Organic acids reduce aluminum toxicity in maize root membranes

Application of 10–50 μ M Al ions to a plasma membrane-enriched microsomal fraction, isolated from roots of maize ( Zea mays L.), resulted in decreased Mg²-ATPase activity. This was probably caused by changes in membrane structure as detected by the use of spin probes. Both enzymatic activity and membrane structure could in part be protected from Al injury when organic acids, similar to those found in maize root tissue, were administered prior to the metal. When stressed by application of Al ions, the Al-tolerant maize hybrid, W64, maintained higher concentrations of organic acids, especially malic and trans -aconitic, than the Al-sensitive maize hybrid, A632. We hypothesize that citric and malic acid, because of their high stability constants with Al and/or the acid's concentration reduce Al toxicity in maize root tissue, especially in the Al-tolerant line.     

Identifying non-sperm particles during flow cytometric physiological assessment: a simple approach

Flow cytometry is now being used more frequently to determine sperm functional characteristics during semen assessment for artificial insemination. With this methodology, viable and potentially functional cells are detected as unstained events differentiated from non-sperm events through their light-scattering characteristics. However, it can be shown mathematically that identification of sperm on the basis of light scatter leads to significant overestimation of unstained viable cells and underestimation of responding cells in tests of sperm function (subpopulations expressing different fluorescence patterns). We have developed a simple and cost-efficient flow cytometric approach for identifying non-sperm particles that can be carried out in parallel with functional assessments. Our method is based on the sperm's osmotic intolerance. Diluted in water, lethal osmotic shock causes major damage to the cell membranes, and all sperm will stain with propidium iodide (PI). Particulate material which is not PI-positive can then be quantitatively evaluated by FACS analysis and the results substituted in mathematical equations to provide true values for sperm counts and subpopulations. In practical tests, the percentage of non-sperm particles determined by this technique was closely comparable to the figure obtained either by SYBR14^®/PI staining or by PI/CFDA staining. As well as being valuable with respect to tests of sperm function, the procedure is also suitable for obtaining accurate sperm counts during routine semen evaluation.     

Thermonastic leaf movements: a synthesis of research with Rhododendron

Thermonastic leaf movements in Rhododendron L. occur in response to freezing temperatures. These movements are composed of leaf curling and leaf angle changes that are distinct leaf movements with different responses to climatic factors. Leaf angle is controlled by the hydration of the petiole, as affected by soil water content, atmospheric vapour pressure, and air temperature. In contrast, leaf curling is a specific response to leaf temperature, and bulk leaf hydration has little effect. The physiological cause of leaf curling is not well understood, but the mechanism must lie in the physiology of the cell wall and/or regional changes in tissue hydration. Available evidence suggests that intercellular freezing is not a cause of leaf curling.
Manipulation experiments demonstrate that changes in leaf orientation in Rhododendron most likely serve to protect the leaves from membrane damage due to high irradiance and cold temperatures. In particular, the pendent leaves protect the chloroplast from photoinhibition. Leaf curling may serve to slow the rate of thaw following freezing, a common phenomenon in the Appalachian mountains of the U.S. The thermonastic leaf movements have a greater importance to plants in a dim environment because the potential impact to canopy carbon gain is greater than in high light environments.
These leaf movements have several implications for horticultural management. There seems to be a trade-off between water stress tolerance and freezing stress tolerance by leaf movements. Thermonastic leaf movements may be a major mechanism of cold stress tolerance in Rhododendron species. The actual physiological cause of leaf movement has not been elucidated and many more species need to be evaluated to verify the general importance of leaf movements to Rhododendron ecology and evolution.     

Indoleamine 2,3-Dioxygenase Tissue Distribution and Cellular Localization in Mice: Implications for Its Biological Functions

Earlier studies have suggested that indoleamine 2,3-dioxygenase (IDO) has a wide tissue distribution in mammals. However, detailed information on its cellular localization and also the levels of expression in various tissues is still scarce. In the present study, we sought to determine the cellular localization of IDO and also to quantify the level of its expression in various mouse tissues by using the branched DNA signal amplification assay, Western blotting, and immunohistochemical staining. The highest levels of constitutive IDO expression were found to be selectively present in the caput of epididymis, except for its initial segment. IDO expression was also detected inside the luminal compartment and even in the stereocilia within this region. In the prostate, high levels of IDO were selectively expressed in the capsular cells. In addition, high levels of IDO expression were also selectively detected in certain types of cells in the placenta, spleen, thymus, lung, and digestive tract. Notably, the morphological features of most of the positively stained cells in these organs closely resembled those of antigen-presenting cells. Based on the tissue distribution and cellular localization characteristics of IDO, it is hypothesized that its expression may serve two main functions: one is to deplete tryptophan in an enclosed microenvironment (such as in the epididymal duct lumen) to prevent bacterial or viral infection, and the other is to produce bioactive tryptophan catabolites that would serve to suppress T-cell–mediated immune responses against self-antigens, fetal antigens, or allogeneic antigens, in different situations. (J Histochem Cytochem 58:17–28, 2010)     

