Effect of sodium chloride on the response of the halophyte species <Emphasis Type="Italic">Sesuvium portulacastrum</Emphasis> grown in mannitol-induced water stress

Sesuvium portulacastrum is a halophytic species well adapted to salinity and drought. In order to evaluate the physiological impact of salt on water deficit-induced stress response, we cultivated seedlings for 12 days, in the presence or absence of 100 mmol l⁻¹ NaCl, on a nutrient solution containing either 0 mmol l⁻¹ or 25 mmol l⁻¹ mannitol. Mannitol-induced water stress reduced growth, increased the root/shoot ratio, and led to a significant decrease in water potential and leaf relative water content, whereas leaf Na⁺ and K⁺ concentrations remained unchanged. The addition of 100 mmol l⁻¹ NaCl to 25 mmol l⁻¹ mannitol-containing medium mitigated the deleterious impact of water stress on growth of S. portulacastrum, improved the relative water content, induced a significant decrease in leaf water potential and, concomitantly, resulted in enhancement of overall plant photosynthetic activity (i.e. CO₂ net assimilation rate, stomatal conductance). Presence of NaCl in the culture medium, together with mannitol, significantly increased the level of Na⁺ and proline in the leaves, but it had no effect on leaf soluble sugar content. These findings suggest that the ability of NaCl to improve plant performance under mannitol-induced water stress may be due to its effect on osmotic adjustment through Na⁺ and proline accumulation, which is coupled with an improvement in photosynthetic activity. A striking recovery in relative water content and growth of the seedlings was also recorded in the presence of NaCl on release of the water stress induced by mannitol.     

Comparison of spatial scale variability of shoot density and epiphytic leaf assemblages of Halophila stipulacea and Cymodocea nodosa on the Eastern Coast of Tunisia

Abstract

A study was undertaken to compare the patterns of spatial variability, epiphytic percentage cover, and distribution of epiphytic fauna and flora between the two adjacent seagrasses Cymodocea nodosa and the invasive species Halophila stipulucea. Samples were taken at six stations separated by 600?m and exposed to different current conditions. The stations G2 and G5 were affected by a high current tide, while G4 was directly exposed to the northern marine currents. The station G3 was situated in the middle of a Posidonia oceanica bed and was less exposed to hydrodynamism, whereas the other stations were relatively protected. Results indicate that for both H. stipulacea and C. nodosa, shoot density and epiphytic cover biomass decreased when exposed to high levels of hydrodynamic activity. In terms of epiphytic leaf assemblages, our results showed significant differences for the two host plants in their mean cover and for the six stations at the largest and smallest spatial scale. Our observations highlight the dominance of Rhodophyta and the low number of epiphytic species and the epiphytic cover on H. stipulacea compared to C. nodosa. In addition, results indicate the absence of two taxa Hydrozoans and Annelida in the epiphytic assemblage of H. stipulacea leaves.     

Influence of organic selenium on hsp70 response of heat-stressed and enteropathogenic Escherichia coli-challenged broiler chickens (Gallus gallus)

The effect of dietary selenium yeast, a source of organic selenium, on heat shock protein 70 (hsp70) responses, redox status, growth and feed utilization were evaluated either in enteropathogenic Escherichia coli-challenged (EPEC) or in heat-stressed (HS) male broiler chickens grown to 42 days of age. One day-old chicks in experiment 1 were challenged orally with EPEC (10(6) cfu/chicken on day 1 and boosted by water application on days 2, 3, and 4) and fed diets with or without selenium yeast. Body weight (BW), feed conversion ratio (FCR), and total mortality were determined at 42 days of age, and this was followed by collection of ileal tissue for the quantification of total glutathione (TGSH), reduced glutathione (GSH), oxidized glutathione (GSSG), and hsp70 in randomly selected chickens from each treatment. In experiment 2, male broiler chickens were fed diets with or without selenium yeast under a thermoneutral rearing condition. At four weeks of age, blood and hepatic tissue were collected from chickens maintained in the thermoneutral environment and from chickens subjected to HS (40 degrees C for 1 h) and analyzed for TGSH, GSH, GSSG, and hsp70. Selenium yeast improved BW, FCR, and decreased mortality in both control and EPEC-challenged chicks. Selenium yeast significantly attenuated hsp70 expression in EPEC-challenged chickens and in those subjected to HS. The EPEC challenge increased TGSH and GSSG levels and decreased GSH/GSSG ratio. However, GSSG level accumulated in chickens fed diets without selenium supplementation resulting in a lower GSH/GSSG ratio in the selenium yeast-fed group. Heat stress increased GSSG level and decreased GSH/GSSG ratio. Selenium yeast-fed groups maintained higher levels of GSSG before and after HS with a resultant lower GSH/GSSG ratio. The hsp70 response was significantly less in those chickens fed selenium yeast and challenged with either EPEC or HS than in those chickens given no supplemental selenium. The results of this study suggest that selenium yeast supplementation had imparted resistance to oxidative stress associated with enteric bacteria infection and to high temperature exposure. It is believed that the resistance to the stressors was due to an improved redox status of the selenium yeast-fed chickens.     

