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Tolerance Mechanisms (tolerance + mechanism)

Distribution by Scientific Domains

Life Sciences	45%
Medical Sciences	40%
Chemistry	9%

Selected Abstracts

REVIEW ARTICLE: Tolerance Mechanisms in Pregnancy: A Reappraisal of the Role of Class I Paternal MHC Antigens,

AMERICAN JOURNAL OF REPRODUCTIVE IMMUNOLOGY, Issue 2 2010
David A. Clark
Citation Clark DA, Chaouat G, Wong K, Gorczynski RM, Kinsky R. Tolerance mechanisms in pregnancy: a reappraisal of the role of class I paternal MHC antigens. Am J Reprod Immunol 2010; 63: 93,103 Problem, Allogeneic pregnancies have a survival advantage over syngeneic pregnancies, and paternal Class I MHC antigens have been implicated. In humans, HLA-C and HLA-G and E are expressed by subpopulations of fetal trophoblast. In mice, Qa-2, a Class Ib antigen, and classical H-2K antigens have been described. However, the mechanism of prevention of embryo demise in utero has not been critically assessed, and a number of conflicting ideas have not been addressed. The ,, T-cell receptor recognizes peptide bound to the groove in Class I MHC, and peptides have profound effects on the interaction of KIR receptors on T and NK cells with Class I MHC. Methods, Data on prevention of pregnancy loss (abortion) in poly IC-treated mice were reviewed along with information about prevention of losses in the abortion-prone CBA × DBA/2 model. This information was combined with data on paternal antigen expression at different times in pregnancy when key events determining outcome are thought to transpire, and role of tolerance signaling molecules such as CD200. Current data on models supporting a role for ,true' uterine NK cells (TuNKs) versus blood NK cells in the uterus (BuNKs) and role of MHC,KIR interaction were reviewed along with incompatible data in the literature. Results, Whilst paternal Class I MHC appears important, there is an important role for paternal non-MHC minor antigens (small peptides) that bind to the antigen-presenting groove of Class I MHC. BuNKs along with CD8+ T cells and Treg cells appear more important than TuNKs where the role of the latter appears primarily to promote angiogenesis. When during pregnancy the maternal immune system cells are first exposed to paternal Class I + peptide is uncertain, but at the time of implantation, if not earlier, seems likely. Conclusion, Suppression of pregnancy loss by paternal/embryo Class I MHC depends on the presence of paternal peptides. This greatly complicates existing models of Class I,KIR interactions in feto-maternal tolerance or rejection. It is important to consider all the data when devising explanatory models. [source]

The Role of Non-Deletional Tolerance Mechanisms in a Murine Model of Mixed Chimerism with Costimulation Blockade

AMERICAN JOURNAL OF TRANSPLANTATION, Issue 6 2005
Sinda Bigenzahn
Peripheral and central clonal deletion are important tolerance mechanisms in models using bone marrow transplantation (BMT) with costimulation blockade (CB). However, since tolerance can be found before peripheral deletion is complete and since elimination of recipient CD4+ cells at the time of BMT prevents tolerance induction, we investigated the potential roles of regulation and anergy in such a murine model. We found that transient elimination of CD25+ cells or neutralization of IL2 immediately after BMT and CB prevented the induction of skin graft tolerance. Cotransfer into SCID mice of CD4+ cells taken from chimeras early after BMT, together with naïve recipient-type CD4+ cells significantly prolonged donor skin graft survival. In contrast, cotransfer of CD4+ cells harvested from chimeras late after BMT did not prolong donor skin graft survival. Besides, depletion of CD25+ cells in established chimeras several months post-BMT did not break tolerance. In vivo administration of recombinant IL2 inhibited chimerism and tolerance neither early nor late post-BMT, arguing against a decisive role for classical anergy. Thus, CD4 cell-mediated regulation contributes significantly to tolerance induction early after BMT, but appears to have no critical role in the maintenance of tolerance. [source]

REVIEW ARTICLE: Tolerance Mechanisms in Pregnancy: A Reappraisal of the Role of Class I Paternal MHC Antigens,

