Border and ecotone detection by vegetation composition along forest‐savanna transects in Ivory Coast

Abstract. Question: How do properties of different vegetation components vary along ecotones of semi‐deciduous forest islands, and can the depth of edge influence (DEI) of the components be detected using a novel combination of analyses? Location: Comoé National Park (CNP), NE Ivory Coast. Methods: Along eight transects at semi‐deciduous forest islands tree individuals > 20 cm DBH were mapped. At one transect, tree and shrub individuals down to 1 cm DBH were measured and cover of species was estimated. Split moving window dissimilarity analysis (SMWDA) and moving window regression analysis (MWRA) were combined to detect statistical significance of borders in multivariate vegetation data along continuous transects, to determine the width of associated ecotones, and, thus, the DEI towards the forest interior. Results: For trees > 20 cm DBH, a distinct boundary formation was detected, dominated by the semi‐fire resistant tree species Anogeissus leiocarpus. The median of DEI towards the forest interior was 55 m. Ecotone detection with all species present revealed an interlocked sequence of ecotones for grasses, herbs, woody climbers, shrubs and trees, with each of these ecotones being narrower than the overall ecotone. DEI ranged from 10 m for grasses up to 120 m for trees and shrubs. Conclusions: The coherent set of analyses applied proved to be an objective method for detecting borders and the width of associated ecotones. The patterns found may be explained by successional processes at the forest‐savanna border. The DEI measured for the forest islands in the nearly undisturbed semi‐natural system of the CNP is of relevance to concepts of core‐area analysis and the protection of forest interior species in semi‐deciduous forests in tropical West Africa.     

Identification of human populations with a high incidence of cellular immunity against breast carcinoma

Summary Cell mediated immunity specifically directed against breast carcinoma, but not against osteogenic sarcoma or other carcinomas, was found to occur in the household contacts of patients with active breast carcinoma (primary and metastatic). Such immunity was not found in the normal population, nor in household contacts of patients with osteogenic sarcoma; it was also not found in household contacts of breast carcinoma patients who had been disease free for two or more years. Patients with breast carcinoma had cytotoxicity indexes (CI) comparable to the normal population, regardless of their clinical condition.     

Biochemical characterization of a strictly specific beta-galactosidase from the digestive juice of the palm weevil Rhynchophorus palmarum larvae

A beta‐galactosidase from the digestive juice of the palm weevil Rhynchophorus palmarum L. larvae was purified by chromatography on ion exchange, gel filtration, and hydrophobic interaction columns. The preparation was shown to be homogeneous on polyacrylamide gel. Beta‐galactosidase was a monomeric protein with a molecular weight of 62 kDa based on its mobility in sodium dodecyl sulfate–polyacrylamide gel electrophoresis and 60 kDa based on gel filtration. Maximal enzyme activity occurred at 55°C and pH 5.0. The purified beta‐galactosidase was stable at 37°C and its pH stability was in the range of 4.6–6.0. Beta‐galactosidase was highly specific for the beta‐d ‐galactosyl residue and beta‐(1‐4) linkage. The catalytic efficiency (V_max/K_m) values for p‐nitrophenyl‐beta‐d ‐galactopyranoside, beta‐d ‐galactosyl(1‐4)‐d ‐glucose (lactose), beta‐d ‐galactosyl(1‐4)‐d ‐galactose and beta‐d ‐galactosyl(1‐4)‐beta‐d ‐galactosyl(1‐4)‐d ‐glucose were, respectively, 72.95, 10.97, 20.74 and 12.73. 5,5‐Dithio‐bis(2‐nitrobenzoate) and sodium dodecyl sulfate inhibited completely the beta‐galactosidase activity. The enzyme was capable of catalyzing transgalactosylation reactions. The yield of galactosylation of 2‐phenylethanol (43%), catalyzed by the beta‐galactosidase in the presence of lactose as galactosyl donor, is higher than those reported previously with conventional sources of beta‐galactosidases. In addition, the optimum pH is different for the hydrolysis (pH 5.0) and transgalactosylation reactions (pH 6.0).     

