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Crassulacean acid metabolism (CAM) is a metabolic adaptation that has evolved convergently in 38 plant families to aid survival in water-limited niches. Whilst primarily considered a photosynthetic adaptation, CAM also has substantial consequences for nocturnal respiratory metabolism. Here, we outline the history, current state and future of nocturnal respiration research in CAM plants, with a particular focus on the energetics of nocturnal respiratory oxygen consumption. Throughout the 20th century, research interest in nocturnal respiration occurred alongside initial discoveries of CAM, although the energetic and mechanistic implications of nocturnal oxygen consumption and links to the operation of the CAM cycle were not fully understood. Recent flux balance analysis (FBA) models have provided new insights into the role that mitochondria play in the CAM cycle. Several FBA models have predicted that CAM requires elevated nocturnal respiratory rates, compared to C3 species, to power vacuolar malic acid accumulation. We provide physiological data, from the genus Clusia , to corroborate these modelling predictions, thereby reinforcing the importance of elevated nocturnal respiratory rates for CAM. Finally, we outline five unanswered questions pertaining to nocturnal respiration which must be addressed if we are to fully understand and utilize CAM plants in a hotter, drier world. [ABSTRACT FROM AUTHOR]

Background and Aims The ATP yield of plant respiration (ATP/hexose unit respired) quantitatively links active heterotrophic processes with substrate consumption. Despite its importance, plant respiratory ATP yield is uncertain. The aim here was to integrate current knowledge of cellular mechanisms with inferences required to fill knowledge gaps to generate a contemporary estimate of respiratory ATP yield and identify important unknowns. Method A numerical balance sheet model combining respiratory carbon metabolism and electron transport pathways with uses of the resulting transmembrane electrochemical proton gradient was created and parameterized for healthy, non-photosynthesizing plant cells catabolizing sucrose or starch to produce cytosolic ATP. Key Results Mechanistically, the number of c subunits in the mitochondrial ATP synthase Fo sector c -ring, which is unquantified in plants, affects ATP yield. A value of 10 was (justifiably) used in the model, in which case respiration of sucrose potentially yields about 27.5 ATP/hexose (0.5 ATP/hexose more from starch). Actual ATP yield often will be smaller than its potential due to bypasses of energy-conserving reactions in the respiratory chain, even in unstressed plants. Notably, all else being optimal, if 25 % of respiratory O2 uptake is via the alternative oxidase – a typically observed fraction – ATP yield falls 15 % below its potential. Conclusions Plant respiratory ATP yield is smaller than often assumed (certainly less than older textbook values of 36–38 ATP/hexose) leading to underestimation of active-process substrate requirements. This hinders understanding of ecological/evolutionary trade-offs between competing active processes and assessments of crop growth gains possible through bioengineering of processes that consume ATP. Determining the plant mitochondrial ATP synthase c -ring size, the degree of any minimally required (useful) bypasses of energy-conserving reactions in the respiratory chain, and the magnitude of any 'leaks' in the inner mitochondrial membrane are key research needs. [ABSTRACT FROM AUTHOR]

Summary: The rate with which crop yields per hectare increase each year is plateauing at the same time that human population growth and other factors increase food demand. Increasing yield potential (Yp) of crops is vital to address these challenges. In this review, we explore a component of Yp that has yet to be optimised – that being improvements in the efficiency with which light energy is converted into biomass (εc) via modifications to CO2 fixed per unit quantum of light (α), efficiency of respiratory ATP production (εprod) and efficiency of ATP use (εuse). For α, targets include changes in photoprotective machinery, ribulose bisphosphate carboxylase/oxygenase kinetics and photorespiratory pathways. There is also potential for εprod to be increased via targeted changes to the expression of the alternative oxidase and mitochondrial uncoupling pathways. Similarly, there are possibilities to improve εuse via changes to the ATP costs of phloem loading, nutrient uptake, futile cycles and/or protein/membrane turnover. Recently developed high‐throughput measurements of respiration can serve as a proxy for the cumulative energy cost of these processes. There are thus exciting opportunities to use our growing knowledge of factors influencing the efficiency of photosynthesis and respiration to create a step‐change in yield potential of globally important crops. [ABSTRACT FROM AUTHOR]

Partitioning of respiration between the cytochrome pathway (CP) and the alternative pathway (AP) may play an important role in plant adaptation to extreme environments. We examined changes in partitioning between CP and AP, and viability of roots associated with plant exposure to high soil temperature for two Agrostis species: Agrostis scabra Willd., a species adapted to high-temperature soils in geothermal areas in Yellowstone National Park, and Agrostis stolonifera L. (cv. Penncross) a heat-sensitive grass widely used in cool-climate regions. Roots of A. scabra and A. stolonifera were exposed to soil temperature of 37 or 20°C, while shoots were exposed to 20°C for 28 days. Root viability decreased, and total root respiration increased for both species at 37°C. The decline in root viability and the increase in respiration rates were less pronounced for A. scabra than for A. stolonifera. A larger proportion of total root respiration was attributed to the AP in A. scabra compared with that in A. stolonifera when both species were exposed to 37°C. At 7 and 14 days at 37°C, the relative proportion of respiration passing through AP increased by 12 and 10%, respectively, in A. scabra, whereas in A. stolonifera, AP increased by 4 and 1%, respectively. Our results suggest that maintaining a higher proportion of AP at a high soil temperature may contribute to root thermo-tolerance in A. scabra in comparison with A. stolonifera, and alternative respiration may play an important role in plant adaptation to high soil temperature. [ABSTRACT FROM AUTHOR]

Background and Aims The carnivorous pitcher plants of the genus Nepenthes have evolved modified leaves that act as pitcher traps. The traps are specialized for prey attraction, capture, digestion and nutrient uptake but not for photosynthetic assimilation. Methods In this study, we used antibodies against different photosynthetic (D1, Lhcb2, Lhcb4, RbcL) and respiratory-related (AOX, COXII) proteins for semi-quantification of these proteins in the assimilation part of the leaves and the pitcher traps of different Nepenthes species and hybrids. Different functional zones of the trap and the traps from different ontogenetic stages were investigated. The pitcher traps of the distantly related species Sarracenia purpurea ssp. venosa were used as an outgroup. In addition, chlorophyll fluorescence and infrared gas analysis were used for measurements of the net rate of photosynthesis (A N) and respiration in the dark (R D). Key Results The pitcher traps contained the same or lower abundance of photosynthesis-related proteins in accordance with their low A N in comparison to the assimilation part of the leaves. Surprisingly, all traps contained a high amount of alternative oxidase (AOX) and low amount of cytochrome c oxidase subunit II (COX II) than in the assimilation part of the leaves. Thermal imaging did not confirm the role of AOX in pitcher thermogenesis. Conclusions The pitcher traps contain a high amount of AOX enzyme. The possible role of AOX in specialized pitcher tissue is discussed based on knowledge of the role and function of AOX in non-carnivorous plants. The roles of AOX in prey attraction, balance between light and dark reactions of photosynthesis, homeostasis of reactive oxygen species, digestive physiology and nutrient assimilation are discussed. [ABSTRACT FROM AUTHOR]

Summary: C4 photosynthesis involves a series of biochemical and anatomical traits that significantly improve plant productivity under conditions that reduce the efficiency of C3 photosynthesis. We explore how evolution of the three classical biochemical types of C4 photosynthesis (NADP‐ME, NAD‐ME and PCK types) has affected the functions and properties of mitochondria. Mitochondria in C4 NAD‐ME and PCK types play a direct role in decarboxylation of metabolites for C4 photosynthesis. Mitochondria in C4 PCK type also provide ATP for C4 metabolism, although this role for ATP provision is not seen in NAD‐ME type. Such involvement has increased mitochondrial abundance/size and associated enzymatic capacity, led to changes in mitochondrial location and ultrastructure, and altered the role of mitochondria in cellular carbon metabolism in the NAD‐ME and PCK types. By contrast, these changes in mitochondrial properties are absent in the C4 NADP‐ME type and C3 leaves, where mitochondria play no direct role in photosynthesis. From an eco‐physiological perspective, rates of leaf respiration in darkness vary considerably among C4 species but does not differ systematically among the three C4 types. This review outlines further mitochondrial research in key areas central to the engineering of the C4 pathway into C3 plants and to the understanding of variation in rates of C4 dark respiration. [ABSTRACT FROM AUTHOR]

