Sinks and sources of methylmercury in a boreal catchment

A simple, catchment-scale, cascade model was used toassess the importance of sinks and sources ofmethylmercury (MeHg) in a boreal catchment thatcontains a forested upland, a lowland peatland and asmall lake. The three compartment model was run usingrealistic flow rates and atmospheric loading of MeHg,and the model was constrained by observedconcentrations of MeHg in each compartment. Assumingno internal sinks and sources of MeHg, modelledcatchment yields showed reasonable agreement withfield observation, but the predicted internal MeHgconcentrations in each compartment were implausible. Only when sources and sinks of MeHg are added to thethree compartments do MeHg-pool concentrations fallinto the range of those measured in the field. Tomaintain both catchment-scale and compartment-scalecontinuity, the upland and peatland were net sourcesof MeHg (0.0007 and 0.1065 mg ha^-1 d^-1respectively), and the lake a net sink (-0.2215 mgha^-1 d^-1). These source/sink rates are 1.73,259 and -539 times the input of MeHg via wetprecipitation input for the modelled ice-free season. Sensitivity analysis revealed that the volume ofrunoff delivered to the peatland by the upland area,peatland size and porewater MeHg concentration in thepeatland are important controls on catchment MeHgyield, and that contemporary atmospheric deposition ofMeHg is insignificant compared to the sources of MeHgwithin the catchment.     

Diurnal activity in the Samoan flying fox,Pteropus samoensis

Speakman and co-workers suggested the diurnal Samoan flying fox, Pteropus samoensis, may be at risk of hyperthermia when flying during the day, particularly at high levels of insolation. We monitored activity of this bat and climate simultaneously at two different sites and four times of year in American Samoa. Flight activity varied significantly with time of day, between days, study sites and seasons. Out of the six data sets collected, the four with the highest mean levels of insolation showed a significant decrease in bat numbers with increasing temperature and sunlight. When each individual activity count was directly compared to the predictions of Speakman and co-workers'' biophysical model, 85 to 95% of bat flight activity was found to be in conditions the model suggested would not pose a risk of hyperthermia. This supports the suggestion that in extreme conditions the animals would not fly as they risked overheating. The 5 to 15% of counts in which animals were seen to fly in conditions the model predicted they should not may be explained by erroneous assumptions underlying the model predictions.     

Functional and structural conservation in the mechanosensitive channel MscL implicates elements crucial for mechanosensation

mscL encodes a channel in Escherichia coli that is opened by membrane stretch force, probably serving as an osmotic gauge. Sequences more or less similar to mscL are found in other bacteria, but the degree of conserved function has been unclear. We subcloned and expressed these putative homologues in E . coli and examined their products under patch clamp. Here, we show that each indeed encodes a conserved mechanosensitive channel activity, consistent with the interpretation that this is an important and primary function of the protein in a wide range of bacteria. Although similar, channels of different bacteria differ in kinetics and their degree of mechanosensitivity. Comparison of the primary sequence of these proteins reveals two highly conserved regions, corresponding to domains previously shown to be important for the function of the wild-type E . coli channel, and a C-terminal region that is not conserved in all species. This structural conservation is providing insight into regions of this molecule that are vital to its role as a mechanosensitive channel and may have broader implications for the understanding of other mechanosensitive systems.     

Rapid, simple and sensitive high-performance liquid chromatographic method for detection and determination of acyclovir in human plasma and its use in bioavailability studies

A rapid, simple and sensitive reversed-phase high-performance liquid chromatographic (HPLC) method has been developed for the measurement of acyclovir concentrations in human plasma and its use in bioavailability studies is evaluated. Unchanged acyclovir has been quantified without the introduction of an internal standard using the present method. Human plasma proteins were selectively precipitated by the addition of 7% perchloric acid to spiked plasma samples or to the plasma samples obtained after acyclovir administration to human volunteers and the mixture was spun at 1000 g for 10 min. The supernatant was directly injected into a Novaflex C₁₈ column and detected at 254 nm. The mobile phase consisted of octane sulfonic acid buffer (pH 2.5) and methanol (92:08). The limit of quantitation for acyclovir in plasma was 20 ng/ml, which enabled the determination of the area under the curve (AUC) more precisely, that is, it is much closer to its extrapolated value. The present method has been successfully applied to samples from bioavailability studies.     

Stability and change in genetic and environmental influences on hand-grip strength in older male twins.

