Incorporation Of 14C-leucine Research Articles

Plant biomass, soil microbial community structure and nitrogen cycling under different organic amendment regimes; a 15N tracer-based approach

Sustainable agriculture requires nutrient management options that lead to a profitable crop yield with relatively low nitrogen (N) losses to the environment. We studied whether the addition of contrasting organic amendments together with inorganic fertilizer can promote both requirements simultaneously. In particular we studied how the chemical composition of organic amendments affects the biomass, activity and composition of the soil microbial community and subsequently carbon (C) and N mineralization, microbial N immobilization and plant growth and nutrient uptake.In a pot experiment, Brussels sprouts (Brassica oleracea, cvar. Cyrus) were grown on arable soil, mixed with 15N-labelled mineral fertilizer and different kinds of organic amendments (cattle manure solid fraction, maize silage, lucerne silage, wheat straw) differing in C:N ratio and lignin content. After 69 and 132days, destructive sampling took place to assess the effects of the different treatments on soil microbial biomass (microscopic measurements), microbial community composition (phospholipid fatty acid profiles), soil microbial activity (14C-leucine incorporation), C and N mineralization, plant biomass and 15N retrieval in soil pools, microbial biomass and plant biomass.Addition of organic amendments increased soil microbial biomass, activity and fungal/bacterial ratio and created distinct microbial community compositions, whereby high C:N ratio organic amendments had stronger effects compared to low C:N ratio amendments. Structural equation modelling showed that higher values of soil microbial activity were associated with increased N mineralization rates, increased plant biomass and plant 15N uptake, while microbial 15N immobilization was associated with soil microbial community composition.The outcomes of this study highlight the importance of the chemical composition and the amount of the organic amendments for finding a balance between plant N uptake, microbial N immobilization and N retention in labile and stable soil pools through the effects on the composition and activity of the soil microbial community. The results provide insights that can be used in designing combined input (nutrient and organic) nutrient management strategies for a more sustainable agriculture.

Nonsecreted cytoplasmic alpha-fetoprotein: a newly discovered role in intracellular signaling and regulation. An update and commentary.

The concept of a non-secreted cytoplasmic-bound form of alpha-fetoprotein is not a new notion in AFP biological activities. Cytoplasmic AFP (CyAFP) is a long known but forgotten protein in search of a function other than a histochemical biomarker. In this report, CyAFP is presented as an "old" protein with a newly described intracellular function. In 1976, CyAFP was shown to be a product of hepatoma cells utilizing 14Cleucine incorporation and demonstrated by autoradiographic procedures. The synthesis of CyAFP without secretion was demonstrated to occur in both malignant and non-malignant cells encompassing hepatomas, ascite fluid cells, immature rodent uterus, MCF-7 breast cancers, and cytosols from human breast cancer patients. Using computer protein matching and alignments in AFP versus members of the nuclear receptor superfamily, a consecutive series of leucine zipper (heptad) repeats in AFP was previously reported, suggesting the possibility for protein-to-protein interactions. The potential for heptad heterodimerization between protein-binding partners provided the rationale for proposing that CyAFP might have the capability to form molecular hetero-complexes with cytoplasmic based transcription factors. More recent investigations have now provided experimental evidence that CyAFP is capable of colocalizing and interacting with transcription-associated factors. Such proteins can modulate intracellular signaling leading to regulation of transcription factors and initiation of growth in human cancer cells. Although circulating serum AFP is known as a growth-enhancing factor during development, cytoplasmic AFP has a lethal role in the oncogenesis, growth, and metastasis of adult liver cancer.