Background and Aims Mangrove plants are mostly found in tropical and sub-tropical tidal flats, and their limited distribution may be related to their responses to growth temperatures. However, the mechanisms underlying these responses have not been clarified. Here, we measured the dependencies of the growth parameters and respiration rates of leaves and roots on growth temperatures in typical mangrove species. Methods We grew two typical species of Indo-Pacific mangroves, Bruguiera gymnorrhiza and Rhizophora stylosa , at four different temperatures (15, 20, 25 and 30 °C) by irrigating with fresh water containing nutrients, and we measured growth parameters, chemical composition, and leaf and root O2 respiration rates. We then estimated the construction costs of leaves and roots and the respiration rates required for maintenance and growth. Key Results The relative growth rates of both species increased with growth temperature due to changes in physiological parameters such as net assimilation rate and respiration rate rather than to changes in structural parameters such as leaf area ratio. Both species required a threshold temperature for growth (12.2 °C in B. gymnorrhiza and 18.1 °C in R. stylosa). At the low growth temperature, root nitrogen uptake rate was lower in R. stylosa than in B. gymnorrhiza , leading to a slower growth rate in R. stylosa. This indicates that R. stylosa is more sensitive than B. gymnorrhiza to low temperature. Conclusions Our results suggest that the mangrove species require a certain warm temperature to ensure respiration rates sufficient for maintenance and growth, particularly in roots. The underground temperature probably limits their growth under the low-temperature condition. The lower sensitivity of B. gymnorrhiza to low temperature shows its potential to adapt to a wider habitat temperature range than R. stylosa. These growth and respiratory features may explain the distribution patterns of the two mangrove species. [ABSTRACT FROM AUTHOR]

Cadmium (Cd) inhibits soybean root growth, but its exact mode of action is still not completely understood. We evaluated the effects of Cd on growth, mitochondrial respiration, lipid peroxidation, total phenols, glutathione, and activities of lipoxygenase (LOX), superoxide dismutase (SOD), and catalase (CAT) in soybean roots. In primary roots, Cd stimulated KCN-insensitive respiration and KCN-SHAM-insensitive respiration, indicating the involvement of the alternative oxidase (AOX) pathway, while it decreased KCN-sensitive respiration, suggesting an inhibition of the cytochrome oxidase pathway (COX). In isolated mitochondria, Cd uncoupled the oxidative phosphorylation since it decreased state III respiration (coupled respiration) and ADP/O and respiratory control ratios, while it increased state IV respiration (depletion of exogenously added ADP). The uncoupling effect increased extramitochondrial LOX activity, lipid peroxidation, and oxidized and reduced glutathione, which induced an antioxidant response with enhanced SOD and CAT activities. In brief, our findings reveal that Cd acts as an uncoupler of the mitochondrial oxidative phosphorylation in soybean roots, disturbing cellular respiration and inducing oxidative cellular stress. [ABSTRACT FROM AUTHOR]

Thioredoxins (TRXs) are ubiquitous proteins engaged in the redox regulation of plant metabolism. Whilst the light-dependent TRX-mediated activation of Calvin–Benson cycle enzymes is well documented, the role of extraplastidial TRXs in the control of the mitochondrial (photo)respiratory metabolism has been revealed relatively recently. Mitochondrially located TRX o1 has been identified as a regulator of alternative oxidase, enzymes of, or associated with, the tricarboxylic acid (TCA) cycle, and the mitochondrial dihydrolipoamide dehydrogenase (mtLPD) involved in photorespiration, the TCA cycle, and the degradation of branched chain amino acids. TRXs are seemingly a major point of metabolic regulation responsible for activating photosynthesis and adjusting mitochondrial photorespiratory metabolism according to the prevailing cellular redox status. Furthermore, TRX-mediated (de)activation of TCA cycle enzymes contributes to explain the non-cyclic flux mode of operation of this cycle in illuminated leaves. Here we provide an overview on the decisive role of TRXs in the coordination of mitochondrial metabolism in the light and provide in silico evidence for other redox-regulated photorespiratory enzymes. We further discuss the consequences of mtLPD regulation beyond photorespiration and provide outstanding questions that should be addressed in future studies to improve our understanding of the role of TRXs in the regulation of central metabolism. [ABSTRACT FROM AUTHOR]

Plant mitochondria harbour complex metabolic routes that are interconnected with those of other cell compartments, and changes in mitochondrial function remotely influence processes in different parts of the cell. This implies the existence of signals that convey information about mitochondrial function to the rest of the cell. Increasing evidence indicates that metabolic and redox signals are important for this process, but changes in ion fluxes, protein relocalization, and physical contacts with other organelles are probably also involved. Besides possible direct effects of these signalling molecules on cellular functions, changes in mitochondrial physiology also affect the activity of different signalling pathways that modulate plant growth and stress responses. As a consequence, mitochondria influence the responses to internal and external factors that modify the activity of these pathways and associated biological processes. Acting through the activity of hormonal signalling pathways, mitochondria may also exert remote control over distant organs or plant tissues. In addition, an intimate cross-talk of mitochondria with energy signalling pathways, such as those represented by TARGET OF RAPAMYCIN and SUCROSE NON-FERMENTING1-RELATED PROTEIN KINASE 1, can be envisaged. This review discusses available evidence on the role of mitochondria in shaping plant growth and stress responses through various signalling pathways. [ABSTRACT FROM AUTHOR]

Respiration is a crucial process that provides all living organisms with energy and metabolites for growth and cellular maintenance. The processes that control respiration in lichens remain poorly understood. We investigated the effects of short-term temperature changes on the respiration rate, as well as the relative contributions of the cytochrome and alternative pathways of thalli from four green-algal lichen species collected from their natural habitats in Antarctica. Lichen respiration was sensitive to short-term temperature increases over a range of 5–35 °C. The total O2 uptake rate was increased by fourfold, and the mean respiratory coefficient (Q10) decreased from 2.5 to 1.3 as the temperature increased. An increase in temperature from 5 to 15 °C had a positive effect on cytochrome respiration coupled with energy production. Temperatures above 15 °C stimulated the activation of the alternative (energy-dissipating) respiratory pathway. Hyperthermia led to increased O2 consumption that was not associated with mitochondrial oxidases. The effects of increased temperature on the respiration rates were more pronounced in the bipolar lichens Umbilicaria decussata and Usnea sphacelata than in the Usnea aurantiaco-atra species with a narrower geographical distribution. [ABSTRACT FROM AUTHOR]

Wetland plants can tolerate long-term strict hypoxia and anoxic conditions and the subsequent re-oxidative stress compared to terrestrial plants. During O2 deficiency, both wetland and terrestrial plants use NAD(P)+ and ATP that are produced during ethanol fermentation, sucrose degradation, and major amino acid metabolisms. The oxidation of NADH by non-phosphorylating pathways in the mitochondrial respiratory chain is common in both terrestrial and wetland plants. As the wetland plants enhance and combine these traits especially in their roots, they can survive under long-term hypoxic and anoxic stresses. Wetland plants show two contrasting strategies, low O2 escape and low O2 quiescence strategies (LOES and LOQS, respectively). Differences between two strategies are ascribed to the different signaling networks related to phytohormones. During O2 deficiency, LOES-type plants show several unique traits such as shoot elongation, aerenchyma formation and leaf acclimation, whereas the LOQS-type plants cease their growth and save carbohydrate reserves. Many wetland plants utilize NH4+ as the nitrogen (N) source without NH4+-dependent respiratory increase, leading to efficient respiratory O2 consumption in roots. In contrast, some wetland plants with high O2 supply system efficiently use NO3− from the soil where nitrification occurs. The differences in the N utilization strategies relate to the different systems of anaerobic ATP production, the NO2−-driven ATP production and fermentation. The different N utilization strategies are functionally related to the hypoxia or anoxia tolerance in the wetland plants. [ABSTRACT FROM AUTHOR]

