126 research outputs found
Tropical and subtropical actinorhizal plants
A maioria dos paĂses tropicais enfrenta dois grandes problemas: o aumento constante da exploração das reservas florestais para extração de madeira ou lenha e a diminuição da fertilidade do solo para produção agrĂcola. O conceito geral Ă© o de que plantas fixadoras de N2 podem evitar a propalada crise de madeira e alimentos. Juntas com um grande nĂșmero de leguminosas fixadoras de N2, plantas actinorrĂzicas podem ter um papel importante na produção de madeira e recuperação de solos. As plantas actinorrĂzicas compreendem oito famĂlias de dicotiledĂŽneas, todas elas representadas nos trĂłpicos. Neste trabalho, as mais promissoras plantas actinorrĂzicas tropicais sĂŁo brevemente apresentadas e a ĂȘnfase Ă© dada principalmente Ă famĂlia Casuarinaceae. Esta famĂlia compreende quatro gĂȘneros (Casuarina, Allocasuarina, Gymnostoma e gĂȘnero C), com 82 espĂ©cies, incluindo muitas ĂĄrvores que podem produzir madeira de boa qualidade. As estirpes de Frankia que tĂȘm sido isoladas das Casuarinaceae crescem lentamente e sĂŁo capazes de reduzir acetileno in vitro sob ar, o que indica uma capacidade de proteção contra o O2 muito mais eficiente do que no Rhizobium. Apenas as espĂ©cies do gĂȘnero Casuarina podem ser noduladas pela estirpe ORS 021001, isolada de Casuarina junghuhniana, o que sugere a existĂȘncia de grupos de inoculação dentro da famĂlia Casuarinaceae. A fixação de N2 de Casuarina equisetifolia, crescida em microparcelas de 1 m2, na estação experimental de ORSTM, em Dakar, foi estimada atravĂ©s da comparação do N total em plantas nĂŁo-inoculadas e plantas inoculadas com a estirpe ORS 021001. Extrapolando para um hectare, a fixação de N2 foi de 131 kg/N em um perĂodo de 6,5 meses. Usando o mĂ©todo de equivalĂȘncia com adubo nitrogenado, a inoculação parece ser equivalente Ă aplicação de 288 kg de N/ha-1.Most tropical countries face two major problems: increasing overexploitation of wood reserves for timber or fuel wood and diminishing soil fertility for agricultural production. The present consensus is that N2 -fixing plants can help prevent the forthcoming wood and food crisis. Together with the vast group of N2 -fixing Leguminoseae, actinorhizal plants (AP) can play a major role in wood production and land regeneration. AP comprise eight families of dicotyledonous plants all of which are represented in the tropics. In this paper the most promising tropical AP are briefly presented and the emphasis is put mainly on Casuarinaceae. This family forms a group of four genera (Casuarina, Allocasuarina, Gymnostoma and genus C) with 82 species, including many trees that can yield wood of good quality. The Frankia strains that have been isolated from Casuarinaceae grow slowly and are able to reduce acetylene in vitro under air, which indicates that the protection against O2 is much more efficient in Frankia than in rhizobia. Only the species belonging to the Casuarina genus could be nodulated by strain ORS 021001, isolated from Casuarina junghuhniana, suggesting the existence of crossinoculation groups within the family Casuarinaceae. N2 fixation of Casuarina equisetifolia, grown in 1 m2 microplots at the ORSTOM experimental station of Dakar, was estimated by comparing total N in non-inoculated plants and plants inoculated with Frankia strain ORS 021001. Extrapolating to 1 hectare, N2 fixation was 131 kg for a 6.5-month period. Using the N fertilizer equivalence method, inoculation appeared to be equivalent to the application of 288 kg of N fertilizer per hectare
Drivers for Rift Valley fever emergence in Mayotte: A Bayesian modelling approach
Rift Valley fever (RVF) is a major zoonotic and arboviral hemorrhagic fever. The conditions leading to RVF epidemics are still unclear, and the relative role of climatic and anthropogenic factors may vary between ecosystems. Here, we estimate the most likely scenario that led to RVF emergence on the island of Mayotte, following the 2006â2007 African epidemic. We developed the first mathematical model for RVF that accounts for climate, animal imports and livestock susceptibility, which is fitted to a 12-years dataset. RVF emergence was found to be triggered by the import of infectious animals, whilst transmissibility was approximated as a linear or exponential function of vegetation density. Model forecasts indicated a very low probability of virus endemicity in 2017, and therefore of re-emergence in a closed system (i.e. without import of infected animals). However, the very high proportion of naive animals reached in 2016 implies that the island remains vulnerable to the import of infectious animals. We recommend reinforcing surveillance in livestock, should RVF be reported is neighbouring territories. Our model should be tested elsewhere, with ecosystem-specific data
Site-Specific and Time-Dependent Activation of the Endocannabinoid System after Transection of Long-Range Projections
Background: After focal neuronal injury the endocannabinioid system becomes activated and protects or harms neurons depending on cannabinoid derivates and receptor subtypes. Endocannabinoids (eCBs) play a central role in controlling local responses and influencing neural plasticity and survival. However, little is known about the functional relevance of eCBs in long-range projection damage as observed in stroke or spinal cord injury (SCI).
