Photosynthetic electron transport and specific photoprotective responses in wheat leaves under drought stress

The photosynthetic responses of wheat (Triticum aestivum L.) leaves to different levels of drought stress were analyzed in potted plants cultivated in growth chamber under moderate light. Low-to-medium drought stress was induced by limiting irrigation, maintaining 20 % of soil water holding capacity for 14 days followed by 3 days without water supply to induce severe stress. Measurements of CO₂ exchange and photosystem II (PSII) yield (by chlorophyll fluorescence) were followed by simultaneous measurements of yield of PSI (by P700 absorbance changes) and that of PSII. Drought stress gradually decreased PSII electron transport, but the capacity for nonphotochemical quenching increased more slowly until there was a large decrease in leaf relative water content (where the photosynthetic rate had decreased by half or more). We identified a substantial part of PSII electron transport, which was not used by carbon assimilation or by photorespiration, which clearly indicates activities of alternative electron sinks. Decreasing the fraction of light absorbed by PSII and increasing the fraction absorbed by PSI with increasing drought stress (rather than assuming equal absorption by the two photosystems) support a proposed function of PSI cyclic electron flow to generate a proton-motive force to activate nonphotochemical dissipation of energy, and it is consistent with the observed accumulation of oxidized P700 which causes a decrease in PSI electron acceptors. Our results support the roles of alternative electron sinks (either from PSII or PSI) and cyclic electron flow in photoprotection of PSII and PSI in drought stress conditions. In future studies on plant stress, analyses of the partitioning of absorbed energy between photosystems are needed for interpreting flux through linear electron flow, PSI cyclic electron flow, along with alternative electron sinks.     

Unique Prokaryotic Consortia in Geochemically Distinct Sediments from Red Sea Atlantis II and Discovery Deep Brine Pools

The seafloor is a unique environment, which allows insights into how geochemical processes affect the diversity of biological life. Among its diverse ecosystems are deep-sea brine pools - water bodies characterized by a unique combination of extreme conditions. The 'polyextremophiles' that constitute the microbial assemblage of these deep hot brines have not been comprehensively studied. We report a comparative taxonomic analysis of the prokaryotic communities of the sediments directly below the Red Sea brine pools, namely, Atlantis II, Discovery, Chain Deep, and an adjacent brine-influenced site. Analyses of sediment samples and high-throughput pyrosequencing of PCR-amplified environmental 16S ribosomal RNA genes (16S rDNA) revealed that one sulfur (S)-rich Atlantis II and one nitrogen (N)-rich Discovery Deep section contained distinct microbial populations that differed from those found in the other sediment samples examined. Proteobacteria, Actinobacteria, Cyanobacteria, Deferribacteres, and Euryarchaeota were the most abundant bacterial and archaeal phyla in both the S- and N-rich sections. Relative abundance-based hierarchical clustering of the 16S rDNA pyrotags assigned to major taxonomic groups allowed us to categorize the archaeal and bacterial communities into three major and distinct groups; group I was unique to the S-rich Atlantis II section (ATII-1), group II was characteristic for the N-rich Discovery sample (DD-1), and group III reflected the composition of the remaining sediments. Many of the groups detected in the S-rich Atlantis II section are likely to play a dominant role in the cycling of methane and sulfur due to their phylogenetic affiliations with bacteria and archaea involved in anaerobic methane oxidation and sulfate reduction.     

Photosynthetic responses of sun- and shade-grown barley leaves to high light: is the lower PSII connectivity in shade leaves associated with protection against excess of light?

In this study, we have compared photosynthetic performance of barley leaves (Hordeum vulgare L.) grown under sun and shade light regimes during their entire growth period, under field conditions. Analyses were based on measurements of both slow and fast chlorophyll (Chl) a fluorescence kinetics, gas exchange, pigment composition; and of light incident on leaves during their growth. Both the shade and the sun barley leaves had similar Chl a/b and Chl/carotenoid ratios. The fluorescence induction analyses uncovered major functional differences between the sun and the shade leaves: lower connectivity among Photosystem II (PSII), decreased number of electron carriers, and limitations in electron transport between PSII and PSI in the shade leaves; but only low differences in the size of PSII antenna. We discuss the possible protective role of low connectivity between PSII units in shade leaves in keeping the excitation pressure at a lower, physiologically more acceptable level under high light conditions.     

The Pleiades are a cluster of fungal effectors that inhibit host defenses

Biotrophic plant pathogens secrete effector proteins to manipulate the host physiology. Effectors suppress defenses and induce an environment favorable to disease development. Sequence-based prediction of effector function is impeded by their rapid evolution rate. In the maize pathogen Ustilago maydis, effector-coding genes frequently organize in clusters. Here we describe the functional characterization of the pleiades, a cluster of ten effector genes, by analyzing the micro- and macroscopic phenotype of the cluster deletion and expressing these proteins in planta. Deletion of the pleiades leads to strongly impaired virulence and accumulation of reactive oxygen species (ROS) in infected tissue. Eight of the Pleiades suppress the production of ROS upon perception of pathogen associated molecular patterns (PAMPs). Although functionally redundant, the Pleiades target different host components. The paralogs Taygeta1 and Merope1 suppress ROS production in either the cytoplasm or nucleus, respectively. Merope1 targets and promotes the auto-ubiquitination activity of RFI2, a conserved family of E3 ligases that regulates the production of PAMP-triggered ROS burst in plants.     