MORPHOLOGICAL AND MOLECULAR CHARACTERIZATION OF PLANKTONIC CYANOBACTERIA FROM BELGIUM AND LUXEMBOURG1

For the first time in Belgium and Luxembourg, the diversity and taxonomy of 95 cyanobacterial strains isolated from freshwater blooms were assessed by the comparison of phenotypes and partial 16S rRNA gene sequences. The results showed the high diversity of nanoplanktonic, picoplanktonic, and benthic–periphytic cyanobacteria accompanying the main bloom‐forming taxa. Indeed, besides 15 morphotypes of bloom‐forming taxa, seven non‐bloom‐forming planktonic morphotypes and 11 morphotypes from benthic–periphytic taxa were isolated in culture from the plankton samples of 35 water bodies. The bloom‐forming strains belonged to the genera Microcystis, Woronichinia, Planktothrix, Anabaena, and Aphanizomenon, whereas the other strains isolated from the same samples were assigned to the nanoplanktonic Aphanocapsa, Aphanothece, Snowella, and Pseudanabaena; to the picoplanktonic Cyanobium; and to the benthic–periphytic Geitlerinema, Komvophoron, Leptolyngbya, Lyngbya, Phormidium, Calothrix, Nostoc, and Trichormus. The results supported both the polyphyletism of genera such as Aphanocapsa, Aphanothece, Leptolyngbya, Geitlerinema, Anabaena, and Aphanizomenon as well as the validity of genera such as Microcystis, Planktothrix, and Pseudanabaena with gas vesicles and cells constricted at the cross wall. The results obtained showed the close relationship between Snowella and Woronichinia for which very few sequences exist. The first sequence of Komvophoron appeared poorly related to other available cyanobacterial sequences. Although in a few cases a good agreement existed between phenotypic and genotypic features, there was generally a discrepancy. Strains with identical morphotypes show small differences in the 16S rRNA sequences, which might be related to the different chemical properties of their habitats. The results showed the importance of the polyphasic approach in order to improve the taxonomy of cyanobacteria.     

Insulin-like growth factors: Putative muscle-derived trophic agents that promote motoneuron survival

Treatment of chick embryos in ovo with IGF-I during the period of normal, developmentally regulated neuronal death (embryonic days 5–10) resulted in a dose-dependent rescue of a significant number of lumbar motoneurons from degeneration and death. IGF-II and two variants of IGF-I with reduced affinity for IGF binding proteins, des(1-3) IGF-I and long R³ IGF-I, also elicited enhanced survival of motoneurons equal to that seen in IGF-I-treated embryos. IGF-I did not enhance mitogenic activity in motoneuronal populations when applied to embryos during the period of normal neuronal proliferation (E2-5). Treatment of embryos with IGF-I also reduced two types of injury-induced neuronal death. Following either deafferentation or axotomy, treatment of embryos with IGF-I rescued approximately 75% and 50%, respectively, of the motoneurons that die in control embryos as a result of these procedures. Consistent with the survival-promoting activity on motoneurons in ovo, IGF-I, -II, and des(1-3) IGF-I elevated choline acetyltransferase activity in embryonic rat spinal cord cultures, with des (1-3) IGF-I demonstrating 2.5 times greater potency than did IGF-I. A single addition of IGF-I at culture initiation resulted in the maintenance of 80% of the initial ChAT activity for up to 5 days, during which time ChAT activity in untreated control cultures fell to 9%. In summary, these results demonstrate clear motoneuronal trophic activity for the IGFs. These findings, together with previous reports that IGFs are synthesized in muscle and may participate in motoneuron axonal regeneration and sprouting, indicate that these growth factors may have an important role in motoneuron development, maintenance, and recovery from injury. © 1993 John Wiley & Sons, Inc.     

