meso-Methylporphyrins and -chlorins

Two efficient synthetic routes to meso-methylporphyrins and -chlorins are described. In the first, meso-formylporphyrins and -chlorins are reduced to the corresponding meso-hydroxymethyl derivatives, and after zinc chelation and treatment with acetic anhydride in pyridine, the resulting meso-acetoxymethylporphyrins are reduced to meso-methyl with sodium borohydride or by catalytic hydrogenation. The second route is more efficient in that copper(II) meso-formylporphyrins and -chlorins can be reduced directly with tetra n-butylammonium borohydride in hot 1,2-dichloroethane to give the copper(II) meso-methyl analog. Using the procedures developed herein, a formal total synthesis of the meso-pheophorbide from Chlorobium chlorophyll “660” band 6 is decribed, and certain photooxidation and electrophilic deuteration problems in the meso-methylchlorin series are clarified.     

The complexity of miRNA-mediated repression

Since their discovery 20 years ago, miRNAs have attracted much attention from all areas of biology. These short (∼22 nt) non-coding RNA molecules are highly conserved in evolution and are present in nearly all eukaryotes. They have critical roles in virtually every cellular process, particularly determination of cell fate in development and regulation of the cell cycle. Although it has long been known that miRNAs bind to mRNAs to trigger translational repression and degradation, there had been much debate regarding their precise mode of action. It is now believed that translational control is the primary event, only later followed by mRNA destabilisation. This review will discuss the most recent advances in our understanding of the molecular underpinnings of miRNA-mediated repression. Moreover, we highlight the multitude of regulatory mechanisms that modulate miRNA function.     

Neutral protease inhibitors from human intervertebral disc and femoral head articular cartilage

Assays of several proteases, incorporating guanidinium chloride extracts of human femoral head cartilage and intervertebral disc, demonstrated that both tissues contain inhibitors of certain serine proteases. Trypsin, chymotrypsin and a granule extract of human polymorphonuclear leukocyte containing elastase and cathepsin G activities, were inhibited by low molecular weight fractions prepared by Sephadex G-75 chromatography. Using a radioassay, it was further shown that these fractions inhibit proteolysis of cartilage proteoglycan. The inhibitor in intervertebral disc is concentrated in the nucleus pulposus, with a decreasing gradient to the periphery of the annulus fibrosus.It is proposed that these inhibitors confer at least partial protection against pathological proteolysis of the proteoglycans in human articular cartilage and nucleus pulposus.     

Vaccination of cattle with dextran sulphate-binding Babesia bigemina antigens.

Dextran sulphate-bound Babesia bigemina antigens were used in a preliminary vaccination study and were shown to elicit a protective immune response in cattle. A dextran sulphate-binding fraction of B. bigemina was further subfractionated on a Phenyl Sepharose column to give two fractions--one that strongly bound to the column (bound fraction) and one that did not (unbound fraction). Two groups of cattle were each vaccinated with either the bound or the unbound fraction. These two groups of animals along with a control group were then challenged with B. bigemina-infected erythrocytes. Both groups of vaccinated animals showed considerably lower mean daily parasitaemias as compared to the control group.     

Indirect cues in selecting a hunting site in a sit‐and‐wait predator

Sit‐and‐wait predators use relatively simple rules for their decisions to choose and leave a patch, such as using the direct presence of prey to select a hunting site. However, the direct presence of prey can only be used when there is a highly visited patch in the proximity of the predator. Therefore, it is plausible that sit‐and‐wait predators also exploit indirect cues of prey presence and, consequently, use associative learning to select a hunting site. The present study tests for the role of associative learning in a sit‐and‐wait predator species for which the ecology is well understood: Misumena vatia Clerck crab spiders. An ecologically relevant scenario is used by selecting flower colour as the conditioned stimulus and prey presence as the unconditioned stimulus. The results provide no evidence that M. vatia crab spiders use the association between flower colour and food presence for selecting a hunting site. After a training phase of being exposed to a colourful artificial flower highly visited by bees, spiders select a hunting site independently of its colour during the testing phase. Investigations of similar scope and ecological relevance are required with other sit‐and‐wait predators to identify the conditions promoting the use of associative learning for foraging site selection when animals face an unpredictable food supply.     

