Silicon nutrition alleviates the negative impacts of arsenic on the photosynthetic apparatus of rice leaves: an analysis of the key limitations of photosynthesis

Silicon (Si) plays important roles in alleviating various abiotic stresses. In rice (Oryza sativa), arsenic (As) is believed to share the Si transport pathway for entry into roots, and Si has been demonstrated to decrease As concentrations. However, the physiological mechanisms through which Si might alleviate As toxicity in plants remain poorly elucidated. We combined detailed gas exchange measurements with chlorophyll fluorescence analysis to examine the effects of Si nutrition on photosynthetic performance in rice plants [a wild‐type (WT) cultivar and its lsi1 mutant defective in Si uptake] challenged with As (arsenite). As treatment impaired carbon fixation (particularly in the WT genotype) that was unrelated to photochemical or biochemical limitations but, rather, was largely associated with decreased leaf conductance at the stomata and mesophyll levels. Indeed, regardless of the genotypes, in the plants challenged with As, photosynthetic rates correlated strongly with both stomatal (r² = 0.90) and mesophyll (r² = 0.95) conductances, and these conductances were, in turn, linearly correlated with each other. The As‐related impairments to carbon fixation could be considerably reverted by Si in a time‐ and genotype‐dependent manner. In conclusion, we identified Si nutrition as an important target in an attempt to not only decrease As concentrations but also to ameliorate the photosynthetic performance of rice plants challenged with As.     

<Emphasis Type="Italic">In vitro</Emphasis> morphogenesis and micropropagation of <Emphasis Type="Italic">Aechmea ramosa</Emphasis> var. <Emphasis Type="Italic">ramosa</Emphasis> Mart. ex Schult. f. (Bromeliaceae) from leaf explants

Aechmea ramosa Mart. ex Schult. f. is an endemic bromeliad of the Brazilian Atlantic Forest. The current habitat degradation of this hotspot biome threatens this species, which besides having an important ecological role, is also of invaluable ornamental interest. Plant tissue culture has been used in mass propagation and conservation of various bromeliads. We have established a micropropagation protocol for A. ramosa var. ramosa using leaf explants grown in MS medium supplemented with 2 μM of 1-naphthaleneacetic acid (NAA) and 2 μM of 6-benzylaminopurine (BAP) that showed higher values of shoot induction. NAA and BAP are associated with the production of proteins involved in stress response modulation, metabolic activity, and cell division, the latter being involved in inducing the differentiation of competent cells. After 120 d of culture, each explant presented 28.9 shoots with an average size of 27.8 mm, with no variation in either Stomatal Index or density of the regenerated shoots. Plantlets measuring above 15-mm height were successfully acclimatized, presenting 100% survival rate. Thus, this protocol can be used for mass propagation of A. ramosa, and to supply demand for the market of ornamental plants. Furthermore, it represents an important tool for the conservation of this species and maintenance of an in vitro germplasm.     

Effect of the mating plug on female chemical attractiveness and mating acceptance in a scorpion

After mating, females may experience a decline in sexual receptivity and attractiveness that may be associated with changes in the production and emission of sex pheromones. In some cases, these changes are produced by chemical substances or structures (e.g., mating plugs) produced by males as a strategy to avoid or reduce sperm competition. In scorpions, sex pheromones may be involved in finding potential mates and starting courtship. Here, we tested the hypothesis that the males of Urophonius brachycentrus, a species that produces a mating plug, use chemical communication (sex pheromones) to detect, localize, and discriminate females according to their mating status (virgin or inseminated), aided by chemical signaling. We also explored the effect of extracting of the mating plug on chemical communication and mating acceptance. We used Y‐maze olfactometers with different stimuli to analyze male choice and exploration time. To evaluate mating acceptance, we measured the attractiveness and receptivity of females of different mating status. We found that chemical communication occurs through volatile pheromones, but not contact pheromones. Males equally preferred sites with virgin or inseminated females with removed mating plug. In turn, females with these mating statuses were more attractive and receptive for males than inseminated females. This study suggests that the mating plug significantly affects female chemical attractiveness with an effect on volatile pheromones and decreasing sexual mating acceptance of females. The decline in the female's sexual receptivity is a complex process that may respond to several non‐exclusive mechanisms imposed by males and strategically modulated by females.     

Interaction of mouse dendritic cells and malaria-infected erythrocytes: uptake, maturation, and antigen presentation

Consistent with their seminal role in detecting infection, both mouse bone marrow-derived and splenic CD11c+ dendritic cells (DCs) exhibited higher levels of uptake of Plasmodium chabaudi-parasitized RBCs (pRBCs) than of noninfected RBCs (nRBCs) as determined by our newly developed flow cytometric technique using the dye CFSE to label RBCs before coculture with DCs. To confirm that expression of CFSE by CD11c+ cells following coculture with CFSE-labeled pRBCs represents internalization of pRBC by DCs, we showed colocalization of CFSE-labeled pRBCs and PE-labeled CD11c+ DCs by confocal fluorescence microscopy. Treatment of DCs with cytochalasin D significantly inhibited the uptake of pRBCs, demonstrating that uptake is an actin-dependent phagocytic process. The uptake of pRBCs by splenic CD11c+ DCs was significantly enhanced after infection in vivo and was associated with the induction of DC maturation, IL-12 production, and stimulation of CD4+ T cell proliferation and IFN-gamma production. These results suggest that DCs selectively phagocytose pRBCs and present pRBC-derived Ags to CD4+ T cells, thereby promoting development of protective Th1-dependent immune responses to blood-stage malaria infection.     

