Cachet, N., Hoakwie, F., Bertani, S., Bourdy, G., Deharo, E., Stien, D., et al. (2009). Antimalarial Activity of Simalikalactone E, a New Quassinoid from Quassia amara L. (Simaroubaceae). Antimicrob. Agents Chemother., 53(10), 4393–4398.
Abstract: We report the isolation and identification of a new quassinoid named simalikalactone E (SkE), extracted from a widely used Amazonian antimalarial remedy made out of Quassia amara L. (Simaroubaceae) leaves. This new molecule inhibited the growth of Plasmodium falciparum cultured in vitro by 50%, in the concentration range from 24 to 68 nM, independently of the strain sensitivity to chloroquine. We also showed that this compound was able to decrease gametocytemia with a 50% inhibitory concentration sevenfold lower than that of primaquine. SkE was found to be less toxic than simalikalactone D (SkD), another antimalarial quassinoid from Q. amara, and its cytotoxicity on mammalian cells was dependent on the cell line, displaying a good selectivity index when tested on nontumorogenic cells. In vivo, SkE inhibited murine malaria growth of Plasmodium vinckei petteri by 50% at 1 and 0.5 mg/kg of body weight/day, by the oral or intraperitoneal routes, respectively. The contribution of quassinoids as a source of antimalarial molecules needs therefore to be reconsidered.
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Patino, S., Lloyd, J., Paiva, R., Baker, T. R., Quesada, C. A., Mercado, L. M., et al. (2009). Branch xylem density variations across the Amazon Basin. Biogeosciences, 6(4), 545–568.
Abstract: Xylem density is a physical property of wood that varies between individuals, species and environments. It reflects the physiological strategies of trees that lead to growth, survival and reproduction. Measurements of branch xylem density, rho(x), were made for 1653 trees representing 598 species, sampled from 87 sites across the Amazon basin. Measured values ranged from 218 kg m(-3) for a Cordia sagotii (Boraginaceae) from Mountagne de Tortue, French Guiana to 1130 kg m(-3) for an Aiouea sp. (Lauraceae) from Caxiuana, Central Para, Brazil. Analysis of variance showed significant differences in average rho(x) across regions and sampled plots as well as significant differences between families, genera and species. A partitioning of the total variance in the dataset showed that species identity (family, genera and species) accounted for 33% with environment (geographic location and plot) accounting for an additional 26%; the remaining “residual” variance accounted for 41% of the total variance. Variations in plot means, were, however, not only accountable by differences in species composition because xylem density of the most widely distributed species in our dataset varied systematically from plot to plot. Thus, as well as having a genetic component, branch xylem density is a plastic trait that, for any given species, varies according to where the tree is growing in a predictable manner. Within the analysed taxa, exceptions to this general rule seem to be pioneer species belonging for example to the Urticaceae whose branch xylem density is more constrained than most species sampled in this study. These patterns of variation of branch xylem density across Amazonia suggest a large functional diversity amongst Amazonian trees which is not well understood.
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Phillips, O. L., Aragao, L. E. O. C., Lewis, S. L., Fisher, J. B., Lloyd, J., Lopez-Gonzalez, G., et al. (2009). Drought Sensitivity of the Amazon Rainforest. Science, 323(5919), 1344–1347.
Abstract: Amazon forests are a key but poorly understood component of the global carbon cycle. If, as anticipated, they dry this century, they might accelerate climate change through carbon losses and changed surface energy balances. We used records from multiple long-term monitoring plots across Amazonia to assess forest responses to the intense 2005 drought, a possible analog of future events. Affected forest lost biomass, reversing a large long-term carbon sink, with the greatest impacts observed where the dry season was unusually intense. Relative to pre-2005 conditions, forest subjected to a 100-millimeter increase in water deficit lost 5.3 megagrams of aboveground biomass of carbon per hectare. The drought had a total biomass carbon impact of 1.2 to 1.6 petagrams (1.2 x 10(15) to 1.6 x 10(15) grams). Amazon forests therefore appear vulnerable to increasing moisture stress, with the potential for large carbon losses to exert feedback on climate change.
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Yatabe, Y., Kane, N. C., Scotti-Saintagne, C., & Rieseberg, L. H. (2007). Rampant gene exchange across a strong reproductive barrier between the annual sunflowers, Helianthus annuus and H-petiolaris. Genetics, 175(4), 1883–1893.