The aim of this study was to investigate aging-related changes in the contribution of genetic and environmental influences to hand-grip strength in late adulthood. Subjects in this study are 152 intact twin pairs (77 monozygotic and 75 dizygotic pairs) from the National Heart, Lung, and Blood Institute Twin Study assessed repeatedly for hand-grip strength at mean ages of 63 and 73 yr. Structural equation genetic modeling was used to investigate stability and change in the genetic and environmental components of variance of hand-grip strength in late adulthood. Average decline in strength over the 10 yr of follow-up was -1.05+/-6.8 (SD) kg and was highly significant (P = 0.003). The test-retest correlation between baseline and follow-up grip strength was 0.62 (P<0.001). Bivariate genetic modeling found significant genetic and shared environmental stability in hand-grip strength over the 10 yr of follow-up, with genetic and shared environmental influences accounting for 35 and 48%, respectively, of the test-retest phenotypic correlation. We conclude from these results that stability in hand-grip strength in late adulthood is due primarily to continuity of genetic and familial influences.     

Genomic factors responsible for abnormal morphology of pollen tubes in the interspecific cross Nicotiana tabacum ×N. rustica

Nicotiana tabacum shows unilateral pollen-pistil incongruity with N. rustica. If N. tabacum is pollinated with N. rustica, growth of the pollen tube is arrested in the middle of the style, and abundant callose deposition, tube swelling and tube winding are observed. An attempt was made to clarify the genomic factors responsible for this pollen-pistil incongruity. N. tabacum was pollinated with N. paniculata or N. undulata, progenitors of amphidiploid N. rustica. When pollinated with N. undulata, growth of the pollen tube was arrested in the middle of the style and showed abnormal morphology similar to that with N. rustica, but when pollinated with N. paniculata the pollen tube reached near the base of the style and was almost normal in appearance. These observations suggest that the factors responsible for the pollen tube abnormality of N. rustica are derived from the N. undulata genome.We also used N. sylvestris, N. glutinosa and N. otophora as pistilar parents and N. rustica or its progenitors as pollen parents to examine the genomic factors of the pistilate parents. The pollen tube features of these three species in the pistils of N. sylvestris were similar to those in the pistil of N. tabacum. Received: 25 October 1999 / Revision accepted: 2 February 2000     

Random Amplified Polymorphic DNA Variation among and within Selected Ixora (Rubiaceae) Populations and Mutants

Random amplified polymorphic DNA (RAPD) analysis was used tostudy variation among and within selectedIxora (Rubiaceae) populationsand mutants. Six populations of I. congesta yielded identicalbanding patterns suggesting genetic uniformity of this species.However, six populations of I. coccinea varieties (three red-flowered,two yellow-flowered and one red-flowered wild-type) exhibitedinfraspecific differences in RAPD profiles. Small and largeleaves of an atavistic mutant cultivar of I. coccinea were alsosubjected to RAPD analysis. An extra band was amplified in thelarge leaves that was absent in small leaves, suggesting thatthe phenotypic alteration in this taxon is due to genetic mutationrather than epigenetic changes. Similarly, an extra band wasdetected in the white sectors of I. Variegated compared to thegreen sectors, suggesting that the shoot apical meristems ofthis cultivar exist as a genetic chimera. DNA gel blot hybridizationwas performed to confirm the specificities of selected bands.Our study indicates that differences among individuals of variouspopulations and mutants may be detected using RAPD markers.Copyright 1999 Annals of Botany Company Ixora L., variegated variety, RAPD fingerprinting, DNA gel blot, intraspecific genetic similarity, atavistic mutant.     

Non-linear control of continuous bioreactors

Control of bioreactors has achieved importance in the recent years. This may be due to the fact that they are difficult to control which may be attributed to its nonlinear dynamic behavior. The model parameters of the bioreactor also vary in an unpredictable manner. The complexity of the biochemical processes inhibits the accurate modeling and also the lack of suitable sensors make the process state difficult to characterize. Considerable emphasis has been placed on the control of fed-batch fermentors because of their prevalence in industries. However, when production of biomass is to be optimized, continuous operation is desirable. Several procedures are available for the nonlinear control of processes, viz., differential geometric approach, internal model control approach, reference synthesis technique, predictive control design, etc., but the major disadvantage of these approaches is the computational time required to perform the prediction optimization. In this study, a nonlinear controller based on a polynomial discrete time model (NARMAX) is evaluated for its performance on a fermentor. It can be shown that a nonlinear self-tuning controller based on NARMAX model can be extended to the control of fermentors. The response is smooth for both load and setpoint changes even when process parameters are assumed to be zero and uncertainty in parameters are present and in the presence of controller constraints. The control action can be made more or less robust by changing the design parameters appropriately. Therefore, nonlinear self-tuning controller is suitable for control of industrial processes.