Punto de corte de espesor de tejido adiposo epicárdico para predecir síndrome metabólico en población venezolana

ObjectiveTo define an echocardiographically-assessed cut-off point for epicardial adipose tissue (EAT) thickness associated to metabolic syndrome (MS) components in Venezuelan subjects.MethodsFifty-two subjects aged 20-65 years diagnosed with MS according to International Diabetes Federation criteria and 45 sex- and age-matched controls were selected. Blood glucose and plasma lipids were tested; EAT thickness and left ventricular mass were measured by echocardiography.ResultsNo significant age and sex differences were found between the two groups. Body weight, body mass index, waist circumference, and systolic and diastolic blood pressure were significantly higher (P = .0001) in the MS group. This group showed significantly higher levels of fasting blood glucose (P = .0001), total cholesterol (P = .002), LDL-C (P = .007), non-HDL-C (P = .0001), triglycerides (P = .0001), Tg-HDL-C ratio (P = .0001), and lower HDL-C levels (P = .0001) as compared to the control group. EAT thickness (P = .0001) and left ventricular mass (P = .017) were significantly higher in the MS group. The ROC curve showed an AUC of 0.852 (P = .0001) with a power of the test of 0.99. A 5-mm EAT thickness showed a sensitivity of 84.62% (95% CI: 71.9-93.1) and a specificity of 71.11% (95% CI: 55.7-83.6) for predicting MS. The odds ratio of this population for experiencing MS due to an EAT ≥ 5 mm was 8.25 (95% CI: 3.15-21.56; P = .0001).ConclusionAn EAT value ≥ 5 mm has good sensitivity and specificity for predicting MS in the Venezuelan population.     

Differential strategies of two species of arbuscular mycorrhizal fungi in the protection of maize plants grown in chromium-contaminated soils

Chromium (Cr) is a nonessential element for plants that is extremely toxic at high concentrations. Zea mays L. is a species of plant that has developed adaptive mechanisms to increase its tolerance and absorption capacity for this metal. One effective mechanism is to form associations with arbuscular mycorrhizal fungi (AMF), which help the plant cope with stress from heavy metals such as Cr. However, it is still not clear which species of AMF are more efficient as bioremediating agents for plants of agricultural importance. Here, we evaluated the effect of Gigaspora gigantea and Rhizophagus irregularis as protective agents of maize plants in soils contaminated with Cr at concentrations of 0, 48.5, 97 and 194 mg kg^?1 under greenhouse conditions. Maize tolerance to Cr was corroborated, as well as increased absorption of this element by plants associated with both species of AMF. G. gigantea caused an increase in nitrogen content and greater translocation of Cr to the aerial part of the plant; R. irregularis registered an increase in the formation of arbuscules and vesicles with increasing metal concentration and greater retention of Cr in the roots of the plants. Based on these results, we can conclude that the analyzed species of fungi use different strategies, with similar effectiveness, to enhance the absorption capacity of Cr by the plant and influence the differential deposition of this metal in various parts of the plant.

     

Engineering Native and Synthetic Pathways in Pseudomonas putida for the Production of Tailored Polyhydroxyalkanoates

Growing environmental concern sparks renewed interest in the sustainable production of (bio)materials that can replace oil-derived goods. Polyhydroxyalkanoates (PHAs) are isotactic polymers that play a critical role in the central metabolism of producer bacteria, as they act as dynamic reservoirs of carbon and reducing equivalents. PHAs continue to attract industrial attention as a starting point toward renewable, biodegradable, biocompatible, and versatile thermoplastic and elastomeric materials. Pseudomonas species have been known for long as efficient biopolymer producers, especially for medium-chain-length PHAs. The surge of synthetic biology and metabolic engineering approaches in recent years offers the possibility of exploiting the untapped potential of Pseudomonas cell factories for the production of tailored PHAs. In this article, an overview of the metabolic and regulatory circuits that rule PHA accumulation in Pseudomonas putida is provided, and approaches leading to the biosynthesis of novel polymers (e.g., PHAs including nonbiological chemical elements in their structures) are discussed. The potential of novel PHAs to disrupt existing and future market segments is closer to realization than ever before. The review is concluded by pinpointing challenges that currently hinder the wide adoption of bio-based PHAs, and strategies toward programmable polymer biosynthesis from alternative substrates in engineered P. putida strains are proposed.     

Sample preparation for sequencing hits from one-bead-one-peptide combinatorial libraries by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Optimization of bead analysis by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) after the screening of one-bead-one-peptide combinatorial libraries was achieved, involving the fine-tuning of the whole process. Guanidine was replaced by acetonitrile (MeCN)/acetic acid (AcOH)/water (H₂O), improving matrix crystallization. Peptide-bead cleavage with NH₄OH was cheaper and safer than, yet as efficient as, NH₃/tetrahydrofuran (THF). Peptide elution in microtubes instead of placing the beads in the sample plate yielded more sample aliquots. Successive dry layers deposit sample preparation was better than the dried droplet method. Among the matrices analyzed, α-cyano-4-hydroxycinnamic acid resulted in the best peptide ion yield. Cluster formation was minimized by the addition of additives to the matrix.