Probabilistic settling in the Local Exchange Model of turbulent particle transport

The Local Exchange Model (LEM) is a stochastic diffusion model of particle transport in turbulent flowing water. It was developed mainly for application to particles of near-neutral buoyancy that are strongly influenced by turbulent eddies. Turbulence can rapidly transfer such particles to the bed, where settlement can then occur by, for example, sticking to biofilms (e.g., fine particulate organic matter, or FPOM) or attaching to the substrate behaviorally (e.g., benthic invertebrates). Previous papers on the LEM have addressed the problems of how long (time) and far (distance) a suspended particle will be transported before hitting the bed for the first time. These are the hitting-time and hitting-distance problems, respectively. Hitting distances predicted by the LEM for FPOM in natural streams tend to be much shorter than the distances at which most particles actually settle, suggesting that particles usually do not settle the first time they hit the bed. The present paper extends the LEM so it can address probabilistic settling, where a particle encountering the bed can either remain there for a positive length of time (i.e., settle) or immediately reflect back into the water column, each with positive probability. Previous results for the LEM are generalized by deducing a single set of equations governing the probability distribution and moments of a broad class of quantities that accumulate during particle trajectories terminated by hitting or settling on the bed (e.g., transport time, transport distance, cumulative energy expenditure during transport). Key properties of the settling-time and settling-distance distributions are studied numerically and compared with the observed FPOM settling-distance distribution for a natural stream. Some remaining limitations of the LEM and possible means of overcoming them are discussed.     

Detection of a hidden folding intermediate in the focal adhesion target domain: Implications for its function and folding

The focal adhesion target (FAT) domain of focal adhesion kinase has a four-helix bundle structure. Based on a hydrogen exchange-constrained computer simulation study and some indirect experimental results, it has been suggested that a partially unfolded state of the FAT domain with the N-terminal helix unfolded plays an important role in its biological function. Here, using a native-state hydrogen exchange method, we directly detected an intermediate with the N-terminal helix unfolded in a mutant (Y925E) of the FAT domain. In addition, kinetic folding studies on the FAT domain suggest that this intermediate exists on the native side of the rate-limiting transition state for folding. These results provide more direct evidence of the existence of the proposed intermediate and help to understand the folding mechanism of small single domain proteins.     

Characterization of a mercury-reducing Bacillus cereus strain isolated from the Pulicat Lake sediments, south east coast of India

Pulicat Lake sediments are often severely polluted with the toxic heavy metal mercury. Several mercury-resistant strains of Bacillus species were isolated from the sediments and all the isolates exhibited broad spectrum resistance (resistance to both organic and inorganic mercuric compounds). Plasmid curing assay showed that all the isolated Bacillus strains carry chromosomally borne mercury resistance. Polymerase chain reaction and southern hybridization analyses using merA and merB3 gene primers/probes showed that five of the isolated Bacillus strains carry sequences similar to known merA and merB3 genes. Results of multiple sequence alignment revealed 99% similarity with merA and merB3 of TnMERI1 (class II transposons). Other mercury resistant Bacillus species lacking homology to these genes were not able to volatilize mercuric chloride, indicating the presence of other modes of resistance to mercuric compounds.     

Root border cells take up and release glucose-C

BACKGROUND AND AIMS: Border cells are released from the root tips of many plant species, and can remain viable in the rhizosphere for 1 week. Whether border cells are capable of controlled glucose exchange with their environment was investigated. METHODS: Border cells were removed from Zea mays L. root tips, and immersed in (14)C-labelled D-glucose. In one experiment, the hexose transport inhibitor, phlorizin, was used to investigate active glucose uptake from a range of glucose concentrations. In another experiment, glucose efflux from border cells was monitored over time. KEY RESULTS: Glucose uptake by the border cells increased with increasing glucose concentration from 0.2 to 20 mm. At 0.2 mm glucose, uptake was mainly active, as evidenced by the approx. 60 % inhibition with phlorizin. At 2 and 20 mm glucose, however, uptake was mainly via diffusion, as phlorizin inhibition was negligible. Glucose efflux increased with time for live border cells in both 2 and 20 mm glucose. There was no clear efflux/time pattern for heat-killed border cells. CONCLUSIONS: Border cells actively take up glucose, and also release it. Under our experimental conditions, glucose uptake and efflux were of similar order of magnitude. In the rhizosphere net glucose exchange will almost certainly depend on local soil conditions.     