Mitogen-activated protein kinase kinase 9 (MKK9) is an upstream activator of mitogen-activated protein kinase 3 (MAPK3) and MAPK6 in planta. To investigate MKK9 roles in mitochondrial respiration in Arabidopsis, MKK9DD, the active allele with mutations of Thr-201 and Ser-205 to Asp, and MKK9KR, the allele lacking MKK9 activity with a mutation of Lys-76 to Arg, were used. Results showed that the total respiratory rate (Vt), alternative pathway capacity (Valt) and cytochrome pathway capacity (Vcyt) increased under 0–100 mM NaCl treatments but decreased under 150–300 mM NaCl treatments in Col-0 callus. However, the activation of MKK9 by dexamethasone (DEX) increased Vt, Valt and Vcyt under 200 mM NaCl treatment; moreover, Valt showed more increase than Vcyt. The activation of MKK9 in MKK9DD callus sharply increased AOX protein expression under normal and NaCl conditions, but the increase was not observed in MKK9KR callus. Further results indicated that MAPK3 and MAPK6 were involved in the MKK9-induced increase of AOX protein levels. qRT-PCR results showed that MKK9-MAPK3/MAPK6 was involved in the NaCl-induced AOX1b and AOX1d expression, but only MKK9-MAPK3 was necessary for AOX2 expression; in addition, MAPK3 regulated the AOX1a transcription in an MKK9-independent manner. MKK9 positively regulated SOD and CAT activities by affecting MAPK3 and MAPK6 and negatively regulated APX and POD activities by affecting MAPK3. Moreover, MKK9 functions as a positive factor in H2O2 accumulation under salt stress. The regulation of ethylene on alternative respiration was also associated with MKK9 under salt stress. Taken together, the MKK9-MAPK3/MAPK6 pathway plays a pivotal role in increasing alternative respiration in the salt-treated Arabidopsis callus. [ABSTRACT FROM AUTHOR]

Summary: 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. Energy requirements for transport of salt (NaCl) to leaf vacuoles for osmotic adjustment could be small if there are no substantial leaks back across plasma membrane and tonoplast in root and leaf. The coupling ratio of the H+‐ATPase also is a critical component. One proposed leak, that of Na+ influx across the plasma membrane through certain aquaporin channels, might be coupled to water flow, thus conserving energy. For the tonoplast, control of two types of cation channels is required for energy efficiency. Transporters controlling the Na+ and Cl− concentrations in mitochondria and chloroplasts are largely unknown and could be a major energy cost. The complexity of the system will require a sophisticated modelling approach to identify critical transporters, apoplastic barriers and root structures. This modelling approach will inform experimentation and allow a quantitative assessment of the energy costs of NaCl tolerance to guide breeding and engineering of molecular components. See also the Commentary on this article by Sanders, 225: 1047–1048. [ABSTRACT FROM AUTHOR]

Background: The detrimental effects of global climate change direct more attention to the survival and productivity of plants during periods of highly fluctuating temperatures. In particular in temperate climates in spring, temperatures can vary between above-zero and freezing temperatures, even during a single day. Freeze-thaw cycles cause cell membrane lesions that can lead to tissue damage and plant death. Whereas the processes of cold acclimation and freeze-thaw injury are well documented, not much is known about the recovery of plants after a freezing event. We therefore addressed the following questions: i. how does the severity of freezing damage influence repair; ii. how are respiration and content of selected metabolites influenced during the repair process; and iii. how do transcript levels of selected genes respond during repair? Results: We have investigated the recovery from freezing to sub-lethal temperatures in leaves of non-acclimated and cold acclimated Arabidopsis thaliana plants over a period of 6 days. Fast membrane repair and recovery of photosynthesis were observed 1 day after recovery (1D-REC) and continued until 6D-REC. A substantial increase in respiration accompanied the repair process. In parallel, concentrations of sugars and proline, acting as compatible solutes during freezing, remained unchanged or declined, implicating these compounds as carbon and nitrogen sources during recovery. Similarly, cold-responsive genes were mainly down regulated during recovery of cold acclimated leaves. In contrast, genes involved in cell wall remodeling and ROS scavenging were induced during recovery. Interestingly, also the expression of genes encoding regulatory proteins, such as 14–3-3 proteins, was increased suggesting their role as regulators of repair processes. Conclusions: Recovery from sub-lethal freezing comprised membrane repair, restored photosynthesis and increased respiration rates. The process was accompanied by transcriptional changes including genes encoding regulatory proteins redirecting the previous cold response to repair processes, e.g. to cell wall remodeling, maintenance of the cellular proteome and to ROS scavenging. Understanding of processes involved in repair of freeze-thaw injury increases our knowledge on plant survival in changing climates with highly fluctuating temperatures. [ABSTRACT FROM AUTHOR]

Summary: Understanding the strategies employed by plant species that live in extreme environments offers the possibility to discover stress tolerance mechanisms. We studied the physiological, antioxidant and metabolic responses to three temperature conditions (4, 15, and 23°C) of Colobanthus quitensis (CQ), one of the only two native vascular species in Antarctica. We also employed Dianthus chinensis (DC), to assess the effects of the treatments in a non‐Antarctic species from the same family.Using fused LASSO modelling, we associated physiological and biochemical antioxidant responses with primary metabolism. This approach allowed us to highlight the metabolic pathways driving the response specific to CQ.Low temperature imposed dramatic reductions in photosynthesis (up to 88%) but not in respiration (sustaining rates of 3.0–4.2 μmol CO2 m−2 s−1) in CQ, and no change in the physiological stress parameters was found. Its notable antioxidant capacity and mitochondrial cytochrome respiratory activity (20 and two times higher than DC, respectively), which ensure ATP production even at low temperature, was significantly associated with sulphur‐containing metabolites and polyamines.Our findings potentially open new biotechnological opportunities regarding the role of antioxidant compounds and respiratory mechanisms associated with sulphur metabolism in stress tolerance strategies to low temperature. [ABSTRACT FROM AUTHOR]

The environment in which eukaryotes first evolved was drastically different from what they experience today, and one of the key limiting factors was the availability of oxygen for mitochondrial respiration. During the transition to a fully oxygenated Earth, other compounds such as sulfide posed a considerable constraint on using mitochondrial aerobic respiration for energy production. The ancestors of animals, and those that first evolved from the simpler eukaryotes have mitochondrial respiratory components that are absent from later-evolving animals. Specifically, mitochondria of most basal metazoans have a sulfide-resistant alternative oxidase (AOX), which provides a secondary oxidative pathway to the classical cytochrome pathway. In this essay, I argue that because of its resistance to sulfide, AOX respiration was critical to the evolution of animals by enabling oxidative metabolism under otherwise inhibitory conditions. I hypothesize that AOX allowed for metabolic flexibility during the stochastic oxygen environment of early Earth which shaped the evolution of basal metazoans. I briefly describe the known functions of AOX, with a particular focus on the decreased production of reactive oxygen species (ROS) during stress conditions. Then, I propose three evolutionary consequences of AOX-mediated protection from ROS observed in basal metazoans: 1) adaptation to stressful environments, 2) the persistence of facultative sexual reproduction, and 3) decreased mitochondrial DNA mutation rates. Recognizing the diversity of mitochondrial respiratory systems present in animals may help resolve the mechanisms involved in major evolutionary processes such as adaptation and speciation. [ABSTRACT FROM AUTHOR]

Cellular respiration via the alternative oxidase pathway (AOP) leads to a considerable loss in efficiency. Compared to the cytochrome pathway (COP), AOP produces 0–50% as much ATP per carbon (C) respired. Relative partitioning between the pathways can be measured in vivo based on their differing isotopic discriminations against 18O in O2. Starting from published methods, we have refined and tested a new protocol to improve measurement precision and efficiency. The refinements detect an effect of tissue water content (P < 0.0001), which we have removed, and yield precise discrimination endpoints in the presence of pathway‐specific respiratory inhibitors [CN− and salicylhydroxamic acid (SHAM)], which improves estimates of AOP/COP partitioning. Fresh roots of Pinus sylvestris were sealed in vials with a CO2 trap. The air was replaced to ensure identical starting conditions. Headspace air was repeatedly sampled and isotopically analyzed using isotope‐ratio mass spectrometry. The method allows high‐precision measurement of the discrimination against 18O in O2 because of repeated measurements of the same incubation vial. COP and AOP respiration discriminated against 18O by 15.1 ± 0.3‰ and 23.8 ± 0.4‰, respectively. AOP contributed to root respiration by 23 ± 0.2% of the total in an unfertilized stand. In a second, nitrogen‐fertilized, stand AOP contribution was only 14 ± 0.2% of the total. These results suggest the improved method can be used to assess the relative importance of COP and AOP activities in ecosystems, potentially yielding information on the role of each pathway for the carbon use efficiency of organisms. [ABSTRACT FROM AUTHOR]

