Surface reflectance properties of Antarctic moss and their relationship to plant species, pigment composition and photosynthetic function

In this study the variations in surface reflectance properties and pigment concentrations of Antarctic moss over species, sites, microtopography and with water content were investigated. It was found that species had significantly different surface reflectance properties, particularly in the region of the red edge (approximately 700 nm), but this did not correlate strongly with pigment concentrations. Surface reflectance of moss also varied in the visible region and in the characteristics of the red edge over different sites. Reflectance parameters, such as the photochemical reflectance index (PRI) and cold hard band were useful discriminators of site, microtopographic position and water content. The PRI was correlated both with the concentrations of active xanthophyll-cycle pigments and the photosynthetic light use efficiency, F-v/F-m, measured using chlorophyll fluorescence. Water content of moss strongly influenced the amplitude and position of the red-edge as well as the PRI, and may be responsible for observed differences in reflectance properties for different species and sites. All moss showed sustained high levels of photoprotective xanthophyll pigments, especially at exposed sites, indicating moss is experiencing continual high levels of photochemical stress.

Function of CMV-encoded MHC class I homologues

Homologues of MHC class I proteins have been identified in the genomes of human, murine and rat cytomegaloviruses (CMVs). Given the pivotal role of the MHC class I protein in cellular immunity, it has been postulated that the viral homologues subvert the normal antiviral immune response of the host, thus promoting virus replication and dissemination in an otherwise hostile environment. This review focuses on recent studies of the CMV MHC class I homologues at the molecular, cellular and whole animal level and presents current hypotheses for their roles in the CMV life cycle.

Dormancy release in Lolium rigidum seeds is a function of thermal after-ripening time and seed water content

Dormancy release in seeds of Lolium rigidum Gaud. (annual ryegrass) was investigated in relation to temperature and seed water content. Freshly matured seeds were collected from cropping fields at Wongan Hills and Merredin, Western Australia. Seeds from Wongan Hills were equilibrated to water contents between 6 and 18% dry weight and after-ripened at constant temperatures between 9 and 50degreesC for up to 23 weeks. Wongan Hills and Merredin seeds at water contents between 7 and 17% were also after-ripened in full sun or shade conditions. Dormancy was tested at regular intervals during after-ripening by germinating seeds on agar at 12-h alternating 15degreesC (dark) and 25degreesC (light) periods. Rate of dormancy release for Wongan Hills seeds was a positive linear function of after-ripening temperature above a base temperature (T-b) of 5.4degreesC. A thermal after-ripening time model for dormancy loss accounting for seed moisture in the range 6-18% was developed using germination data for Wongan Hills seeds after-ripened at constant temperatures. The model accurately predicted dormancy release for Wongan Hills seeds after-ripened under naturally fluctuating temperatures. Seeds from Merredin responded similarly but had lower dormancy at collection and a faster rate of dormancy release in seeds below 9% water content.

Calcium-activated potassium channels: Multiple contributions to neuronal function

Calcium-activated potassium channels are a large family of potassium channels that are found throughout the central nervous system and in many other cell types. These channels are activated by rises in cytosolic calcium largely in response to calcium influx via voltage-gated calcium channels that open during action potentials. Activation of these potassium channels is involved in the control of a number of physiological processes from the firing properties of neurons to the control of transmitter release. These channels form the target for modulation for a range of neurotransmitters and have been implicated in the pathogenesis of neurological and psychiatric disorders. Here the authors summarize the varieties of calcium-activated potassium channels present in central neurons and their defining molecular and biophysical properties.

Cytokine expanded myeloid precursors function as regulatory antigen presenting cells and induce tolerance through IL-10 producing regulatory T cells

The initiation of graft vs. host disease (GVHD) after stem cell transplantation is dependent on direct antigen presentation by host antigen presenting cells (APC) while the effect of indirect antigen presentation by donor APC is unknown. We have studied the role of indirect antigen presentation in allogenic responses by adding populations of cytokine-expanded donor APC to haematopoietic grafts that would otherwise induce lethal GVHD. Progenipoietin-1 (a synthetic G-CSF/Flt-3 L molecule) and G-CSF expanded myeloid DC, plasmacytoid DC and a novel granulocyte-monocyte precursor population (GM) that differentiate into class IIpos, CD80/CD86pos, CD40neg APC during GVHD. Whereas addition of plasmacytoid and myeloid donor DC augmented GVHD, GM cells induced transplant tolerance via MHC class II restricted generation of IL-10-secreting regulatory T cells. Thus a population of cytokine expanded granulocyte-monocyte precursors function as regulatory antigen presenting cells, suggesting that G-CSF derivatives may have application in disorders characterised by a loss of self-tolerance.

