Impact of active transport and transpiration on nickel and cadmium accumulation in the leaves of the Ni-hyperaccumulator Leptoplax emarginata: a biophysical approach

Aims

The primary aim of this study was to investigate the impact of active nickel and cadmium transport, transpiration and shoot biomass production on Ni and Cd accumulation in the leaves of the Ni-hyperaccumulator Leptoplax emarginata. A secondary objective was to observe the effects of various concentrations of nickel and cadmium in solutions on the plant growth and ecophysiological characteristics of these plants. Finally, the study sought to identify possible nickel and cadmium concentration gradients in solution as a function of the root distance.

Methods

The Intact Plant Transpiration Stream Concentration Factor (TSCF=xylem/solution solute concentration ratio) was determined for both Ni and Cd and for the selected intact transpiring Ni-hyperaccumulator Leptoplax emarginata, cultivated on two contrasting fertilized and Ni-Cd-contaminated sandy porous media (rhizotrons with central root compartments, linked to Mariotte tubes operated at ?1?kPa). IPTSCF_Ni and IPTSCF_Cd were calculated as the ratios between the hyperaccumulator plant’s nickel or cadmium mass in the leaves and the nickel or cadmium concentration in solution by the volume of water transpired during the period of culture. Plant growth characteristics and gas exchanges were also recorded.

Results

IPTSCF values were much greater than 1 (IPTSCF_Ni?=?5.2?±?0.9 and IPTSCF_Cd?=?4.4?±?0.6) whatever the amount of available Ni and Cd. This characterized a predominantly active plant metal uptake. Moreover, biological regulation was reported: plant growth and transpiration were significantly lower for hyperaccumulator plants cultivated in sand which was rich in available Ni and Cd, than for hyperaccumulator plants cultivated in topsoil, poor in available Ni and Cd. In the soil rhizosphere, capillary flow was related to transpiration and a depletion pattern was developed for Ni and sometimes for Cd.

Conclusions

Overall, the Intact Plant Transpiration Stream Concentration Factor appeared to be a relevant metal bioconcentration factor taking into account the predominant type of metal transport from roots to leaves, plant growth and transpiration coupling and metal availability. IPTSCF_Ni and IPTSCF_Cd values were much greater than 1 and similar whatever the amount of available Ni and Cd. This characterized a predominantly active plant combining Ni and Cd uptake and biological regulations dependent of the Ni and Cd concentrations in solution.     

Characteristics of protectant synthesis of infective juveniles of Steinernema carpocapsae and importance of glycerol as a protectant for survival of the nematodes during osmotic dehydration

Two hypotheses on the synthesis of the protectants glycerol and trehalose of the infective juveniles (IJs) of Steinernema carpocapsae during osmotic dehydration were tested and utilised to evaluate the function and importance of glycerol on survival of the nematodes during osmotic dehydration. This was achieved by comparing the changes in survival, morphology, behaviour and levels of glycerol, trehalose and permeated compounds of the IJs dehydrated in seven hypertonic solutions at two temperature regimes: (1) 5 °C for 15 days; and (2) 23 °C for 1 day followed by 5 °C for another 14 days. The results substantiate both hypotheses tested: (1) the permeability of the IJs to various compounds, such as sucrose or ethylene glycol, when they are dehydrated in hypertonic solutions of these compounds; and (2) suppression of the synthesis of protectant glycerol but not trehalose when IJs are dehydrated at low temperature. The results also showed that: (1) although trehalose was the preferred dehydration protectant, glycerol played an important role in rapidly balancing the osmotic pressure when IJs were exposed in hypertonic solutions; (2) the presence of glycerol was essential for the IJs to survive and function properly even under moderate osmotic dehydration, especially when IJs were dehydrated in salt solutions; and (3) some exogenous compounds permeated into IJs during osmotic dehydration such as ethylene glycol, may function in the same way as glycerol and significantly improve the survival and function of the IJs. The results indicate that each of the protectants glycerol and trehalose has a specific function and neither is replaceable by the other.     

Water quality parameters and tipping points of dragonfly diversity and abundance in fishponds

Fishponds are often enriched with nutrients in order to increase phytoplankton and zooplankton populations to support fish production. This eutrophication often leads to a global decrease of biodiversity. This biodiversity shift may be identified by a tipping point, the value of an environmental parameter above which a significant change of species richness and abundance occurs. A total of 110 eutrophic to highly eutrophic fishponds were studied in two areas in France to investigate parameters governing dragonfly species richness and species abundance by determining tipping points. Parameters investigated were chlorophyll a (CHL), water transparency, total N (TN), total P (TP), aquatic plant richness and coverage, adult dragonfly richness and abundance, and fish harvest. A high species richness of dragonflies was found in fishponds, with a total of 34 species, including six species of conservation concern. Dragonfly richness and abundance was shown to be negatively influenced by higher degrees of eutrophication. A high diversity of dragonflies occurred in the fishponds with CHL concentrations below 127 µg/l, water transparency above 67 cm, TN concentrations below 2.30 mg/l, and a fish harvest smaller than 253 kg/ha. A minimum of 5% of aquatic plant cover and the presence of a minimum 9 aquatic plant species seem to promote the richness and abundance of dragonflies. According to tipping points, 19 dragonfly species could be determined as indicator species for water quality in fishponds.     

