Altering the balance between AOX1A and NDB2 expression affects a common set of transcripts in Arabidopsis.

Stress-responsive components of the mitochondrial alternative electron transport pathway have the capacity to improve tolerance of plants to abiotic stress, particularly the alternative oxidase AOX1A but also external NAD(P)H dehydrogenases such as NDB2, in Arabidopsis. NDB2 and AOX1A can cooperate to entirely circumvent the classical electron transport chain in Arabidopsis mitochondria. Overexpression of AOX1A or NDB2 alone can have slightly negative impacts on plant growth under optimal conditions, while simultaneous overexpression of NDB2 and AOX1A can reverse these phenotypic effects.

Legume Alternative Oxidase Isoforms Show Differential Sensitivity to Pyruvate Activation.

Alternative oxidase (AOX) is an important component of the plant respiratory pathway, enabling a route for electrons that bypasses the energy-conserving, ROS-producing complexes of the mitochondrial electron transport chain. Plants contain numerous isoforms of AOX, classified as either AOX1 or AOX2. AOX1 isoforms have received the most attention due to their importance in stress responses across a wide range of species.

Dark respiration rates are not determined by differences in mitochondrial capacity, abundance and ultrastructure in C leaves.

Our understanding of the regulation of respiration in C plants, where mitochondria play different roles in the different types of C photosynthetic pathway, remains limited. We examined how leaf dark respiration rates (R ), in the presence and absence of added malate, vary in monocots representing the three classical biochemical types of C photosynthesis (NADP-ME, NAD-ME and PCK) using intact leaves and extracted bundle sheath strands. In particular, we explored to what extent rates of R are associated with mitochondrial number, volume and ultrastructure.

The crucial roles of mitochondria in supporting C photosynthesis.

C photosynthesis involves a series of biochemical and anatomical traits that significantly improve plant productivity under conditions that reduce the efficiency of C photosynthesis. We explore how evolution of the three classical biochemical types of C photosynthesis (NADP-ME, NAD-ME and PCK types) has affected the functions and properties of mitochondria. Mitochondria in C NAD-ME and PCK types play a direct role in decarboxylation of metabolites for C photosynthesis.

Soybean Yellow Stripe-like 7 is a symbiosome membrane peptide transporter important for nitrogen fixation.

Legumes form a symbiosis with rhizobia that convert atmospheric nitrogen (N2) to ammonia and provide it to the plant in return for a carbon and nutrient supply. Nodules, developed as part of the symbiosis, harbor rhizobia that are enclosed in a plant-derived symbiosome membrane (SM) to form an organelle-like structure called the symbiosome. In mature nodules exchanges between the symbionts occur across the SM.

Iron Transport across Symbiotic Membranes of Nitrogen-Fixing Legumes.

Iron is an essential nutrient for the legume-rhizobia symbiosis and nitrogen-fixing bacteroids within root nodules of legumes have a very high demand for the metal. Within the infected cells of nodules, the bacteroids are surrounded by a plant membrane to form an organelle-like structure called the symbiosome. In this review, we focus on how iron is transported across the symbiosome membrane and accessed by the bacteroids.

Salt-induced expression of intracellular vesicle trafficking genes, CaRab-GTP, and their association with Na accumulation in leaves of chickpea (Cicer arietinum L.).

Background: Chickpea is an important legume and is moderately tolerant to salinity stress during the growing season. However, the level and mechanisms for salinity tolerance can vary among accessions and cultivars. A large family of CaRab-GTP genes, previously identified in chickpea, is homologous to intracellular vesicle trafficking superfamily genes that play essential roles in response to salinity stress in plants.

GmVTL1a is an iron transporter on the symbiosome membrane of soybean with an important role in nitrogen fixation.

Legumes establish symbiotic relationships with soil bacteria (rhizobia), housed in nodules on roots. The plant supplies carbon substrates and other nutrients to the bacteria in exchange for fixed nitrogen. The exchange occurs across a plant-derived symbiosome membrane (SM), which encloses rhizobia to form a symbiosome.

