A break in the nitrogen cycle in aridlands? Evidence from δp15N of soils

We examined the content and isotopic composition of nitrogen within soils of a juniper woodland and found that a cryptobiotic crust composed of cyanobacteria, lichens, and mosses was the predominant source of nitrogen for this ecosystem. Disturbance of the crust has resulted in considerable spatial variability in soil nitrogen content and isotopic composition; intercanopy soils were significantly depleted in nitrogen and had greater abundance of ¹⁵N compared to intra-canopy soils. Variations in the ¹⁵N/¹⁴N ratio for inter- and intra-canopy locations followed similar Rayleigh distillation curves, indicating that the greater ¹⁵N/¹⁴N ratios for inter-canopy soils were due to relatively greater net nitrogen loss. Coverage of cryptobiotic crusts has been reduced by anthropogenic activities during the past century, and our results suggest that destruction of the cryptobiotic crust may ultimately result in ecosystem degradation through elimination of the predominant source of nitrogen input.     

Spectroscopic studies of the manganese complex of Photosystem II

Our recent EPR and EXAFS experiments investigating the structure of the oxygen-evolving complex of PS II are discussed. PS II treatments which affect the cofactors calcium and chloride have been used to poise samples in modified forms of the S-states, S₁, S₂ and S₃. X-ray absorption studies indicate a similar overall structure for the manganese complex between treated and native samples although the influence of the treatments and cofactors is observed. Manganese oxidation (or oxidation of a ligand to the manganese cluster) is indicated to occur on each of the transitions S₁ S₂ and S₂ S₃ in these modified samples. The cluster appears to contain at least two inequivalent Mn-Mn pairs. In the native samples the Mn-Mn distance is 2.7 Å, but in samples where the calcium site is affected, one of the pairs has a 3.0 Å Mn-Mn distance. The intensity of the 3.3/3.6 Å interaction is reduced on sodium chloride treatment (calcium depletion) perhaps indicating calcium binding close to the manganese cluster. From EPR data we also propose that treatments which affect calcium and chloride binding cause a modification of the native S₂ state, slow the reduction of Y_z and allow an S3 EPR signal to be observed following illumination. The origin of the S3 EPR signal, a modified S₃ or S₂ X where X is an organic radical of unknown charge, is discussed in relation to the results from the EXAFS studies.Abbreviations EPR electron paramagnetic resonance spectroscopy - EXAFS extended X-ray absorption fine structure - HTG n-heptyl -d-thioglucoside - MES 2(N-morpholino)ethanesulfonic acid - OEC oxygen evolving complex - PPBQ phenyl-1,4-benzoquinone - PS II Photosystem II - Y_z redox active tyrosine     

4-Hydroxy-2-Nonenal Levels Increase in the Plasma of Patients with Adult Respiratory Distress Syndrome as Linoleic Acid Appears to Fall

Gas chromatography-mass spectrometry has been applied to the analysis of plasma linoleic acid and one of its oxidation products, 4-hydroxy-2-nonenal (HNE), in adult patients with the acute respiratory distress syndrome (ARDS). Peak areas of total ion chromatograms showed there to be negative correlations between loss of linoleic acid and formation of HNE (measured by selective ion monitoring) in 7 out 10 patients studied. When HNE was quantitated by selective ion monitoring, with reference to a pure standard of HNE and an internal standard of nonanoic acid, ARDS patients showed significantly increased levels of HNE (0.412 ± 0.023 nmol/ml) compared with normal healthy controls (0.205 ± 0.018 nmol/ml).     

Striatal L-DOPA Decarboxylase Activity in Parkinson's Disease In Vivo: Implications for the Regulation of Dopamine Synthesis

Abstract: L-DOPA is a large neutral amino acid subject to transport out of, as well as into, brain tissue. Competition between dopamine synthesis and L-DOPA egress from striatum must favor L-DOPA egress if decarboxylation declines relatively more than transport in Parkinson's disease. To test this hypothesis, we injected patients with Parkinson's disease with a radidabeled analogue of L-DOPA and recorded regional brain radioactivity as a function of time by means of positron emission tomography. We simultaneously estimated the activity of the decarboxylating enzyme and the amino acid transport. In the striatum of patients, we found the L-DOPA decarboxylase activity to be reduced in the head of the caudate nucleus and the putamen. However, the rate of egress of the DOPA analogue was unaffected by the disease and thus inhibited dopamine synthesis more than predicted in the absence of L-DOPA egress.     

A linkage study in seven breast cancer families.

