880. EUPHORBIA TUCKEYANA

Euphorbia tuckeyana is a dendroid spurge endemic to Cabo Verde. It belongs to E. subgenus Esula section Aphyllis subsection Macaronesicae, a monophyletic group of eleven species restricted to the Canaries, Madeira archipelago, the Selvagens islands, Cabo Verde, a small area of Atlantic Morocco, and Portugal, that have high horticultural potential for xeric gardens. Among them E. tuckeyana grows well in tropical environments with a summer rainy season. History of early collections and records is reviewed. The species has been previously depicted on one postage stamp and in papers focusing on the Cabo Verde flora. Three other phylogenetically distant groups of dendroid spurges, also with leaves spirally arranged in clusters located on stem tips, occur in the West Indies, Africa, and Asia. They also show high potential for tropical gardens. We present a previously unpublished ink‐drawing of E. tuckeyana that was made by the great Spanish plant illustrator Eugeni Sierra Ràfols (1919–1999). The name is lectotypified with a specimen housed in the Muséum National d'Histoire Naturelle (Paris) that was collected by the Portuguese naturalist João da Silva Feijó in the late 18th century.     

Phylogeography of the eight-barbel loach <Emphasis Type="Italic">Lefua nikkonis</Emphasis> (Cypriniformes: Nemacheilidae): how important were straits in northern Japan as biogeographical barriers?

Many straits in the Japanese archipelago have been proposed as biogeographical boundaries, but there is disagreement regarding their importance as historic barriers against dispersal of terrestrial and freshwater taxa. Mitochondrial DNA haplotype and phylogenetic analyses of Lefua nikkonis, a primary freshwater fish inhabiting northern Japan and descendent from Siberia, revealed that the species is genetically structured within its geographic range, but that two major haplotypes are widely distributed across the Ishikari Lowland of Hokkaido Island as well as across the Tsugaru Strait between Hokkaido and Honshu Islands, two well-known biogeographical boundaries of northern Japan. The two major haplotypes were separated from each other by only one mutational step, and many other haplotypes, including those endemic to the region south of these barriers, have diverged from the major haplotypes, suggesting rapid range expansion and local differentiation. Divergence-time estimates, based on vicariance of the Honshu endemic congener L. echigonia via uplift of the Central Highlands, demonstrated that the southward dispersal of L. nikkonis from Hokkaido Island to Honshu Island occurred less than 0.08–0.19 Mya, suggesting that a land bridge emerged at the Tsugaru Strait during the Riss glaciation. Given that other freshwater taxa crossed the strait earlier (during the Middle Pleistocene), it is likely that land bridges in the strait have repeatedly emerged. The fact that L. nikkonis invaded only the northern part of Honshu, and that many other freshwater species also have the limit of their distribution ranges in this area as well, indicates that a faunal transition zone might persist even without the Tsugaru Strait. Thus, straits and lowlands in northern Japan are likely to have been less important as dispersal barriers to freshwater taxa than is currently thought.     

Arabidopsis HIPP27 is a host susceptibility gene for the beet cyst nematode Heterodera schachtii

Sedentary plant‐parasitic cyst nematodes are obligate biotrophs that infect the roots of their host plant. Their parasitism is based on the modification of root cells to form a hypermetabolic syncytium from which the nematodes draw their nutrients. The aim of this study was to identify nematode susceptibility genes in Arabidopsis thaliana and to characterize their roles in supporting the parasitism of Heterodera schachtii. By selecting genes that were most strongly upregulated in response to cyst nematode infection, we identified HIPP27 (HEAVY METAL‐ASSOCIATED ISOPRENYLATED PLANT PROTEIN 27) as a host susceptibility factor required for beet cyst nematode infection and development. Detailed expression analysis revealed that HIPP27 is a cytoplasmic protein and that HIPP27 is strongly expressed in leaves, young roots and nematode‐induced syncytia. Loss‐of‐function Arabidopsis hipp27 mutants exhibited severely reduced susceptibility to H. schachtii and abnormal starch accumulation in syncytial and peridermal plastids. Our results suggest that HIPP27 is a susceptibility gene in Arabidopsis whose loss of function reduces plant susceptibility to cyst nematode infection without increasing the susceptibility to other pathogens or negatively affecting the plant phenotype.     

