Ionic Balance of Root-Shoot Nitrate Transfer in Dwarf Bean

The Dijkshoorn-Ben Zioni model about potassium recycling in higher plants proposes a stoichiometric coupling between the upward transport of nitrate and potassium, and therefore a 1:1 ratio of these ions in the xylem sap. Phaseolus vulgaris grown in media with different NO₃: K⁺ ratios, however, only rarely showed equimolar concentrations of the two ions in the bleeding sap. Ratios between 0.2 and 11 were observed and the ratios between concentrations of the ions in the exudate and in the external solution were positively correlated. An analysis of the major inorganic constituents of the exudate revealed an ionic balance that requires negligible amounts of charges from organic molecules.     

Phylogeny,diversification patterns and historical biogeography of euglossine orchid bees (Hymenoptera: Apidae)

The orchid bees constitute a clade of prominent insect pollinators distributed throughout the Neotropical region. Males of all species collect fragrances from natural sources, including flowers, decaying vegetation and fungi, and store them in specialized leg pockets to later expose during courtship display. In addition, orchid bees provide pollination services to a diverse array of Neotropical angiosperms when foraging for food and nesting materials. However, despite their ecological importance, little is known about the evolutionary history of orchid bees. Here, we present a comprehensive molecular phylogenetic analysis based on ～4.0 kb of DNA from four loci [cytochrome oxidase (CO1), elongation factor 1‐α (EF1‐α), arginine kinase (ArgK) and RNA polymerase II (Pol‐II)] across the entire tribe Euglossini, including all five genera, eight subgenera and 126 of the approximately 200 known species. We investigated lineage diversification using fossil‐calibrated molecular clocks and the evolution of morphological traits using disparity‐through‐time plots. In addition, we inferred past biogeographical events by implementing model‐based likelihood methods. Our dataset supports a new view on generic relationships and indicates that the cleptoparasitic genus Exaerete is sister to the remaining orchid bee genera. Our divergence time estimates indicate that extant orchid bee lineages shared a most recent common ancestor at 27–42 Mya. In addition, our analysis of morphology shows that tongue length and body size experienced rapid disparity bursts that coincide with the origin of diverse genera (Euglossa and Eufriesea). Finally, our analysis of historical biogeography indicates that early diversification episodes shared a history on both sides of Mesoamerica, where orchid bees dispersed across the Caribbean, and through a Panamanian connection, thus reinforcing the hypothesis that recent geological events (e.g. the formation of the isthmus of Panama) contributed to the diversification of the rich Neotropical biota. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 552–572.     

Effect of Plant Growth Regulators on Nitrate Utilization by Roots of Nitrogen-Depleted Dwarf Bean

We examined the effect of pretreatments (18 h at 5 µmoldm^–3) with abscisic acid, the ethylene-releasing substance‘Ethephon’, gibberellic acid, indoleacetic acid,kinetin and zeatin on nitrate uptake and in vivo nitrate reductaseactivity (NRA) in roots of nitrogen-depleted Phaseolus vulgarisL. Nitrate uptake showed an apparent induction pattern witha steady state after about 6 h, in all treatments. The nitrateuptake rate after 6 h was unaffected or at most 30% lower aftertreatments with the plant growth regulators. Gibberellic acid, kinetin and zeatin induced substantial NRAin roots in the absence of nitrate, whereas Ethephon enhancedNRA only during nitrate nutrition. Kinetin-induced NRA (Ki-NRA)was maximal after a pretreatment at 1 µmol dm^–3,and showed a lag phase of 6–8 h. Ki-NRA was additive tonitrate-induced NRA (NO^–₃-NRA) for at least 24 h, independentof the induction sequence. After full induction, Ki-NRA approximated20% of NO-₃-NRA. Abscisic acid counteracted the developmentof Ki-NRA, but not of NO^–₃-NRA. Cycloheximide and tungstatewere equally effective to suppress the development of nitratereductase activity after supply of kinetin or NO^–₃. Our data are consistent with the operation of two independentenzyme fractions (Ki-NRA and NO^–₃-NRA) with apparentlyidentical properties but with separate control mechanisms. Theabsence of major effects of plant growth regulators on the time-courseand rate of nitrate uptake suggests that exogenous regulators,and possibly endogenous phytohormones are of minor importancefor initial nitrate uptake. The differential effect of someregulators on nitrate uptake and root NRA furthermore indicatesthat the processes of uptake and reduction of NO^–₃ arenot obligatory or exclusively coupled to each other.     