Contrasting Effects of Singlet Oxygen and Hydrogen Peroxide on Bacterial Community Composition in a Humic Lake

Light excitation of humic matter generates reactive oxygen species (ROS) in surface waters of aquatic ecosystems. Abundant ROS generated in humic matter rich lakes include singlet oxygen (1O2) and hydrogen peroxide (H2O2). Because these ROS differ in half-life time and toxicity, we compared their effects on microbial activity (14C-Leucine incorporation) and bacterial community composition (BCC) in surface waters of humic Lake Grosse Fuchskuhle (North-eastern Germany). For this purpose, experiments with water samples collected from the lake were conducted in July 2006, September 2008 and August 2009. Artificially increased 1O2 and H2O2 concentrations inhibited microbial activity in water samples to a similar extent, but the effect of the respective ROS on BCC varied strongly. BCC analysis by 16S rRNA gene clone libraries and RT-PCR DGGE revealed ROS specific changes in relative abundance and activity of major bacterial groups and composition of dominating phylotypes. These changes were consistent in the three experiments performed in different years. The relative abundance of Polynucleobacter necessarius, Limnohabitans-related phylotypes (Betaproteobacteria), and Novosphingobium acidiphilum (Alphaproteobacteria) increased or was not affected by photo-sensitized 1O2 exposure, but decreased after H2O2 exposure. The opposite pattern was found for Actinobacteria of the freshwater AcI-B cluster which were highly sensitive to 1O2 but not to H2O2 exposure. Furthermore, group-specific RT-PCR DGGE analysis revealed that particle-attached P. necessarius and Limnohabitans-related phylotypes exhibit higher resistance to 1O2 exposure compared to free-living populations. These results imply that 1O2 acts as a factor in niche separation of closely affiliated Polynucleobacter and Limnohabitans-related phylotypes. Consequently, oxidative stress caused by photochemical ROS generation should be regarded as an environmental variable determining abundance, activity, and phylotype composition of environmentally relevant bacterial groups, in particular in illuminated and humic matter rich waters.

Metacommunity dynamics of bacteria in an arctic lake: the impact of species sorting and mass effects on bacterial production and biogeography

To understand mechanisms linking ecosystem processes and microbial diversity in freshwater ecosystems, bacterial productivity and the metacommunity dynamics of species sorting and mass effects were investigated in an 18 ha headwater lake in northern Alaska. On most sampling dates, the phylogenetic composition of bacterial communities in inflowing streams (inlets) was strikingly different than that in the lake and the outflowing stream (outlet) (16S DGGE fingerprinting), demonstrating the shift in composition that occurs as these communities transit the lake. Outlet and downstream communities were also more productive than inlet and upstream communities (14C-leucine incorporation). Inlet bacteria transplanted to the outlet stream in dialysis bags were equally or less productive than control bacteria, suggesting that the inlet bacteria are capable of growing under lake conditions, but do not remain abundant because of species sorting in the lake. Outlet bacteria (representative of epilimnetic bacteria) transplanted to the inlet stream were less productive than control bacteria, suggesting that lake bacteria are not as well adapted to growing under inlet conditions. Based on water density, inlet stream water and bacteria generally entered the lake at the base of the epilimnion. However, during low to medium flow in the inlet stream the residence time of the epilimnion was too long relative to bacterial doubling times for these allochthonous bacteria to have a mass effect on the composition of outlet bacteria. The highest community similarity between inlet and outlet bacteria was detected after a large rain event in 2003, with over 61% similarity (average non-storm similarities were 39 ± 8%). While mass effects may be important during large storm events, species sorting appears to be the predominant mechanism structuring bacterial communities within the lake, leading to the assembly of a lake community that has lost some ability to function in stream habitats.

Chronic hypobaric hypoxia mediated skeletal muscle atrophy: role of ubiquitin–proteasome pathway and calpains