‘The importance of symbiosis in philosophy of biology: an analysis of the current debate on biological individuality and its historical roots’

Symbiosis plays a fundamental role in contemporary biology, as well as in recent thinking in philosophy of biology. The discovery of the importance and universality of symbiotic associations has brought new light to old debates in the field, including issues about the concept of biological individuality. An important aspect of these debates has been the formulation of the hologenome concept of evolution, the notion that holobionts are units of natural selection in evolution. This review examines the philosophical assumptions that underlie recent proposal of the hologenome concept of evolution, and traces those debates back in time to their historical origins, to the moment when the connection between the topics of symbiosis and biological individuality first caught the attention of biologists. The review is divided in two parts. The first part explores the historical origins of the connection between the notion of symbiosis and the concept of biological individuality, and emphasizes the role of A. de Bary, R. Pound, A. Schneider and C. Merezhkowsky in framing the debate. The second part examines the hologenome concept of evolution and explores four parallelisms between contemporary debates and the debates presented in the first part of the essay, arguing that the different debates raised by the hologenome concept were already present in the literature. I suggest that the novelty of the hologenome concept of evolution lies in the wider appreciation of the importance of symbiosis for maintaining life on Earth as we know it. Finally, I conclude by suggesting the importance of exploring the connections among contemporary biology, philosophy of biology and history of biology in order to gain a better understanding of contemporary biology.     

Ethnobotany and domestication in Xoconochtli,Stenocereus stellatus (Cactaceae), in the Tehuacán Valley and La Mixteca Baja, México

Ethnobotanical information is presented on use, management, folk nomenclature and classification of the “xoconochtli” (Stenocereus stellatus) as well as on the role of this plant in subsistence of the Nahua, Mixtec and Popoloca peoples from the Tehuacán Valley and La Mixteca Baja in Central Mexico. Among all three groups, S. stellatus was used for various purposes but mainly for its edible fruits. Different variants of this species were distinguished, named and classified by indigenous people according to characteristics of the fruit; particularly size, color and flavor of the pulp, spininess and thickness of the peel. Wild plants characteristically had small red sour fruits with many spines and thick peel, while individuals selected for cultivation usually differed in one or more of these characters. Three general forms of interaction between people and this species were found: 1) gathering of useful products from the wild; 2) management of wild populations in situ which involves the sparing and enhancing of individuals with more desirable characteristics and the removal of others during clearance of the land for agriculture; and 3) cultivation, mainly in home gardens, by propagation of vegetative parts from desirable individuals. Fruit yields per individual and per population were measured and compared in wild, managed in situ and cultivated populations from the Tehuacán Valley and La Mixteca Baja. Wild and cultivated individuals from La Mixteca Baja yielded more than wild and cultivated individuals from the Tehuacán Valley. Within each region, fruit yields were similar in wild and managed in situ populations but significantly larger in cultivated populations. Forms of management of this plant species are discussed in terms of availability of products and demand for them in the local economy.     

Role of prostaglandin H synthase-2-mediated conversion of arachidonic acid in controlling 3T6 fibroblast growth

The specific role(s) of arachidonic acid (AA) and itsmetabolites in the signaling pathways that regulated fibroblast growth was studied. A Western blot analysis demonstrated that prostaglandin Hsynthase-2 (PGHS-2) was expressed by 3T6 fibroblast cultures in RPMI1640 supplemented with fetal calf serum (10%). Dexamethasone, whichinhibits AA release and PGHS-2 expression, significantly reduced cellproliferation. Ketoprofen, a dual cyclooxygenase inhibitor, andCGP-28238, a specific PGHS-2 inhibitor, reduced fibroblastproliferation in a dose-dependent manner. These drugs also reduced[³H]thymidineincorporation into the DNA of fibroblasts. These effects werecorrelated with a decrease in prostaglandin (PG)E₂ levels in the cell medium.However, piroxicam at doses that selectively inhibit PGHS-1 did nothave a significant effect on fibroblast proliferation. Finally, weshowed that the antiproliferative effect of dexamethasone and PGHS-2inhibitors was significantly antagonized whenPGE₂ was added to the culturemedium. Our results suggest that PGHS-2 and prostaglandins such asPGE₂ might play an important rolein the regulation of 3T6 fibroblast growth stimulated by growth factorsof serum.

