Mesoderm-specific B104 expression in the Drosophila embryo is mediated by internal cis-acting elements of the transposon

The Drosophila melanogaster genome contains about 100 copies of the B104 transposable element, which is strongly expressed during embryogenesis. Here we show that B104 expression is restricted to the esophageal and amnioproctodeal regions of the embryo and to the developing mesoderm. Mesoderm-specific B104 expression requires the activity of the mesoderm-determining factors twist and snail. Virtually the same expression patterns were observed in Drosophila yakuba, a species that a separated from D. melanogaster by some 15 million years of evolution. We show that B104 expression is directed by internal sequences of the retrotransposon that are capable of acting as a cis-acting regulatory element in front of a heterologous Drosophila promoter. Our findings suggest that retrotransposon insertions can affect the expression patterns of endogenous genes by adding and distributing specific cis-acting control elements throughout the host genome. We therefore propose that transposable elements in addition to reducing the fitness of their hosts may also provide a rich pool of cis-acting sequences that contribute to the long-term evolutionary potential of the population in a beneficial manner.     

The PM2 virion has a novel organization with an internal membrane and pentameric receptor binding spikes

Biological membranes are notoriously resistant to structural analysis. Excellent candidates to tackle this problem in situ are membrane-containing viruses where the membrane is constrained by an icosahedral capsid. Cryo-EM and image reconstruction of bacteriophage PM2 revealed a membrane bilayer following the internal surface of the capsid. The viral genome closely interacts with the inner leaflet. The capsid, at a resolution of 8.4 A, reveals 200 trimeric capsomers with a pseudo T = 21 dextro organization. Pentameric receptor-binding spikes protrude from the surface. It is evident from the structure that the PM2 membrane has at least two important roles in the life cycle. First, it acts as a scaffold to nucleate capsid assembly. Second, after host recognition, it fuses with the host outer membrane to promote genome entry. The structure also sheds light on how the viral supercoiled circular double-stranded DNA genome might be packaged and released.     

Studies of 13C in the foliage reveal interactions between nutrients and water in forest fertilization experiments

The severity of a root rot disease of cereals, caused by Rhizoctonia solani Kühn AG8, was inversely correlated to the Zn status of plants in field studies in 1989 and 1990. In 1989, a preliminary survey was conducted in a farmer's field in South Australia where Zn deficiency and disease were both widespread. Zn concentration in Spear wheat plants at the 3-leaf to early tillering stage was negatively correlated with severity of the disease. For the elevent elements analysed, a correlation matrix showed that Zn had the highest, and only significant (R²=0.52^**) association with disease. The effect of Zn applications and their residual value on disease severity was further studied in a long-term field experiment in 1989 and 1990 to which Zn had been applied in 1986. There was a decrease in the area of Rhizoctonia bare patch as Zn rate was increased, a result consistent with the field survey results; the recommended rate of 2.5 kg Zn ha^–1 reduced the area affected by bare patch from 42% to 21% of the total crop area compared with no Zn application, overcame Zn deficiency and increased grain yield from 1.1 to 2.8 t ha^–1. In 1990, fresh Zn application treatments were applied to trial plots designed for this purpose, in order to compare the response with the older Zn treatments applied in 1986. The areas of bare patch in the older Zn treatments were approximately 5% greater than those in the fresh Zn treatments. The results are consistent with the hypothesis that Zn deficient plants are more susceptible to root rot caused by R. solani. Testing this hypothesis is the subject of a companion paper.     

A cytochrome P450 and a ferredoxin isolated from Mycobacterium sp. strain HE5 after growth on morpholine

A cytochrome P450 and an iron-sulfur protein, whose expression was specifically induced during growth of Mycobacterium sp. strain HE5 on morpholine as the sole source of carbon, nitrogen, and energy were purified to apparent homogeneity. Due to the lack of enzymatic activity, carbon monoxide difference spectra and determination of the acid-labile sulfur, respectively, were used to detect the proteins during purification. The cytochrome P450, designated P450mor, was characterized as a monomer with an apparent molecular mass of 44.7 kDa. The amino acid sequence of an internal peptide comprising 19 amino acids was identical to the sequence derived from a gene encoding a cytochrome P450 from Mycobacterium smegmatis mc(2)155 suggested to be involved in the utilization of piperidine and pyrrolidine. The iron-sulfur protein was characterized as a ferredoxin exhibiting a molecular mass of 6.8 kDa and named Fdmor. An identity of 48-77% was obtained for the 30 N-terminal amino acids of Fdmor and the corresponding sequences of different 3Fe-4S-ferredoxins known to be involved in P450-dependent reactions. From these data we concluded that growth of Mycobacterium sp. strain HE5 on morpholine led to the expression of a cytochrome P450-dependent monooxygenase system composed of at least two different proteins.     