Remediation of Pb and Cd Polluted Soils Using In Situ Immobilization and Phytoextraction Techniques

In situ immobilization and phytoextraction techniques have been used for remediation of Pb and Cd polluted soils. Three rates (0.25, 0.5 and 1.0%) of seven immobilizing agents (cement, slag, phosphate rock, bitumen, Fe- and Al-gels, and δ-MnO₂) were tested on three soils containing various levels of Pb (48–192.0 ug/g) and Cd (0.75–3.45 ug/g). All immobilizing agents reduced the plant available Pb and Cd as extracted by DTPA (diethylenetriaminepentaacetic acid). The effectiveness of the various agents in immobilizing Pb and Cd followed the descending order: bitumen > cement > slag > Fe-gel > Al-gel > phosphate rock > δ -MnO₂. Cement and phosphate rock fixed Pb and Cd mainly in the carbonate form, whereas the slag, bitumen, Fe-gel, Al-gel and δ -MnO₂ fixed the metals mainly in the oxide form.

The results of pot experiment proved the high ability of barnyard grass (Echinnochloa stagninum) to accumulate elevated amounts of Pb and Cd (ranging from 291–2421 and 6.1–45.9 ug metal/g dry matter, respectively). These amounts are higher than those reported for hyperaccumulators, particularly for Pb. The amounts of Pb and Cd removed by barnyard grass represent, on average, 46 and 72% of their initial total contents in the soils, respectively. These results proved that, without any other soil treatments, barnyard grass is highly efficient in removing considerable amounts of Pb and Cd from polluted soil within a reasonably short period of time. Therefore, use of barnyard grass for the phytoremediation of Pb and Cd polluted soils is feasible and recommended as an environmentally safe and cheap method. The most significant finding of this study is to name the barnyard grass as an efficient lead accumulator plant.     

T-antigen of the human polyomavirus JC attenuates faithful DNA repair by forcing nuclear interaction between IRS-1 and Rad51

JC polyomavirus (JCV), which infects 90% of the human population, is detectable in human tumors. Its early protein, JCV T-antigen, transforms cells in vitro and is tumorigenic in experimental animals. Although T-antigen-mediated transformation involves genetic alterations of the affected cells, the mechanism underlying this genomic instability is not known. We show that JCV T-antigen inhibits homologous recombination DNA repair (HRR), which results in an accumulation of mutations. T-antigen does not operate directly but utilizes a cytosolic molecule, insulin receptor substrate 1 (IRS-1). Following T-antigen-mediated nuclear translocation, IRS-1 binds Rad51 at the site of damaged DNA. This T-antigen-mediated inhibition of HRR does not function in cells lacking IRS-1, and can be reproduced in the absence of T-antigen by IRS-1 with artificial nuclear localization signal. Our observations define a new mechanism by which viral protein utilizes cytosolic molecule to inhibit faithful DNA repair, and suggest how polyomaviruses could compromise stability of the genome. (c) 2005 Wiley-Liss, Inc.     

Effects of N and P supply on phytoplankton in Bizerte Lagoon (western Mediterranean)

Enriched bottle experiments were conducted in situ during winter (January and February) and summer (July and August) 2001 to examine the effects of nutrient enrichments (+ N, + P and + NP) on phytoplankton in Bizerte Lagoon, Tunisia. Chlorophyll a (Chl a), ranging from 3.05 μg L⁻¹ in winter to 4.52 μg L⁻¹ in summer, was dominated by the small size-faction (<5 μm) during both seasons. However, the contribution of the large size-fraction (5-200 μm) to Chl a increased from winter (26%) to summer (37%). Similarly, the carbon biomass of the 5-200 μm algae increased during the July/August period that was characterised by the high proliferation of several diatom taxa. In winter, N was the limiting element for phytoplankton growth. Its addition alone (+ N) or with P (+ NP) increased both the <5 μm and 5-200 μm Chl a concentrations. There was no change in the phytoplankton size structure, with the small cells dominating the final algal biomass in all treatments after 5 days. In summer, N and P limited the phytoplankton, but small and large algae exhibited diverse responses to different nutrient enrichments: addition of P increased the Chl a only in the 5-200 μm fraction, the + N treatment enhanced both size classes, and the NP fertilisation mostly stimulated the biomass of large cells. Consequently, the N and P addition in summer was followed by a significant change in the phytoplankton size structure, since both size-fractions contributed equally to the final Chl a biomass. Within the 5-200 μm algal community, various taxa had diverse responses to the nutrient supply during both seasons, leading to a change in the final community composition. The autotrophic flagellates appeared to grow well under N-deficient conditions. In contrast, diatom growth and biomass were mostly stimulated by the N enrichment while dinoflagellates exhibited the highest increase in their growth and biomass with P fertilisation. Our results suggest that the increasing anthropogenic supply of nutrients in the lagoon may influence algal dynamics as well as productivity in different ways depending on the nutrient composition.