kPa O2 Research Articles

Bioenergetic shift and proteomic signature induced by lentiviral-transduction of GFP-based biosensors

Fluorescent proteins (FPs) stand as pivotal tools extensively employed across diverse biological research endeavors in various model systems. However, long-standing concerns surround their use due to the numerous side effects associated with their expression. Recent investigations have brought to light the significance of hydrogen peroxide (H2O2) that is associated with the maturation process of green fluorescent protein (GFP) fluorophores. The structural and functional impairments associated with GFP expression are possibly linked to this amount of H2O2. In this study, we assess the impact of the GFP-based HyPer7 biosensor on cellular homeostasis and proteome changes, aiming to identify potential risks related to oxidative stress responses that potentially risks the application of such tools. Cells expressing genome-integrated HyPer7 demonstrated altered mitochondrial membrane potential (MMP), which was alleviated by the addition of antioxidants or culturing cells at physiological normoxia (5 kPa O2). Additionally, HyPer7-expressing cells also exhibited significant impairment in mitochondrial oxidative respiration, suggesting broader mitochondrial dysfunction. Through untargeted proteomics analysis, we identified 26 proteins exhibiting differential expression in HyPer7-expressing cells compared to respective control cells. Functional annotation analysis showed that the list of the delineated proteins is associated with cellular responses to stress and the regulation of antioxidant mechanisms. Our findings underscore the significance of caution and validation in ensuring a thorough comprehension of cellular responses when using fluorescent protein-based tools, thereby enhancing the reliability of the results.

Extending Raspberry Shelf Life and Maintaining Postharvest Quality with CO2 Atmospheres

Raspberry (Rubus idaeus L.) fruit are known for their extremely short shelf life. Decay, leakiness, and loss of firmness are the most common limiting factors contributing to their short storage life. However, storage in elevated CO2 and reduced O2 atmospheres can delay senescence in fruit by reducing softening, respiration and ethylene production rates, and pathogen growth. In this study, raspberries were exposed to four different CO2 atmospheres—15 kPa CO2 and 6 kPa O2 (15 kPa); 8 kPa CO2 and 13 kPa O2 (8 kPa); 5 kPa CO2 and 16 kPa O2 (5 kPa); or 0.03 kPa CO2 and 21 kPa O2 (0.03 kPa)—and were evaluated for their postharvest quality periodically during two weeks of storage in 2020 and 2021. Raspberry fruits kept in a 15 kPa CO2 atmosphere followed by 8 kPa CO2 had higher firmness, brighter red color, and the least fungal decay or leakiness. In all atmospheres, the total anthocyanin content increased over time, although the rate of increase was slowed by high CO2. The raspberries’ visual attributes deteriorated over time in all atmospheres, but high CO2 atmospheres slowed the rate of deterioration. After five days, the quality of air-stored raspberries was significantly degraded, while the raspberries stored in elevated CO2 maintained good quality for up to ten days.

HIF signaling in the prothoracic gland regulates growth and development in hypoxia but not normoxia in Drosophila.

The developmental regulation of body size is a fundamental life-history characteristic that in most animals is tied to the transition from juvenile to adult form. In holometabolous insects, this transition is ostensibly initiated at the attainment of a critical weight in the final larval instar. It has been hypothesized that the size-sensing mechanism used to determine attainment of critical weight exploits oxygen limitation as a larvae grows beyond the oxygen-delivery capacity of its fixed tracheal system; that is, developmentally induced cellular hypoxia initiates the synthesis of the molting hormone ecdysone by the prothoracic gland. We tested this hypothesis in Drosophila by assaying cellular hypoxia throughout the third larval instar at 21 and 10 kPa O2, using the activity of the HIF (hypoxia inducible factor)-signaling pathway as a measure of hypoxia. While HIF signaling was elevated at low levels of environmental O2, it did not markedly increase during development at either oxygen level, and was only suppressed by hyperoxia after feeding had ceased. Further, changes in HIF signaling in the prothoracic gland alone did not alter body size or developmental time in a way that would be expected if cellular hypoxia in the prothoracic gland was part of the critical weight mechanism. Our data do show, however, that reduced HIF signaling in the prothoracic gland decreases survival and retards development at 10 kPa O2, suggesting that prothoracic HIF signaling is a necessary part of the beneficial plasticity mechanism that controls growth and development in response to low oxygen level.