The T-cell receptor repertoire of regulatory T cells

IMMUNOLOGY, Issue 4 2008
Rafal Pacholczyk
Summary The CD4+ CD25+ regulatory population of T cells (Treg cells), which expresses the forkhead family transcription factor (Foxp3), is the key component of the peripheral tolerance mechanism that protects us from a variety of autoimmune diseases. Experimental evidence shows that Treg cells recognize a wide range of antigenic specificities with increased reactivity to self antigens, although the affinity of these interactions remains to be further defined. The Treg repertoire is highly diverse with a distinct set of T-cell receptors (TCRs), and yet is overlapping to some extent with the repertoire of conventional T cells (Tconv cells). The majority of Treg cells are generated in the thymus. However, the role of the TCR specificity in directing thymic precursors to become Treg or Tconv cells remains unclear. On the one hand, the higher self reactivity of Treg cells and utilization of different TCRs in Treg and Tconv repertoires suggest that in TCR interactions an initial decision is made about the ,suitability' of a developing thymocyte to become a Treg cell. On the other hand, as Treg cells can recognize a wide range of foreign antigens, have a diverse TCR repertoire, and show some degree of overlap with Tconv cells, the signals through the TCR may be complementary to the TCR-independent process that generates precursors of Treg cells. In this review, we discuss how different features of the Treg repertoire influence our understanding of Treg specificities and the role of self reactivity in the generation of this population. [source]

Heat shock protein 101 effects in A. thaliana: genetic variation, fitness and pleiotropy in controlled temperature conditions

MOLECULAR ECOLOGY, Issue 6 2008
S. J. TONSOR
Abstract The Hsp100/ClpB heat shock protein family is ancient and required for high temperature survival, but natural variation in expression and its phenotypic effects is unexplored in plants. In controlled environment experiments, we examined the effects of variation in the Arabidopsis cytosolic AtHsp101 (hereafter Hsp101). Ten wild-collected ecotypes differed in Hsp101 expression responses across a 22 to 40 °C gradient. Genotypes from low latitudes expressed the least Hsp101. We tested fitness and pleiotropic consequences of varying Hsp101 expression in ,control' vs. mild thermal stress treatments (15/25 °C D/N vs. 15/25° D/N plus 3 h at 35 °C 3 days/week). Comparing wild type and null mutants, wt Columbia (Col) produced ~33% more fruits compared to its Hsp101 homozygous null mutant. There was no difference between Landsberg erecta null mutant NIL (Ler) and wt Ler; wt Ler showed very low Hsp101 expression. In an assay of six genotypes, fecundity was a saturating function of Hsp101 content, in both experimental treatments. Thus, in addition to its essential role in acquired thermal tolerance, Hsp101 provides a substantial fitness benefit under normal growth conditions. Knocking out Hsp101 decreased fruit production, days to germination and days to bolting, total dry mass, and number of inflorescences; it increased transpiration rate and allocation to root mass. Root : total mass ratio decayed exponentially with Hsp101 content. This study shows that Hsp101 expression is evolvable in natural populations. Our results further suggest that Hsp101 is primarily an emergency high-temperature tolerance mechanism, since expression levels are lower in low-latitude populations from warmer climates. Hsp101 expression appears to carry an important trade-off in reduced root growth. This trade-off may select for suppressed expression under chronically high temperatures. [source]

The mechanism of boron tolerance for maintenance of root growth in barley (Hordeum vulgare L.)

PLANT CELL & ENVIRONMENT, Issue 8 2007
EUN-YOUNG CHOI
ABSTRACT Cultivar differences in root elongation under B toxic conditions were observed in barley (Hordeum vulgare L.). A significant increase in the length and width of the root meristematic zone (RMZ) was observed in Sahara 3771 (B tolerant) when it was grown under excessive B concentration, compared to when grown at adequate B supply. This coincided with an increase in cell width and cell numbers in the meristematic zone (MZ), whereas a significant decrease in the length and no significant effect on the width of the MZ was observed in Clipper (B intolerant) when it was grown under excessive B supply. This was accompanied by a decrease in cell numbers, but an increase in the length and width of individual cells present along the MZ. Excessive B concentrations led to a significantly lower osmotic potential within the cell sap of the root tip in SloopVic (B tolerant) and Sahara 3771, while the opposite was observed in Clipper. Enhanced sugar levels in the root tips of SloopVic were observed between 48 and 96 h after excess B was applied. This coincided with an increase in the root elongation rate and with a 2.7-fold increase in sucrose level within mature leaf tissue. A significant decrease in reducing sugar levels was observed in the root tips of Clipper under excessive B concentrations. This coincided with significantly lower root elongation rates and lower sucrose levels in leaf tissues. Results indicate a B tolerance mechanism associated with a complex control of sucrose levels between leaf and root tip that assist in maintaining root growth under B toxicity. [source]

