing-over per physical length.

Surveys in Drosophila have consistently found reduced levels of DNA sequence polymorphism in genomic regions experiencing low crossing-over per physical length, while these same regions exhibit normal amounts of interspecific divergence. Here we show that for 36 loci across the genomes of eight Lycopersicon species, naturally occurring DNA polymorphism (scaled by locus-specific divergence between species) is positively correlated with the density of crossing-over per physical length. Large between-species differences in the amount of DNA sequence polymorphism reflect breeding systems: selfing species show much less within-species polymorphism than outcrossing species. The strongest association of expected heterozygosity with crossing-over is found in species with intermediate levels of average nucleotide diversity. All of these observations appear to be in qualitative agreement with the hitchhiking effects caused by the fixation of advantageous mutations and/or "background selection" against deleterious mutations.     

Molecular weight averages and 13C NMR intensities provide evidence for branching in proanthocyanidin polymers

Molecular weight distributions for several proanthocyanidin polymers (condensed tannins) have previously been shown to be characterized by DP_w/DP_n > 2, where DP denotes the degree of polymerization. Molecular weight ratios of the size observed experimentally are expected if a few percent of the units form trifunctional branch points. An independent assessment of the extent of branching can be obtained from analysis of intensities of resonances in the ¹³C NMR spectra. Similar branch contents are deduced from DP_w/DP_n and from the spectral analysis. In the case of the Chinese quince (Chaenomeles chinensis) polymer, about 3% of the epicatechin units form trifunctional branch points.     

Social Behavior in the Leaf-Nosed Bat,Carollia perspicillata

Social and behavioral interactions as well as individual roosting positions were followed in a colony of Carollia perspicillata under seminaturalistic captive conditions. Nearest neighbor and grid analyses were used to define the composition of basic social units and mapping data permitted an analysis of the compositional stability of these units. Correlations between female reproductive cycles and individual roosting patterns provided insight into the function of Carollia social groups and indicate that optimal strategies to enhance reproductive success are probably being used.     

An Early Indicator of Resistance in Barley to Russian Wheat Aphid

During early stages of infestation by Russian wheat aphids (Diuraphis noxia [Mordvilko]; RWAs), barley (Hordeum vulgare L.) leaf cells collapsed and showed autofluorescence in the mesophyll and bundle sheath adjacent to the RWA stylet sheath. The response was visually similar to the hypersensitive cell death response, typical of resistance to microbial pathogens. Resistant barley produced significantly more collapsed, autofluorescent cells (CAC) than did susceptible barley. RWA stylet entry sites and sheath paths also fluoresced, making them easy to observe in whole leaf sections. The number of CAC increased with the number of RWAs and with the number of days of feeding in resistant plants. The CAC could be observed 1 d following infestation, making this the most rapid plant response toward the RWAs known to date. The response may be useful in screening for resistant plants and may provide insight into resistance mechanisms in barley.     

An investigation of the physico-chemical basis of foaming in fungal fermentations

A detailed physico-chemical analysis of two foaming fungal fermentations was carried out to identify that key groups of compounds responsible for foam formation. Fermentations were carried out on a 20-L scale in a stirred aerated tank, over 7 days, using a commercial, defined medium. The organisms investigated were Penicillium herqueii, a hyphomycete, and an unidentified Ingoldian fungus. Samples of broth and, where possible, foam were analyzed to determine which groups of compounds were concentrated into generated foams. Surface tension, bulk viscosity, and antifoam A concentration were additionally determined in broth samples. To date the cause of foaming in fermentations has been attributed to the surfactant properties of extracellular proteins. This assumption was tested and found to be incomplete as many additional groups of biochemicals were found to be enriched into the foam. The results of the investigation revealed the presence of proteins, carbohydrates, alpha-keto acids, and lipophilic biosurfactants, particularly extracellular pigments, enriched within stable foams. (c) 1994 John Wiley & Sons, Inc.     

Telomere directed fragmentation of mammalian chromosomes.

Cloned human telomeric DNA can integrate into mammalian chromosomes and seed the formation of new telomeres. This process occurs efficiently in three established human cell lines and in a mouse embryonic stem cell line. The newly seeded telomeres appear to be healed by telomerase. The seeding of new telomeres by cloned telomeric DNA is either undetectable or very inefficient in non-tumourigenic mouse or human somatic cell lines. The cytogenetic consequences of the seeding of new telomeres include large chromosome truncations but most of the telomere seeding events occur close to the pre-existing ends of natural chromosomes.