How to deal with oxygen radicals stemming from mitochondrial fatty acid oxidation

Oxygen radical formation in mitochondria is an incompletely understood attribute of eukaryotic cells. Recently, a kinetic model was proposed, in which the ratio between electrons entering the respiratory chain via FADH₂ or NADH determines radical formation. During glucose breakdown, the ratio is low; during fatty acid breakdown, the ratio is high (the ratio increasing—asymptotically—with fatty acid length to 0.5, when compared with 0.2 for glucose). Thus, fatty acid oxidation would generate higher levels of radical formation. As a result, breakdown of fatty acids, performed without generation of extra FADH₂ in mitochondria, could be beneficial for the cell, especially in the case of long and very long chained ones. This possibly has been a major factor in the evolution of peroxisomes. Increased radical formation, as proposed by the model, can also shed light on the lack of neuronal fatty acid oxidation and tells us about hurdles during early eukaryotic evolution. We specifically focus on extending and discussing the model in light of recent publications and findings.     

Vitrification of one-cell mouse embryos in cryotubes

Preventing intracellular ice formation is essential to cryopreserve cells. Prevention can be achieved by converting cell water into a non-crystalline glass, that is, to vitrify. The prevailing belief is that to achieve vitrification, cells must be suspended in a solution containing a high concentration of glass-inducing solutes and cooled rapidly. In this study, we vitrified 1-cell mouse embryos and examined the effect of the cooling rate, the warming rate, and the concentration of cryoprotectant on cell survival. Embryos were vitrified in cryotubes. The vitrification solutions used were EFS20, EFS30, and EFS40, which contained ethylene glycol (20, 30 and 40% v/v, respectively), Ficoll (24%, 21%, and 18% w/v, respectively) and sucrose (0.4 0.35, and 0.3 M, respectively). A 5-μl EFS solution suspended with 1-cell embryos was placed in a cryotube. After 2 min in an EFS solution at 23 °C, embryos were vitrified by direct immersion into liquid nitrogen. The sample was warmed at 34 °C/min, 4,600 °C/min and 6,600 °C/min. With EFS40, the survival was low regardless of the warming rate. With EFS30 and EFS20, survival was also low when the warming rate was low, but increased with higher warming rates, likely due to prevention of intracellular ice formation. When 1-cell embryos were vitrified with EFS20 and warmed rapidly, almost all of the embryos developed to blastocysts in vitro. Moreover, when vitrified 1-cell embryos were transferred to recipients at the 2-cell stage, 43% of them developed to term. In conclusion, we developed a vitrification method for 1-cell mouse embryos by rapid warming using cryotubes.     

Spatial metrics for detecting ecosystem degradation in the ridge-slough patterned landscape

Indicators of landscape condition should be selected based on their sensitivity to environmental changes and their capacity to provide early warning detection of those changes. We assessed the performance of a suite of spatial-pattern metrics selected to quantify the condition of the ridge-slough landscape in the Everglades (South Florida, USA). Spatial pattern metrics (n = 14) that describe landscape composition, geometry and hydrologic connectivity were enumerated from vegetation maps of twenty-five 2 × 2 km primary sampling units (PSUs) that span a gradient of hydrologic and ecological condition across the greater Everglades ecosystem. Metrics were assessed in comparison with field measurements from each PSU of landscape condition obtained from regional surveys of soil elevation, which have previously been shown to capture dramatic differences between conserved and degraded locations. Elevation-based measures of landscape condition included soil elevation bi-modality (BI_SE), a binary measure of landscape condition, and also the standard deviation of soil elevation (SD_SE), a continuous measure of condition. Metric performance was assessed based on the strength (sensitivity) and shape (leading vs. lagging) of the relationship between spatial pattern metrics and these elevation-based measures. We observed significant logistic regression slopes with BI_SE for only 4 metrics (slough width, ridge density, directional connectivity index – DCI, and least flow cost – LFC). More significant relationships (n = 8 metrics) were observed with SD_SE, with the strongest associations for slough density, mean ridge width, and the average length of straight flow, as well as for a suite of hydrologic connectivity metrics (DCI, LFC and landscape discharge competence – LDC). Leading vs. lagging performance, inferred from the curvature of the association obtained from the exponent of fitted power functions, suggest that only DCI was a leading metric of the loss of soil elevation variation; most metrics were indeterminate, though some were clearly lagging. Our findings support the contention that soil elevation changes from altered peat accretion dynamics precede changes in landscape pattern, and offer insights that will enable efficient monitoring of the ridge-slough landscape as part of the ongoing Everglades restoration effort.     

Tree island pattern formation in the Florida Everglades

The Florida Everglades freshwater landscape exhibits a distribution of islands covered by woody vegetation and bordered by marshes and wet prairies. Known as “tree islands”, these ecogeomorphic features can be found in few other low gradient, nutrient limited freshwater wetlands. In the last few decades, however, a large percentage of tree islands have either shrank or disappeared in apparent response to altered water depths and other stressors associated with human impacts on the Everglades. Because the processes determining the formation and spatial organization of tree islands remain poorly understood, it is still unclear what controls the sensitivity of these landscapes to altered conditions. We hypothesize that positive feedbacks between woody plants and soil accretion are crucial to emergence and decline of tree islands. Likewise, positive feedbacks between phosphorus (P) accumulation and trees explain the P enrichment commonly observed in tree island soils. Here, we develop a spatially-explicit model of tree island formation and evolution, which accounts for these positive feedbacks (facilitation) as well as for long range competition and fire dynamics. It is found that tree island patterns form within a range of parameter values consistent with field data. Simulated impacts of reduced water levels, increased intensity of drought, and increased frequency of dry season/soil consuming fires on these feedback mechanisms result in the decline and disappearance of tree islands on the landscape.     

