Markus Niessen

Chloroplastic photorespiratory bypass increases photosynthesis and biomass production in Arabidopsis thaliana

We introduced the Escherichia coli glycolate catabolic pathway into Arabidopsis thaliana chloroplasts to reduce the loss of fixed carbon and nitrogen that occurs in C3 plants when phosphoglycolate, an inevitable by-product of photosynthesis, is recycled by photorespiration. Using step-wise nuclear transformation with five chloroplast-targeted bacterial genes encoding glycolate dehydrogenase, glyoxylate carboligase and tartronic semialdehyde reductase, we generated plants in which chloroplastic glycolate is converted directly to glycerate. This reduces, but does not eliminate, flux of photorespiratory metabolites through peroxisomes and mitochondria. Transgenic plants grew faster, produced more shoot and root biomass, and contained more soluble sugars, reflecting reduced photorespiration and enhanced photosynthesis that correlated with an increased chloroplastic CO2 concentration in the vicinity of ribulose-1,5-bisphosphate carboxylase/oxygenase. These effects are evident after overexpression of the three subunits of glycolate dehydrogenase, but enhanced by introducing the complete bacterial glycolate catabolic pathway. Diverting chloroplastic glycolate from photorespiration may improve the productivity of crops with C3 photosynthesis.

Development and Control of an Integrated and Distributed Inverter for a Fault Tolerant Five-Phase Switched Reluctance Traction Drive

A concept of an integrated and distributed inverter for switched reluctance machines is introduced. The application at hand is an outer-rotor direct drive designed for railway traction applications. A five-phase switched reluctance machine was developed and is used to demonstrate the function of the integrated and distributed inverter. The distribution is achieved by supplying each phase coil with its own modular inverter. Each inverter module is placed evenly around the end of the stator stack next to its dedicated coil. This increases the redundancy of the drive significantly. The likelihood of phase-to-phase faults is reduced, because no overlapping end-turns are necessary. Also, the integration of machine and inverter is simplified, because the semiconductors can be evenly distributed around the machine. The concept reduces the amount of terminals between drive and vehicle to communication, power supply, and cooling, independent of the number of machine phases. With the integrated and distributed inverter new control strategies can be developed to influence machine vibration and radiated noise. In this paper, the design of the prototype, the direct torque control of the five-phase machine, and the behavior in the case of a fault inside a module is analyzed.

Metabolic Engineering Towards the Enhancement of Photosynthesis

Photosynthetic capacity is a promising target for metabolic engineering of crop plants towards higher productivity. Crop photosynthesis is limited by multiple factors dependent on the environmental conditions. This includes photosynthetic electron transport, regeneration of CO2 acceptor molecules in the reductive pentose phosphate cycle, the activity and substrate specificity of the CO2‐fixing enzyme Ribulose‐1,5‐bisphosphate carboxylase/oxygenase, and the associated flow through the photorespiratory pathway. All these aspects of the photosynthetic network have been the subject of recently published metabolic engineering approaches in model species. Together, the novel results raise hopes that engineering of photosynthesis in crop species can significantly increase agricultural productivity.

Two alanine aminotranferases link mitochondrial glycolate oxidation to the major photorespiratory pathway in Arabidopsis and rice

The major photorespiratory pathway in higher plants is distributed over chloroplasts, mitochondria, and peroxisomes. In this pathway, glycolate oxidation takes place in peroxisomes. It was previously suggested that a mitochondrial glycolate dehydrogenase (GlcDH) that was conserved from green algae lacking leaf-type peroxisomes contributes to photorespiration in Arabidopsis thaliana. Here, the identification of two Arabidopsis mitochondrial alanine:glyoxylate aminotransferases (ALAATs) that link glycolate oxidation to glycine formation are described. By this reaction, the mitochondrial side pathway produces glycine from glyoxylate that can be used in the glycine decarboxylase (GCD) reaction of the major pathway. RNA interference (RNAi) suppression of mitochondrial ALAAT did not result in major changes in metabolite pools under standard conditions or enhanced photorespiratroy flux, respectively. However, RNAi lines showed reduced photorespiratory CO2 release and a lower CO2 compensation point. Mitochondria isolated from RNAi lines are incapable of converting glycolate to CO2, whereas simultaneous overexpression of GlcDH and ALAATs in transiently transformed tobacco leaves enhances glycolate conversion. Furthermore, analyses of rice mitochondria suggest that the side pathway for glycolate oxidation and glycine formation is conserved in monocotyledoneous plants. It is concluded that the photorespiratory pathway from green algae has been functionally conserved in higher plants.