Wickerhamomyces anomalus strain LBCM1105 was originally isolated from the wort of cachaça (the Brazilian fermented sugarcane juice-derived Brazilian spirit) and has been shown to grow exceptionally well at high amounts of glycerol. This paramount residue from the biodiesel industry is a promising cheap carbon source for yeast biotechnology. The assessment of the physiological traits underlying the W. anomalus glycerol consumption ability in opposition to Saccharomyces cerevisiae is presented. A new WaStl1 concentrative glycerol-H+ symporter with twice the affinity of S. cerevisiae was identified. As in this yeast, WaSTL1 is repressed by glucose and derepressed/induced by glycerol but much more highly expressed. Moreover, LBCM1105 aerobically growing on glycerol was found to produce ethanol, providing a redox escape to compensate the redox imbalance at the level of cyanide-resistant respiration (CRR) and glycerol 3P shuttle. This work is critical for understanding the utilization of glycerol by non-Saccharomyces yeasts being indispensable to consider their industrial application feeding on biodiesel residue. [ABSTRACT FROM AUTHOR]

ContentsSummary670I.Introduction671II.Principle 1 – Plant respiration performs three distinct functions673III.Principle 2 – Metabolic pathway flexibility underlies plant respiratory performance676IV.Principle 3 – Supply and demand interact over time to set plant respiration rate677V.Principle 4 – Plant respiratory acclimation involves adjustments in enzyme capacities679VI.Principle 5 – Respiration is a complex trait that helps to define, and is impacted by, plant lifestyle strategies680VII.Future directions680Acknowledgements682References682 Summary: Respiration is a core biological process that has important implications for the biochemistry, physiology, and ecology of plants. The study of plant respiration is thus conducted from several different perspectives by a range of scientific disciplines with dissimilar objectives, such as metabolic engineering, crop breeding, and climate‐change modelling. One aspect in common among the different objectives is a need to understand and quantify the variation in respiration across scales of biological organization. The central tenet of this review is that different perspectives on respiration can complement each other when connected. To better accommodate interdisciplinary thinking, we identify distinct mechanisms which encompass the variation in respiratory rates and functions across biological scales. The relevance of these mechanisms towards variation in plant respiration are explained in the context of five core principles: (1) respiration performs three distinct functions; (2) metabolic pathway flexibility underlies respiratory performance; (3) supply and demand interact over time to set respiration rates; (4) acclimation involves adjustments in enzyme capacities; and (5) respiration is a complex trait that helps to define, and is impacted by, plant lifestyle strategies. We argue that each perspective on respiration rests on these principles to varying degrees and that broader appreciation of how respiratory variation occurs can unite research across scales. [ABSTRACT FROM AUTHOR]

Summary: The combined action of the electron transport chain (ETC) and ATP synthase is essential in determining energy efficiency in plants, and so is important for cellular biosynthesis, growth and development. Owing to the sessile nature of plants, mitochondria must operate over a wide temperature range in the environment, necessitating a broad temperature tolerance of their biochemical reactions.We investigated the temperature response of mitochondrial respiratory processes in isolated mitochondria and intact plants of Arabidopsis thaliana and considered the effect of instantaneous responses to temperature and acclimation responses to low temperatures.We show that at 4°C the plant mitochondrial ATP synthase is differentially inhibited compared with other elements of the respiratory pathway, leading to decreased ADP : oxygen ratios and a limitation to the rate of ATP synthesis. This effect persists in vivo and cannot be overcome by cold‐temperature acclimation of plants.This mechanism adds a new element to the respiratory acclimation model and provides a direct means of temperature perception by plant mitochondria. This also provides an alternative explanation for non‐phosphorylating ETC bypass mechanisms, like the alternative oxidase to maintain respiratory rates, albeit at lower ATP synthesis efficiency, in response to the sensitivity of ATP synthase to the prevailing temperature. [ABSTRACT FROM AUTHOR]

The respiration rate of plant tissues decreases when the amount of available O2 is reduced. There is, however, a debate on whether the respiration rate is controlled either by diffusion limitation of oxygen or through regulatory processes at the level of the transcriptome. We used experimental and modelling approaches to demonstrate that both diffusion limitation and metabolic regulation affect the response of respiration of bulky plant organs such as fruit to reduced O2 levels in the surrounding atmosphere. Diffusion limitation greatly affects fruit respiration at high temperature, but at low temperature respiration is reduced through a regulatory process, presumably a response to a signal generated by a plant oxygen sensor. The response of respiration to O2 is time dependent and is highly sensitive, particularly at low O2 levels in the surrounding atmosphere. Down-regulation of the respiration at low temperatures may save internal O2 and relieve hypoxic conditions in the fruit. [ABSTRACT FROM AUTHOR]

The non-energy-conserving alternative oxidase (AOX) respiration of plant mitochondria is known to interact with chloroplast photosynthesis. This may have consequences for growth, particularly under sub-optimal conditions when energy imbalances can impede photosynthesis. This hypothesis was tested by comparing the metabolism and growth of wild-type Nicotiana tabacum with that of AOX knockdown and overexpression lines during a prolonged steadystate mild to moderate water deficit. Under moderate water deficit, the AOX amount was an important determinant of the rate of both mitochondrial respiration in the light and net photosynthetic CO2 assimilation (A) at the growth irradiance. In particular, AOX respiration was necessary to maintain optimal proton and electron fluxes at the chloroplast thylakoid membrane, which in turn prevented a water-deficit-induced biochemical limitation of photosynthesis. As a result of differences in A, AOX overexpressors gained more biomass and knockdowns gained less biomass than wild-type during moderate water deficit. Biomass partitioning also differed, with the overexpressors having a higher percentage, and the knockdowns having a lower percentage, of total above-ground biomass in reproductive tissue than wild-type. The results establish that improving chloroplast energy balance by using a non-energy-conserving respiratory electron sink can increase photosynthesis and growth during prolonged water deficit. [ABSTRACT FROM AUTHOR]

Senna obtusifolia L., a common weed in the tropical and subtropical regions of the world, is able to germinate under adverse environmental conditions, suggesting that this species has efficient stress-adaptation strategies. The aims of the present work were to examine the energy metabolism and the antioxidant defense system of the Senna obtusifolia L. during seed germination and initial growth, and the responses to allelochemical-induced stress. Respiratory activity, the activities of alcohol dehydrogenase (ADH), superoxide dismutase (SOD), catalase (CAT),guaicol peroxidase (POD), ascorbate peroxidase (APX), glutathione reductase (GR), lipoxygenase (LOX) and the content of malondialdehyde (MDA) and glutathione (GSSG and GSH) were measured. Shortly after seed imbibition, mitochondrial respiratory activity was active and the presence of SOD, CAT, GR and LOX activity in embryos, along with significant KCN-insensitive respiration, indicated that the production of reactive oxygen species (ROS) is initiated as soon as mitochondrial respiration resumes. Among the fourteen allelochemicals assayed, only coumarin significantly supressed the growth of S. obtusifolia seedlings. Although coumarin reduced the activities of CAT, POD and APX, the GSH, GSSG and MDA levels were not altered. Alpha-pinene, quercetin and ferulic acid did not modify the activity of the antioxidant enzymes or the contents of GSH, GSSH and MDA. Thus the antioxidant defense system of S. obstusifolia may be effective in counteracting the harmful effects of ROS generated during seed germination and initial growth in the presence of toxic allelochemicals. [ABSTRACT FROM AUTHOR]

