9,583 research outputs found
FTIR-ATR-based prediction and modelling of lignin and energy contents reveals independent intra-specific variation of these traits in bioenergy poplar
Get PDFBackground: there is an increasing demand for renewable resources to replace fossil fuels. However, different applications such as the production of secondary biofuels or combustion for energy production require different wood properties. Therefore, high-throughput methods are needed for rapid screening of wood in large scale samples, e.g., to evaluate the outcome of tree breeding or genetic engineering. In this study, we investigated the intra-specific variability of lignin and energy contents in extractive-free wood of hybrid poplar progenies (Populus trichocarpa × deltoides) and tested if the range was sufficient for the development of quantitative prediction models based on Fourier transform infrared spectroscopy (FTIR). Since lignin is a major energy-bearing compound, we expected that the energy content of wood would be positively correlated with the lignin content.Results: lignin contents of extractive-free poplar wood samples determined by the acetyl bromide method ranged from 23.4% to 32.1%, and the calorific values measured with a combustion calorimeter varied from 17260 to 19767 J g-1. For the development of calibration models partial least square regression and cross validation was applied to correlate FTIR spectra determined with an attenuated total reflectance (ATR) unit to measured values of lignin or energy contents. The best models with high coefficients of determination (R2 (calibration) = 0.91 and 0.90; R2 (cross-validation) = 0.81 and 0.79) and low root mean square errors of cross validation (RMSECV = 0.77% and 62 J g-1) for lignin and energy determination, respectively, were obtained after data pre-processing and automatic wavenumber restriction. The calibration models were validated by analyses of independent sets of wood samples yielding R2 = 0.88 and 0.86 for lignin and energy contents, respectively.Conclusions: these results show that FTIR-ATR spectroscopy is suitable as a high-throughput method for lignin and energy estimations in large data sets. Our study revealed that the intra-specific variations in lignin and energy contents were unrelated to each other and that the lignin content, therefore, was no predictor of the energy content. Employing principle component analyses we showed that factor loadings for the energy content were mainly associated with carbohydrate ring vibrations, whereas those for lignin were mainly related to aromatic compounds. Therefore, our analysis suggests that it may be possible to optimize the energy content of trees without concomitant increase in ligni
Theory of proton flow along appressed thylakoid membranes under both non-stationary and stationary conditions
No full textUnder illumination thylakoids take up protons from the suspending medium, e.g., at Photosystem II which is located in appressed portions of stacked thylakoid membranes (partitions). The rise of alkalization in the suspending medium after one single turnover of Photosystem II is rather slow (typically, half-rise time 100 ms) in stacked thylakoids and fast (2.7 ms) in unstacked ones (Polle, A. and Junge, W. (1986) Biochim. Biophys. Acta 848, 257–264). We described the transient alkalization of the suspending medium of stacked thylakoids by the theory of evaporation from a cylinder. The calculated time-course fitted the experimentally observed one with a single fit parameter, namely the ‘effective’ diffusion coefficient of hydroxyl anions in the narrow domain between appressed membranes. Its magnitude was 105-times lower than for diffusion of hydroxyl in water. This large decrease could be rationalized by the action of fixed buffers in this domain, which decreased the ‘effective’ diffusion coefficient (in Fick's second law), but left the ‘true’ diffusion coefficient (Fick's first law) unaffected. We also modeled the continuous flow of hydroxyl anions through the alkaline partitions which is required for steady ATP synthesis. For stacked thylakoids and with a diffusion coefficient as in bulk water we calculated a lateral pH drop of some 0.1 units between center and fringes of thylakoids. This provided a physical basis to understand quantitatively slightly different efficiencies of the two photosystems in ATP synthesis without necessity to invoke nebulous-localized coupling devices
The slow rise of the flash-light-induced alkalization by Photosystem II of the suspending medium of thylakoids is reversibly related to thylakoid stacking
No full textWe studied the kinetics of flash-induced proton uptake at the reducing site of Photosystem II with Cresol red as indicator for pH transients in the suspending medium. The rise of the alkalization which was observed when Photosystem II was hidden in the stacked regions of the thylakoid membranes was much slower (100 ms) than the reduction of the bound quinones (less than 1 ms). We asked for the delay mechanism. We found that the rise of the alkalization became biphasic if thylakoids were unstacked. This was reversed upon restacking. The portion of the fast phase (half-rise time, 2.7 ms) increased, if the concentration of Mg2+ was lowered. After EDTA-treatment we observed solely fast proton uptake. Experiments with dark-adapted chloroplasts showed that the biphasicity was not attributable to the alternating transitions of the bound quinone acceptors through the semiquinone and the hydroquinone stages. The dependence of fast proton uptake on the degree of membrane stacking was on line with our previous proposal (Hong and Junge (1983) Biochim. Biophys. Acta 722, 197–205) that the propagation of a pH pulse in the narrow gaps between stacked membranes was slowed down by multiple reactions of protons with fixed buffering groups. This concept was corroborated by a theory which was given in the subsequent article (Junge, W. and Polle, A. (1986) Biochim. Biophys. Acta 848, 265–273)