1140915445 Increased numbers of FoxP3+ cells in vaginal mucus from normal pregnant mice suggest early antigen-specific tolerance mechanism during pregnancy

AMERICAN JOURNAL OF REPRODUCTIVE IMMUNOLOGY, Issue 6 2006
C Thuere
The fetal survival within the maternal uterus is thought to be due to a transient immunological tolerance, being CD4+CD25+ T regulatory cells (Tregs) crucial players. Former studies confirmed diminished total numbers of this unique population in abortion-prone mice (DBA/2J-mated CBA/J females) as compared to a control with normal pregnancy outcome (BALB/c-mated CBA/J females) and suggested that Tregs act in an antigen-specific fashion. This hypothesis led us to investigate the kinetics of Tregs during pregnancy (day 0, 2, 5, 8, 10 or 12 of pregnancy) in abortion-prone mice and the control group. Our data confirmed diminished number of Tregs in immunological relevant organs such as lymph nodes and thymus within the abortion-prone mice. The enormous augmentation in the number of FoxP3+ cells in vaginal mucus already on day 0.5 after conception, followed by increased Tregs levels at early pregnancy stages, suggest, that Tregs need to be activated by male antigens for being protective. Notably, the abortion-prone mice displayed again a lower total amount of Tregs as compared to the control. Similar progesterone levels in spite of different pregnancy outcome reinforce the theory of antigen specificity of pregnancy-induced Tregs. The antigen presentation would take place in the periphery e.g. in vaginal mucus, the first site of contact with paternal antigens, directly after insemination. Interestingly the transfer of Tregs from normal pregnant mice at this time point prevented fetal rejection. Our results suggest the crucial role of Tregs already shortly after conception. [source]

Distinct physiological responses of two rice cultivars subjected to iron toxicity under field conditions

ANNALS OF APPLIED BIOLOGY, Issue 2 2009
R.J. Stein
Abstract Iron toxicity is recognised as the most widely distributed nutritional disorder in lowland and irrigated rice, derived from the excessive amounts of ferrous ions generated by the reduction of iron oxides in flooded soils. Rice cultivars with variable degrees of tolerance to iron toxicity have been developed, and cultural practices such as water management and fertilisation can be used to reduce its negative impact. However, because of the complex nature of iron toxicity, few physiological data concerning tolerance mechanisms to excess iron in field conditions are available. To analyse the physiological responses of rice to iron excess in field conditions, two rice cultivars with distinct tolerance to iron toxicity [BR-IRGA 409 (susceptible) and IRGA 420 (tolerant)] were grown in two areas, with a well-established history of iron toxicity (in Camaquã, RS, Brazil) and without iron toxicity (in Cachoeirinha, RS, Brazil). Plants from the susceptible cultivar grown in the iron-toxic site showed lower levels of chlorophylls and soluble proteins (together with higher carbonyl levels) indicating photooxidative and oxidative damage. The toxic effects observed were because of the accumulation of high levels of iron and not because of any indirectly induced shoot deficiency of other nutrients. Higher activities of antioxidative enzymes were also observed in leaves of plants from the susceptible cultivar only in the iron-toxic site, probably as a result of oxidative stress rather than because of specific involvement in a tolerance mechanism. There was no difference between cultivars in iron accumulation in the symplastic and apoplastic space of leaves, with both cultivars accumulating 85,90% of total leaf iron in the symplast. However, susceptible plants accumulated higher levels of iron in low-molecular-mass fractions than tolerant plants. The accumulation of iron in the low-molecular-mass fraction probably has a direct influence on iron toxicity, and the adaptive strategy of tolerant plants may rely on their capacity to buffer the iron amounts present in the low mass fraction, a new parameter to be considered when evaluating tolerance to iron excess in field-cultivated rice plants. [source]