Background: Mitochondrial respiration in the dark (Rdark) is a critical plant physiological process, and hence a reliable, efficient and high-throughput method of measuring variation in rates of Rdark is essential for agronomic and ecological studies. However, currently methods used to measure Rdark in plant tissues are typically low throughput. We assessed a high-throughput automated fluorophore system of detecting multiple O2 consumption rates. The fluorophore technique was compared with O2-electrodes, infrared gas analysers (IRGA), and membrane inlet mass spectrometry, to determine accuracy and speed of detecting respiratory fluxes. Results: The high-throughput fluorophore system provided stable measurements of Rdark in detached leaf and root tissues over many hours. High-throughput potential was evident in that the fluorophore system was 10 to 26-fold faster per sample measurement than other conventional methods. The versatility of the technique was evident in its enabling: (1) rapid screening of Rdark in 138 genotypes of wheat; and, (2) quantification of rarely-assessed whole-plant Rdark through dissection and simultaneous measurements of above- and below-ground organs. Discussion: Variation in absolute Rdark was observed between techniques, likely due to variation in sample conditions (i.e. liquid vs. gas-phase, open vs. closed systems), indicating that comparisons between studies using different measuring apparatus may not be feasible. However, the high-throughput protocol we present provided similar values of Rdark to the most commonly used IRGA instrument currently employed by plant scientists. Together with the greater than tenfold increase in sample processing speed, we conclude that the high-throughput protocol enables reliable, stable and reproducible measurements of Rdark on multiple samples simultaneously, irrespective of plant or tissue type. [ABSTRACT FROM AUTHOR]

A total of 140 diverse spring wheat lines were characterized for agronomic and physiological traits under hot field conditions, and a subset of thirteen were selected for dark leaf respiration studies (Rd). These genetic resources included syntheticderived lines, landraces, landrace-derived lines, bread wheats, and durum wheats. Initial phenotyping showed that better heat-adapted genotypes (best yielding) exhibited high early biomass (assessed by normalized difference of vegetative index, NDVI), high grainfilling rates, and low canopy temperatures. As for other studies Rd increased as temperature increased (within the range of 15-40 C), and decreased with plant age. Correlations between Rd and leaf temperature ranged between 0.50 and 0.85. Rd was negatively associated with yield when recorded at 30-35 C during anthesis and grainfilling. Comparisons between wheat groups showed that synthetic-derived materials expressed lower leaf respiration rates and larger yields than the other groups at warm temperatures. [ABSTRACT FROM AUTHOR]

In eukaryotes, the Cu/Zn superoxide dismutase (SOD1) is a major cytosolic cuproprotein with a small fraction residing in the mitochondrial intermembrane space (IMS) to protect against respiratory superoxide. Curiously, the opportunistic human fungal pathogen Candida albicans is predicted to express two cytosolic SODs including Cu/Zn containing SOD1 and manganese containing SOD3. As part of a copper starvation response, C. albicans represses SOD1 and induces the non-copper alternative SOD3. While both SOD1 and SOD3 are predicted to exist in the same cytosolic compartment, their potential role in mitochondrial oxidative stress had yet to be investigated. We show here that under copper replete conditions, a fraction of the Cu/Zn containing SOD1 localizes to the mitochondrial IMS to guard against mitochondrial superoxide. However in copper starved cells, localization of the manganese containing SOD3 is restricted to the cytosol leaving the mitochondrial IMS devoid of SOD. We observe that during copper starvation, an alternative oxidase (AOX) form of respiration is induced that is not coupled to ATP synthesis but maintains mitochondrial superoxide at low levels even in the absence of IMS SOD. Surprisingly, the copper-dependent cytochrome c oxidase (COX) form of respiration remains high with copper starvation. We provide evidence that repression of SOD1 during copper limitation serves to spare copper for COX and maintain COX respiration. Overall, the complex copper starvation response of C. albicans involving SOD1, SOD3 and AOX minimizes mitochondrial oxidative damage whilst maximizing COX respiration essential for fungal pathogenesis. [ABSTRACT FROM AUTHOR]

Background: In modern agriculture, the call for an alternative crop protection strategy increases because of the desired reduction of fungicide and pesticide use and the continuously evolving resistance of pathogens and pests to agrochemicals. The direct activation of the plant immune system does not provide a promising plant protection measure because of high fitness costs. However, upon treatment with certain natural or synthetic compounds, plant cells can promote to a fitness cost-saving, primed state of enhanced defense. In the primed state, plants respond to biotic and abiotic stress with faster and stronger activation of defense, and this is often associated with immunity and abiotic stress tolerance. Until now, the identification of chemical compounds with priming-inducing activity (so-called plant activators) relied on tedious and invasive approaches, or required the late detection of secreted furanocoumarin phytoalexins in parsley cell cultures. Thus, simple, fast, straightforward, and noninvasive techniques for identifying priming-inducing compounds for plant protection are very welcome. Results: This report demonstrates that a respiration activity-monitoring system (RAMOS) can identify compounds with defense priming-inducing activity in parsley cell suspension in culture. RAMOS relies on the quasi-continuous, noninvasive online determination of the oxygen transfer rate (OTR). Treatment of parsley culture cells with the known plant activator salicylic acid (SA), a natural plant defense signal, resulted in an OTR increase. Addition of the defense elicitor Pep13, a cell wall peptide of Phythophthora sojae, induced two distinctive OTR peaks that were higher in SA-primed cells than in unprimed cells upon Pep13 challenge. Both, the OTR increase after priming with SA and the Pep13 challenge were dose-dependent. Furthermore, there was a close correlation of a compound's activity to enhance the oxygen consumption in parsley cells and its capacity to prime Pep13-induced furanocoumarin secretion as evaluated by fluorescence spectroscopy. Conclusions: RAMOS noninvasively determines the OTR as a measure of the metabolic activity of plant cells. Chemical enhancement of oxygen consumption by salicylic derivatives in parsley cell suspension cultures correlates with the induction of the primed state of enhanced defense that enhances the quantity of Pep13-induced furanocoumarin phytoalexins. Treatment with the priming-active compounds methyl jasmonate and pyraclostrobin also resulted in an enhanced respiration activity. Thus, RAMOS is a novel technology for identifying priminginducing compounds for agriculture. [ABSTRACT FROM AUTHOR]

The alternative oxidase is a membrane-bound ubiquinol oxidase found in the majority of plants as well as many fungi and protists, including pathogenic organisms such as Ttypanosoma brucei. It catalyzes a qcyanide-and antimycin-A-resistant oxidation of ubiquinol and the reduction of oxygen to water, short-circuiting the mitochondrial electron-transport chain prior to proton translocation by complexes III and IV, thereby dramatically reducing ATP formation. In plants, it plays a key role in cellular metabolism, thermogenesis, and energy homeostasis and is generally considered to be a major stress-induced protein. We describe recent advances in our understanding of this protein's structure following the recent successful crystallization of the alternative oxidase from T. brucei. We focus on the nature of the active site and ubiquinol-binding channels and propose a mechanism for the reduction of oxygen to water based on these structural insights. We also consider the regulation of activity at the posttranslational and retrograde levels and highlight challenges for future research. [ABSTRACT FROM AUTHOR]

Extensive past efforts have been taken toward understanding heat tolerance mechanisms of the aboveground organs. Root systems play critical roles in whole-plant adaptation to heat stress, but are less studied. This review discusses recent research results revealing some critical physiological and metabolic factors underlying root thermotolerance, with a focus on temperate perennial grass species. Comparative analysis of differential root responses to supraoptimal temperatures by a heat-adapted temperate C3 species, Agrostis scabra, which can survive high soil temperatures up to 45 °C in geothermal areas in Yellow Stone National Park, and a heat-sensitive cogeneric species, Agrostis stolonifera, suggested that efficient carbon and protein metabolism is critical for root thermotolerance. Superior root thermotolerance in a perennial grass was associated with a greater capacity to control respiratory costs through respiratory acclimation, lowering carbon investment in maintenance for protein turnover, and efficiently partitioning carbon into different metabolic pools and alternative respiration pathways. Proteomic analysis demonstrated that root thermotolerance was associated with an increased maintenance of stability and less degradation of proteins, particularly those important for metabolism and energy production. In addition, thermotolerant roots are better able to maintain growth and activity during heat stress by activating stress defence proteins such as those participating in antioxidant defence (i.e. superoxide dismutase, peroxidase, glutathione S-transferase) and chaperoning protection (i.e. heat shock protein). [ABSTRACT FROM PUBLISHER]

