Community composition and soil properties in northern Bolivian savanna vegetation

Abstract. Direct gradient analysis (Canonical Correspondence Analysis) of northern Bolivian savanna vegetation revealed correlations between the composition of plant communities and physical and chemical soil properties. Cover/abundance values for 193 species from 27 sites were related to data on eight soil factors. A water-regime variable and the percentage of sand and silt were correlated with the first axis of the species-environment biplot and explained most of the variation in community composition. Along this axis, species and sites of flood-plain vegetation were separated from sites not affected by flooding rivers. The second axis of the biplot was correlated with soil-chemical variables, namely extract-able phosphate, base saturation, organic carbon, pH, and effective cation exchange capacity. Part of the variation in community composition can be explained by these soil nutrient variables. Grassland communities were separated from woody vegetation along the soil nutrient gradient, and floodplain communities of white-water rivers from those of clear-water rivers. The results of the gradient analysis indicate that the soil texture-moisture gradient is the prime factor determining the variation in the floristic composition of the savanna communities examined, and that, in addition, the soil nutrient gradient accounts for some of the variation.     

Long term study on the influence of eutrophication, restoration and biomanipulation on the structure and development of phytoplankton communities in Feldberger Haussee (Baltic Lake District, Germany)

Feldberger Haussee provides a classic example of eutrophication history of hardwater lakes in the Baltic Lake District (Germany) and of changes in their algal flora during the 20th century. The lake originally was regarded as slightly eutrophic. A process of drastic eutrophication from the 1950s until the end of the 1970s caused mass developments of blue-green and green algae. A restoration program was started in the 1980s to improve the water quality of the lake using both diversion of sewage outside the catchment area, and biomanipulation by altering the fish community. This restoration program led to positive changes in the lake ecosystem. Direct effects of biomanipulation resulted in an increase of herbivorous zooplankton, a decrease of phytoplankton biomass, and an increase of water transparency. The recovery of Feldberger Haussee also may have been indirectly enhanced by an increase in nutrient sedimentation as a consequence of intensified calcite precipitation, decrease in phosphorus remobilization due to a pH-decrease, increased NIP-ratio, and recolonization of the littoral zone by macrophytes. This paper concentrates on the long term development of the phytoplankton community as a response to changes in the food web structure as well as to alterations in the chemical environment of the algae. Both are reflected in four major stages passed by the algal assemblage between 1980 and 1994: (1) From 1980-summer 1985 dense green algal populations were found indicating similar conditions as in the 1970s during the period of maximum eutrophication. (2) A diverse phytoplankton community during summer 1985–1989 showed the first effects of a recovery. (3) From 1990–1992 the phytoplankton was characterized by ungrazeable filamentous blue-green algae first of all as a response to increased herbivory of zooplankton on edible species and to increasing N/P-ratios. (4) Finally, the algal species diversity increased in 1993 and 1994 whereas the phytoplankton biomass decreased showing the success of the combined restoration measures.     

HSP25 in isolated perfused rat hearts: Localization and response to hyperthermia

Recent investigations concentrate on the correlation between the myocardial expression of the inducible 70-kDa heat shock protein (HSP70i) by different stress conditions and its possible protective effects. Only few studies have focused on the involvement of small heat shock proteins in this process. We analyzed the location of the small heat shock protein HSP25 in isolated cardiomyocytes as well as its location and induction in isolated perfused hearts of rats. By immunofluorescence microscopy HSP25 was found to colocalize with actin in the I-band of myofibrils in cardiomyocytes of isolated perfused hearts as well as in isolated neonatal and adult cardiomyocytes. Hyperthermic perfusion of isolated hearts for 45 min resulted in modulation of different parameters of heart function and in induction of HSP25 and HSP70i. Temperatures higher than 43°C (44–46°C) were lethal with respect to the contractile function of the hearts. Compared to control hearts perfused at 37°C, significant increases during hyperthermic perfusion at 42°C and 43°C were obtained for heart rate, contraction velocity and relaxation velocity. In response to hyperthermia at 43°C and after subsequent normothermic perfusion for 135 min at 37°C, left ventricular pressure, contraction velocity and relaxation velocity remained significantly elevated. However, heart rate returned to control values immediately after the period of heat treatment. HSP25 is constitutively expressed even in normothermic perfused hearts as shown by Western blotting. Hyperthermia increased the content of HSP25 only in the left ventricular tissue. In contrast, HSP70i was strongly induced in all analyzed parts of the myocardium (left ventricle, right ventricle, septum). Our findings suggest a differential regulation of HSP25 and HSP70i expression in response to hyperthermia in isolated perfused hearts. The constitutively expressed HSP25 seems to be located adjacent to the myofibrils which implies a specific role of this protein even under unstressed conditions for the contractile function of the myocardium.     

