Comparison of mitochondrial ascorbate peroxidase in the cultivated tomato, Lycopersicon esculentum, and its wild, salt-tolerant relative, L. pennellii– a role for matrix isoforms in protection against oxidative damage

Mitochondria require robust antioxidant defences to prevent lipid peroxidation and to protect tricarboxylic acid cycle enzymes from oxidative damage. Mitochondria from wild, salt‐tolerant tomato, Lycopersicon pennellii (Lpa) did not exhibit lipid peroxidation in response to high salinity (100 mm NaCl), whereas those isolated from cultivated tomato, L. esculentum (Lem), accumulated malondialdehyde. The activity, intraorganellar distribution and salt response of mitochondrial ascorbate peroxidase (mAPX) differed dramatically in the two species. In Lem mitochondria, the majority (84%) of mAPX was associated with membranes, being located either on the inner membrane, facing the intermembrane space, or on the outer membrane. Total mAPX activity did not increase substantially in response to salt, although the proportion of matrix APX increased. In contrast, 61% of Lpa mAPX activity was soluble in the matrix, the remainder being bound to the matrix face of the inner membrane. Salt treatment increased the activity of all mAPX isoforms in Lpa, without altering their intramitochondrial distribution. The membrane‐bound isoforms were detected in mitochondria of both species by western blotting and found to be induced by salt in Lpa. These observations suggest that matrix‐associated APX isoforms could act in concert with other mitochondrial antioxidants to protect against salt‐induced oxidative stress.     

Intraspecific variation in limblessness in vertebrates: a unique example of microevolution

Many species of arboreal marine snails in the genus Littoraria are polymorphic for shell colour, with morphs that correspond in both colour and frequency to those predominant in the habitat. Although the combined effects of selection for crypsis and apostasy have been suggested as the most likely reasons for this, they have not been demonstrated directly in the field. We investigated whether two parasitoid flies, Sarcophaga megafilosia and Sarcophaga meiofilosia, select for crypsis in Littoraria filosa . It was possible to compare the proportions that matched and did not match the background between samples of live and dead snails because the shells of individuals killed by these parasitoids, within which the larva and pupa develop, remain attached to the substratum. This comparison was necessary because these snails frequently move among different coloured microhabitats, which will tend to obscure any effect of selection for crypsis if only live individuals are censused. The method appeared reliable since there was no change in background colour and very little loss of shells between larviposition and emergence of flies. S. megafilosia killed a significantly greater than expected proportion of snails that did not match their background. In contrast, there was no evidence of selective attack by S. meiofilosia. These results are discussed in relation to previous work on polymorphisms in Littoraria species. We also suggest that the role of parasitoid insects as selective agents contributing to the maintenance of colour polymorphisms in terrestrial molluscs may have been overlooked.  © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 77, 367−377.     

Liana structure, function and selection: a comparative study of xylem cylinders of tropical rainforest species in Africa and America

CABALLÉ, G., 1993. Liana structure, function and selection: a comparative study of xylem cylinders of tropical rainforest species in Africa and America A general analysis of xylem cylinders is presented on the basis of intercontinental (Africa-America) comparisons of 448 species (35 families) of tropical forest lianas. Drawings of stem transverse sections are presented for 58 species. From an evolutionary point of view, the liana represents a woody plant form at the crossroads of two life-form types: either self-supporting or non-self-supporting. The interconnections between anatomy, life-form, and dynamics of forest space occupation are highly integrated. The American lianas show a distinct propensity to form a crown in the forest canopy constituted of multiple leafy units (small crowns) which grow apart with an increasing distance between each unit (expansion with a centrifugal tendency). Xylem cylinders associated into polystelic and multiple stems appear to facilitate this behaviour (nearly 80% of American species compared to less than 50% in Africa). Neotropical forests seem to show a comparatively higher range of sites exposed to light than African ones.     

Observations on Idiotypy of Rabbit Antibodies against <Emphasis Type="Italic">Salmonella abortus-equi</Emphasis>

IDIOTYPIC specificities are antigenic specificities each of which seems to be peculiar to antibodies of one given individual (or perhaps of one group of individuals) against one given antigen^1,2. They are detected by reactions—usually of specific precipitation-using anti-idiotypic sera³. We have used anti-Salmonella abortus-equi (SAE) sera of two rabbits to agglutinate bacteria which were injected into two series of six rabbits; three rabbits of each series gave precipitating anti-idiotypic sera.     

Do geographic distribution,niche property and life form explain plants' vulnerability to global change?