The effect of previous light conditions on metabolite and transcript levels was investigated in leaves of Arabidopsis thaliana during illumination and after light-enhanced dark respiration (LEDR), when dark respiration was measured., Primary carbon metabolites and the expression of light-responsive respiratory genes were determined in A. thaliana leaves before and after 30 min of darkness following different light conditions. In addition, metabolite levels were determined in the middle of the night and the in vivo activities of cytochrome and alternative respiratory pathways were determined by oxygen isotope fractionation., A large number of metabolites were increased in leaves of plants growing in or transiently exposed to higher light intensities. Transcript levels of respiratory genes were also increased after high light treatment. For the majority of the light-induced metabolites and transcripts, the levels were maintained after 30 min of darkness, where higher and persistent respiratory activities were also observed. The levels of many metabolites were lower at night than after 30 min of darkness imposed in the day, but respiratory activities remained similar., The results obtained suggest that 'dark' respiration measurements, as usually performed, are probably made under conditions in which the overall status of metabolites is strongly influenced by the previous light conditions. [ABSTRACT FROM AUTHOR]

Mitochondrial repair is of fundamental importance for seed germination. When mature orthodox seeds are imbibed and germinated, they lose their desiccation tolerance in parallel. To gain a better understanding of this process, we studied the recovery of mitochondrial structure and function in pea (Pisum sativum cv. Jizhuang) seeds with different tolerance to desiccation. Mitochondria were isolated and purified from the embryo axes of control and imbibed-dehydrated pea seeds after (re-)imbibition for various times. Recovery of mitochondrial structure and function occurred both in control and imbibed-dehydrated seed embryo axes, but at different rates and to different maximum levels. The integrity of the outer mitochondrial membrane reached 96% in all treatments. However, only the seeds imbibed for 12 h and then dehydrated recovered the integrity of the inner mitochondrial membrane (IMM) and State 3 (respiratory state in which substrate and ADP are present) respiration (with NADH and succinate as substrate) to the control level after re-imbibition. With increasing imbibition time, the degree to which each parameter recovered decreased in parallel with the decrease in desiccation tolerance. The tolerance of imbibed seeds to desiccation increased and decreased when imbibed in CaCl2 and methylviologen solution, respectively, and the recovery of the IMM integrity similarly improved and weakened in these two treatments, respectively. Survival of seeds after imbibition-dehydration linearly increased with the increase in ability to recover the integrity of IMM and State 3 respiration, which indicates that recovery of mitochondrial structure and function during germination has an important role in seed desiccation tolerance. [ABSTRACT FROM AUTHOR]

Filamentous fungi are arguably the most industrially important group of microorganisms. Production processes involving these simple eukaryotes are often highly aerobic in nature, which implies these cultures are routinely subject to oxidative stress. Despite this, little is known about how filamentous fungi cope with high levels of oxidative stress as experienced in fermenter systems. More surprisingly, much of our knowledge of oxidative stress responses in fungi comes from environmental or medical studies. Here, the current understanding of oxidative stress effects and cellular responses in filamentous fungi is critically discussed. In particular the role of alternative respiration is evaluated, and the contributions of the alternative oxidase and alternative dehydrogenases in defence against oxidative stress, and their profound influence on fungal metabolism is critically examined. Finally, the importance of further research which would underpin a less empirical approach to optimising fungal strains for the fermenter environment is emphasised. [ABSTRACT FROM AUTHOR]

The relationship between solar radiation capture and potential plant growth is of theoretical and practical importance. The key processes constraining the transduction of solar radiation into phyto-energy (i.e. free energy in phytomass) were reviewed to estimate potential solar-energy-use efficiency. Specifically, the output : input stoichiometries of photosynthesis and photorespiration in C3 and C4 systems, mobilization and translocation of photosynthate, and biosynthesis of major plant biochemical constituents were evaluated. The maintenance requirement, an area of important uncertainty, was also considered. For a hypothetical C3 grain crop with a full canopy at 30 °C and 350 ppm atmospheric [CO2], theoretically potential efficiencies (based on extant plant metabolic reactions and pathways) were estimated at c. 0.041 J J-1 incident total solar radiation, and c. 0.092 J J-1 absorbed photosynthetically active radiation (PAR). At 20 °C, the calculated potential efficiencies increased to 0.053 and 0.118 J J-1 (incident total radiation and absorbed PAR, respectively). Estimates for a hypothetical C4 cereal were c. 0.051 and c. 0.114 J J-1, respectively. These values, which cannot be considered as precise, are less than some previous estimates, and the reasons for the differences are considered. Field-based data indicate that exceptional crops may attain a significant fraction of potential efficiency. [ABSTRACT FROM AUTHOR]

The present study shows the importance of alternative oxidase (AOX) pathway in optimizing photosynthesis under high light (HL). The responses of photosynthesis and respiration were monitored as O2 evolution and O2 uptake in mesophyll protoplasts of pea pre‐incubated under different light intensities. Under HL (3000 µmol m−2 s−1), mesophyll protoplasts showed remarkable decrease in the rates of NaHCO3‐dependent O2 evolution (indicator of photosynthetic carbon assimilation), while decrease in the rates of respiratory O2 uptake were marginal. While the capacity of AOX pathway increased significantly by two fold under HL, the capacity of cytochrome oxidase (COX) pathway decreased by >50% compared with capacities under darkness and normal light (NL). Further, the total cellular levels of pyruvate and malate, which are assimilatory products of active photosynthesis and stimulators of AOX activity, were increased remarkably parallel to the increase in AOX protein under HL. Upon restriction of AOX pathway using salicylhydroxamic acid (SHAM), the observed decrease in NaHCO3‐dependent O2 evolution or p‐benzoquinone (BQ)‐dependent O2 evolution [indicator of photosystem II (PSII) activity] and the increase in total cellular levels of pyruvate and malate were further aggravated/promoted under HL. The significance of raised malate and pyruvate levels in activation of AOX protein/AOX pathway, which in turn play an important role in dissipating excess chloroplastic reducing equivalents and sustenance of photosynthetic carbon assimilation to balance the effects of HL stress on photosynthesis, was depicted as a model. [ABSTRACT FROM AUTHOR]

Thermogenesis during the blooming of inflorescence is found in several but not all aroids. To understand what is critical for thermogenesis, we investigated the difference between thermogenic and non-thermogenic skunk cabbages ( Symplocarpus renifolius and Lysichiton camtschatcensis), which are closely related in morphology and phylogeny. Critical parameters of mitochondrial biogenesis, including density, respiratory activity, and protein expression were compared between these two species. Mitochondrial density, respiratory activity, and the amount of alternative oxidase (AOX) in L. camtschatcensis spadix mitochondria were lower than in S. renifolius spadix mitochondria, while the level of uncoupling protein (UCP) was higher. AOX and UCP mRNAs in L. camtschatcensis were constitutively expressed in various tissues, such as the spadix, the spathe, the stalk, and the leaves. cDNA encoding two putative thermogenic proteins, AOX and UCP were isolated from L. camtschatcensis, and their primary structure was analyzed by multiple alignment and phylogenetic tree reconstruction. AOX and UCP protein of two the skunk cabbage species are closely related in structure, compared with other isoforms in thermogenic plants. Our results suggest that mitochondrial density, respiratory activity, and protein expression, rather than the primary structure of AOX or UCP proteins, may play critical roles in thermogenesis in plants. [ABSTRACT FROM AUTHOR]

Mitochondrial respiratory chain defects are now recognized to underlie a large number of human diseases with a spectacular variety in their phenotypic presentations. Despite progress made in the elucidation of their molecular basis, these diseases remain essentially untreatable. To date, most strategies to counteract these diseases, either in vitro or in vivo have proven unsuccessful. In humans, the respiratory chain lacks several redox active proteins long known in many micro-organisms, as well as in plants, and, as found recently, even in some metazoans. These alternative enzymes, e.g. the cyanide-insensitive alternative oxidase and the internal rotenone-insensitive NADH dehydrogenase, confer a significant flexibility to the respiratory chain, allowing it to overcome potential constraints exerted by the cell phosphorylation potential or by environmental xenobiotics. In plants, these alternative enzymes, activated by a subset of keto-acids, including pyruvate, are essentially engaged under highly reducing conditions. Because these are conditions observed in patients with respiratory chain dysfunction, we made the hypothesis that expression of these proteins might be of benefit in such situations. The observation that a functional alternative oxidase from Ciona intestinalis could be expressed in mammalian cells without obvious detrimental effect has provided a basis to develop a research programme to test the hypothesis, within an ad hoc international consortium, that this paper aims to describe. Combining research on human cells, flies and mice, the project aims, firstly, to verify that expressing these alternative enzymes is physiologically benign, useful as a tool to delineate the mechanisms of respiratory chain dysfunction and, finally, test their potential therapeutic benefit. [ABSTRACT FROM AUTHOR]

