Maturation stress generation in poplar tension wood studied by synchrotron radiation microdiffraction

Tension wood is widespread in the organs of woody plants. During its formation, it generates a large tensile mechanical stress called maturation stress. Maturation stress performs essential biomechanical functions such as optimizing the mechanical resistance of the stem, performing adaptive movements, and ensuring the long-term stability of growing plants. Although various hypotheses have recently been proposed, the mechanism generating maturation stress is not yet fully understood. In order to discriminate between these hypotheses, we investigated structural changes in cellulose microfibrils along sequences of xylem cell differentiation in tension and normal wood of poplar (Populus deltoides × Populus trichocarpa 'I45-51'). Synchrotron radiation microdiffraction was used to measure the evolution of the angle and lattice spacing of crystalline cellulose associated with the deposition of successive cell wall layers. Profiles of normal and tension wood were very similar in early development stages corresponding to the formation of the S1 layer and the outer part of the S2 layer. Subsequent layers were found with a lower microfibril angle (MFA), corresponding to the inner part of the S2 layer of normal wood (MFA approximately 10°) and the G layer of tension wood (MFA approximately 0°). In tension wood only, this steep decrease in MFA occurred together with an increase in cellulose lattice spacing. The relative increase in lattice spacing was found close to the usual value of maturation strains. Analysis showed that this increase in lattice spacing is at least partly due to mechanical stress induced in cellulose microfibrils soon after their deposition, suggesting that the G layer directly generates and supports the tensile maturation stress in poplar tension wood.     

Effects of superovulation on endogenous LH secretion in cattle, and consequences for embryo production

Stimulation of follicular growth during superovulation is achieved by the injection of FSH or compounds with high FSH-bioactivities. However, some LH-activity is required for follicle maturation. It is of relevance to evaluate, therefore, the effect of superovulatory treatments on endogenous LH secretion. Luteinizing hormone is secreted in discrete pulses, and the pattern of pulsatile LH secretion during superovulation is reviewed. Four of five published studies have shown that LH pulse frequency is significantly reduced by injection of eCG or FSH preparations. This suppression appears within 8 h of treatment Effects of superovulation on LH pulse amplitude are less consistent. The reasons for the decrease in pulse frequency have been investigated, and although the answer is not definitive, it would seem that increased follicular estradiol, acting perhaps in synergism with progesterone, may play a role. Changes in plasma progesterone concentrations are not related to changes in LH pulse frequency. What is the significance of decreased LH pulse frequency? We attempted to investigate this by inducing LH pulses during superovulation, but the result was a major reduction in ovulation rate. More research is required to determine if modification of endogenous LH secretion can improve superovulatory responses.     

MAP kinase activation by hypoosmotic stress of tobacco cell suspensions: towards the oxidative burst response?

Hypoosmotic stress activates a phosphorylation-dependent oxidative burst. In-gel kinase assays were performed to characterize the protein kinases that could be implicated in osmoregulation and in the activation of the oxidative burst. Hypoosmotic stress activated several kinases among which 50 and 46 kDa proteins displayed mitogen-activated protein kinase (MAP kinase) properties. They phosphorylated myelin basic protein in the absence of calcium, were recognized by antibodies directed against human MAP kinases, and were phosphorylated on tyrosine. Immunoprecipitation with an antibody directed against the tobacco MAP kinase Ntf4 showed that at least one of the activated kinases would be Ntf4-like. Apigenin, a MAP kinase and cyclin-dependent kinase inhibitor which prevents the hypoosmotically induced oxidative burst ( Cazaléet al. 1998 ; Plant Physiol. 116, 659–669), inhibited these kinases in vitro suggesting that they may play a role in the activation of the oxidative burst. Like the oxidative response, activation of the kinases depended on extracellular calcium influx and protein kinases sensitive to staurosporine and 6-DMAP. However, kinase activation did not depend on effluxes through anion channels or on the oxidative burst. Two-dimensional in-gel kinase assays revealed the presence of three protein kinases with an apparent molecular mass of 50 kDa and one of 46 kDa, all four being activated by hypoosmotic stress. The same kinases were also activated by oligogalacturonides and salicylic acid, underlying the importance of these MAP kinases as common components of different signaling pathways triggered by different extracellular stimuli.     