Induction and ionic basis of slow wave potentials in seedlings of Pisum sativum L.

Slow wave potentials (SWPs) are transient depolarizations which propagate substantial distances from their point of origin. They were induced in the epidermal cells of pea epicotyls by injurious methods such as root excision and heat treatment, as well as by externally applied defined steps in xylem pressure (Px) in the absence of wounding. The common principle of induction was a rapid increase in Px. Such a stimulus appeared under natural conditions after (i) bending of the epicotyl, (ii) wounding of the epidermis, (iii) rewatering of dehydrated roots, and (iv) embolism. The induced depolarization was not associated with a change in cell input resistance. This result and the ineffectiveness of ion channel blockers point to H(+)-pumps rather than ion channels as the ionic basis of the SWP. Stimuli such as excision, heat treatment and pressure steps, which generate SWPs, caused a transient increase in the fluorescence intensity of epicotyls loaded with the pH-indicator DM-NERF, a 2',7'-dimethyl derivative of rhodol, but not of those loaded with the pH indicator 2',7'bis(2-carboxyethyl)-5-(and-6)-carboxyfluorescein (BCECF). Matching kinetics of depolarization and pH response identify a transient inactivation of proton pumps in the plasma membrane as the causal mechanism of the SWP. Feeding pump inhibitors to the cut surface of excised epicotyls failed to chemically simulate a SWP; cyanide, azide and 2,4-dinitrophenol caused sustained, local depolarizations which did not propagate. Of all tested substances, only sodium cholate caused a transient and propagating depolarization whose arrival in the growing region of the epicotyl coincided with a transient growth rate reduction.     

Isolation and characterization of two cDNA clones encoding ATP-sulfurylases from potato by complementation of a yeast mutant

Sulfur plays an important role in plants, being used for the biosynthesis of amino acids, sulfolipids and secondary metabolites. After uptake sulfate is activated and subsequently reduced to sulfide or serves as donor for sulfurylation reactions. The first step in the activation of sulfate in all cases studied so far is catalyzed by the enzyme ATP-sulfurylase (E.C. 2.7.7.4.) which catalyzes the formation of adenosine-5′-phosphosulfate (APS). Two cDNA clones from potato encoding ATP-sulfurylases were identified following transformation of a Saccharomyces cerevisiae mutant deficient in ATP-sulfurylase activity with a cDNA library from potato source leaf poly(A)⁺ RNA cloned in a yeast expression vector. Several transformants were able to grow on a medium with sulfate as the only sulfur source, this ability being strictly linked to the presence of two classes of cDNAs. The clones StMet3-1 and StMet3-2 were further analyzed. DNA analysis revealed an open reading frame encoding a protein with a molecular mass of 48 kDa in the case of StMet3-1 and 52 kDa for StMet3-2. The deduced polypeptides are 88% identical at the amino acid level. The clone StMet3-2 has a 48 amino acid N-terminal extension which shows common features of a chloroplast transit peptide. Sequence comparison of the ATP-sulfurylase Met3 from Saccharomyces cerevisiae with the cDNA StMet3-1 (StMet3-2) reveals 31% (30%) identity at the amino acid level. Protein extracts from the yeast mutant transformed with the clone StMet3-1 displayed ATP-sulfurylase activity. RNA blot analysis demonstrated the expression of both genes in potato leaves, root and stem, but not in tubers. To the best of the authors' knowledge this is the first cloning and identification of genes involved in the reductive sulfate assimilation pathway from higher plants.     

