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Expression of Arabidopsis thaliana glutamate dehydrogenase genes is very low in the light and high in the dark. The molecular signals and mechanisms that provide the light-dependent glutamate dehydrogenase genes regulation remain unknown. The aim of this work was to study a role of redox signals which occur during light shifts in the regulation of the glutamate dehydrogenase genes expression. Using photosynthetic electron transport inhibitors 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) and 2,5-dibromo-3-methyl-6-isopropyl benzoquinone (DBMIB) we demonstrate that transcript levels of the GDH1 and GDH2 genes in Arabidopsis leaves change in accordance with a redox state of plastoquinone pool: they are low when it is highly reduced and high when it is oxidized. Hydrogen peroxide or high light treatment did not result in decreasing of GDH1 or GDH2 expression, so reactive oxygen species cannot be the signals that reduce expression of these genes during dark-to-light shifts. There was no significant difference between the glucose content in the leaves of plants treated with DCMU and the plants treated with DBMIB, so glucose is not the only or the main factor that regulates expression of the studied genes. We presume that expression of Arabidopsis GDH1 and GDH2 genes depends on the plastoquinone pool redox state. Expression of Arabidopsis glutamate dehydrogenase genes during light-to-dark and dark-to-light shifts depends on chloroplast electron transport chain redox state rather than reactive oxygen species or glucose content.

In this paper, we studied the possibility of increasing the Brillouin frequency shift (BFS) detection accuracy in distributed fibre-optic sensors by the separate and joint use of different algorithms for finding the spectral maximum: Lorentzian curve fitting (LCF, including the Levenberg–Marquardt (LM) method), the backward correlation technique (BWC) and a machine learning algorithm, the generalized linear model (GLM). The study was carried out on real spectra subjected to the subsequent addition of extreme digital noise. The precision and accuracy of the LM and BWC methods were studied by varying the signal-to-noise ratios (SNRs) and by incorporating the GLM method into the processing steps. It was found that the use of methods in sequence gives a gain in the accuracy of determining the sensor temperature from tenths to several degrees Celsius (or MHz in BFS scale), which is manifested for signal-to-noise ratios within 0 to 20 dB. We have found out that the double processing (BWC + GLM) is more effective for positive SNR values (in dB): it gives a gain in BFS measurement precision near 0.4 °C (428 kHz or 9.3 με); for BWC + GLM, the difference of precisions between single and double processing for SNRs below 2.6 dB is about 1.5 °C (1.6 MHz or 35 με). In this case, double processing is more effective for all SNRs. The described technique’s potential application in structural health monitoring (SHM) of concrete objects and different areas in metrology and sensing were also discussed.

It is known that mitochondrial population of living organisms is heterogeneous. Using the density gradient of Percoll or sucrose, we obtained and characterized two distinct mitochondrial subfractions (named “light” and “heavy” according to their sedimentation) from three plant species (Brassica rapa, Zea mays, and Arabidopsis thaliana). Electron microscopy showed that mitochondria of a light subfraction have a poorly developed cristae structure. The respiratory control of these mitochondria was reduced; however the degree of their outer membrane integrity remained high. These data suggest that mitochondrial subfractions purified in the density gradient differ in their maturity. We carried out DNA import assays to study the ability of these two subfractions for DNA transport. We have shown that the mitochondria of light subfraction in all three plant species uptakes DNA more efficiently than the mitochondria of heavy subfraction. In addition, import of DNA with different sizes into the light and heavy mitochondrial subfractions has different sensitivity to specific inhibitors of the voltage-dependent anion channel and adenine nucleotide translocase, proteins playing a central role in DNA transport across the mitochondrial membrane. The obtained results suggest that DNA import depends on organization of the transport system in the double mitochondrial membrane influenced by the maturity of the mitochondria.

Mitochondria have retained indispensable but limited genetic information and they import both proteins and nucleic acids from the cytosol. RNA import is essential for gene expression and regulation, whereas competence for DNA uptake is likely to contribute to organellar genome dynamics and evolution. Contrary to protein import mechanisms, the way nucleic acids cross the mitochondrial membranes remains poorly understood. Using proteomic, genetic and biochemical approaches with both plant and yeast organelles, we develop here a model for DNA uptake into mitochondria. The first step includes the voltage-dependent anion channel and an outer membrane-located precursor fraction of a protein normally located in the inner membrane. To proceed, the DNA is then potentially recruited in the intermembrane space by an accessible subunit of one of the respiratory chain complexes. Final translocation through the inner membrane remains the most versatile but points to the components considered to make the mitochondrial permeability transition pore. Depending on the size, DNA and RNA cooperate or compete for mitochondrial uptake, which shows that they share import mechanisms. On the other hand, our results imply the existence of more than one route for nucleic acid translocation into mitochondria.

