Effects of Ca(II) ions on Mn(II) dynamics in chick glia and rat astrocytes: Potential regulation of glutamine synthetase

Previous studies have demonstrated that in glia and astrocytes Mn(II) is distributed with ca. 30–40% in the cytoplasm, 60–70% in mitochondria. Ca(II) ions were observed to alter both the flux rates and distribution of Mn(II) ions in primary cultues of chick glia and rat astrocytes. External (influxing) Ca(II) ions had the greatest effect on Mn(II) uptake and efflux, compared to internal (effluxing) or internal-external equilibrated Ca(II) ions. External (influxing) Ca(II) ions inhibited the net rate and extent of Mn(II) uptake but enhanced Mn(II) efflux from mitochondria. These observations differ from Ca(II)–Mn(II) effects previously reported with brain (neuronal) mitochondria. Overall, increased cytoplasmic Ca(II) acts to block Mn(II) uptake and enhance Mn(II) release by mitochondria, which serve to increase the cytoplasmic concentration of free Mn(II). A hypothesis is presented involving external L-glutamate acting through membrane receptors to mobilize cell Ca(II), which in turn causes mitochondrial Mn(II) to be released. Because the concentration of free cytoplasmic Mn(II) is poised near the K_d for Mn(II) with glutamine synthetase, a slight increase in cytoplasmic Mn(II) will directly enhance the activity of glutamine synthetase, which catalyzes removal of neurotoxic glutamate and ammonia.     

Multiple pyruvate decarboxylase genes in maize are induced by hypoxia

Two cDNA clones corresponding to anaerobically induced maize mRNAs were found to have homology to a previously identified maize pyruvate decarboxylase gene. DNA sequencing and RFLP mapping indicate that these cDNAs represent two additional maize pdc genes. Each of the clones is approximately 85% identical in predicted amino acid sequence to the other two. All three clones are induced by hypoxic stress, but with different levels and kinetics of induction.     

Elevation of cytosolic calcium precedes anoxic gene expression in maize suspension-cultured cells.

Based on pharmacological evidence, we previously proposed that intracellular Ca2+ mediates the perception of O2 deprivation in maize seedlings. Herein, using fluorescence imaging and photometry of Ca2+ in maize suspension-cultured cells, the proposal was further investigated. Two complementary approaches were taken: (1) real time analysis of anoxia-induced changes in cytosolic Ca2+ concentration ([Ca]i) and (2) experimental manipulation of [Ca]i and then assay of the resultant anoxia-specific responses. O2 depletion caused an immediate increase in [Ca2+]i, and this was reversible within a few seconds of reoxygenation. The [Ca]i elevation proceeded independent of extracellular Ca2+. The kinetics of the Ca2+ response showed that it occurred much earlier than any detectable changes in gene expression. Ruthenium red blocked the anoxic [Ca]i elevation and also the induction of adh1 (encoding alcohol dehydrogenase) and sh1 (encoding sucrose synthase) mRNA. Ca2+, when added along with ruthenium red, prevented the effects of the antagonist on the anoxic responses. Verapamil and bepridil failed to block the [Ca]i rise induced by anoxia and were equally ineffective on anoxic gene expression. Caffeine induced an elevation of [Ca]i as well as ADH activity under normoxia. The data provide direct evidence for [Ca]i elevation in maize cells as a result of anoxia-induced mobilization of Ca2+ from intracellular stores. Furthermore, any manipulation that modified the [Ca]i rise brought about a parallel change in the expression of two anoxia-inducible genes. Thus, these results corroborate our proposal that [Ca]i is a physiological transducer of anoxia signals in plants.     