Development of immunoassays for human interleukin 3 and interleukin 4, some of which discriminate between different recombinant DNA-derived molecules

Two panels of hybridomas were produced that secreted monoclonal antibodies (MAbs) against recombinant DNA-derived human interleukin 3 and interleukin 4 (rhIL-3 and rhIL-4). From each panel, sensitive immunoradiometric assays (IRMAs) were developed which were capable of detecting the recombinant molecule used as the immunogen but were unable to recognize natural or other recombinant forms of the same cytokine. Subsequent studies using the MAbs from each panel showed that a number of the MAbs appeared only to recognize that particular recombinant molecule used as immunogen, with little or no binding to other recombinant forms of the molecule. By using MAbs that were found to be unrestricted in their recognition for different recombinant forms of the cytokines, it was possible to develop an IRMA for IL-4 that was capable of detecting natural IL-4 as well as all the recombinant forms equally. An IRMA was also developed for IL-3 but was not of equivalent sensitivity in detecting the different recombinant forms of IL-3 used in the study. The recombinant DNA-derived cytokine molecules used to raise the two panels of MAbs contained amino acid substitutions relative to the natural sequences, and these findings indicate that caution should be exercised when using immunoassays to estimate natural sequence molecules if antibodies raised to modified rDNA-derived molecules are used.     

Plasma Membrane Profiling Defines an Expanded Class of Cell Surface Proteins Selectively Targeted for Degradation by HCMV US2 in Cooperation with UL141

Human cytomegalovirus (HCMV) US2, US3, US6 and US11 act in concert to prevent immune recognition of virally infected cells by CD8+ T-lymphocytes through downregulation of MHC class I molecules (MHC-I). Here we show that US2 function goes far beyond MHC-I degradation. A systematic proteomic study using Plasma Membrane Profiling revealed US2 was unique in downregulating additional cellular targets, including: five distinct integrin α-chains, CD112, the interleukin-12 receptor, PTPRJ and thrombomodulin. US2 recruited the cellular E3 ligase TRC8 to direct the proteasomal degradation of all its targets, reminiscent of its degradation of MHC-I. Whereas integrin α-chains were selectively degraded, their integrin β1 binding partner accumulated in the ER. Consequently integrin signaling, cell adhesion and migration were strongly suppressed. US2 was necessary and sufficient for degradation of the majority of its substrates, but remarkably, the HCMV NK cell evasion function UL141 requisitioned US2 to enhance downregulation of the NK cell ligand CD112. UL141 retained CD112 in the ER from where US2 promoted its TRC8-dependent retrotranslocation and degradation. These findings redefine US2 as a multifunctional degradation hub which, through recruitment of the cellular E3 ligase TRC8, modulates diverse immune pathways involved in antigen presentation, NK cell activation, migration and coagulation; and highlight US2’s impact on HCMV pathogenesis.     

Negative clonal selection in tumor evolution

Development of cancer requires the acquisition of multiple oncogenic mutations and selection of the malignant clone. Cancer evolves within a finite host lifetime and mechanisms of carcinogenesis that accelerate this process may be more likely to contribute to the development of clinical cancers. Mutator mutations are mutations that affect genome stability and accelerate the acquisition of oncogenic mutations. However, mutator mutations will also accelerate the accumulation of mutations that decrease cell proliferation, increase apoptosis, or affect other key fitness parameters. These "reduced-fitness" mutations may mediate "negative clonal selection," i.e., selective elimination of premalignant mutator clones. Target reduced-fitness loci may be "recessive" (both copies must be mutated to reduce fitness) or "dominant" (single-copy mutation reduces fitness). A direct mathematical analysis is applied to negative clonal selection, leading to the conclusion that negative clonal selection against mutator clones is unlikely to be a significant effect under realistic conditions. In addition, the relative importance of dominant and recessive reduced-fitness mutations is quantitatively defined. The relative predominance of mutator mutations in clinical cancers will depend on several variables, including the tolerance of the genome for reduced-fitness mutations, particularly the number and potency of dominant reduced-fitness loci.     