Influence of temperature, oxygen partial pressure, and microstructure on the high-temperature oxidation behavior of the SiC Layer of TRISO particles

Tristructural isotropic (TRISO)-coated fuel particles are designed for use in high-temperature gas-cooled nuclear reactors, featuring a structural SiC layer that may be exposed to oxygen-rich environments over 1000 °C. Surrogate TRISO particles were tested in 0.2–20 kPa O2 atmospheres to observe the differences in oxidation behavior. Oxide growth mechanisms remained consistent from 1200–1600 °C for each PO2, with activation energies of 228 ± 7 kJ/mol for 20 kPa O2 and 188 ± 8 kJ/mol for 0.2 kPa O2. At 1600 °C, kinetic analysis revealed a change in oxide growth mechanisms between 0.2 and 6 kPa O2. In 0.2 kPa O2, oxidation produced raised oxide nodules on pockets with nanocrystalline SiC. Oxidation mechanisms were determined using Atom probe tomography. Active SiC oxidation occurred in C-rich grain boundaries with low PO2, leading to SiO2 buildup in porous nodules. This phenomenon was not observed at any temperature in 20 kPa O2 environments.

Controlled atmosphere as cold chain support for extending postharvest life in cabbage

Postharvest management of cabbage relies on high-intensity cooling to control postharvest physiology, minimising quality loss despite incurring significant energy and environmental costs. As an alternative, we hypothesised that controlled atmosphere (CA) could allow increased storage temperature by supporting physiological regulation, while maintaining quality and reducing energy demand. This study examined the effect CA (1.5 kPa CO2 and 6 kPa O2) at 5 or 10 °C on cabbage quality, with the aim of proposing a more sustainable and resilient supply chain. CA treatment was effective at reducing head respiration at higher temperature, with CA/10 °C treatment achieving lower respiration rates than Control/5 °C. Improved head colour retention and maintenance of stump quality were observed in cabbage under CA conditions. CA effects were seen also at a regulatory level; CA promoted an average of 25.4% reduction in abscisic acid accumulation potentially as part of a wider hypoxia stress response and was successful in decreasing expression of the senescence-coordinating transcription factor BoORE15. This finding was linked with a lower in downstream expression of pheophytinase and subtilisin protease. These results demonstrated that CA treatment fundamentally modified postharvest physiology in cabbage, which can be exploited to enable storage at warmer temperatures, contributing to supply chains with lower energy demand and its associated environmental benefits.

Changes in raspberry sensory quality after harvest as affected by CO2 atmospheres

CO2 atmospheres have the potential to influence raspberry (Rubus idaeus L.) sensory quality after harvest. Our study determined the optimal postharvest atmosphere to extend shelf life without negatively impacting sensory quality. Raspberry fruit were stored at 5 ℃ in 15, 8, 5 or 0.03 kPa CO2 in combination with 6, 13, 16 or 21 kPa O2, respectively. A trained sensory panel conducted a descriptive sensory evaluation of the raspberry fruit after 5, 10, and 13 d of storage. Raspberries stored in 15 kPa CO2 with 6 kPa O2 (15 kPa) atmosphere followed by that in 8 kPa CO2 with 13 kPa O2 (8 kPa) atmosphere had higher firmness than that in 5 kPa CO2 with 16 kPa O2 (5 kPa) and 0.03 kPa CO2 with 21 kPa O2 (0.03 kPa) atmosphere. Panelists found that raspberries stored in 8 kPa and 15 kPa CO2 atmosphere had the least off-flavor and highest tartness. Raspberries stored in 8 kPa scored highest in raspberry flavor with substantial juiciness and sweetness scores. The fermentative volatiles acetaldehyde and ethanol were higher in raspberries stored in 15 kPa despite the low off-flavor scores, while most other raspberry volatiles decreased with increasing CO2 concentration, including flavor-related volatiles α-ionone, α-terpineol, limonene and linalool. After 10 d, the quality of raspberries stored in 0.03 kPa or 5 kPa atmosphere had degraded considerably. While 15 kPa atmosphere prolonged shelf life the longest, 8 kPa atmosphere prolonged shelf life to 10 d while maintaining sensory quality and was the best overall atmosphere.

