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

Parametric evaluation for powder flowability using a freeman rheometer: a discrete element method study

A discrete element method (DEM) using the Hertz-Mindlin and JKR models was used to model the flowability measurement on a cohesive particulate material in the Freeman FT4 powder rheometer. An assessment of DEM parameterswas carried out to understand the operation of this equipment and to study the correlation between inter-particle properties and flowability. Simulation results indicate that the static and rolling friction coefficients, and JKR cohesion energy density are all negatively correlated with powder flowability, meaning that an increase in any of these parameters results in a decrease in powder flowability. At higher level friction, the force and torque have a larger measurement deviation, which is possibly due to local jamming in the particle bed. The powder flowability decreases as particle size increases for the current coarse grained system. Particles size distribution width has very little effect on the flowability changes. Particles with lower sphericity tend to have lower flowability possibly due to particle interlocking. It was demonstrated that rolling friction has a large effect on flowability for a give non-spherical particle shape

Global transcript levels respond to small changes of the carbon status during progressive exhaustion of carbohydrates in Arabidopsis rosettes

The balance between the supply and utilization of carbon (C) changes continually. It has been proposed that plants respond in an acclimatory manner, modifying C utilization to minimize harmful periods of C depletion. This hypothesis predicts that signaling events are initiated by small changes in C status. We analyzed the global transcriptional response to a gradual depletion of C during the night and an extension of the night, where C becomes severely limiting from 4 h onward. The response was interpreted using published datasets for sugar, light, and circadian responses. Hundreds of C-responsive genes respond during the night and others very early in the extended night. Pathway analysis reveals that biosynthesis and cellular growth genes are repressed during the night and genes involved in catabolism are induced during the first hours of the extended night. The C response is amplified by an antagonistic interaction with the clock. Light signaling is attenuated during the 24-h light/dark cycle. A model was developed that uses the response of 22K genes during a circadian cycle and their responses to C and light to predict global transcriptional responses during diurnal cycles of wild-type and starchless pgm mutant plants and an extended night in wild-type plants. By identifying sets of genes that respond at different speeds and times during C depletion, our extended dataset and model aid the analysis of candidates for C signaling. This is illustrated for AKIN10 and four bZIP transcription factors, and sets of genes involved in trehalose signaling, protein turnover, and starch breakdown

An application of the finite-discrete element method in the simulation of ceramic breakage: methodology for a validation study for alumina specimens

Alumina (aluminum oxide, Al2O3) particles are pelletised and fired to produce high porosity catalyst pellets of complex shapes. These pellets fill cylindrical reactor columns with particulate packing structures that are key to the in-service performance, but will suffer breakages which impact on catalyst performance. The combined Finite- Discrete Element Method (FEMDEM) is ideally suited to the simulation of both the multi-body pellet dynamic packing and quasi-static interactions as well as the stress field of each individual pellet, its deformations and fragmentation. The application of FEMDEM fracture modelling to a fine-grained brittle and porous material is novel. This paper presents a methodology for a validation study through comparison with three point- bending and Brazilian tests and discusses FEMDEMs potential in modelling multi-body fragile systems

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