The most frequently reported symptom of exposure to high altitude is loss of body mass and decreased performance which has been attributed to altered protein metabolism affecting skeletal muscles mass. The present study explores the mechanism of chronic hypobaric hypoxia mediated skeletal muscle wasting by evaluating changes in protein turnover and various proteolytic pathways. Male Sprague-Dawley rats weighing about 200 g were exposed to hypobaric hypoxia (7,620 m) for different durations of exposure. Physical performance of rats was measured by treadmill running experiments. Protein synthesis, protein degradation rates were determined by (14)C-Leucine incorporation and tyrosine release, respectively. Chymotrypsin-like enzyme activity of the ubiquitin-proteasome pathway and calpains were studied fluorimetrically as well as using western blots. Declined physical performance by more than 20%, in terms of time taken in exhaustion on treadmill, following chronic hypobaric hypoxia was observed. Compared to 1.5-fold increase in protein synthesis, the increase in protein degradation was much higher (five-folds), which consequently resulted in skeletal muscle mass loss. Myofibrillar protein level declined from 46.79 ± 1.49 mg/g tissue at sea level to 37.36 ± 1.153 (P < 0.05) at high altitude. However, the reduction in sarcoplasmic proteins was less as compared to myofibrillar protein. Upregulation of Ub-proteasome pathway (five-fold over control) and calpains (three-fold) has been found to be important factors for the enhanced protein degradation rate. The study provided strong evidences suggesting that elevated protein turnover rate lead to skeletal muscle atrophy under chronic hypobaric hypoxia via ubiquitin-proteasome pathway and calpains.

Prokaryotic community dynamics in the sedimentary microenvironment of the demosponge Tentorium semisuberites from deep Arctic waters

The sedimentary microenvironment of a sessile epibenthic deep-sea species, the small demosponge Tentorium semisuberites, has been investigated to determine its effect on the distribu- tion, physiology and community structure of benthic bacteria and archaea. The upper sediment lay- ers (0 to 2 cm) in the immediate sponge vicinity were characterized by an increased bacterial coloni- sation with cell abundances on average 3 times higher than those in reference sediments. Similar results were obtained for bacterial secondary production, measured by simultaneous incorporation of the radioactive-labeled substrates 3 H-thymidine and 14 C-leucine. Our data show a high heterogene- ity of deep-sea sediments with a pronounced patchy distribution of particulate organic carbon (POC), and a significant enrichment of POC in the sediments next to T. semisuberites. Cell-specific 3 H-thymidine and 14 C-leucine incorporation rates indicate that the quality rather than the quantity of POC around sponges may lead to the observed increase in cell abundances and protein synthesis. Terminal restriction fragment length polymorphism (T-RFLP) analysis revealed that the sponges sup- port a specific benthic bacterial and archaeal community with some unique OTUs (Operational Tax- onomic Units), while other OTUs were entirely missing from its surrounding microenvironment. Our data indicate that the small demosponge T. semisuberites causes highly productive patches as hot spots of biochemical cycling, potentially increasing habitat heterogeneity in deep-sea sediments.

Bacterial carbon utilization in vertical subsurface flow constructed wetlands

Subsurface vertical flow constructed wetlands with intermittent loading are considered as state of the art and can comply with stringent effluent requirements. It is usually assumed that microbial activity in the filter body of constructed wetlands, responsible for the removal of carbon and nitrogen, relies mainly on bacterially mediated transformations. However, little quantitative information is available on the distribution of bacterial biomass and production in the “black-box” constructed wetland. The spatial distribution of bacterial carbon utilization, based on bacterial 14C-leucine incorporation measurements, was investigated for the filter body of planted and unplanted indoor pilot-scale constructed wetlands, as well as for a planted outdoor constructed wetland. A simple mass-balance approach was applied to explain the bacterially catalysed organic matter degradation in this system by comparing estimated bacterial carbon utilization rates with simultaneously measured carbon reduction values. The pilot-scale constructed wetlands proved to be a suitable model system for investigating microbial carbon utilization in constructed wetlands. Under an ideal operating mode, the bulk of bacterial productivity occurred within the first 10 cm of the filter body. Plants seemed to have no significant influence on productivity and biomass of bacteria, as well as on wastewater total organic carbon removal.