Mitochondrial gene products are essential for the viability of eukaryote obligate aerobes. Consequently, mutations of the mitochondrial genome cause severe diseases in man and generate traits widely used in plant breeding. Pathogenic mutations can often be identified but direct genetic rescue remains impossible because mitochondrial transformation is still to be achieved in higher eukaryotes. Along this line, it has been shown that isolated plant and mammalian mitochondria are naturally competent for importing linear DNA. However, it has proven difficult to understand how such large polyanions cross the mitochondrial membranes. The genetic tractability of Saccharomyces cerevisae could be a powerful tool to unravel this molecular mechanism. Here we show that isolated S. cerevisiae mitochondria can import linear DNA in a process sharing similar characteristics to plant and mammalian mitochondria. Based on biochemical data, translocation through the outer membrane is believed to be mediated by voltage-dependent anion channel (VDAC) isoforms in higher eukaryotes. Both confirming this hypothesis and validating the yeast model, we illustrate that mitochondria from S. cerevisiae strains deleted for the VDAC-1 or VDAC-2 gene are severely compromised in DNA import. The prospect is now open to screen further mutant yeast strains to identify the elusive inner membrane DNA transporter.

Plant mitochondria are remarkable with respect to their content in foreign, alien and plasmid-like DNA, raising the question of the transfer of this information into the organelles. We demonstrate the existence of an active, transmembrane potential-dependent mechanism of DNA uptake into plant mitochondria. The process is restricted to double-strand DNA, but has no obvious sequence specificity. It is most efficient with linear fragments up to a few kilobase pairs. When containing appropriate information, imported sequences are transcribed within the organelles. The uptake likely involves the voltage-dependent anion channel and the adenine nucleotide translocator, i.e. the core components of the mitochondrial permeability transition pore complex in animal cells, but it does not rely on known mitochondrial membrane permeabilization processes. We conclude that DNA import into plant mitochondria might represent a physiological phenomenon with some functional relevance.

Inside-out inner mitochondrial membranes free of matrix proteins were isolated from purified potato tuber (Solanum tuberosum L.) mitochondria and incubated with (Q- 32 P)ATP. Proteins were separated by SDS^PAGE and visualized by autoradiography. Phosphorylation of inner mem- brane proteins, including ATPase subunits, was strongly inhibited by the phosphoprotein phosphatase inhibitor NaF. We propose that an inner membrane phosphoprotein phosphatase is required for activation of the inner membrane protein kinase. When prelabelled inner membranes were incubated in the absence of (Q Q- 32 P)ATP, there was no phosphoprotein dephosphorylation unless a soluble matrix fraction was added. This dephosphoryla- tion was inhibited by NaF, but not by okadaic acid. We conclude that the mitochondrial matrix contains a phosphoprotein phosphatase that is responsible for dephosphorylation of inner membrane phosphoproteins. fl 2000 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.

Mitochondrial transcription rate and RNA steady-state levels were examined in shoots of Arabidopsis seedlings. The shoots were treated with inhibitors of complex III and IV of the cytochrome pathway (CP) and with an inhibitor of the alternative oxidase (AOX) of the mitochondrial electron transport chain. The inhibition of AOX and CP complexes III and IV affected transcription and transcript levels in different ways. CP and AOX inhibitors had opposite effects. Our data support the idea that the redox state of the electron transport chain is involved in the regulation of mitochondrial gene expression at transcriptional and post-transcriptional levels.

Subunit 9 of the mitochondrial ATPase, but also other hydrophobic mitochondrially encoded proteins, contains a high frequency of the leucine motif, -Leu-X9-Leu-, which is highly conserved through RNA editing. The leucine motif may provide specific recognition sites between membrane-spanning domains of the F0-ATPase and between other hydrophobic subunits during the assembly of multienzyme complexes in the inner mitochondrial membrane.