On-Line Control Architecture for Enabling Real-Time Traffic System Operations

COMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 5 2004
Srinivas Peeta
Critical to their effectiveness are the control architectures that provide a blueprint for the efficient transmission and processing of large amounts of real-time data, and consistency-checking and fault tolerance mechanisms to ensure seamless automated functioning. However, the lack of low-cost, high-performance, and easy-to-build computing environments are key impediments to the widespread deployment of such architectures in the real-time traffic operations domain. This article proposes an Internet-based on-line control architecture that uses a Beowulf cluster as its computational backbone and provides an automated mechanism for real-time route guidance to drivers. To investigate this concept, the computationally intensive optimization modules are implemented on a low-cost 16-processor Beowulf cluster and a commercially available supercomputer, and the performance of these systems on representative computations is measured. The results highlight the effectiveness of the cluster in generating substantial computational performance scalability, and suggest that its performance is comparable to that of the more expensive supercomputer. [source]

Analyses of ultraviolet-induced focus formation of hREV1 protein

GENES TO CELLS, Issue 3 2006
Yoshiki Murakumo
Translesional DNA synthesis (TLS) is one of the DNA damage tolerance mechanisms that allow cells with DNA damage to continue DNA replication. Each of the mammalian Y-family DNA polymerases (Pol ,, Pol ,, Pol ,, and REV1) has been shown to carry out TLS by itself or in combination with another enzyme in vitro. Recently, the C-terminal region of mammalian REV1 (the total 1251 residues in human) was found to interact with Pol ,, Pol ,, and Pol ,, as well as with the REV7 subunit of another TLS enzyme, Pol ,. Thus, it is proposed that REV1 plays a pivotal role in TLS in vivo. We here describe our study on the localization of human REV1 protein (hREV1) in nondamaged and ultraviolet (UV)-irradiated cells. Ectopically expressed hREV1 in mammalian cells was localized to the nucleus and exhibited dozens of tiny foci in approximately 3% of nondamaged cells. The percentage of focus-forming cells markedly increased after UV irradiation in a time- and dose-dependent manner. The focus formation was associated with UV-induced DNA damage. Interestingly, although the hREV1 foci in S-phase cells colocalized with PCNA foci, suggesting the association of hREV1 with the replication machinery, hREV1 focus formation was observed not only in the S phase but also outside S phase. Furthermore, it was found that the hREV1 focus formation after UV irradiation required a region near the C-terminal (826,1178). [source]

Peripheral tolerance limits CNS accumulation of CD8 T cells specific for an antigen shared by tumor cells and normal astrocytes

GLIA, Issue 15 2008
Thomas Calzascia
Abstract T cell mediated immunotherapies are proposed for many cancers including malignant astrocytoma. As such therapies become more potent, but not necessarily more tumor-specific, the risk of collateral autoimmune damage to normal tissue increases. Tumors of the brain present significant challenges in this respect, as autoimmune destruction of brain tissue could have severe consequences. To investigate local immune reactivity toward a tumor-associated antigen in the brain, transgenic mice were generated that express a defined antigen (CW3170,179) in astroglial cells. The resulting six transgenic mouse lines expressed the transgenic self-antigen in cells of the gastrointestinal tract and CNS compartments, or in the CNS alone. By challenging transgenic mice with tumor cells that express CW3, self/tumor-specific immune responses were visualized within a normal polyclonal T cell repertoire. A large expansion of the endogenous CW3170,179 -specific CD8 T cell population was observed in nontransgenic mice after both subcutaneous and intracerebral implantation of tumor cells. In contrast, CW3170,179 -specific immune responses were not observed in transgenic mice that exhibited extracerebral transgene expression. Importantly, in certain groups of mice in which transgene expression was restricted to the CNS, antigen-specific immune responses occurred when tumor was implanted subcutaneously, but not intracerebrally. This local immune tolerance in the brain was induced via peripheral (extrathymic) rather than central (thymic) tolerance mechanisms. Thus, this study highlights the role of regional immune regulation in the prevention of autoimmunity in the brain, and the potential impact of these mechanisms for brain tumor immunotherapy. © 2008 Wiley-Liss, Inc. [source]

