Phytoextraction of toxic metals: a central role for glutathione

Phytoextraction has a promising potential as an environmentally friendly clean-up method for soils contaminated with toxic metals. To improve the development of efficient phytoextraction strategies, better knowledge regarding metal uptake, translocation and detoxification in planta is a prerequisite. This review highlights our current understanding on these mechanisms, and their impact on plant growth and health. Special attention is paid to the central role of glutathione (GSH) in this process. Because of the high affinity of metals to thiols and as a precursor for phytochelatins (PCs), GSH is an essential metal chelator. Being an important antioxidant, a direct link between metal detoxification and the oxidative challenge in plants growing on contaminated soils is observed, where GSH could be a key player. In addition, as redox couple, oxidized and reduced GSH transmits specific information, in this way tuning cellular signalling pathways under environmental stress conditions. Possible improvements of phytoextraction could be achieved by using transgenic plants or plant-associated microorganisms. Joined efforts should be made to cope with the challenges faced with phytoextraction in order to successfully implement this technique in the field.     

CO2 uptake is offset by CH4 and N2O emissions in a poplar short‐rotation coppice

The need for renewable energy sources will lead to a considerable expansion in the planting of dedicated fast‐growing biomass crops across Europe. These are commonly cultivated as short‐rotation coppice (SRC), and currently poplar (Populus spp.) is the most widely planted. In this study, we report the greenhouse gas (GHG) fluxes of carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) measured using eddy covariance technique in an SRC plantation for bioenergy production. Measurements were made during the period 2010–2013, that is, during the first two rotations of the SRC. The overall GHG balance of the 4 years of the study was an emission of 1.90 (±1.37) Mg CO₂eq ha^?1; this indicated that soil trace gas emissions offset the CO₂ uptake by the plantation. CH₄ and N₂O contributed almost equally to offset the CO₂ uptake of ?5.28 (±0.67) Mg CO₂eq ha^?1 with an overall emission of 3.56 (±0.35) Mg CO₂eq ha^?1 of N₂O and of 3.53 (±0.85) Mg CO₂eq ha^?1 of CH₄. N₂O emissions mostly occurred during one single peak a few months after the site was converted to SRC; this peak comprised 44% of the total N₂O loss during the two rotations. Accurately capturing emission events proved to be critical for deriving correct estimates of the GHG balance. The nitrogen (N) content of the soil and the water table depth were the two drivers that best explained the variability in N₂O and CH_4, respectively. This study underlines the importance of the ‘non‐CO₂ GHGs’ on the overall balance. Further long‐term investigations of soil trace gas emissions should monitor the N content and the mineralization rate of the soil, as well as the microbial community, as drivers of the trace gas emissions.     

Greater impact of extreme drought on photosynthesis of grasslands exposed to a warmer climate in spite of acclimation

In view of the projected increase in the frequency of extreme events during this century, we investigated the impact of a drought extreme on leaf ecophysiological parameters and carbon isotope composition (δ¹³C) of grassland communities with species richness (S) of one, three or nine species. The communities, grown for 3 years at either ambient air temperatures (ambient T_air) or ambient T_air + 3°C (elevated T_air), were additionally subjected to an imposed drought by withholding water for 24 days. During the previous 3 years equal precipitation was applied in both temperature treatments, thus communities at elevated T_air had experienced more frequent, mild droughts. However, it was unknown whether this resulted in a higher resistance for facing extreme droughts. At similar soil matric potentials stomatal conductance (g_s) and transpiration (Tr) were higher at elevated than ambient T_air, indicating acclimation to lower soil water content. Despite the stomatal acclimation observed, plants in elevated T_air showed a lower resistance to the drought extreme as indicated by their lower photosynthetic rate (A_max), g_s and Tr during the entire duration of the drought extreme. Lower values for A_max, Tr and g_s were also recorded in species at S = 3 as compared with species at S = 1 for both temperature treatments, but no further differences with S = 9 suggesting that stress was not alleviated at higher S‐levels. The discrimination of ¹³C was poorly correlated with measurements of instantaneous leaf water‐use efficiency (A_max/Tr) and, with this time scale and sampling method, it was not possible to detect any potential change in plant water‐use efficiency using leaf δ¹³C.     

Cloning and structure analysis of the rat apolipoprotein A-I cDNA

Apolipoprotein A-I, the major protein in mammalian high-density lipoprotein, acts as a cofactor for lecithin-cholesterol acyltransferase during the formation of cholesterol ester and as such, is thought to promote cholesterol efflux from peripheral cells to the liver. In this paper, we report the partial purification of rat liver apolipoprotein A-I mRNA by a polysome immunoadsorption technique, and its cDNA cloning. Isolation of two overlapping cDNA clones enabled us to derive the whole rat apolipoprotein A-I cDNA coding sequence. Comparison of the deduced protein sequence with its human counterpart reveals a striking homology between the prepropeptide precursors. Both mature protein amino-terminal regions are very homologous, suggesting that this particular domain could be involved in lipid/protein binding or lecithin-cholesterol acyltransferase activation.     

