Interaction between zinc and calcium in skeletal muscle in young growing rats

The purpose of the present study was to determine whether zinc and calcium could interact at the tissue level. In the first part of the study, adult rats were injected with ZnCl₂ dissolved in a physiological saline solution to determine the effects of Zn on Ca levels in various tissues. In the second part of the study, weaned rats (at day 22 postnatally) were fed a diet supplemented with Zn until day 50 and were then sacrificed. In both instances, blood, brain, heart, liver, and skeletal muscle were taken and analyzed. In the Zn-injected group, the brain, heart, and liver showed no interaction between Zn and Ca. The skeletal muscle, in contrast, showed a decrease in Ca in the homogenate, whereas Zn contents showed a significant increase at the sarcoplasmic reticulum (SR). Likewise, in the Zn-supplemented group, the Zn content of the SR vesicle of the skeletal muscle showed an increase, whereas Ca content of the pellet (14,000 g), which contains cell debris, nucleus, mitochondria, and SR vesicles of this group, showed a decrease. Current findings suggest antagonistic effects between Zn and Ca on this tissue. Zn may play a critical role in cellular function through the alteration of itnracellular distribution of Ca in skeletal muscle.     

Effect of a salt-osmotic upshock on the edaphic microalga Neochloris oleoabundans

Abstract. The edaphic microalga Neochloris oleoabundans (isolated from desert soil) was subjected to a salt-osmotic shock from 0 to 0·6 kmol m⁻³ NaCl. The effect of the osmotic upshock on the cell composition was determined. The cell dry weight and the lipid, glycerol and soluble amino acids contents remained unchanged during 5d of osmotic upshock. The protein content increased after 2d of initial osmotic shock, and it appears to be a long-term haloadaptation process of the cells. The most important short-term effects of salt osmotic upshock were a decrease in polysaccharide content and an increase in the soluble carbohydrate content of Neochloris oleoabundans cells. Within the first 4h after the initial shock, there was a transfer of carbon units from polysaccharides to sucrose which was independent of photosynthesis. The increase of intracellular concentration of sucrose contributed to cell osmoregulation.     

Local predator composition and landscape affects biological control of aphids in alfalfa fields

The biological control service supplied to croplands is a result of the predator community present within a focal crop, which is likely influenced by surrounding landscape composition and configuration. In this study, using cage experiments in two regions near Santiago, we determined if predator communities supplied a significant biological control service in alfalfa fields, examined how the abundance of exotic and native coccinellids, as well as other key predator groups, influenced biological control of aphids and measured how landscape composition and heterogeneity at three spatial scales influenced this service. We found that predators significantly suppressed aphid populations in both regions, but the relative importance of predators versus landscape variables on biological control differed between regions. In the region where predators were abundant, biological control was higher and related to the abundance of native coccinellids and syrphids, highlighting the importance of native species as providers of crucial ecological services. In the region where predators were not abundant, biological control was lower, and it was related to landscape composition, being positively associated with the abundance of woodlots and urban habitats, and negatively associated with fruit crops in the landscape. Therefore, landscape effects on biological control service may be weaker than local factors, and only become important when local predator abundance is low.     

Ribosomal Tag Pyrosequencing of DNA and RNA Reveals “Rare” Taxa with High Protein Synthesis Potential in the Sediment of a Hypersaline Lake in Western Australia

Little is known about the potential activity of microbial communities in hypersaline sediment ecosystems. Ribosomal tag libraries of DNA and RNA extracted from the sediment of Lake Strawbridge (Western Australia) revealed bacterial and archaeal operational taxonomic units (OTUs) with high RNA/DNA ratios providing evidence for the presence of ‘rare’ but potentially “active” taxa. Among the ‘rare’ bacterial taxa Halomonas, Salinivibrio and Idiomarina showed the highest protein synthesis potential. Rare but ‘active’ archaeal OTUs were related to the KTK 4A cluster and the Marine-Benthic-Groups B and D. We present the first molecular analysis of the microbial diversity and protein synthesis potential of rare microbial taxa in a hypersaline sediment ecosystem.     

Biogeography of Iberian freshwater fishes revisited: the roles of historical versus contemporary constraints

Aim The question of how much of the shared geographical distribution of biota is due to environmental vs. historical constraints remains unanswered. The aim of this paper is to disentangle the contribution of historical vs. contemporary factors to the distribution of freshwater fish species. In addition, it illustrates how quantifying the contribution of each type of factor improves the classification of biogeographical provinces. Location Iberian Peninsula, south‐western Europe (c. 581,000 km²). Methods We used the most comprehensive data on native fish distributions for the Iberian Peninsula, compiled from Portuguese and Spanish sources on a 20‐km grid‐cell resolution. Overall, 58 species were analysed after being categorized into three groups according to their ability to disperse through saltwater: (1) species strictly intolerant of saltwater (primary species); (2) species partially tolerant of saltwater, making limited incursions into saltwaters (secondary species); and (3) saltwater‐tolerant species that migrate back and forth from sea to freshwaters or have invaded freshwaters recently (peripheral species). Distance‐based multivariate analyses were used to test the role of historical (basin formation) vs. contemporary environmental (climate) conditions in explaining current patterns of native fish assemblage composition. Cluster analyses were performed to explore species co‐occurrence patterns and redefine biogeographical provinces based on the distributions of fishes. Results River basin boundaries were better at segregating species composition for all species groups than contemporary climate variables. This historical signal was especially evident for primary and secondary freshwater fishes. Eleven biogeographical provinces were delineated. Basins flowing to the Atlantic Ocean north of the Tagus Basin and those flowing to the Mediterranean Sea north of the Mijares Basin were the most dissimilar group. Primary and secondary freshwater species had higher province fidelity than peripheral species. Main conclusions The results support the hypothesis that historical factors exert greater constraints on native freshwater fish assemblages in the Iberian Peninsula than do current environmental factors. After examining patterns of assemblage variation across space, as evidenced by the biogeographical provinces, we discuss the likely dispersal and speciation events that underlie these patterns.     