• Correlation methods originating in the growth and maintenance paradigm (GMP) are traditionally used to calculate a ‘growth coefficient’ ( g) or the ‘growth potential’ (1/ g) of entire plants. The enthalpy balance approach is usually applied to plant organs and relies on determination of both CO2 release and O2 reduction to provide a measure of instantaneous rates of enthalpic growth ( RSGΔ HB). • Aspects of both the approaches to explore physiological mechanisms that govern enthalpic growth (variation in rates of CO2 release versus rates of O2 reduction) were combined. • Respiration and growth rates of apical buds of Pinus radiata were affected strongly by canopy position, and moderately by branching order. A linear relation between enthalpic growth and CO2 respiration explained 69% of the observed variation. Despite faster rates of growth, enthalpic growth potential (1/ gH) was comparatively low in the upper canopy. Low enthalpic growth potential entailed comparatively low enthalpy conversion efficiency (ηH, ratio of RSGΔ HB to ; proportional to CO2:O2 and to carbon conversion efficiency ℇ) at large RSGΔHB. Maximizing enthalpic growth requires a large capacity for O2 reduction. • Relations between RSGΔ HB and ηH could be described by hyperbolae using two parameters. One parameter, P1, is equivalent to enthalpic growth potential (1/ gH). [ABSTRACT FROM AUTHOR]

Abstract  Differences between the respiratory chain of the fungus Paracoccidioides brasiliensis and its mammalian host are reported. Respiration, membrane potential, and oxidative phosphorylation in mitochondria from P. brasiliensis spheroplasts were evaluated in situ, and the presence of a complete (Complex I–V) functional respiratory chain was demonstrated. In succinate-energized mitochondria, ADP induced a transition from resting to phosphorylating respiration. The presence of an alternative NADH–ubiquinone oxidoreductase was indicated by: (i) the ability to oxidize exogenous NADH and (ii) the lack of sensitivity to rotenone and presence of sensitivity to flavone. Malate/NAD+supported respiration suggested the presence of either a mitochondrial pyridine transporter or a glyoxylate pathway contributing to NADH and/or succinate production. Partial sensitivity of NADH/succinate-supported respiration to antimycin A and cyanide, as well as sensitivity to benzohydroxamic acids, suggested the presence of an alternative oxidase in the yeast form of the fungus. An increase in activity and gene expression of the alternative NADH dehydrogenase throughout the yeast’s exponential growth phase was observed. This increase was coupled with a decrease in Complex I activity and gene expression of its subunit 6. These results support the existence of alternative respiratory chain pathways in addition to Complex I, as well as the utilization of NADH-linked substrates by P. brasiliensis. These specific components of the respiratory chain could be useful for further research and development of pharmacological agents against the fungus. [ABSTRACT FROM AUTHOR]

• Gas exchange, fluorescence, western blot and chemical composition analyses were combined to assess if three functional groups (forbs, grasses and evergreen trees/shrubs) differed in acclimation of leaf respiration ( R) and photosynthesis ( A) to a range of growth temperatures (7, 14, 21 and 28°C). • When measured at a common temperature, acclimation was greater for R than for A and differed between leaves experiencing a 10-d change in growth temperature (PE) and leaves newly developed at each temperature (ND). As a result, the R :  A ratio was temperature dependent, increasing in cold-acclimated plants. The balance was largely restored in ND leaves. Acclimation responses were similar among functional groups. • Across the functional groups, cold acclimation was associated with increases in nonstructural carbohydrates and nitrogen. Cold acclimation of R was associated with an increase in abundance of alternative and/or cytochrome oxidases in a species-dependent manner. Cold acclimation of A was consistent with an initial decrease and subsequent recovery of thylakoid membrane proteins and increased abundance of proteins involved in the Calvin cycle. • Overall, the results point to striking similarities in the extent and the biochemical underpinning of acclimation of R and A among contrasting functional groups differing in overall rates of metabolism, chemical composition and leaf structure. [ABSTRACT FROM AUTHOR]

An increase in ultraviolet (UV) B radiation on the earth's surface is a feature of current global climate changes. It has been reported that alternative oxidase (AOX) may have a protective role against oxidative stress induced by environmental stresses, such as UV-B. To better understand the characteristic tolerance of plants to UV-B radiation, the effects of enhanced UV-B radiation on the activity and expression of AOX in red kidney bean ( Phaseolus vulgaris) leaves were investigated in the present study. The results show that the total respiration rate and AOX activity in red kidney bean leaves increased significantly during treatment with enhanced UV-B. However, cytochrome oxidase (COX) activity did not change significantly. The H2O2 content was also markedly increased and reached a maximum of 4.45 mmol·L−1·g−1 DW (dry weight) at 24 h of UV-B treatment, before dropping rapidly. Both alternative pathway content and alternative pathway activity were increased in the presence of exogenous H2O2. Immunoblotting analysis with anti-AOX monoclonal antibody revealed that expression of the AOX protein increased in red kidney bean leaves under enhanced UV-B radiation, reaching a peak at 72 h. In addition, AOX expression in red kidney bean leaves was induced by exogenous H2O2. These data indicate that the increase in AOX activity in red kidney bean leaves under enhanced UV-B radiation was mainly due to H2O2-induced AOX expression. [ABSTRACT FROM AUTHOR]

• Here, we investigated the impact of temperature on the carbon economy of two Plantago species from contrasting habitats. • The lowland Plantago major and the alpine Plantago euryphylla were grown hydroponically at three constant temperatures: 13, 20 and 27°C. Rates of photosynthetic CO2 uptake ( P) and respiratory CO2 release ( R) in shoots and R in roots were measured at the growth temperature using intact plants. At each growth temperature, air temperatures were changed to establish short-term temperature effects on the ratio of R to P ( R/ P). • In both species, R/ P was essentially constant in plants grown at 13 and 20°C. However, R/ P was substantially greater in 27°C-grown plants, particularly in P. euryphylla. The increase in R/ P at 27°C would have been even greater had biomass allocation to roots not decreased with increasing growth temperature. Short-term increases in air temperature increased R/ P in both species, with the effects of air temperature being most pronounced in 13°C-grown plants. • We conclude that temperature-mediated changes in biomass allocation play an important role in determining whole-plant R/ P values, and, while homeostasis of R/ P is achieved across moderate growth temperatures, homeostasis is not maintained when plants are exposed to growth temperatures higher than usually experienced in the natural habitat. [ABSTRACT FROM AUTHOR]

The activities of the cytochrome and alternative respiratory pathways were measured during the growth cycle in Arabidopsis thaliana using a newly developed Isotope Ratio Mass Spectrometer (IRMS) dual-inlet system that allows very precise measurements of oxygen-isotope fractionation under low oxygen consumption rates. Under optimum growth conditions, the relative growth rate was highly dependent on the activity of the cytochrome pathway. The activity of the alternative pathway was almost constant irrespective of the growth rate and appeared mostly involved in the maintenance respiration component, although the alternative pathway also played a role under optimum growth conditions. This is the first time that the contribution of the two respiratory pathways to the two main respiratory components (growth and maintenance) has been analyzed with the use of the oxygen-isotope fractionation technique. The respiration efficiency of the specific costs for growth and maintenance (adenosine triphosphate/O2 ratio) was determined by a modified regression model. The ability to measure oxygen-isotope fractionation during respiration in A. thaliana opens the door to a wider set of studies that are discussed. [ABSTRACT FROM AUTHOR]

