PHYSIOLOGICAL INDICATORS OF NUTRIENT DEFICIENCY IN CLADOPHORA (CHLOROPHYTA) IN THE CLARK FORK OF THE COLUMBIA RIVER,MONTANA1

Cellular nutrient concentrations and nutrient uptake rates of Cladophora glomerata (L.) Kuetzing were determined during summer and fall in 1989–1990 at a site on the upper Clark Fork of the Columbia River, Montana. Both physiological tests indicated that Cladophora growth is likely to be limited by nitrogen during late summer-early fall. Maximum uptake rates of ammonia-N and nitrate-N were 5935–6991 and 507–984 μg · g DW^?1· h^?1, respectively, during July–October when dissolved inorganic nitrogen (DIN) concentrations in the river were less than 10 μg · L^?1. During November-December, when DIN was 72–376 μg · L^?1, maximum ammonia-N uptake was 1137–1633 μg · g DW^?1· h^?1 and maximum nitrate-N uptake was 0–196 μg · g DW^?1· h^?1. Cellular nitrogen during summer–early fall was 0.78–1.80% of Cladophora dry weight, frequently at or below 1.1%, a level suggested as a critical minimum N concentration for maximum growth. In contrast, cellular P was 0.18–0.36% of dry weight, 3–6 times the suggested critical P concentration of 0.06%. Molar ratios of cellular N:P (< 16:1) and DIN: SRP (< 4:1) during late summer-early fall also indicated potential N limitation. Cellular N and P from Cladophora collected from a second site influenced by a municipal wastewater discharge in 1990 displayed similar seasonal trends. At both sites, seasonal fluctuations in DIN were closely tracked by changes in cellular N, Cellular P, however, increased through the growing season despite declining levels of SRP in the river.     

Effect of temperature and host plant on the development of the blackfaced leafhopper

Population dynamics of the blackfaced leafhopper, Graminella nigrifrons (Forbes) (Homoptera: Cicadellidae), was studied at five temperatures (18, 21, 24, 27, & 30°C) in the laboratory on seedling maize (Zea mays L.), oats (Avena sativa L.), and the perennial johnsongrass (Sorghum halepense (L.) Pers.). Effects of temperature and host plant on egg to adult mean development time, adult size and weight, and fecundity were determined. Leafhoppers on all three hosts developed fastest at the highest temperature tested (21.3 days), and slowest at the lowest temperature tested (73.2 days). The duration from first to last adult eclosion was shortest at 30°C, (11.5 days) and longest at 18°C (43 days). The sex ratio of males to females did not differ from 1:1, but males developed an average of 1.2 days faster than females on all three hosts. Mean percent development/day ranged from 1.4% at 18°C to 4.7% at 30°C. The relationship of this development rate and temperature was determined using both a linear model and a variable parameter biophysical model. Based on these models, the developmental threshold is estimated at 12–15°C. The lowest temperature yielded larger and heavier adults (312 g, dry weight) than did the highest temperature (225 g). Fewer leafhoppers developed on the perennial than the annuals at 30°C and fewer on the annuals than the perennial at 18°C. Our results suggest that early in the season johnsongrass and perhaps other perennials are the superior developmental hosts for this leafhopper, whereas in midsummer when temperatures are highest, annuals are the better hosts.

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Résumé La dynamique des populations (durée de développement de l'uf à l'adulte, poids et taille des adultes, fécondité) de G. nigrifrons Forbes (Homop. Cicadellidae) a été étudiée au laboratoire à 5 températures sur plantules de maïs (Zea mays L.), avoine (Avena sativa L.) et sorgho vivace (Shorgum halepense (L.) Pers.). Sur les 3 plantes, les mâles se développent en moyenne 1,2 j plus vite que les femelles. Les relations entre vitesse de développement et température ont été déterminées en utilisant à la fois un modèle linéaire et le modèle biophysique à 2 paramètres de Sharpe & DeMichele (1977).Les températures plus basses donnent des adultes des 2 sexes plus gros et plus lourds. Moins de G. nigrifrons se sont développés sur la graminée vivace que sur les 2 graminées annuelles à la température la plus élevée (30°C), tandis qu'à la température la plus basse (18°C) moins de cicadelles se sont développées sur les graminées annuelles. La température semble jouer un rôle significatif en déterminant l'adéquation des plantes comme hôtes convenant au développement de G. nigrifrons. Le potentiel de ponte de cette cicadelle avait été sous-estimé par les étudies précédentes.

