Glutamate in plants: metabolism, regulation, and signalling

Glutamate occupies a central position in amino acid metabolism in plants. The acidic amino acid is formed by the action of glutamate synthase, utilizing glutamine and 2-oxoglutarate. However, glutamate is also the substrate for the synthesis of glutamine from ammonia, catalysed by glutamine synthetase. The alpha-amino group of glutamate may be transferred to other amino acids by the action of a wide range of multispecific aminotransferases. In addition, both the carbon skeleton and alpha-amino group of glutamate form the basis for the synthesis of gamma-aminobutyric acid, arginine, and proline. Finally, glutamate may be deaminated by glutamate dehydrogenase to form ammonia and 2-oxoglutarate. The possibility that the cellular concentrations of glutamate within the plant are homeostatically regulated by the combined action of these pathways is examined. Evidence that the well-known signalling properties of glutamate in animals may also extend to the plant kingdom is reviewed. The existence in plants of glutamate-activated ion channels and their possible relationship to the GLR gene family that is homologous to ionotropic glutamate receptors (iGluRs) in animals are discussed. Glutamate signalling is examined from an evolutionary perspective, and the roles it might play in plants, both in endogenous signalling pathways and in determining the capacity of the root to respond to sources of organic N in the soil, are considered.     

T1- Thresholds in Black Holes Increase Clinical-Radiological Correlation in Multiple Sclerosis Patients

Background

Magnetic Resonance Imaging (MRI) is an established tool in diagnosing and evaluating disease activity in Multiple Sclerosis (MS). While clinical-radiological correlations are limited in general, hypointense T1 lesions (also known as Black Holes (BH)) have shown some promising results. The definition of BHs is very heterogeneous and depends on subjective visual evaluation.

Objective

We aimed to improve clinical-radiological correlations by defining BHs using T1 relaxation time (T1-RT) thresholds to achieve best possible correlation between BH lesion volume and clinical disability.

Method

40 patients with mainly relapsing-remitting MS underwent MRI including 3-dimensional fluid attenuated inversion recovery (FLAIR), magnetization-prepared rapid gradient echo (MPRAGE) before and after Gadolinium (GD) injection and double inversion-contrast magnetization-prepared rapid gradient echo (MP2RAGE) sequences. BHs (BH_vis) were marked by two raters on native T1-weighted (T1w)-MPRAGE, contrast-enhancing lesions (CE lesions) on T1w-MPRAGE after GD and FLAIR lesions (total-FLAIR lesions) were detected separately. BH_vis and total-FLAIR lesion maps were registered to MP2RAGE images, and the mean T1-RT were calculated for all lesion ROIs. Mean T1 values of the cortex (CTX) were calculated for each patient. Subsequently, Spearman rank correlations between clinical scores (Expanded Disability Status Scale and Multiple Sclerosis Functional Composite) and lesion volume were determined for different T1-RT thresholds.

Results

Significant differences in T1-RT were obtained between all different lesion types with highest T1 values in visually marked BHs (BH_vis: 1453.3±213.4 ms, total-FLAIR lesions: 1394.33±187.38 ms, CTX: 1305.6±35.8 ms; p<0.05). Significant correlations between BH_vis/total-FLAIR lesion volume and clinical disability were obtained for a wide range of T1-RT thresholds. The highest correlation for BH_vis and total-FLAIR lesion masks were found at T1-RT>1500 ms (Expanded Disability Status Scale vs. lesion volume: r_BHvis = 0.442 and r_total-FLAIR = 0.497, p<0.05; Multiple Sclerosis Functional Composite vs. lesion volume: r_BHvis = -0.53 and r_total-FLAIR = -0.627, p<0.05).

Conclusion

Clinical-radiological correlations in MS patients are increased by application of T1-RT thresholds. With the short acquisition time of the MP2RAGE sequences, quantitative T1 maps could be easily established in clinical studies.     

Physiological role of neuropeptide Y in the regulation of the ascending phase of the peristaltic reflex

The physiological role of neuropeptide Y (NPY) and of specific NPY receptors in regulating the intestinal peristaltic reflex was examined in three-compartment flat-sheet preparations of rat colon. Graded muscle stretch or mucosal stimulation applied to the central compartment inhibited NPY release in the orad compartment where ascending contraction was measured. NPY and the Y1-receptor agonist [Leu31, Pro34]NPY inhibited, whereas the selective Y1-receptor antagonist BIBP 3226 augmented ascending contraction and substance P (SP) release in the orad compartment induced by muscle stretch or mucosal stimulation. Neither agonist nor antagonist had any effect on descending relaxation or VIP release in the caudad compartment. The Y2-receptor agonist NPY13-36 and antagonist BIIE 0246 had no effect on peptide release or mechanical response. The results indicate that suppression of a tonic inhibitory influence of NPY neurons on excitatory neurotransmitter release contributes substantially to the orad contractile phase of the peristaltic reflex. The effect of NPY on neurotransmitter release is mediated by Y1 receptors.     

Exine Sculpture in Pariana Pollen (Gramineae)

Pollen grains of eieven species of Pariana, a small genus of herbaceous bamboos, were studied using LM, SEM and TEM. Ten of them have the Pariana stenolemma-type of pollen characterized by areolate exine due to relatively high and well separated denticulate processes on a slightly undulated tectum, vestigial columellae and no distinct annulus. At the pore edge the foot layer is thickened and folded.