Benzene Oxidation in Air by an Amine-Functionalized Metal-Organic Framework-Derived Carbon- and Nitrogen-Loaded Zirconium Dioxide-Supported Platinum Catalyst.

To learn more about the behavior of amine (NH2)-functionalized metal-organic framework (MOF)-derived noble metal catalysts in the removal of aromatic volatile organic compounds in air, benzene oxidation at low temperatures has been investigated using 0.2-, 0.8-, and 1.5%-platinum (Pt)/Universitetet i Oslo (UiO)-66-NH2. The benzene conversion (XB) of x%-Pt/UiO-66-NH2-R under dry conditions (175 °C) was 23% (x = 0.2%) < 52% (x = 0.8%) < 100% (x = 1.5%): 'R' suffix denotes reduction pretreatment using a hydrogen (10 vol %) and nitrogen mixture at 300 °C for the generation of metallic Pt (Pt0) sites and simultaneous partial MOF decomposition into carbon- and nitrogen-loaded zirconium dioxide. The prominent role of reduction pretreatment was apparent in benzene oxidation as 1.5%-Pt/UiO-66-NH2 did not exhibit catalytic activity below 175 °C (dry condition). The promotional role of moisture in benzene oxidation by 1.5%-Pt/UiO-66-NH2-R was evident with a rise in the steady-state reaction rate (r) at 110 °C (21 kPa molecular oxygen (O2)) from 1.3 × 10-3 to 5.0 × 10-3 μmol g-1 s-1 as the water (H2O) partial pressure increased from 0 to 1.88 kPa. In contrast, the activity was lowered with increasing RH due to catalyst poisoning by excess moisture (r (110 °C) of 6.6 × 10-04 μmol g-1 s-1 at 2.83 kPa H2O (21 kPa O2)). Kinetic modeling suggests that XB proceeds through the Langmuir-Hinshelwood mechanism on the Pt/UiO-66-NH2-R surface (dissociative O2 chemisorption and the involvement of two oxygen species in benzene oxidation). According to the density functional theory simulation, the carbon and nitrogen impurities are to make the first XB step (i.e., hydrogen migration from the benzene molecule to the substrate) energetically favorable. The second hydrogen atom from the benzene molecule is also extracted effectively, while the oxygen derived from O2 facilitates further XB. The Pt0 sites dissociate the O2 and H2O molecules, while the product of the latter, i.e., free hydrogen and hydroxyl, makes the subsequent XB steps energetically favorable.

Effects of Delaying the Storage of 'Hass' Avocados under a Controlled Atmosphere on Skin Color, Bioactive Compounds and Antioxidant Capacity.

During ripening, 'Hass' avocado skin changes from green to purple/black. Low-temperature storage with a controlled atmosphere (CA) is the most widely used method for avocado storage; however, few studies have simulated this technology and considered the days of regular air (RA) storage prior to CA storage. Herein, the effect of delaying the storage of 'Hass' avocado (>30% dry matter) in a CA was examined. Long-term storage conditions (5 °C for 50 days) corresponded to (i) regular air storage (RA), (ii) CA (4 kPa O2 and 6 kPa CO2) and (iii) 10 days in RA + 40 days in a CA and (iv) 20 days in RA + 30 days in a CA. Evaluations were performed during storage and at the ready-to-eat (RTE) stage. Skin color remained unchanged during storage, but at the RTE stage, more color development was observed for fruits stored under CA conditions, as these fruits were purple/black (>50%). At the RTE stage, the anthocyanin content increased, and compared to fruit under RA, fruit under a CA contained a five-fold greater content. A 20-day delay between harvest and CA storage increased the fruit softening rate and skin color development after cold storage, reducing the effectiveness of CA as a postharvest technology for extending storage life.

