1,718 research outputs found
SLAH1, a homologue of the slow type anion channel SLAC1, modulates shoot Cl(-) accumulation and salt tolerance in Arabidopsis thaliana
Formally published in vol. 67, no. 15, 2016Salinity tolerance is correlated with shoot chloride (Clâ») exclusion in multiple crops, but the molecular mechanisms of long-distance Clâ» transport are poorly defined. Here, we characterize the in planta role of AtSLAH1 (a homologue of the slow type anion channel-associated 1 (SLAC1)). This protein, localized to the plasma membrane of root stelar cells, has its expression reduced by salt or ABA, which are key predictions for a protein involved with loading Clâ into the root xylem. Artificial microRNA knockdown mutants of AtSLAH1 had significantly reduced shoot Clâ accumulation when grown under low Clâ», whereas shoot Clâ increased and the shoot nitrate/chloride ratio decreased following AtSLAH1 constitutive or stelar-specific overexpression when grown in high Clâ. In both sets of overexpression lines a significant reduction in shoot biomass over the null segregants was observed under high Clâ» supply, but not low Clâ» supply. Further in planta data showed AtSLAH3 overexpression increased the shoot nitrate/chloride ratio, consistent with AtSLAH3 favouring nitrate transport. Heterologous expression of AtSLAH1 in Xenopus laevis oocytes led to no detectible transport, suggesting the need for post-translational modifications for AtSLAH1 to be active. Our in planta data are consistent with AtSLAH1 having a role in controlling root-to-shoot Clâ» transport.Jiaen Qiu, Sam W Henderson, Mark Tester, Stuart J Roy and Mathew Gilliha
Nearshore marine ecology at Hutchinson Island, Florida: 1971-1974. VI. plankton dynamics, 1971-1973, VII. phytoplankton 1971-1973, VIII. zooplankton, 1971-1973, IX. diel plankton, 1973-1974, X. benthic algae species list
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Free oxygen radicals regulate plasma membrane Ca2+- and K+-permeable channels in plant root cells
Free oxygen radicals are an irrefutable component of life, underlying important biochemical and physiological phenomena in animals. Here it is shown that free oxygen radicals activate plasma membrane CaÂČâș- and Kâș-permeable conductances in Arabidopsis root cell protoplasts, mediating CaÂČâș influx and Kâș efflux, respectively. Free oxygen radicals generate increases in cytosolic CaÂČâș mediated by a novel population of nonselective cation channels that differ in selectivity and pharmacology from those involved in toxic Naâș influx. Analysis of the free oxygen radical-activated Kâș conductance showed its similarity to the Arabidopsis root Kâș outward rectifier. Significantly larger channel activation was found in cells responsible for perceiving environmental signals and undergoing elongation. Quenching root free oxygen radicals inhibited root elongation, confirming the role of radical-activated CaÂČâș influx in cell growth. Net free oxygen radical-stimulated CaÂČâș influx and Kâș efflux were observed in root cells of monocots, dicots, C3 and C4 plants, suggesting conserved mechanisms and functions. In conclusion, two functions for free oxygen radical cation channel activation are proposed: initialization/amplification of stress signals and control of cell elongation in root growth.Vadim Demidchik, Sergey N. Shabala, Katherine B. Coutts, Mark A. Tester and Julia M. Davie
Yield-related salinity tolerance traits identified in a nested association mapping (NAM) population of wild barley
Producing sufficient food for nine billion people by 2050 will be constrained by soil salinity, especially in irrigated systems. To improve crop yield, greater understanding of the genetic control of traits contributing to salinity tolerance in the field is needed. Here, we exploit natural variation in exotic germplasm by taking a genome-wide association approach to a new nested association mapping population of barley called HEB-25. The large population (1,336 genotypes) allowed cross-validation of loci, which, along with two years of phenotypic data collected from plants irrigated with fresh and saline water, improved statistical power. We dissect the genetic architecture of flowering time under high salinity and we present genes putatively affecting this trait and salinity tolerance. In addition, we identify a locus on chromosome 2H where, under saline conditions, lines homozygous for the wild allele yielded 30% more than did lines homozygous for the Barke allele. Introgressing this wild allele into elite cultivars could markedly improve yield under saline conditions.Stephanie Saade, Andreas Maurer, Mohammed Shahid, Helena Oakey,