Apparent survival of tropical birds in a wet,premontane forest in Costa Rica

Despite the importance of tropical birds in the development of life history theory, we lack information about demographic rates and drivers of population dynamics for most species. We used a 7‐year (2007–2013) capture‐mark‐recapture dataset from an exceptionally wet premontane forest at mid‐elevation in Costa Rica to estimate apparent survival for seven species of tropical passerines. For four of these species, we provide the first published demographic parameters. Recapture probabilities ranged from 0.21 to 0.53, and annual estimates of apparent survival varied from 0.23 to 1.00. We also assessed the consequences of inter‐annual variation in rainfall on demographic rates. Our results are consistent with inter‐annual rainfall increasing estimates of apparent survival for two species and decreasing estimates for three species. For the three species where we could compare our estimates of apparent survival to estimates from drier regions, our estimates were not consistently higher or lower than those published previously. The temporal and spatial variability in demographic rates we document within and among species highlights the difficulties of generalizing life history characteristics across broad biogeographic gradients. Most importantly, this work emphasizes the context‐specific role of precipitation in shaping tropical avian demographic rates and underscores the need for mechanistic studies of environmental drivers of tropical life histories.     

Structural insight into the molecular basis of polyextremophilicity of short-chain alcohol dehydrogenase from the hyperthermophilic archaeon Thermococcus sibiricus

Biochemical analysis of enantioselective short-chain alcohol dehydrogenase from the hyperthermophilic archaeon Thermococcus sibiricus (TsAdh319) revealed unique polyextremophilic properties of the enzyme – half-life of 1 h at 100 °C, tolerance to high salt (up to 4 M) and organic solvents (50% v/v) concentrations. To elucidate the molecular basis of TsAdh319 polyextremophilicity, we determined the crystal structure of the enzyme in a binary complex with 5-hydroxy-NADP at 1.68 Å resolution. TsAdh319 has a tetrameric structure both in the crystals and in solution with an intersubunit disulfide bond. The substrate-binding pocket is hydrophobic, spacious and open that is consistent with the observed promiscuity in substrate specificity of TsAdh319. The present study revealed an extraordinary number of charged residues on the surface of TsAdh319, 70% of which were involved in ion pair interactions. Further we compared the structure of TsAdh319 with the structures of other homologous short-chain dehydrogenases/reductases (SDRs) from thermophilic and mesophilic organisms. We found that TsAdh319 has the highest arginine and aspartate + glutamate contents compared to the counterparts. The frequency of occurrence of salt bridges on the surface of TsAdh319 is the highest among the SDRs under consideration. No differences in the proline, tryptophan, and phenylalanine contents are observed; the compactness of the protein core of TsAdh319, the monomer and tetramer organization do not differ from that of the counterparts. We suggest that the unique thermostability of TsAdh319 is associated with the rigidity and simultaneous “resilience” of the structure provided by a compact hydrophobic core and a large number of surface ion pairs. An extensive salt bridge network also might maintain the structural integrity of TsAdh319 in high salinity.     

Incorporation of [35S]methionine in higher plants reveals that stimulation of the D1 reaction centre II protein turnover accompanies tolerance to heavy metal stress

The effects of cadmium stress (CdCl₂) on photochemical activity and protein behaviour of photosystem II (PSII) were studied in vivo and in vitro . Treatments of pea ( Pisum sativum ) and broad bean ( Vicia faba ) plants with 0·05–5 m M cadmium (CdCl₂) modified PSII activity with a resulting increase in electron transfer followed by an inhibition and damage to the oxygen-evolving complex. Pulse-chase experiments with [³⁵S]methionine in vivo followed by the separation of the radiolabelled thylakoids into grana and stroma exposed regions indicated that the synthesis, degradation and assembly of the D1 protein were greatly affected by cadmium. Initially D1 synthesis increased, later slowing down when the stress became advanced; at the same time the D1 degradation was increased. Binding studies with radiolabelled [¹⁴C]herbicide revealed that the Q_B pocket activity was also altered. However, the primary consequence of cadmium stress was the disassembly of the stacked regions. The measurements indicated differential tolerance to cadmium stress between the two plant species, which was not caused by either differential metal uptake or binding to the PSII complex. This suggests that the resulting changes in D1 turnover are a consequence of an unknown primary effect of cadmium on the PSII apparatus. However, we show that the higher tolerance to heavy metal stress found in broad bean plants relative to pea is accompanied by stimulation of D1 turnover. These experiments supported by previous data suggest that modulation of D1 turnover under stress is a commonly occurring process.     

Individual differences in the cortisol-awakening response during the first two years of shift work: A longitudinal study in novice police officers

Cortisol acts as a critical biological intermediary through which chronic stressors like shift work impact upon multiple physiological, neuro-endocrine and hormonal functions. Therefore, the cortisol awakening response (CAR) is suggested as a prime index of shift work tolerance. Repeated assessments of the CAR (calculated as MnInc) in a group of 25 young novice police officers showed that in the interval between about 4 and 14 months after transitioning from regular day work to rotating shift work, mean values began to rise from baseline to significantly higher levels at about 14 months after they commenced shift work. Visual inspection of the individual trends revealed that a subgroup of 10 subjects followed a monotonically rising trend, whereas another 14 subjects, after an initial rise from about 4–14 months, reverted to a smaller, baseline level cortisol response at about 20 months after the start of shift work. If the initial increase in the cortisol response marks the development of a chronic stress response, the subsequent reversal to baseline levels in the subgroup of 14 participants might be indicative of a process of recovery, possibly the development of shift work tolerance.