     

Plasma Membrane Water Permeability of Cultured Cells and Epithelia Measured by Light Microscopy with Spatial Filtering

A method was developed to measure the osmotic water permeability (P_f) of plasma membranes in cell layers and applied to cells and epithelia expressing molecular water channels. It was found that the integrated intensity of monochromatic light in a phase contrast or dark field microscope was dependent on relative cell volume. For cells of different size and shape (Sf9, MDCK, CHO, A549, tracheal epithelia, BHK), increased cell volume was associated with decreased signal intensity; generally the signal decreased 10–20% for a twofold increase in cell volume. A theory relating signal intensity to relative cell volume was developed based on spatial filtering and changes in optical path length associated with cell volume changes. Theory predictions were confirmed by signal measurements of cell layers bathed in solutions of various osmolarities and refractive indices. The excellent signal-to-noise ratio of the transmitted light detection permitted measurement of cell volume changes of <1%. The method was applied to characterize transfected cells and tissues that natively express water channels. P_f in control Chinese hamster ovary cells was low (0.0012 cm/s at 23°C) and increased more than fourfold upon stable transfection with aquaporins 1, 2, 4, or 5. P_f in apical and basolateral membranes in polarized epithelial cells grown on porous supports was measured. P_f ^bl and P_f ^ap were 0.0011 and 0.0024 cm/s (MDCK cells), and 0.0039 and 0.0052 cm/s (human tracheal cells) at 23°C. In intact toad urinary bladder, basolateral P_f was 0.036 cm/s and apical membrane P_f after vasopressin stimulation was 0.025 cm/s at 23°C. The results establish light microscopy with spatial filtering as a technically simple and quantitative method to measure water permeability in cell layers and provide the first measurement of the apical and basolateral membrane permeabilities of several important epithelial cell types.     

Comparison among DNA polymerases 1, 2 and 3 from maize embryo axes. A DNA primase activity copurifies with DNA polymerase 2

Three DNA polymerase activities, named 1, 2 and 3 were purified from maize embryo axes and were compared in terms of ion requirements, optimal pH, temperature and KCl for activity, response to specific inhibitors and use of templates. All three enzymes require a divalent cation for activity, but main differences were observed in sensitivity to inhibitors and template usage: while DNA polymerases 1 and 2 were inhibited by N-ethyl maleimide and aphidicolin, inhibitors of replicative-type enzymes, DNA polymerase 3 was only marginally or not affected at all. In contrast, DNA polymerase 3 was highly inhibited by very low concentrations of ddTTP, an inhibitor of repair-type enzymes, and a 100-fold higher concentration of the drug was needed to inhibit DNA polymerases 1 and 2. Additionally, DNA polymerases 1 and 2 used equally or more efficiently the synthetic template polydA-oligodT, as compared to activated DNA, while polymerase 3 used it very poorly. Whereas DNA polymerases 1 and 2 shared properties of replicative-type enzymes, DNA polymerase 3 could be a repair-type enzyme. Moreover, a DNA primase activity copurified with the 8000-fold purified DNA polymerase 2, strenghtening the suggestion that polymerase 2 is a replicative enzyme, of the -type. This DNA primase activity was also partially characterized. The results are discussed in terms of relevant data about other plant DNA polymerases and primases reported in the literature.     

Episodic development of Cambrian eocrinoid-sponge meadows in the Iberian Chains (NE Spain)

Summary The Lower-Middle Cambrian transition in the Iberian Chains (NE Spain) records a transgressive deposition from peritidal to open-shelf environments. This overall trangressive trend took place across an interval of syndepositional tectonic processes. which have been illustrated during late Bilbilian to Leonian times. The scarcity of building organisms in this areas seems to be directly related to a rhythmic influence of fine terrigenous decantation, which inhibited and interrupted the carbonate production. Only in the more proximal and quiet environments, the episodic establishment of stromatolitic boundstones is evidence. Eocrinoid-sponge meadows were developed in shallow subtidal environments, and were completed by the presence of trilobites, inarticulate brachiopods, hyoliths and Chancelloriid sclerites. The biggest accumulation rates associated to these complex meadow communities seem to be reflected by differential synsedimentary faulting processes.