The Function of Tocopherols and Tocotrienols in Plants

Referee: Dr. Kozi Asada, Department of Biotechnology, Faculty of Engineering, Fukuyama University, Gakuencho 1, Fukuyama 729-0292, Japan Tocopherols and tocotrienols, which differ only in the degree of saturation of their hydrophobic prenyl side chains, are lipid-soluble molecules that have a number of functions in plants. Synthesized from homogentisic acid and isopentenyl diphosphate in the plastid envelope, tocopherols and tocotrienols are essential to maintain membrane integrity. α-Tocopherol is the major form found in green parts of plants, while tocotrienols are mostly found in seeds. These compounds are antioxidants, thus they protect the plant from oxygen toxicity. Tocopherols and tocotrienols scavenge lipid peroxy radicals, thereby preventing the propagation of lipid peroxidation in membranes, and the ensuing products tocopheroxyl and tocotrienoxyl radicals, respectively, are recycled back to tocopherols and tocotrienols by the concerted action of other antioxidants. Furthermore, tocopherols and tocotrienols protect lipids and other membrane components by physically quenching and reacting chemically with singlet oxygen. The scavenging of singlet oxygen by α-tocopherol in chloroplasts results in the formation of, among other products, α -tocopherol quinone, a known contributor to cyclic electron transport in thylakoid membranes, therefore providing photoprotection for chloroplasts. Moreover, given that α-tocopherol increases membrane rigidity, its concentration, together with that of the other membrane components, might be regulated to afford adequate fluidity for membrane function. Furthermore, α-tocopherol may affect intracellular signaling in plant cells. The effects of this compound in intracellular signaling may be either direct, by interacting with key components of the signaling cascade, or indirect, through the prevention of lipid peroxidation or the scavenging of singlet oxygen. In the latter case, α-tocopherol may regulate the concentration of reactive oxygen species and plant hormones, such as jasmonic acid, within the cell, which control both the growth and development of plants, and also plant response to stress.     

Allosteric modulation of dopamine D2 receptors by homocysteine

It has been suggested that L-DOPA-induced hyperhomocysteinemia can increase the risk of stroke, heart disease, and dementia and is an additional pathogenetic factor involved in the progression of Parkinson's disease. In Chinese hamster ovary (CHO) cells stably cotransfected with adenosine A(2A) and dopamine D2 receptors, homocysteine selectively decreased the ability of D2 receptor stimulation to internalize adenosine A(2A)-dopamine D2 receptor complexes. Radioligand-binding experiments in the same cell line demonstrated that homocysteine acts as an allosteric D2 receptor antagonist, by selectively reducing the affinity of D2 receptors for agonists but not for antagonists. Mass spectrometric analysis showed that, by means of an arginine (Arg)-thiol electrostatic interaction, homocysteine forms noncovalent complexes with the two Arg-rich epitopes of the third intracellular loop of the D2 receptor, one of them involved in A(2A)-D2 receptor heteromerization. However, homocysteine was unable to prevent or disrupt A(2A)-D2 receptor heteromerization, as demonstrated with Fluorescence Resonance Energy Transfer (FRET) experiments in stably cotransfected HEK cells. The present results could have implications for Parkinson's disease.     

North African Populations Carry the Signature of Admixture with Neandertals

One of the main findings derived from the analysis of the Neandertal genome was the evidence for admixture between Neandertals and non-African modern humans. An alternative scenario is that the ancestral population of non-Africans was closer to Neandertals than to Africans because of ancient population substructure. Thus, the study of North African populations is crucial for testing both hypotheses. We analyzed a total of 780,000 SNPs in 125 individuals representing seven different North African locations and searched for their ancestral/derived state in comparison to different human populations and Neandertals. We found that North African populations have a significant excess of derived alleles shared with Neandertals, when compared to sub-Saharan Africans. This excess is similar to that found in non-African humans, a fact that can be interpreted as a sign of Neandertal admixture. Furthermore, the Neandertal''s genetic signal is higher in populations with a local, pre-Neolithic North African ancestry. Therefore, the detected ancient admixture is not due to recent Near Eastern or European migrations. Sub-Saharan populations are the only ones not affected by the admixture event with Neandertals.     

The xanthophyll cycle is induced by light irrespective of water status in field-grown lavender (Lavandula stoechas) plants

The water relations, the photosynthetic capacity and the pigment content of leaves, i.e. chlorophylls, carotenes and xanthophylls, were analysed during the summer drought and recovery after autumn rainfalls in lavender ( Lavandula stoechas L.) plants grown in Mediterranean field conditions. Summer drought caused photoinhibition of photosynthesis and significant decreases in chlorophylls (by ca 75%), β -carotene (by ca 65%), and lutein and neoxanthin (by ca 50%), although their contents remained unaltered between predawn and midday, suggesting a progressive decrease in response to drought. In contrast, the levels of violaxanthin decreased from predawn to midday, giving rise to enhanced formation of zeaxanthin and antheraxanthin in high light. Zeaxanthin and antheraxanthin formation was not induced by water deficit. Although the levels of photosynthetic pigments were severely affected by water deficit, carotenoids decreased less than chlorophylls, which resulted in increased levels of carotenoids per unit of chlorophyll. We conclude that the enhanced formation of zeaxanthin in high light and the increased levels of carotenoids per unit of chlorophyll observed in water-stressed plants may help to avoid photoinhibitory damage to the photosynthetic apparatus.     