Parasitoid vibrations as potential releasing stimulus of evasive behaviour in a leafminer

Abstract. The aim of this study was to characterize the vibratory signals produced by the parasitoid Sympiesis sericeicornis Nees (Hymenoptera: Eulophidae) while foraging on apple leaves infested by one of its hosts, the spotted tentiform leafminer Phyllonorycter malella (Ger.) (Lepidoptera: Gracillariidae).This leafminer changes its behaviour as a function of the parasitoid's behaviour to escape parasitization.We propose that the leafminer uses vibrations triggered by the parasitoid to detect the presence of its enemy.We measured vibrations produced by a foraging parasitoid on a mine with a laser vibrometer.By recording concurrently the behaviour of the parasitoid on video, vibrations could be assigned to particular behaviours.Subsequently, vibrations were characterized by their dominant frequencies and intensities.The behaviours Landing and Take-off both produced strong impact-like vibrations characterized by an initial irregular phase during which frequencies up to 25 kHz occurred followed by a slow decaying regular phase.Vibrations elicited by Moving, Standing and Probing showed no clear temporal pattern.During Probing , dominant frequencies of up to 5.6 kHz were observed frequently at intensities well above the background noise (>10 dB).During Moving and Standing , vibrations were more scarce and of lower frequencies and intensities.Due to their impact-like nature, vibrations produced by Landing and Take-off are probably not specific to the parasitoid.Vibrations produced by Moving and Standing are difficult to detect and not reliable because of their non-specificity.Therefore, only Probing provides a reliable and detectable source of information for the host.The vibrations elicited during Probing could account for the evasive behaviour that is observed in this and other leafminers.     

Pollination ecology of Arum italicum (Araceae)

The pollination ecology of Arum italicum was studied in south-western France. This plant attracts olfactory dung-breeding flies through deceit. These insects are principally represented by Diptera, all belonging to saprophyte families. The volatilization of the odouriferous compounds, responsible for their attraction, is achieved through the production of heat by the appendix. The insects are trapped for 24 h in order to participate in both sexual phases of the protogynous inflorescence. The male flowers produce three heat events during flowering. These peaks of heat seem to be involved in the spathe movements, since they occur during the opening of the inflorescence and the liberation of the insects. The last male heat event may be linked with the liberation of pollen and its dispersion by stimulating trapped flies. According to their frequency and pollen-load, two Psychoda species appear to be the most efficient pollinators ( P. crassipenis and P. pusilla ). Nevertheless, each of the other attracted species could play a significant role under different spatio-temporal conditions. Experiments on self-pollination have shown that obligate cross-pollination is necessary for A. italicum to set seeds. Moreover, hand- and natural-pollinated plants showed similarly high abortion frequencies suggesting that seed set may be more constrained by resources rather than by pollination limitation.  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 141 , 205–214.     

How did an annual plant react to Pleistocene glaciations? Postglacial history of Rhinanthus angustifolius in Europe

The impact of climate fluctuations during the Pleistocene on the geographic structure of genetic variation in plant populations is well documented, but there is a lack of studies of annual species at the European scale. The present study aimed to infer the history of the widespread European annual Rhinanthus angustifolius C. C. Gmelin (Orobanchaceae). We explored variation in chloroplast DNA (cpDNA) sequences and amplified fragment length polymorphism (AFLP) in twenty-nine populations covering the entire distribution area of the species. Five AFLP groups were identified, suggesting at least two glacial refugial areas: one area in southwestern Europe and one large eastern area in the Balkan/Caucasus. Recolonization of previously glaciated areas mainly took place from the east of Europe. Despite the difference in life-history traits, the patterns found for the annual R. angustifolius show similarities with those of perennial species in terms of genetic diversity and geographic organization of genetic variation. Although organelle markers have typically been preferred in phylogeographic studies, the cpDNA variation in R. angustifolius did not show any clear geographic structure. The absence of geographic structure in the cpDNA variation may reflect persistence of ancestral polymorphisms or hybridization and introgression with closely-related species.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 98 , 1–13.