Sandra M. Schmöckel, Sónia Negrão, Klaus Pillen and Mark Teste
AtNPF2.5 modulates chloride (Cl -bar) efflux from roots of Arabidopsis thaliana
The accumulation of high concentrations of chloride (Cl(-)) in leaves can adversely affect plant growth. When comparing different varieties of the same Cl(-) sensitive plant species those that exclude relatively more Cl(-) from their shoots tend to perform better under saline conditions; however, the molecular mechanisms involved in maintaining low shoot Cl(-) remain largely undefined. Recently, it was shown that the NRT1/PTR Family 2.4 protein (NPF2.4) loads Cl(-) into the root xylem, which affects the accumulation of Cl(-) in Arabidopsis shoots. Here we characterize NPF2.5, which is the closest homolog to NPF2.4 sharing 83.2% identity at the amino acid level. NPF2.5 is predominantly expressed in root cortical cells and its transcription is induced by salt. Functional characterisation of NPF2.5 via its heterologous expression in yeast (Saccharomyces cerevisiae) and Xenopus laevis oocytes indicated that NPF2.5 is likely to encode a Cl(-) permeable transporter. Arabidopsis npf2.5 T-DNA knockout mutant plants exhibited a significantly lower Cl(-) efflux from roots, and a greater Cl(-) accumulation in shoots compared to salt-treated Col-0 wild-type plants. At the same time, [Formula: see text] content in the shoot remained unaffected. Accumulation of Cl(-) in the shoot increased following (1) amiRNA-induced knockdown of NPF2.5 transcript abundance in the root, and (2) constitutive over-expression of NPF2.5. We suggest that both these findings are consistent with a role for NPF2.5 in modulating Cl(-) transport. Based on these results, we propose that NPF2.5 functions as a pathway for Cl(-) efflux from the root, contributing to exclusion of Cl(-) from the shoot of Arabidopsis.Bo Li, Jiaen Qiu, Maheswari Jayakannan, Bo Xu, Yuan Li, Gwenda M. Mayo, Mark Tester, Matthew Gilliham and Stuart J. Ro
Broadcasting graphic war violence: the moral face of Channel 4
Drawing on empirical data from Channel 4 (C4) regarding the broadcasting of violent war imagery, and positioned within Goffmanâs notion of the interaction ritual (1959, 1967), this article investigates how C4 negotiate potentially competing commercial, regulatory and moral requirements through processes of discretionary decision-making. Throughout, the article considers the extent to which these negotiations are presented through a series of âimaginingsâ â of C4 and its audience â which serve to simultaneously guide and legitimate the decisions made. This manifestation of imaginings moves us beyond more blanket explanations of âbrandingâ and instead allows us to see the final programmes as the end product of a series of complex negotiations and interactions between C4 and those multiple external parties significant to the workings of their organization. The insights gleaned from this case study are important beyond the workings of C4 because they help elucidate how all institutions and organizations may view, organize and justify their practices (to both themselves and others) within the perceived constraints in which they operate
Transition from a maternal to external nitrogen source in maize seedlings
Maximizing NO3â uptake during seedling development is important as it has a major influence on plant growth and yield. However, little is known about the processes leading to, and involved in, the initiation of root NO3â uptake capacity in developing seedlings. This study examines the physiological processes involved in root NO3â uptake and metabolism, to gain an understanding of how the NO3â uptake system responds to meet demand as maize seedlings transition from seed N use to external N capture. The concentrations of seedâderived free amino acids within root and shoot tissues are initially high, but decrease rapidly until stabilizing eight days after imbibition (DAI). Similarly, shoot N% decreases, but does not stabilize until 12â13 DAI. Following the decrease in free amino acid concentrations, root NO3â uptake capacity increases until shoot N% stabilizes. The increase in root NO3â uptake capacity corresponds with a rapid rise in transcript levels of putative NO3â transporters, ZmNRT2.1 and ZmNRT2.2 . The processes underlying the increase in root NO3â uptake capacity to meet N demand provide an insight into the processes controlling N uptake