Cultivars of maize ( Zea mays L.) with different sensitivity to drought were exposed to 0.3 mol/L sorbitol (-1.4 MPa water potential) for 24 h. Exposure to water deficiency significantly reduced the growth of both shoots (coleoptile and hypocotyl) and roots. Shoot growth was inhibited more than the growth of roots. Osmotic stress enhanced accumulation of soluble sugars. Electrolyte leakage, a cell injury index, was slightly increased after 0.3 mol/L sorbitol. Respiration was measured in the presence and absence of 2,6-dichlorophenol indophenol. 2, 6-Dichlorophenol indophenol did not influence respiration rates, because statistically equal results were observed under both conditions. Total respiration (vT) decreased after osmoticum treatment. There were no significant differences in the vT among the cultivars analysed. The decrease in vT was caused by a decline in the activities and capacities of both cytochrome (vcyt, Vcyt) and alternative pathway (valt, Valt) of respiration. A high residual respiration (vres) was observed, up to 27% of total uninhibited respiration. The result of uncoupler use clearly indicated that coupling was maintained after 24 h of osmotic stress. The recovery of the respiration rate was comparable with that of non-stressed control rates. According to these observations, no possible mitochondrial damage is expected. Water deficiency did not induce a stimulation of the alternative oxidase, so we assume that the stimulation of the alternative pathway is not related to drought stress resistance; rather, the function of the alternative pathway is to balance carbon metabolism and electron transport in a response to a changing environment. (Managing editor: Ping He) [ABSTRACT FROM AUTHOR]

The effects of growth irradiance and respiration on ascorbic acid (AA) synthesis and accumulation were studied in the leaves of wild-type and transformed Arabidopsis thaliana with modified amounts of the mitochondrial alternative oxidase (AOX) protein. Plants were grown under low (LL; 50 μmol photons m−2 s−1), intermediate (IL; 100 μmol photons m−2 s−1), or high (HL; 250 μmol photons m−2 s−1) light. Increasing growth irradiance progressively elevated leaf AA content and hence the values of dark-induced disappearance of leaf AA, which were 11, 55, and 89 nmol AA lost g−1 fresh weight h−1, from LL-, IL-, and HL-grown leaves, respectively. When HL leaves were supplied with L-galactone-1,4-lactone (L-GalL; the precursor of AA), they accumulated twice as much AA and had double the maximal L-galactone-1,4-lactone dehydrogenase (L-GalLDH) activities of LL leaves. Growth under HL enhanced dehydroascorbate reductase and monodehydroascorbate reductase activities. Leaf respiration rates were highest in the HL leaves, which also had higher amounts of cytochrome c and cytochrome c oxidase (CCO) activities, as well as enhanced capacity of the AOX and CCO electron transport pathways. Leaves of the AOX-overexpressing lines accumulated more AA than wild-type or antisense leaves, particularly at HL. Intact mitochondria from AOX-overexpressing lines had higher AA synthesis capacities than those from the wild-type or antisense lines even though they had similar L-GalLDH activities. AOX antisense lines had more cytochrome c protein than wild-type or AOX-overexpressing lines. It is concluded that regardless of limitations on L-GalL synthesis by regulation of early steps in the AA synthesis pathway, the regulation of L-GalLDH activity via the interaction of light and respiratory controls is a crucial determinant of the overall ability of leaves to produce and accumulate AA. [ABSTRACT FROM PUBLISHER]

Potato ( Solanum tuberosum L. cv. Désirée) plants with an antisense reduction in the P-protein of the glycine decarboxylase complex (GDC) were used to study the interaction between respiration and photorespiration. Mitochondria isolated from transgenic plants had a decreased capacity for glycine oxidation and glycine accumulated in the leaves. Malate consumption increased in leaves of GDC deficient plants and the capacity for malate and NADH oxidation increased in isolated mitochondria. A lower level of alternative oxidase protein and decreased partitioning of electrons to the alternative pathway was found in these plants. The adenylate status was altered in protoplasts from transgenic plants, most notably the chloroplastic ATP/ADP ratio increased. The lower capacity for photorespiration in leaves of GDC deficient plants was compensated for by increased respiratory decarboxylations in the light. This is interpreted as a decreased light suppression of the tricarboxylic acid cycle in GDC deficient plants in comparison to wild-type plants. The results support the view that respiratory decarboxylations in the light are restricted at the level of the pyruvate dehydrogenase complex and/or isocitrate dehydrogenase and that this effect is likely to be mediated by mitochondrial photorespiratory products. [ABSTRACT FROM AUTHOR]

When wild-type (wt) tobacco (Nicotiana tabacum cv. Petit Havana SR1) cells are grown under macronutrient (P or N) limitation, they induce large amounts of alternative oxidase (AOX), which constitutes a non-energy-conserving branch of the respiratory electron transport chain. To investigate the significance of AOX induction, wt cells were compared with transgenic (AS8) cells lacking AOX. Under nutrient limitation, growth of wt cell cultures was dramatically reduced and carbon use efficiency (g cell dry weight gain g−1 sugar consumed) decreased by 42–63%. However, the growth of AS8 was only moderately reduced by the nutrient deficiencies and carbon use efficiency values remained the same as under nutrient-sufficient conditions. As a result, the nutrient limitations more severely compromised the tissue nutrient status (P or N) of AS8 than wt cells. Northern analyses and a comparison of the mitochondrial protein profiles of wt and AS8 cells indicated that the lack of AOX in AS8 under P limitation was associated with increased levels of proteins commonly associated with oxidative stress and/or stress injury. Also, the level of electron transport chain components was consistently reduced in AS8 while tricarboxylic acid cycle enzymes did not show a universal trend in abundance in comparison to the wt. Alternatively, the lack of AOX in AS8 cells under N limitation resulted in enhanced carbohydrate accumulation. It is concluded that AOX respiration provides an important general mechanism by which plant cells can modulate their growth in response to nutrient availability and that AOX also has nutrient-specific roles in maintaining cellular redox and carbon balance. [ABSTRACT FROM PUBLISHER]

• Background and Aims Respiration is an important component of plant carbon balance, but it remains uncertain how respiration will respond to increases in atmospheric carbon dioxide concentration, and there are few measurements of respiration for crop plants grown at elevated [CO2] under field conditions. The hypothesis that respiration of leaves of soybeans grown at elevated [CO2] is increased is tested; and the effects of photosynthesis and acclimation to temperature examined.• Methods Net rates of carbon dioxide exchange were recorded every 10 min, 24 h per day for mature upper canopy leaves of soybeans grown in field plots at the current ambient [CO2] and at ambient plus 350 µmol mol−1 [CO2] in open top chambers. Measurements were made on pairs of leaves from both [CO2] treatments on a total of 16 d during the middle of the growing seasons of two years.• Key Results Elevated [CO2] increased daytime net carbon dioxide fixation rates per unit of leaf area by an average of 48 %, but had no effect on night-time respiration expressed per unit of area, which averaged 53 mmol m−2 d−1 (1·4 µmol m−2 s−1) for both the ambient and elevated [CO2] treatments. Leaf dry mass per unit of area was increased on average by 23 % by elevated [CO2], and respiration per unit of mass was significantly lower at elevated [CO2]. Respiration increased by a factor of 2·5 between 18 and 26 °C average night temperature, for both [CO2] treatments.• Conclusions These results do not support predictions that elevated [CO2] would increase respiration per unit of area by increasing photosynthesis or by increasing leaf mass per unit of area, nor the idea that acclimation of respiration to temperature would be rapid enough to make dark respiration insensitive to variation in temperature between nights. [ABSTRACT FROM AUTHOR]

• Background Elevated levels of atmospheric [CO2] are likely to enhance photosynthesis and plant growth, which, in turn, should result in increased specific and whole-plant respiration rates. However, a large body of literature has shown that specific respiration rates of plant tissues are often reduced when plants are exposed to, or grown at, high [CO2] due to direct effects on enzymes and indirect effects derived from changes in the plant's chemical composition.• Scope Although measurement artefacts may have affected some of the previously reported effects of CO2 on respiration rates, the direction and magnitude for the effects of elevated [CO2] on plant respiration may largely depend on the vertical scale (from enzymes to ecosystems) at which measurements are taken. In this review, the effects of elevated [CO2] from cells to ecosystems are presented within the context of the enzymatic and physiological controls of plant respiration, the role(s) of non-phosphorylating pathways, and possible effects associated with plant size.• Conclusions Contrary to what was previously thought, specific respiration rates are generally not reduced when plants are grown at elevated [CO2]. However, whole ecosystem studies show that canopy respiration does not increase proportionally to increases in biomass in response to elevated [CO2], although a larger proportion of respiration takes place in the root system. Fundamental information is still lacking on how respiration and the processes supported by it are physiologically controlled, thereby preventing sound interpretations of what seem to be species-specific responses of respiration to elevated [CO2]. Therefore the role of plant respiration in augmenting the sink capacity of terrestrial ecosystems is still uncertain. [ABSTRACT FROM AUTHOR]