Interactions of mercury in rat brain

In order to study the metabolism of mercury (Hg), its affinity to metallothionein (MT), and its influence on levels of the essential metals copper and zinc in the brain tissue of rats exposed to elemental mercury (Hg^O) vapor was investigated. The major findings were:

Genetic diversity assessment in Portugal accessions of <Emphasis Type="Italic">Olea europaea</Emphasis> by RAPD markers

Eighty seven olive (Olea europaea ssp. sativa L.) cultivar accessions from Portugal were characterized by means of randomly amplified polymorphic DNA (RAPD) markers. Of the 11 arbitrary 10-mer primers tested a total of 92 polymorphic bands were obtained, representing 87.6 % of the total amplification products. Twenty nine different genotypes were clearly discriminated. Differences were not found among the amplification profiles from different individuals of the same cultivar. All the genotypes could be identified by the combination of three primers: OPR-1, OPK-14 and OPA-1, seven genotype-specific markers being detected. Genetic relationships were estimated by the unweighted pair-group method with arithmetic averaging (UPGMA). The genetic analysis of the results showed a gradual distance between the various cultivars, making it difficult to identify well-differentiated phylogenetic groups, although two clusters were distinguishable with 35 % similarity, in addition to three independent branches with lower similarity: Galega, Tentilheira and Redondal. The dendrogram reflect some relationships for most of the cultivars according to the use of the fruit and ecological adaptation.     

Lead uptake,toxicity and accumulation in <Emphasis Type="Italic">Phaseolus vulgaris</Emphasis> plants

The effects of lead were investigated in bean plants (Phaseolus vulgaris L. cv. Zlota Saxa) grown hydroponically in nutrient solution and exposed to Pb(NO₃)₂ (0.1, 0.5, 1 mM) with or without equimolar concentrations of chelator ethylenediaminetetraacetic acid (EDTA). The roots treated only with Pb(NO₃)₂ accumulated up to 25 g(Pb) kg⁻¹(d.m.), during 4-d exposure. However, in bean plants exposed to 0.5 mM Pb + 0.5 mM EDTA or 1 mM Pb + 1 mM EDTA 2.5 times less Pb was determined. In bean plants treated only with Pb, less than 6 % of total lead accumulated was transported to the aboveground parts, while in the case of plants grown with Pb + EDTA, around 50 % of total Pb was transported to the shoots.     

Determination of oxalate in plant tissues with oxalate oxidase prepared from wheat

A method for determination of oxalate with oxalate oxidase (OxO, EC 1.2.3.4) prepared from wheat bran, is based on specific oxidation of oxalate to produce H₂O₂. The H₂O₂ formed was colorimetrically determined using horseradish peroxidase-catalyzed oxidation of 4-aminoantipyrine and N,N-dimethylaniline by H₂O₂. The new method was tested on rice, buckwheat, soybean and oxalis leaves, showing it is precise, sensitive, inexpensive, highly reproducible and simple to perform. Good agreement could be obtained between this method and the HPLC.     

Cadmium effects on the organization of microtubular cytoskeleton in interphase and mitotic cells of Allium sativum

We have investigated the effects of cadmium on the microtubular (MT) cytoskeleton in the root tip cells of Allium sativum L. using indirect immunofluorescence microscopy. Cd affected the mechanisms controlling the organization of MT cytoskeleton, as well as tubulin assembly/disassembly processes. Cd induced the formation of abnormal MT arrays, consisting of discontinuous wavy MTs or short MT fragments at the cell periphery. Cadmium caused irregular nuclear disorder in cells where the MT organization and function was disturbed. Furthermore, with increased Cd concentration and duration of treatment the MTs depolymerized more severely, the frequency of abnormal cell increased and the mitotic index decreased progressively. The above findings showed that MT cytoskeleton is one of target sites of Cd toxicity in root tip cells.     

Modelling the dynamics of the electron transport rate measured by PAM fluorimetry during Rapid Light Curve experiments

We propose a dynamic model specifically designed to simulate changes in the photosynthetic electron transport rate, which is calculated from fluorescence measurements when plants are exposed, for a short time, to a series of increasing photon flux densities. This model simulates the dynamics of the effective yield of photochemical energy conversion from the maximum and natural chlorophyll fluorescence yields, taking into account a cumulative effect of successive irradiations on photosystems. To estimate a characteristic time of this effect on photosystems, two series of experiments were performed on two benthic diatom culture concentrations. For each concentration, two different series of irradiations were applied. Simplified formulations of the model were established based on the observed fluorescence curves. The simplified versions of the model streamlined the parameters estimation procedure. For the most simplified version of the model (only 4 parameters) the order of magnitude of the characteristic time of the residual effect of irradiation was about 38 s (within a confidence interval between 20 and 252 s). The model and an appropriate calibration procedure may be used to assess the physiological condition of plants experiencing short time-scale irradiance changes in experimental or field conditions.     

