The application of δ¹⁸O and δD for understanding water pools and fluxes in a Typha marsh

The δ¹⁸O and δD composition of water pools (leaf, root, standing water and soil water) and fluxes [transpiration (T), evaporation (E)] were used to understand ecohydrological processes in a managed Typha latifolia L. freshwater marsh. We observed isotopic steady‐state T and deep rooting in Typha. The isotopic mass balance of marsh standing water showed that E accounted for 3% of the total water loss, T accounted for 17% and subsurface drainage (D) accounted for the majority (80%). There was a vertical gradient in water vapour content and isotopic composition within and above the canopy sufficient for constructing an isotopic mass balance of water vapour during some sampling periods. During these periods, the proportion of T in evapotranspiration (T/ET) was between 56 ± 17% and 96 ± 67%, and the estimated error was relatively high (>37%) because of non‐local, background sources in vapour. Independent estimates of T/ET using eddy covariance measurements yielded similar mean values during the Typha growing season. The various T/ET estimates agreed that T was the dominant source of marsh vapour loss in the growing season. The isotopic mass balance of water vapour yielded reasonable results, but the mass balance of standing water provided more definitive estimates of water losses.     

Phytochemistry and biosynthesis of δ-lactone withanolides

Withanolides are highly oxygenated natural products. These C₂₈ steroids with ergostane-based skeletons functionalized at C-22 and C-26 form six-membered δ-lactone rings. Withanolides containing a δ-lactone side chain often occur in Solanaceae and have a variety of biological activities because of their complicated structures. Characteristic spectroscopic behaviors and biosynthesis of withanolides are conducive to their structural elucidation and “biomimetic synthesis”, respectively. However, the last review to summarize their spectroscopic features and biosynthesis was in 1996. Since then, many withanolides with novel structures have been described by their spectra with biosynthesis investigated with many bioassays. This review surveys δ-lactone withanolides and emphasizes their spectral features, configurations and biosynthetic genes. The period reviewed includes through January 2014. We also include phytochemical species.     

Biosynthesis,cDNA and amino acid sequences of a precursor of conglutin δ, a sulphur-rich protein from Lupinus angustifolius

The biosynthesis of conglutin has been studied in developing cotyledons of Lupinus angustifolius L. Precursors of conglutin formed the major sink for [³⁵S]-cysteine incorporated by developing lupin cotyledons, and these precursors were rapidly sequestered into the endoplasmic reticulum. The sequence of a cDNA clone coding for one such precursor of conglutin was determined. The structure of the precursor polypeptide for conglutin predicted from the cDNA sequence contained an N-terminal leader peptide of 22 amino acids directly preceding a subunit polypeptide of M _r 4520, together with a linking region of 13 amino acids and a subunit polypeptide of M _r 9558 at the C-terminus. The amino acid sequence predicted from the cDNA sequence showed minor variations from that established by sequencing of the protein purified from mature dried seeds (Lilley and Inglis, 1986). These were consistent with the existence of a multi-gene family coding for conglutin . Comparison of the sequences of conglutin with those of other 2S storage proteins showed that the cysteines involved in internal disulphide bridges between the mature subunits of conglutin , were maintained throughout this family of proteins but that little else was conserved either at the protein or DNA level.     

Variability in δ13C and δ15N trophic discrimination factors for teleost fishes: a meta-analysis of temperature and dietary effects

Reviews in Fish Biology and Fisheries - Stable isotope analysis (SIA) is widely used to assess animal diet and movements, requiring accurate estimates of trophic discrimination factors (TDFs)....     

Long-term changes of the δ15N natural abundance of plants and soil in a temperate grassland

Tracing back the N use efficiency of long-term fertilizer trials is important for future management recommendations. Here we tested the changes in natural N-isotope composition as an indicator for N- management within a long-term fertilization lysimeter experiment in a low mountain range pasture ecosystem at Rengen (Eifel Mountains), Germany. Cattle slurry (δ¹⁵N?=?8.9?±?0.5‰) and mineral fertilizers (calcium ammonium nitrate; δ¹⁵N?=??1.0?±?0.2‰) were applied at a rate between 0 and 480 kg N ha^?1?yr^?1 throughout 20 years from 1985 onwards. In 2006, samples were taken from different grass species, coarse and fine particulate soil organic matter, bulk soil and leachates. Total soil N content hardly changed during fertilization experiment. As also N leaching has been small within the stagnant water regime, most N was lost through the gaseous phase beside plant uptake and cutting. Unlike N uptake by plants, the process of N volatilization resulted in strong discrimination against the ¹⁵N isotope. As a consequence, the δ¹⁵N values of top soil samples increased from 1.8?±?0.4‰ to 6.0?±?0.4‰ and that of the plants from ?1.2?±?1.3‰ to 4.8?±?1.2‰ with increasing N fertilizer rate. Samples receiving organic fertilizer were most enriched in δ¹⁵N. The results suggest that parts of the fertilizer N signal was preserved in soils and even discovered in soil organic matter pools with slow N turnover. However, a ¹⁵N/¹⁴N isotope fractionation of up to 1.5‰ added to the δ¹⁵N values recovered in soils and plants, rendering the increase in δ¹⁵N value a powerful indicator to long-term inefficient N usage and past N management in the terrestrial environment.     