Development and control of an integrated and distributed inverter for a fault tolerant five-phase switched reluctance traction drive

A concept of an integrated and distributed inverter for switched reluctance machines is introduced. The application at hand is an outer-rotor direct drive designed for railway traction applications. A five-phase switched reluctance machine (SRM) was developed and is used to demonstrate the function of the integrated and distributed inverter. The distribution is achieved by supplying each phase coil with its own modular inverter. Each inverter module is placed evenly around the end of the stator stack next to its dedicated coil. This increases the redundancy of the drive significantly. The likelihood of phase-to-phase faults is reduced, because no overlapping end-turns are necessary. Also, the integration of machine and inverter is simplified, because the semiconductors can be evenly distributed around the machine. The concept reduces the amount of terminals between drive and vehicle to communication, power supply and cooling, independent of the number of machine phases. With the integrated and distributed inverter new control strategies can be developed to influence machine vibration and radiated noise. In this paper the design of the prototype, the direct torque control of the five-phase machine and the behavior in case of a fault inside a module is analyzed.

Microholes in zirconia-coated Ni-superalloys for transpiration cooling of turbine blades

Drillings in zirconia coated Ni-superalloys is done by melt extraction with pulsed laser radiation provided by a Nd:YAG slab laser with microsecond pulse duration. This laser system distinguishes itself by a high beam quality and offers the possibility to investigate drilling of holes with a diameter of 200 micrometer by percussion drilling and trepanning. The quality of drilled holes, e.g. the heat affected zone (HAZ), the recast layer and the conicality, are presented. During drilling different process gases are used. The results in drilling velocities, melt thickness and chemical composition of the melting zone are shown for oxygen, argon and nitrogen by SEM and EDX. A numerical simulation of the trepanning process will be presented. The different time scales of the contributing physical processes related, for example, to the small melt film layer during trepanning are described. A coating is distributed on the multilayer system to protect the blade from recast. Aim of the investigation is the production of holes in a multilayer system, consisting of CMSX-4, VPS-MCrAlY and EB-PVD-zirconia. With this used laser system inclined holes up to 60 degrees in this layer system can be drilled. No recast layer and no spalling of the zirconia-layer are observed.

Core promoter acetylation is not required for high transcription from the phosphoenolpyruvate carboxylase promoter in maize

BackgroundAcetylation of promoter nucleosomes is tightly correlated and mechanistically linked to gene activity. However, transcription is not necessary for promoter acetylation. It seems, therefore, that external and endogenous stimuli control histone acetylation and by this contribute to gene regulation. Photosynthetic genes in plants are excellent models with which to study the connection between stimuli and chromatin modifications because these genes are strongly expressed and regulated by multiple stimuli that are easily manipulated. We have previously shown that acetylation of specific histone lysine residues on the photosynthetic phosphoenolpyruvate carboxylase (Pepc) promoter in maize is controlled by light and is independent of other stimuli or gene activity. Acetylation of upstream promoter regions responds to a set of other stimuli which include the nutrient availability of the plant. Here, we have extended these studies by analysing histone acetylation during the diurnal and circadian rhythm of the plant.ResultsWe show that histone acetylation of individual lysine residues is removed from the core promoter before the end of the illumination period which is an indication that light is not the only factor influencing core promoter acetylation. Deacetylation is accompanied by a decrease in gene activity. Pharmacological inhibition of histone deacetylation is not sufficient to prevent transcriptional repression, indicating that deacetylation is not controlling diurnal gene regulation. Variation of the Pepc promoter activity during the day is controlled by the circadian oscillator as it is maintained under constant illumination for at least 3 days. During this period, light-induced changes in histone acetylation are completely removed from the core promoter, although the light stimulus is continuously applied. However, acetylation of most sites on upstream promoter elements follows the circadian rhythm.ConclusionOur results suggest a central role of upstream promoter acetylation in the quantitative regulation of gene expression in this model gene. Induced core promoter acetylation is dispensable for the highest gene expression in the diurnal and circadian rhythm.

