Nomenclatural correction — Eimeria chalcides (Probert,Roberts & Wilson, 1988) n. comb. for Tyzzeria chalcides (Apicomplexa: Eimeriidae)

The following nomenclatural correction is made: a new combination, Eimeria chalcides (Probert, Roberts &; Wilson, 1988) for Tyzzeria chalcides Probert et al., 1988 from the ocellated skink Chalcides ocellatus. The sporulated oöcyst is redescribed and compared with other Eimeria spp. reported from the family Scincidae in order to verify the species. Oöcysts of E. chalcides are cylindrical, 35 × 18.6 (32–37 × 17–20.5) μm with a thin bi-layered wall; the shape-index (mean length/mean width) is 1.88. A micropyle, oöcyst residuum and polar granule are absent. The sporocysts are broadly ellipsoidal, 11.9 × 8.9 (8.5–13 × 7.5–11) μm and without a Stieda body; the shape index is 1.35.     

Soil pCO2, soil respiration,and root activity in CO2-fumigated and nitrogen-fertilized ponderosa pine

The purpose of this paper is to describe the effects of CO₂ and N treatments on soil pCO₂, calculated CO₂ efflux, root biomass and soil carbon in open-top chambers planted with Pinus ponderosa seedlings. Based upon the literature, it was hypothesized that both elevated CO₂ and N would cause increased root biomass which would in turn cause increases in both total soil CO₂ efflux and microbial respiration. This hypothesis was only supported in part: both CO₂ and N treatments caused significant increases in root biomass, soil pCO₂, and calculated CO₂ efflux, but there were no differences in soil microbial respiration measured in the laboratory. Both correlative and quantitative comparisons of CO₂ efflux rates indicated that microbial respiration contributes little to total soil CO₂ efflux in the field. Measurements of soil pCO₂ and calculated CO₂ efflux provided inexpensive, non-invasive, and relatively sensitive indices of belowground response to CO₂ and N treatments.     

Characterization of the kinetic, regulatory, and structural properties of ADP-glucose pyrophosphorylase from Chlamydomonas reinhardtii.

ADP-glucose pyrophosphorylase (ADP-Glc PPase) from Chlamydomonas reinhardtii cells was purified over 2000-fold to a specific activity of 81 units/mg protein, and its kinetic and regulatory properties were characterized. Inorganic orthophosphate and 3-phosphoglycerate were the most potent inhibitor and activator, respectively. Rabbit antiserum raised against the spinach leaf ADP-Glc PPase (but not the one raised against the enzyme from Escherichia coli) inhibited the activity of the purified algal enzyme, which migrated as a single protein band in native polyacrylamide gel electrophoresis. Two-dimensional and sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicate that the enzyme from C. reinhardtii is composed of two subunits with molecular masses of 50 and 53 kD, respectively. The molecular mass of the native enzyme is estimated to be 210 kD. Antisera raised against the spinach leaf holoenzyme and against the 51-kD spinach subunit cross-reacted with both subunits of the algal ADP-Glc PPase in immunoblot hybridization, but the cross-reaction was stronger for the 50-kD algal subunit than for the 53-kD subunit. No cross-reaction was observed when antiserum raised against the spinach leaf pyrophosphorylase 54-kD subunit was used. These results suggest that the ADP-Glc PPase from C. reinhardtii is a heterotetrameric protein, since the enzyme from higher plants and its two subunits are structurally more related to the small subunit of the spinach leaf enzyme than to its large subunit. This information is discussed in the context of the possible evolutionary changes leading from the bacterial ADP-Glc PPase to the cyanobacterial and higher plant enzymes.     

Presence of double‐stranded RNAs and virus‐like particles in the entomopathogenic fungus Metarhizium anisopliae

Nucleic acids from 41 strains of Metarhizium anisopliae, obtained from different parts of the world were extracted and examined by electrophoresis. Strong bands of double‐stranded RNA (dsRNA) were detected in two isolates from Brazil, V215 and V291, which had, respectively, 13 and 9 distinct bands ranging in size from ca. 0.75 to 3.5 kb. Icosahedral virus‐like particles (VLPs) (ca. 33 nm in diameter) were observed by transmission electron microscopy in extracts of these isolates. The VLPs and dsRNA were both absent from a clone of the isolate V291 which had been subcultured successively on solid medium. Bioassays against the aphid Myzus persicae showed no detectable difference in virulence between the clone of V291 which contained dsRNA and the clone that did not.     

