Perception and modification of plant flavonoid signals by rhizosphere microorganisms

Flavonoids are a diverse class of polyphenolic compounds that are produced as a result of plant secondary metabolism. They are known to play a multifunctional role in rhizospheric plant-microbe and plant-plant communication. Most familiar is their function as a signal in initiation of the legume-rhizobia symbiosis, but, flavonoids may also be signals in the establishment of arbuscular mycorrhizal symbiosis and are known agents in plant defence and in allelopathic interactions. Flavonoid perception by, and impact on, their microbial targets (e.g. rhizobia, plant pathogens) is relatively well characterized. However, potential impacts on 'non-target' rhizosphere inhabitants ('non-target' is used to distinguish those microorganisms not conventionally known as targets) have not been thoroughly investigated. Thus, this review first summarizes the conventional roles of flavonoids as nod gene inducers, phytoalexins and allelochemicals before exploring questions concerning 'non-target' impacts. We hypothesize that flavonoids act to shape rhizosphere microbial community structure because they represent a potential source of carbon and toxicity and that they impact on rhizosphere function, for example, by accelerating the biodegradation of xenobiotics. We also examine the reverse question, 'how do rhizosphere microbial communities impact on flavonoid signals?' The presence of microorganisms undoubtedly influences the quality and quantity of flavonoids present in the rhizosphere, both through modification of root exudation patterns and microbial catabolism of exudates. Microbial alteration and attenuation of flavonoid signals may have ecological consequences for below-ground plant-microbe and plant-plant interaction. We have a lack of knowledge concerning the composition, concentration and bioavailability of flavonoids actually experienced by microbes in an intact rhizosphere, but this may be addressed through advances in microspectroscopic and biosensor techniques. Through the use of plant mutants defective in flavonoid biosynthesis, we may also start to address the question of the significance of flavonoids in shaping rhizosphere community structure and function.

Life cycle of the QBO-modulated 11-year solar cycle signals in the Northern Hemispheric winter

This paper provides some insights on the quasi-biennial oscillation (QBO) modulated 11-year solar cycle (11-yr SC) signals in Northern Hemisphere (NH) winter temperature and zonal wind. Daily ERA-40 Reanalysis and ECMWF Operational data for the period of 1958-2006 were used to examine the seasonal evolution of the QBO-solar cycle relationship at various pressure levels up to the stratopause. The results show that the solar signals in the NH winter extratropics are indeed QBO-phase dependent, moving poleward and downward as winter progresses with a faster descent rate under westerly QBO than under easterly QBO. In the stratosphere, the signals are highly significant in late January to early March and have a life span of 30-50 days. Under westerly QBO, the stratospheric solar signals clearly lead and connect to those in the troposphere in late March and early April where they have a life span of 10 days. As the structure changes considerably from the upper stratosphere to the lower troposphere, the exact month when the maximum solar signals occur depends largely on the altitude chosen. For the low-latitude stratosphere, our analysis supports a vertical double-peaked structure of positive signature of the 11-yr SC in temperature, and demonstrates that this structure is further modulated by the QBO. These solar signals have a longer life span (3-4 months) in comparison to those in the extratropics. The solar signals in the lower stratosphere are stronger in early winter but weaker in late winter, while the reverse holds in the upper stratosphere.

Domestically produced food: Consumer perceptions of origin, safety and the issue of trust

It is becoming increasingly difficult for the public to attempt to assess risks using traditional methods such as smell, taste or other physical attributes of food. The existence of extrinsic cues such as the country of origin (COO) of food can help to make food purchase decisions easier for consumers. However, the use of extrinsic cues depends heavily on the extent to which consumers trust such signals to be indicative of quality or safety, which in turn depends on the credibility behind that cue. This paper aims to examine consumers association of domestically produced food with increased food safety standards and the association of COO and food safety information with socio-demographics and other aspects of consumer psychology such as attitudes, risk perception and trust. Using an ordered probit model, domestic production is examined as an extrinsic cue for food safety by looking at the relationship with trust in food safety information provided by national food standards agencies (NFSAs) and other socio-demographic characteristics, based on nationally representative data from 2725 face-to-face interviews across five European countries. Results suggest that domestic production of food is an extrinsic cue for food safety and as consumers place increasing importance on food safety they are more interested in food produced in their own country. This, coupled with consumer trust in a strong, and independent national food standards agency, suggests the potential exists for the increased consumption of domestically produced foods.

