Micro-chemical imaging of cesium distribution in Arabidopsis thaliana plant and its interaction with potassium and essential trace elements.

Cesium as an alkali element exhibits a chemical reactivity similar to that of potassium, an essential element for plants. It has been suggested that Cs phytotoxicity might be due either to its competition with potassium to enter the plant, resulting in K starvation, or to its intracellular competition with K binding sites in cells. Such elemental interactions can be evidenced by chemical imaging, which determines the elemental distributions. In this study, the model plant Arabidopsis thaliana was exposed to 1 mM cesium in the presence (20 mM) or not of potassium. The quantitative imaging of Cs and endogenous elements (P, S, Cl, K, Ca, Mn, Fe, and Zn) was carried out using ion beam micro-chemical imaging with 5 microm spatial resolution. Chemical imaging was also evidenced by microfocused synchrotron-based X-ray fluorescence (microXRF) which presents a better lateral resolution (<1 microm) but is not quantitative. Cesium distribution was similar to potassium which suggests that Cs can compete with K binding sites in cells. Cesium and potassium were mainly concentrated in the vascular system of stems and leaves. Cs was also found in lower concentration in leaves mesophyll/epidermis. This late representing the larger proportion in mass, mesophyll/epidermis can be considered as the major storage site for cesium in A. thaliana. Trichomes were not found to accumulate cesium. Interestingly, increased Mn, Fe, and Zn concentrations were observed in leaves at high chlorosis. Mn and Fe increased more in the mesophyll than in veins, whereas zinc increased more in veins than in the mesophyll suggesting a tissue specific interaction of Cs with these trace elements homeostasis. This study illustrates the sensitivity of ion beam microprobe and microfocused synchrotron-based X-ray fluorescence to investigate concentrations and distributions of major and trace elements in plants. It also shows the suitability of these analytical imaging techniques to complement biochemical investigations of metallic stress in plants.

An interdisciplinary approach to investigate the impact of cobalt in a human keratinocyte cell line.

Since in nuclear power plants, risks of skin contact contamination by radiocobalt are significant, we focused on the impact of cobalt on a human cutaneous cell line, i.e. HaCaT keratinocytes. The present paper reports an interdisciplinary approach aimed at clarifying the biochemical mechanisms of metabolism and toxicity of cobalt in HaCaT cells. Firstly, a brief overview of the used instrumental techniques is reported. The following parts present description and discussion of results concerning: (i) toxicological studies concerning cobalt impact towards HaCaT cells (ii) structural and speciation fundamental studies of cobalt-bioligand systems, through X-ray absorption spectroscopy (XAS), ab initio and thermodynamic modelling (iii) preliminary results regarding intracellular cobalt speciation in HaCaT cells using size exclusion chromatography/inductively coupled plasma-atomic emission spectroscopy (SEC/ICP-AES) and direct in situ analysis by ion beam micropobe analytical techniques.

Organization and function of the plant pleiotropic drug resistance ABC transporter family.

Among the ABC transporters, the pleiotropic drug resistance (PDR) family is particular in that its members are found only in fungi and plants and have a reverse domain organization, i.e., the nucleotide binding domain precedes the transmembrane domain. In Arabidopsis and rice, for which the full genome has been sequenced, the family of plant ABC transporters contains 15 and 23 PDR genes, respectively, which can be tentatively organized using the sequence data into five subfamilies. Most of the plant PDR genes so far characterized belong to subfamily I and have been shown to be involved in responses to abiotic and biotic stress, in the latter case, probably by transporting antimicrobial secondary metabolites to the cell surface. Only a single subfamily II member has been characterized. Induction of its expression by iron deficiency suggests its involvement in iron deficiency stress, thus, enlightening a new physiological role for a PDR gene.

A systematic mutagenesis study of Ile-282 in transmembrane segment M4 of the plasma membrane H+-ATPase.

Homology models of plasma membrane H(+)-ATPase (Bukrinsky, J. T., Buch-Pedersen, M. J., Larsen, S., and Palmgren, M. G. (2001) FEBS Lett. 494, 6-10) has pointed to residues in transmembrane segment M4 as being important for proton translocation by P-type proton pumps. To test this model, alanine-scanning mutagenesis was carried out through 12 residues in the M4 of the plant plasma membrane H(+)-ATPase AHA2. An I282A mutation showed apparent reduced H(+) affinity, and this residue was subsequently substituted with all other naturally occurring amino acids by saturation mutagenesis. The ability of mutant enzymes to substitute for the yeast proton pump PMA1 was found to correlate with the size of the side chain rather than its chemical nature. Thus, smaller side chains (Gly, Ala, and Ser) at this position resulted in lower H(+) affinity and lowered levels of H(+) transport in vivo, whereas substitution with side chains of similar and larger size resulted in only minor effects. Substitutions of Ile-282 had only minor effects on ATP affinity and sensitivity toward vanadate, ruling out an indirect effect through changes in the enzyme conformational equilibrium. These results are consistent with a model in which the backbone carbonyl oxygen of Ile-282 contributes directly to proton translocation.

In vivo effects of the GH-releasing heptapeptide GHRP-1 in lambs.

