Carbon partitioning and export in transgenic Arabidopsis thaliana with altered capacity for sucrose synthesis grown at low temperature: a role for metabolite transporters

We investigated the role of metabolite transporters in cold acclimation by comparing the responses of wild-type (WT) Arabidopsis thaliana (Heynh.) with that of transgenic plants over-expressing sucrose-phosphate synthase (SPSox) or with that of antisense repression of cytosolic fructose-1,6-bisphosphatase (FBPas). Plants were grown at 23 degrees C and then shifted to 5 degrees C. We compared the leaves shifted to 5 degrees C for 3 and 10 d with new leaves that developed at 5 degrees C with control leaves on plants at 23 degrees C. At 23 degrees C, ectopic expression of SPS resulted in 30% more carbon being fixed per day and an increase in sucrose export from source leaves. This increase in fixation and export was supported by increased expression of the plastidic triose-phosphate transporter AtTPT and, to a lesser extent, the high-affinity Suc transporter AtSUC1. The improved photosynthetic performance of the SPSox plants was maintained after they were shifted to 5 degrees C and this was associated with further increases in AtSUC1 expression but with a strong repression of AtTPT mRNA abundance. Similar responses were shown by WT plants during acclimation to low temperature and this response was attenuated in the low sucrose producing FBPas plants. These data suggest that a key element in recovering flux through carbohydrate metabolism in the cold is to control the partitioning of metabolites between the chloroplast and the cytosol, and Arabidopsis modulates the expression of AtTPT to maintain balanced carbon flow. Arabidopsis also up-regulates the expression of AtSUC1, and to lesser extent AtSUC2, as down-stream components facilitate sucrose transport in leaves that develop at low temperatures.info:eu-repo/semantics/publishedVersio

Integration of metabolite with transcript and enzyme activity profiling during diurnal cycles in Arabidopsis rosettes

ABSTRACT: BACKGROUND: Genome-wide transcript profiling and analyses of enzyme activities from central carbon and nitrogen metabolism has shown that transcript levels undergo marked and rapid changes during diurnal cycles and after transfer to darkness, whereas changes of enzyme activities are smaller and delayed. In the starchless pgm mutant, where sugars are depleted every night, there are accentuated diurnal changes of transcript levels. Enzyme activities do not show larger diurnal changes; instead they shift towards the levels found in wild-type after several days of darkness. These results indicate that enzyme activities change slowly, integrating the changes of transcript levels over several diurnal cycles. RESULTS: To generalize this conclusion, 137 metabolites were profiled using GC-MS and LC-MS. Amplitudes of the diurnal changes of metabolites in pgm were (with the exception of sugars) similar or smaller than in wild-type. The average levels shifted towards those found after several days of darkness in wild-type. Examples include increased levels of many amino acids due to protein degradation, decreased levels of many fatty acids, increased tocopherol and decreased myo-inositol. Many metabolite-transcript correlations were found and the proportion of transcripts correlated with sugars increased dramatically in the starchless pgm mutant. CONCLUSION: Rapid diurnal changes of transcripts are integrated over time to generate quasi-stable changes across large sectors of metabolism. The slow response of enzyme activities and metabolites implies that correlations between metabolites and transcripts are due to regulation of gene expression by metabolites, rather than metabolites being changed as a consequence of a change in gene expression

Overexpression of Plastid Transketolase in Tobacco Results in a Thiamine Auxotrophic Phenotype

