Soil nutrient dissimilarity and litter nutrient limitation as major drivers of home field advantage in riparian tropical forests

Decomposition is a key process driving carbon and nutrient cycling in ecosystems worldwide. The home field advantage effect (HFA) has been found to accelerate decomposition rates when litter originates from “home” when compared to other (“away”) sites. It is still poorly known how HFA plays out in tropical, riparian forests, particularly in forests under restoration. We carried out three independent reciprocal litter transplant experiments to test how litter quality, soil nutrient concentrations, and successional stage (age) influenced HFA in tropical riparian forests. These experimental areas formed a wide gradient of soil and litter nutrients, which we used to evaluate the more general hypothesis that HFA varies with dissimilarity in soil nutrients and litter quality. We found that HFA increased with soil nutrient dissimilarity, suggesting that litter translocation uncouples relationships between decomposers and litter characteristics; and with litter N:P, indicating P limitation in this system. We also found negative HFA effects at a site under restoration that presented low decomposer ability, suggesting that forest restoration does not necessarily recover decomposer communities and nutrient cycling. Within each of the independent experiments, the occurrence of HFA effects was limited and their magnitude was not related to forest age, nor soil and litter quality. Our results imply that HFA effects in tropical ecosystems are influenced by litter nutrient limitation and soil nutrient dissimilarity between home and away sites, but to further disentangle major HFA drivers in tropical areas, a gradient of dissimilarity between litter and soil properties must be implemented in future experimental designs.     

Bioguided Fractionation and Isolation of an Antiplasmodial Saponin from the Roots of Nauclea xanthoxylon (A.Chev.) Aubrév. (Rubiaceae)

The root extract of Nauclea xanthoxylon (A.Chev.) Aubrév. displayed significant 50 % inhibition concentration (IC₅₀s) of 0.57 and 1.26 μg/mL against chloroquine resistant and sensitive Plasmodium falciparum (Pf) Dd2 and 3D7 strains, respectively. Bio-guided fractionation led to an ethyl acetate fraction with IC₅₀s of 2.68 and 1.85 μg/mL and subsequently, to the new quinovic acid saponin named xanthoxyloside ( 1 ) with IC₅₀s of 0.33 and 1.30 μM, respectively against the tested strains. Further compounds obtained from ethyl acetate and hexane fractions were the known clethric acid ( 2 ), ursolic acid ( 3 ), quafrinoic acid ( 4 ), quinovic acid ( 5 ), quinovic acid 3-O-β-D-fucopyranoside ( 6 ), oleanolic acid ( 7 ), oleanolic acid 3-acetate ( 8 ), friedelin ( 9 ), β-sitosterol ( 10a ), stigmasterol ( 10b ) and stigmasterol 3-O-β-D-glucopyranoside ( 11 ). Their structures were characterised with the aid of comprehensive spectroscopic methods (1 and 2D NMR, Mass). Bio-assays were performed using nucleic acid gel stain (SYBR green I)-based fluorescence assay with chloroquine as reference. Extracts and compounds exhibited good selectivity indices (SIs) of >10. Significant antiplasmodial activities measured for the crude extract, the ethyl acetate fraction and xanthoxyloside ( 1 ) from that fraction can justify the use of the root of N. xanthoxylon in ethnomedicine to treat malaria.     

Parentage and host preference in the common cuckoo Cuculus canorus

Microsatellite DNA markers were used to investigate parentage relationships in a population of common cuckoo Cuculus canorus . Thirty adults and 55 nestlings were genotyped at six loci from blood samples collected over a four-year period. To test whether each cuckoo female specialises in parasitising one single host species (Host Preference Hypothesis), the maternal relationships were used to record each female's host choice. The results supported the Host Preference Hypothesis since no female (N=3) was recorded to have parasitised more than one of four congeneric host species breeding in the area. In contrast, the males (N=4) did not show such specialisation since two of them sired offspring reared by different host species.     

In vitro characterization of a plastid terminal oxidase (PTOX).

The plastid terminal oxidase (PTOX) encoded by the Arabidopsis IMMUTANS gene was expressed in Escherichia coli cells and its quinone/oxygen oxidoreductase activity monitored in isolated bacterial membranes using NADH as an electron donor. Specificity for plastoquinone was observed. Neither ubiquinone, duroquinone, phylloquinone nor benzoquinone could substitute for plastoquinone in this assay. However, duroquinol (fully reduced chemically) was an accepted substrate. Iron is also required and cannot be substituted by Cu(2+), Zn(2+) or Mn(2+). This plastoquinol oxidase activity is independent of temperature over the 15-40 degrees C range but increases with pH (from 5.5 to 9.0). Unlike higher plant mitochondrial alternative oxidases, to which PTOX shows sequence similarity (but also differences, especially in a putative quinone binding site and in cysteine conservation), PTOX activity does not appear to be regulated by pyruvate or any other tested sugar, nor by AMP. Its activity decreases, however, with increasing salt (NaCl or KCl) concentration. Various quinone analogues were tested for their inhibitory activity on PTOX. Pyrogallol analogues were found to be inhibitors, especially octyl gallate (I50 = 0.4 microM ) that appears far more potent than propyl gallate or gallic acid. Thus, octyl gallate is a useful inhibitor for future in vivo or in organello studies aimed at studying the roles of PTOX in chlororespiration and as a cofactor for carotenoid biosynthesis.     