Seven breast cancer families are examined for evidence of linkage to a site in the region of 17q12-q21, by using five markers. The families constitute a subset of a larger series of familial breast cancer; the seven families were selected because constitutional DNA was available on informative members, either from clinical samples or extracted from paraffin blocks. Two-point lod scores are reported. The maximum lod score, 0.8824, is obtained with marker NM23 at theta = 0. This is clearly not significant in itself; however, when taken in context with evidence from existing reports, it provides support for linkage to this region.     

Solutions for transients in arbitrarily branching cables: I. Voltage recording with a somatic shunt.

An analytical solution is derived for voltage transients in an arbitrarily branching passive cable neurone model with a soma and somatic shunt. The response to injected currents can be represented as an infinite series of exponentially decaying components with different time constants and amplitudes. The time constants of a given model, obtained from the roots of a recursive transcendental equation, are independent of the stimulating and recording positions. Each amplitude is the product of three factors dependent on the corresponding root: one constant over the cell, one varying with the input site, and one with the recording site. The amplitudes are not altered by interchanging these sites. The solution reveals explicitly some of the parameter dependencies of the responses. An efficient recursive root-finding algorithm is described. Certain regular geometries lead to "lost" roots; difficulties associated with these can be avoided by making small changes to the lengths of affected segments. Complicated cells, such as a CA1 pyramid, produce many closely spaced time constants in the range of interest. Models with large somatic shunts and dendrites of unequal electrotonic lengths can produce large amplitude waveform components with surprisingly slow time constants. This analytic solution should complement existing passive neurone modeling techniques.     

The purification and immunocharacterisation of N-methylputrescine oxidase from transformed root cultures of Nicotiana tabacum L. cv SC58

The enzyme N-methylputrescine oxidase which catalyses the conversion of N-methylputrescine to N-methylpyrrolinium salt has been purified to homogeneity from transformed roots of Nicotiana tabacum L. cv SC58. The enzyme has an apparent sub-unit molecular weight of 53 kDa by sodium dodecyl sulphate-polyacrylamide gel electrophoresis with gel-filtration studies, indicating that the native form is a dimer. The K _m of the enzyme for N-methylputrescine has been estimated to be 0.1 mM. Polyclonal antibodies raised to the purified protein recognise one product in an immunoblot of a crude extract of transformed root tissue and will immunoprecipitate N-methylputrescine oxidase activity from such an extract. The antibodies also show a high degree of specificity in immunoblots of crude extracts of transformed root cultures from a range of other solanaceous and non-solanaceous species but do not cross-react with a partially purified preparation of pea-seedling diamine oxidase.Abbreviations MPO N-methylputrescine oxidase - PVDF polyvinylidene difluoride - SDS-PAGE sodium dodecyl sulphate-polyacrylamide gel electrophoresis We would like to thank members of the Plant Cell Biotechnology Group, Institute of Food Research, Norwich Laboratory, for their helpful discussions during the preparation of this paper.     

The relative significance for stem elongation and flowering in Lolium temulentum of 3β-hydroxylation of gibberellins

In previous experiments with many gibberellins (GAs) and GA derivatives applied to Lolium temulentum L., quite different structural requirements were evident for stem elongation on the one hand and for the promotion of flowering on the other. Whereas hydroxylation at carbons 12, 13 and 15 enhanced flowering relative to stem growth, the reverse was the case at carbon 3 (L.T. Evans et al. 1990, Planta 182, 97–106). The significance of hydroxylation at carbon 3 is examined in this paper. The application of inhibitors of 3β-hydroxylation, including C/D-ring-rearranged GAs, reduced stem growth but, in the case of the two acylcyclohexanediones, increased the flowering response when applied on the inductive long day. Later applications of the acylcyclohexanediones, made after floral initiation had occurred, were inhibitory to flowering, suggesting that subsequent inflorescence development requires 3β-hydroxylated GAs. Applications of the 3α-hydroxy epimers of GA₁, GA₃ and GA₄ gave slightly less promotion of flowering in comparison with the 3β-hydroxy GAs, but far less promotion of stem elongation, except in the case of 3-epi-GA₄, which was comparable to GA₄. The 3α-hydroxy epimer of 2,2-dimethyl GA₄ gave less promotion of flowering than its 3β-hydroxy epimer but almost no promotion of stem elongation. The 3α-hydroxy epimers of GA₃ and 2,2-dimethyl GA₄ did not act as competitive inhibitors of the stem elongation elicited by GA₃ and 2,2-dimethyl GA₄, respectively. These results extend the differences in GA structure which favour flowering as opposed to stem elongation, and indicate that 3-hydroxylation and its epimeric configuration are of much greater importance to stem elongation than to flower initiation in Lolium.