Alterations in cardiac dihydropyridine receptors and calcium channel function in mdx mice

Duchenne muscular dystrophy (DMD) is a fatal neuromuscular condition affecting approximately one in 3500 live male births resulting from the lack of the myocyte protein dystrophin. The absence of dystrophin in cardiac myocytes is associated with calcium overload which in turn activates calcium-dependent proteolytic enzymes contributing to congestive heart failure, muscle necrosis and fibrosis. To date, the basis for the calcium overload has not been determined. Since L-type calcium channels are a major mediator of calcium influx we determined their potential contribution to the calcium overload. Male muscular dystrophy (mdx) mice and control C57BL10ScSn (C57) mice aged 12– 16 weeks were used in all experiments. In tissue bath studies, isolated contracting left atria from mdx revealed a reduced potency to the dihydropyridine (DHP) agonist BayK8644 and antagonist nifedipine (P < 0.05). Similarly, radioligand binding studies using the DHP antagonist [3H]-PN 200-110 showed a reduced potency (P < 0.05) in isolated membranes, associated with an increased receptor density (P < 0.05). The increased receptor density was supported by RT-PCR experiments revealing increased RNAfor the DHP receptor. Patch clamp studies revealed the presence of a diltiazem sensitive calcium current that showed delayed inactivation in isolated mdx myocytes (P < 0.01). In conclusion, the increased number of DHP binding sites and the delay in L-type current inactivation may both contribute to increased calcium influx and hence calcium overload in the dystrophin deficient mdx cardiac myocytes.

Homocysteine-lowering treatment with folic acid, cobalamin, and pyridoxine does not reduce blood markers of inflammation, endothelial dysfunction, or hypercoagulability in patients with previous transient ischemic attack or stroke - a randomized substudy

Background and Purpose - Epidemiological and laboratory studies suggest that increasing concentrations of plasma homocysteine ( total homocysteine [tHcy]) accelerate cardiovascular disease by promoting vascular inflammation, endothelial dysfunction, and hypercoagulability. Methods - We conducted a randomized controlled trial in 285 patients with recent transient ischemic attack or stroke to examine the effect of lowering tHcy with folic acid 2 mg, vitamin B-12 0.5 mg, and vitamin B-6 25 mg compared with placebo on laboratory markers of vascular inflammation, endothelial dysfunction, and hypercoagulability. Results - At 6 months after randomization, there was no significant difference in blood concentrations of markers of vascular inflammation (high-sensitivity C-reactive protein [P = 0.32]; soluble CD40L [ P = 0.33]; IL-6 [P = 0.77]), endothelial dysfunction ( vascular cell adhesion molecule-1 [P = 0.27]; intercellular adhesion molecule-1 [P = 0.08]; von Willebrand factor [P = 0.92]), and hypercoagulability (P-selectin [P = 0.33]; prothrombin fragment 1 and 2 [P = 0.81]; D-dimer [P = 0.88]) among patients assigned vitamin therapy compared with placebo despite a 3.7-mumol/L (95% CI, 2.7 to 4.7) reduction in total homocysteine (tHcy). Conclusions - Lowering tHcy by 3.7 mumol/L with folic acid-based multivitamin therapy does not significantly reduce blood concentrations of the biomarkers of inflammation, endothelial dysfunction, or hypercoagulability measured in our study. The possible explanations for our findings are: ( 1) these biomarkers are not sensitive to the effects of lowering tHcy (eg, multiple risk factor interventions may be required); ( 2) elevated tHcy causes cardiovascular disease by mechanisms other than the biomarkers measured; or ( 3) elevated tHcy is a noncausal marker of increased vascular risk.

Association of tumor necrosis factor-alpha polymorphisms and ozone-induced change in lung function

Ozone is a major air pollutant with adverse health effects which exhibit marked inter-individual variability. In mice, regions of genetic linkage with ozone-induced lung injury include the tumor necrosis factor-alpha (TNF), lymphotoxin-alpha (LTA), Toll-like receptor 4 (TLR4), superoxide dismutase (SOD2), and glutathione peroxidase (GPX1) genes. We genotyped polymorphisms in these genes in 51 individuals who had undergone ozone challenge. Mean change in FEV1 with ozone challenge, as a percentage of baseline, was -3% in TNF -308G/A or A/A individuals, compared with -9% in G/G individuals (p = 0.024). When considering TNF haplotypes, the smallest change in FEV1 with ozone exposure was associated with the TNF haplotype comprising LTA +252G/TNF -1031T/TNF -308A/TNF -238G. This association remained statistically significant after correction for age, sex, disease, and ozone concentration (p = 0.047). SOD2 or GPX1 genotypes were not associated with lung function, and the TLR4 polymorphism was too infrequent to analyze. The results of this study support TNF as a genetic factor for susceptibility to ozone-induced changes in lung function in humans, and has potential implications for stratifying health risks of air pollution.

Il-1 beta breaks tolerance through inhibition of regulatory T cell function

IL-1 is a key proinflammatory driver of several autoimmune diseases including juvenile inflammatory arthritis, diseases with mutations in the NALP/cryopyrin complex and Crohn’s disease, and is genetically or clinically associated with many others. IL-1 is a pleiotropic proinflammatory cytokine; however the mechanisms by which increased IL-1 signaling promotes autoreactive T cell activity are not clear. Here we show that autoimmune-prone NOD and IL-1 receptor antagonist-deficient C57BL/6 mice both produce high levels of IL-1, which drives autoreactive effector cell expansion. IL-1beta drives proliferation and cytokine production by CD4+CD25+FoxP3– effector/memory T cells, attenuates CD4+CD25+FoxP3+ regulatory T cell function, and allows escape of CD4+CD25– autoreactive effectors from suppression. Thus, inflammation or constitutive overexpression of IL-1beta in a genetically predisposed host can promote autoreactive effector T cell expansion and function, which attenuates the ability of regulatory T cells to maintain tolerance to self.