A time series of prokaryote secondary production in the oxygen minimum zone of the Humboldt current system, off central Chile

Because the marine picoplanktonic communities are made up of phylogenetically different microbial groups, the re-evaluation of key processes such as bacterial secondary production (BSP) has become an important contemporary issue. The difficulty of differentiating the metabolic processes of Bacteria from the rest of the microorganisms in the water column (i.e., Archaea and Eukarya) has made it difficult to estimate in situ BSP. This work presents the seasonal variability of the prokaryote secondary production (PSP) measured by the incorporation of 14C-leucine in the oxygen minimum zone (OMZ) off central-southern Chile. The BSP and potential archaeal secondary production (PASP) were determined through the combined use of 14C-leucine and N 1-guanyl-1, 7-diaminoheptane (GC 7), an efficient inhibitor of archaeal and eukaryote cell growth. BSP accounted for the majority of the PSP (total average, 59 ± 7.5%); maximum values were ∼600 μg C m −3 h −1 and, on several dates, BSP represented 100% of the PSP. Similarly, PASP was also an important fraction of the PSP (total average, 42.4 ± 8.5%), although with levels that ranged from not detectable (on given dates) to levels that represented up to ∼97% of PSP (winter 2003). Our results showed that both Bacteria and Archaea accounted for almost equal portions of the prokaryote heterotrophic metabolism in the OMZ, and that PASP is notoriously enhanced through temporal pulses of heterotrophy. This indicates that, at least in marine systems with high abundance of Archaea (e.g., mesopelagic realm), the secondary production obtained through methods measuring the uptake of radiolabeled substrates should be considered as PSP and not as BSP. If the latter is the target measurement, then the use of an inhibitor of both archaeal and eukaryote cell growth such as GC 7 is recommended.

Copper effects on bacterial activity of estuarine silty sediments

Bacteria of silty estuarine sediments were spiked with copper to 200 μg Cu g −1 dry weight sediment in order to assess the impact of copper on bacterial degradation of organic matter and on bacterial biomass production. Bacterial density was determined by direct counting under epifluorescence microscopy and bacterial production by the incorporation of 3H-Leucine. Leucine turnover rate was evaluated by 14C-leucine incorporation and ectoenzymatic activities were estimated as the hydrolysis rate of model substrates for β-glucosidase and leucine-aminopeptidase. The presence of added copper in the microcosms elicited, after 21 days of incubation, generalised anoxia and a decrease in organic matter content. The non-eroded surface of the copper-spiked sediment showed, when compared to the control, a decrease in bacterial abundance and significant lower levels of bacterial production and of leucine turnover rate. Bacterial production and leucine turnover rate decreased to 1.4% and 13% of the control values, respectively. Ectoenzymatic activities were also negatively affected but by smaller factors. After erosion by the water current in laboratory flume conditions, the eroded surface of the control sediment showed a generalised decline in all bacterial activities. The erosion of the copper-spiked sediment showed, however, two types of responses with respect to bacterial activities at the exposed surface: positive responses of bacterial production and leucine turnover rate contrasting with slight negative responses of ectoenzymatic activities. The effects of experimental erosion in the suspended cells were also different in the control and in the copper-spiked sediment. Bacterial cells in the control microcosm exhibited, when compared to the non-eroded sediment cells, decreases in all activities after the 6-h suspension. The response of the average suspended copper-spiked sediment cell differed from the control by a less sharp decrease in ectoenzymatic activities and, mainly, by the great intensification of bacterial biomass production and leucine turnover rate. We conclude that the bacterial community of silty estuarine sediments seems to withstand considerable concentrations of copper at the cost of reduced bacterial organic matter degradation and of the almost halting of bacterial production. The toxic effects elicited by copper on protein and carbohydrate degradation were not rapidly repaired by erosion and oxygenation of the sediment cells but, in contrast, bacterial biomass production and leucine turnover were rapidly and efficiently reactivated.

Solar UV radiation modulates daily production and DNA damage of marine bacterioplankton from a productive upwelling zone (36°S), Chile