     

Structural relationship between tRNA2 Lys and tRNA4 Lys from mouse lymphoma cells

Summary Mouse lymphoma cells have three major isoaccepting lysine tRNAs. Two of these isoacceptors, tRNA₂ ^Lys and tRNA₄ ^Lys, were sequenced by rapid gel or chromatogram readout methods. They have the same primary sequence but differ in two modified nucleotides. tRNA₄ ^Lys has an unmodified uridine replacing one dihydrouridine and an unidentified nucleotide, t⁶A^*, replacing t⁶A. This unidentified nucleotide is not a hypomodified form of t⁶A. Thus, tRNA4ys is not a simple precursor of tRNA₂ ^Lys. Both tRNAs have an unidentified nucleotide, U^**, in the third position of the anticodon. Also, partial sequences of minor homologs of tRNA₂ ^Lys and tRNA₄ ^Lys were obtained. The distinctions between tRNA₂ ^Lys and tRNA₄ ^Lys may be part of significant cellular roles as illustrated by the differential effects of these isoacceptors on the synthesis by lysyl-tRNA synthetase of diadenosine-5,5-P₁,P₄-tetraphosphate, a putative signal in DNA replication.     

Recruitment of β-Arrestin into Neuronal Cilia Modulates Somatostatin Receptor Subtype 3 Ciliary Localization

Primary cilia are essential sensory and signaling organelles present on nearly every mammalian cell type. Defects in primary cilia underlie a class of human diseases collectively termed ciliopathies. Primary cilia are restricted subcellular compartments, and specialized mechanisms coordinate the localization of proteins to cilia. Moreover, trafficking of proteins into and out of cilia is required for proper ciliary function, and this process is disrupted in ciliopathies. The somatostatin receptor subtype 3 (Sstr3) is selectively targeted to primary cilia on neurons in the mammalian brain and is implicated in learning and memory. Here, we show that Sstr3 localization to cilia is dynamic and decreases in response to somatostatin treatment. We further show that somatostatin treatment stimulates β-arrestin recruitment into Sstr3-positive cilia and this recruitment can be blocked by mutations in Sstr3 that impact agonist binding or phosphorylation. Importantly, somatostatin treatment fails to decrease Sstr3 ciliary localization in neurons lacking β-arrestin 2. Together, our results implicate β-arrestin in the modulation of Sstr3 ciliary localization and further suggest a role for β-arrestin in the mediation of Sstr3 ciliary signaling.     

Effect of resistance exercise on postprandial lipemia.

The purpose of this study was to examine the effect of resistance exercise on postprandial lipemia. Fourteen young men and women participated in each of three treatments: 1) control (Con), 2) resistance exercise (RE), and 3) aerobic exercise (AE) estimated to have an energy expenditure (EE) equal that for RE. Each trial consisted of performing a treatment on day 1 and ingesting a fat-tolerance test meal 16 h later (day 2). Resting metabolic rate and fat oxidation were measured at baseline and at 3 and 6 h postprandial on day 2. Blood was collected at baseline and at 0.5, 1, 2, 3, 4, 5, and 6 h after meal ingestion. RE and AE were similar in EE [1.7 +/- 0.1 vs. 1.6 +/- 0.1 (SE) MJ, respectively], as measured by using the Cosmed K4b(2). Baseline triglycerides (TG) were significantly lower after RE than after Con (19%) and AE (21%). Furthermore, the area under the postprandial response curve for TG, adjusted for baseline differences, was significantly lower after RE than after Con (14%) and AE (18%). Resting fat oxidation was significantly greater after RE than after Con (21%) and AE (28%). These results indicate that resistance exercise lowers baseline and postprandial TG, and increases resting fat oxidation, 16 h after exercise.     

The malaria parasite's chloroquine resistance transporter is a member of the drug/metabolite transporter superfamily

The malaria parasite's chloroquine resistance transporter (CRT) is an integral membrane protein localized to the parasite's acidic digestive vacuole. The function of CRT is not known and the protein was originally described as a transporter simply because it possesses 10 transmembrane domains. In wild-type (chloroquine-sensitive) parasites, chloroquine accumulates to high concentrations within the digestive vacuole and it is through interactions in this compartment that it exerts its antimalarial effect. Mutations in CRT can cause a decreased intravacuolar concentration of chloroquine and thereby confer chloroquine resistance. However, the mechanism by which they do so is not understood. In this paper we present the results of a detailed bioinformatic analysis that reveals that CRT is a member of a previously undefined family of proteins, falling within the drug/metabolite transporter superfamily. Comparisons between CRT and other members of the superfamily provide insight into the possible role of the protein and into the significance of the mutations associated with the chloroquine resistance phenotype. The protein is predicted to function as a dimer and to be oriented with its termini in the parasite cytosol. The key chloroquine-resistance-conferring mutation (K76T) is localized in a region of the protein implicated in substrate selectivity. The mutation is predicted to alter the selectivity of the protein such that it is able to transport the cationic (protonated) form of chloroquine down its steep concentration gradient, out of the acidic vacuole, and therefore away from its site of action.     