Abstract: Plant species may remain morphologically distinct despite gene exchange with congeners, yet little is known about the genomewide pattern of introgression among species. Here we analyze the effects of persistent gene flow on genomic differentiation between the sympatric sunflower species Helianthus annuus and H. petiolaris. While the species are strongly isolated in testcrosses, genetic distances at 108 microsatellite loci and 14 sequenced genes are highly variable and much lower (on average) than for more closely related but historically allopatric congeners. Our analyses failed to detect a positive association between levels of genetic differentiation and chromosomal rearrangements (as reported in a prior publication) or proximity to QTL for morphological differences or hybrid sterility. However, a significant increase in differentiation was observed for markers within 5 cM of chromosomal breakpoints. Together, these results suggest that islands of differentiation between these two species are small, except in areas of low recombination. Furthermore, only microsatellites associated with ESTs were identified as outlier loci in tests for selection, which might indicate that the ESTs themselves are the targets of selection rather than linked genes (or that coding regions are not randomly distributed). In general, these results indicate that even strong and genetically complex reproductive barriers cannot prevent widespread introgression.
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Fang, C. H., Clair, B., Gril, J., & Almeras, T. (2007). Transverse shrinkage in G-fibers as a function of cell wall layering and growth strain. Wood Sci. Technol., 41(8), 659–671.
Abstract: Transverse drying shrinkage was measured at microscopic and mesoscopic levels in poplar wood characterised by an increasing growth strain (GS), from normal to tension wood. Results show that: (a) the drying shrinkage, measured as a relative thickness decrease, was significantly higher for G-layer (GL) than for the other layers (OL), GL shrinkage was not significantly correlated with GS, and OL shrinkage was negatively correlated with GS. (b) In gelatinous fibre (G-fibre), lumen size increased during drying and this increase was positively related with GS, but in normal wood fibre, lumen size decreased during drying. These findings suggest that GL shrank outwards (i.e., its internal perimeter increases), so that its shrinkage weakly affected the total cell shrinkage and the mesoscopic shrinkage was controlled by the OL shrinkage which shrank inwards (i.e., its external perimeter decreases). (c) Measurements done on 7 x 7 mm(2) thin sections evidenced a negative correlation between transverse shrinkage and GS, significant in T direction but weak in R direction. These observations at both levels allow to discuss the contribution of GL to the mesoscopic shrinkage of tension wood.
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Nasr, H., Domenach, A. M., Ghorbel, M. H., & Benson, D. R. (2007). Divergence in symbiotic interactions between same genotypic PCR-RFLP Frankia strains and different Casuarinaceae species under natural conditions. Physiol. Plant., 130(3), 400–408.
Abstract: The symbiotic interactions between Frankia strains and their associated plants from the Casuarinaceae under controlled conditions are well documented but little is known about these interactions under natural conditions. We explored the symbiotic interactions between eight genotypically characterized Frankia strains and five Casuarinaceae species in long-term field trials. Characterization of strains was performed using the polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) for the nifD-nifK intergenic transcribed spacer (ITS) and 16S-23S ITS. Assessments of the symbiotic interactions were based on nodulation patterns using nodule dry weight and viability, and on actual N-2 fixation using the delta N-15 method. The PCR-RFLP patterns showed that the analyzed strains belonged to the same genotypic group (CeD group), regardless of the host species and environment of origin. The nodule viability index is introduced as a new tool to measure the viability of perennial nodules and to predict their effectiveness. The host Casuarinaceae species was a key factor influencing both the actual N-2-fixing activity of the associated Frankia strain and the viability of nodules within a location. This is the first study providing information on the symbiotic interactions between genotypically characterized Frankia strains and actinorhizal plants under natural conditions. The results revealed a way to improve a long-term management of the Casuarinaceae symbiosis.
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Coutand, C., Fournier, M., & Moulia, B. (2007). The gravitropic response of poplar trunks: Key roles of prestressed wood regulation and the relative kinetics of cambial growth versus wood maturation. Plant Physiol., 144(2), 1166–1180.