In upwelling ecosystems, such as the Humboldt Current system (HCS) off Concepción, the effects of solar radiation on bacterioplankton incorporation rates have been related to previous light acclimation and responses to irradiance. In this paper, we study the daily effect of Photosynthetic Active Radiation (PAR, 400–700 nm) and ultraviolet radiation UVR (280–400 nm) on bacterial secondary production (BSP). We also considered the DNA damage–repair response to solar radiation stress by the induction of cyclobutane pyrimidine dimers (CPDs). Experiments were conducted with natural bacterioplankton assemblages (0.2–0.7 μm) collected off Concepción (36°S), during the austral Spring, October–November, 2004. Surface (0.5 m) and subsurface (80 m) bacterioplankton samples were exposed to different solar radiation treatments for 5–20 h. BSP was estimated by 14C-leucine and 3H-thymidine incorporation at several time intervals, whereas CPDs accumulation was assessed using immunoassay techniques. During high irradiance periods, BSP was mainly affected by PAR in both surface and subsurface assemblages and, to a lesser, but significant (Tukey < 0.05) extent, by UV-A (320–400 nm) and UV-B (280–320 nm) radiation. Maximum inhibition of BSP in surface waters was 78%; growth rates ( μ) and bacterial growth efficiency (BGE) were also low (78% and 66% respectively). Subsurface water assemblages, on the contrary, showed a ∼ 25 fold enhancement of BSP, μ, and BGE. Both types of assemblages had a rapid CPDs accumulation (maximum 60 CPDs Mb − 1 ) during high irradiance periods. Recovery of BSP inhibition and DNA damage in surface bacteria was total after sunset and after the night incubation period, resembling pre-exposure levels. Despite subsurface BSP enhancement during day–night exposure, residual DNA damage was detected at the end of the experiment (20 CPDs Mb − 1 ) suggesting a chronic DNA damage. Our results represent the worst case scenario (i.e., assemblages receiving surface irradiances as may occur in this upwelling zone) and indicate that surface and subsurface bacterial assemblages in the HCS are both highly sensitive to solar irradiance. However, they showed different responses, with surface bacteria having more effective photorepair mechanisms, and sustaining higher BSP than subsurface assemblages.

Action of fentrazamide on protein metabolism and cell division in plants

Fentrazamide [4-(2-chlorophenyl)-N-cyclohexyl-N-ethyl-4,5-dihydro-5-oxo-1H-tetrazole-1-carboxamide] is a new tetrazolinone class herbicide. Fentrazamide at and above 1 μM showed marked phytotoxic activity on the growth of early watergrass 15 days after treatment (95% reduction in the total dry weight at 100 μM), but showed less toxicity to rice. Dry weight of early watergrass and rice was reduced by 50% with 1.8 μM and 95.1 μM of fentrazamide, respectively. The pattern of soluble amino acid composition in early watergrass treated with fentrazamide was more similar to that treated with cafenstrole (an inhibitor of fatty acid elongation) than that with mefenacet (an inhibitor of cell division). The inhibition of fatty acid elongation in microsomal fractions of early watergrass by fentrazamide was comparable to that by cafenstrole, but inhibition by fentrazamide was 28–38% even at the highest concentration (2 μM). The cell division of leek roots was not affected by 100 μM of fentrazamide. Cycloheximide (an inhibitor of protein biosynthesis) at 10 μM showed a marked inhibitory effect on the incorporation of 14C-leucine into protein, but fentrazamide showed less inhibitory effect even at 100 μM; however, fentrazamide at and above 10 μM markedly reduced the soluble protein content in early watergrass by 84%, which was much greater than that in rice. These results suggest that fentrazamide has a mode of action which leads to the degradation of protein.

Effect of severe undernutrition and subsequent refeeding on gut mucosal protein fractional synthesis in human subjects

Objective Undernutrition has been associated with gut mucosal atrophy, impaired absorption, and increased permeability. This study investigated the effect of severe undernutrition and subsequent refeeding on gastric and duodenal mucosal protein fractional syntheses (MPFS). Methods MPFS was investigated in the gastric body, antrum, and duodenum of 23 severely undernourished patients by means of 14C-leucine incorporation into tissue protein and repeated after a period of refeeding. Results were evaluated in comparison with a group of 22 healthy controls and presented as mean ± standard error of the mean. Results The mean body index of the undernourished patients was 13.29 ± 0.33 kg/m 2 versus 22.67 ± 0.63 kg/m 2 in the controls ( P < 0.001). MPFS in the controls and undernourished patients were similar (gastric body, 36.49 ± 2.88 versus 33.41 ± 3.08%/d; gastric antrum, 25.51 ± 2.20 versus 24.95 ± 2.32%/d; duodenum, 25.90 ± 2.58 versus 25.49 ± 1.99%/d). After refeeding, the body mass index of the undernourished patients increased to 15.87 ± 0.44 kg/m 2 ( P < 0.001). The MPFS increased significantly (gastric body, 51.80 ± 8.12%/d, P < 0.05; gastric antrum, 33.44 ± 3.66%/d, P < 0.05; duodenum, 46.27 ± 8.02%/d, P < 0.01), with the MPFS of the duodenum significantly greater than the control values ( P = 0.01). Conclusion Despite severe undernutrition, MPFS of the gastric body, antrum, and duodenum remained similar to control values. Enteral feeding resulted in a significant increase in MPFS, indicating a trophic response.