Viral nucleolar localisation signals determine dynamic trafficking within the nucleolus

Localisation of both viral and cellular proteins to the nucleolus is determined by a variety of factors including nucleolar localisation signals (NoLSs), but how these signals operate is not clearly understood. The nucleolar trafficking of wild type viral proteins and chimeric proteins, which contain altered NoLSs, were compared to investigate the role of NoLSs in dynamic nucleolar trafficking. Three viral proteins from diverse viruses were selected which localised to the nucleolus; the coronavirus infectious bronchitis virus nucleocapsid (N) protein, the herpesvirus saimiri ORF57 protein and the HIV-1 Rev protein. The chimeric proteins were N protein and ORF57 protein which had their own NoLS replaced with those from ORF57 and Rev proteins, respectively. By analysing the sub-cellular localisation and trafficking of these viral proteins and their chimeras within and between nucleoli using confocal microscopy and photo-bleaching we show that NoLSs are responsible for different nucleolar localisations and trafficking rates.

Design and analysis of climate model experiments for the efficient estimation of anthropogenic signals

Presented herein is an experimental design that allows the effects of several radiative forcing factors on climate to be estimated as precisely as possible from a limited suite of atmosphere-only general circulation model (GCM) integrations. The forcings include the combined effect of observed changes in sea surface temperatures, sea ice extent, stratospheric (volcanic) aerosols, and solar output, plus the individual effects of several anthropogenic forcings. A single linear statistical model is used to estimate the forcing effects, each of which is represented by its global mean radiative forcing. The strong colinearity in time between the various anthropogenic forcings provides a technical problem that is overcome through the design of the experiment. This design uses every combination of anthropogenic forcing rather than having a few highly replicated ensembles, which is more commonly used in climate studies. Not only is this design highly efficient for a given number of integrations, but it also allows the estimation of (nonadditive) interactions between pairs of anthropogenic forcings. The simulated land surface air temperature changes since 1871 have been analyzed. The changes in natural and oceanic forcing, which itself contains some forcing from anthropogenic and natural influences, have the most influence. For the global mean, increasing greenhouse gases and the indirect aerosol effect had the largest anthropogenic effects. It was also found that an interaction between these two anthropogenic effects in the atmosphere-only GCM exists. This interaction is similar in magnitude to the individual effects of changing tropospheric and stratospheric ozone concentrations or to the direct (sulfate) aerosol effect. Various diagnostics are used to evaluate the fit of the statistical model. For the global mean, this shows that the land temperature response is proportional to the global mean radiative forcing, reinforcing the use of radiative forcing as a measure of climate change. The diagnostic tests also show that the linear model was suitable for analyses of land surface air temperature at each GCM grid point. Therefore, the linear model provides precise estimates of the space time signals for all forcing factors under consideration. For simulated 50-hPa temperatures, results show that tropospheric ozone increases have contributed to stratospheric cooling over the twentieth century almost as much as changes in well-mixed greenhouse gases.

Amyloid-like fibril-forming supramolecular beta-sheets from a beta-turn forming tripeptide containing non-coded amino acids: the crystallographic signature

The crystal structure of a terminally protected tripeptide Boc-Leu-Aib-beta-Ala-OMe 1 containing non-coded amino acids reveals that it adopts a beta-turn structure, which sell-assembles to form a supramolecular beta-sheet via non-covalent interactions. The SEM image of peptide 1 exhibits amyloid-like fibrillar morphology in the solid state. (C) 2002 Elsevier Science Ltd. All rights reserved.

Supramolecular peptide helix from a novel double turn forming peptide containing a beta-amino acid

A single-crystal X-ray diffraction study of the terminally protected tetrapeptide Boc-beta-Ala-Aib-Leu-Aib-OMe 1 (Aib: alpha-aminoisobutyric acid; beta-Ala: beta-Alanine) reveals that it adopts a new type of double turn structure which self-associates to form a unique supramolecular helix through intermolecular hydrogen bonds. Scanning electron microscopic studies show that peptide 1 exhibits amyloid-like fibrillar morphology in the solid state. (C) 2003 Elsevier Science Ltd. All rights reserved.

Can a consecutive double turn conformation be considered as a peptide based molecular scaffold for supramolecular helix in the solid state?