Effect of Inhibitors of Eicosanoid Metabolism on Release of [3H]Noradrenaline from the Human Neuroblastoma, SH-SY5Y

Abstract: Nordihydroguaiaretic acid (NDGA; a lipoxygenase inhibitor), LY-270766 (an inhibitor of 5-lipoxygenase), and the diacylglycerol lipase inhibitor RG 80267 completely eliminated potassium-evoked release of [³H]noradrenaline ([³H]NA) from the human neuroblastoma clone SH-SY5Y with IC₅₀ values of 10, 15, and 30 μ M , respectively. In contrast, these inhibitors only partially inhibited carbachol-evoked release and had little effect on the calcium ionophore A23187-evoked release of NA in this cell line. Arachidonic acid partially inhibited potassium- and A23187-evoked release but did not reverse the inhibition of potassium-evoked release observed in the presence of RG 80267. These studies suggest that arachidonic acid (or its lipoxygenase products) are not important intermediates in the regulation of exocytosis in SH-SY5Y. This conclusion is strengthened by our studies in which SH-SY5Y cells were grown in medium supplemented with bovine serum albumin-linoleic acid (50 μ M ). Under these conditions there was a selective increase in content of membrane polyunsaturated fatty acids of the ω6 series, including arachidonic acid; however, these changes did not effect potassium-, veratridine-, carbachol-, or calcium ionophoreevoked release of [³H]NA.     

Chromosome 14 and late-onset familial Alzheimer disease (FAD)

Familial Alzheimer disease (FAD) is genetically heterogeneous. Two loci responsible for early-onset FAD have been identified: the amyloid precursor protein gene on chromosome 21 and the as-yet-unidentified locus on chromosome 14. The genetics of late-onset FAD is unresolved. Maximum-likelihood, affected-pedigree-member (APM), and sib-pair analyses were used, in 49 families with a mean age at onset ≥60 years, to determine whether the chromosome 14 locus is responsible for late-onset FAD. The markers used were D14S53, D14S43, and D14S52. The LOD score method was used to test for linkage of late-onset FAD to the chromosome 14 markers, under three different models: age-dependent penetrance, an affected-only analysis, and age-dependent penetrance with allowance for possible age-dependent sporadic cases. No evidence for linkage was obtained under any of these conditions for the late-onset kindreds, and strong evidence against linkage (LOD score ≤ –2.0) to this region was obtained. Heterogeneity tests of the LOD score results for the combined group of families (early onset, Volga Germans, and late onset) favored the hypothesis of linkage to chromosome 14 with genetic heterogeneity. The positive results are primarily from early-onset families. APM analysis gave significant evidence for linkage of D14S43 and D14S52 to FAD in early-onset kindreds (P < .02). No evidence for linkage was found for the entire late-onset family group. Significant evidence for linkage to D14S52, however, was found for a subgroup of families of intermediate age at onset (mean age at onset ≥60 years and <70 years). These results indicate that the chromosome 14 locus is not responsible for Alzheimer disease in most late-onset FAD kindreds but could play a role in a subset of these kindreds.     

Causal inference and large-scale expert validation shed light on the drivers of SDM accuracy and variance

Aim

To develop a causal understanding of the drivers of Species distribution model (SDM) performance.

Location

United Kingdom (UK).

Methods

We measured the accuracy and variance of SDMs fitted for 518 species of invertebrate and plant in the UK. Our measure of variance reflects variation among replicate model fits, and taxon experts assessed model accuracy. Using directed acyclic graphs, we developed a causal model depicting plausible effects of explanatory variables (e.g. species' prevalence, sample size) on SDM accuracy and variance and quantified those effects using a multilevel piecewise path model.

Results

According to our model, sample size and niche completeness (proportion of a species' niche covered by sampling) directly affect SDM accuracy and variance. Prevalence and range completeness have indirect effects mediated by sample size. Challenging conventional wisdom, we found that the effect of prevalence on SDM accuracy is positive. This reflects the facts that sample size has a positive effect on accuracy and larger sample sizes are possible for widespread species. It is possible, however, that the omission of an unobserved confounder biased this effect. Previous studies, which reported negative correlations between prevalence and SDM accuracy, conditioned on sample size.