Simultaneous radioassays of bacterial production and mercury methylation in the periphyton of a tropical and a temperate wetland

Laboratory radioassays were made to study mercury (Hg) methylation together with bacterial production in the periphyton of two aquatic macrophytes, the submerged Myriophyllum spicatum, from a constructed wetland in Sweden and the floating Eichhornia crassipes, from a eutrophied tropical lake in Brazil. Time course incubations were made by addition of 203HgCl 2 and the methylmercury formed was extracted at pre-defined time intervals. Bacterial production ( 14C-leucine incorporation) was measured at the same time intervals, with plants removed from parallel incubations made with and without addition of cold HgCl 2. For E. crassipes, higher methylmercury production was observed at elevated bacterial production, whereas for M. spicatum, the bacterial production was significantly lower, and Hg methylation was below the detection limit. The combined results confirm the importance of microbial processes for Hg methylation, although other factors are known to influence this process in complex ways. The addition of Hg did not significantly influence bacterial production, while the incubation temperatures used (25 and 35 °C) resulted in different methylation rates. Radiotracer techniques for measurements of bacterial production such as 14C-leucine uptake can provide useful insights into the Hg cycle in aquatic environments, and our data suggest that they may be used as a proxy of mercury methylation potentials.

Discriminating between effects of metals and natural variables in terrestrial bacterial communities

This study aimed to assess effects of metals on bacterial communities in grassland soil and to discriminate these effects from natural variability in soil properties. Changes in gross parameters of bacterial communities were investigated by the determination of 14C-leucine and 3H-thymidine incorporation rates, CO 2 evolution, biomass indicators and N mineralization rates. 14C-leucine incorporation rate and CO 2 evolution showed correlations with all metals tested as well as with organic matter content. 3H-thymidine incorporation rates, biomass indicators and N mineralization rates did not strongly correlate with any physical or chemical parameters. Further, community-level physiological profiles (CLPP) and polymerase chain reaction (PCR)-amplified denaturing gradient gel electrophoresis (DGGE) of 16S rDNA were performed. Monte-Carlo permutation testing was performed to analyse CLPP and DGGE data to allow for a stringent discrimination between sources of effects. CLPP changes correlated with the Pb concentration and pH in the soil. DGGE changes correlated with Pb and Cu concentrations and organic matter content. Pollution-induced community tolerance (PICT) was not found for any of the metals assessed. A causal relation between the effects observed on bacterial communities and the presence of metals was not established with PICT. The negative outcome of PICT can probably be attributed to indirect effects or to methodological problems. We concluded that the observed shifts in CLPP and DGGE patterns are a strong indication of metals effects on bacterial communities in this grassland. These effects could only be filtered from the total variation by multivariate analyses.

Characteristics of the interactions of cortisol-apolipoprotein A-I and tetrahydrocortisol-apolipoprotein A-I complexes with eukaryotic DNA

Primary hepatocyte culture has been used to demonstrate that the cortisol-apolipoprotein A-I complex does not affect the DNA and protein biosynthesis rates, whereas the tetrahydrocortisol-apolipoprotein A-I complex (THC-apoA-I) substantially increases the rates of 3H-thymidine and 14C-leucine incorporation into DNA and protein, respectively. Small-angle X-ray scattering data show that only THC-apoA-I effectively interacts with eukaryotic DNA, which is accompanied by local DNA melting. The (GCC)n repeat, a component of many human and other eukaryotic genes, is the most probable region of the interaction of this complex with DNA. An oligonucleotide (duplex) of this type has been synthesized. Its interaction with THC-apoA-I yields a larger complex, which breaks up, giving rise to complementary oligonucleotide strands. They also interact with THC-apoA-I. The equilibrium kinetics of this multiphase process is described. The interaction of the cortisol-apolipoprotein A-I complex with the duplex is less specific and does not cause its breakup or the formation of complementary oligonucleotides.

