Recolonization of methyl bromide sterilized soils under four different field conditions

Summary The course of recovery in biological activity was assessed in the top 5 cm of undisturbed soil cores (29.7 cm diameter, 30 cm deep) that had been fumigated in the laboratory with methyl bromide. The cores were returned to their original pasture and forest sites, two with a moderate and two with a high rainfall, and untreated soils at all sites served as baselines. Sampling took place over 166 days (midsummer to midwinter). Microbial biomass (as measured by fumigation-extraction and substrate-induced respiration procedures) and dehydrogenase activity both recovered rapidly, but remained consistently lower in the fumigated than in untreated samples at both forest sites and at the moister of the two pasture sites. Bacterial numbers also recovered rapidly. Fungal hyphal lengths were, on average over 166 days, 25% lower in the fumigated soils. Levels of mineral N were initially highest in the fumigated soils, but declined with time. Fumigation generally had no detectable effects on the subsequent rates of net N mineralization and little effect on nitrification rates. Fumigation almost totally eliminated protozoa, with one to three species being recovered on day 0; the numbers recovered most rapidly in the moist forest soil and slowly in the dry pasture soil. The recoionization rate of protozoan species was similar in all soils, with species numbers on day 110 being 33 and 34 in the fumigated and untreated soils, respectively. Nematodes were eliminated by fumigation; recolonization was first detected on day 26 but by day 166, nematode numbers were still lower in fumigated than in untreated soils, the abundance being 10 and 62 g^-1 soil and diversity 10 and 31 species, respectively. Overall, the results suggest that protozoan and nematode populations and diversities could provide a useful medium-term ecological index of the recovery in comprehensive soil biological activity following major soil pollution or disturbance.     

Boundary processes between a desert sand dune community and an encroaching suburban landscape

In contrast to the body of work in more mesic habitats, few studies have examined boundary processes between natural and anthropogenic desert landscapes. Our research examined processes occurring at boundaries between a desert sand dune community and an encroaching suburban habitat. We measured responses to an anthropogenic boundary by species from multiple trophic levels, and incorporated measures of habitat suitability, and temporal variation, at multiple spatial scales. At an edge versus core habitat scale the only aeolian sand species that demonstrated an unambiguous negative response to the anthropogenic habitat edges was the flat-tailed horned lizard (Phrynosoma mcallii). Conversely loggerhead shrikes (Lanius ludovicianus) demonstrated a positive response to that edge. At a finer scale, species that exhibited a response to a habitat edge within the first 250 m included the horned lizards along with desert kangaroo rats (Dipodomys deserti). The latter species’ response was confined to 25 m from the edge. For the flat-tailed horned lizard, edge effects were measured up to 150 m from the habitat boundary. Three potential causal hypotheses were explored to explain the edge effect on horned lizards: (1) invasions of exotic ant species reducing potential prey for the lizards; (2) road avoidance and road associated mortalities; and (3) predation from a suite of avian predators whose occurrence and abundance may be augmented by resources available in the suburban habitat. We rejected the exotic ant hypothesis due to the absence of exotic ants within the boundary region, and because native ant species (prey for horned lizards) did not show an edge effect. Our data supported the predation and road mortality hypotheses. Mechanisms for regulating population dynamics of desert species are often “bottom-up,” stochastic processes driven by precipitation. The juxtaposition of an anthropogenic edge appears to have created a shift to a “top-down,” predator-mediated dynamic for these lizards.     

Antioxidant activity in lingonberries (Vaccinium vitis-idaea L.) and its inhibitory effect on activator protein-1, nuclear factor-kappaB, and mitogen-activated protein kinases activation

Lingonberry has been shown to contain high antioxidant activity. Fruits from different cultivars of lingonberry (Vaccinium vitis-idaea L.) were evaluated for fruit quality, antioxidant activity, and anthocyanin and phenolic contents. The fruit soluble solids, titratable acids, antioxidant capacity, and anthocyanin and phenolic contents varied with cultivars. Lingonberries contain potent free radical scavenging activities for DPPH*, ROO*, *OH, and O2*- radicals. Pretreatment of JB6 P+ mouse epidermal cells with lingonberry extracts produced a dose-dependent inhibition on the activation of activator protein-1 (AP-1) and nuclear factor-kappaB (NF-kappaB) induced by either 12-O-tetradecanoylphorbol-13-acetate (TPA) or ultraviolet-B (UVB). Lingonberry extract blocked UVB-induced phosphorylation of the mitogen-activated protein kinase (MAPK) signaling members ERK1, ERK2, p38, and MEK1/2 but not JNK. Lingonberry extract also prevented TPA-induced phosphorylation of ERK1, ERK2, and MEK1/2. Results of soft agar assays indicated that lingonberry extract suppressed TPA-induced neoplastic transformation of JB6 P(+) cells in a dose-dependent manner. Lingonberry extract also induced the apoptosis of human leukemia HL-60 cells in a dose-independent manner. These results suggest that ERK1, ERK2, and MEK1/2 may be the primary targets of lingonberry that result in suppression of AP-1, NF-kappaB, and neoplastic transformation in JB6 P(+) cells and causes cancer cell death by an apoptotic mechanism in human leukemia HL-60 cells.     