To investigate the effect of increased plastid transketolase on photosynthetic capacity and growth, tobacco (Nicotiana tabacum) plants with increased levels of transketolase protein were produced. This was achieved using a cassette composed of a full-length Arabidopsis thaliana transketolase cDNA under the control of the cauliflower mosaic virus 35S promoter. The results revealed a major and unexpected effect of plastid transketolase overexpression as the transgenic tobacco plants exhibited a slow-growth phenotype and chlorotic phenotype. These phenotypes were complemented by germinating the seeds of transketolase-overexpressing lines in media containing either thiamine pyrophosphate or thiamine. Thiamine levels in the seeds and cotyledons were lower in transketolase-overexpressing lines than in wild-type plants. When transketolase-overexpressing plants were supplemented with thiamine or thiamine pyrophosphate throughout the life cycle, they grew normally and the seed produced from these plants generated plants that did not have a growth or chlorotic phenotype. Our results reveal the crucial importance of the level of transketolase activity to provide the precursor for synthesis of intermediates and to enable plants to produce thiamine and thiamine pyrophosphate for growth and development. The mechanism determining transketolase protein levels remains to be elucidated, but the data presented provide evidence that this may contribute to the complex regulatory mechanisms maintaining thiamine homeostasis in plants

Sugars and circadian regulation make major contributions to the global regulation of diurnal gene expression in Arabidopsis

The diurnal cycle strongly influences many plant metabolic and physiological processes. Arabidopsis thaliana rosettes were harvested six times during 12-h-light/12-h-dark treatments to investigate changes in gene expression using ATH1 arrays. Diagnostic gene sets were identified from published or in-house expression profiles of the response to light, sugar, nitrogen, and water deficit in seedlings and 4 h of darkness or illumination at ambient or compensation point [CO2]. Many sugar-responsive genes showed large diurnal expression changes, whose timing matched that of the diurnal changes of sugars. A set of circadian-regulated genes also showed large diurnal changes in expression. Comparison of published results from a free-running cycle with the diurnal changes in Columbia-0 (Col-0) and the starchless phosphoglucomutase (pgm) mutant indicated that sugars modify the expression of up to half of the clock-regulated genes. Principle component analysis identified genes that make large contributions to diurnal changes and confirmed that sugar and circadian regulation are the major inputs in Col-0 but that sugars dominate the response in pgm. Most of the changes in pgm are triggered by low sugar levels during the night rather than high levels in the light, highlighting the importance of responses to low sugar in diurnal gene regulation. We identified a set of candidate regulatory genes that show robust responses to alterations in sugar levels and change markedly during the diurnal cycle

Twitter, la nueva era de la comunicación política : un análisis del manejo de la red social en las elecciones a la alcaldía de Bogotá 2015

La nueva era de la comunicación política inicia con la aparición de las redes sociales. Nuevas herramientas y mecanismos de propaganda nacen con el nacimiento de los mismos. Pero no es hasta que el presidente norteamericano Barak Obama utiliza las redes sociales en pro de su campaña que se tornan en elementos indispensables para una estrategia política. El 25 de octubre de 2015 se llevan a cabo las elecciones a la alcaldía de Bogotá, y cuatro candidatos son los más opcionados para ganar la contienda: Enrique Peñalosa, Clara López, Francisco Santos y Rafael Pardo. La propuesta del trabajo de investigación consta en el análisis de los manejos de Twitter por parte de dichos candidatos, todo esto para determinar la eficacia de una estrategia de comunicación dentro de este medio, y si es relevante a la hora de las votaciones.The new era in the political communication starts with the birth of social networks. New tools and mechanisms of propaganda rise due to the birth of them. But it's not until Barak Obama's campaign that they have become important to a political strategy. On October 25th of 2015, Bogotá has the elections for mayor. There are four main candidates that have a chance to win: Enrique Peñalosa, Clara López, Francisco Santos and Rafael Pardo. The main idea of this paper is to analyze the usage of Twitter by each of the candidates, for it to determine the efficiency of a communicational strategy during elections.Comunicador (a) SocialPregrad

A pivotal role for starch in the reconfiguration of 14C-partitioning and allocation in Arabidopsis thaliana under short-term abiotic stress.

