Respiratory electron transfer pathways in plant mitochondria

The respiratory electron transport chain (ETC) couples electron transfer from organic substrates onto molecular oxygen with proton translocation across the inner mitochondrial membrane. The resulting proton gradient is used by the ATP synthase complex for ATP formation. In plants, the ETC is especially intricate. Besides the "classical" oxidoreductase complexes (complex I-IV) and the mobile electron transporters cytochrome c and ubiguinone, it comprises numerous "alternative oxidoreductases." Furthermore, several dehydrogenases localized in the mitochondrial matrix and the mitochondrial intermembrane space directly or indirectly provide electrons for the ETC. Entry of electrons into the system occurs via numerous pathways which are dynamically regulated in response to the metabolic state of a plant cell as well as environmental factors. This mini review aims to summarize recent findings on respiratory electron transfer pathways in plants and on the involved components and supramolecular assemblies.DFG/BR/1829/10-

3-hydroxyisobutyrate dehydrogenase is involved in both, valine and isoleucine degradation in arabidopsis thaliana

In plants, amino acid catabolism is especially relevant in metabolic stress situations (e.g. limited carbohydrate availability during extended darkness). Under these conditions, amino acids are used as alternative substrates for respiration. Complete oxidation of the branched-chain amino acids (BCAAs) leucine, isoleucine (Ile), and valine (Val) in the mitochondria efficiently allows the formation of ATP by oxidative phosphorylation. However, the metabolic pathways for BCAA breakdown are largely unknown so far in plants. A systematic search for Arabidopsis (Arabidopsis thaliana) genes encoding proteins resembling enzymes involved in BCAA catabolism in animals, fungi, and bacteria as well as proteomic analyses of mitochondrial fractions from Arabidopsis allowed the identification of a putative 3-hydroxyisobutyrate dehydrogenase, AtHDH1 (At4g20930), involved in Val degradation. Systematic substrate screening analyses revealed that the protein uses 3-hydroxyisobutyrate but additionally 3-hydroxypropionate as substrates. This points to a role of the enzyme not only in Val but possibly also in Ile metabolism. At4g20930 knockdown plants were characterized to test this conclusion. Root toxicity assays revealed increased root growth inhibition of the mutants if cultivated in the presence of Val or Ile but not in the presence of leucine. We conclude that AtHDH1 has a dual role in BCAA metabolism in plants

Mineral inclusions in rutile: A novel recorder of HP-UHP metamorphism

The ability to accurately constrain the secular record of high- and ultra-high pressure metamorphism on Earth is potentially hampered as these rocks are metastable and prone to retrogression, particularly during exhumation. Rutile is among the most widespread and best preserved minerals in high- and ultra-high pressure rocks and a hitherto untested approach is to use mineral inclusions within rutile to record such conditions. In this study, rutiles from three different high- and ultrahigh-pressure massifs have been investigated for inclusions. Rutile is shown to contain inclusions of high-pressure minerals such as omphacite, garnet and high silica phengite, as well as diagnostic ultrahigh-pressure minerals, including the first reported occurrence of exceptionally preserved monomineralic coesite in rutile from the Dora–Maira massif. Chemical comparison of inclusion and matrix phases show that inclusions generally represent peak metamorphic assemblages; although rare prograde phases such as titanite, omphacite and corundum have also been identified implying that rutile grows continuously during prograde burial and traps mineralogic evidence of this evolution. Pressure estimates obtained from mineral inclusions, when used in conjunction with Zr-in-rutile thermometry, can provide additional constraints on the metamorphic conditions of the host rock. This study demonstrates that rutile is an excellent repository for high- and ultra-high pressure minerals and that the study of mineral inclusions in rutile may profoundly change the way we investigate and recover evidence of such events in both detrital populations and partially retrogressed samples

L-galactono-1,4-lactone dehydrogenase (GLDH) forms part of three subcomplexes of mitochondrial complex I in Arabidopsis thaliana

L-Galactono-1,4-lactone dehydrogenase (GLDH) catalyzes the terminal step of the Smirnoff-Wheeler pathway for vitamin C (L-ascorbate) biosynthesis in plants. A GLDH in gel activity assay was developed to biochemically investigate GLDH localization in plant mitochondria. It previously has been shown that GLDH forms part of an 850-kDa complex that represents a minor form of the respiratory NADH dehydrogenase complex (complex I). Because accumulation of complex I is disturbed in the absence of GLDH, a role of this enzyme in complex I assembly has been proposed. Here we report that GLDH is associated with two further protein complexes. Using native gel electrophoresis procedures in combination with the in gel GLDH activity assay and immunoblotting, two mitochondrial complexes of 470 and 420 kDa were identified. Both complexes are of very low abundance. Protein identifications by mass spectrometry revealed that they include subunits of complex I. Finally, the 850-kDa complex was further investigated and shown to include the complete "peripheral arm" of complex I. GLDH is attached to a membrane domain, which represents a major fragment of the "membrane arm" of complex I. Taken together, our data further support a role of GLDH during complex I formation, which is based on its binding to specific assembly intermediates.Instituto de Fisiología Vegeta