Induction of <Emphasis Type="Italic">in vitro</Emphasis> flowering in the orchid <Emphasis Type="Italic">Dendrobium</Emphasis> Sonia 17

In this study, Dendrobium Sonia 17 plantlets were used to induce in vitro flowering. Inflorescences were induced and rooting was inhibited in the half-strength Murashige and Skoog medium containing 20 μM N ⁶-benzyladenine (BA). The medium with high P and low N contents was effective to induce inflorescences while the medium with low P and high N contents was only effective to promote forming of shoots. In addition, the induced in vitro inflorescences were able to multiply and maintain without exhibiting a distinctive vegetative phase. Different morphologies of in vitro flowers such as incomplete flower structures, abnormal and unresupinated in vitro flowers were observed.     

Polyamine metabolism in hants : Arginine and omithine decarboxylase activity in ripeningTrlticum durum seeds

The pattern of the activity of arginine decarboxylase (ADC) and omithine decarboxylase (ODC) involved in polyamine synthesis in ripening wheat seeds was examined. The aim was to study the polyamines and the activity of the two enzymes in correlation with the growth processes occurring in the developing wheat seeds. The results obtained showed a very different pattern of polyamine content in the two organs of caryopsis, and that the two enzymes in the embryos have a higher activity than in the endosperms. Moreover, while in the embryos the ADC exhibits higher activity than the ODC, in the endosperms the activity of ODC is about similar to that of ADC. This pattern is discussed in relation to the different histological characteristics of embryo and endosperm tissues during seed development.     

MPEC: an important gene in the chlorophyll biosynthesis pathway in photosynthetic organisms

One of the least understood enzymatic steps in chlorophyll biosynthesis is the formation of isocyclic ring, which is catalyzed by the Mg-protoporphyrin IX monomethyl ester (MgPME) cyclase that is involved in the conversion of MgPME to protochlorophyllide. Several genes encoding part of this enzyme have been identified and functional analysis of them has been performed. The enzyme plays important roles in higher plants and photosynthetic bacteria. The review focuses on the current knowledge of MgPME cyclase coding genes, with emphasis on their organization, expression pattern, and functional analysis obtained from mutants.     

Different levels of inbreeding depression between outcrossing and selfing Serapias species

We quantified inbreeding depression for fruit production, embryo vitality and seed germination in three deceptive orchids, Serapias vomeracea, S. cordigera and S. parviflora, which do not provide any reward to their pollinators, and are predicted to experience high outcrossing. Of the three species examined only S. parviflora was autonomously selfing. Both S. vomeracea and S. cordigera showed highly significant differences in fitness between selfed and outcrossed progenies, resulting in high levels of inbreeding depression, which increased in magnitude from seed set to seed germination. Inbreeding depression may promote outcrossing in Serapias by acting as a post-pollination barrier to selfing. Cumulative inbreeding depression across three stages in S. parviflora was lower that in both outcrossing species. The large difference in germination between selfed and outcrossed seeds is an important issue in conservation biology.     

Elevated CO2 concentration enhances the role of the ear to the flag leaf in determining grain yield of wheat

Net photosynthetic rate (P _N) of ear and flag leaf during grain filling stage and grain yield of plants with non-darkened or darkened flag leaf or darkened ear were examined in two different CO₂ concentrations: ambient (AC) and AC+200 μmol mol⁻¹ (EC). Ear showed much higher enhancement (56 %) of P _N than flag leaf (23 %) under EC. Moreover, CO₂ enrichment shortened the photosynthetic duration of flag leaf relative to ear. In this way the ratio of ear to flag leaf contribution to grain yield increased from 1.18 (AC) to 1.39 (EC).     

Gut retention of metals in rats

In sucklings, a high fraction of orally administered metals and radionuclides is retained in the gut. The location of elements in the gut is of interest because of their potential local health effect. The purpose of this work was to evaluate the influence of chelation therapy on gut retention and location of cadmium, mercury, and cerium in-suckling rats. Radionuclides^115mCd,²⁰³Hg, and¹⁴¹Ce were administered orally to 6-d-old rats. Chelating agent Zn-DTPA (3.64 mmol/kg) was administered to animals that received^115m Cd or¹⁴¹Ce and Na-DMPS (375 μmol/kg) to those that received²⁰³Hg, immediately and 24 h or 24 and 48 h after radionuclide administration. Radio-activity was determined in the whole body and gastrointestinal tract 6 d later. Both early and delayed chelation treatment very effectively reduced whole body retention, and this was mainly owing to reduced gut retention. Although chelation therapy reduced gut retention of administered radionuclides 3–30 times, the site of metal accumulation and retention in the intestine remained unchanged. For all 3 radionuclides, both after early and delayed therapy, the site of metal accumulation was always the lower part of small intestine—ileum.     