Mitotic Recombination and Genetic Changes in Saccharomyces cerevisiae during Wine Fermentation

Natural strains of Saccharomyces cerevisiae are prototrophic homothallic yeasts that sporulate poorly, are often heterozygous, and may be aneuploid. This genomic constitution may confer selective advantages in some environments. Different mechanisms of recombination, such as meiosis or mitotic rearrangement of chromosomes, have been proposed for wine strains. We studied the stability of the URA3 locus of a URA3/ura3 wine yeast in consecutive grape must fermentations. ura3/ura3 homozygotes were detected at a rate of 1 × 10⁻⁵ to 3 × 10⁻⁵ per generation, and mitotic rearrangements for chromosomes VIII and XII appeared after 30 mitotic divisions. We used the karyotype as a meiotic marker and determined that sporulation was not involved in this process. Thus, we propose a hypothesis for the genome changes in wine yeasts during vinification. This putative mechanism involves mitotic recombination between homologous sequences and does not necessarily imply meiosis.     

A randomized placebo-controlled trial of intermittent preventive treatment in pregnant women in the context of insecticide treated nets delivered through the antenatal clinic

Background

Current recommendations to prevent malaria in African pregnant women rely on insecticide treated nets (ITNs) and intermittent preventive treatment (IPTp). However, there is no information on the safety and efficacy of their combined use.

Methods

1030 pregnant Mozambican women of all gravidities received a long-lasting ITN during antenatal clinic (ANC) visits and, irrespective of HIV status, were enrolled in a randomised, double blind, placebo-controlled trial, to assess the safety and efficacy of 2-dose sulphadoxine-pyrimethamine (SP). The main outcome was the reduction in low birth weight.

Findings

Two-dose SP was safe and well tolerated, but was not associated with reductions in anaemia prevalence at delivery (RR, 0.92 [95% CI, 0.79–1.08]), low birth weight (RR, 0.99 [95% CI, 0.70–1.39]), or overall placental infection (p = 0.964). However, the SP group showed a 40% reduction (95% CI, 7.40–61.20]; p = 0.020) in the incidence of clinical malaria during pregnancy, and reductions in the prevalence of peripheral parasitaemia (7.10% vs 15.15%) (p<0.001), and of actively infected placentas (7.04% vs 13.60%) (p = 0.002). There was a reduction in severe anaemia at delivery of borderline statistical significance (p = 0.055). These effects were not modified by gravidity or HIV status. Reported ITN''s use was more than 90% in both groups.

Conclusions

Two-dose SP was associated with a reduction in some indicators, but these were not translated to significant improvement in other maternal or birth outcomes. The use of ITNs during pregnancy may reduce the need to administer IPTp. ITNs should be part of the ANC package in sub-Saharan Africa.

Trial Registration

ClinicalTrials.gov {"type":"clinical-trial","attrs":{"text":"NCT00209781","term_id":"NCT00209781"}}NCT00209781     

Ecology and morphological variability of Aulacoseira granulata (Bacillariophyceae) in Spanish reservoirs

The ecology of Aulacoseira (formerly Melosira) granulata andits different forms in     

Screening for FMR1 and FMR2 mutations in 222 individuals from Spanish special schools: identification of a case of FRAXE-associated mental retardation

Fragile X syndrome is the most common inherited form of familial mental retardation. It results from a (CGG) _n trinucleotide expansion in the FMR1 gene leading to the typical Martin-Bell phenotype. Clinical features vary depending on age and sex. Expansion of a (CCG) _n repeat in the FMR2 gene corresponds to the FRAXE fragile site which lies distal to FRAXA and is also associated with mental retardation, but it is less frequent and lacks a consistent phenotype. Analysis of repeat expansions in these two genes allows the molecular diagnosis of these different entities. We report here the screening of the FRAXA and FRAXE mutations in 222 unrelated mentally retarded individuals attending Spanish special schools. PCR and/or Southern blotting methods were used. We detected full mutations in the FMR1 gene in 11 boys (4.9%) and 1 boy (0.5%) with a CCG repeat expansion in the FMR2 gene. The latter shows mild mental retardation with psychotic behaviour and no remarkable physical traits. Molecular studies revealed a mosaicism for methylation in the FMR2 gene. This case supports the observation that expansions greater than 100 repeats can be partially methylated and cause the phenotype. Received: 11 February 1997 / Accepted: 9 June 1997     

Nitrogen Removal by Riparian Buffers along a European Climatic Gradient: Patterns and Factors of Variation

We evaluated nitrogen (N) removal efficiency by riparian buffers at 14 sites scattered throughout seven European countries subject to a wide range of climatic conditions. The sites also had a wide range of nitrate inputs, soil characteristics, and vegetation types. Dissolved forms of N in groundwater and associated hydrological parameters were measured at all sites; these data were used to calculate nitrate removal by the riparian buffers. Nitrate removal rates (expressed as the difference between the input and output nitrate concentration in relation to the width of the riparian zone) were mainly positive, ranging from 5% m⁻¹ to 30% m⁻¹, except for a few sites where the values were close to zero. Average N removal rates were similar for herbaceous (4.43% m⁻¹) and forested (4.21% m⁻¹) sites. Nitrogen removal efficiency was not affected by climatic variation between sites, and no significant seasonal pattern was detected. When nitrate inputs were low, a very large range of nitrate removal efficiencies was found both in the forested and in the nonforested sites. However, sites receiving nitrate inputs above 5 mg N L⁻¹ showed an exponential negative decay of nitrate removal efficiency (nitrate removal efficiency = 33.6 e^{−0.11 NO3input}, r ² = 0.33, P < 0.001). Hydraulic gradient was also negatively related to nitrate removal (r = −0.27, P < 0.05) at these sites. On the basis of this intersite comparison, we conclude that the removal of nitrate by biological mechanisms (for example, denitrification, plant uptake) in the riparian areas is related more closely to nitrate load and hydraulic gradient than to climatic parameters. Received 15 August 2001; accepted 2 May 2002.