A Metabolic Shift Favoring Sphingosine 1-Phosphate at the Expense of Ceramide Controls Glioblastoma Angiogenesis

Studies in cell culture and mouse models of cancer have indicated that the soluble sphingolipid metabolite sphingosine 1-phosphate (S1P) promotes cancer cell proliferation, survival, invasiveness, and tumor angiogenesis. In contrast, its metabolic precursor ceramide is prodifferentiative and proapoptotic. To determine whether sphingolipid balance plays a significant role in glioma malignancy, we undertook a comprehensive analysis of sphingolipid metabolites in human glioma and normal gray matter tissue specimens. We demonstrate, for the first time, a systematic shift in sphingolipid metabolism favoring S1P over ceramide, which increases with increasing cancer grade. S1P content was, on average, 9-fold higher in glioblastoma tissues compared with normal gray matter, whereas the most abundant form of ceramide in the brain, C18 ceramide, was on average 5-fold lower. Increased S1P content in the tumors was significantly correlated with increased sphingosine kinase 1 (SPHK1) and decreased sphingosine phosphate phosphatase 2 (SGPP2) expression. Inhibition of S1P production by cultured glioblastoma cells, using a highly potent and selective SPHK1 inhibitor, blocked angiogenesis in cocultured endothelial cells without affecting VEGF secretion. Our findings validate the hypothesis that an altered ceramide/S1P balance is an important feature of human cancers and support the development of SPHK1 inhibitors as antiangiogenic agents for cancer therapy.     

Removal of lead and cadmium by halophilic bacteria isolated from the Dead Sea shore, Jordan

Ten Gram-positive and Gram-negative bacterial cultures were recovered from nine water, mud, and soil samples from the Dead Sea shore at Suwaymah. They were able to grow at 10% NaCl and at 45 degrees C. Bacterial cultures 6 and 8 were able to grow in nutrient media supplemented with 2250 ppm of Pb. Bacterial cultures 1, 3-6, 9, and 10 were able to grow in nutrient medium supplemented with 1000 ppm of Cd. Atomic absorption spectrometry was used to estimate the absorbed Pb and Cd by bacterial cultures from 5-, 25-, 100-, and 500-ppm stock solutions of both elements. After 2 wk, the results showed that the maximum absorption for Pb was achieved by culture 6 in the following percentages: 79.8%, 70.48%, 89.48%, and 83.39%, respectively. The maximum absorption of the same concentration of Cd was achieved by culture 9 with the following percentages: 69.2%, 32.24%, 44.98%, and 60.0%, respectively. After 3 wk of incubation, the estimated absorption of both heavy metals was achieved by the same cultures (6 and 9), respectively, in the following percentages: 86.8%, 76.72%, 96.25%, and 96.0% for Pb and 82.60%, 93.2%, 92.74%, and 89.79% for Cd. The accumulation of the absorbed metals was found to be maximum in the protoplast of all the cultures. The accumulation at the cell wall was maximum in culture 2, and between the cell wall and the plasma membrane, it was maximum in cultures 2 and 8 for Pb and Cd, respectively.     

The effect of aging and increasing ascorbate concentrations on respiratory chain activity in cultured human fibroblasts

The specific activities of Complexes I‐III, II‐III, and IV of the respiratory chain, and citrate synthase, were determined in mitochondrial sonicates of six control passage 5 fibroblast cultures, cultivated in growth medium containing fetal calf serum as the only source of ascorbate. The enzymes were also assayed in serially subcultured fibroblasts which were characterized as aged at passage 20 and beyond. Results indicated a significant loss of all enzyme activities in aged cells at passage 20, 25, and 30. Further studies involved maintenance of serially subcultured cells in serum free media to which increasing ascorbate concentrations (100, 200, and 300 µmol 1^?1) were added. Results indicated that ascorbate at 100 µmol 1^?1 was not sufficient to restore any of the enzyme activities in aged cells. An ascorbate concentration of 200 µmol 1^?1 however, could totally restore Complex IV and citrate synthase activities, but had no effect on complexes I‐III and II‐III activities which required 300 µmol 1^?1 ascorbate to be partially or totally restored respectively. In conclusion, this study demonstrates an age related drop in mitochondrial respiratory chain activity in cultured human fibroblasts. Enzyme activities could be completely or partially restored in the presence of double or triple normal human plasma ascorbate concentrations. Copyright © 2010 John Wiley & Sons, Ltd.     

Ideal Cardiovascular Health Metrics Are Associated with Disability Independently of Vascular Conditions

Background

Vascular risk factors may be associated with disability independently of vascular events. We examined whether the American Heart Association’s 7 ideal cardiovascular health (CVH) metrics were independently associated with disability in a nationally representative cohort.

Methods

Adults age ≥20 years from the National Health and Nutrition Examination Survey 2005–2012 were included. Ideal CVH was calculated as a composite of 7 measures, each scored 0–2. Primary predictors were number of ideal CVH metrics and score of CVH metrics. The outcome was a dichotomous score from 20 activities of daily living (ADL) and instrumental ADLs. Unadjusted and adjusted weighted logistic models estimated associations between ideal CVH and disability. The data were analyzed in 2015.

Results

Among 22692 participants, mean age was 46.9 years. Cardiac disease and stroke were present in 6.6% and 2.8%; 90.3% had poor physical activity and 89.9% poor diet. Among 3975 individuals with full CVH data, in fully adjusted models, OR for disability was 0.90 (95% CI 0.83–0.98) per point increase in ideal CVH score, and 0.84 (0.73–0.97) per additional number of ideal CVH metrics.

Conclusions

CVH metrics were strongly and significantly associated with reduced odds of disability independently of vascular and non-vascular conditions. Poorer CVH may cause subclinical vascular disease resulting in disability.