Postmortem oxygen consumption by mitochondria and its effects on myoglobin form and stability

The objective of this study was to assess the morphological integrity and functional potential of mitochondria from postmortem bovine cardiac muscle and evaluate mitochondrial interactions with myoglobin (Mb) in vitro. Electron microscopy revealed that mitochondria maintained structural integrity at 2 h postmortem; prolonged storage resulted in swelling and breakage. At 2 h, 96 h, and 60 days postmortem, the mitochondrial state III oxygen consumption rate (OCR) and respiratory control ratio decreased with time at pH 7.2 and 5.6 (p < 0.05). Mitochondria isolated at 60 days did not exhibit ADP-induced transitions from state IV to state III oxygen consumption. Tissue oxygen consumption also decreased with time postmortem (p < 0.05). Mitochondrial oxygen consumption was inhibited by decreased pH in vitro (p < 0.05). In a closed system, mitochondrial respiration resulted in decreased oxygen partial pressure (pO(2)) and enhanced conversion of oxymyoglobin (OxyMb) to deoxymyoglobin (DeoMb) or metmyoglobin (MetMb). Greater mitochondrial densities caused rapid decreases in pO(2) and favored DeoMb formation at pH 7.2 in closed systems (p < 0.05); there was no effect on MetMb formation (p > 0.05). MetMb formation was inversely proportional to mitochondrial density at pH 5.6 in closed systems. Mitochondrial respiration in open systems resulted in greater MetMb and DeoMb formation at pH 5.6 and pH 7.2, respectively, vs controls (p < 0.05). The greatest MetMb formation was observed with a mitochondrial density of 0.5 mg/mL at both pH values in open systems. Mitochondrial respiration facilitated a shift in Mb form from OxyMb to DeoMb or MetMb, and this was dependent on pH, oxygen availability, and mitochondrial density.     

Carbon mineralization in an organic soil, with and without added grass litter, from a high-CO2 environment at a carbon dioxide spring

Both CO₂-C production and the decomposability of grass leaf litter in a gley soil from a naturally occurring CO₂ spring were previously shown to be influenced by the atmospheric CO₂ concentrations under which the soil and litter were sampled. Here we investigate C mineralization in an organic soil from very high CO₂ environments (range 1220-3900 μl l⁻¹) at the same spring, and the effect of added leaf litter on CO₂-C production. Carbon mineralization in the organic soil was unusual in two respects: (1) the proportion of labile components was very high, with more than 11% of the initial soil C being metabolized to CO₂-C after 56 d at 25 °C; (2) rates of CO₂-C production in autumn samples increased on incubation, after an initial decline. Decomposition was initially more rapid in C3 Holcus lanatus (Yorkshire fog) than in C4 Pennisetum clandestinum (kikuyu) litter, but differed little in samples from different atmospheric CO₂ concentrations. Overall, the effects of environmental variables on estimates of litter decomposability in the organic soil were similar to, although much less marked than, those in the gley soil. Results suggest that organic components in the organic soil were metabolized at least as readily as those of added litter during the later stages of the 56-d incubation.     

Characterization of a salt-independent pectin methylesterase purified from valencia orange peel

The pectin methylesterase (PME; EC 3.1.1.11) present in a commercial orange peel enzyme preparation was characterized to establish its identity among the multiple PME isozymes present in Valencia orange (Citrus sinensis L.) peel. We show the commercial enzyme corresponds to the major peak 2 PME previously separated by heparin-Sepharose chromatography (Cameron et al., J. Food Sci. 1998, 63, 253). Both PMEs have comparable elution profiles on cation-exchange and hydrophobic-interaction perfusion chromatography columns, molecular weights (ca. 34 kDa) and pI (pH 9.2), and biochemical properties, including a broad pH activity range and activity in the absence of added cations. An identical partial amino terminal peptide sequence was also obtained for the PMEs, which further demonstrated a structural identity with other plant PMEs. The biochemical and structural properties readily distinguish this Valencia orange PME from salt-dependent isozymes and further suggest that it is an ortholog to the salt-independent fruit-specific isozyme of tomato. This work provides a well-defined, enzymatically homogeneous, salt-independent (type 1) plant PME isozyme that is suitable for studying details of the enzyme's mode of action and for use in modifying methylester patterns for studying the structure-functional property relationships in pectin.     