Nω-Hydroxyamino-α-amino acids as a new class of very strong inhibitors of arginases

 The effects of various compounds bearing an N-OH group such as N-hydroxy-guanidines, amidoximes, and hydroxylamines, on bovine and rat liver arginases was studied. Some of these compounds with an l-α-amino acid function at an appropriate distance from the N-OH group acted as strong competitive liver arginase inhibitors, displaying Ki values between 4 and 150 μM. Two compounds, N ^ε-hydroxy-l-lysine and N ^ω-hydroxy-d,l-indospicine, which exhibited Ki values of 4 and 20 μM (at pH 7.4), were the most potent inhibitors of arginase described to date. The distance between the α-amino acid and N-OH functions appeared to be crucial for potent inhibition of arginase, as N ^δ-hydroxy-l-ornithine, which has one -CH₂ group less than N ^ε-hydroxy-l-lysine, exhibited a 37-fold higher Ki value than N ^ε-hydroxy-l-lysine. Based on these results, a model for the interaction of N ^ω-hydroxyamino-l-α-amino acids with the arginase active site is proposed. This model involves the binding of the N-OH group of the inhibitors to the arginase Mn(II) center and suggests that N ^ε-hydroxy-l-lysine is a good transition state analog of arginase.     

Allelic diversity at the Mhc-DP locus in rhesus macaques (Macaca mulatta)

Allelic diversity at the major histocompatibility complex class II DP locus of rhesus macaques was studied by sequencing exon 2 of Mamu-DPA1 and -DPB1 genes. The Mamu-DPA1 gene is apparently invariant, whereas the Mamu-DPB1 locus displays polymorphism. Here we report the characterization of 1 Mamu-DPA1 and 13 Mamu-DPB1 alleles which were compared with other available primate Mhc-DPA1 and -DPB1 sequences. As compared with Mhc-DRB and -DQB1, most codons for the contact residues in the antigen binding site of the primate Mhc-DPB1 gene have a relatively low degree of variation in encoding various types of amino acids. In contrast to Mhc-DRB and -DQB, the HLA- and Mamu-DPB1 sequences cluster in a species-specific manner in phylogenetic trees. Mhc-DPB1 polymorphisms, however, are inherited in a transspecies mode of evolution, as is demonstrated by the sharing of lineage members between closely related macaque species. The data demonstrate that the transspecies character of Mhc-DPB1 polymorphism was retained over much shorter periods of time as compared with its sister class II loci, Mhc-DQ and -DR.The nucleotide sequence data reported in this paper have been submitted to the EMBL nucleotide sequence database and have been assigned the accession numbers Z32402–Z32415     

Phospholipase D from Soybean (Glycine max L.) Suspension-Cultured Cells: Purification, Structural and Enzymatic Properties

Phospholipase D (phosphatidylcholine phosphatidohydrolase EC3.1.4.4 [EC] ) from soybean (Glycine max L.) suspension-cultured cellwas purified around 1,200-fold to homogeneity by acetone precipitation,Macro-Prep High Q anion exchange, and octyl-Sepharose CL-4Baffinity chromatography. The purified enzyme released 1,600µmol of choline per min per mg of protein. The enzymeis monomeric with a molecular mass of 92 kDa, as estimated bySDS-PAGE. One of the most interesting characteristics of thepurified soybean phospholipase D was the dependence of the pHoptimum on the Ca²⁺ ion concentration in the assay. With 10mM, 20 mM and 40 mM Ca²⁺ ions, the optima were at pH 7.5, 6and 5.5, respectively. The specific adsorption of phospholipaseD onto octyl-Sepharose gel suggests that the molecule becomesmore hydrophobic in the presence of Ca²⁺ ions. The amino acidsequence of the first 18 N-terminal residues of soybean phospholipaseD revealed a high degree of homology with those previously publishedfor cabbage leaf and castor bean endosperm enzymes. Westernblots of the soybean phospholipase D showed an immunoreactivitywith antibodies raised against a synthetic peptide correspondingto the 15 N-terminal aminoacid residues of phospholipase D fromcabbage leaves. (Received March 13, 1995; Accepted May 29, 1995)     

Rapid Degeneration of Cultured Human Brain Pericytes by Amyloid β Protein

Abstract: Amyloid β protein (Aβ) deposition in the cerebral arterial and capillary walls is one of the major characteristics of brains from patients with Alzheimer's disease and hereditary cerebral hemorrhage with amyloidosis-Dutch type (HCHWA-D). Vascular Aβ deposition is accompanied by degeneration of smooth muscle cells and pericytes. In this study we found that Aβ_1–40 carrying the "Dutch" mutation (HCHWA-D Aβ_1–40) as well as wild-type Aβ_1–42 induced degeneration of cultured human brain pericytes and human leptomeningeal smooth muscle cells, whereas wild-type Aβ_1–40 and HCHWA-D Aβ_1–42 were inactive. Cultured brain pericytes appeared to be much more vulnerable to Aβ-induced degeneration than leptomeningeal smooth muscle cells, because in brain pericyte cultures cell viability already decreased after 2 days of exposure to HCHWA-D Aβ_1–40, whereas in leptomeningeal smooth muscle cell cultures cell death was prominent only after 4–5 days. Moreover, leptomeningeal smooth muscle cell cultures were better able to recover than brain pericyte cultures after short-term treatment with HCHWA-D Aβ_1–40. Degeneration of either cell type was preceded by an increased production of cellular amyloid precursor protein. Both cell death and amyloid precursor protein production could be inhibited by the amyloid-binding dye Congo red, suggesting that fibril assembly of Aβ is crucial for initiating its destructive effects. These data imply an important role for Aβ in inducing perivascular cell pathology as observed in the cerebral vasculature of patients with Alzheimer's disease or HCHWA-D.