Abstract: In tree trunks, the motor of gravitropism involves radial growth and differentiation of reaction wood (Archer, 1986). The first aim of this study was to quantify the kinematics of gravitropic response in young poplar (Populus nigra x Populus deltoides, 'I4551') by measuring the kinematics of curvature fields along trunks. Three phases were identified, including latency, upward curving, and an anticipative autotropic decurving, which has been overlooked in research on trees. The biological and mechanical bases of these processes were investigated by assessing the biomechanical model of Fournier et al. (1994). Its application at two different time spans of integration made it possible to test hypotheses on maturation, separating the effects of radial growth and cross section size from those of wood prestressing. A significant correlation between trunk curvature and Fournier's model integrated over the growing season was found, but only explained 32% of the total variance. Moreover, over a week's time period, the model failed due to a clear out phasing of the kinetics of radial growth and curvature that the model does not take into account. This demonstrates a key role of the relative kinetics of radial growth and the maturation process during gravitropism. Moreover, the degree of maturation strains appears to differ in the tension woods produced during the upward curving and decurving phases. Cell wall maturation seems to be regulated to achieve control over the degree of prestressing of tension wood, providing effective control of trunk shape.
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Delaval, M., & Charles-Dominique, P. (2006). Edge effects on frugivorous and nectarivorous bat communities in a neotropical primary forest in French Guiana. Rev. Ecol.-Terre Vie, 61(4), 343–352.
Abstract: The impact of a road crossing a continuous Guyana primary forest was studied through the analysis of qualitative and quantitative changes in a frugivorous and nectarivorous bat community at different distances from forest edge. Bats were captured along three 3-km forest transects perpendicular to the edge, and at the Nouragues Station located 150 km in the interior of the primary forest block, in an uninhabited area. Along the 3-km transects, we caught over seven times more individuals than in primary forest, this value decreasing according to the distance from the edge. Moreover, at the very edge, species richness was higher than along transects, probably due to exchanges between primary forest and the open habitats. On the contrary, diversity values at forest edges were lower than in primary forest, with a demographic explosion of a few opportunistic phyllostomid species such as Carollia perspicillata and Artibeus jamaicensis. Species restricted to degraded habitat like Glossophaga soricina and Artibeus cinereus were still present 3 km away from the edge, where the proportion of C perspicillata was seven times higher than in primary forest at Nouragues. These changes in the community of bats have important consequences on seed and pollen dispersal. So edge effects may significantly affect both faunal and floral assemblage. We conclude that changes in bat community occur up to at least 3 km from forest edge, i. e. at a greater distance than that found for all other vertebrates previously studied. By their implications our results should be considered in habitat and species conservation management plans.
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Rahali, H., & Stien, D. (2006). Highly-loaded amphiphilic polyimino resin: quench reagent and solid support for peptide synthesis. Tetrahedron Lett., 47(47), 8205–8207.
Abstract: We demonstrate herein that polyimino resin 4a prepared by condensation of alpha,alpha'-dichloro-p-xylene, ethylenediamine and tris-(2-aminoethyl)-amine can be successfully exploited as a quench reagent for acids and electrophiles both in aqueous and organic solutions. Scope and limitations of such a resin as a solid support for peptide synthesis were also investigated. (c) 2006 Elsevier Ltd. All rights reserved.
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Picard, N., Gourlet-Fleury, S., & Sist, P. (2003). Using process-dependent groups of species to model the dynamics of a tropical rainforest. Modelling Forest Systems, , 237–248.
Abstract: The high tree species diversity in tropical forests is difficult to take into account in models. The usual solution consists of defining groups of species and then adjusting a set of parameters for each group. In this study, we address this issue by allowing a species to move from one species group to another, depending on the biological process that is concerned. We developed this approach with a matrix model of forest dynamics, for a tropical rainforest in French Guiana, at Paracou, focusing on the methodological aspects. The forest dynamics is split into three components: recruitment, growth and mortality. We then built five recruitment groups, five growth groups and five mortality groups. One species is characterized by a combination of the three groups, thus yielding in total 5 X 5 X 5 = 125 possibilities, out of which 43 are actually observed. The resulting matrix model provides a better view of the floristic composition of the forest, and does not have more parameters than it would have with five global species groups. However, its predictions are no more precise than those of the matrix model based on five global groups.
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