Regulation of Ammonium Accumulation during Salt Stress in Rice (Oryza sativa L.) Seedlings

Metabolic processes related to ammonium release and assimilation were investigated in a salt-sensitive rice (Oryza sativa L.) cultivar Anapurna. Ammonium content of the 3rd leaves increased 3-4 times when seedlings were treated with 100 mM NaCl for 6 days under both growth chamber light condition and in darkness (nonphotorespiration). An in vitro experiment revealed strong inhibition of protein synthesis as an effect of NaCl on the incorporation of 14C-leucine into protein. Exposure to salt stress slightly increased leaf proteolytic activity. The increase of proteolytic activity and decrease of protein synthesis, which directly causes accumulation of free amino acids, might lower the need for ammonium incorporation to form amino acids and indirectly cause the excessive accumulation of ammonium. No significant changes in the assimilatory activities of glutamine synthetase (GS; EC 6.3.1.2) and ferredoxin-dependent glutamate synthase (Fd-GOGAT; EC 1.4.7.1) were found under salt stress. Salt treatment changed the balance of the direction of glutamate dehydrogenase (NAD(H); EC 1.4.1.2); the aminating (NADH-GDH) activity increased while deaminating (NAD-GDH) activity decreased. We conclude that the accumulation of ammonium under salt stress was not due to inhibition of assimilatory activity of GS/GOGAT cycle or aminating GDH. Since these enzymes require supply of C-skeleton in the form of 2-oxoglutarate, reductant and energy to function, the reduction of photosynthetic capacity and the decrease of 2-oxoglutarate might be responsible for the excess accumulation of ammonium in salt-stressed seedlings.

Insulinomimetic effects of kaempferitrin on glycaemia and on 14C-glucose uptake in rat soleus muscle

Bauhinia forficata is one of the Bauhinia species mostly used as an antidiabetic herbal remedy in Brazil. Kaempferitrin (kaempferol-3,7-O-(α)- l-dirhamnoside) is the predominant flavonol glycoside found in the B. forficata leaves. The aim of the present work was to study the long-term effect of kaempferitrin on glycaemia in diabetic rats, as well as the in vitro effect of this compound on 14C- d-glucose uptake and 14C-leucine incorporation into protein in normal rat soleus muscle. Kaempferitrin was found to have an acute lowering effect on blood glucose in diabetic rats and to stimulate the glucose uptake percentile, as efficiently as insulin in muscle from normal rats. This compound did not have any effect on glucosuria or on protein synthesis in muscle from normal and diabetic animals. However, the protein synthesis in the kaempferitrin-treated groups was maintained at the same level as the respective controls. Thus, the hypoglycaemic effect and the prompt efficiency of the kaempferitrin in stimulating [U- 14C]-2-deoxi- d-glucose uptake in muscle -constitute the first evidence to indicate that the acute effect of this compound on blood glucose lowering may occur as a consequence of the altered intrinsic activity of the glucose transporter (Vmax or glucose transporters translocation?) not involving directly the synthesis of new carriers.