Developmental changes of antioxidative systems in tobacco leaves as affected by limited sucrose export in transgenic plants expressing yeast-invertase in the apoplastic space
No full textIt is generally believed that a restricted export of carbohydrates from source leaves causes oxidative stress because of an enhanced utilisation of O2 instead of NADP+ as electron acceptor in photosynthesis. To test this hypothesis, developmental changes of antioxidative systems were investigated in wild-type and transgenic tobacco (Nicotiana tabacum L.) suffering from disturbed sink-source relations by expression of yeast invertase in the apoplastic space. Young expanding leaves of the wild type contained higher activities of Superoxide dismutase (EC 1.15.1.1), ascorbate peroxidase (EC 1.11.1.11), catalase (EC 1.11.1.6), dehydroascorbate reductase (EC 1.8.5.1), glutathione reductase (EC 1.6.4.2) and a higher glutathione content than mature source leaves. The activity of monodehydroascorbate-radical reductase (EC 1.1.5.4) and the ascorbate content remained unaffected by the developmental stage in the wild type. In young expanding leaves of the transgenic plants the capacity of the antioxidative systems was similar to or higher than in corresponding leaves from the wild type. Source leaves of transgenic tobacco with an increased carbohydrate content showed a small chlorophyll loss, an increased malondialdehyde content, a selective loss of the activities of Cu/Zn-superoxide dismutase isoenzymes and a fourfold decrease in ascorbate compared with the wild type. There was no evidence that the protection from H2O2 was insufficient since source leaves of transgenic tobacco contained increased activities of catalase, ascorbate peroxidase, and monodehydroascorbate-radical reductase and an increased ascorbate-to-dehydroascorbate ratio compared with source leaves of the wild type. In severely chlorotic leaf sections of the transgenic plants, most components of the antioxidative system were lower than in green leaf sections, but the ascorbate-to-dehydroascorbate ratio was increased. These results suggest that carbohydrate-accumulating cells have an increased availability of reductant, which can increase the degree of reduction of the ascorbate system via glutathione-related systems or via the activity of monodehydroascorbate-radical reductase. At the same time, transgenic tobacco leaves seem to suffer from an increased oxidative stress, presumably as a result of a decreased consumption of O 2 .- by Cu/Zn-superoxide dismutases in the chloroplasts. There was no evidence that carbohydrate-accumulating leaves acclimated to enhanced O 2 .- production rates in the chloroplasts
Vom Wald in die Küchenplatte und zurück – Entstehung, Eigenschaften und Einsatz des biologischen Verbundpolymers Holz
No full textDissecting the Superoxide Dismutase-Ascorbate-Glutathione-Pathway in Chloroplasts by Metabolic modeling. Computer Simulations as a Step towards Flux Analysis
Get PDFThe present study introduces metabolic modeling as a new tool to analyze the network of redox reactions composing the superoxide dismutase-ascorbate (Asc)-glutathione (GSH) cycle. Based on previously determined concentrations of antioxi-dants and defense enzymes in chloroplasts, kinetic properties of antioxidative enzymes, and nonenzymatic rate constants of antioxidants with reactive oxygen, models were constructed to simulate oxidative stress and calculate changes in concen-trations and fluxes of oxidants and antioxidants. Simulated oxidative stress in chloroplasts did not result in a significant accumulation of O2.2 and H2O2 when the supply with reductant was sufficient. Model results suggest that the coupling between Asc- and GSH-related redox systems was weak because monodehydroascorbate radical reductase prevented dehydroascorbate (DHA) formation efficiently. DHA reductase activity was dispensable. Glutathione reductase was mainly required for the recycling of GSH oxidized in nonenzymatic reactions. In the absence of monodehydroascorbate radical reductase and DHA reductase, glutathione reductase and GSH were capable to maintain the Asc pool more than 99% reduced. This suggests that measured DHA/Asc ratios do not reflect a redox balance related to the Asc-GSH-cycle. Decreases in Asc peroxidase resulted in marked H2O2 accumulation without significant effects on the redox balance of Asc/DHA or GSH/GSSG. Simulated loss of SOD resulted in higher H2O2 production rates, thereby affecting all subsequent steps of the Asc-GSH-cycle. In conclusion, modeling approaches contribute to the theoretical understanding of the functioning of antioxidant systems by pointing out questions that need to be validated and provide additional informatio
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