Regional differences in the carbon isotopic compositions of teak from two monsoonal regimes of India

Inter and intra-annual carbon isotope compositions (δ¹³C) of several annual growth rings of teak trees from two monsoonal regimes from India were studied and compared with the corresponding oxygen isotopic (δ¹⁸O) variations. In teak from both the regimes, amplitudes of intra-annual δ¹³C were ∼2-3 times lower than that observed in δ¹⁸O. Seasonal cycle with lower δ¹³C values at the middle and higher at ring boundaries was observed for teak from central India, dominated by the southwest monsoon. Positive correlations of intra-annual δ¹³C values with the corresponding δ¹⁸O values of the same rings and with relative humidity (RH) of the concurrent period suggest a dominant role of RH in controlling δ¹³C values of teak from central India. Intra-annual δ¹³C variations of teak from southern India, receiving both the southwest and northeast monsoons, revealed an initial decreasing trend followed by an increasing trend before culminating in depleted ¹³C values at the end of the growing season. No correlation was observed between intra-annual δ¹³C and δ¹⁸O variations of teak trees from southern India. Regional differences in the climatology of δ¹³C of atmospheric CO₂ or the lengths of growing season could be likely reasons for differing intra-annual δ¹³C variations of teak from the two climatic regimes.     

Stable isotope-based statistical tools as ecological indicator of pollution sources in Mediterranean transitional water ecosystems

N-stable isotope analysis of macroalgae has become a popular method for the monitoring of nitrogen pollution in aquatic ecosystems. Basing on changes in their δ¹⁵N, macroalgae have been successfully used as biological traps to intercept nitrogen inputs. As different nitrogen sources differ in their isotopic signature, this technique provides useful information on the origin of pollutants and their extension in the water body. However, isotopic fractionation potentially resulting from microbial nitrogen processing, and indirect isotopic variations due to effects of physicochemical conditions on algal nutrient uptake and metabolism, may affect anthropogenic N isotopic values during transportation and assimilation. This in turn can affect the observed isotopic signature in the algal tissue, inducing isotopic variations not related to the origin of assimilated nitrogen, representing a “background noise” in isotope-based water pollution studies.In this study, we focused on three neighbouring coastal lakes (Caprolace, Fogliano and Sabaudia lakes) located south of Rome (Italy). Lakes were characterized by differences in terms of anthropogenic pressure (i.e. urbanization, cultivated crops, livestock grazing) and potential “background noise” levels (i.e. nutrient concentration, pH, microbial concentration). Our aim was to assess nitrogen isotopic variations in fragments of Ulva lactuca specimens after 48 h of submersion to identify and locate the origins of nitrogen pollutants affecting each lake. δ¹⁵N were obtained for replicated specimens of U. lactuca spatially distributed to cover the entire surface of each lake, previously collected from a benchmark, unpolluted site. In order to reduce the environmental background noise on isotopic observations, a Bayesian hierarchical model relating isotopic variation to environmental covariates and random spatial effects was used to describe and understand the distribution of isotopic signals in each lake.Our procedure (i) allowed to remove background noise and confounding effects from the observed isotopic signals; (ii) allowed to detect “hidden” pollution sources that would not be detected when not accounting for the confounding effect of environmental background noise; (iii) produced maps of the three lakes providing a clear representation of the isotopic signal variation even where background noise was high. Maps were useful to locate nitrogen pollution sources, identify the origin of the dissolved nitrogen and quantify the extent of pollutants, showing localized organic pollution impacting Sabaudia and Fogliano, but not Caprolace. This method provided a clear characterization of both intra- and inter-lake anthropogenic pressure gradients, representing a powerful approach to the ecological indication and nitrogen pollution management in complex systems, as transitional waterbodies are.     

