Centric diatoms of Lake Tahoe

An understanding of the mechanisms of phytoplankton species interaction is dependent on a precise knowledge of what species exist within the community. The centric diatoms of Lake Tahoe, California-Nevada, which are often the dominant component of the phytoplankton community, are presented in both light and scanning electron microscopy (SEM) photographs. Specific attention has been given to initial cell forms of Cyclotella stelligera Cleve and Grunow and C. comta (Ehrenberg) Kützing through the aid of the SEM.     

Comment on “Low-frequency sea level variation and its correlation with climate events in the Pacific”

The tide gauge results exhibit strong multi-decadal oscillations with detected periodicities up to a quasi-60 years. This translates in the requirement of at least 60-70 years of continuously recorded data without any quality issue and the use of a procedure appropriate for time series with periodic components to infer the acceleration trend. This is not what is done in many recent papers where the oscillating behaviour is neglected and short or incomplete records arbitrarily extended or reconstructed are used to infer wrong accelerating trends. All the tide gauges of enough length and quality show the sea levels are oscillating with important multi-decadal periodicities but absolutely not positively accelerating. The satellite radar altimeter reconstruction of the global mean sea level only available since 1993 shows despite the many uncertainties of a still imperfect procedure a not positively accelerating behaviour. The presence of acceleration in the reconstructed or extended data sets and the lack of acceleration in all the individual tide gauge measurements of enough quality and length certainly deserve further discussion. This is a comment to a previously published original paper made on the basis of other previously published results and not a new original paper.     

Composition and abundance of periphyton and aquatic insects in Sierra Nevada, California, stream

The species composition of periphyton and benthic insect communities and abundances of common taxa (&;gt;0.1&;#37; of individuals) were examined during snow-free months in Convict Creek, a permanent snowmelt- and spring-fed stream in the Sierra Nevada of California. The communities were highly diverse. The most abundant taxa in the periphyton were diatoms ( Achnanthes minutissima, Cocconeis placentula lineata, Cymbella microcephala, C. sinuata, Fragilaria construens, F. crotonensis , Navicula spp., Synedra acus , and S. rumpens ), except in late spring and summer when several seasonal blue-green algae ( Chamaesiphon incrustans, Lyngbya spp. and Oscillatoria spp.) are at their maximum densities. Most common periphyton taxa vary systematically in abundance with season, but relative abundances of taxa also appear to be influenced by streambed scouring and by concentrations of ambient nutrients. Data on population densities and length frequencies of larval and nymphal stages of common benthic insects and occurrences of pupal and adult stages were examined to determine life history patterns. Taxa hatching in winter and spring and abundant as immatures in late spring include ephemeropterans ( Epeorus longimanus, Drunella flavilinea , and Caudatella heterocaudata ), plecopterans ( Calineuria californica, Doroneuria baumanni, and Pteronarcys princeps ) and dipterans ( Cryptolabis sp.). Common taxa hatching in late spring or summer are the plecopteran Malenka ( californica? ) and the trichopterans Arctopsyche grandis and Rhyacophila acropedes . Several bivoltine and multivoltine ephemeropterans ( Baetis devinctus and B. tricaudatus ) and dipterans ( Simulium spp. and Chironomidae) have summer cohorts. Taxa hatching in late summer or autumn and most abundant in autumn include ephemeropterans ( Baetis spp., Ephemerella infrequens, Epeorus dulciana, Ironodes lepidus , and Paraleptophlebia pallipes ), trichopterans ( Hydropsyche oslari, Lepidostoma spp., Glossosoma califica, Micrasema sp., Brachycentrus americanus, Neophylax sp., and Rhyacophila vaccua ) and dipterans ( Antocha monticola, Pericoma sp., and Chironomidae). Major recurring events that may influence life history patterns and structure of the benthic insect community are (1) near-freezing, nighttime winter water temperatures and occasional anchor ice, (2) a prolonged period of high discharge in late spring and early summer (3) a brief summer, and (4) a prolonged period of moderate stream discharge in autumn when the substratum is stable and food is abundant.     