Effects of Pb-EDTA and EDTA on oxidative stress reactions and mineral uptake in Phaseolus vulgaris

Sequestration of Pb by synthetic chelates has been reported to increase bioavailability, uptake, and translocation of this metal in plants. In this work the potential phytotoxic effects of Pb-EDTA were investigated in Phaseolus vulgaris L. cv. Limburgse vroege plants grown on hydroponics. Addition of 50 µ M Pb-EDTA to the nutrient solution caused a significant induction of syringaldazine peroxidase (SPOD; EC 1.11.1.7) in roots and primary leaves and guaiacol peroxidase (GPOD; EC 1.11.1.7) in leaves. Addition of 100 µ M Pb-EDTA further exacerbated ascorbate peroxidase (APOD; EC 1.11.1.11), GPOD, dehydroascorbate reductase (DHAR; EC 1.8.5.1), glutathione reductase (GR; EC 1.6.4.2) and malic enzyme (ME; EC 1.1.1.40) in roots and APOD and ME in primary leaves. Addition of 200 µ M Pb-EDTA also induced DHAR in leaves. This induction of peroxidases (SPOD, GPOD, APOD), enzymes of the ascorbate-glutathione cycle (DHAR, GR in roots) and of an NADP⁺ reducing enzyme in roots and primary leaves indicates that oxidative stress has been initiated. At 200 µ M Pb-EDTA, chlorophyll a and b content in leaves was significantly reduced while visible effects on root morphology and shoot length were observed, while no significant morphological effects were found in the leaves, confirming the sensitive character of the measured enzymes as plant stress indicators. Elevation of the Pb-EDTA concentration in the growth medium significantly reduced the content of Ca, Fe, Mn and Zn taken up by plants, probably due to ion leakage as a result of observed toxicity. Addition of up to 200 µ M EDTA increased chelation of divalent cations in nutrient solution resulting in reduced plant uptake of Zn, Cu, Fe and Mn. This did not result in phytotoxicity.     

The structure of the human RNase H2 complex defines key interaction interfaces relevant to enzyme function and human disease

Ribonuclease H2 (RNase H2) is the major nuclear enzyme involved in the degradation of RNA/DNA hybrids and removal of ribonucleotides misincorporated in genomic DNA. Mutations in each of the three RNase H2 subunits have been implicated in a human auto-inflammatory disorder, Aicardi-Goutières Syndrome (AGS). To understand how mutations impact on RNase H2 function we determined the crystal structure of the human heterotrimer. In doing so, we correct several key regions of the previously reported murine RNase H2 atomic model and provide biochemical validation for our structural model. Our results provide new insights into how the subunits are arranged to form an enzymatically active complex. In particular, we establish that the RNASEH2A C terminus is a eukaryotic adaptation for binding the two accessory subunits, with residues within it required for enzymatic activity. This C-terminal extension interacts with the RNASEH2C C terminus and both are necessary to form a stable, enzymatically active heterotrimer. Disease mutations cluster at this interface between all three subunits, destabilizing the complex and/or impairing enzyme activity. Altogether, we locate 25 out of 29 residues mutated in AGS patients, establishing a firm basis for future investigations into disease pathogenesis and function of the RNase H2 enzyme.     

Diatom Communities and Water Quality Assessment in Mountain Rivers of the Upper Segre Basin (La Cerdanya,Oriental Pyrenees)

Epilithic diatoms of mountain rivers from the upper Segre catchment (Oriental Pyrenees) were studied in 1998, during three different seasons: March, July and September. Four rivers, the river Segre and its three most important tributaries, Duran, Molina and Querol, were sampled in upstream and downstream stretches. The diatom communities were comparable in all upstream stretches of these mountain rivers draining siliceous substrates. Dominant taxa were Achnanthidium subatomus, Diatoma mesodon, Encyonema cf. minutum, E. silesiacum, Fragilaria arcus, F. capucina, Gomphonema calcifugum, G. pumilum, Meridion circulare and Nitzschia pura. Changes in water quality in the downstream stretches lead to the appearance of pollution tolerant taxa, such as Eolimna minima, Gomphoneis minuta, Navicula gregaria, and Nitzschia inconspicua. As a result, the values obtained with the diatom water quality indices (IPS Specific Polluosensitivity Index, CEE and IBD Biological Diatom Index) decreased. The diatom community composition and the derived water quality values did not change in the upstream stretches over the year. In contrast, significant changes were observed in the downstream stretches with best water␣quality in July, during high flows due to melting snow, and worst values in September, during low␣discharge. The diatom indices, especially the IPS, showed a good performance in these mountain rivers.