Suppression of methanogenesis by dissimilatory Fe(III)-reducing bacteria in tropical rain forest soils: implications for ecosystem methane flux

Tropical forests are an important source of atmospheric methane (CH₄), and recent work suggests that CH₄ fluxes from humid tropical environments are driven by variations in CH₄ production, rather than by bacterial CH₄ oxidation. Competition for acetate between methanogenic archaea and Fe(III)‐reducing bacteria is one of the principal controls on CH₄ flux in many Fe‐rich anoxic environments. Upland humid tropical forests are also abundant in Fe and are characterized by high organic matter inputs, steep soil oxygen (O₂) gradients, and fluctuating redox conditions, yielding concomitant methanogenesis and bacterial Fe(III) reduction. However, whether Fe(III)‐reducing bacteria coexist with methanogens or competitively suppress methanogenic acetate use in wet tropical soils is uncertain. To address this question, we conducted a process‐based laboratory experiment to determine if competition for acetate between methanogens and Fe(III)‐reducing bacteria influenced CH₄ production and C isotope composition in humid tropical forest soils. We collected soils from a poor to moderately drained upland rain forest and incubated them with combinations of ¹³C‐bicarbonate, ¹³C‐methyl labeled acetate (¹³CH₃COO^?), poorly crystalline Fe(III), or fluoroacetate. CH₄ production showed a greater proportional increase than Fe²⁺ production after competition for acetate was alleviated, suggesting that Fe(III)‐reducing bacteria were suppressing methanogenesis. Methanogenesis increased by approximately 67 times while Fe²⁺ production only doubled after the addition of ¹³CH₃COO^?. Large increases in both CH₄ and Fe²⁺ production also indicate that the two process were acetate limited, suggesting that acetate may be a key substrate for anoxic carbon (C) metabolism in humid tropical forest soils. C isotope analysis suggests that competition for acetate was not the only factor driving CH₄ production, as ¹³C partitioning did not vary significantly between ¹³CH₃COO^? and ¹³CH₃COO^?+Fe(III) treatments. This suggests that dissimilatory Fe(III)‐reduction suppressed both hydrogenotrophic and aceticlastic methanogenesis. These findings have implications for understanding the CH₄ biogeochemistry of highly weathered wet tropical soils, where CH₄ efflux is driven largely by CH₄ production.     

Parallel phenotypic evolution in a wolf spider radiation on Galápagos

Within island archipelagos, repeated ecological settings may lead to radiations wherein similar niches are recurrently occupied. Although it has been shown that species with common habitat requirements share particular traits, it remains relatively unexplored to what extent this may lead to the repeated evolution of almost identical phenotypes (phenocopies) and how this correlates with traits subjected to sexual selection. Exploring divergence patterns of ecological and sexual relevant traits within spiders seem promising to enhance our understanding of the relative role of natural and sexual selection. Here, we conduct a detailed morphological analysis on a large set of genital and non‐genital traits (morphometrics, colour pattern) within a radiation of the wolf spider genus Hogna Simon, 1885 on Galápagos and interpret these data, taking into account their known phylogenetic relationship. Our results show that recurrent environmental gradients have led to the parallel evolution of almost identical phenotypes, which not only proves that natural selection has driven morphological divergence, but also suggests that a similar genetic or developmental basis most likely underlies this divergence. Among‐species variation in genital traits in contrast rather reflects the phylogenetic relationships on Santa Cruz and San Cristóbal. The combination of these data indicate that speciation in this system is driven by the combined effect of ecological mechanisms and allopatric divergence in sexual traits. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106 , 123–136.     