Cloning and expression of a rat D2 dopamine receptor cDNA

Dopamine receptors are classified into D1 and D2 subtypes on the basis of their pharmacological and biochemical characteristics. The D2 dopamine receptor has been implicated in the pathophysiology and treatment of movement disorders, schizophrenia and drug addiction. The D2 dopamine receptor interacts with guanine nucleotide-binding proteins to induce second messenger systems. Other members of the family of receptors that are coupled to G proteins share a significant similarity in primary amino-acid sequence and exhibit an archetypical topology predicted to consist of seven putative transmembrane domains. We have taken advantage of the expected nucleotide sequence similarities among members of this gene family to isolate genes coding for new receptors. Using the hamster beta 2-adrenergic receptor gene as a hybridization probe we have isolated related genes including a cDNA encoding the rat D2 dopamine receptor. This receptor has been characterized on the basis of three criteria: the deduced amino-acid sequence which reveals that it is a member of the family of G-protein-coupled receptors; the tissue distribution of the mRNA which parallels that of the D2 dopamine receptor; and the pharmacological profile of mouse fibroblast cells transfected with the cDNA.     

New human and simian HIV-related retroviruses possess functional transactivator (tat) gene

New human retroviruses antigenically related to HIV and even more closely to STLV-III have been recently isolated from individuals from some West African countries. One of these viruses, HTLV-IVP, was reportedly isolated from lymphocytes of a healthy female prostitute. Another isolate, LAV-2FG, was obtained from an AIDS patient and third, SBL-6669, from an individual with lymphadenopathy. Current epidemiological studies indicate that some of these virus isolates cause immune deficiency whereas others may not or may be less efficient at inducing immune deficiency. Similarly, STLV-III apparently does not cause immune deficiency in its natural host, African green monkey. A novel feature of HIV is the possession of a gene termed tat, which is implicated in its pathobiology. We report here that, like HIV, HTLV-IVP, LAV-2FG (HIV-2) and SBL-6669, as well as STLV-IIIAGM possess the putative tat gene, irrespective of their pathogenic potential in vivo. Interestingly, HTLV-IVP/LAV-2FG long terminal repeat (LTR) is equally well transactivated by the HTLV-IVP/LAV-2FG and HTLV-IIIB tat function, HTLV-IIIB LTR responds better to its own tat function.     

Protein kinase C injection into hippocampal pyramidal cells elicits features of long term potentiation

Long-term potentiation (LTP) in the hippocampus is an interesting example of synaptic plasticity because of its induction by physiological discharge rates and its long duration. Of the possible biochemical mechanisms that regulate prolonged changes in cell function, protein phosphorylation is a particularly attractive candidate. We have therefore examined the effect of intracellular injection of calcium/diacylglycerol-dependent protein kinase (protein kinase C (PKC] in CA1 pyramidal neurones in hippocampal slices. Injection of the active enzyme elicited long-lasting enhancement of synaptic transmission, similar to LTP, whereas inactivated kinase failed to do so. The observed changes included an increased amplitude of the excitatory post-synaptic potential (e.p.s.p.) and an increased probability of firing and a reduced latency of the associated actin potential.     

Tunable gold catalysts for selective hydrocarbon oxidation under mild conditions

Oxidation is an important method for the synthesis of chemical intermediates in the manufacture of high-tonnage commodities, high-value fine chemicals, agrochemicals and pharmaceuticals: but oxidations are often inefficient. The introduction of catalytic systems using oxygen from air is preferred for 'green' processing. Gold catalysis is now showing potential in selective redox processes, particularly for alcohol oxidation and the direct synthesis of hydrogen peroxide. However, a major challenge that persists is the synthesis of an epoxide by the direct electrophilic addition of oxygen to an alkene. Although ethene is epoxidized efficiently using molecular oxygen with silver catalysts in a large-scale industrial process, this is unique because higher alkenes can only be effectively epoxidized using hydrogen peroxide, hydroperoxides or stoichiometric oxygen donors. Here we show that nanocrystalline gold catalysts can provide tunable active catalysts for the oxidation of alkenes using air, with exceptionally high selectivity to partial oxidation products ( approximately 98%) and significant conversions. Our finding significantly extends the discovery by Haruta that nanocrystalline gold can epoxidize alkenes when hydrogen is used to activate the molecular oxygen; in our case, no sacrificial reductant is needed. We anticipate that our finding will initiate attempts to understand more fully the mechanism of oxygen activation at gold surfaces, which might lead to commercial exploitation of the high redox activity of gold nanocrystals.