Distribution of the infection by Camallanus corderoi (Nemata: Spiruroidea) in different autochthonous hosts and localities of the Valdivia river basin, Chile

Six hundred and thirty nine autochthonous fish were examined in 1986-1987 in search for Camallanus corderoi infection on different biotopes from Valdivia River basin (between 39 degrees 30'-40 degrees 00'S, 73 degrees 30'-71 degrees 45' W). Brachigalaxias bullocki, Galaxias maculatus, Galaxias platei, Aplochiton taeniatus, Cheirodon australe, Basilichthys australis and Cauque mauleanum are new hosts for C. corderoi. Infection by C. corderoi in fish is acquired by ingestion of infected copepods and prevalence and intensity of infection showed differences between host fish and biotopes. In general, infrapopulations of C. corderoi showed overdispersion in different hosts.     

Chemical biology: Paper alert

A selection of interesting papers that were published in the two months before our press date in major journals most likely to report significant results in chemical biology.     

Characterization of a site-specific restriction endonuclease SphI from Streptomyces phaeochromogenes

A new type-II restriction endonuclease SphI, has been partially purified from Streptomyces phaeochromogenes. SphI recognizes the hexanucleotide sequence 5′-GCATG↓C and cleaves it at the position marked by the arrow. This nucleotide sequence is present twice in SV40 DNA, four times in λ DNA and only once in the cloning vehicles pBR322, pBR325, pBR327 and pBR328.     

Ligand-specific state transitions of the membrane-bound acetylcholine receptor

We have developed a simple, direct and time-resolved method to monitor ligand-induced changes in agonist affinity of the membrane-bound acetylcholine receptor. The assay is based on the quenching of fluorescence of NBD-5-acylcholine observed upon binding of this cholinergic agonist to the receptor. Under conditions of partial saturation with the fluorescent agonist, agonists and local anesthetics but not antagonists can induce an increase in affinity of the receptor for NBD-5-acylcholine. The effect is not observed with receptor fully saturated with the fluorescent agonist. The half-life of the observed change in affinity is independent of the nature of the agonist or local anesthetic applied (t1/2 approximately 60 s at 22 degrees C). We conclude that the same state transition of the receptor can be induced by two groups of cholinergic ligands that are assumed to be non-competitive with each other and to have distinctly different modes of action. The time course of the transition is reminiscent of the slow process of desensitization observed in vivo.     

Acclimation or stress symptom? An integrated study of intraspecific variation in the clonal plant Aechmea bromeliifolia,a widespread CAM tank‐bromeliad

The clonal tank-bromeliad Aechmea bromeliifolia (Rudge) Baker was found in four different habitats in a restinga (vegetation mosaic on sandy coastal plains), of south-eastern Brazil. These habitats (swamp forest, dry forest, dry shrubland and herbaceous marsh) lie within a few hundred metres of each other along a gradient extending inland from the coast, and differ markedly in terms of light and flood regime. We compared ramet morphology, leaf anatomy and physiology, and population parameters to examine the amplitude of trait variation of this widespread species in the studied restinga. This integrated approach allowed us to examine which variation conferred acclimation and which was merely a stress symptom. A . bromeliifolia showed site-specific differences in abundance, distribution, rosette size and shape, leaf anatomical arrangement and photochemical efficiency (potential quantum yield; F _v/ F _m) during the day. Most of the variation found seemed to be related to the interaction of light and flooding. The lowest number and size of ramets at the exposed, dry shrubland was matched by a marked leaf photoinhibition, which suggested poor acclimation to local levels of light intensity and limited water supply. In the other habitats, the morpho-physiological parameters measured suggested adequate foraging behaviour and site acclimation.  © 2002 The Linnean Society of London, Botanical Journal of the Linnean Society, 2002, 140 , 391-401.