The novel synthetic growth hormone-releasing heptapeptide GHRP-1 is reported to be more potent than growth hormone-releasing hormone (GHRH) in eliciting GH release in vivo in rats and man. However, in ovine pituitary cells in primary culture in a perifusion system, GHRP-1 was 10-fold less active than GHRH. The purpose of this work was to study the effect of GHRP-1 in sheep in vivo. Ovine GH release stimulated by either GHRP-1 or GHRH(1-29)NH2, in eight pre-ruminant lambs, was determined. GHRP-1 was administered at doses of 1.2, 2.4 and 6 nmole/kg by i.v. bolus, and GHRH(1-29)NH2 at 0.3 nmole/kg. Mean+/-s.e.m. peak GH levels in the plasma after injection of saline, 1.2, 2.4, 6 nmole/kg GHRP-1 and 0.3 nmole/kg GHRH were 2.2+/-0.9, 9.3+/-2.5, 8.8+/-2.4, 35.1+/-5.8 and 51.6+/-10.5 ng/mL, respectively. As spontaneous 20 ng/mL peaks were observed, only peaks above this level can be considered as significant. The highest dose of GHRP-1 (6 nmole/kg) elicited oGH release, but its action was surpassed by GHRH 0.3 nmole/kg. Furthermore GHRP-1 and GHRH appear to behave inversely when response amplitudes are considered. Animals exhibiting a strong reaction to GHRH-1, show a correspondingly weak reaction to GHRH and vice-versa. This may reflect differences in intracellular mechanisms at the pituitary level. Our data support the results in vitro that in sheep GHRP-1 is a weaker stimulant of GH secretion than GHRH.

Children's conception of object, as revealed by their categorizations.

Six- to 11-year-old children were asked to sort objects in a construction set, to examine what types of objects they group together when performing a classification task. Half of the objects were simple pieces, and the other half were constructions made from those pieces. The results showed that these two types of objects are not clearly differentiated by children until relatively late: age 8 years in the first experiment and age 10 or 11 in the second. Children based their sorting on either perceptual or functional equivalency relations (logical sorting) or on suitability relations between objects of different levels (schemas).

Adjectives or nouns to refer to objects: effects on the complementation and inclusion performance of 6- to 9-year-old children.

Due to the exclusivity bias (a given object is considered to have only one generic name), inclusion problem solving by children should be adversely affected by the use of nouns rather than adjectives to refer to objects. In contrast, the children's complementation behavior should be facilitated, because naming promotes the organization of objects into additive subclasses under a generic class. Groups of children 6 to 9 years old were asked to solve complementation and inclusion problems about a set of objects designated by nouns or by real or nonsensical adjectives. The results showed that complementation performance was indeed enhanced by the use of nouns, but inclusion behavior was not affected by the type of term used.

Referential set presentation effects on complementation by 6-year-olds.

What difficulties do children encounter when responding to complementation instructions? The responses of 50 children to six complementation requests were examined. For half of the children, the objects in the referential set were pooled, and for the other half, they were physically separated by category (pencils were presented in a pencil box, buttons in a sewing kit, and balls of yarn in a knitting basket). Reinforcing the identifying status of the semantic property by separating the objects into categories led to an increase in the number of responses bearing on the subset designated in the instructions (e.g., in response to "Give me everything that is not a black button," the children handed over only the nonblack buttons). In contrast, older children gave responses based on the entire set. The meaning attributed by children to object properties and the effects of that attribution on processing mode merit further study.

The influence of experimenter attitude on the performance of children of different cognitive ability levels.

We investigated the influence of the experimenter's attitude on children's performance in a classification task. We chose 96 children (M age: 5 years, 9 months) on the basis of their performance in a spontaneous classification task. Forty-eight children made partial alignments on the basis of a link established from one object to the next (O-level group); 48 looked for objects having one common property (P-level group). The children had to perform a dichotomy task in two testing situations: one with a caring experimenter, and one with an indifferent experimenter. In the O-level group, the children's performance was superior when the experimenter was caring even though they did not seem to notice the difference between the two attitudes. P-level children clearly distinguished the experimenter attitudes, but their performance remained the same. To determine children's actual abilities accurately, researchers must take into account children's interactions with both objects and partners.

[Dysmorphic syndrome and vascular dysplasia: an atypical form of type IV Ehlers-Danlos syndrome]. / Syndrome dysmorphique et dysplasie vasculaire: une forme atypique d'Ehlers-Danlos type IV.

A 29 year old woman was hospitalized for the successive onset of extremely serious vascular accidents: rupture of the gastro-duodenal artery, aneurysm of the posterior tibial artery, discovery of bilateral carotid and vertebral aneurysm with development of a carotid-cavernous fistula. The patient had a very unusual morphotype with dwarfism, white hair and alopecia. Histological investigations failed to reveal atheromatous lesions and by contrast showed involvement of the skin (dermal atrophy) and in the blood vessels fibro-dysplasia of the media. This picture was suggestive of a vascular form of Ehlers-Danlos disease (Sack's syndrome or type IV Ehlers-Danlos disease). This syndrome is characterized by minor skin or joint manifestations replaced by arterial accidents (arterial rupture or development of aneurysms). The etiology is faulty maturation of procollagen III and the diagnosis is based upon fibroblast culture.