Melt Expulsion by a Coaxial Gas Jet in Trepanning of CMSX-4 with Microsecond Nd:YAG Laser Radiation

Trepanning of 200 μm holes in 2-5mm thick CMSX-4 sheets is done by laser radiation provided by a lamp-pumped Nd:YAG slab laser with pulse durations of 100 - 500 μs. Pulse energies <1J determine the material removal mainly by melt expulsion assisted by a processing gas jet coaxial to the laser beam. Stagnation and deflection of the gas jet at the entrance of the kerf, friction in the molten material, and friction at the liquid/solid interface hinder an efficient melt expulsion. A simulation tool for supersonic gas flow solving Euler equations by the Finite Volume Method is developed in order to investigate the gas flow through the trepanning kerf. Gas pressures above and within the kerfs while trepanning at different inclination angles, geometries and arrangements of nozzles as well nozzle reservoir pressures are presented. The computed gas flow is compared to melt expulsion investigated metallographically by the determination of kerf widths and the thickness of the resolidified melt.

Constitutive and dark‐induced expression of Solanum tuberosum phosphoenolpyruvate carboxylase enhances stomatal opening and photosynthetic performance of Arabidopsis thaliana

The effect of constitutive and dark‐induced expression of Solanum tuberosum phosphoenolpyruvate carboxylase (PEPC) on the opening state of stomata and photosynthetic performance in Arabidopsis thaliana plants was studied. Transcript accumulation analyses of the A. thaliana dark‐induced (Din10 and Din6) and the Pisum sativum asparagine synthetase 2 promoters (Asn2) in transiently transformed tobacco leaves showed that Din10 promoter induced more DsRed accumulation in the dark compared to the other din genes. Overexpression of PEPC under the control of the constitutive enhanced CaMV 35S (p35SS) and dark‐induced Din10 promoter in stably transformed A. thaliana plants increased the number of opened stomata in dark adapted leaves. Gas exchange measurements using A. thaliana plants transgenic for p35SS‐PEPC and Din10‐PEPC revealed a marked increase in stomatal conductance, transpiration, and dark respiration rates measured in the dark compared to wild‐type plants. Moreover, measurement of CO2 assimilation rates at different external CO2 concentrations (Ca) and different light intensities shows an increase in the CO2 assimilation rates in transgenic Arabidopsis lines compared to wild‐type plants. This is considered as first step towards transferring the aspects of Crassulacean acid metabolism‐like photosynthetic mechanism into C3 plants. Biotechnol. Bioeng. 2012; 109:536–544.

Temperature field and residual stress distribution for laser metal deposition

Laser metal deposition (LMD) process has been widely used in many industrial applications such as automotive, defense, aerospace, and so on. Modeling has to address physical phenomena like laser-powder interaction, heat transfer, fusion, solidification, and track formation. LMD induces a complex thermal stress field that results in residual stress distributions. Depending on its magnitude and nature (i.e., whether tensile or compressive), the residual stresses can cause unpredicted in-service failures. Therefore, the prediction of its distribution in the deposited structure as a function of the process strategy is essential to improve the process and the part quality. LMD represents mathematically a free boundary value problem. This means that the track geometry is part of the solution. The authors developed a three-dimensional time-dependent finite element model for LMD with coaxial powder feeding supply. The model encompasses the powder stream, its interaction with the laser radiation, and the melt pool computation. The model was validated by a comparison of the experimental and computed shapes of the melt pool surfaces concerning cross section, longitudinal section and high-speed photographs [Pirch et al., in Proceedings of the ICALEO Conference, 16–20 October 2016]. In this paper, the model was applied to overlapping tracks for single and multilayer processing for different process strategies. The simulation allows us to analyze the time- and space-resolved evolution of temperature and stresses. The influence of the powder feed rate on the residual stresses is investigated.Laser metal deposition (LMD) process has been widely used in many industrial applications such as automotive, defense, aerospace, and so on. Modeling has to address physical phenomena like laser-powder interaction, heat transfer, fusion, solidification, and track formation. LMD induces a complex thermal stress field that results in residual stress distributions. Depending on its magnitude and nature (i.e., whether tensile or compressive), the residual stresses can cause unpredicted in-service failures. Therefore, the prediction of its distribution in the deposited structure as a function of the process strategy is essential to improve the process and the part quality. LMD represents mathematically a free boundary value problem. This means that the track geometry is part of the solution. The authors developed a three-dimensional time-dependent finite element model for LMD with coaxial powder feeding supply. The model encompasses the powder stream, its interaction with the laser radiation, and the melt pool...