Identification of Alternative Mitochondrial Electron Transport Pathway Components in Chickpea Indicates a Differential Response to Salinity Stress between Cultivars.

All plants contain an alternative electron transport pathway (AP) in their mitochondria, consisting of the alternative oxidase (AOX) and type 2 NAD(P)H dehydrogenase (ND) families, that are thought to play a role in controlling oxidative stress responses at the cellular level. These alternative electron transport components have been extensively studied in plants like Arabidopsis and stress inducible isoforms identified, but we know very little about them in the important crop plant chickpea. Here we identify AP components in chickpea () and explore their response to stress at the transcript level.

Molecular and physiological responses during thermal acclimation of leaf photosynthesis and respiration in rice.

To further our understanding of how sustained changes in temperature affect the carbon economy of rice (Oryza sativa), hydroponically grown plants of the IR64 cultivar were developed at 30°C/25°C (day/night) before being shifted to 25/20°C or 40/35°C. Leaf messenger RNA and protein abundance, sugar and starch concentrations, and gas-exchange and elongation rates were measured on preexisting leaves (PE) already developed at 30/25°C or leaves newly developed (ND) subsequent to temperature transfer. Following a shift in growth temperature, there was a transient adjustment in metabolic gene transcript abundance of PE leaves before homoeostasis was reached within 24 hr, aligning with R (leaf dark respiratory CO release) and A (net CO assimilation) changes.

AtNDB2 Is the Main External NADH Dehydrogenase in Mitochondria and Is Important for Tolerance to Environmental Stress.

In addition to the classical electron transport pathway coupled to ATP synthesis, plant mitochondria have an alternative pathway that involves type II NAD(P)H dehydrogenases (NDs) and alternative oxidase (AOX). This alternative pathway participates in thermogenesis in select organs of some species and is thought to help prevent cellular damage during exposure to environmental stress. Here, we investigated the function and role of one alternative path component, AtNDB2, using a transgenic approach in Arabidopsis ().

Energy costs of salt tolerance in crop plants.

Agriculture is expanding into regions that are affected by salinity. This review considers the energetic costs of salinity tolerance in crop plants and provides a framework for a quantitative assessment of costs. Different sources of energy, and modifications of root system architecture that would maximize water vs ion uptake are addressed.

Alternative Oxidase Is Positive for Plant Performance.

The alternative pathway of mitochondrial electron transport, which terminates in the alternative oxidase (AOX), uncouples oxidation of substrate from mitochondrial ATP production, yet plant performance is improved under adverse growth conditions. AOX is regulated at different levels. Identification of regulatory transcription factors shows that Arabidopsis thaliana AOX1a is under strong transcriptional suppression.

Alternative Respiratory Pathway Component Genes (AOX and ND) in Rice and Barley and Their Response to Stress.

Plants have a non-energy conserving bypass of the classical mitochondrial cytochrome c pathway, known as the alternative respiratory pathway (AP). This involves type II NAD(P)H dehydrogenases (NDs) on both sides of the mitochondrial inner membrane, ubiquinone, and the alternative oxidase (AOX). The AP components have been widely characterised from Arabidopsis, but little is known for monocot species.

Genomic structure and expression of alternative oxidase genes in legumes.

Mitochondria isolated from chickpea (Cicer arietinum) possess substantial alternative oxidase (AOX) activity, even in non-stressed plants, and one or two AOX protein bands were detected immunologically, depending on the organ. Four different AOX isoforms were identified in the chickpea genome: CaAOX1 and CaAOX2A, B and D. CaAOX2A was the most highly expressed form and was strongly expressed in photosynthetic tissues, whereas CaAOX2D was found in all organs examined.

Isolation and Respiratory Measurements of Mitochondria from Arabidopsis thaliana.

Mitochondria are essential organelles involved in numerous metabolic pathways in plants, most notably the production of adenosine triphosphate (ATP) from the oxidation of reduced compounds such as nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FADH2). The complete annotation of the Arabidopsis thaliana genome has established it as the most widely used plant model system, and thus the need to purify mitochondria from a variety of organs (leaf, root, or flower) is necessary to fully utilize the tools that are now available for Arabidopsis to study mitochondrial biology. Mitochondria are isolated by homogenization of the tissue using a variety of approaches, followed by a series of differential centrifugation steps producing a crude mitochondrial pellet that is further purified using continuous colloidal density gradient centrifugation.