Fungal endophyte communities in above- and belowground olive tree organs and the effect of season and geographic location on their structures

Studies comparing fungal endophytes between above- and belowground woody crop organs and the factors that may structure their communities are lacking. Due to its great impact on the Mediterranean Basin, the olive tree was chosen for the isolation of endophytic fungi from roots, leaves and twigs in two seasons in north-eastern Portugal. Nine hundred seventy-six isolates belonging to 38 fungal species were obtained. Phomopsis columnaris, Fusarium oxysporum and Trichoderma gamsii were the most frequently isolated, collectively representing 69% of the isolates. Fungal diversity in the roots was higher than in the aboveground organs and higher in spring than autumn. Endophyte community similarity between the above- and belowground organs and between seasons was low. Species composition also varied spatially, with the fungal composition of the roots varying more among locations than that of the aboveground organs. Our results suggest olive tree endophyte community structure is affected by plant organ, location and season.     

Response of winter chemical defense in Alaska paper birch and green alder to manipulation of plant carbon/nutrient balance

Summary Plant carbon/nutrient balance has been implicated as an important factor in plant defensive chemistry and palatability to herbivores. We tested this hypothesis by fertilizing juvenile growth form Alaska paper birch and green alder with N, P and N-plus-P in a balanced 2x2 factorial experiment. Additionally, we shaded unfertilized plants of both species. Fertilization with N and N-plus-P increased growth of Alaska paper birch, reduced the concentration of papyriferic acid in internodes and increased the palatability of birch twigs to snowshoe hares. Shading decreased birch growth, decreased the concentration of papyriferic acid in internodes and increased twig palatability. These results indicate that the defensive chemistry and palatability of winter-dormant juvenile Alaska paper birch are sensitive to soil fertility and shade. Conversely the defensive chemistry and palatability of green alder twigs to snowshoe hares were not significantly affected by soil fertility or shade. The greater sensitivity of Alaska paper birch defensive chemistry and palatability to snowshoe hares in comparison to green alder is in agreement with the hypothesis that early successional woody plants that are adapted to high resource availability are more plastic in their chemical responses to the physical environment than are species from less favorable environments.     

The chemical composition of Astragalus: a comparison of seleniferous and non-seleniferous plants growing side by side

COWGILL, U. M. & LANDENBERGER, B.D., 1992. The chemical composition of Astragalus: a comparison of seleniferous and non-seleniferous plants growing side by side. This paper describes how non-seleniferous plant species coexist with seleniferous ones and what chemical changes occur in non-seleniferous species that allow the toleration of large quantities of volatilized Se-bearing compounds. These compounds are known for their phytotoxicity as well as for their toxicity to mammals and insects. Twenty-three sites (Colorado, Utah, New Mexico, U.S.A.) were examined over a 6-year period. Plants collected from these sites were divided into four groups: seleniferous astragali, seleniferous Brassicaceae, non-seleniferous astragali and non-seleniferous associated genera. Furthermore, it was possible to categorize these sites: Type 1 sites supported all four groups of plants, Type 2 sites contained only seleniferous astragali, whereas Type 3 sites sustained only non-seleniferous astragali. When concentrations of Cu, Zn (P <0.0001), Si (P<0.02), As, Pb (P<0.03) and Cs (P<0.05) were measured, the values for those seleniferous astragali that coexisted with other species were significantly different from the values found for those seleniferous astragali that grew alone. There were four areas that in some years supported all four groups of plants (Type 1 site) and in other years contained only seleniferous astragali. In this way, the latter may be used as a chemical control for the former. The seleniferous astragali collected at Type 1 sites always contained more Cu, As, Si and Pb than the solitary astragali of Type 2 sites. When seleniferous astragali of Type 1 sites that support all four groups of plants develop in a year where the usually associated species of past years are absent, they contain in their tissues concentrations of Cu, As, Si, Pb, Zn and Cs typical of Type 2 sites where the seleniferous astragali grew alone. Non-seleniferous astragali of Type 1 sites that support all four groups of plants have a chemical composition that differs significantly in the quantity of 15 elements from non-seleniferous astragali of Type 3 sites where the latter grew alone. Since allelochemicals such as phenolic acids and flavonoids are well known to be able to alter mineral absorption by plants and since the astragali are known to produce such substances, it is suggested that the possible production of phenolic acids and flavonoids may permit coexistence of seleniferous plants with non-seleniferous ones and thus explain the chemical differences among the plants of the four types of sites.