Seasonal survey of the composition and degradation state of particulate organic matter in the Rhône River using lipid tracers

International audienceLipid tracers including fatty acids, hydroxyacids, n-alkanols, sterols and triterpenoids were used to determine the origin and fate of suspended particulate organic matter (POM) collected in the Rhône River (France). This seasonal survey (April 2011 to May 2013) revealed a year-round strong terrestrial higher-plant contribution to the particulate organic matter (POM), with significant algal inputs observed in March and attributed to phytoplanktonic blooms likely dominated by diatoms. Major terrigenous contributors to our samples are gymnosperms, and more precisely their roots and stems, as evidenced by the presence of high proportions of ω-hydroxydocosanoic acid (a suberin biomarker). The high amounts of coprostanol detected clearly show that the Rhône River is significantly affected by sewage waters. Specific sterol degradation products were quantified and used to assess the part of biotic and abiotic degradation of POM within the river. Higher-plant-derived organic matter appears to be mainly affected by photo-oxidation and au-toxidation (free radical oxidation), while organic matter of mammal or human origin, evidenced by the presence of co-prostanol, is clearly more prone to bacterial degradation. Despite the involvement of an intense autoxidation-inducing ho-molytic cleavage of peroxy bonds, a significant proportion of hydroperoxides is still intact in higher plant debris. These compounds could affect the degradation of terrestrial material by inducing an intense autoxidation upon its arrival at sea

Synthesis of Nitrogenated Heterocycles by Asymmetric Transfer Hydrogenation of N-(tert-Butylsulfinyl)haloimines

Highly optically enriched, protected, nitrogenated heterocycles with different ring sizes have been synthesized by a very efficient methodology consisting of the asymmetric transfer hydrogenation of N-(tert-butylsulfinyl)haloimines followed by treatment with a base to promote an intramolecular nucleophilic substitution process. N-Protected aziridines, pyrrolidines, piperidines, and azepanes bearing aromatic, heteroaromatic, and aliphatic substituents have been obtained in very high yields and diastereomeric ratios up to >99:1. The free heterocycles can be easily obtained by a simple and mild desulfinylation procedure. Both enantiomers of the free heterocycles can be prepared with the same good results by changing the absolute configuration of the sulfur atom of the sulfinyl group.This work was generously supported by the Spanish Ministerio de Ciencia e Innovación (MICINN; grant no. CONSOLIDER INGENIO 2010, CSD2007-00006, CTQ2007-65218 and CTQ2011-24151) and the Generalitat Valenciana (PROMETEO/2009/039 and FEDER). O.P. thanks the Spanish Ministerio de Educación for a predoctoral fellowship (grant no. AP-2008-00989)

Transcriptional responses of winter barley to cold indicate nucleosome remodelling as a specific feature of crown tissues

We report a series of microarray-based comparisons of gene expression in the leaf and crown of the winter barley cultivar Luxor, following the exposure of young plants to various periods of low (above and below zero) temperatures. A transcriptomic analysis identified genes which were either expressed in both the leaf and crown, or specifically in one or the other. Among the former were genes responsible for calcium and abscisic acid signalling, polyamine synthesis, late embryogenesis abundant proteins and dehydrins. In the crown, the key organ for cereal overwintering, cold treatment induced transient changes in the transcription of nucleosome assembly genes, and especially H2A and HTA11, which have been implicated in cold sensing in Arabidopsis thaliana. In the leaf, various heat-shock proteins were induced. Differences in expression pattern between the crown and leaf were frequent for genes involved in certain pathways responsible for osmolyte production (sucrose and starch, raffinose, γ-aminobutyric acid metabolism), sugar signalling (trehalose metabolism) and secondary metabolism (lignin synthesis). The action of proteins with antifreeze activity, which were markedly induced during hardening, was demonstrated by a depression in the ice nucleation temperature

Antioxidative responses of oak species under ozone and water stress conditions

The Mediterranean basin is considered a global biodiversity hotspot but Mediterranean plants are threatened by natural and anthropogenic factors (e.g., tropospheric ozone, O3) which are expected to be harsher in the near future. The objective of this work was to give a thorough description of the detoxification mechanisms at the basis of the high plasticity of Mediterranean oak species. Two-year-old seedlings of Quercus ilex, Q. pubescens and Q. robur were grown under the combination of three levels of O3 (1.0, 1.2 and 1.4 times the ambient O3 concentration; AA, 1.2×AA and 1.4×AA) and water irrigation [1.2, 0.6 and 0.12 l day-1; well-watered (WW), moderate drought (MD) and severe drought (SD)] from June to October 2015. In Q. ilex, no symptoms due to O3 and/or drought were observed. This was confirmed by the minor propagation of reactive oxygen species (ROS) and the subsequent reduced cellular oxidative burst. Q. pubescens exposed to 1.4×AA and subjected to SD developed O3 injuries, consisting in minute roundish browning necrosis scattered among the leaf veins of both surfaces of mature leaves. An induction of the phenylpropanoid biosynthetic pathway by both stressors leaded to an increase of phenolic acids (+61% in comparison to AA). This enhanced antiradical ability of cell wall components partially balanced the ROS production but did not prevent foliar damage. In Q. robur, O3 symptoms were induced by both 1.2×AA and 1.4×AA concentrations under WW or MD conditions. Increasing O3 levels induced a significant rise of total flavonoids (+43 and +16% in 1.2×AA and1.4×AA). This species also displayed higher constitutive level of ascorbate. These mechanisms did not preserve the PSII photochemistry from impairment, as confirmed by the decrease of total chlorophylls under O3. A different species-specific degree of tolerance to single and combined stress was observed