Functional ecology of growth in seedlings versus root sprouts of Fagus grandifolia Ehrh.

We assessed growth differences and the foliar traits underpinning production in paired samples of juvenile American beech (Fagus grandifolia Ehrh.) that originated from seed versus root sprouts. Root sprouts had significantly greater relative extension growth rate and slightly greater leaf mass per unit area compared to seed-derived individuals, but neither light-saturated net photosynthetic rate nor foliar chlorophyll and nitrogen concentrations differed significantly between paired seedlings and sprouts. The greater height growth rate of saplings originating as root sprouts does not result from differing foliar function, but rather depends on translocation of assimilates from the parent tree to sustain this unusual and ecologically important dual regeneration strategy in American beech.     

Niche breadth and range area in North American trees

Identifying factors affecting species distribution is a longstanding goal in ecology and evolution that is accentuated by our need to anticipate climate change impacts. We sought to test whether any phylogenetic effect can be detected in either the environmental characteristics or range attributes of North American trees, and to explore the existence of a general interspecific pattern in the environmental factors influencing species range size. To do so we tested prevailing hypotheses relating climatic and edaphic characteristics to species range size in the North American arboflora (n = 598), using spatial null models to test for the relevance of observed patterns. We found that interspecific variation in the range area of North American trees is strongly related to the environmental regimes characteristic of the species range. Linear models and phylogenetic regressions involving six environmental characteristics explained 83% of the variance in species range area, and affirmed a positive relationship between niche breadth and range size. Tree species that can tolerate a larger variability in local climatic conditions, deal with harsher edaphic conditions, and weak levels of environmental energy tend to have larger range area; this can account for the greater geographic range of species at higher latitudes, the Rapoport effect. There is a significant phylogenetic signal for both range area and limits in North American trees, and for climatic limits, but not for energy or edaphic characteristics associated with species range. These findings highlight the possibility that species with small geographic ranges may be more sensitive to the effects of climate change.     

Overexpression of the rabies virus glycoprotein results in enhancement of apoptosis and antiviral immune response

A recombinant rabies virus (RV) carrying two identical glycoprotein (G) genes (SPBNGA-GA) was constructed and used to determine the effect of RV G overexpression on cell viability and immunity. Immunoprecipitation analysis and flow cytometry showed that tissue culture cells infected with SPBNGA-GA produced, on average, twice as much RV G as cells infected with RV carrying only a single RV G gene (SPBNGA). The overexpression of RV G in SPBNGA-GA-infected NA cells was paralleled by a significant increase in caspase 3 activity followed by a marked decrease in mitochondrial respiration, neither of which was observed in SPBNGA-infected cells. Furthermore, fluorescence staining and confocal microscopy revealed an increased extent of apoptosis and markedly reduced neurofilament and F actin in SPBNGA-GA-infected primary neuron cultures compared with neuronal cells infected with SPBNGA, supporting the concept that RV G or motifs of the RV G gene trigger the apoptosis cascade. Mice immunized with SPBNGA-GA showed substantially higher antibody titers against the RV G and against the nucleoprotein than SPBNGA-immunized mice, suggesting that the speed or extent of apoptosis directly determines the magnitude of the antibody response.     

BOOK REVIEWS

Book reviewed in this article: Lieth, H. & Schwartz, M.D. (eds.) 1997. Phenology in seasonal climates I . Progress in Biometeorology, Vol. 12. 143 pp. Backhuys Publishers, Leiden. ISBN 90–73348–79-X. Price: USD 42.25.     

Are correlations among foliar traits in ferns consistent with those in the seed plants?

Broad-based studies of gymnosperms and angiosperms reveal consistent and functionally significant correlations among foliar traits such as leaf mass per area (LMA), maximum photosynthetic rate (A(area)), foliar nitrogen (N(area)), foliar chlorophyll (Chl) and leaf longevity. To assess the generality of these relationships, we studied 20 fern species growing in the understorey of a temperate deciduous forest. We found that foliar N(area) increases with LMA, and that foliar N(area) and A(area) are positively correlated with one another, as are foliar N(area) and Chl. The ferns in general have very low LMA compared with most seed plants; A(area), N(area) and Chl are below median values for seed plants but are not extreme. Species with overwintering fronds have significantly higher LMA than species with fronds that senesce at the end of the growing season, as well as a significantly higher C : N ratio in frond tissue and relatively high foliar N on an areal basis. Correlations among foliar traits associated with gas exchange in these forest understorey ferns are in accordance with patterns reported for seed plants, suggesting a high degree of functional constraint on the interrelationships among key elements in foliar design.     

Risk of all-cause mortality in HIV infected patients is associated with clinical, immunologic predictors and the CCR5 Δ32 deletion

Objective

Investigation of the interplay between the CCR5 Δ32/wt genotype and demographic, epidemiological, clinical and immunological factors associated with mortality in the cART era.

Design

Longitudinal data from 507 HIV-infected patients following the Δ32 allele detection were analyzed.

Methods

Cumulative 15 years mortality was calculated using Kaplan-Meyer methodology. Hazard ratios were estimated using univariate Cox models. Basing on Akakie information criteria and statistical significance multivariate Cox model was constructed and effect plots presenting adjusted hazard ratio time-dependency were drawn. Analysis of the association of all-cause mortality and CCR5 Δ32/wt genotype prior to the antiretroviral treatment (cART) initiation (n = 507) and on the therapy (n = 422) was also performed.