Biophoton emission

The phenomenon of ultraweak photon emission from living systems was further investigated in order to elucidate the physical properties of this radiation and its possible source. We obtained evidence that the light has a high degree of coherence because of (1) its photon count statistics, (2) its spectral distribution, (3) its decay behavior after exposure to light illumination, and (4) its transparency through optically thick materials. Moroever, DNA is apparently at least an important source, since conformational changes induced with ethidium bromide in vivo are clearly reflected by changes of the photon emission of cells. The physical properties of the radiation are described, taking DNA as an exciplex laser system, where a stable state can be reached far from thermal equilibrium at threshold.     

Methanol and other VOC fluxes from a Danish beech forest during late springtime

In-canopy mixing ratio gradients and above-canopy fluxes of several volatile organic compounds (VOCs) were measured using a commercial proton transfer reaction mass spectrometer (PTR-MS) in a European beech (Fagus sylvatica) forest in Denmark. Fluxes of methanol were bidirectional: Emission occurred during both day and night with highest fluxes (0.2 mg C m⁻² h⁻¹) during a warm period; deposition occurred dominantly at daytime. Confirming previous branch-level measurements on beech, the forest’s monoterpene emissions (0–0.5 mg C m⁻² h⁻¹), and in-canopy mixing ratios showed a diurnal cycle consistent with light-dependent emissions; a result contrasting temperature-only driven emissions of most conifer species. Also emitted was acetone, but only at ambient temperatures exceeding 20°C. Slow deposition dominated at lower temperatures. Our in-canopy gradient measurements contrast with earlier results from tropical and pine forest ecosystems in that they did not show this beech ecosystem to be a strong sink for oxygenated VOCs (OVOCs). Instead, their gradients were flat and only small deposition velocities (<0.2 cm s⁻¹) were observed to the onsite soil. However, as methanol soil uptake was consistent and possibly related to soil moisture, more measurements are needed to evaluate its soil sink strength. In turn, as canopy scale fluxes are net fluxes with stomatal emissions from photosynthesizing leaves potentially affecting non-stomatal oxygenated VOC uptake, only independent, controlled laboratory experiments may be successful in separating gross fluxes.     

Effects of UV-B on motility and photobehavior in the green flagellate,Euglena gracilis

UV-B inhibits the motility of the green flagellate, Euglena gracilis, at fluences rates higher than those expected to occur in the natural sunlight even when the stratospheric ozone layer is partially reduced by manmade pollutants. The phototactic orientation of the cells, however, is drastically impaired by only slightly enhanced levels of UV-B irradiation. Since only negative phototaxis (movement away from a strong light source) is impaired while positive phototaxis (movement toward a weak light source) is not, the delicate balance by which the organisms adjust their position in their habitat is disturbed. Under these conditions the cells are unable to retreat from hazardous levels of radiation and are eventually killed not by the UV-B irradiation but by photobleaching of their photosynthetic pigments in the strong daylight at the surface.     

The Dictyostelium Bcr/Abr-related protein DRG regulates both Rac- and Rab-dependent pathways

Dictyostelium discoideum DdRacGap1 (DRG) contains both Rho-GEF and Rho-GAP domains, a feature it shares with mammalian Bcr and Abr. To elucidate the physiological role of this multifunctional protein, we characterized the enzymatic activity of recombinant DRG fragments in vitro, created DRG-null cells, and studied the function of the protein in vivo by analysing the phenotypic changes displayed by DRG-depleted cells and DRG-null cells complemented with DRG or DRG fragments. Our results show that DRG-GEF modulates F-actin dynamics and cAMP-induced F-actin formation via Rac1-dependent signalling pathways. DRG's RacE-GAP activity is required for proper cytokinesis to occur. Additionally, we provide evidence that the specificity of DRG is not limited to members of the Rho family of small GTPases. A recombinant DRG-GAP accelerates the GTP hydrolysis of RabD 30-fold in vitro and our complementation studies show that DRG-GAP activity is required for the RabD-dependent regulation of the contractile vacuole system in Dictyostelium.     

Systematics ofPrimula veris (Primulaceae)

Primarily, 50 characters taken from herbarium specimens, cultivated plants, and whole populations ofPrimula veris L. were critically evaluated. Only 24 characters were found to be suitable for taxonomic use. The geographical and multivariate analysis of about 1000 herbarium specimens from the whole area lead to a reduction of the number of subspecies. Only a less restricted subsp.veris (incl. subsp.canescens, subsp.inflata and probably including subsp.macrocalyx) and subsp.columnae (incl. subsp.suaveolens) can be distinguished considering the variability of characters within an individuum, under different culture conditions, and during the growth period. The status of the taxon macrocalyx cannot be cleared presently.