Multiple Growth Mechanisms of Jadeite in Cuban Metabasite

Samples of rocks reported in the literature to be jadeite jade from the subduction-zone complex of the Escambray Massif in\ud central Cuba have been studied by optical and transmission electron microscopy, electron microprobe and hot-cathode cathodoluminescence\ud (CL) microscopy. Although these rocks are indeed rich in jadeite, the bulk rock composition generally conforms to\ud MORB, with Na2O enriched by . 3 wt% and CaO depleted by .2 wt%. Al2O3 contents are unchanged. These changes are attributed\ud to early pre-subduction spilitization of the ocean-floor protolith. Relics of magmatic augite preserving an ophitic texture are common.\ud Disequilibrium textures are the rule. Extensively recrystallized rocks show fine, felty intergrowths of predominantly Al-rich\ud glaucophane and jadeite, the latter with rims and patches of omphacite. TEM observations indicate extensive replacement of\ud pyroxene by amphibole. Glaucophane developed rims of magnesiokatophorite and edenite. Chlorite and epidote are also present.\ud Late development of actinolite, chlorite, epidote and albite is observed. Quartz is present. Less recrystallized samples with numerous\ud large (.1.5 mm) grains of augite show several types of sodic and sodic-calcic clinopyroxene development: (1) Topotactic\ud replacement of magmatic pyroxene by jadeite and omphacite along a broad front encroaching upon the augite grain from the rock\ud matrix. Jadeite dominates where presumably plagioclase was formerly present. Omphacite dominates where augite is internally\ud replaced along cleavage and fractures. Late chlorite, taramite and ferropargasite replace these pseudomorphs. (2) Former plagioclase\ud laths of the ophitic fabric are replaced by jadeite together with lesser omphacite in epitactic relationship with the enclosing augite.\ud Former plagioclase-augite grain boundaries remain preserved. Late pumpellyite is associated with the omphacite. (3) Jadeite þ\ud omphacite þ pumpellyite þ chlorite with irregular grain boundaries dominate in the rock matrix between the augite relics, with\ud idiomorphic crystals of epidote scattered throughout and in chlorite–epidote clusters. Pumpellyite is interpreted to be a late retrograde\ud product. Quartz is present. (4) Jadeite þ omphacite þ chlorite assemblages, in which monomineralic sheaf-like jadeite aggregates are\ud common, fill very thin (500–1500 mm) fractures criss-crossing the sample, including ophitic augite remnants. Cathodoluminescence\ud microscopy shows that jadeite in the veins is distinctly different from CL in the other types of jadeite, showing features like oscillatory\ud growth zoning indicative of crystallization from a fluid. Generally omphacite develops irregularly along jadeite rims, but recrystallization\ud may lead to pairs with straight grain boundaries suggestive of phase equilibration. Comparison with published solvus\ud relationships suggests temperatures of 425–500 C. This unusual occurrence of different types of jadeite in a metabasic rock suggests\ud two contrasting sources. The first – in the rock matrix, as topotactic alteration of igneous pyroxene and as plagioclase replacement\ud epitactically growing on augite – can be explained as due to local domain equilibration in a rapidly subducted ‘‘spilitized’’ gabbroic\ud rock. The second, in very thin fracture fillings, conforms to an origin as a crystallization product from a pervasive fluid. Conceivably,\ud ‘‘pooling’’ of the fluids flowing through the fractures in larger cavities could lead to larger masses of jadeitite. These have not yet been\ud conclusively documented in the Escambray Massif

L-galactono-1,4-lactone dehydrogenase (GLDH) forms part of three subcomplexes of mitochondrial complex I in Arabidopsis thaliana

L-Galactono-1,4-lactone dehydrogenase (GLDH) catalyzes the terminal step of the Smirnoff-Wheeler pathway for vitamin C (L-ascorbate) biosynthesis in plants. A GLDH in gel activity assay was developed to biochemically investigate GLDH localization in plant mitochondria. It previously has been shown that GLDH forms part of an 850-kDa complex that represents a minor form of the respiratory NADH dehydrogenase complex (complex I). Because accumulation of complex I is disturbed in the absence of GLDH, a role of this enzyme in complex I assembly has been proposed. Here we report that GLDH is associated with two further protein complexes. Using native gel electrophoresis procedures in combination with the in gel GLDH activity assay and immunoblotting, two mitochondrial complexes of 470 and 420 kDa were identified. Both complexes are of very low abundance. Protein identifications by mass spectrometry revealed that they include subunits of complex I. Finally, the 850-kDa complex was further investigated and shown to include the complete "peripheral arm" of complex I. GLDH is attached to a membrane domain, which represents a major fragment of the "membrane arm" of complex I. Taken together, our data further support a role of GLDH during complex I formation, which is based on its binding to specific assembly intermediates