Effects of aboveground herbivory on plants with long-term belowground biomass storage

Plant tolerance to herbivory is contingent on multiple traits and adaptive mechanisms, which makes it a complex response with ecological implications. In plants with long-term belowground storage, allocation of biomass to inaccessible parts belowground in response to folivory is a well-recognized tolerance mechanism. In temperate regions, spring growth from buried rootstock is common among winter deciduous plants and is often followed by regrowth after defoliation, both of which draws resources from the stored reserves. We developed a mathematical model to analyze this tolerance response in a winter deciduous plant with long-term belowground biomass when it is defoliated by a specialist insect folivore. The model explores how three closely associated traits—(1) belowground biomass allocation to roots, (2) spring utilization of stored reserves, and (3) post-defoliation regrowth capacity—modulate the persistence and dynamics of the plant and herbivore populations. Model results show that allocation to belowground storage is not only a critical component of tolerance but also influences the herbivore population dynamics in ways that depend on how and when plant biomass is allocated and used. Low belowground biomass allocation and high storage utilization combined with poor photosynthetic growth caused extirpation of the plant population by the defoliating insects. Stable coexistence of the plant at low biomass along with its specialist insect required a moderate amount of post-herbivory belowground allocation. High values of belowground biomass allocation, storage utilization, and photosynthetic growth resulted in sustained cycles of the herbivore and plant populations. Interestingly, utilization of stored reserves had conflicting influence on above and belowground biomass, and strongly affected herbivore population dynamics. Our model thus highlights the complexity of tolerance response when it involves multiple traits and mechanisms as evinced by winter deciduous plants. We close by discussing the implications of our findings for the contributions of defoliating insects to biocontrol programs.     

Myocardial dysfunction in an animal model of cancer cachexia

AimsFatigue is a common occurrence in cancer patients regardless of tumor type or anti-tumor therapies and is an especially problematic symptom in persons with incurable tumor disease. In rodents, tumor-induced fatigue is associated with a progressive loss of skeletal muscle mass and increased expression of biomarkers of muscle protein degradation. The purpose of the present study was to determine if muscle wasting and expression of biomarkers of muscle protein degradation occur in the hearts of tumor-bearing mice, and if these effects of tumor growth are associated with changes in cardiac function.Main methodsThe colon26 adenocarcinoma cell line was implanted into female CD2F1 mice and skeletal muscle wasting, in vivo heart function, in vitro cardiomyocyte function, and biomarkers of muscle protein degradation were determined.Key findingsExpression of biomarkers of protein degradation were increased in both the gastrocnemius and heart muscle of tumor-bearing mice and caused systolic dysfunction in vivo. Cardiomyocyte function was significantly depressed during both cellular contraction and relaxation.SignificanceThese results suggest that heart muscle is directly affected by tumor growth, with myocardial function more severely compromised at the cellular level than what is observed using echocardiography.     

From richer to poorer: successful invasion by freshwater fishes depends on species richness of donor and recipient basins

Evidence for the theory of biotic resistance is equivocal, with experiments often finding a negative relationship between invasion success and native species richness, and large‐scale comparative studies finding a positive relationship. Biotic resistance derives from local species interactions, yet global and regional studies often analyze data at coarse spatial grains. In addition, differences in competitive environments across regions may confound tests of biotic resistance based solely on native species richness of the invaded community. Using global and regional data sets for fishes in river and stream reaches, we ask two questions: (1) does a negative relationship exist between native and non‐native species richness and (2) do non‐native species originate from higher diversity systems. A negative relationship between native and non‐native species richness in local assemblages was found at the global scale, while regional patterns revealed the opposite trend. At both spatial scales, however, nearly all non‐native species originated from river basins with higher native species richness than the basin of the invaded community. Together, these findings imply that coevolved ecological interactions in species‐rich systems inhibit establishment of generalist non‐native species from less diverse communities. Consideration of both the ecological and evolutionary aspects of community assembly is critical to understanding invasion patterns. Distinct evolutionary histories in different regions strongly influence invasion of intact communities that are relatively unimpacted by human actions, and may explain the conflicting relationship between native and non‐native species richness found at different spatial scales.