Modulation of Rubisco activity in leaves of <Emphasis Type="Italic">Prosopis juliflora</Emphasis> in response to tropical conditions in north India

The success of P. juliflora, an evergreen woody species has been largely attributed to temperature acclimation and stomatal control of photosynthesis under wide range of environmental conditions prevalent in India. We studied the contribution of the enzyme ribulose-1,5 bisphosphate carboxylase/oxygenase (Rubisco) in diurnal and seasonal photosynthesis changes in P. juliflora. The changes observed in photosynthesis under natural conditions could be effected by the growth temperatures, which ranged from 10–30 °C in winter to 30–47 °C in summer. However, the Total Rubisco activity displayed a constant diurnal pattern and showed a maximum at 1200 in all seasons namely spring, summer, monsoon and winter irrespective of the changes in temperature. The Total Rubisco activity from two cohorts of leaves produced in spring and monsoon appeared to be down-regulated differentially at low PPFD during the evening. The in vivo and in vitro measurements of carboxylation efficiency of Rubisco showed wide variation during the day and were correlated with the photosynthesis rate. The light activation of Rubisco showed the acclimation to moderately high temperatures in different seasons except in summer. The exceptionally high temperatures (>45 °C) in summer, though not affecting Total activity, severely inhibited the light activation of Rubisco and also modulated the recovery process for the activation of Rubisco. Our studies suggest that the modulation of Rubisco driven by Rubisco activase and not Rubisco per se was crucial for the diurnal regulation of photosynthesis. NBRI Publication No.: 528     

Selenium supplementation on plasma glutathione peroxidase activity in patients with end-stage chronic renal failure

Patients with chronic renal failure (CRF) usually have a lower than healthy level of selenium (Se) in whole blood and plasma. Plasma glutathione peroxidase (GSH-Px) is synthesized mostly in the kidney. In CRF patients, activity of this enzyme is significantly reduced and its reduction increases with the progress of the disease. The aim of the study was to evaluate the effect of Se supplementation to CRF patients at various stages of the disease on Se concentration in blood components and on plasma GSH-Px activity. The study group comprised 53 CRF patients at various stages of the disease supplemented with Se (200 μg/d for 3 mo as Se-enriched yeast, containing about 70% l-selenomethionine [SeMet]). The control group consisted of 20 healthy subjects. The Se concentration in blood components was measured spectrofluorometrically with 2,3-diaminonaphthalene as a complexing reagent. GSH-Px activity in red cell hemolysates and plasma was assayed by the coupled method with tert-butyl hydroperoxide as a substrate. The Se concentration in whole blood and plasma of CRF patients is significantly lower as compared with healthy subjects, but similar at all stages of the disease. In the patients’ plasma, total protein and albumin levels are also significantly lower than in healthy subjects. Plasma GSH-Px activity in patients is extremely low, and contrary to Se concentration, it decreases linearly with the increasing stage of the illness. Se-supplied patients show an increased Se concentration in all blood components and at all disease stages, whereas plasma GSH-Px activity is enhanced only at the incipient stage of the disease. Se supply has no effect on plasma GSH-Px activity in uremic patients at the end stage of the disease. Total plasma protein and albumin levels did not change after Se supplementation. Our data seem to show that in patients with CRF lower total protein and albumin levels in plasma may be the chief cause of the low blood and plasma Se concentrations. GSH-Px activity decreases along with the kidney impairment. At the end stage of the disease, Se supplementation in the form of Se-enriched yeast has no effect on the increase in plasma GSH-Px activity.     

