Enzymic synthesis,chemical characterisation and Sda activity of GalNAcß1-4[NeuAcα2-3]Galß1-4GlcNAc and GalNAcß1-4[NeuAcα2-3]Galß1-4Glc

The tetrasaccharides GalNAcß1-4[NeuAc2-3]Galß1-4Glc and GalNAcß1-4[NeuAc2-3]Galß1-4GlcNAc were synthesised by enzymic transfer of GalNAc from UDP-GalNAc to 3-sialyllactose (NeuAc2-3Galß1-4Glc) and 3-sialyl-N-acetyllactosamine (NeuAc2-3Galß1-4GlcNAc). The structures of the products were established by methylation and¹H-500 MHz NMR spectroscopy. In Sd^a serological tests the product formed with 3-sialyl-N-acetyllactosamine was highly active whereas that formed with 3-sialyllactose had only weak activity.     

Approaches to breeding for salinity tolerance - a case study on Porteresia coarctata

Cereals are the world's major source of food for human nutrition. Among these, rice (Oryza sativa) is the most prominent and represents the staple diet for more than two-fifths (2.4 billion) of the world's population, making it the most important food crop of the developing world (Anon., 2000a). Rice production in vast stretches of coastal areas is hampered due to high soil salinity. This is because rice is a glycophyte and it does not grow well under saline conditions. In order to increase rice production in these areas there is a need to develop rice varieties suited to saline environments. Research has shown that Porteresia coarctata, a highly salt tolerant wild relative of rice growing in estuarine soils, is an important material for transferring salt tolerant characteristics to rice. It is quite possible that Porteresia may be used as a parent for evolving better and truly salt resistant varieties. The inadequate results and the difficulties associated with conventional breeding techniques necessitate the use of the tools of crop biotechnology in unravelling some of the characteristics of Porteresia that have been highlighted in this report. In view of the limited resources available for increasing salinity tolerance to the breeders to wild rice germplasm, Porteresia is undoubtedly one of the key source species for elevating salinity tolerance in cultivated rice.     

Characterization of a spinach psbS cDNA encoding the 22 kDa protein of photosystem II.

An intrinsic 22 kDa polypeptide is found associated with the oxygen-evolving photosystem II (PSII) core complex in all green plants and cyanobacteria so far examined, although it does not appear to be required for oxygen evolution. Amino acid sequence information obtained from the purified 22 kDa protein was used to construct a probe that was employed to isolate a full-length cDNA clone encoding the 274-residue precursor of the 22 kDa protein. Hydropathy plot analysis predicts the existence of four membrane-spanning helices in the mature protein. The two halves of the approximately 200-residue mature protein show high sequence similarity to each other, suggesting that the psbS gene arose from an internal gene duplication. The 22 kDa protein has some sequence similarity to chlorophyll a/b-binding proteins.     

Effect of neurotensin on pancreatic function in man

The effect of neurotensin on submaximally-stimulated hepatobiliary and pancreatic secretion was studied in 6 healthy subjects. An intravenous infusion of neurotensin 1.4 ± 0.3 pmol/kg/min, designed to reproduce plasma neurotensin immunoreactivity levels within the physiological range, produced a significant increase in pancreatic bicarbonate output. Plasma concentrations of pancreatic polypeptide rose by 83 ± 16 pmol/l and were associated with a small reduction in trypsin, but no significant change in bilirubin outputs.     

Visual Cues Given by Humans Are Not Sufficient for Asian Elephants (Elephas maximus) to Find Hidden Food

Recent research suggests that domesticated species – due to artificial selection by humans for specific, preferred behavioral traits – are better than wild animals at responding to visual cues given by humans about the location of hidden food. \Although this seems to be supported by studies on a range of domesticated (including dogs, goats and horses) and wild (including wolves and chimpanzees) animals, there is also evidence that exposure to humans positively influences the ability of both wild and domesticated animals to follow these same cues. Here, we test the performance of Asian elephants (Elephas maximus) on an object choice task that provides them with visual-only cues given by humans about the location of hidden food. Captive elephants are interesting candidates for investigating how both domestication and human exposure may impact cue-following as they represent a non-domesticated species with almost constant human interaction. As a group, the elephants (n = 7) in our study were unable to follow pointing, body orientation or a combination of both as honest signals of food location. They were, however, able to follow vocal commands with which they were already familiar in a novel context, suggesting the elephants are able to follow cues if they are sufficiently salient. Although the elephants’ inability to follow the visual cues provides partial support for the domestication hypothesis, an alternative explanation is that elephants may rely more heavily on other sensory modalities, specifically olfaction and audition. Further research will be needed to rule out this alternative explanation.     