Results

A mortality rate of 2.66 (CI 2.57–3.19) per 100 person-years was observed. Univariate analysis factors modifying the risk of death included the CCR5 genotype, gender, history of cART, AIDS diagnosis and also CD4 lymphocyte nadir, zenith, the latest CD4 count and stable levels >500 cells/µl. For multivariate analysis the following predictors were selected: CCR5 genotype (HR for wt/wt 2.53, CI 1.16–5.53, p = 0.02), gender (HR for males 1.91, 95%CI 1.1–3.36, p = 0.023), introduction of combined antiretroviral treatment (HR 4.85, CI 3.0–7.89, if untreated or treated <1 month, p<0.0001) CD4 count of 500 cells/µl for six months or more (HR 4.16, CI 1.95–8.88 if not achieved, p = 0.028), the latest CD4 count (HR 5.44, CI 3.39–8.74 for <100 cells/µl, p<0.0001) and history of AIDS (HR 1.69, CI 1.03–2.79, p = 0.039). Among untreated individuals the Δ32/wt genotype was associated with notably better survival (p = 0.026), while among cART treated individuals the Δ32 mutation did not correlate significantly with higher survival rates (p = 0.23).

Conclusions

The Δ32 CCR5 allele is associated with a reduction of the risk of all-cause mortality in HIV (+) patients alongside clinical and immunologic predictors such as AIDS, history of cART, lymphocyte CD4 cell count and gender.     

Responses to moisture stress in male and female plants of Rumex acetosella L. (Polygonaceae)

Summary Male and female plants of Rumex acetosella were grown on a moisture gradient to measure possible differences in the drought tolerance of the sexes. The growth of both sexes declined under water stress but males were significantly more drought tolerant. This could not be explained by greater water use efficiency in the male plants; measured rates of both photosynthesis and leaf conductance did not differ significantly between the sexes. Multiple discriminant analysis showed that the sexes differed at all moisture regimes in their overall patterns of biomass allocation. Males had proportionately greater investment in root and leaf tissue which could explain their growth advantage over females under water stress. Despite essentially equal water use efficiencies, on a per plant basis males, with more leaf and root biomass, could fix more carbon and more rapidly exploit the local water resource than females. Thus the pattern of biomass allocation rather than intrinsic physiological differences appears to explain the greater drought tolerance of male plants of Rumex acetosella.     

SPATIAL AND TEMPORAL VARIATION IN CHASMOGAMY AND CLEISTOGAMY IN OXALIS MONTANA (OXALIDACEAE)

Chasmogamous (CH) and cleistogamous (CL) flower production was investigated in natural populations of the perennial herb Oxalis montana in southern Quebec, Canada. Every 10–12 days during two flowering seasons, we recorded the reproductive output of approximately 2,000 plants distributed among five forest sites. The percentage of plants flowering, proportion of flowering plants producing CH and CL flowers, CH and CL flower number per flowering plant, and the proportion of flowers that are CL differed significantly among sites and corresponded to site differences in forest type and habitat quality. Unlike patterns in most CL species, however, reproduction by cleistogamy increased in sites with habitat conditions favorable to plant growth and sexual reproduction, and decreased in less productive sites. Chasmogamous and CL flower production increased with increasing plant size but plant size explained a significantly greater proportion of the variation in CL flower numbers. The percentage of flowering plants producing CH flowers decreased between years while the proportion of CL flowers increased at all sites during the second flowering season. The somewhat unusual aspects of reproduction in Oxalis may stem from its perennial habit which allows use of stored resources in adjusting the balance of cleistogamy versus chasmogamy in different environmental regimes.     

A single amino acid change in rabies virus glycoprotein increases virus spread and enhances virus pathogenicity

Several rabies virus (RV) vaccine strains containing an aspartic acid (Asp) or glutamic acid (Glu) instead of an arginine (Arg) at position 333 of the RV glycoprotein (G) are apathogenic for immunocompetent mice even after intracranial inoculation. However, we previously showed that the nonpathogenic phenotype of the highly attenuated RV strain SPBNGA, which contains a Glu at position 333 of G, is unstable when this virus is passaged in newborn mice. While the Glu(333) remained unchanged after five mouse passages, an Asn(194)-->Lys(194) mutation occurred in RV G. This mutation was associated with increased pathogenicity for adult mice. Using site-directed mutagenesis to exchange Asn(194) with Lys(194) in the G protein of SPBNGA, resulting in SPBNGA-K, we show here that this mutation is solely responsible for the increase in pathogenicity and that the Asn(194)-->Lys(194) mutation does not arise when Asn(194) is exchanged with Ser(194) (SPBNGA-S). Our data presented indicate that the increased pathogenicity of SPBNGA-K is due to increased viral spread in vivo and in vitro, faster internalization of the pathogenic virus into cells, and a shift in the pH threshold for membrane fusion. These results are consistent with the notion that the RV G protein is a major contributor to RV pathogenesis and that the more pathogenic RVs escape the host responses by a faster spread than that of less pathogenic RVs.