We modelled the future distribution in 2050 of 975 endemic plant species in southern Africa distributed among seven life forms, including new methodological insights improving the accuracy and ecological realism of predictions of global changes studies by: (i) using only endemic species as a way to capture the full realized niche of species, (ii) considering the direct impact of human pressure on landscape and biodiversity jointly with climate, and (iii) taking species' migration into account. Our analysis shows important promises for predicting the impacts of climate change in conjunction with land transformation. We have shown that the endemic flora of Southern Africa on average decreases with 41% in species richness among habitats and with 39% on species distribution range for the most optimistic scenario. We also compared the patterns of species' sensitivity with global change across life forms, using ecological and geographic characteristics of species. We demonstrate here that species and life form vulnerability to global changes can be partly explained according to species' (i) geographical distribution along climatic and biogeographic gradients, like climate anomalies, (ii) niche breadth or (iii) proximity to barrier preventing migration. Our results confirm that the sensitivity of a given species to global environmental changes depends upon its geographical distribution and ecological proprieties, and makes it possible to estimate a priori its potential sensitivity to these changes.     

Immobilization Antigens from Tetrahymena thermophila Are Glycosyl-Phosphatidylinositol-Linked Proteins

We have studied four strains of Tetrahymena thermophila , each of which expresses a different allele of the SerH gene and produces a distinctive surface protein of the immobilization antigen (i-antigen) class. Following exposure of the strains to [³H]ethanolamine or [³H]myristic acid, a protein corresponding in molecular mass to the characteristic i-antigen for that strain became highly labeled, as determined by mobility in sodium dodecylsulfate-polyacrylamide eiectrophoresis gels. Furthermore, antibodies raised to the i-antigens of the T. thermophila strains selectively immunoprecipitated radioactive proteins having molecular mass identical to that of the i-antigen characteristic for that particular strain. The lipid moieties labeled by [³H]myristate were not susceptible to hydrolysis by exogenous phosphatidylinositol-specific phospholipase C from bacteria. However, when protein extraction was carried out in the absence of phospholipase C inhibitors, radioactive fatty acids derived from [³H]myristate were rapidly cleaved from the putative i-antigens. On the basis of available data, it was concluded that T. thermophila i-antigens contain covalently-Iinked glycosyl-phospha-tidylinositol anchors.     

Endemic species and ecosystem sensitivity to climate change in Namibia

We present a first assessment of the potential impacts of anthropogenic climate change on the endemic flora of Namibia, and on its vegetation structure and function, for a projected climate in ～2050 and ～2080. We used both niche‐based models (NBM) to evaluate the sensitivity of 159 endemic species to climate change (of an original 1020 plant species modeled) and a dynamic global vegetation model (DGVM) to assess the impacts of climate change on vegetation structure and ecosystem functioning. Endemic species modeled by NBM are moderately sensitive to projected climate change. Fewer than 5% are predicted to experience complete range loss by 2080, although more than 47% of the species are expected to be vulnerable (range reduction >30%) by 2080 if they are assumed unable to migrate. Disaggregation of results by life‐form showed distinct patterns. Endemic species of perennial herb, geophyte and tree life‐formsare predicted to be negatively impacted in Namibia, whereas annual herb and succulent endemic species remain relatively stable by 2050 and 2080. Endemic annual herb species are even predicted to extend their range north‐eastward into the tree and shrub savanna with migration, and tolerance of novel substrates. The current protected area network is predicted to meet its mandate by protecting most of the current endemicity in Namibia into the future. Vegetation simulated by DGVM is projected to experience a reduction in cover, net primary productivity and leaf area index throughout much of the country by 2050, with important implications for the faunal component of Namibia's ecosystems, and the agricultural sector. The plant functional type (PFT) composition of the major biomes may be substantially affected by climate change and rising atmospheric CO₂– currently widespread deciduous broad leaved trees and C₄ PFTs decline, with the C₄ PFT particularly negatively affected by rising atmospheric CO₂ impacts by ～2080 and deciduous broad leaved trees more likely directly impacted by drying and warming. The C₃ PFT may increase in prominence in the northwestern quadrant of the country by ～2080 as CO₂ concentrations increase. These results suggest that substantial changes in species diversity, vegetation structure and ecosystem functioning can be expected in Namibia with anticipated climate change, although endemic plant richness may persist in the topographically diverse central escarpment region.     

Extension of Gatlin's Informational Divergence to Markovian Stochastic Processes

In the information theoretic framework, to some extent, the complexity ofa system can be measured by its informational divergence which is thedifference between the maximum possible value of its entropy and theactual value of the latter. In her analysis of the DNA chain, Gatlinput in evidence two different divergences. One which drops the mutualdependences between the bases (A, C, G, T) and the other one whichexplicitly refers to this dependence via conditional entropies, and thus,provides a measure of the structural complexity of the system. One showshow the explicit form of this structural divergence can be obtained fordiscrete and continuous Markovian stochastic processes, and in the lattercase, as expected, this divergence is invariant under a transformation ofvariables.