Clutch size, offspring performance, and intergenerational fitness

It is now generally recognized that clutch size affects morethan offspring number. In particular, clutch size affects asuite of traits associated with offspring reproductive performance.Optimal clutch size is therefore determined not by the numericallymost productive clutch but by the clutch that maximizes collectiveoffspring reproductive success. Calculation of optimal clutchsize thus requires a consideration of ecological factors operatingduring an intergenerational time frame, spanning the lifetimeof the egglaying adult and the lifetimes of her offspring. Theoptimal clutch cannot define reproductive values in advance,but instead requires that the strategy chosen is the best responseto the set of reproductive values that it itself generates.In this article, we introduce methods for solving this problem,based on an iterative solution of the equation characterizingexpected lifetime reproductive success. We begin by consideringa semelparous organism, in which case lifetime reproductivesuccess is a function only of the state of the organism. Foran iteroparous organism, lifetime reproductive success dependsupon both state and time, so that our methods extend the usualstochastic dynamic programming approach to the evaluation oflifetime reproductive success. The methods are intuitive andeasily used. We consider both semelparous and iteroparous organisms,stable and varying environments, and describe how our methodscan be employed empirically.     

Pan-Arctic soil moisture control on tundra carbon sequestration and plant productivity

Long-term atmospheric CO₂ concentration records have suggested a reduction in the positive effect of warming on high-latitude carbon uptake since the 1990s. A variety of mechanisms have been proposed to explain the reduced net carbon sink of northern ecosystems with increased air temperature, including water stress on vegetation and increased respiration over recent decades. However, the lack of consistent long-term carbon flux and in situ soil moisture data has severely limited our ability to identify the mechanisms responsible for the recent reduced carbon sink strength. In this study, we used a record of nearly 100 site-years of eddy covariance data from 11 continuous permafrost tundra sites distributed across the circumpolar Arctic to test the temperature (expressed as growing degree days, GDD) responses of gross primary production (GPP), net ecosystem exchange (NEE), and ecosystem respiration (ER) at different periods of the summer (early, peak, and late summer) including dominant tundra vegetation classes (graminoids and mosses, and shrubs). We further tested GPP, NEE, and ER relationships with soil moisture and vapor pressure deficit to identify potential moisture limitations on plant productivity and net carbon exchange. Our results show a decrease in GPP with rising GDD during the peak summer (July) for both vegetation classes, and a significant relationship between the peak summer GPP and soil moisture after statistically controlling for GDD in a partial correlation analysis. These results suggest that tundra ecosystems might not benefit from increased temperature as much as suggested by several terrestrial biosphere models, if decreased soil moisture limits the peak summer plant productivity, reducing the ability of these ecosystems to sequester carbon during the summer.     

Carbon uptake in Eurasian boreal forests dominates the high-latitude net ecosystem carbon budget

Arctic-boreal landscapes are experiencing profound warming, along with changes in ecosystem moisture status and disturbance from fire. This region is of global importance in terms of carbon feedbacks to climate, yet the sign (sink or source) and magnitude of the Arctic-boreal carbon budget within recent years remains highly uncertain. Here, we provide new estimates of recent (2003–2015) vegetation gross primary productivity (GPP), ecosystem respiration (R_eco), net ecosystem CO₂ exchange (NEE; R_eco − GPP), and terrestrial methane (CH₄) emissions for the Arctic-boreal zone using a satellite data-driven process-model for northern ecosystems (TCFM-Arctic), calibrated and evaluated using measurements from >60 tower eddy covariance (EC) sites. We used TCFM-Arctic to obtain daily 1-km² flux estimates and annual carbon budgets for the pan-Arctic-boreal region. Across the domain, the model indicated an overall average NEE sink of −850 Tg CO₂-C year⁻¹. Eurasian boreal zones, especially those in Siberia, contributed to a majority of the net sink. In contrast, the tundra biome was relatively carbon neutral (ranging from small sink to source). Regional CH₄ emissions from tundra and boreal wetlands (not accounting for aquatic CH₄) were estimated at 35 Tg CH₄-C year⁻¹. Accounting for additional emissions from open water aquatic bodies and from fire, using available estimates from the literature, reduced the total regional NEE sink by 21% and shifted many far northern tundra landscapes, and some boreal forests, to a net carbon source. This assessment, based on in situ observations and models, improves our understanding of the high-latitude carbon status and also indicates a continued need for integrated site-to-regional assessments to monitor the vulnerability of these ecosystems to climate change.     

