Alluvial fans along the foothills of the Elburz Mountains,Iran

Alluvial fans are particularly well developed along the southern margins of the Elburz Mountains, Iran. In this work, 26 alluvial fans situated to the southeast of Tehran are examined. The fan of the River Jaj is extremely large and covers, with its drainage basin, an area of more that 2,500 km². The other 25 fans and their related drainage basin systems comprise all together an area of only 130 km². The fan/drainage basin systems show a direct relationship between the fan area and the drainage basin area and an inverse relationship between fan area and the mean slope of the fan. Hydrometeorological studies suggest that the severest storms under present environment conditions are possibly capable of moving many of the larger stones observed on one of the smaller fans. The poorly sorted sediments composing the fans suggest, however, that deposition occurred under debris-flow conditions. Fanhead trenching, the occurrence of desert varnish on stones over large areas of the fans and gully erosion of the lower portions of the fans indicate that alluviation is not of great importance at the present day. Archaeological evidence also suggests that sediment deposition on the fans has been of only minor importance during the last 750 years. Optimum conditions for fan formation are believed to have occurred during the glacial periods of the Quaternary era.     

Adrenocorticoid receptors in C6 glioma cells: Effects on cell growth

Rat C6 glioma cells contain two receptors for adrenocorticoids—the predominant glucocorticoid receptor and low densities of the Type I corticosteroid (mineralocorticoid) receptor. Nanomolar concentrations of deoxycorticosterone, corticosterone and aldosteceptor. Nanomolar concentrations of deoxycorticosterone, corticosterone and aldosterone, which fully occupy Type I receptors, produced a slight stimulatory effect on C6 cell growth in serum-free media. However, spironolactone, a Type I receptor antagonist, and pregnenolone, which does not bind to Type I receptors, had similar effects. Therefore, the slight growth stimulation produced by low steroid concentrations is not mediated by Type I or glucocorticoid receptors, but may be due to an effect on cell membrane properties or other receptor-independent action. Occupation of glucocorticoid receptors by higher concentrations of corticosteroids inhibited C6 cell growth.     

A laser flash photolysis study of the reactivities of the triplet states of 8-methoxypsoralen and 4,5',8-trimethylpsoralen with nucleic acid bases in solution.

The extinction coefficients, quantum yields and reactivities of the triplet states of 8-methoxypsoralen and 4,5',8-trimethylpsoralen in methanolic solution have been determined using laser flash photolysis techniques. The second-order rate constants for the quenching of these triplet states by pyrimidine and purine bases were found to be several orders of magnitude lower than those found for other furocoumarin derivatives. This may suggest, therefore, that the skin photosensitising ability of such compounds does not necessarily correlate with in vitro triplet state reactivity. Preliminary experiments on the reactivity of the psoralen triplet state with DNA itself indicate that no transient absorptions due to psoralen excited states can be observed when a photon is absorbed by the psoralen-DNA complex.     

A simple activity monitoring radio tag for fish

A radio tag is described which facilitates the long-term monitoring of activity events in fish. The tag is a simple peritoneal implant and thus requires no complicated surgery to deploy. A motion-sensing mercury switch interfaced to a microcontroller is used to modulate pulse rate and thus indicate periods of activity. The tag is being used to study the feeding and activity patterns of pike (Esox lucius L.) where laboratory and field trials have shown the system to be robust, long lasting and reliable.     

Identiflcation of a Proenkephalin Precursor in Striatal Tissue

Recent studies have supported the suggestion that proenkephalin is the same in both adrenal medulla and brain. However, although previous investigations have characterized enkephalin-containing adrenal intermediates derived from proenkephalin, as yet no such intermediates have been isolated from the brain. This has led to the belief that the processing of proenkephalin in the brain is extremely rapid and enkephalin-containing intermediates do not accumulate. In this investigation Sephacryl-300 gel filtration chromatography of guinea pig striata, extracted in 8 M urea, demonstrated several peaks of both bioactive and immunoreactive enkephalin-like peptides after enzymatic digest (trypsin followed by carboxypeptidase B). Comparable profiles were obtained using rat and bovine striatal tissue. In guinea pig the major species emerging from gel filtration, eluting with an apparent molecular weight of 29,000, represented approximately 9% of the total (methionine) enkephalin immunoreactivity. It had an apparent pI of 5.0 when subjected to chromatofocusing. This species was further characterized using sodium dodecyl sulphate-polyacrylamide gel electrophoresis and nitrocellulose blotting techniques as well as highly specific radioimmunoassays to (Met5)-enkephalin, (Leu5)-enkephalin, and (Met5)-enkephalin-Arg6-Phe7. This species was found to contain these opioid peptides in an approximately 6:1:1 ratio, respectively, and to have an apparent molecular weight of 31,000. It was also indicated that (Met5)-enkephalin-Arg6-Phe7 constituted the C-terminal seven residues of this molecule.     

Bistability in a Metabolic Network Underpins the De Novo Evolution of Colony Switching in Pseudomonas fluorescens

Phenotype switching is commonly observed in nature. This prevalence has allowed the elucidation of a number of underlying molecular mechanisms. However, little is known about how phenotypic switches arise and function in their early evolutionary stages. The first opportunity to provide empirical insight was delivered by an experiment in which populations of the bacterium Pseudomonas fluorescens SBW25 evolved, de novo, the ability to switch between two colony phenotypes. Here we unravel the molecular mechanism behind colony switching, revealing how a single nucleotide change in a gene enmeshed in central metabolism (carB) generates such a striking phenotype. We show that colony switching is underpinned by ON/OFF expression of capsules consisting of a colanic acid-like polymer. We use molecular genetics, biochemical analyses, and experimental evolution to establish that capsule switching results from perturbation of the pyrimidine biosynthetic pathway. Of central importance is a bifurcation point at which uracil triphosphate is partitioned towards either nucleotide metabolism or polymer production. This bifurcation marks a cell-fate decision point whereby cells with relatively high pyrimidine levels favour nucleotide metabolism (capsule OFF), while cells with lower pyrimidine levels divert resources towards polymer biosynthesis (capsule ON). This decision point is present and functional in the wild-type strain. Finally, we present a simple mathematical model demonstrating that the molecular components of the decision point are capable of producing switching. Despite its simple mutational cause, the connection between genotype and phenotype is complex and multidimensional, offering a rare glimpse of how noise in regulatory networks can provide opportunity for evolution.