Spatio-temporal growth dynamics of a subAlpine Pinus uncinata stand in the French Alps

Natural forests are characterised by a high level of both spatial and temporal heterogeneity. The major processes involved in the creation and maintenance of forest heterogeneity in temperate climates are small-sized canopy disturbances. The resulting openings also modify the growth conditions for the remaining trees. The analysis of tree growth responses using dendrochronological techniques allows the reconstruction of the time sequence of the disturbances. The radial growth analysis is coupled here with both a spatial analysis and a demographic analysis of the forest structure. The age classes are temporally organised in cohorts and spatially distributed in spatial aggregates. The analysis of the most documented disturbance event allowed us to determine the size of the disturbance response patch (between 0.036 and 0.073 ha) and the duration of the disturbance (six years). We considered that this small-scale disturbance event may have been caused by the fall of a single tree and has freed the surrounding trees of its competition.     

Engineering tolerance and accumulation of lead and cadmium in transgenic plants

We have studied the utility of the yeast protein YCF1, which detoxifies cadmium by transporting it into vacuoles, for the remediation of lead and cadmium contamination. We found that the yeast YCF1-deletion mutant DTY167 was hypersensitive to Pb(II) as compared with wild-type yeast. DTY167 cells overexpressing YCF1 were more resistant to Pb(II) and Cd(II) than were wild-type cells, and accumulated more lead and cadmium. Analysis of transgenic Arabidopsis thaliana plants overexpressing YCF1 showed that YCF1 is functionally active and that the plants have enhanced tolerance of Pb(II) and Cd(II) and accumulated greater amounts of these metals. These results suggest that transgenic plants expressing YCF1 may be useful for phytoremediation of lead and cadmium.     

Light scattering studies of the solution properties of chitosans of varying degrees of acetylation

The use of two techniques, differential interferometry and quasi-elastic light scattering (QELS), allowed us to study solutions of chitosan varying in degree of acetylation (DA), degree of dissociation (alpha), and concentration (C(p)). With the first technique, we demonstrated the modification of the electric polarizability of the polymer chains, through a law of behavior of the variation of the refractive index increment dn/dC with DA and alpha. This brought us information on the various kinds of interactions (H-bonds, electrostatic, and hydrophobic) involved in the evolution of the solution properties. QELS experiments performed in dilute regime showed the presence of supramolecular structures depending on DA and alpha. The topology and the nature of these objects are discussed. The typical presence of aggregates and their evolution with concentration was also demonstrated in semidilute regime.     

Acute inflammation increases selective uptake of HDL cholesteryl esters into adrenals of mice overexpressing human sPLA2

The acute-phase protein secretory phospholipase A2 (sPLA2) influences the metabolism of high-density lipoproteins (HDL). The adrenals are known to utilize HDL cholesterol as a source of sterols. The aim of the present study was to test the hypothesis that sPLA2 enhances the selective uptake of HDL into the adrenals in response to acute inflammation as a possible physiological role for the sPLA2-HDL interaction. Human sPLA2-transgenic mice, in which sPLA2 expression is upregulated by inflammatory stimuli, were used. Ten hours after induction of the acute-phase response (APR) by injection of bacterial lipopolysaccharide (LPS), plasma levels of HDL cholesterol decreased significantly in sPLA2-transgenic mice (-18%, P < 0.05) but remained unchanged in wild-type mice. The fractional catabolic rates of both 125I-labeled tyraminecellobiose (TC)-HDL and [3H]cholesteryl ether increased significantly in the sPLA2-transgenic mice after induction of the APR (0.18 +/- 0.01 vs. 0.21 +/- 0.01 pool/h, P < 0.05, and 0.31 +/- 0.02 vs. 0.42 +/- 0.05 pool/h, P < 0.05, respectively) but remained unchanged in the wild-type mice (0.10 +/- 0.01 vs. 0.22 +/- 0.02 pool/h, respectively). After induction of the APR, in both groups HDL holoparticle uptake by the liver was increased (P < 0.001). sPLA2-transgenic mice had 2.4-fold higher selective uptake into the adrenals after induction of the APR than wild-type mice (156 +/- 6 vs. 65 +/- 5%/ micro g tissue protein, P < 0.001). In summary, upregulation of sPLA2 expression during the APR specifically increases the selective uptake of HDL cholesteryl ester into the adrenals. These data suggest a novel metabolic role for sPLA2: modification of HDL during the APR to promote increased adrenal uptake of HDL cholesteryl ester to serve as source for steroid hormone synthesis.     

Exposure to low irradiances favors the synthesis of 9-cis beta, beta-carotene in Dunaliella salina (Teod.)