Main conclusions

Our model explicates the causal basis of previously reported correlations between SDM performance and species/data characteristics. It also suggests that niche completeness has similarly large effects on SDM accuracy and variance as sample size. Analysts should consider niche completeness, or proxies thereof, in addition to sample size when deciding whether modelling is worthwhile.     

Xcp-mediated protein secretion in Pseudomonas aeruginosa: identification of two additional genes and evidence for regulation of xcp gene expression

In Pseudomonas aeruginosa, several exoproteins synthesized with a signal sequence (elastase, lipase, phospholipases, alkaline phosphatase and exotoxin A) are secreted by a two-step mechanism. They first cross the inner membrane in a signal sequence-dependent way, and are further translocated across the outer membrane in a second step requiring secretion functions encoded by several xcp genes. Ten xcp genes have already been characterized (Bally et al., 1992a). In this study, two additional xcp genes, xcpP and xcpQ, are described. They are located in the 40 min region of the chromosome where they probably define an operon, divergent from the xcpR–Z operon previously characterized in this region. These two genes encode two proteins, XcpP and XcpQ, similar to PulC and PulD of the pul system of Klebsiella oxytoca. Moreover, the two divergent operons share a common regulation which is growth-phase dependent.     

Relationships between carbon and hydrogen isotope ratios and nitrogen levels in leaves ofClusia species and two other Clusiaceae genera at various sites and different altitudes in Venezuela

Samples of the Clusiaceae generaClusia, Oedematopus andDystovomita were collected at various sites and different altitudes in northern and south-western Venezuela. Analyses of stable isotopes of carbon and hydrogen and of leaf-nitrogen levels were performed on the dried samples. Correlations among these variables, i.e. carbon isotope discrimination (), hydrogen isotope ratio (D) and N-levels, and with altitude were assessed. In the samples, where values of above 15 indicate predominant performance of C₃ photosynthesis, there were slight tendencies of increasing , D and N-levels with increasing altitude and of increasing with increasing N. Although these correlations taken separately were not statistically significant, they support each other and indicate increasing transpiration and increased leaf-nutrient supply at increasing altitude. Performance of crassulacean acid metabolism (CAM) in species ofClusia appears to be restricted to altitudes below 1500 m a.s.l. There was a significant negative correlation of with altitude in the samples, where values of below 10 indicated predominant performance of CAM. This suggests that phases II and IV of CAM are progressively suppressed towards the upper altitudinal limit of CAM inClusia in northern Venezuela. It is concluded that among the large number of environmental factors and combinations thereof, which determine the expression of CAM inClusia and trigger C₃-CAM transitions in C₃/CAM intermediate species, low availability of water is the most important.     

The effect of light levels on daily patterns of chlorophyll fluorescence and organic acid accumulation in the tropical CAM treeClusia hilariana

Sandy plains are characteristic of the coastal region of Brazil. We investigated the diel patterns of changes in organic acid levels, leaf conductance and chlorophylla fluorescence for sun-exposed and shaded plants ofClusia hilariana, one of the dominant woody species in the sandy coastal plains of northern Rio de Janeiro state. Both exposed and shaded plants showed a typical CAM pattern with considerable diel oscillations in organic acid levels. The degradation of both malic and citric acids during the midday stomatal closure period could lead to potential CO₂ fixation rates of 28 mol m^-2 s^-1 in exposed leaves. Moreover, exposed leaves exhibited large increases in total non-photochemical quenching (q_N) accompanied by a substantial decrease in effective quantum yield during the course of the day. However, these potential high rates of CO₂ fixation and the increases inqn of exposed plants were not enough to maintain the primary electron acceptor of photosystem II (q_A) in a low reduction state, similar to that of shaded plants. As a result, there was a moderate increase in the reduction state of q_A throughout the day. Most of the decline in photochemical efficiency of exposed leaves ofC. hilariana was reversible, as evidenced by the high levels of pre-dawn potential quantum yields (F_v/F_m) and their rapid recovery after sunset. However, the depletion of the organic acid pool in the afternoon resulted in an accentuated subsequent drop in F_v/F_m, suggesting that prolonged periods of water stress accompanied by high irradiance levels may expose plants ofC. hilariana in unprotected habitats to the danger of photoinhibition.