Hypersensitivity and oral tolerance in the absence of a secretory immune system

ALLERGY, Issue 5 2010
M. R. Karlsson
To cite this article: Karlsson M-R, Johansen F-E, Kahu H, Macpherson A, Brandtzaeg P. Hypersensitivity and oral tolerance in the absence of a secretory immune system. Allergy 2010; 65: 561,570. Abstract Background:, Mucosal immunity protects the epithelial barrier by immune exclusion of foreign antigens and by anti-inflammatory tolerance mechanisms, but there is a continuing debate about the role of secretory immunoglobulins (SIgs), particularly SIgA, in the protection against allergy and other inflammatory diseases. Lack of secretory antibodies may cause immune dysfunction and affect mucosally induced (oral) tolerance against food antigens. Methods:, We used polymeric Ig receptor (pIgR) knockout (KO) mice, which cannot export SIgA or SIgM, to study oral tolerance induction by ovalbumin (OVA) feeding and for parenteral antigen sensitization in the same animal. Results:, Remarkable systemic hyperreactivity was observed in pIgR KO mice, as 50% died after intradermal OVA challenge, which was not seen in similarly sensitized and challenged wild-type (WT) mice. Oral tolerance induced by OVA completely protected the sensitized pIgR KO mice against anaphylaxis and suppressed antibody levels (particularly IgG1) as well as delayed-type hypersensitivity (DTH) to OVA. Delayed-type hypersensitivity to a bystander antigen, human serum albumin, was also suppressed and T-cell proliferation against OVA in vitro was reduced in tolerized compared with non-tolerized pIgR KO mice. This effect was largely mediated by CD25+ T cells. Adoptive transfer of splenic putative regulatory T cells (CD4+ CD25+) obtained from OVA-fed pIgR KO mice to naïve WT mice mediated suppression of DTH against OVA after sensitization of the recipients. Conclusion:, Compensatory regulatory T-cell function becomes critical in pIgR-deficient mice to avoid the potentially catastrophic effects of systemic immune hyperreactivity, presumably resulting from defective secretory antibody-mediated immune exclusion of microbial components. [source]

Tolerance to apical and foliar damage: costs and mechanisms in Raphanus raphanistrum

OIKOS, Issue 12 2007
Elin Boalt
To study mechanisms underlying plant tolerance to herbivore damage, we used apical and foliar damage as experimental treatments to study whether there are similar tolerance mechanisms to different types of damage. We also studied whether tolerance to different types of damage are associated, and whether there is a cost involved in plant tolerance to different types of herbivore damage. Our greenhouse experiment involved 480 plants from 30 full-sib families of an annual weed Raphanus raphanistrum, wild radish, which were subjected to control and two different simulated herbivore damage treatments, apex removal and foliar damage of 30% of leaf area. Apical damage significantly decreased seed production, whereas foliar damage had no effect. There was a significant genetic variation for tolerance to foliar, but not apical damage. No costs were observed in terms of negative correlation between tolerance to either damage type and fitness of undamaged plants. Tolerances to apical and foliar damage were not significantly correlated with each other. We observed a larger number of significant associations between tolerance and reproductive traits than between tolerance and vegetative traits. Plant height and leaf size of damaged plants interacted in their association to tolerance to foliar damage. Inflorescence number and pollen quantity per flower of damaged plants were positively associated with tolerance to apical damage. In late-flowering genotypes, petal size of undamaged plants and pollen quantity of damaged plants were positively associated with tolerance to foliar damage. In summary, traits involved in floral display and male fitness were associated with plant tolerance to herbivore damage. [source]

The importance of early complementary feeding in the development of oral tolerance: Concerns and controversies

PEDIATRIC ALLERGY AND IMMUNOLOGY, Issue 5 2008
Susan L. Prescott
Rising rates of food allergies in early childhood reflect increasing failure of early immune tolerance mechanisms. There is mounting concern that the current recommended practice of delaying complementary foods until 6 months of age may increase, rather than decrease, the risk of immune disorders. Tolerance to food allergens appears to be driven by regular, early exposure to these proteins during a ,critical early window' of development. Although the timing of this window is not clear in humans, current evidence suggests that this is most likely to be between 4 and 6 months of life and that delayed exposure beyond this period may increase the risk of food allergy, coeliac disease and islet cell autoimmunity. There is also evidence that other factors such as favourable colonization and continued breastfeeding promote tolerance and have protective effects during this period when complementary feeding is initiated. This discussion paper explores the basis for concern over the current recommendation to delay complementary foods as an approach to preventing allergic disease. It will also examine the growing case for introducing complementary foods from around 4 months of age and maintaining breastfeeding during this early feeding period, for at least 6 months if possible. [source]

