Exploring gravity with the MIGA large scale atom interferometer.

We present the MIGA experiment, an underground long baseline atom interferometer to study gravity at large scale. The hybrid atom-laser antenna will use several atom interferometers simultaneously interrogated by the resonant mode of an optical cavity. The instrument will be a demonstrator for gravitational wave detection in a frequency band (100 mHz-1 Hz) not explored by classical ground and space-based observatories, and interesting for potential astrophysical sources. In the initial instrument configuration, standard atom interferometry techniques will be adopted, which will bring to a peak strain sensitivity of [Formula: see text] at 2 Hz. This demonstrator will enable to study the techniques to push further the sensitivity for the future development of gravitational wave detectors based on large scale atom interferometers. The experiment will be realized at the underground facility of the Laboratoire Souterrain à Bas Bruit (LSBB) in Rustrel-France, an exceptional site located away from major anthropogenic disturbances and showing very low background noise. In the following, we present the measurement principle of an in-cavity atom interferometer, derive the method for Gravitational Wave signal extraction from the antenna and determine the expected strain sensitivity. We then detail the functioning of the different systems of the antenna and describe the properties of the installation site.

Effects of exogenous salicylic acid pre-treatment on cadmium toxicity and leaf lipid content in Linum usitatissimum L.

The effects of salicylic acid (SA) on cadmium (Cd) toxicity in flax plants were studied by investigating plant growth, lipid peroxidation and fatty acid composition. Cadmium inhibited biomass production as well as the absorption of K, Ca, Mg and Fe. Furthermore, it dramatically increased Cd accumulation in both roots and shoots. The pre-soaking of dry flax grains in SA-containing solutions partially protected seedlings from Cd toxicity during the following growth period. SA treatment decreased the uptake and the transport of Cd, alleviated the Cd-induced inhibition of Ca, Mg and Fe absorption and promoted plant growth. At leaf level, Cd significantly decreased both total lipid (TL) and chlorophyll (Chl) content and enhanced electrolyte leakage and lipid peroxidation as indicated by malondialdehyde (MDA) accumulation. Concomitantly, Cd caused a shift in fatty acid composition, resulting in a lower degree of their unsaturation. SA pre-soaking ameliorated the increased electrolyte leakage as well as Chl, MDA and TL content. SA particularly increased the percentage of linolenic acid and lowered that of palmitic acid by the same proportion. These results suggest that SA could be used as a potential growth regulator and a stabilizer of membrane integrity to improve plant resistance to Cd stress.

Ultrastructure and lipid alterations induced by cadmium in tomato (Lycopersicon esculentum) chloroplast membranes.

The effects of cadmium (Cd) uptake on ultrastructure and lipid composition of chloroplasts were investigated in 28-day-old tomato plants (Lycopersicon esculentum var. Ibiza F1) grown for 10 days in the presence of various concentrations of CdCl2. Different growth parameters, lipid and fatty acid composition, lipid peroxidation, and lipoxygenase activity were measured in the leaves in order to assess the involvement of this metal in the generation of oxidative stress. We first observed that the accumulation of Cd increased with external metal concentration, and was considerably higher in roots than in leaves. Cadmium induced a significant inhibition of growth in both plant organs, as well as a reduction in the chlorophyll and carotenoid contents in the leaves. Ultrastructural investigations revealed that cadmium induced disorganization in leaf structure, essentially marked by a lowered mesophyll cell size, reduced intercellular spaces, as well as severe alterations in chloroplast fine structure, which exhibits disturbed shape and dilation of thylakoid membranes. High cadmium concentrations also affect the main lipid classes, leading to strong changes in their composition and fatty acid content. Thus, the exposure of tomato plants to cadmium caused a concentration-related decrease in the fatty acid content and a shift in the composition of fatty acids, resulting in a lower degree of fatty acid unsaturation in chloroplast membranes. The level of lipid peroxides and the activity of lipoxygenase were also significantly enhanced at high Cd concentrations. These biochemical and ultrastructural changes suggest that cadmium, through its effects on membrane structure and composition, induces premature senescence of leaves.

Root growth and lignification of two wheat species differing in their sensitivity to NaCl, in response to salt stress.

Application of a 100-mM NaCl salt stress to wheat seedlings of a salt-tolerant (Triticum durum var. Ben Béchir) and a salt-sensitive (Triticum aestivum var. Tanit) species decreases the fresh and dry weights of roots especially in the salt-sensitive species, and slightly increases the ratio of dry to fresh weight, especially in the salt-resistant species. All peroxidase activities are increased by salt stress, the water-soluble peroxidase activity being increased much more in the salt-sensitive than in the salt-tolerant species, while the opposite result is observed with the cell-wall peroxidase activity. Some water-soluble peroxidases have been hypothesised to have auxin oxidase activity (which might explain the effect observed on the root biomass), while the cell-wall peroxidases would be involved in lignification. Histochemical observation confirms a more intense lignification in the root cells of the salt-tolerant species compared to the sensitive species, under the effect of NaCl.