Influence of cadmium on the distribution of the essential trace elements zinc and copper in the liver and kidneys of rats

Cd induced changes of Zn and Cd distribution in the liver and kidneys were studied in relation to Cd metallothionein (MT) synthesis. Wistar male rats were given CdCl₂ by sc injection of .8, 1.5, and 3.0 mg Cd/kg three times a week for three weeks. Cd levels of liver and kidneys increased with the increment of Cd dosage and 80–90% of Cd was found in the cytosol. The MT fractions contained 80–89% cytosolic Cd in the liver and 55–75% Cd in the kidneys. Zn concentrations in the liver increased following Cd administration, But Zn in the kidneys showed only slight increase. There was a distinct decrease of Cu concentration in the liver of the 3.0 mg group. In contrast, Cu concentrations in the kidneys increased about three times in the .8 and 1.5 mg Cd groups, but Cu in the 3.0 mg group showed only 1.5 times increase. The changes of these metal concentrations were observed mainly in the cytosol. Non-MT-Cd in the kidneys was maximum in the 1.5 mg group, but the 3.0 mg group showed significant decrease. In parallel with this decrease of Cd, Cu and Zn in the kidneys showed similar decrease. When the kidneys are injured, Zn and Cu appear to leak from this organ.     

A triple-resonance pulse scheme for selectively correlating amide1HN and15N nuclei with the1Hα proton of the preceding residue

Summary A 3D¹H–¹⁵N–¹³C triple resonance experiment is presented that contains exclusively cross peaks between the¹H^N and¹⁵N nuclei of one residue with the H of the preceding residue. The pulse sequence, designed to minimize the time coherence, is transverse on nuclei with short T₂ values. The experiment consists of coherence transfers via one-bond couplings from the H^N via N, CO, C to the H and back to the H^N for detection; it is called HN(COCA)HA. The experiment was tested on uniformly¹⁵N- and¹³C-enriched T4 lysozyme.     

Evaluation of the availability ofAzolla-N and urea-N to rice using15N

Summary The symbiotic association of the water fernAzolla with the blue-green algaAnabaena azollae can fix 30–60 kg N ha^–1 per rice cropping season. The value of this fixed N for rice production, however, is only realized once the N is released from theAzolla biomass and taken up by the rice plants. The availability of N applied asAzolla or as urea was measured in field experiments by two¹⁵N methods. In the first,Azolla caroliniana (Willd.) was labelled with¹⁵N in nutrient solution and incorporated into the soil at a rate of 144 kg N ha^–1. The recovery ofAzolla-N in the above ground parts of rice [Oryza sativa (L) cv. Nucleoryza] was found to be 32% vs. 26% for urea applied at a rate of 100 kg N/ha; there was no significant difference in recovery. In the second, 100 kg N/ha of¹⁵N-urea was applied separately or in combination with either 250 or 330 kg N ha^–1 of unlabelledAzolla. At the higher rate, the recovery ofAzolla-N was significantly greater than that of urea. There was a significant interaction when both N sources were applied together, which resulted in a greater recovery of N from each source in comparison to that source applied separately. Increasing the combined urea andAzolla application rate from 350 kg N ha^–1 to 430 kg N ha^–1 increased the N yield but had no effect on the dry matter yield of rice plants. The additional N taken up at the higher level of N application accumulated to a greater extent in the straw compared to the panicles. Since no assumptions need to be made about the contribution of soil N in the method using¹⁵N-labelledAzolla, this method is preferable to the¹⁵N dilution technique for assessing the availability ofAzolla-N to rice. Pot trials usingAzolla stored at –20°C or following oven-drying showed that both treatments decreased the recovery of N by one third in comparison to freshAzolla.     

Competition between siratro and kleingrass for15N labelled mineralized nitrogen

Summary Isotope dilution provides a method for measuring plant competition for mineral N and transfer of biologically fixed N from a legume to a grass. A plant growth medium was enriched with¹⁵N, and used to grow Siratro (Macropitilium atropurpureum D.C. Urb.) and Kleingrass 75 (Panicum coloratum L.) in 20 liter pots for 98 days in a glasshouse. The plants were grown in pure stand and in mixtures. When grown in 50∶50 mixture the grass obtained 59% of the labelled N and the legume obtained 41%. The grass produced nearly as much root mass as the legume even though biomass of the shoots were less than half that of the legume. Reducing the proportion of either plant species in the mixture reduced the proportion of the mineralized N absorbed by that species. The shoots of the grass were significantly more enriched (1.166 atom%¹⁵N excess) than the roots (1.036). The grass received 12% of its N as biologically fixed N from the legume.     