K+(Rb+) and Ca2+ fluxes in young winter wheat plants exposed to sub-zero temperatures

Ice crystal formation temperature was determined in the region of the crown in one group of 7-day-old intact unhardened high-salt plants of winter wheat (Triticum aestivum L. cv. Weibulls Starke II) with TA (Thermal Analysis) and DTA (Differential Thermal Analysis) methods. After exposure of another group of plants, grown for the first 7 days in the same way as the first group, to various sub-zero temperatures (-1 to 5°C), influx in roots of Rb⁺(⁸⁶Rb⁺) and Ca²⁺(⁴⁵Ca²⁺) and contents of K⁺ and Ca²⁺ were determined at intervals during 7 days of recovery. Ice crystal formation in the crown tissue was probably extracellular and took place at about -4°C. There was a large loss of K⁺ from the roots after treatment at sub-zero temperatures. This loss increased as the temperature of the sub-zero treatment decreased. During recovery, roots of plants exposed to -1, -2 and -3°C gradually reabsorbed K⁺. Reabsorption of K⁺ in roots of plants exposed to -4°C was greatly impaired. Rb⁺ influx decreased and Ca²⁺ influx increased after sub-zero temperature treatments of the plants. Active Rb⁺ influx mechanisms and active extrusion of Ca²⁺ were impaired or irreversibly damaged by the exposure. While Rb⁺ influx mechanisms were apparently repaired during recovery in plants exposed to temperatures down to -3°C, Ca²⁺ extrusion mechanisms were not. The temperature for ice crystal formation in the region of the crown tissue coincides with the temperature at which the plants lost the ability to reabsorb K⁺ and to repair Rb⁺ influx mechanisms during the recovery period. Plants were lethally damaged at temperatures below ?4°C.     

The influence of alkyl pyridinium sponge toxins on membrane properties, cytotoxicity, transfection and protein expression in mammalian cells

The ability of two alkyl pyridinium sponge toxin preparations (poly-APS and halitoxin) to form transient pores/lesions in cell membranes and allow transfection of plasmid cDNA have been investigated using HEK 293 cells. Poly-APS and halitoxin preparations caused a collapse in membrane potential, reductions in input resistance and increased Ca²⁺ permeability. At least partial recovery was observed after poly-APS application but recovery was more rarely seen with halitoxin. The transfection with plasmid cDNAs for an enhanced green fluorescent protein (EGFP) and human tumour necrosis factor receptor 2 (TNFR2) was assessed for both toxin preparations and compared with lipofectamine. Stable transfection was achieved with poly-APS although it was less efficient than lipofectamine. These results show that viable cells transfected with alien cDNA can be obtained using novel transient pore-forming alkyl pyridinium sponge toxins and a simple pre-incubation protocol. This provides the first proof of principle that pore-forming alkyl pyridinium compounds can be used to deliver cDNA to the intracellular environment without permanently compromising the plasma membrane.     

The role of the cysteine-rich region of the β2 integrin subunit in the leukocyte function-associated antigen-1 (LFA-1, αLβ2, CD11a/CD18) heterodimer formation and ligand binding

The cysteine-rich region (CRR) of the β2 integrin subunit was replaced by that of β1 to give the chimera β2NV1. β2NV1 can combine with αL to form a variant leukocyte-function-associated antigen (LFA)-1 on COS cell surface, suggesting that the specificity of the β2 interaction with αL does not lie in the CRR. Unlike those expressing wild-type LFA-1, COS cells expressing αLβ2NV1 are constitutively active in intercellular adhesion molecule (ICAM)-1 adhesion. These results suggest that activation of LFA-1 involves the release of an intramolecular constraint, which is maintained, in part, by the authentic β2 CRR.     

Arthropod-induced neoplastic formations on trees change photosynthetic pigment levels and oxidative enzyme activities

Abstract

In order to test the hypothesis that arthropod-induced neoplastic formations on trees affect biochemical characteristics of both the newly formed galls and host plant tissues, biochemical characteristics with a possible adaptive role were determined in nine gall-former–host tree combinations. Photosynthetic pigments, extractable protein content, and oxidative enzyme activities were determined in gall tissues, leaf tissues of galled leaves, and leaves on ungalled tree branches. Neoplastic tissues were characterized by a low content of photosynthetic pigments, decreased chlorophyll a/b ratio, lower extractable protein content, and decreased activities of peroxidase and polyphenol oxidase as compared with ungalled host leaf tissues. In galled leaves or in leaves adjacent to galls, increased level of peroxidase activity was found. In several gall-inducer–host plant combinations, galled host plant tissues contained increased activity of polyphenol oxidase as well. The presented data reflect long-term systemic effects of neoplastic formation on host tree physiology suggesting that gall inducers affect potential adaptive responses of host plants.