Efficient generation of chimaeric mice using embryonic stem cells after long-term culture in the presence of ciliary neurotrophic factor

The aim of our study was to evaluate whether ciliary neurotrophic factor (CNTF) can substitute for leukaemia inhibitory factor (LIF) in maintaining pluripotential embryonic stem (ES) cells in culture. Two subclones of D3 ES cells were used to assess cell proliferation and differentiation in the presence of CNTF, LIF or Buffalo rat liver (BRL) cell-conditioned medium, or in the absence of exogenous differentiation inhibiting factors. ES cells maintained in medium supplemented with CNTF for up to four weeks were injected into blastocysts to investigate theirin vivo pluripotency in terms of chimaera formation. CNTF inhibited ES cell differentiation in a dose-dependent manner. The most effective concentration was 10 ng CNTF per ml of medium. The effects of CNTF on ES cell differentiation and proliferation were comparable to those of LIF at the same concentration. BRL cell-conditioned medium was less effective at preventing ES cell differentiation but induced their proliferation very markedly. Both ES cell clones efficiently formed chimaeras after long-term culture with CNTF as the only differentiation inhibiting agent. The ability of these ES cells to colonize the germ-line is the ultimate proof that CNTF can preserve the pluripotency of ES cells.     

Adrenergic Stimulation of Cyclic GMP Formation Requires NO-Dependent Activation of Cytosolic Guanylate Cyclase in Rat Pinealocytes

Abstract: Cyclic GMP (cGMP) formation in rat pinealocytes is regulated through a synergistic dual receptor mechanism involving β-and α₁-adrenergic receptors. The effects of N -monomethyl- l -arginine (NMMA), which inhibits nitric oxide (NO) synthase and NO-mediated activation of cytosolic guanylate cyclase, and methylene blue (MB), which inhibits cytosolic guanylate cyclase, were investigated in an attempt to understand the role of NO in adrenergic cGMP formation. Both NMMA and MB inhibited β-adrenergic stimulation of cGMP formation as well as α₁-adrenergic potentiation of β-adrenergic stimulation of cGMP formation, whereas they had no effect in unstimulated pinealocytes. The inhibitory action of NMMA was antagonized by addition of l -arginine. On the basis of these findings it can be concluded that the adrenergic stimulation of cGMP formation involves NO synthesis followed by activation of cytosolic guanylate cyclase.     

Evidence for two different blue-light-receptor systems for the fast responses of stimulation of photosynthetic capacity and acidification of the plant surface in brown algae

Two blue-light responses of Phaeophyta that are expressed within a few seconds of a blue-light stimulus were characterized with respect to their photoreception properties. The first response is the activation of red-light-saturated photosynthesis which can be stimulated to values up to 5 times the rates in red light, depending on the species. The second response is a blue-light-induced acidification measurable at the plant surface. Both responses have similar kinetic characteristics and thus led us initially to hypothesise that they were causally connected in the same transduction mechanism. The two responses have action spectra [measured for Ectocarpus siliculosus (Dillwyn) Lyngb. and Laminaria saccharina (L.) Lamouroux] that are indistinguishable within the relatively large limits of error. However, in all species tested, the threshold sensitivity for blue light of the photosynthetic response is lower than that of the pH-shift by a factor of 2 to 150. Furthermore, stimulation of photosynthesis is sensitive to the flavin inhibitors, KI and phenylacetic acid, but the pH response is not affected by these inhibitors. Thus, the blue-light-induced pH-shift does not cause the stimulation of photosynthesis. In contrast, the different fluence-response relationships of the two responses and particularly the differential effect of the inhibitors are clear evidence for the action of two independent transduction pathways and photoreceptor systems for blue light. At least photoreception for stimulation of photosynthesis involves a flavin-or and a pterin.Abbreviations DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - PAA phenylacetic acid We thank Dr. C. A. Maggs for collecting P. pavonica. This research was supported by National Environment Research Council grant No. GR3/8102.