Mycorrhiza formation and elevated CO2 both increase the capacity for sucrose synthesis in source leaves of spruce and aspen

The effects of mycorrhiza formation in combination with elevated CO₂ concentrations on carbon metabolism of Norway spruce ( Picea abies ) seedlings and aspen ( Populus tremula × Populus tremuloides ) plantlets were analysed. Plants were inoculated for 6 wk with the ectomycorrhizal fungi Amanita muscaria and Paxillus involutus (aspen only) in an axenic Petri-dish culture at 350 and 700 μl l⁻¹ CO₂ partial pressure. After mycorrhiza formation, a stimulation of net assimilation rate was accompanied by decreased activities of sucrose synthase, an increased activation state of sucrose-phosphate synthase, decreased fructose-2,6-bisphosphate and starch, and slightly elevated glucose-6-phosphate contents in source leaves of both host species, independent of CO₂ concentration. Exposure to elevated CO₂ generally resulted in higher net assimilation rates, increased starch as well as decreased fructose-2,6-bisphosphate (aspen only) content in source leaves of both mycorrhizal and nonmycorrhizal plants. Our data indicate only slightly improved carbon utilization by mycorrhizal plants at elevated CO₂. They demonstrate however, that both factors which modulate the sink-source properties of plants increase the capacity for sucrose synthesis in source leaves mainly by allosteric enzyme regulation.     

La reproduction saisonniére chez les isopodes terrestres: Contrôle photopériodique et neurohumoral

Summary

Seasonal reproduction in terrestrial Isopods is regulated by a neurohormone (VIH) synthesized in neurosecretory cells located in the protocerebrum median part. VIH restrains vitellogenin synthesis by the fat body. This inhibitory system is driven by the photoperiodic variations. Long days introduce a decrease in synthesis and—or—VIH release, allowing the oocytes to carry out the last vitellogenic phase. Other signals (mating, eggs in brood-pouch) tune the activity of the inhibitory system. Various aspects of photoperiodic and neurohormonal controls of reproduction are discussed: geographical variability and genetic determinism of the photoperiodic response; chemical nature, specificity and VIH mode of action; male physiology and VE synthesis, modalities of VIH synthesis and release.     

Comparative phylogeography and postglacial colonization routes in Europe

The Quaternary cold periods in Europe are thought to have heavily influenced the amount and distribution of intraspecific genetic variation in both animals and plants. The phylogeographies of 10 taxa, including mammals ( Ursus arctos , Sorex spp., Crocidura suaveolens , Arvicola spp.), amphibians ( Triturus spp.), arthropods ( Chorthippus parallelus ), and plants ( Abies alba , Picea abies , Fagus sylvatica , Quercus spp.), were analysed to elucidate general trends across Europe. Only a small degree of congruence was found amongst the phylogeographies of the 10 taxa, but the likely postglacial colonization routes exhibit some similarities. A Brooks parsimony analysis produced an unrooted area phylogram, showing that: (i) the northern regions were colonized generally from the Iberic and Balkanic refugia; and (ii) the Italian lineages were often isolated due to the presence of the Alpine barrier. The comparison of colonization routes highlighted four main suture-zones where lineages from the different refugia meet. Some of the intraspecific genetic distances among lineages indicated a prequaternary divergence that cannot be connected to any particular cold period, but are probably related mainly to the date of arrival of each taxon in the European continent. As a consequence, molecular genetics so far appears to be of limited use in dating Quaternary events.     

A Comparative Study of 14 Strains of Naegleria australiensis Demonstrates the Existence of a Highly Virulent Subspecies: N. australiensis italica n. spp.1

Fourteen strains of Naegleria australiensis, including the type strain, were compared for virulence for mice, maximum growth temperature, lectin agglutination, isoenzyme pattern, and total protein banding pattern. Their relation to other species of Naegleria also was compared by immunoelectrophoretic analysis. Strains with high virulence, comparable to that of N. fowleri, were found to be different in concanavalin A agglutination as well as with regard to zymograms and total protein patterns. Although serologically different from N. fowleri and reacting with N. australiensis antiserum in the fluorescent antibody test, these high-virulence strains differed in number of immunoelectrophoretic precipitin bands. Because of these results, the high-virulence strains are considered to be a subspecies of N. australiensis. The low-virulence strains showed minor differences from the type strain. Thus, N. australiensis does not appear to be as homogenous a species as N. fowleri. Pathogenic N. australiensis also seems to be more widespread than previously thought.     