Alternative Oxidase Isoforms Are Differentially Activated by Tricarboxylic Acid Cycle Intermediates.

The cyanide-insensitive alternative oxidase (AOX) is a non-proton-pumping ubiquinol oxidase that catalyzes the reduction of oxygen to water and is posttranslationally regulated by redox mechanisms and 2-oxo acids. Arabidopsis () possesses five AOX isoforms (AOX1A-AOX1D and AOX2). AOX1D expression is increased in knockout mutants from Arabidopsis (especially after restriction of the cytochrome pathway) but cannot compensate for the lack of AOX1A, suggesting a difference in the regulation of these isoforms.

Characterisation of Arabidopsis calnexin 1 and calnexin 2 in the endoplasmic reticulum and at plasmodesmata.

Calnexin (CNX) is a highly conserved endoplasmic reticulum (ER) chaperone protein. Both calnexin and the homologous ER-lumenal protein, calreticulin, bind calcium ions and participate in protein folding. There are two calnexins in Arabidopsis thaliana, CNX1 and CNX2.

Proteomic analysis of the soybean symbiosome identifies new symbiotic proteins.

Legumes form a symbiosis with rhizobia in which the plant provides an energy source to the rhizobia bacteria that it uses to fix atmospheric nitrogen. This nitrogen is provided to the legume plant, allowing it to grow without the addition of nitrogen fertilizer. As part of the symbiosis, the bacteria in the infected cells of a new root organ, the nodule, are surrounded by a plant-derived membrane, the symbiosome membrane, which becomes the interface between the symbionts.

Transport processes of the legume symbiosome membrane.

The symbiosome membrane (SM) is a physical barrier between the host plant and nitrogen-fixing bacteria in the legume:rhizobia symbiosis, and represents a regulated interface for the movement of solutes between the symbionts that is under plant control. The primary nutrient exchange across the SM is the transport of a carbon energy source from plant to bacteroid in exchange for fixed nitrogen. At a biochemical level two channels have been implicated in movement of fixed nitrogen across the SM and a uniporter that transports monovalent dicarboxylate ions has been characterized that would transport fixed carbon.

Online oxygen kinetic isotope effects using membrane inlet mass spectrometry can differentiate between oxidases for mechanistic studies and calculation of their contributions to oxygen consumption in whole tissues.

The reduction chemistry of molecular oxygen underpins the energy metabolism of multicellular organisms, liberating free energy needed to catalyze a plethora of enzymatic reactions. Measuring the isotope signatures of (16)O and (18)O during O2 reduction can provide insights into both kinetic and equilibrium isotope effects. However, current methods to measure O2 isotope signatures are time-consuming and disruptive.

Soybean SAT1 (Symbiotic Ammonium Transporter 1) encodes a bHLH transcription factor involved in nodule growth and NH4+ transport.

Glycine max symbiotic ammonium transporter 1 was first documented as a putative ammonium (NH4(+)) channel localized to the symbiosome membrane of soybean root nodules. We show that Glycine max symbiotic ammonium transporter 1 is actually a membrane-localized basic helix-loop-helix (bHLH) DNA-binding transcription factor now renamed Glycine max bHLH membrane 1 (GmbHLHm1). In yeast, GmbHLHm1 enters the nucleus and transcriptionally activates a unique plasma membrane NH4(+) channel Saccharomyces cerevisiae ammonium facilitator 1.

Iron: an essential micronutrient for the legume-rhizobium symbiosis.

Legumes, which develop a symbiosis with nitrogen-fixing bacteria, have an increased demand for iron. Iron is required for the synthesis of iron-containing proteins in the host, including the highly abundant leghemoglobin, and in bacteroids for nitrogenase and cytochromes of the electron transport chain. Deficiencies in iron can affect initiation and development of the nodule.