Community-based mental health care in Africa: mental health workers’ views

The World Health Organization (WHO) has for long proposed the development of community-based mental health services worldwide. However, the progress toward community mental health care in most African countries is still hampered by a lack of resources, with specialist psychiatric care essentially based in large, centrally located mental hospitals. It is again time to reconsider the direction of mental health care in Africa. Based on a small inquiry to a number of experienced mental health professionals in sub-Saharan Africa, we discuss what a community concept of mental health care might mean in Africa. There is a general agreement that mental health services should be integrated in primary health care. A critical issue for success of this model is perceived to be provision of appropriate supervision and continuing education for primary care workers. The importance of collaboration between modern medicine and traditional healers is stressed and the paper ends in a plea for WHO to take the initiative and develop mental health services according to the special needs and the socio-cultural conditions prevailing in sub-Saharan Africa.     

Increased Transformation Efficiency of Simian Virus 40 in Rat Embryo Cells infected with Rauscher Leukaemia Virus

SIMIAN virus 40 (SV40) is oncogenic for hamsters¹ and Mastomys². In vitro studies have shown that SV40 is capable of transforming cells derived from hamster³, mouse⁴, rabbit⁴, pig⁴, cow⁵, monkey⁶, human⁷, guinea-pig⁸ and rat⁹. We have established and studied continuous lines of uninfected and Rauscher leukaemia virus (RLV) infected rat embryo (RE) cells¹⁰. Rat embryo cells exposed to RLV have produced infectious virus and complement-fixing (CF) antigen characteristic of the murine leukaemia-sarcoma virus complex for more than 18 months. This communication describes increased transformation efficiency of SV40 in RLV infected RE cells (RLV-RE) compared with uninfected RE cells.     

Comparative Enzyme Differentiation in Grass Roots: II PEROXIDASE

Results of histochemical tests for peroxidase activity in sevenspecies of grasses have been reported. The root epidermis ofthe festucoid grasses is characterized by rows of alternatingshorter hair and longer hairless cells which can be recognizedthroughout their development. Peroxidase activity occurred inall the growing cells, but intensified reactions were observedin the hair cell initials in the bases portion of the elongationzone. The panicoid species have a root epidermis in which anycell seems capable of producing a root hair, and in these speciesall cells in the growing regions showed equal peroxidase activity.The close correlation between the differentiations of enzymesand cell types implies that physiological changes occur longbefore the morphological maturation of the tissue.     

Acoustic convergence and divergence in two sympatric burrowing nocturnal seabirds

Shearwaters are nocturnal burrowing seabirds. They return to their colony at dusk and exhibit high vocal activity, underlining the usefulness of acoustic cues to nocturnal communication. The present study aimed to test whether acoustic communication systems of two sympatric shearwater species, the Yelkouan shearwater Puffinus yelkouan and the Mediterranean Cory's shearwater Calonectris diomedea diomedea , converge to similar strategies. Inter-annual mate fidelity and incubation relays led us to focus on sex and individual acoustic signatures. We first characterized those two signatures by analysing the major call emitted by incubating birds. Second, we performed playback experiments to assess ability of birds to vocally discriminate between sexes and mate versus non-mate. The results obtained show that both species use a reliable sex vocal signature supported by frequency and energy features, enabling sex identification of the emitter. By responding only to conspecific same-sex calls, birds may ensure burrow and mate guarding. Conversely, individual vocal signature was mainly supported by temporal parameters, and was more reliable in the Cory's shearwater. Moreover, this species uses vocal exchanges to identify the mate during incubation relays, whereas Yelkouan shearwaters probably need additional cues. In conclusion, we observe an evolutionary convergence in intra-sex communication process but a divergence in mate greeting strategy.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 115–134.