Metal toxicity and ectomycorrhizas

PHYSIOLOGIA PLANTARUM, Issue 2 2000
G. Jentschke
Metal toxicity (Al and heavy metals) is a major constraint affecting root growth in a number of natural or managed ecosystems. Fine roots of the majority of plant species are associated with mycorrhizal fungi, which may modify the sensitivity of roots to metal stress. In this review, we summarise the available evidence demonstrating beneficial effects of ectomycorrhizas in alleviation of metal toxicity in forest tree seedlings. We identify experimental shortcomings of past research (e.g. the use of shoot metal concentrations as a measure of metal uptake, use of microanalytical techniques biased by element redistribution) that may confound major conclusions drawn from these experiments. Although there is no doubt that in many cases ectomycorrhizal fungi indeed ameliorate metal stress in their host plants, the mechanism(s) involved remain(s) unclear. The role of metal sorption on fungal tissues thought to reduce metal exposure of the host plant is critically reviewed. As direct evidence (both under artificial and soil conditions) supporting a unique role of fungal immobilisation of metals is lacking so far, there is an urgent need to also test alternative tolerance mechanisms such as the release of metal chelating substances, or nutritional and hormonal effects mediated by mycorrhizal fungi. [source]

Determination of nickel, calcium and magnesium in xylem sap by flame atomic absorption spectrometry using a microsampling technique

PHYTOCHEMICAL ANALYSIS, Issue 5 2009
Sheila Alves
Abstract Introduction Knowledge of xylem sap chemical composition is important to the understanding of translocation, detoxification and tolerance mechanisms. However, the small amount of sample available often hampers its characterisation. Hence, low volume consumption techniques are needed for xylem sap analysis. Objective To develop a microsampling technique for the determination of elements in xylem sap from different plants by flame atomic absorption spectrometry (FAAS). Methodology The microsampling device was optimised in terms of sample volume and integration time. The analytical characteristics of the microsampling technique (µ -FAAS) were established and compared with those of FAAS with traditional continuous nebulisation. The method was validated by means of an independent technique. Results Ca, Mg and Ni were determined in a 50 µL aliquot of xylem sap solution/element that was introduced directly into the flame via the microsampling accessory. Good precision was obtained with relative standard deviations of 1.1, 0.6 and 2.3% for Ca, Mg and Ni, respectively. Matrix effects resulting from the physical characteristics of the samples and possible chemical interferences caused by phosphate and/or sulphate were ruled out. Conclusion A simple, rapid and reproducible microsampling technique coupled to FAAS was developed and successfully applied in the determination of Ca, Mg and Ni in xylem sap. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Quantifying the three main components of salinity tolerance in cereals

PLANT CELL & ENVIRONMENT, Issue 3 2009
KARTHIKA RAJENDRAN
ABSTRACT Salinity stress is a major factor inhibiting cereal yield throughout the world. Tolerance to salinity stress can be considered to contain three main components: Na+ exclusion, tolerance to Na+ in the tissues and osmotic tolerance. To date, most experimental work on salinity tolerance in cereals has focused on Na+ exclusion due in part to its ease of measurement. It has become apparent, however, that Na+ exclusion is not the sole mechanism for salinity tolerance in cereals, and research needs to expand to study osmotic tolerance and tissue tolerance. Here, we develop assays for high throughput quantification of Na+ exclusion, Na+ tissue tolerance and osmotic tolerance in 12 Triticum monococcum accessions, mainly using commercially available image capture and analysis equipment. We show that different lines use different combinations of the three tolerance mechanisms to increase their total salinity tolerance, with a positive correlation observed between a plant's total salinity tolerance and the sum of its proficiency in Na+ exclusion, osmotic tolerance and tissue tolerance. The assays developed in this study can be easily adapted for other cereals and used in high throughput, forward genetic experiments to elucidate the molecular basis of these components of salinity tolerance. [source]

Distribution of Zn in functionally different leaf epidermal cells of the hyperaccumulator Thlaspi caerulescens