Cardiolipin supports respiratory enzymes in plants in different ways

In eukaryotes the presence of the dimeric phospholipid cardiolipin (CL) is limited to the mitochondrial membranes. It resides predominantly in the inner membrane where it interacts with components of the mitochondrial electron transfer chain. CL deficiency has previously been shown to affect abundances of the plant NADHdehydrogenase complex and its association with dimeric cyctochrome c reductase. Using an Arabidopsis thaliana knock-out mutant for the final enzyme of CL biosynthesis we here extend current knowledge on the dependence of plant respiration on CL. By correlating respiratory enzyme abundances with enzymatic capacities in mitochondria isolated from wild type, CL deficient and CL complemented heterotrophic cell culture lines a new picture of the participation of CL in plant respiration is emerging. Data indicate a loss of a general reduction of respiratory capacity in CL deficient mitochondria which cannot solely be attributed to decreased abundances or capacities of mitochondrial electron transfer protein complexes and supercomplexes. Instead, it most likely is the result of a loss of the mobile electron carrier cytochrome c. Furthermore, enzymes of the tricarboxylic acid cycle are found to have lower maximum activities in the mutant, including the succinate dehydrogenase complex. Interestingly, abundance of the latter is not altered, indicative of a direct impact of CL deficiency on the enzymatic capacity of this electron transfer chain protein complex

L-galactono-1,4-lactone dehydrogenase (GLDH) forms part of three subcomplexes of mitochondrial complex I in Arabidopsis thaliana

L-Galactono-1,4-lactone dehydrogenase (GLDH) catalyzes the terminal step of the Smirnoff-Wheeler pathway for vitamin C (L-ascorbate) biosynthesis in plants. A GLDH in gel activity assay was developed to biochemically investigate GLDH localization in plant mitochondria. It previously has been shown that GLDH forms part of an 850-kDa complex that represents a minor form of the respiratory NADH dehydrogenase complex (complex I). Because accumulation of complex I is disturbed in the absence of GLDH, a role of this enzyme in complex I assembly has been proposed. Here we report that GLDH is associated with two further protein complexes. Using native gel electrophoresis procedures in combination with the in gel GLDH activity assay and immunoblotting, two mitochondrial complexes of 470 and 420 kDa were identified. Both complexes are of very low abundance. Protein identifications by mass spectrometry revealed that they include subunits of complex I. Finally, the 850-kDa complex was further investigated and shown to include the complete "peripheral arm" of complex I. GLDH is attached to a membrane domain, which represents a major fragment of the "membrane arm" of complex I. Taken together, our data further support a role of GLDH during complex I formation, which is based on its binding to specific assembly intermediates.Instituto de Fisiología Vegeta

Multi-stage subduction-related metasomatism recorded in whiteschists from the Dora-Maira Massif, Western Alps

Whiteschists from the Dora-Maira massif (Western Alps, Italy) are Mg and K-rich metasomatised granites which experienced ultra-high pressure metamorphism and fluid-rock interaction during Alpine continental subduction. The sources and timing of fluid infiltration are a source of significant debate. In this study we present boron (B) isotopes and other fluid-mobile trace element (FME) concentrations in various generations of phengite from whiteschists and their country rock protoliths to investigate the sources and timing of metasomatic fluid influx. Reconstructed bulk rock concentrations based on modal data and mineral compositions indicate that significant amounts B and other FME were added to the rock during prograde metamorphism, but that this fluid influx postdates the main Mg metasomatic event. High B concentrations (150–350 µg/g) and light δ11B values (-16 to -4 ‰) recorded in phengite point to a B-rich sediment-derived fluid as the main source of B in the whiteschists. Further redistribution of FME during metamorphism was associated with breakdown of hydrous minerals such as talc, phlogopite and ellenbergerite. The source of the Mg-rich fluids cannot be constrained based on the B data in phengite, since its signature was overprinted by the later main B metasomatic event. Rare tourmaline-bearing whiteschists record additional information about B processes. Tourmaline δ11B values (-6 to +1 ‰) are in isotopic equilibrium with similar fluids to those recorded in most phengite, but phengites in tourmaline-bearing samples records anomalous B isotope compositions that reflect later redistribution of B. This study demonstrates the utility of in situ analyses in unravelling complex fluid-rock interaction histories, where whole rock analyses make it difficult to distinguish between different stages of fluid-rock interaction. Polymetasomatism may result in decoupling of different isotopic systems, thus complicating their interpretation. The Dora-Maira whiteschists interacted with multiple generations of fluids during subduction and therefore may represent a long-lived fluid pathway