We examined the effect of irradiance on the synthesis of beta-carotene and its isomers by Dunaliella salina. Growth irradiance had a marked effect both on growth of the alga (which was suppressed at both low and high irradiances) and on the accumulation of beta-carotene. The accumulation of beta-carotene but not alpha-carotene was closely linked to an increase in irradiance. Growth at low irradiances (20-50 micromol m(-2) s(-1)) promoted a high ratio of 9-cis to all-trans beta-carotene (>2:1), while exposure to high irradiances (200-1,250 micromol m(-2) s(-1)) resulted in a large reduction in this ratio (to <0.45:1). A similar pattern was seen for the geometric isomers of alpha-carotene, with exposure to low irradiance favoring the accumulation of the 9-cis form. The carotenoid biosynthesis inhibitors 4-chloro-5(methylamino)-2-(alpha-alpha-alpha-trifluoro-m-tolyl)-3-(sH )-pyridazinone and 2-(4-chlorophenylthio)triethylamine caused the accumulation of the precursors phytoene and lycopene, respectively, in D. salina. High-performance liquid chromatography and infrared analysis showed that phytoene adopted the 15-cis and all-trans forms (as in higher plants), and that lycopene primarily adopted the all-trans form. This indicates that isomerization of beta-carotene takes place during or after cyclization.     

Rapid <Emphasis Type="Italic">Leptospira</Emphasis> identification by direct sequencing of the diagnostic PCR products in New Caledonia

Background  

Most of the current knowledge of leptospirosis epidemiology originates from serological results obtained with the reference Microscopic Agglutination Test (MAT). However, inconsistencies and weaknesses of this diagnostic technique are evident. A growing use of PCR has improved the early diagnosis of leptospirosis but a drawback is that it cannot provide information on the infecting Leptospira strain which provides important epidemiologic data. Our work is aimed at evaluating if the sequence polymorphism of diagnostic PCR products could be used to identify the infecting Leptospira strains in the New Caledonian environment.     

The problem of characters susceptible to parallel evolution in phylogenetic analysis: a reply to Marquès and Gnaspini (2001) with emphasis on cave life phenotypic evolution

Marquès and Gnaspini [Cladistics 17 (2001) 371–381] analyzed the problem of the phylogenetic treatment of characters submitted to parallel evolution. Their proposal aimed at preserving the potential phylogenetic significance of supposedly homoplastic characters and considering them for phylogeny reconstruction. As an example, they used the troglobiomorphic features of animals restricted to caves; according to their preliminary hypothesis of homoplasy, troglobitic animals would exhibit a particular phenotype, referred to as troglobiomorphic, which they would acquire under similar selective pressures from the subterranean environment. We examined Marquès and Gnaspini's approach not from the point of view of its technical flaws, but from the point of view of the authors’ basic assertions on the treatment of troglobiomorphic characters and more generally the inclusion/exclusion/transformation of characters prior to phylogenetic analysis. In the present paper, we argue that this approach is invalidated by the repeated use of ad hoc hypotheses, which are supported neither by an existing phylogenetic pattern nor by available data. We consequently contest the adequateness of this approach with a cladistic analysis of historical questions.     

Endocrine regulation of energy metabolism by the skeleton

The regulation of bone remodeling by an adipocyte-derived hormone implies that bone may exert a feedback control of energy homeostasis. To test this hypothesis we looked for genes expressed in osteoblasts, encoding signaling molecules and affecting energy metabolism. We show here that mice lacking the protein tyrosine phosphatase OST-PTP are hypoglycemic and are protected from obesity and glucose intolerance because of an increase in beta-cell proliferation, insulin secretion, and insulin sensitivity. In contrast, mice lacking the osteoblast-secreted molecule osteocalcin display decreased beta-cell proliferation, glucose intolerance, and insulin resistance. Removing one Osteocalcin allele from OST-PTP-deficient mice corrects their metabolic phenotype. Ex vivo, osteocalcin can stimulate CyclinD1 and Insulin expression in beta-cells and Adiponectin, an insulin-sensitizing adipokine, in adipocytes; in vivo osteocalcin can improve glucose tolerance. By revealing that the skeleton exerts an endocrine regulation of sugar homeostasis this study expands the biological importance of this organ and our understanding of energy metabolism.     

Thorezia vezerensisgen. et sp. nov., a new seed plant with multiovulate cupules from the Late Devonian of Belgium

The multiovulate cupule of a new spermatophyte, Thorezia vezerensisgen. et sp. nov., is described from the Late Devonian aged sediments from Trooz Quarry in Belgium. In gross morphology, it conforms to the Moresnetia morphotype and has a cupule that is composed of four independent quarters that each dichotomises three times. Each cupule quarter contains one single ovoid preovule with a long pedicel and an integument that has small apical teeth surrounding a rudimentary micropyle. Morphological variability in the materials examined is interpreted as being related to preovule maturity, and from this a good understanding of the ontogenetic development from preceding dispersal has been developed. Up to now, 17 spermatophyte species have been described, 11 of which come from eastern Laurussia. This diversity in eastern Laurussia contrasts strongly with the low diversity characterizing contemporaneous floras from other phytogeographical areas. We suggest here that the arid climatic conditions prevailing in eastern Laurussia favoured the development of diverse spermatophyte communities and contributed to reduced diversity and abundance of contemporaneous free-sporing plant diversity.