PLANT CELL & ENVIRONMENT, Issue 7 2000
B. Frey
ABSTRACT The aim of this study was to show the potential of Thlaspi caerulescens in the cleaning-up of a moderately Zn -contaminated soil and to elucidate tolerance mechanisms at the cellular and subcellular level for the detoxification of the accumulated metal within the leaf. Measured Zn concentrations in shoots were high and reached a maximum value of 83 mmol kg,1 dry mass, whereas total concentrations of Zn in the roots were lower (up to 13 mmol kg,1). In order to visualize and quantify Zn at the subcellular level in roots and leaves, ultrathin cryosections were analysed using energy-dispersive X-ray micro-analysis. Elemental maps of ultrathin cryosections showed that T. caerulescens mainly accumulated Zn in the vacuoles of epidermal leaf cells and Zn was almost absent from the vacuoles of the cells from the stomatal complex, thereby protecting the guard and subsidiary cells from high Zn concentrations. Observed patterns of Zn distribution between the functionally different epidermal cells were the same in both the upper and lower epidermis, and were independent of the total Zn content of the plant. Zinc stored in vacuoles was evenly distributed and no Zn-containing crystals or deposits were observed. From the elemental maps there was no indication that P, S or Cl was associated with the high Zn concentrations in the vacuoles. In addition, Zn also accumulated in high concentrations in both the cell walls of epidermal cells and in the mesophyll cells, indicating that apoplastic compartmentation is another important mechanism involved in zinc tolerance in the leaves of T. caerulescens. [source]

REVIEW ARTICLE: B7 Family Molecules as Regulators of the Maternal Immune System in Pregnancy

AMERICAN JOURNAL OF REPRODUCTIVE IMMUNOLOGY, Issue 6 2010
Margaret G. Petroff
Citation Petroff MG, Perchellet A. B7 family molecules as regulators of the maternal immune system in pregnancy. Am J Reprod Immunol 2010 Placental and fetal growth and development are associated with chronic exposure of the maternal immune system to fetally derived, paternally inherited antigens. Because maternal lymphocytes are aware of fetal antigens, active tolerance mechanisms are required to ensure unperturbed progression of pregnancy and delivery of a healthy newborn. These mechanisms of tolerance may include deletion, receptor downregulation, and anergy of fetal antigen-specific cells in lymphoid tissues, as well as regulation at the maternal,fetal interface by a variety of locally expressed immunoregulatory molecules. The B7 family of costimulatory molecules comprises one group of immunoregulatory molecules present in the decidua and placenta. B7 family members mediate both inhibitory and stimulatory effects on T-cell activation and effector functions and may play a critical role in maintaining tolerance to the fetus. Here, we review the known functions of the B7 family proteins in pregnancy. [source]

The Role of Non-Deletional Tolerance Mechanisms in a Murine Model of Mixed Chimerism with Costimulation Blockade

Distinct physiological responses of two rice cultivars subjected to iron toxicity under field conditions

Abiotic stress and plant responses from the whole vine to the genes

AUSTRALIAN JOURNAL OF GRAPE AND WINE RESEARCH, Issue 2010
G.R. CRAMER
Abstract Drought, salinity and extreme temperatures significantly limit the distribution of grapes around the world. In this review, the literature of grape responses to abiotic stress with particular reference to whole plant and molecular responses observed in recent studies is discussed. A number of short-term and long-term studies on grapevine shoots and berries have been conducted using a systems biology approach. Transcripts, proteins and metabolites were profiled. Water deficit, salinity and chilling altered the steady-state abundance of a large number of transcripts. Common responses to these stresses included changes in hormone metabolism, particularly abscisic acid (ABA), photosynthesis, growth, transcription, protein synthesis, signalling and cellular defences. Some of the transcriptional changes induced by stress were confirmed by proteomic and metabolomic analyses. More than 2000 genes were identified whose transcript abundance was altered by both water deficit and ABA. Different gene sets were used to map molecular pathways regulated by ABA, water deficit, salinity and chilling in grapevine. This work supports the hypothesis that ABA is a central regulator of abiotic stress tolerance mechanisms. ABA affects signalling pathways that trigger important molecular activities involving metabolism, transcription, protein synthesis, and cellular defence and also regulates important physiological responses such as stomatal conductance, photoprotection and growth. Systems biology approaches are providing more comprehensive understanding of the complex plant responses to abiotic stress. The molecular sets generated from mapping the ABA-inducible stress responses provide numerous targets for genetic and cultural manipulation for improved plant protection and grape quality. [source]