Assessing the risk of primary infection of cereals by barley yellow dwarf virus in autumn in the Rennes basin of France

In the Rennes basin, Rhopalosiphum padi is anholocyclic and represents more than 90% of suction trap catches of potential vectors of barley yellow dwarf virus (BYDV) during autumn. From 1983 to 1987 the possibility of predicting the risk of BYDV infection of batches of barley test seedlings (sampling units) exposed each week from September to December near a 12.2 m high suction trap was investigated. Three kinds of variables were checked as possible predictors: weekly mean or maximum temperatures; weekly catches of R. padi (including or excluding males); and percentage of sampling units infested by aphids. Three contrasting examples were observed: during the first three years (1983–1985), infection was high and its change with time followed temperature, aphid catches and plant infestation changes; in 1986, high numbers of aphids caught and a high proportion of plants infested resulted in only low infection and in 1987, both infestation and infection were very low. Simple linear regression analysis showed that the more reliable predictors of infection were the proportion of infested plants and to a lesser extent the numbers of trapped aphids. Multiple linear regressions including either of the three groups of ‘predicting’ variables did not result in any improvement in the prediction. At a practical level, the use of counts of aphid catches would seem a better compromise between accuracy and consistency of prediction and ease of gathering data than that of plant infestation but any significant improvement of the prediction should be sought in an early estimate of the amount of virus available to aphids before they colonise the plants.     

Caractéristiques Ultrastructurales du Cortex et des Membranelles du CiliéEspejoia mucicola (Oligohymenophora, Hymenostomata, Tetrahymenina)

RESUME. L' étude détaillée du cortex et des organelles buccaux adoraux d' Espejoia montre que ce Cilié possède une organisation ultrastructurale comparable à celle des Tétrahyméniens. Tout en restant conforme au plan général d'organisation de ces derniers, des variations spécifiques décelées tant au niveau du cortex d'une part, que des membranelles, d'autre part, font ressortir des affinités trés marquées pour le genre Glaucoma et autres Ciliés voisins. En conséquence, en nous appuyant en outre sur les données récentes de la morphogenèse, nous confirmons la position d' E. mucicola parmi les Tetrahymenina, dans la famille des Glaucomidae.     

Effects of phosphorus and nitrogen enrichment on the yield of some strains of Stigeoclonium Kütz. (Chlorophyceae)

SUMMARY.

• 1 The combined effect of nitrate and phosphate concentrations on the yields of five selected strains of Stigeoclonium is demonstrated in a synthetic medium as well as in natural waters.
• 2 Increase of yield after addition of one nutrient depends on the concentration of the other. A graphic growth model based on the experiments in synthetic medium is presented, which allows prediction of yields at different combinations of nitrate and phosphorus concentrations.
• 3 In general, yields in natural waters before and after addition of nitrate and/or phosphate agree with the model. In some cases, other limiting factors appear to be involved.
• 4 The possible effects of nitrogen and phosphorus limitation on the phosphorus and nitrogen metabolism of the alga are discussed.
• 5 Neither an exponential model (Baule-Mitscherlich) nor a hyperbolic model adequately describe the interaction demonstrated between nitrogen and phosphorus limitation.

     

Inclusive Fitness and Human Family Structure

The implications of sociobiology, and especially of "inclusive fitness" or "kin-selection" theory, to human family structures are explored. Kin-selection theory provides a model to formulate testable hypotheses predicting cooperation and conflict for categories of kinsmen; it also suggests an alternative way of looking at incest, endogamy, exogamy, rule of descent, and type of marriage in terms of such biological concepts as mating strategies, inclusive fitness, parental investment, and sexual dimorphism and bimaturism. [sociobiology, kin-selection theory, inclusive fitness, family structure, marriage]