Plant carbon status is optimized for normal growth but is affected by abiotic stress. Here, we used 14C-labeling to provide the first holistic picture of carbon use changes during short-term osmotic, salinity, and cold stress in Arabidopsis thaliana. This could inform on the early mechanisms plants use to survive adverse environment, which is important for efficient agricultural production. We found that carbon allocation from source to sinks, and partitioning into major metabolite pools in the source leaf, sink leaves and roots showed both conserved and divergent responses to the stresses examined. Carbohydrates changed under all abiotic stresses applied; plants re-partitioned 14C to maintain sugar levels under stress, primarily by reducing 14C into the storage compounds in the source leaf, and decreasing 14C into the pools used for growth processes in the roots. Salinity and cold increased 14C-flux into protein, but as the stress progressed, protein degradation increased to produce amino acids, presumably for osmoprotection. Our work also emphasized that stress regulated the carbon channeled into starch, and its metabolic turnover. These stress-induced changes in starch metabolism and sugar export in the source were partly accompanied by transcriptional alteration in the T6P/SnRK1 regulatory pathway that are normally activated by carbon starvation

Is Extended Volume of External Beam Irradiation Beneficial in Post-esophagectomy High Risk Patients Receiving Combined Chemoradiation Therapy?

OBJECTIVE: To assess the value of extended volume irradiation with anastomotic coverage in high risk resected esophageal cancer patients. METHOD: A retrospective study was undertaken at LRCC from 1989-1999 for high risk resected esophageal cancer patients. Adjuvant treatments consisted of 4 cycles of chemotherapy (epirubicin/fluorouracil/cisplatin or cisplatin/fluorouracil), and local regional irradiation with or without coverage of the anastomotic site. Radiation dose ranged from 45-60Gy at 1.8-2.0 Gy/fraction given with initial anterior-posterior/posterior-anterior arrangement with either extended (with anastomotic coverage) or small (without anastomotic coverage) field followed by oblique fields for boost. RESULT: One hundred eighty-eight charts were reviewed. Seventy-two patients were eligible for post-resection chemoradiation therapy. Three patients had disease progression prior to therapy, and 69 patients were analyzed. There were 81% T3N1 and 13% T2N1. Thirty-four patients had margin involvements (radial 53%; proximal/distal 32%), 65% were adenocarcinoma and 33% were squamous carcinoma. Median followup was 23.6 months (3.4 - 78.4 months). Two year survival was 50%; 5yr 24%. Relapse rate was 62.3% and median time to relapse was 20 months. Recurrence locally to anastomosis or adjacent to anastomosis was 9/43(20.9%) with small field and 2/26(7.7%) with extended field. Of 31 patients with relapse outside anastomosis, 14/20(70%) relapsed locoregional/distal when treated with small field and 3/11(27%) relapsed locoregional/distal when treated with extended field (p=0.02). There was no excess treatment interruption or chronic gastrointestinal toxicity with extended field irradiation. CONCLUSION: There is significant decrease in locoregional/distal relapse with use of extended field in high risk resected esophageal cancer patients

Diurnal changes of polysome loading track sucrose content in the rosette of wildtype Arabidopsis and the starchless pgm mutant

Growth is driven by newly fixed carbon in the light, but depends at night on reserves, like starch, that are laid down in the light. Unless plants coordinate their growth with diurnal changes in the carbon supply, they will experience acute carbon starvation during the night. Protein synthesis represents a major component of cellular growth. Polysome loading was investigated during the diurnal cycle, an extended night and low CO2 in Arabidopsis Col-0 and in the starchless pgm mutant. In Col-0, polysome loading was 60-70% in the light, 40-45% for much of the night and <20% in an extended night, whilst in pgm it fell to <25% early in the night. Quantification of rRNA species using qRT-PCR revealed that polysome loading remained high for much of the night in the cytosol, was strongly light-dependent in the plastid, and was always high in mitochondria. The rosette sucrose content correlated with overall and with cytosolic polysome loading. Ribosome abundance did not show significant diurnal changes. However, compared to Col-0, pgm had decreased and increased abundance of plastidic and mitochondrial ribosomes, respectively. Incorporation of label from 13CO2 into protein confirmed that protein synthesis continues at a diminished rate in the dark. Modelling revealed that a decrease in polysome loading at night is required to balance protein synthesis with the availability of carbon from starch breakdown. Costs are also reduced by using amino acids that accumulated in previous light period. These results uncover a tight coordination of protein synthesis with the momentary supply of carbon