Combined use of δ¹³C, δ18O and δ15N tracks nitrogen metabolism and genotypic adaptation of durum wheat to salinity and water deficit

? Accurate phenotyping remains a bottleneck in breeding for salinity and drought resistance. Here the combined use of stable isotope compositions of carbon (δ13C), oxygen (δ1?O) and nitrogen (δ1?N) in dry matter is aimed at assessing genotypic responses of durum wheat under different combinations of these stresses. ? Two tolerant and two susceptible genotypes to salinity were grown under five combinations of salinity and irrigation regimes. Plant biomass, δ13C, δ1?O and δ1?N, gas-exchange parameters, ion and N concentrations, and nitrate reductase (NR) and glutamine synthetase (GS) activities were measured. ? Stresses significantly affected all traits studied. However, only δ13C, δ1?O, δ1?N, GS and NR activities, and N concentration allowed for clear differentiation between tolerant and susceptible genotypes. Further, a conceptual model explaining differences in biomass based on such traits was developed for each growing condition. ? Differences in acclimation responses among durum wheat genotypes under different stress treatments were associated with δ13C. However, except for the most severe stress, δ13C did not have a direct (negative) relationship to biomass, being mediated through factors affecting δ1?O or N metabolism. Based upon these results, the key role of N metabolism in durum wheat adaptation to salinity and water stress is highlighted.     

Cloning and sequencing of the hemA gene of Rhodobacter capsulatus and isolation of a δ-aminolevulinic acid-dependent mutant strain

Summary The Rhodobacter capsulatus hemA gene, coding for the enzyme -aminolevulinic acid synthase (ALAS), was isolated from a genome bank by hybridization with a hemT probe from Rhodobacter sphaeroides. Subcloning of the initial 3.9 kb HindIII fragment allowed the isolation of a 2.5 kb HindIII-BglII fragment which was able to complement the -aminolevulinic acid-requiring (ALA-requiring) Escherichia coli mutant SHSP19. DNA sequencing revealed an open reading frame coding for a protein with 401 amino acids which displayed similarity to the amino acid sequences of other known ALASs. However, no resemblance was seen to the HemA protein of E. coli K12. Based on the sequence data, an ALA-requiring mutant strain of R. capsulatus was constructed by site-directed insertion mutagenesis. Introduction of a plasmid, containing the hemA gene of R. capsulatus on the 3.9 kb HindIII fragment, restored ALA-independent growth of the mutant indicating that there is only one gene for ALA biosynthesis in R. capsulatus. Transfer of the R factor pRPS404 and hybridization analysis revealed that the ALAS gene is not located within the major photosynthetic gene cluster.Part of this research was presented at the Symposium on Molecular Biology of Membrane-Bound Complexes in Phototrophic Bacteria, Freiburg, FRG, 2–5 August 1989     

Synthesis of a conformationally constrained δ-amino acid building block

Conformationally restricted amino acids are important components in peptidomimetics and drug design. Herein, we describe the synthesis of a novel, non-proteinogenic constrained delta amino acid containing a cyclobutane ring, cis-3(aminomethyl)cyclobutane carboxylic acid (ACCA). The synthesis of the target amino acid was achieved in seven steps, with the key reaction being a base induced intramolecular nucleophilic substitution. A small library of dipeptides was prepared through the coupling of ACCA with proteinogenic amino acids.     

Synthesis of a bicyclic δ-amino acid as a constrained Gly-Asn dipeptide isostere

Delta-amino acids are very attractive in drug discovery, especially in the peptidomimetic area, because of their capability to act as dipeptide isosteres and reverse turn mimetics. Herein we report the synthesis of a rigid delta-amino acid constrained by a 3-aza-6,8-dioxabicyclo[3.2.1]octane-based scaffold, which can be considered as a Gly-Asn dipeptide mimetic. Key steps are the condensation of glycidol and tartaric acid derivatives, and the intramolecular trans-acetalization of the oxidized adduct to give the bicyclic delta-amino acid. Starting from L-tartaric acid derivative, it was achieved the corresponding Gly-D-Asn isostere, whereas from the enantiomeric D-tartaric acid derivative the corresponding Gly-L-Asn isostere could be obtained, thus giving access to both enantiomeric dipeptide sequences.     