Differential effects of testosterone on protein synthesis activity in male and female quail brain

In Japanese quail, testosterone (T) increases the Nissl staining density in the medial preoptic nucleus (POM) in relation to the differential activation by T of copulatory behavior. The effect of T on protein synthesis was quantified here in 97 discrete brain regions by the in vivo autoradiographic 14C-leucine (Leu) incorporation method in adult gonadectomized male and female quail that had been treated for 4 weeks with T or left without hormone. T activated male sexual behaviors in males but not females. Overall Leu incorporation was increased by T in five brain regions, many of which contain sex steroid receptors such as the POM, archistriatum and lateral hypothalamus. T decreased Leu incorporation in the medial septum. Leu incorporation was higher in males than females in two nuclei but higher in females in three nuclei including the hypothalamic ventromedial nucleus. Significant interactions between effects of T and sex were seen in 13 nuclei: in most nuclei ( n=12), T increased Leu incorporation in males but decreased it in females. The POM boundaries were defined by a denser Leu incorporation than the surrounding area and incorporation was increased by T more in males (25%) than in females (6%). These results confirm that protein synthesis in brain areas relevant to the control of sexual behavior can be affected by the sex of the subjects or their endocrine condition and that T can have differential effects in the two sexes. These anabolic changes should reflect the sexually differentiated neurochemical mechanisms mediating behavioral activation.

Phytotoxicity of the Fungicide Metalaxyl and Its Optical Isomers.

Metalaxyl is a systemic fungicide commonly used in citrus production to control Phytophthora root rot and foot rot. When applied as a drench, injury was observed on newly planted, young citrus trees. The visual injury symptoms ranged from light- to bright-yellow leaves. It was learned that the commercial formulation of metalaxyl contained various isomers and that these isomers may vary in phytotoxic effects on citrus leaves. The objective of this study was to determine the difference in herbicidal activity between the two optical isomers of metalaxyl on pepper plants and citrus leaves. The phytotoxicity of the fungicide metalaxyl and its optical isomers (CGA76538, S+; CGA76539, R-) was determined using a pepper seedling growth bioassay and by measuring protein synthesis as estimated by the incorporation of 14C-leucine by citrus mesophyll cells. The two isomers and metalaxyl differed in their herbicidal activity to pepper plants and citrus cells. Pepper seedlings treated with R- had significantly higher mean fresh weight than plants treated with metalaxyl or S+ at 0.1, 1.0, 10.0, and 100 ppm. Protein synthesis, as measured by the inhibition of 14C-leucine incorporation by citrus mesophyll cells, also was inhibited more by metalaxyl and the S+ isomer than by the R- isomer. After 30 min of incubation at 100 μM, the R- isomer inhibited 14C-leucine incorporation by 29%, whereas incorporation of 14C-leucine in the metalaxyl and the S+ isomer treatments was higher (46 and 81%, respectively). Similarly, the highest 14C-leucine uptake at 60 min was obtained by R- at all concentrations. The assays showed that the R- and S+ isomers differ in their biological activity as expressed by weight loss of pepper plants and inhibition of protein synthesis and that the S+ isomer is responsible for the phytotoxicity of metalaxyl. The findings in this study show that the phytotoxicity of metalaxyl was due to the presence of the S+ optical isomer. Removal of this isomer from metalaxyl has enabled the continued use of this fungicide for control of foot rot and root rot in citrus.

The relationship between organic matter, invertebrates, and bacteria in the sediments of Lake Malawi

In the surface sediments below the oxic-anoxic interface in meromictic Lake Malawi, there is little or no evidence of biological activity. As the water depth increases, even in sediments within the oxic zone microbial activity, as measured by 14C leucine incorporation, decreases; the benthic invertebrates decrease in biomass and diversity; and the amount of detrital material remaining in the sediments increases from &amp;lt;1% at 10 m to &amp;gt;14% at 125 m. This relationship with depth could be owing to several factors. At shallower depths, there is terrestrial material available for bacteria to use, as well as detrital material derived from autochthonous production. This detrital material can be degraded in the sediments by the benthic invertebrates, which release dissolved organic carbon and smaller particles through excretion that bacteria can use. As the water depth increases, the bacteria in the water column are able to degrade much of the planktonic debris, leaving the more refractory carbon particles to settle to the sediment. It appears that when there are enough benthic invertebrates, there is still substantial bacterial activity. As the depth increases, the benthic invertebrates disappear and, although there is still detrital carbon available, the bacteria appear unable to utilize it. We suggest that the benthic invertebrates are essential to the processing of detrital carbon and a shift in the degree of anoxia within the lake could seriously alter the cycling of carbon.