Integrin alpha9beta1 directly binds to vascular endothelial growth factor (VEGF)-A and contributes to VEGF-A-induced angiogenesis

Vascular endothelial growth factor A (VEGF-A) is a potent inducer of angiogenesis. We now show that VEGF-A-induced adhesion and migration of human endothelial cells are dependent on the integrin alpha9beta1 and that VEGF-A is a direct ligand for this integrin. Adhesion and migration of these cells on the 165 and 121 isoforms of VEGF-A depend on cooperative input from alpha9beta1 and the cognate receptor for VEGF-A, VEGF receptor 2 (VEGF-R2). Unlike alpha3beta1or alphavbeta3 integrins, alpha9beta1 was also found to bind the 121 isoform of VEGF-A. This interaction appears to be biologically significant, because alpha9beta1-blocking antibody dramatically and specifically inhibited angiogenesis induced by VEGF-A165 or -121. Together with our previous findings that alpha9beta1 directly binds to VEGF-C and -D and contributes to lymphangiogenesis, these results identify the integrin alpha9beta1 as a potential pharmacotherapeutic target for inhibition of pathogenic angiogenesis and lymphangiogenesis.     

Induced root-secreted phenolic compounds as a belowground plant defense

Rhizosphere is the complex place of numerous interactions between plant roots, microbes and soil fauna. Whereas plant interactions with aboveground organisms are largely described, unravelling plant belowground interactions remains challenging. Plant root chemical communication can lead to positive interactions with nodulating bacteria, mycorriza or biocontrol agents or to negative interactions with pathogens or root herbivores. A recent study¹ suggested that root exudates contribute to plant pathogen resistance via secretion of antimicrobial compounds. These findings point to the importance of plant root exudates as belowground signalling molecules, particularly in defense responses. In our report,² we showed that under Fusarium attack the barley root system launched secretion of phenolic compounds with antimicrobial activity. The secretion of de novo biosynthesized t-cinnamic acid induced within 2 days illustrates the dynamic of plant defense mechanisms at the root level. We discuss the costs and benefits of induced defense responses in the rhizosphere. We suggest that plant defense through root exudation may be cultivar dependent and higher in wild or less domesticated varieties.Key words: root exudates, plant defense, t-cinnamic acid, fusarium, induced defensePlants grow and live in very complex and changing ecosystems. Because plants lack the mobility to escape from attack by pathogens or herbivores, they have developed constitutive and in addition inducible defenses that are triggered by spatiotemporally dynamic signaling mechanisms. These defenses counteract the aggressor directly via toxins or defense plant structures or indirectly by recruitment of antagonists of aggressors. Whereas induced defenses are well described in aboveground interactions, evidence of the occurrence of such mechanisms in belowground interactions remains limited. The biosynthesis of a defensive molecule could be both constitutive and inducible with a low level of a preformed pool (Fig. 1). In addition, upon encounter of an attacking organism, those levels could be induced to rise locally to a high level of active compound that is able to disarm the pathogen.^2,3 Only a few examples show that root exudates play a role in induced plant defense. Hairy roots of Ocimum basilicum secrete rosmarinic acid only when challenged by the pathogenic fungus Pythium ultimum.⁴ Wurst et al.⁵ reported on the induction of irridoid glycosides in root exudates of Plantago lanceolata in presence of nematodes. In vivo labelling experiments² with ¹³CO₂ showed the induction of phenolic compounds secreted by barley roots after Fusarium graminearum infection and the de novo biosynthesis of root secreted t-cinnamic acid within 2 days. These results show that the pool of induced t-cinnamic acid originated from both pre-formed and newly formed carbon pools (Fig. 1), highlighting a case of belowground induced defense inside and outside the root system.Open in a separate windowFigure 1Suggested mechanisms for the induction of root defense exudates in barley in response to Fusarium attack. Upon pathogen attack by Fusarium, the initial preformed pool of phenolic compounds is increased by the addition of inducible, de novo biosynthesized t-cinnamic acid. Both, the preformed pool and the de novo biosynthesized pool fuel the exudation of defense compounds from infected roots.The concept of fitness costs is frequently presented to explain the coexistence of both constitutive and induced defense.