Effects of the nitrification inhibitor dicyandiamide on potassium, magnesium and calcium leaching in grazed grassland

Abstract. Leaching of calcium (Ca), potassium (K) and magnesium (Mg) from urine patches in grazed grassland represents a significant loss of valuable nutrients. We studied the effect on cation loss of treating the soil with a nitrification inhibitor, dicyandiamide (DCD), which was used to reduce nitrate loss by leaching. The soil was a free-draining Lismore stony silt loam (Udic Haplustept loamy skeletal) and the pasture was a mixture of perennial ryegrass ( Lolium perenne ) and white clover ( Trifolium repens ). The treatment of the soil with DCD reduced Ca²⁺ leaching by the equivalent of 50%, from 213 to 107 kg Ca ha⁻¹ yr⁻¹ on a field scale. Potassium leaching was reduced by 65%, from 48 to 17 kg K ha⁻¹ yr⁻¹. Magnesium leaching was reduced by 52%, from 17 to 8 kg Mg ha⁻¹ yr⁻¹. We postulate that the reduced leaching loss of these cations was due to the decreased leaching loss of nitrate under the urine patches, and follows from their reduced requirement as counter ions in the drainage water. The treatment of grazed grassland with DCD thus not only decreases nitrate leaching and nitrous oxide emissions as reported previously, but also decreases the leaching loss of cation nutrients such as Ca²⁺, K⁺ and Mg²⁺.     

Separation and characterization of a salt-dependent pectin methylesterase from Citrus sinensis var. Valencia fruit tissue

A pectin methylesterase (PME) from sweet orange fruit rag tissue, which does not destabilize citrus juice cloud, has been characterized. It is a salt-dependent PME (type II) and exhibits optimal activity between 0.1 and 0.2 M NaCl at pH 7.5. The pH optimum shifted to a more alkaline range as the salt molarity decreased (pH 8.5-9.5 at 50 mM NaCl). It has an apparent molecular mass of 32.4 kDa as determined by gel filtration chromatography, an apparent molecular mass of 33.5 kDa as determined by denaturing electrophoresis, and a pI of 10.1 and exhibits a single activity band after isoelectric focusing (IEF). It has a K(m) of 0.0487 mg/mL and a V(max) of 4.2378 nkat/mg of protein on 59% DE citrus pectin. Deblocking the N-terminus revealed a partial peptide composed of SVTPNV. De-esterification of non-calcium-sensitive pectin by 6.5% increased the calcium-sensitive pectin ratio (CSPR) from 0.045 +/- 0.011 to 0.829 +/- 0.033 but had little, if any, effect on pectin molecular weight. These properties indicate this enzyme will be useful for studying the PME mode of action as it relates to juice cloud destabilization.     

Comparison of iron bioavailability from 15 rice genotypes: studies using an in vitro digestion/caco-2 cell culture model

An in vitro digestion/Caco-2 model was used to compare iron bioavailability from 15 selected Fe-dense and normal genotypes of unpolished rice from the International Rice Research Institute. Iron uptake was determined using Caco-2 cell ferritin formation in response to exposure to a digest of the cooked rice. Iron bioavailabilities from all rice genotypes were ranked as a percent relative to a control variety (Nishiki). Iron concentration in the rice samples ranged from 14 to 39 microg/g. No correlation was observed between Fe uptake and grain-Fe concentration. Furthermore, phytic acid levels were not correlated with Fe bioavailability. Genotypes with low Fe bioavailability (Tong Lan Mo Mi, Zuchein, Heibao, and Xua Bue Nuo) were noticeably more brown to purple in color. The results suggest that certain unknown compounds related to rice grain color may be a major factor limiting Fe bioavailability from unpolished rice.     

Enzymatic-spectrophotometric method for determination of cholinesterase activity in whole blood: collaborative study

Ten collaborating laboratories assayed 4 blind duplicate pairs of whole bovine blood for cholinesterase activity. The 4 sample pairs ranged from normal (100%) to severely organo-phosphorus-inhibited (less than 10%) activity. Collaborators also received commercially available human lyophillized serum as an external control and a chromate solution to evaluate spectrophotometer performance. The Ellman kinetic assay was performed on a 1:1000 dilution of the whole blood in pH 8.0 phosphate buffer. The method monitors the increase in absorbance at 412 nm caused by formation of 5-thio-2-nitrobenzoic acid (yellow reaction product). Repeatability standard deviations (RSDr) ranged from 4.30 to 14.2%; reproducibility standard deviations (RSDR) ranged from 6.99 to 19.3%. The lower limit of detection was estimated to be 0.10 mumole/mL/min. The method has been approved interim official first action by AOAC.