Helices and sheets are ubiquitous in nature. However, there are also some examples of self-assembling molecules forming supramolecular helices and sheets in unnatural systems. Unlike supramolecular sheets there are a very few examples of peptide sub-units that can be used to construct supramolecular helical architectures using the backbone hydrogen bonding functionalities of peptides. In this report we describe the design and synthesis of two single turn/bend forming peptides (Boc-Phe-Aib-Ile-OMe 1 and Boc-Ala-Leu-Aib-OMe 2) (Aib: alpha-aminoisobutyric acid) and a series of double-turn forming peptides (Boc-Phe-Aib-IIe-Aib-OMe 3, Boc-Leu-Aib-Gly-Aib-OMe 4 and Boc-gamma-Abu-Aib-Leu-Aib-OMe 5) (gamma-Abu: gamma-aminobutyric acid). It has been found that, in crystals, on self-assembly, single turn/bend forming peptides form either a supramolecular sheet (peptide 1) or a supramolecular helix (peptide 2). unlike self-associating double turn forming peptides, which have only the option of forming supramolecular helical assemblages. (c) 2005 Elsevier Ltd. All rights reserved.

m-aminobenzoic acid inserted beta-turn in acyclic tripeptides: a peptidomimetic design

X-ray diffraction studies show that peptides Boc-Leu-Aib-m-ABA-OMe (I) (Aib, alpha-aminoisobutyric acid; m-ABA, meta-aminobenzoic acid) and Boc-Phe-Aib-m-ABA-OMe, (II) adopt a type-II beta-turn conformation, solely stabilized by co-operative steric interactions amongst the amino acid residues. This type of U-turn without any intramolecular hydrogen bonding is generally referred to as an open turn. Although there are some examples of constrained cyclic peptides in which o-substituted benzenes have been inserted to mimic the turn region of the neurotrophin, a nerve growth factor, peptides I and II present novel two examples where m-aminobenzoic acid has been incorporated in the beta-turn of acyclic tripeptides. The result also demonstrates the first crystallographic evidence of a beta-turn structure containing an inserted m-aminobenzoic acid, which can be considered as a rigid gamma-aminobutyric acid with an all-trans extended configuration. (c) 2005 Elsevier Ltd. All rights reserved.

Design of a turn-linker-turn foldamer by incorporating meta-amino benzoic acid in the middle of a helix forming hexapeptide sequence: A helix breaking approach

Single crystal X-ray diffraction studies reveal that the incorporation of meta-amino benzoic acid in the middle of a helix forming hexapeptide sequence such as in peptide I Boc-Ile(1)-Aib(2)-Val(3)-m-ABA(4)-Ile(5)-Aib(6)-Leu(7)-OMe (Aib: alpha-amino isobutyric acid: m-ABA: meta-amino benzoic acid) breaks the helix propagation to produce a turn-linker-turn (T-L-T) foldamer in the solid state. In the crystalline state two conformational isomers of peptide I self-assemble in antiparallel fashion through intermolecular hydrogen bonds and aromatic pi-pi interactions to form a molecular duplex. The duplexes are further interconnected through intermolecular hydrogen bonds to form a layer of peptides. The layers are stacked one on top of the other through van der Waals interactions to form hydrophilic channels filled with solvent methanol. (C) 2009 Elsevier B.V. All rights reserved.

Design of a new foldamer turn-linker-turn in acyclic hexapeptides and formation of channels through self-assembly

Single crystal X-ray diffraction studies and solvent dependent NMR titration reveal that the designed pepticles I and 11, Boc-Xx(1)-Aib(2)-Yy(3)-NH(CH2)(2)NH-Yy(3)-Aib(2)-Xx(1)-Boc, where Xx and Yy are lie and Leu in peptide I and Leu and Val in peptide 11, respectively, fold into a turn-linker-turn (T-L-T) conformation both in the solid state and in solution. In the crystalline state the T-L-T foldamers; of peptide I and II self-assemble to form a three-dimensional framework of channels. The insides of the channels are hydrophilic and found to contain solvent CHCl3 hydrogen bonded to exposed C=O of Aib located at the turn regions. (c) 2008 Elsevier B.V. All rights reserved.

Overlapping double turn conformations adopted by tetrapeptides containing non-coded alpha-Amino Isobutyric Acid (AIB) and formation of tape-like structures through supramolecular helix mediated self-assembly

Single crystal X-ray diffraction studies and solvent dependent H-1 NMR titrations reveal that a set of four tetrapeptides with general formula Boc-Xx(1)-Aib(2)-Yy(3)-Zz(4)-OMe, where Xx, Yy and Zz are coded L- amino acids, adopt equivalent conformations that can be described as overlapping double turn conformations stabilized by two 4 -> 1 intramolecular hydrogen bonds between Yy(3)-NH and Boc C=O and Zz(4)-NH and Xx(1)C=O. In the crystalline state, the double turn structures are packed in head-to-tail fashion through intermolecular hydrogen bonds to create supramolecular helical structures. Field emission scanning electron microscopic (FE-SEM) images of the tetrapeptides in the solid state reveal that they can form flat tape-like structures. The results establish that synthetic Aib containing supramolecular helices can form highly ordered self-aggregated amyloid plaque like human amylin.