Design and synthesis of KNT-127, a δ-opioid receptor agonist effective by systemic administration

We have reported previously the novel δ-opioid agonist, SN-28, which was more potent in in vitro assays than the prototype δ-agonists, TAN-67 and SNC-80. However, when administered by subcutaneous injection, this compound showed no analgesic effect at dosages greater than 30 mg/kg in the acetic acid writhing test. We speculated that SN-28 was not effective in the test because the presence of the charged ammonium groups prevented its penetration through the blood–brain barrier. On the basis of our proposal, we designed the novel δ-agonist, KNT-127, which was effective with systemic administration.     

Occurrence and Some Properties of Two Types of δ-Aminolevulinic Acid Synthase in a Facultative Methylotroph,Protaminobacter ruber

In addition to the α-ALA synthase already reported (Fraction I: molecular weight, 100,000; optimal pH, ca. 8.0), an isozyme (Fraction II: molecular weight, 64,000; optimal pH, ca. 6.4) was found in Protaminobacter ruber grown in the dark after an initial light period (20~30hr). The fraction I- and II-enzymes were separable by gel-filtration through Sepharose 6B. While the former was formed constitutively, the latter was formed inducibly under the conditions for bacteriochlo-rophyll formation. Therefore, the fraction II-isozyme seems to be responsible for the biosynthesis of bacteriochlorophyll.     

Climatic implications of δ13C and δ18O ratios from C3 and C4 plants growing in a tropical montane habitat in southern India

The stable carbon and oxygen isotope ratios in cellulose of C3 and C4 plants growing on the surface of a montane peat bog in the Nilgiri hills, southern India, were measured. The mean monthly δ¹³C values in cellulose of both C3 and C4 plants are found to be significantly related to rainfall, while the δ¹⁸O values are sensitive to changes in maximum temperature and relative humidity of the region. Further, higher δ¹⁸O values were observed in C4 plants compared to C3 plants, suggesting that C4 plants are probably less sensitive to relative humidity as compared to C3 plants and are able to photosynthesize even during drier conditions. The plant isotope-climate correlations thus established can be used for reconstructing the past temperature and rainfall conditions of the tropics from the isotopic ratios of peat deposits, derived from a mixture of C3 and C4 plants in the region.     

Stipa tenacissima Does not Affect the Foliar δ13C and δ15N of Introduced Shrub Seedlings in a Mediterranean Semi-arid Steppe

Recent studies have shown that the tussock grass Stipa tenacissima L. facilitates the establishment of late-successional shrubs, in what constitutes the first documented case of facilitation of woody plants by grasses. With the aim of increasing our knowledge of this interaction, in the present study we investigated the effects of S. tenacissima on the foliar δ13C, δ15N, nitrogen concentration, and carbon: nitrogen ratio of introduced seedlings of Pistacia lentiscus L., Quercus coccifera L., and Medicago arborea L. in a semi-arid Mediterranean steppe. Six months after planting, the values of δ13C ranged between -26.9‰ and -29.6‰,whereas those of δ15N ranged between -1.9‰ and 2.7‰. The foliar C: N ratio ranged between 10.7 and 53.5,and the nitrogen concentration ranged between 1.0% and 4.4%. We found no significant effect of the microsite provided by S. tenacissima on these variables in any of the species evaluated. The values of δ13C were negatively correlated with predawn water potentials in M. arborea and were positively correlated with relative growth rate in Q. coccifera. The values of δ15N were positively correlated with the biomass allocation to roots in the latter species. The present results suggest that the modification of environmental conditions in the are surrounding S. tenacissima was not strong enough to modify the foliar isotopic and nitrogen concentration of shrubs during the early stages after planting.     