A platinum–quinacridine hybrid as a G-quadruplex ligand

A novel platinum–quinacridine hybrid, comprising a monofunctional Pt moiety and a G-quadruplex ligand (mono-para-quinacridine or MPQ), has been synthesized and shown to interact with quadruplex DNA via a dual noncovalent/covalent binding mode. Denaturing gel electrophoresis was used to separate the various platination products of 22AG (an oligonucleotide that mimics the human telomeric repeat) by Pt-MPQ, and it was shown that two platinated adducts are highly stable quadruplex structures. Dimethylsulfate/piperidine treatment and 3′-exonuclease digestion of the isolated adducts allowed us to precisely determine the platination pattern of 22AG by Pt-MPQ, which displays three main sites G2, G10 and G22. Data presented herein support the hypothesis that Pt-MPQ traps preferentially the antiparallel structure of the 22AG quadruplex. Finally, the kinetics of Pt-MPQ platination using a construct containing both quadruplex DNA and a duplex DNA parts provide the first insights into the Pt-MPQ preference for quadruplex DNA over duplex DNA.     

The TD6 level lithic industry from Gran Dolina, Atapuerca (Burgos, Spain): production and use.

Technological analysis of lithic artefacts recovered at the Aurora stratum of Atapuerca-TD6 shows that this Lower Pleistocene assemblage is similar to Mode I Technology (=Oldowan tradition) documented at many African sites. Diachronic comparison of the different levels of Gran Dolina allows us to conclude that this particular form of early European technology lacks the production of big flakes to manufacture large tools such as bifaces and cleavers. Rather, it is characterized by the presence of small artefacts, including flakes, denticulates, notches, and side-scrapers, many of which bear use-wear traces of butchery and woodworking. The dominant production technique is orthogonal, which is also reflected in the core recovered at the slightly older level of TD4. The raw materials also found in the Middle Pleistocene occupations at Atapuerca, though with significant proportion differences, have a local origin and include varieties of flint, quartzite and sandstone as well as limestone and quartz. TD6 small artefacts were made from most of these, although the retouched pieces seem to have been preferentially made of the best quality flint, i.e., Cretaceous flint, pointing to the existence of differential use of lithic material, and therefore, some degree of planned knapping behaviour. Most of the "cha?nes opératoires" or reduction sequences took place inside the cave, although some artefacts, elaborated on Cretaceous flint, seem to have been retouched off site, possibly near the supply sources.     

A virus-Drosophila association: the first steps towards co-evolution?

Drosophila melanogaster can be parasitized by a picornavirus, the Drosophila C virus (DCV). The virus is not hereditary, but it is horizontally transmitted (by ingestion or contact). When first larval instars come into contact with DCV unusual interactions are observed between host and microparasite. DCV acts differently depending on the stage in the host's life cycle. It boosts the reproductive capacity of adults, but it diminishes survival during the pre-reproductive period. In infected flies, the DCV target organs are principally the follicular cells and the fat body. The infected cells resemble DCV-free cells. According to the parameters of the Drosophila lifecycle, measured for different Drosophila strains, at different temperatures, and for different viral doses, DCV could be considered either as a parasite, because it increases pre-adult mortality, or as a mutualist, because it increases the reproductive capacity of the host and decreases its developmental time. Like many viruses, DCV is extremely pathogenic when injected into flies, which then die within a few days. Only one strain resists the disease longer. The resistant phenotype is dominant. Genes of chromosome 3 of the host are involved. Interactions are discussed in terms of an arms race and peaceful cohabitation. They are also considered in terms of biodiversity for the host and for the microparasite.     

Habitat use under predation risk: hunting, roads and human dwellings influence the spatial behaviour of roe deer

Wildlife populations are subjected to increasing pressure linked to human activities, which introduce multiple stressors. Recently, in addition to direct effects, it has been shown that indirect (non-lethal) effects of predation risk are predominant in many populations. Predation risk is often structured in space and time, generating a heterogeneous “landscape of fear” within which animals can minimize risks by modifying their habitat use. Furthermore, for ungulates, resource quality seems to be positively correlated with human-related sources of risk. We studied the trade-off between access to resources of high-quality and risk-taking by contrasting habitat use of roe deer during daytime with that during nighttime for 94 roe deer in a hunted population. Our first hypothesis was that roe deer should avoid human disturbance by modifying their habitat use during daytime compared to nighttime. Our results supported this, as roe deer mainly used open fields during nighttime, but used more forested habitats during daytime, when human disturbance is higher. Moreover, we found that diel patterns in habitat use were influenced by hunting disturbance. Indeed, the roe deer decreased their use of high-crops during daytime, an important source of cover and food, during the hunting season. The proximity of roads and dwellings also affected habitat use, since roe deer used open fields during daytime to a greater extent when the distance to these sources of disturbance was higher. Hence, our results suggest that roe deer resolve the trade-off between the acquisition of high-quality resources and risk avoidance by modifying their habitat use between day and night.