336 research outputs found
Assessing the role of root plasma membrane and tonoplast Na(+)/H(+) exchangers in salinity tolerance in wheat: in planta quantification methods
No full textThis work investigates the role of cytosolic Na⁺ exclusion in roots as a means of salinity tolerance in wheat, and offers in planta methods for the functional assessment of major transporters contributing to this trait. An electrophysiological protocol was developed to quantify the activity of plasma membrane Na⁺ efflux systems in roots, using the microelectrode ion flux estimation (MIFE) technique. We show that active efflux of Na⁺ from wheat root epidermal cells is mediated by a SOS1-like homolog, energized by the plasma membrane H⁺-ATPase. SOS1-like efflux activity was highest in Kharchia 65, a salt-tolerant bread wheat cultivar. Kharchia 65 also had an enhanced ability to sequester large quantities of Na⁺ into the vacuoles of root cells, as revealed by confocal microscopy using Sodium Green. These findings were consistent with the highest level of expression of both SOS1 and NHX1 transcripts in plant roots in this variety. In the sensitive wheat varieties, a greater proportion of Na⁺ was located in the root cell cytosol. Overall, our findings suggest a critical role of cytosolic Na⁺ exclusion for salinity tolerance in wheat and offer convenient protocols to quantify the contribution of the major transporters conferring this trait, to screen plants for salinity tolerance.Tracey A. Cuin, Jayakumar Bose, Giovanni Stefano, Deepa Jha, Mark Tester, Stefano Mancuso & Sergey Shabal
The Na+ transporter AtHKT1;1 controls retrieval of Na+ from the xylem in Arabidopsis
No full textThe definitive version may be found at www.blackwell-synergy.comHKT-type transporters appear to play key roles in Na+ accumulation and salt sensitivity in plants. In Arabidopsis HKT1;1 has been proposed to influx Na+ into roots, recirculate Na+ in the phloem and control root : shoot allocation of Na+. We tested these hypotheses using 22Na+ flux measurements and ion accumulation assays in an hkt1;1 mutant and demonstrated that AtHKT1;1 contributes to the control of both root accumulation of Na+ and retrieval of Na+ from the xylem, but is not involved in root influx or recirculation in the phloem. Mathematical modelling indicated that the effects of the hkt1;1 mutation on root accumulation and xylem retrieval were independent. Although AtHKT1;1 has been implicated in regulation of K+ transport and the hkt1;1 mutant showed altered net K+ accumulation, 86Rb+ uptake was unaffected by the hkt1;1 mutation. The hkt1;1 mutation has been shown previously to rescue growth of the sos1 mutant on low K+; however, HKT1;1 knockout did not alter K+ or 86Rb+ accumulation in sos1.Romola Jane Davenport, Alicia Muñoz-Mayor, Deepa Jha, Pauline Adobea Essah, Ana Rus, Mark Teste
Type-B response regulators ARR1 and ARR12 regulate expression of AtHKT1;1 and accumulation of sodium in Arabidopsis shoots
No full textSoil salinity affects a large proportion of the land worldwide, forcing plants to evolve a number of mechanisms to cope with salt stress. Cytokinin plays a role in the plant response to salt stress, but little is known about the mechanism by which cytokinin controls this process. We used a molecular genetics approach to examine the influence of cytokinin on sodium accumulation and salt sensitivity in Arabidopsis thaliana. Cytokinin application was found to increase sodium accumulation in the shoots of Arabidopsis, but had no significant affect on the sodium content in the roots. Consistent with this, altered sodium accumulation phenotypes were observed in mutants of each gene class of the cytokinin signal transduction pathway, including receptors, phospho-transfer proteins, and type-A and type-B response regulators. Expression of the gene encoding Arabidopsis high-affinity K(+) transporter 1;1 (AtHKT1;1), a gene responsible for removing sodium ions from the root xylem, was repressed by cytokinin treatment, but showed significantly elevated expression in the cytokinin response double mutant arr1-3 arr12-1. Our data suggest that cytokinin, acting through the transcription factors ARR1 and ARR12, regulates sodium accumulation in the shoots by controlling the expression of AtHKT1;1 in the roots.Michael G. Mason, Deepa Jha, David E. Salt, Mark Tester, Kristine Hill, Joseph J. Kieber and G. Eric Schalle
Characterization of ion contents and metabolic responses to salt stress of different arabidopsis AtHKT1;1 genotypes and their parental strains