An Analysis of the Mechanism of the Low-wave Phenomenon of Chlorophyll Fluorescence

The low-wave phenomenon, i.e., the transient drop of yield of modulated chlorophyll fluorescence shortly after application of a pulse of saturating light, was investigated in intact leaves of tobacco and Camellia by measuring fluorescence, CO(2) assimilation and absorption at 830 nm simultaneously. Limitations on linear electron flow, due to low electron acceptor levels that were induced by low CO(2), induced the low waves of chlorophyll fluorescence. Low-wave amplitudes obtained under different CO(2) concentrations and photon-flux densities yielded single-peak curves when plotted as functions of fluorescence parameters such as PhiPS II (quantum yield of Photosystem II) and qN (coefficient of non-photochemical quenching), suggesting that low-wave formation depends on the redox state of the electron transport chain. Low waves paralleled redox changes of P700, the reaction center of Photosystem I (PS I), and an additional electron flow through PS I was detected during the application of saturating pulses that induced low-waves. It is suggested that low waves of chlorophyll fluorescence are induced by increased non-photochemical quenching, as a result of the formation of a trans-thylakoid proton gradient due to cyclic electron flow around PS I.     

Plasmalemmal vacuolar-type H+-ATPase in cancer biology

Vacuolar-type H⁺-adenosine triphosphatase (V-ATPase) is one of the most fundamental enzymes in nature. V-ATPases are responsible for the regulation of proton concentration in the intracellular acidic compartments. It has similar structure with the mitochondrial F₀F₁-ATP synthase (F-ATPase).^† The V-ATPases are composed of multiple subunits and have various physiological functions, including membrane and organelle protein sorting, neurotransmitter uptake, cellular degradative processes, and cytosolic pH regulation. The V-ATPases have been involved in multidrug resistance. Recently, plasma membrane V-ATPases have been involved in regulation of extracellular acidity, essential for cellular invasiveness and proliferation in tumor metastasis. The current knowledge regarding the structure and function of V-ATPase and its role in cancer biology is discussed. F in F₀F₁ ATPase is the coupling energy factor.     

Characteristics of arylsulfatase in Russian sturgeon (Acipenser gueldenstaedti) semen

Spermatozoa of sturgeons (Acipenseriformes), unlike teleosts, possess an acrosome. This paper provides data concerning biochemical characteristics of arylsulfatase (AS), an acrosomal enzyme, found in Russian sturgeon spermatozoa and seminal plasma. The enzymes were purified by a four-step procedure, using n-butanol extraction, ion-exchange chromatography repeated twice and gel filtration. High purity of our enzymes was confirmed by silver staining electrophoresis and an immunological experiment. Kinetic parameters indicated that the purified enzymes belong to arylsulfatase type A. Similarity of the seminal plasma arylsulfatase to the spermatozoan enzyme showed us that arylsulfatase from seminal plasma might originate from damaged spermatozoa. The possible physiological consequences of the presence of arylsulfatase in Russian sturgeon semen are discussed.     

Comparison of response of two C3 species to leaf water relation,proline synthesis,gas exchange and water use under periodic water stress

Water relations, proline content and gas exchange of leaf were investigated under periodic water stress for two C3 plants (eggplant and tomato) in a greenhouse to study comparative adaptive responses. Although both species showed reduced water content of leaf and increased osmolality and proline content under low soil water potential, the recovery capacity after the stress was better in eggplant than tomato. Both species over-accumulated proline under low soil water potential and returned to its initial concentration during the recovery, indicating that proline may act as an osmoprotectant during drought. Proline was directly corresponding with osmolality during stress, and dehydration stress reduced the gas exchange parameters such as transpiration rate (ET), stomatal conductance (GS), and photosynthesis rate (Pn). At the final stage of the experiment both species showed 2.6 and 3.3 times lower Pn and 27 and 19 times lower GS for eggplant and tomato, respectively, as compared to control. But after stress was relieved by rewatering, both plants increased GS for 2 to 3 times and Pn for 4.5 times. Eggplant showed better water use efficiency (WUE) in relation to fruit production under the stress than tomato. Higher biomass allocation at root and fruit parts in eggplant indicated more efficient recovery than that of tomato. These findings inferred that both C3 plants developed internal complementary drought survival mechanism by lowering relative water content, increasing proline, and decreasing stomatal conductance but eggplants withstood the periodic draughting better than tomato, mainly due to its ability to recover from a water stress condition.