16S rDNA analysis reveals phylogenetic diversity among the polysaccharolytic clostridia

Abstract Small subunit rDNA sequences were determined for 13 mesophilic, polysaccharolytic, mainly cellulolytic species of the genus Clostridium and one cellulolytic Eubacterium specues. Sequences were compared to those of 36 representatives of mesophilic and thermophilic clostridia, including those of nine thermophilic polysaccharolytic species published previously. The majority of strains group with 23S rRNA clusters I and III, while the others group with the thermophilic polysaccharolytic clostridia, i.e. C. stercorarium, C. thermolacticum and C. thermocellum . Lack of close genetic relationships between the various polysaccharolytic species is unexpected and may indicate that these biotechnologically important organisms differ with respect to the enzymology of polysaccharolytic degradation as well.     

PHYLOGENY OF THE ULVOPHYCEAE (CHLOROPHYTA): CLADISTIC ANALYSIS OF NUCLEAR-ENCODED rRNA SEQUENCE DATA1

Cladistic analysis of nuclear-encoded rRNA sequence data provided us with the basis for some new hypotheses of relationships within the green algal class Ulvophyceae. The orders Ulotrichales and Ulvales are separated from the clade formed by the remaining orders of siphonous and siphonocladous Ulvophyceae (Caulerpales, Siphonocladales /Cladophorales [S/C] complex, and the Dasycladales), by the Chlorophyceae and Pleurastrophyceae. Our results suggest that the Ulvophyceae is not a monophyletic group. Examination of inter- and intra-ordinal relationships within the siphonous and siphonocladous ulvophycean algae revealed that Cladophora, Chaetomorpha, Anadyomene, Microdictyon, Cladophoropsis and Dictyosphaeria form a clade. Thus the hypothesis, based on ultrastructural features, that the Siphonocladales and Cladophorales are closely related is supported. Also, the Caulerpales is a monophyletic group with two lineages; Caulerpa, Halimeda, and Udotea comprise one, and Bryopsis and Codium comprise the other. The Dasycladales (Cymopolia and Batophora) also forms a clade, but this clade is not inferred to be the sister group to the S/C complex as has been proposed. Instead, it is either the sister taxon to the Caulerpales or basal to the Caulerpales and S/C clade The Trentepohliales is also included at the base of the siphonous and siphonocladous ulvophycean clade. The Pleurastrophyceae, which, like the Ulvophyceae, posses a counter-clockwise arrangement of flagellar basal bodies, are more closely related to the Chlorophyceae than to the Ulvophyceae based on rRNA sequences. Thus, the arrangement of basal bodies does not diagnose a monophyletic group. Previously reported hypotheses of phylogenetic relationships of ulvophycean algae were tested. In each case, additional evolutionary steps were required to obtain the proposed relationships. Relationships of ulvophycean algae to other classes of green algae are discussed.     

Simultaneous addition of EGF prolongs the increase in cytosolic free calcium seen in response to bradykinin in NRK-49F cells

The calcium-sensitive fluorescent indicator fura-2 and a microscope equipped for rapidly changing excitation wavelengths were used to look at the effects of growth factors on cytosolic free calcium ([Ca²⁺]_i,) in NRK-49F cells. In these cells bradykinin induced a rapid increase in [Ca²⁺]_i, which generally decayed to near basal [Ca²⁺]_i within 3 minutes. The initial rise in [Ca²⁺]_i in response to bradykinin was relatively independent of extracellular calcium; however, the decay to basal [Ca²⁺]_i was more rapid in the absence of extracellular calcium. Measurements made on individual cells showed a heterogeneity in the response to bradykinin. Epidermal growth factor (EGF) had no effect on [Ca²⁺]_i in NRK-49F cells when added alone in the presence of extracellular calcium. Simultaneous addition of bradykinin and EGF produced a more prolonged increase in [Ca²⁺]_i than bradykinin alone. The prolongation was dependent on the presence of extracellular calcium and did not occur in its absence. Transient increases in [Ca²⁺]_i occurring after the initial peak were occasionally seen in these cells. Our results indicate that there is rapid interaction between the signaling mechanisms for bradykinin and EGF. When this occurs, one effect is the transport of calcium into the cell from the extracellular environment, causing a more prolonged rise in [Ca²⁺]_i. This effect occurs within 1 minute after combined addition of bradykinin and EGF.