No full textPlants employ several strategies to maintain cellular ion homeostasis under salinity stress, including mediating ion fluxes by transmembrane transport proteins and adjusting osmotic pressure by accumulating osmolytes. The HKT (high-affinity potassium transporter) gene family comprises Na+ and Na+/K+ transporters in diverse plant species, with HKT1;1 as the only member in Arabidopsis thaliana. Cell-type-specific overexpression of AtHKT1;1 has been shown to prevent shoot Na+ overaccumulation under salinity stress. Here, we analyzed a broad range of metabolites and elements in shoots and roots of different AtHKT1;1 genotypes and their parental strains before and after salinity stress, revealing a reciprocal relationship of metabolite differences between an AtHKT1;1 knockout line (hkt1;1) and the AtHKT1;1 overexpressing lines (E2586 UAS GAL4 :HKT1;1 and J2731*UAS GAL4 :HKT1;1). Although levels of root sugars were increased after salt stress in both AtHKT1;1 overexpressing lines, E2586 UAS GAL4 :HKT1;1 showed higher accumulation of the osmoprotectants trehalose, gentiobiose, and melibiose, whereas J2731*UAS GAL4 :HKT1;1 showed higher levels of sucrose and raffinose, compared with their parental lines, respectively. In contrast, the knockout line hkt1;1 showed strong increases in the levels of the tricarboxylic acid (TCA) cycle intermediates in the shoots after salt treatment. This coincided with a significant depletion of sugars, suggesting that there is an increased rate of carbon influx into the TCA cycle at a constant rate of C-efflux from the cycle, which might be needed to support plant survival during salt stress. Using correlation analysis, we identified associations between the Na+ content and several sugars, suggesting that regulation of sugar metabolism is important in plant responses to salinity stress.Camilla B. Hill, Deepa Jha, Antony Bacic, Mark Tester and Ute Roessne
Generating multilingual subjectivity resources using english language
No full textThe text data can be of two types: facts and opinions. With the introduction of UTF-8 standards and development of Web 2.0, we are in abundance of opinionated text data available in many languages on the web. Subjectivity analysis aims at dividing those opinionated data into subjective and objective sentences and automatic extraction of subjective information from it. Many subjectivity resources as well as subjectivity analysis works are available in English language. In this paper, we examine different methods of generating subjectivity resources in Hindi language and other Indian languages using resources and tools available in English language. Two methods are proposed using wordlevel subjectivity annotations. These methods use English language OpinionFinder subjectivity lexicon and a small seed word list of Hindi language which can be expanded to generate subjectivity lexicon, respectively. Four methods are proposed using sentencelevel subjectivity annotations. These methods use subjectivity annotated corpora and tools available in English language. Different evaluation strategies are used to validate the generated lexicon and corpora in Hindi language. The simulations conducted confirm that these methods are effective in rapidly creating subjectivity resources in Hindi language and other Indian languages
MECHANISTIC CHARACTERIZATION OF THE TUMOR SUPPRESSIVE ROLE OF TIP60 IN CANCER
No full textPh.DDOCTOR OF PHILOSOPHY (SOM
Computational chemistry and molecular modeling : principles and applications / K.I. Ramachandran, G. Deepa, K. Namboori.
No full text"An exclusive URL (http://www.amrita.edu/cen/ccmm/) for this book with the required support materials has been provided for readers ..."--Preface.pharmacy bookfair2015Includes bibliographical references and index.xxi, 397 pages
Micro-raman spectroscopy of caries lesion formation in dental enamel
No full textCaries lesions form by a complex process of chemical interactions between dental enamel and its environment. They can cause cavities and pain, and are expensive to fix. Lesions form by slow demineralization over many months, even years. It is hard to characterize in vivo as a result of environmental factors and remineralization by ions in the oral cavity. In this thesis the process of demineralization was carried out in vitro and micro-Raman spectroscopy used to investigate and characterize the lesion's chemistry. Demineralization occurs by diffusion across the depth of the lesion of mineral ions via interstitial spaces in the dental enamel. Hydroxyl ions are initially lost by acidic attack, which increases the interstitial space. The demineralization is retarded by diffusion processes in the opposite direction, and a balance in the charges of the ions must be maintained. Having multiple ions diffusing simultaneously is termed “coupled diffusion”. A subsurface highly demineralized region is formed, but this can be remineralized.