Inhibition of germination and α-amylase induction by 6-methoxy-2-benzoxazolinone in twelve plant species

6-Methoxy-2-benzoxazolinone (MBOA) inhibited germination of rice (Oryza sativa L.), wheat (Triticum aethiopicum Jakubz), rye (Secale cereale L.), onion (Allium cepa L.), wild oat (Avena fatua L.), barnyard grass [Echinochloa crus-galli (L.) Beauv.], ryegrass (Lolium rigidum Gaudin), cress (Lepidium sativum L.), lettuce (Lactuca sativa L.), tomato (Lycopersicum esculentum Mill.), carrot (Daucus carota L.) and amaranth (Amaranthus retroflexus L) and the inhibition increased with increasing MBOA concentrations. MBOA also inhibited the induction of α-amylase in these plant seeds and the inhibition increased with increasing MBOA concentrations. There were variations in sensitivity of these plant species to MBOA, and species of family Poaceae (barnyard grass, wild oat, rice, rye, ryegrass, and wheat) were less sensitive to MBOA than the other plant species.     

Photosynthetic electron transport at low temperatures in the green algal foliose lichens <Emphasis Type="Italic">Lasallia pustulata</Emphasis> and <Emphasis Type="Italic">Umbilicaria hirsuta</Emphasis> affected by manipulated levels of ribitol

In lichens, ribitol is known as a carbon storage compound, an osmotic agens involved effectively in cell compartments protection during dehydration of lichen thalli and as a cryoprotective compound. In our study, we investigated the effect of ribitol on photochemical processes of photosynthesis in foliose lichens [Lasallia pustulata (L.) Mérat., Umbilicaria hirsuta (Sw. ex Westr.) Hoffm.] at low temperature. The effects of three concentrations of ribitol, added externally to thalli segments on several chlorophyll (Chl) fluorescence parameters, were evaluated. The 72 h exposition to 8, 16, and 26 mM ribitol led to a concentration-dependent increase in F_V/F_M, decrease in non-photochemical quenching (NPQ) but no change in quantum yield of photosystem II photochemistry (Φ_PSII) values at −5 °C). At higher temperature (0, +5 °C), no effect of ribitol addition on the photosynthetic parameters was apparent.     

Carbon isotope ratios and the variation in the diurnal pattern of malate accumulation in aerial roots of CAM species of <Emphasis Type="Italic">Phalaenopsis</Emphasis> (Orchidaceae)

We investigated the carbon isotope ratios and the diurnal pattern of malate accumulation in leaves and aerial roots of eight species of Phalaenopsis grown in greenhouses. The leaves of all the species showed carbon isotope ratios and the diurnal patterns of malate content typical of CAM plants. However, the aerial roots exhibited a large variation in the diurnal pattern of malate content among species and even among plants within the same species, although carbon isotope ratios were always CAM-like values. Some aerial roots showed the typical diurnal pattern of CAM, but others maintained high or low malate contents during a day without fluctuation. In order to characterize more strictly the nature of the malate variation in the aerial roots, we further investigated a possible variation of the diurnal pattern of malate among different aerial roots within an individual for Phalaenopsis amabilis and P. cornu-cervi. The diurnal pattern of malate content was varied even among different aerial roots within the same plant. Thus the photosynthetic carbon metabolism in aerial roots of orchids is fairly complex.     

Effect of wounding on chalcone synthase and pathogenesis related <Emphasis Type="Italic">PR-10</Emphasis> gene expression and content of phenolic compounds in bilberry leaves

The influence of artificial wounding on biosynthesis of flavonoids and hydroxycinnamic acids was studied in bilberry leaves using two separate wounding experiments. In the first experiment bilberry leaves were wounded by cutting. The expression of the first gene from flavonoid pathway, chalcone synthase (CHS) and a wound induced pathogenesis related PR-10 gene was analysed from samples collected immediately and after 3, 6, 24 h and 4 d from the wounding treatment. In the second experiment annual shoots were removed. Proanthocyanidins, flavonol glycosides and hydroxycinnamic acids were quantified in leaf samples after 0–5 d (experiment 1) and 5 weeks (experiment 2) from the treatment. In the first experiment, no change was observed in the expression of CHS whereas increase in expression of PR-10 gene was detected after 6 h of wounding treatment. In both experiments, the contents of flavonol glycosides and hydroxycinnamic acids were not influenced by the wounding treatment and the contents of proanthocyanidins were decreased.     

Effects of evening and nighttime leaf wetting on stomatal behavior of Cryptomeria japonica growing in dry soil

To examine the hypothesis that stomatal behavior of plants in dry soil is influenced by a slow recovery from daytime water deficit, we studied the effect of repeated wetting of leaves during evening and night in Cryptomeria japonica seedlings grown in dry soil. After 7 and 10 days of leaf wetting treatment the midday leaf water potential decreased and the transpiration rate increased, respectively. Therefore, we suggest that rapid recovery from daytime water deficit could weaken the water conserving stomatal behavior that adapts to drought conditions in the roots.