Modulation of lymphocyte function with inhibitory CD2: loss of NK and NKT cells

Analysis of the NK cell developmental pathway suggests that CD2 expression may be important in regulating NK maturation. To test this hypothesis, we developed mice containing only an inhibitory CD2 molecule by linking the extracellular domain of CD2 to an intracellular immunoreceptor tyrosine-based inhibitory motif (ITIM) motif. Mice containing the CD2 Tg(ITIM) transgene, introduced into a CD2 KO background, have no morphologically detectable lymph nodes, although development of the thymus appears normal. In addition, these mice had major loss of both NK and NKT subsets in peripheral organs, while T and B cell frequencies were intact. Expression of CD2 was low on T cells and lacking on B cells and functional defects were observed in these populations. NKT cells expressing CD4 were absent, while the CD8⁺ and double negative NKT cells were retained. Small subsets of NK cells were detected but expression of CD2 on these cells was very low or absent, and their maturation was impaired. Based on the phenotype described here, we believe that these mice represent a unique model to study lymphoid organ and lymphocyte development.     

Consequences of terbium (111) binding on the conformation and enzymatic activity of Guinea pig liver transglutaminase

Calcium ions are crucial for expression of transglutaminase activity. Although lanthanides have been reported to substitute for calcium in a variety of protein functions, they did not replace the calcium requirement during transglutaminase activity measurements. Furthermore, lanthanides strongly inhibited purified liver transglutaminase activity using either casein or fibrinogen as substrates. Terbium (III) inhibition of transglutaminase-catalyzed putrescine incorporation into casein was not reversed by the presence of 10–200 fold molar excess of calcium ions (Ki for Tb(III)=60 µM). Conformational changes in purified liver transglutaminase upon Tb(III) binding were evident from a biphasic effect of Tb(III) on transglutaminase binding to fibrin. Low concentrations of Tb(III) (1 µM to 10 µM inhibited the binding of transglutaminase to fibrin, whereas higher concentrations (20 µM to 100 µM promoted binding. Conformational changes in purified liver transglutaminase consequent to Tb(III) binding were also demonstrated by fluorescence spectroscopy due to Forster energy transfer. Fluorescence emission was stable to the presence of 200 mM NaCl and 100 mM CaCl₂ only partially quenched emission. Purified liver transglutaminase strongly bound to Tb(III)-Chelating Sepharose beads and binding could not be disrupted by 100 mM CaCl₂ solution. Our data suggest that Tb(III)-induced conformational changes in transglutaminase are responsible for the observed effects on enzyme structure and function. The potential applications of Tb(III)-transglutaminase interactions in elucidating the structure-function relationships of liver transglutaminase are discussed.     

Mapping the economic costs and benefits of conservation

Resources for biodiversity conservation are severely limited, requiring strategic investment. Understanding both the economic benefits and costs of conserving ecosystems will help to allocate scarce dollars most efficiently. However, although cost-benefit analyses are common in many areas of policy, they are not typically used in conservation planning. We conducted a spatial evaluation of the costs and benefits of conservation for a landscape in the Atlantic forests of Paraguay. We considered five ecosystem services (i.e., sustainable bushmeat harvest, sustainable timber harvest, bioprospecting for pharmaceutical products, existence value, and carbon storage in aboveground biomass) and compared them to estimates of the opportunity costs of conservation. We found a high degree of spatial variability in both costs and benefits over this relatively small (~3,000 km²) landscape. Benefits exceeded costs in some areas, with carbon storage dominating the ecosystem service values and swamping opportunity costs. Other benefits associated with conservation were more modest and exceeded costs only in protected areas and indigenous reserves. We used this cost-benefit information to show that one potential corridor between two large forest patches had net benefits that were three times greater than two otherwise similar alternatives. Spatial cost-benefit analysis can powerfully inform conservation planning, even though the availability of relevant data may be limited, as was the case in our study area. It can help us understand the synergies between biodiversity conservation and economic development when the two are indeed aligned and to clearly understand the trade-offs when they are not.     

New insights into creatine function and synthesis

The text-book view of the role of the creatine/creatine phosphate system as an energy buffer has been expanded to include functions such as energy shuttling, proton buffering and regulating cytosolic ADP levels. There is continuous need for creatine replacement due to creatinine formation. Replacement involves a combination of diet and de novo synthesis. Creatine synthesis makes very significant demands on amino acid metabolism, in particular that of glycine, arginine and methionine. It uses about 40% of all methyl groups transferred from S-adenosylmethionine. Although the traditional view of the function of the creatine/creatine phosphate system is largely concerned with its role in skeletal and cardiac muscle, recent work obliges us to take a broader view. In particular, its role in the brain is brought into sharp focus by the neurological symptoms displayed by children suffering from inborn errors of creatine synthesis and transport, as well as by suggestions that brain creatine status may play a role in cognitive performance in adults.