Salicylic acid and its location in response to biotic and abiotic stress

Salicylic acid (SA) is an important signal involved in the activation of plant defence responses against abiotic and biotic stress. SA may derive from the phenylpropanoid pathway or via isochorismate synthase as demonstrated in Nicotiana benthamiana, tomato and Arabidopsis thaliana. The phenylpropanoid pathway as well as isochorismate synthase are localized in the chloroplasts but it remains unknown if the end product SA is in the same organelle. We have studied the localization of SA in A. thaliana using the salicylate hydroxylase (NahG) gene expressed with a chloroplast targeting sequence. Plants expressing NahG in the chloroplasts are unable to accumulate SA induced after pathogen or UV exposure. Our data infer that SA is initially located in the chloroplasts.     

Cre-loxP recombination system for large genome rearrangements in Lactococcus lactis

We have used a new genetic strategy based on the Cre-loxP recombination system to generate large chromosomal rearrangements in Lactococcus lactis. Two loxP sites were sequentially integrated in inverse order into the chromosome either at random locations by transposition or at fixed points by homologous recombination. The recombination between the two chromosomal loxP sites was highly efficient (approximately 1 x 10(-1)/cell) when the Cre recombinase was provided in trans, and parental- or inverted-type chromosomal structures were isolated after removal of the Cre recombinase. The usefulness of this approach was demonstrated by creating three large inversions of 500, 1,115, and 1,160 kb in size that modified the lactococcal genome organization to different extents. The Cre-loxP recombination system described can potentially be used for other gram-positive bacteria without further modification.     

Microbial transformation of ethylpyridines

Pyridine and its derivatives have been found as pollutants in the environment. Although alkylpyridines constitute the largest class of pyridines contaminating the environment, little information is available concerning the fate and transformation of these compounds. In this investigation ethylpyridines have been used as model compounds for investigating the biodegradability of alkylpyridines. A mixed culture of ethylpyridine-degrading microorganisms was obtained from a soil that had been exposed to a variety of pyridine derivatives for several decades. The enrichment culture was able to degrade 2-, 3-, and 4-ethylpyridine (100 mg/L) at 28° C and pH 7 within two weeks under aerobic conditions. The degradation rate was greatest for 2-ethylpyridine and least for 3-ethylpyridine. Transformation of ethylpyridines was dependent on substrate concentration, pH, and incubation temperature. Studies on the metabolic pathway of 4-ethylpyridine revealed two products; these chemicals were identified by MS and NMR analyses as 4-ethyl-2(1H)-pyridone and 4-ethyl-2-piperidone. 6-Ethyl-2(1H)-pyridone was determined to be a product of 2-ethylpyridine degradation. These results indicate that the transformation mechanism of ethylpyridines involves hydroxylation and reduction of the aromatic ring before ring cleavage.     

Analysis of a xyloglucan endotransglycosylase/hydrolase (XTH) from the lycopodiophyte Selaginella kraussiana suggests that XTH sequence characteristics and function are highly conserved during the evolution of vascular plants

A tissue print followed by a xyloglucan endotransglycosylase assay revealed that XET activity is present at sites of cell elongation in both roots and shoots of the lycopodiophyte Selaginella kraussiana. This paper provides the first report and analysis of a xyloglucan endotransglycosylase/hydrolase (XTH) cDNA sequence, isolated from a club moss. In silico analysis of the deduced amino acid sequence revealed a strong conservation of the XET-domain described in higher plants. The catalytic site (DEIDLEFLG) varies in only one amino acid compared with the consensus sequence and was shown to be functional after recombinant expression of Sk-XTH1 in Pichia pastoris. Sk-XTH1 displays xyloglucan endotransglycosylase activity over a broad pH (4.5-7.5) and temperature range (4-30 degrees C), but it shows no hydrolase activity. The catalytic site is followed by a consensus sequence for N-linked glycosylation. Four terminal cysteines were shown to stabilize a putative XET-C terminal extension region, which includes conserved amino acids, involved in the recognition and binding of the substrates. The N-linked sugar interactions as well as the disulphide bridges were shown to be necessary to perform XET activity. The presence of a highly conserved XTH sequence and function in a microphyllophyte suggests that XTHs were present before the divergence of lycopodiophytes and euphyllophytes. It also points to a possible key role for XTHs in the production of a cell wall that allowed the further evolution of land plants.     

X-chromosome polysomy in the male

Summary A review of 569 male patients with X-chromosome polysomies (544 Klinefelter and 25 patients with other types of X-chromosome polysomy) is presented here. These patients were detected among the 77000 persons karyotyped in the Leuven cytogenetic center between the years 1966 and 1987. In the group of 544 Klinefelter patients special attention was paid to (1) the age at diagnosis, (2) social and marital status of the postpubertal males, (3) physical and intellectual abilities of the prepubertal boys, (4) delineation of the concurrence of Klinefelter syndrome and fragile X syndrome, and (5) the frequency of malignancies. In 25 patients with other X-chromosome polysomies (2 n48 chromosomes) genotype/phenotype correlation is reviewed, especially for the patients with 48,XXYY and 49,XXXXY karyotypes. Finally, double aneuploidy and rare structural X-chromosome aberrations are briefly discussed.     

Heavy metals in sewage sludges contribute to their adverse effects on the arbuscular mycorrhizal fungus<Emphasis Type="Italic">Glomus mosseae</Emphasis>

Applying sewage sludges to agricultural land is a widespread practice because of the sludges’ agronomic value as a source of plant nutrients and organic matter. Nevertheless, sludges often contain micropollutants that can constitute a menace for health and the environment. Arbuscular mycorrhizal fungi are sensitive to sewage sludges that have been spiked, or not, with metallic trace elements (MTE). Here we have investigated if MTE in sewage sludges could be responsible for effects on mycorrhizal development betweenGlomus mosseae andMedicago truncatula. The impact of a dehydrated or composted urban sewage sludge spiked or not with MTE, was tested on spore germination and root colonization byG. mosseae. The sewage sludges depressed both the presymbiotic andin planta stages of development of the mycorrhizal fungus. This negative effect was more related to the metallic pollutant contents of the sludges than to the presence of antagonistic microorganisms or phosphorus.     

Group composition in wild and commensal hamadryas baboons: A comparative study in Saudi Arabia

Papio hamadryas was surveyed throughout its range in Saudi Arabia and was observed at altitudes ranging from 0 to 2300 m. Wild populations occur along the whole range of altitude, while commensal populations are only found above 850 m altitude. No variation in group size was found with altitude. Comparison of wild and commensal populations showed the following. (1) Their composition in terms of age and sex classes, overall adult sex ratios, and group size does not significantly differ. (2) Groups of both populations include, in similar proportions, three types of parties: one-male units (>70%), two-male units (>13%), and a few other units of variable composition. (3) The mean size of commensal parties is significantly larger than in the wild population; specifically one-male units are larger in the commensal population due to a larger number of females per male. Thus, female distribution in commensal groups is more inequitable than that in wild groups. (4) Finally, the number of females included in two-male units increases with altitude. These differences are discussed in terms of food availability and predator pressure and are compared with results obtained on other Arabian and Ethiopian populations.