Image-based phenotyping for non-destructive screening of different salinity tolerance traits in rice
Background: Soil salinity is an abiotic stress wide spread in rice producing areas, limiting both plant growth and yield. The development of salt-tolerant rice requires efficient and high-throughput screening techniques to identify promising lines for salt affected areas. Advances made in image-based phenotyping techniques provide an opportunity to use non-destructive imaging to screen for salinity tolerance traits in a wide range of germplasm in a reliable, quantitative and efficient way. However, the application of image-based phenotyping in the development of salt-tolerant rice remains limited. Results: A non-destructive image-based phenotyping protocol to assess salinity tolerance traits of two rice cultivars (IR64 and Fatmawati) has been established in this study. The response of rice to different levels of salt stress was quantified over time based on total shoot area and senescent shoot area, calculated from visible red-green-blue (RGB) and fluorescence images. The response of rice to salt stress (50, 75 and 100 mM NaCl) could be clearly distinguished from the control as indicated by the reduced increase of shoot area. The salt concentrations used had only a small effect on the growth of rice during the initial phase of stress, the shoot Na+ accumulation independent phase termed the âosmotic stressâ phase. However, after 20 d of treatment, the shoot area of salt stressed plants was reduced compared with non-stressed plants. This was accompanied by a significant increase in the concentration of Na+ in the shoot. Variation in the senescent area of the cultivars IR64 and Fatmawati in response to a high concentration of Na+ in the shoot indicates variation in tissue tolerance mechanisms between the cultivars. Conclusions: Image analysis has the potential to be used for high-throughput screening procedures in the development of salt-tolerant rice. The ability of image analysis to discriminate between the different aspects of salt stress (shoot ion-independent stress and shoot ion dependent stress) makes it a useful tool for genetic and physiological studies to elucidate processes that contribute to salinity tolerance in rice. The technique has the potential for identifying the genetic basis of these mechanisms and assisting in pyramiding different tolerance mechanisms into breeding lines.Aris Hairmansis, Bettina Berger, Mark Tester, and Stuart John Ro
Contrast in chloride exclusion between two grapevine genotypes and its variation in their hybrid progeny
Potted grapevines of 140 Ruggeri (Vitis berlandieri Ă Vitis rupestris), a good Clâ excluder, and K 51-40 (Vitis champinii Ă Vitis riparia âGloireâ), a poor Clâ excluder, and of a family obtained by crossing the two genotypes, were used to examine the inheritance of Clâ exclusion. Rooted leaves were then used to further investigate the mechanism for Clâ exclusion in 140 Ruggeri. In both a potting mix trial (plants watered with 50 mM Clâ) and a solution culture trial (plants grown in 25 mM Clâ), the variation in Clâ accumulation was continuous, indicating multiple rather than single gene control for Clâ exclusion between hybrids within the family. Upper limits of 42% and 35% of the phenotypic variation in Clâ concentration could be attributed to heritable sources in the potting mix and solution culture trials, respectively. Chloride transport in roots of rooted leaves of both genotypes appeared to be via the symplastic pathway, since addition of 8-hydroxy-1,3,6-pyrenetrisulphonic acid (PTS), an apoplastic tracer, revealed no obvious PTS fluorescence in the laminae of either genotype, despite significant accumulation of Clâ in laminae of K 51-40 during the PTS uptake period. There was no significant difference in either unidirectional 36Clâ flux (10 min) or 36Clâ uptake (3 h) into roots of rooted leaves exposed to 5, 10, or 25 mM Clâ. However, the percentage of 36Clâ transported to the lamina (3 h) was significantly lower in 140 Ruggeri than in K 51-40, supporting reduced Clâ loading into xylem and implicating the root stele in the Clâ exclusion mechanism
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