Termite Prey Specialization in the Pitcher Plant Nepenthes albomarginata--Evidence from Stable Isotope Analysis

Old World pitcher plants (Nepenthes spp., Nepenthaceae) trapand digest invertebrate prey to derive nutrients, primarilynitrogen (N). In the majority of lowland Nepenthes species studiedto date, ants (Hymenoptera, Formicidae) are numerically thedominant prey taxon. Nepenthes albomarginata is unusual in showingan apparent bias towards the capture of termites (Isoptera).We tested the hypothesis that N. albomarginata derives N fromtermite capture, by comparison of foliar stable N isotope abundance(     

Acclimation response of spring wheat in a free-air CO2 enrichment (FACE) atmosphere with variable soil nitrogen regimes. 1. Leaf position and phenology determine acclimation response

We have examined the photosynthetic acclimation of wheat leaves grown at an elevated CO₂ concentration, and ample and limiting N supplies, within a field experiment using free-air CO₂ enrichment (FACE). To understand how leaf age and developmental stage affected any acclimation response, measurements were made on a vertical profile of leaves every week from tillering until maturity. The response of assimilation (A) to internal CO₂ concentration (C_i) was used to estimate the in vivo carboxylation capacity (Vc_max) and maximum rate of ribulose-1,5-bisphosphate limited photosynthesis (A _sat). The total activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), and leaf content of Rubisco and the Light Harvesting Chlorophyll a/b protein associated with Photosystem II (LHC II), were determined. Elevated CO₂ did not alter Vc_max in the flag leaf at either low or high N. In the older shaded leaves lower in the canopy, acclimatory decline in Vc_max and A _sat was observed, and was found to correlate with reduced Rubisco activity and content. The dependency of acclimation on N supply was different at each developmental stage. With adequate N supply, acclimation to elevated CO₂ was also accompanied by an increased LHC II/Rubisco ratio. At low N supply, contents of Rubisco and LHC II were reduced in all leaves, although an increased LHC II/Rubisco ratio under elevated CO₂ was still observed. These results underscore the importance of leaf position, leaf age and crop developmental stage in understanding the acclimation of photosynthesis to elevated CO₂ and nutrient stress. This revised version was published online in June 2006 with corrections to the Cover Date.     

Cytologic diagnosis of Pneumocystis carinii infection by bronchoalveolar lavage in acquired immune deficiency syndrome

Twenty-six patients with pulmonary infiltrates and suspected acquired immune deficiency syndrome (AIDS) underwent 29 fiberoptic bronchoscopies, including bronchoalveolar lavage. Seventeen of the 18 patients (94.4%) shown to have Pneumocystis carinii pneumonia were diagnosed by examination of the bronchoalveolar lavage specimen. Minor complications occurred in 7 of 29 total bronchoscopies and included transient fever and hypoxemia. Bronchoalveolar lavage is a safe, easy and effective procedure for making the diagnosis of P. carinii pneumonia in patients at high risk for AIDS and should be included routinely when performing fiberoptic bronchoscopy.     

Identification of a novel 7-cis-11-trans-lipoxin A4 generated by human neutrophils: total synthesis, spasmogenic activities and comparison with other geometric isomers of lipoxins A4 and B4

Addition of (15S)-hydroxy-5,8,11-cis-13-trans-eicosatetraenoic acid (15-HETE) and the ionophore A23187 (2.5 microM) to human neutrophils led to the formation of both lipoxin A4 and lipoxin B4 as well as a novel 5,6,15-trihydroxyeicosatetraenoic acid. The new compound was identified using an improved isolation and detection system and its basic structure was determined by physical methods. On the basis of biosynthetic considerations, geometric isomers of lipoxin A4 and lipoxin B4 were prepared by total synthesis. Comparison of these synthetic materials with the neutrophil-derived product showed that the new compound is (5S,6R,15S)-trihydroxy-9,11,13-trans-7-cis-eicosatetraenoic acid or the 7-cis-11-trans-isomer of LXA4 (7-cis-11-trans-LXA4). LXA4, 11-trans-LXA4, 7-cis-LXA4 and 7-cis-11-trans-LXA4 all evoked dose-dependent (0.1-10 microM) contractions of the guinea pig lung strip, whereas 6-cis-LXB4 and 6-cis-8-trans-LXB4 relaxed this preparation. LXA4 and 7-cis-LXA4 were approx. 10-times more potent than the compounds with 11-trans geometry. However, all four double-bond isomers of LXA4 caused contractions which, based upon pharmacological evidence, appeared to involve specific activation of the same site as cysteinyl-containing leukotrienes. In conclusion, 7-cis-11-trans-LXA4 was isolated and identified as a novel biologically active eicosanoid formed by human neutrophils.     

Separate hypoglycaemic thresholds for gastric acid and pepsin secretion following insulin or posterior hypothalamic stimulation.

The level of hypoglycaemia required to elicit gastric secretion of acid and pepsin was studied in urethane-anaesthetized rats. Hypoglycaemia was induced by intravenous injection of insulin or by electrical stimulation of the posterior hypothalamus. In each case the blood glucose values below which gastric secretion was stimulated were significantly higher for pepsin than for acid secretion. This consistently resulted in the onset of pepsin secretion in advance of the onset of acid secretion. These observations suggest that the production of the different components of the gastric juice was under the influence of either separate hypothalamic glucoreceptors, or a single set of glucoreceptors able to respond selectively to different blood glucose levels.     

Chronic antioxidant therapy reduces oxidative stress in a mouse model of Alzheimer's disease

Oxidative modifications are a hallmark of oxidative imbalance in the brains of individuals with Alzheimer's, Parkinson's and prion diseases and their respective animal models. While the causes of oxidative stress are relatively well-documented, the effects of chronically reducing oxidative stress on cognition, pathology and biochemistry require further clarification. To address this, young and aged control and amyloid-β protein precursor-over-expressing mice were fed a diet with added R-alpha lipoic acid for 10 months to determine the effect of chronic antioxidant administration on the cognition and neuropathology and biochemistry of the brain. Both wild type and transgenic mice treated with R-alpha lipoic acid displayed significant reductions in markers of oxidative modifications. On the other hand, R-alpha lipoic acid had little effect on Y-maze performance throughout the study and did not decrease end-point amyloid-β load. These results suggest that, despite the clear role of oxidative stress in mediating amyloid pathology and cognitive decline in ageing and AβPP-transgenic mice, long-term antioxidant therapy, at levels within tolerable nutritional guidelines and which reduce oxidative modifications, have limited benefit.