⁶ In the case of induced defense, resources are invested in defenses only when the plant is under attack. In the absence of an infection, plants can optimize allocation of their resources to reproduction and growth to compete with neighbours.⁷ Constitutive defenses are thought to be more beneficial when the probability of attack is high, whereas adjustable, induced defenses are more valuable to fight against an unpredictable pathogen. Non disturbed soil is a heterogeneous matrix where biodiversity is very high and patchy^8,9 and organism motility is rather restricted.¹⁰ As a consequence of the patchiness, belowground environment is expected to be favourable to selection for induced responses.¹¹ The absence of defense root exudates between two infections may form an unpredictable environment for soil pathogens and reduce the chance for adaptation of root attackers. Plants may also use escape strategies to reduce the effect of belowground pathogens. Henkes et al. (unpublished) showed that Fusarium-infected barley plants reduced carbon allocation towards infected roots within a day and increased allocation carbon to uninfected roots. These results illustrate how reallocation of carbon toward non infected root parts represents a way to limit the negative impact of root infection.We have demonstrated the potential of barley plants to defend themselves against soil pathogen by root exudation.² Even the barley cultivar ‘Barke’ used in our study, a modern cultivated variety, was able to launch defense machinery via exudation of antimicrobial compounds when infected by F. graminearum. We suggest that plant defense through root exudation might be cultivar dependent and perhaps higher in wild or less domesticated varieties. Taddei et al.¹² reported that constitutivelyproduced root exudates from a resistant Gladiolus cultivar inhibit spore germination of Fusarium oxysporum whereas root exudates from a susceptible cultivar do not affect F. oxysporum germination. Root exudates from the resistant cultivar contained higher amounts of aromaticphenolic compounds compared to the susceptible cultivar and these compounds may be responsible for the inhibition of spore germination. Metabolic profiling of wheat cultivars, ‘Roblin’ and ‘Sumai3’, respectively, susceptible and resistant to Fusarium Head Blight, showed that t-cinnamic acid was a discriminating factor responsible for resistance/defense function.¹³ Therefore it is likely that wild barley varieties hold higher defense capacities compare to cultivated varieties selected for high yield. In the future, plant breeders in organic and low-input farming could use root-system defense ability as new trait in varietal variation.     

Glycoprotein 120 binding to CXCR4 causes p38-dependent primary T cell death that is facilitated by, but does not require cell-associated CD4

HIV-1 infection causes the depletion of host CD4 T cells through direct and indirect (bystander) mechanisms. Although HIV Env has been implicated in apoptosis of uninfected CD4 T cells via gp120 binding to either CD4 and/or the chemokine receptor 4 (CXCR4), conflicting data exist concerning the molecular mechanisms involved. Using primary human CD4 T cells, we demonstrate that gp120 binding to CD4 T cells activates proapoptotic p38, but does not activate antiapoptotic Akt. Because ligation of the CD4 receptor alone or the CXCR4 receptor alone causes p38 activation and apoptosis, we used the soluble inhibitors, soluble CD4 (sCD4) or AMD3100, to delineate the role of CD4 and CXCR4 receptors, respectively, in gp120-induced p38 activation and death. sCD4 alone augments gp120-induced death, suggesting that CXCR4 signaling is principally responsible. Supporting that model, AMD3100 reduces death caused by gp120 or by gp120/sCD4. Finally, prevention of gp120-CXCR4 interaction with 12G5 Abs blocks p38 activation and apoptosis, whereas inhibition of CD4-gp120 interaction with Leu-3a has no effect. Consequently, we conclude that gp120 interaction with CXCR4 is required for gp120 apoptotic effects in primary human T cells.