Micro-Raman spectroscopy is a powerful tool for studying material composition by exciting chemical bonds in the sample. Using micro-Raman to characterize the chemical composition of lesions may help in developing preventative measures to stop their formation. Raman (λ=785 nm) was used to characterize lesions grown over 5, 7, 9, 11 and 14 days. The amide I peak at ~1605 cm-1, which has not been observed previously, was seen in the maturing lesions. The extreme demineralization in these lesions enables the organic peaks to be seen rather than the normally stronger mineral peaks. Analysis of crystallinity shows that there is always a reduction in mineral content with distance below the enamel surface, but this becomes magnified as the lesion matures. Type B carbonate substitution for phosphate ions can also be examined with Raman. Correcting for crystallinity shows that both carbonate and phosphate ions are lost at the same rate during demineralization.
In summary, micro-Raman is an effective and relatively easy tool to use in lesion characterization. It also has the advantage that it can be used to identify changes in both the mineral and protein phases of enamel.M.S.Includes bibliographical references (p. 53-55)
Shoot Na+ exclusion and increased salinity tolerance engineered by cell type-specific alteration of Na+ transport in arabidopsis
No full textSoil salinity affects large areas of cultivated land, causing significant reductions in crop yield globally. The Na+ toxicity of many crop plants is correlated with overaccumulation of Na+ in the shoot. We have previously suggested that the engineering of Na+ exclusion from the shoot could be achieved through an alteration of plasma membrane Na+ transport processes in the root, if these alterations were cell type specific. Here, it is shown that expression of the Na+ transporter HKT1;1 in the mature root stele of Arabidopsis thaliana decreases Na+ accumulation in the shoot by 37 to 64%. The expression of HKT1;1 specifically in the mature root stele is achieved using an enhancer trap expression system for specific and strong overexpression. The effect in the shoot is caused by the increased influx, mediated by HKT1;1, of Na+ into stelar root cells, which is demonstrated in planta and leads to a reduction of root-to-shoot transfer of Na+. Plants with reduced shoot Na+ also have increased salinity tolerance. By contrast, plants constitutively expressing HKT1;1 driven by the cauliflower mosaic virus 35S promoter accumulated high shoot Na+ and grew poorly. Our results demonstrate that the modification of a specific Na+ transport process in specific cell types can reduce shoot Na+ accumulation, an important component of salinity tolerance of many higher plants.Inge S. Møller, Matthew Gilliham, Deepa Jha, Gwenda M. Mayo, Stuart J. Roy, Juliet C. Coates, Jim Haseloff and Mark Teste
Root plasma membrane transporters controlling K+/Na+ homeostasis in salt-stressed barley
No full textCopyright © 2007 American Society of Plant BiologistsPlant salinity tolerance is a polygenic trait with contributions from genetic, developmental, and physiological interactions, in addition to interactions between the plant and its environment. In this study, we show that in salt-tolerant genotypes of barley (Hordeum vulgare), multiple mechanisms are well combined to withstand saline conditions. These mechanisms include: (1) better control of membrane voltage so retaining a more negative membrane potential; (2) intrinsically higher H+ pump activity; (3) better ability of root cells to pump Na+ from the cytosol to the external medium; and (4) higher sensitivity to supplemental Ca2+. At the same time, no significant difference was found between contrasting cultivars in their unidirectional 22Na+ influx or in the density and voltage dependence of depolarization-activated outward-rectifying K+ channels. Overall, our results are consistent with the idea of the cytosolic K+-to-Na+ ratio being a key determinant of plant salinity tolerance, and suggest multiple pathways of controlling that important feature in salt-tolerant plants.Zhonghua Chen, Igor I. Pottosin, Tracey A. Cuin, Anja T. Fuglsang, Mark Tester, Deepa Jha, Isaac Zepeda-Jazo, Meixue Zhou, Michael G. Palmgren, Ian A. Newman and Sergey Shabal
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