Methods: In rat organotypic entorhino-hippocampal slice cultures (OHSC) as a relevant and suitable model for investigating projection fibers in the CNS we performed perforant pathway transection (PPT) and subsequently analyzed the spatial and temporal dynamics of eCB levels. This approach allows proper distinction of responses in originating neurons (entorhinal cortex), areas of deafferentiation/anterograde axonal degeneration (dentate gyrus) and putative changes in more distant but synaptically connected subfields (cornu ammonis (CA) 1 region).
Results: Using LC-MS/MS, we measured a strong increase in arachidonoylethanolamide (AEA), oleoylethanolamide (OEA) and palmitoylethanolamide (PEA) levels in the denervation zone (dentate gyrus) 24 hours post lesion (hpl), whereas entorhinal cortex and CA1 region exhibited little if any changes. NAPE-PLD, responsible for biosynthesis of eCBs, was increased early, whereas FAAH, a catabolizing enzyme, was up-regulated 48hpl.
Conclusion: Neuronal damage as assessed by transection of long-range projections apparently provides a strong time-dependent and area-confined signal for de novo synthesis of eCB, presumably to restrict neuronal damage. The present data underlines the importance of activation of the eCB system in CNS pathologies and identifies a novel site-specific intrinsic regulation of eCBs after long-range projection damage
Biophysical interactions in tropical agroforestry systems
sequential systems, simultaneous systems Abstract. The rate and extent to which biophysical resources are captured and utilized by the components of an agroforestry system are determined by the nature and intensity of interac-tions between the components. The net effect of these interactions is often determined by the influence of the tree component on the other component(s) and/or on the overall system, and is expressed in terms of such quantifiable responses as soil fertility changes, microclimate modification, resource (water, nutrients, and light) availability and utilization, pest and disease incidence, and allelopathy. The paper reviews such manifestations of biophysical interactions in major simultaneous (e.g., hedgerow intercropping and trees on croplands) and sequential (e.g., planted tree fallows) agroforestry systems. In hedgerow intercropping (HI), the hedge/crop interactions are dominated by soil fertility improvement and competition for growth resources. Higher crop yields in HI than in sole cropping are noted mostly in inherently fertile soils in humid and subhumid tropics, and are caused by large fertility improvement relative to the effects of competition. But, yield increases are rare in semiarid tropics and infertile acid soils because fertility improvement does not offse
History on the biological nitrogen fixation research in graminaceous plants: special emphasis on the Brazilian experience
Nodulation of Acacia Species by Fast- and Slow-Growing Tropical Strains of Rhizobium
Thirteen Acacia species were classified into three groups according to effective nodulation response patterns with fast- and slow-growing tropical strains of Rhizobium. The first group nodulated effectively with slow-growing, cowpea-type Rhizobium strains; the second, with fast-growing Rhizobium strains; and the third, with both fast- and slow-growing Rhizobium strains. The Rhizobium requirements of the Acacia species of the second group were similar to those of Leucaena leucocephala
Polyacrylamide-Entrapped Rhizobium as an Inoculant for Legumes
Pot experiments showed that Rhizobium japonicum cells entrapped in a polyacrylamide gel could be used as an inoculant for soybeans and compared favorably to laboratory-made peat base inoculant containing the same bacterial strain
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