P. campetris (P. campestris-type) shows this exine feature only at magnifications higher than x 2000, whereas the denticulate processes are clearly visible at x 400 magnification in the other ten species. The pores are bordered by a distinct annulus.

The high relief of the Pariana pollen forming a relatively rough surface would offer more friction in wind transport than the smooth surface of other grass pollen grains. Insects visiting the flowers have been observed which support the idea of possible insect pollination. If this would be the case, the parianas would be an example of correlation between pollen form and function in the evolution of the Gramineae.     

Optimizing Dendritic Cell-Based Approaches for Cancer Immunotherapy

Dendritic cells (DC) are professional antigen-presenting cells uniquely suited for cancer immunotherapy. They induce primary immune responses, potentiate the effector functions of previously primed T-lymphocytes, and orchestrate communication between innate and adaptive immunity. The remarkable diversity of cytokine activation regimens, DC maturation states, and antigen-loading strategies employed in current DC-based vaccine design reflect an evolving, but incomplete, understanding of optimal DC immunobiology. In the clinical realm, existing DC-based cancer immunotherapy efforts have yielded encouraging but inconsistent results. Despite recent U.S. Federal and Drug Administration (FDA) approval of DC-based sipuleucel-T for metastatic castration-resistant prostate cancer, clinically effective DC immunotherapy as monotherapy for a majority of tumors remains a distant goal. Recent work has identified strategies that may allow for more potent “next-generation” DC vaccines. Additionally, multimodality approaches incorporating DC-based immunotherapy may improve clinical outcomes.     

Biogenic methane contributes to the food web of a large,shallow lake

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Biochemistry and physiology of monoamine oxidase (MAO) activity in the ring dove (Streptopelia risoria). II. Distribution of MAO in different tissues

Monoamine oxidase (MAO) activity was measured fluorometrically in liver, kidney, intestine and brain of adult male and female ring doves. Liver MAO was inhibited in a concentration-related fashion by clorgyline and harmaline (MAO type A inhibitors) where a plateau in the inhibition curve occurred with about 15% activity remaining, and also by the type B inhibitor deprenyl, which produced a plateau when about 85% activity remained. Kidney, intestine and brain MAO were inhibited in a biphasic manner by harmaline. Results with inhibitors suggest that 85% of liver MAO, 86% of kidney MAO, 88% of intestine and 75% of brain MAO is type A. Using 10(-6) M harmaline to differentiate between MAO-A and MAO-B type activities, the apparent maximal velocities (Vmax) and Michaelis constants (Km) were determined in different tissues. Most activity occurred in the intestine, with proportionally lesser amounts of kidney, liver and brain. The majority of MAO present was in the A form. Except for kidney, Km of MAO-B was higher than that of MAO-A. Both MAO-A and -B activities were higher in the intestines of male birds, although sex differences in content and type of MAO activity were not observed in other tissues of the ring dove.     

The spliceosomal snRNAs of Caenorhabditis elegans.

Nematodes are the only group of organisms in which both cis- and trans-splicing of nuclear mRNAs are known to occur. Most Caenorhabditis elegans introns are exceptionally short, often only 50 bases long. The consensus donor and acceptor splice site sequences found in other animals are used for both cis- and trans-splicing. In order to identify the machinery required for these splicing events, we have characterized the C. elegans snRNAs. They are similar in sequence and structure to those characterized in other organisms, and several sequence variations discovered in the nematode snRNAs provide support for previously proposed structure models. The C. elegans snRNAs are encoded by gene families. We report here the sequences of many of these genes. We find a highly conserved sequence, the proximal sequence element (PSE), about 65 bp upstream of all 21 snRNA genes thus far sequenced, including the SL RNA genes, which specify the snRNAs that provide the 5' exons in trans-splicing. The sequence of the C. elegans PSE is distinct from PSE's from other organisms.     

Multiclonal asymptomatic Plasmodium falciparum infections predict a reduced risk of malaria disease in a Tanzanian population

Protective immunity to malaria is acquired after repeated exposure to the polymorphic Plasmodium falciparum parasite. Whether the number of concurrent antigenically diverse clones in asymptomatic infections predicts the risk of subsequent clinical malaria needs further understanding. We assessed the diversity of P. falciparum infections by merozoite surface protein 2 genotyping in a longitudinal population based study in Tanzania. The number of clones was highest in children 6-10 years and in individuals with long time to previous anti-malarial treatment. Individual exposure, analysed by circumsporozoite protein antibody levels, was associated with parasite prevalence but not with the number of clones. The risk of subsequent clinical malaria in children free of acute disease or recent treatment was, compared to one clone, reduced in individuals with multiclonal infections or without detectable parasites, with the lowest hazard ratio 0.28 (95% confidence interval 0.10-0.78 Cox regression) for 2-3 clones. The number of clones was not associated with haemoglobin levels. A reduced risk of malaria in asymptomatic individuals with multiclonal persistent P. falciparum infections suggests that controlled maintenance of diverse infections is important for clinical protection in continuously exposed individuals, and needs to be considered in the design and evaluation of new malaria control strategies.