Microbial fermentative preparation of L-[15N2]lysine and its tracer: application to serum amino acid kinetic studies

The microorganism Brevibacterium flavum 21129 has been used to produce multigram batches of L-[15N2]lysine of high purity and isotopic enrichment by supplementation of the growth medium with (15NH4)2SO4 of 98.0 atom% excess. The doubly 15N-labeled lysine can be detected at dilutions 10 times greater than singly labeled lysine when isotope dilution curves are analyzed by gas chromatography-mass spectrometry. This enhanced sensitivity permits kinetic measurements of plasma free-lysine isotope content over a 300-fold dilution during 6 h following a single oral bolus of 5 mg/kg body wt. This inexpensive preparation method lends itself to the production of highly useful biochemical compounds for kinetic studies of human nutrition.     

A novel isotope labeling protocol for bacterially expressed proteins

Summary A novel protocol for isotopically labeling bacterially expressed proteins is presented. This method circumvents problems related to poor cell growth, commonly associated with the use of minimal labeled media, and problems with protein induction encountered, less commonly, when using enriched labeled media. The method involves initially growing the bacterial cells to high optical density in a commercially available enriched labeled medium. Following a suitable growth period, the cells are transferred to a different (minimal) labeled medium, appropriate for induction. The method is demonstrated using the protein melanoma growth stimulating activity (MGSA).     

Hydrolysis of Butteroil by Immobilized Lipase Using a Hollow-Fiber Reactor: Part VI. Multiresponse Analyses of Temperature and pH Effects

A lipase from Aspergillus niger, immobilized by physical adsorption on hydrophobic hollow fibers made of microporous polypropylene, was used to effect the hydrolysis of the glycerides of melted butterfat at 40, 50, 55, and 60°C (pH 7.0), and at pH 3.0, 4.0, 5.0, 7.0, 8.0, and 9.0 (40°C). McIlvane buffer and melted butterfat were pumped cocurrently through the hollow fiber reactor. The concentrations of ten different free fatty acids in the effluent oil stream were measured by HPLC. Multiresponse nonlinear regression methods were employed to fit the data to multisubstrate rate expressions derived from a Ping Pong Bi Bi mechanism in which the rate controlling step is deacylation of the enzyme. Thermal deactivation of the immobilized lipase was also included in the mathematical model of reactor performance. A postulated normal distribution of v_max with respect to the number of carbon atoms of the fatty acid residue (with an additive correction for the number of double bonds) was found to provide the best statistical fit of the data. The models developed can be used to independently predict the effects of either the pH or the temperature, as well as the reactor space time and the time elapsed after immobilization, on the free fatty acid profile of the lipolyzed butteroil product.     

The greenhouse effect: the impacts of carbon dioxide (CO2), ultraviolet-B (UV-B) radiation and ozone (O3) on vegetation (crops)

Man's influence on the greenhouse effect, the heating of the atmosphere due to increasing concentrations of tropospheric trace gases, is of much international concern. Among the climatic variables, elevated levels of carbon dioxide (CO₂), ultraviolet-B (UV-B) radiation and ozone (O₃) are known to have a direct effect on vegetation. Our current knowledge of these effects is mainly based on studies involving single stress mode. Thus, the joint effects of CO₂, UV-B and O₃ on vegetation are poorly understood. Nevertheless, based on the literature analysis of plant response to individual stress factors, it can be concluded that sorghum, pea, bean, potato, oat, lettuce, cucumber, rice and tomato are among the crop species potentially sensitive to the joint effects of the aforementioned three variables. Similar information for tree species is essentially lacking.At least with some climatic variables such as O₃, present modeling efforts of cause-effect relationships have proven to be controversial. While at a regional geographic scale ambient CO₂ concentrations appear to be relatively homogeneous, ambient concentrations of O₃ exhibit significant temporal and spatial variability. Because of the protective action of O₃ against UV-B, similar but inverse temporal and spatial variability is expected in the surface levels of UV-B. Thus, future experimental designs should consider these exposure dynamics and modeling cuase-effect relationships should be directed to stochastic processes.