Dynamics and orientation of amphipathic peptides in solution and bound to membranes: a steady-state and time-resolved fluorescence study of staphylococcal δ-toxin and its synthetic analogues

The environment of both the hydrophilic and hydrophobic sides of alpha-helical delta-toxin are probed by tryptophanyl (Trp) fluorescence, when self-association occurs in solution and on binding to membranes. The fluorescence parameters of staphylococcal delta-toxin (Trp15 on the polar side of the amphipathic helix) and synthetic analogues with single Trp at position 5 or 16 (on the apolar side) were studied. The time-resolved fluorescence decays of the peptides in solution show that the local environment of their single Trp is always heterogeneous. Although the self-association degree increases with concentration, as shown by fluorescence anisotropy decays, the lifetimes (and their statistical weight) of Trp16 do not change, contrary to what is observed for Trp15. The first step of self-association is then driven by hydrophobic interactions between apolar sides of alpha-helices, whilst further oligomerization involves their polar side (Trp15) via electrostatic interactions. This is supported by dissociation induced by salt. For all self-associated peptides, the polarity of the Trp microenvironment was not significantly modified upon binding to phospholipid vesicles, as indicated by the small shifts of the fluorescence emission spectra and lifetime values. However, the relative populations of the lifetime classes vary with bound-peptide density similar to the rates of their global motions in bilayers or smaller particles. Quenching experiments by water or lipid-soluble compounds show changes of the orientation of membrane-inserted peptides, from probably dimers lying flat at the interface at low peptide density, to oligomers spanning the membrane and inducing membrane fragmentation at high peptide density.     

The isolation and properties of δ-tocotrienol from Hevea latex

1. delta-Tocotrienol (8-methyltocotrienol) was isolated from the latex of Hevea brasiliensis. This new member of the tocopherol family is a pale-yellow oil at room temperature. 2. The properties of delta-tocotrienol are very similar to those of delta-tocopherol and the small differences can be explained by the change in side chain. 3. The ultraviolet and infrared spectra of delta-tocotrienol were determined and a conversion factor for use with the Emmerie-Engel reaction was worked out. Details are given for the chromatography of delta-tocotrienol on thin layers (adsorption and partition) and reversed-phase paper, and the nitroso derivatives were formed. 4. An ethyl carbonate ester of delta-tocotrienol was prepared and compared with a similar ester of delta-tocopherol. 5. Hydroxymethylation of delta-tocotrienol followed by reduction gave beta-tocotrienol as a major product.     

Conservation of δ-crystallin gene structure between ducks and chickens

A cloned chicken delta-crystallin cDNA was used to identify two putative delta-crystallin genes in the duck by Southern blot hybridization. A DNA fragment containing most of one of these genes was isolated from a library made in bacteriophage lambda Charon 28A containing genomic DNA from 14-day-old embryonic ducks. Electron microscopy, partial gene sequencing, primer extension analysis using duck mRNA, and comparison with the well-characterized chicken delta-crystallin genes suggest that our cloned duck delta-crystallin gene, like the chicken delta-crystallin genes, is 8-10 kb long and contains 17 exons. Hybridization and sequencing data show great similarity between the homologous 5' untranslated and coding exons of the duck and chicken delta-crystallin genes. Overall, the homologous introns also appear to have approximately 30% sequence similarity, and have been subject to deletion/insertion events. Our partial characterization of duck delta-crystallin gene sequences suggests that this avian and reptilian crystallin family has been conserved during evolution, as have the other crystallin gene families that are expressed in the eye lens.     

Carbon storage change and δ13C transitions of peat columns in a partially forestry-drained boreal bog

Background and aims

In forestry-drained peatlands, drying leads to changes in C cycling which could affect peat δ¹³C. Furthermore, the δ¹³C profile of the entire peat column may reveal effects of earlier climatic periods.

Methods

We measured peat δ¹³C and C inventories in adjacent peat profiles, two collected from undrained and two from the drained side of a bog that was partially ditch-drained 37 years earlier. The cores were sliced into 10-cm subsamples for analyses; matching of the profiles based on surface levelling, peat stratigraphic correlation and a horizontal ash layer found in both profiles.

Results

Surface subsidence of 30 cm was observed in the dried site and the uppermost 160 cm in the undrained site contained an excess of 5.9 kg m⁻² of C compared with the corresponding strata of the ditch-drained site. The δ¹³C values increased but markedly only in the thin surface layer of the drained site, indicating low δ¹³C of the missing C (ca. –30‰). In the deeper strata, dating to Mid-Holocene, high dry bulk density, C%, N%, humification index and low C/N ratio were connected to low δ¹³C of peat.

Conclusions

Drainage of 37 years increased δ¹³C values in the upper peat profile of the drained bog and led to the selective loss of ¹³C depleted C. Results indicate that C balance studies can be aided by C isotope analyses. Low δ¹³C values in the peat profile indicate the existence of a wet fen stage during the moist and warm period during Mid-Holocene.