Immunocytochemical devidence for hypophysial projections of the cells of the nucleus lateralis tuberis pars lateralis in the rainbow trout (Salmo gairdneri)

In the rainbow trout the pars lateralis is the most prominent part of the nucleus lateralis tuberis (NLT). To demonstrate a morphological relationship between this lateral part of the NLT and the pituitary, immunocytochemistry was applied as a staining method. Experiments were carried out on glutaraldehyde-picric acid-acetic acid-fixed brain sections of mature male and female rainbow trout using the peroxidase-anti-peroxidase immune technique with an antiserum against 27-S-methylglucagon as the first antibody. Most of the cells in the NLT/pars lateralis reacted with the antiserum. Axons from these cells enter the pituitary, extending exclusively in the numerous neurohypophysial digitations in the pars intermedia. No immunoreactive neurohypophysial protrusions were found in those parts of the adenohypophysis where the gonadotropic cells are located, indicating that the lateral part of the NLT is not directly involved in the control of gonadotropin secretion. In addition to cells of the NLT/pars lateralis only prolactin cells in the rostral pars distalis of the adenohypophysis reacted with the antiserum used.     

Effect of 17α-methyltestosterone,estradiol-17β and synthetic LHRH on production of gonadotropic hormone in pituitaries of rainbow trout (organ culture)

Pituitary glands from 6-month-old sexually immature female rainbow trout, Salmo gairdneri, were kept in organ culture for 48 or 72 h. Certain groups of pituitaries were cultivated for 48 h on either control medium or medium with 17 alpha-methyltestosterone (MT), or with estradiol-17 beta (E2) in concentrations of 8.5 X 10(-7) M. Other groups of pituitaries were cultivated for 72 h on control medium, or for 48 h on either control medium or MT-medium or E2-medium, and subsequently for 24 h on medium with synthetic LHRH in concentrations of 8.5 X 10(-7) M and 8.5 X 10(-10) M. Gonadotropic (GTH) cells are identified by Alcian Blue-Periodic Acid Schiff-Orange G staining and the double-antibody immunoenzyme-cytochemical technique using anti-carp beta GTH as the first antibody. A quantitative histological procedure was used to study the nuclear size of the GTH cells in response to the different hormones. Secretory activity was estimated by measuring the gonadotropin (GTH) content in extracts of pituitaries, plasma, and the culture media every 24 h by radioimmunoassay. Cultivation on MT- or E2-enriched medium results in an increase of the total amount of GTH in the pituitary and medium, an accumulation of GTH in GTH-cells (approximately 20 percentage points) and an increase in their nuclear size, indicating a stimulation of GTH synthesis. However, autonomous GTH-release is not affected by these steroids. Subsequent cultivation of the pituitaries for 24 h with LHRH causes stimulation of GTH synthesis (approximately 20 percentage points). Preincubation with steroids increases the GTH synthesis capacity of LHRH only when used in a concentration of 8.5 X 10(-10) M. Moreover, 8.5 X 10(-7) M LHRH causes a stimulation of GTH-release. Preincubation of the pituitaries with steroids increases the responsiveness of GTH-cells to LHRH. It is concluded that GTH-production in pituitaries of immature female rainbow trout can be directly influenced by gonadal steroids and by a hypophysiotropic substance.     

Synthesis of 16α-3H androgen and estrogen substrates for 16α-hydroxylase

The synthesis of 16α-³H androgens and estrogens is described. 1-(³H)-Acetic acid in the presence of zinc dust reacts with 16α-bromo-17-ketosteroids to produce 16α-³H-17-ketosteroids. This chemical reaction was used to prepare 16α-³H-dehydroepiandrosterone (I) and 16α-³H-estrone acetate (XI) from 16α-bromo-dehydroepiandrosterone (X) and from 16α-bromo-estrone acetate (XII), respectively. Using appropriate microbiological techniques, it was possible to convert these radiolabelled substrates into 16α-³H-androstenedione (II) and 16α-³H-estradiol-17β (VII). 16α-³H-Estrone (VI) was obtained by the chemical hydrolysis of 16α-³H-estrone acetate. The label distribution as determined by microbiological 16α-hydroxylations indicated a specific labelling of 77% for androgens and 65% for estrogens in the 16α position. These substrates can be used for measuring the 16α hydroxylase activity, an important step in the biosynthesis of estriol (VIII) and estetrol (IX).     

Partial retraining: a new approach to input relevance determination.

In this article we introduce partial retraining, an algorithm to determine the relevance of the input variables of a trained neural network. We place this algorithm in the context of other approaches to relevance determination. Numerical experiments on both artificial and real-world problems show that partial retraining outperforms its competitors, which include methods based on constant substitution, analysis of weight magnitudes, and "optimal brain surgeon".