Visualizing hydrogen peroxide and nitric oxide dynamics in endothelial cells using multispectral imaging under controlled oxygen conditions

The complex interplay between hydrogen peroxide (H2O2) and nitric oxide (NO) in endothelial cells presents challenges due to technical limitations in simultaneous measurement, hindering the elucidation of their direct relationship. Previous studies have yielded conflicting findings regarding the impact of H2O2 on NO production. To address this problem, we employed genetically encoded biosensors, HyPer7 for H2O2 and geNOps for NO, allowing simultaneous imaging in single endothelial cells. Optimization strategies were implemented to enhance biosensor performance, including camera binning, temperature regulation, and environmental adjustments to mimic physiological normoxia. Our results demonstrate that under ambient oxygen conditions, H2O2 exhibited no significant influence on NO production. Subsequent exploration under physiological normoxia (5 kPa O2) revealed distinct oxidative stress levels characterized by reduced basal HyPer7 signals, enhanced H2O2 scavenging kinetics, and altered responses to pharmacological treatment. Investigation of the relationship between H2O2 and NO under varying oxygen conditions revealed a lack of NO response to H2O2 under hyperoxia (18 kPa O2) but a modest NO response under physiological normoxia (5 kPa O2). Importantly, the NO response was attenuated by l-NAME, suggesting activation of eNOS by endogenous H2O2 generation upon auranofin treatment. Our study highlights the intricate interplay between H2O2 and NO within the endothelial EA.hy926 cell line, emphasizing the necessity for additional research within physiological contexts due to differential response observed under physiological normoxia (5 kPa O2). This further investigation is essential for a comprehensive understanding of the H2O2 and NO signaling considering the physiological effects of ambient O2 levels involved.

Linking red blood cell functional phenotypes to environmental tolerance in high-altitude adapted deer mice

Oxygen (O2) is essential for vertebrate life, and complex cardio-respiratory systems have evolved to transport the gas from the environment to each individual cell. Even short disruptions of this O2 flux can have deleterious effects that are linked to numerous disease states. Animals that have adapted to hypoxic environments, such as deer mice ( Peromyscus maniculatus) native to high altitude, can provide valuable insight into naturally evolved solutions to O2 deprivation. Previous work has shown that high-altitude deer mice have evolved a higher hemoglobin O2 affnity and other coordinated changes across the O2 transport cascade that enable higher metabolic rates in hypoxia. Red blood cells (RBC) are the functional unit of O2 and carbon dioxide transport in the blood and play central roles in matching O2 supply and demand in the microcirculation by releasing signaling molecules such as ATP and gasotransmitters; but how these cellular mechanisms respond to hypoxic environments has not been studied. We hypothesized that high-altitude adaptation in deer mice has improved the function of RBCs for cardiovascular gas transport in hypoxia. Lab-raised breeding colonies of deer-mice were established from wild mice caught at low altitude (~400 m in the Great Plains of Nebraska) and at high altitude (~4300 m in the Rocky Mountains of Colorado). Using a common-garden experimental design, third-generation deer mice from high- and low-altitude populations were acclimated to warm normoxia (21°C, 21 kPa O2) or cold hypobaric hypoxia (5°C, 12 kPa O2) for 8 weeks. Blood samples were collected for measurements of hematocrit, hemoglobin concentration, RBC volume, plasma erythropoietin concentration, RBC contents of membrane transport and channel proteins (anion exchanger, aquaporin 1 and rhesus associated glycoprotein) by immunocytochemistry and western blotting, and carbonic anhydrase activity using biochemical techniques. The release of ATP from RBCs was measured in tonometers at decreasing levels of O2 by luminometry, and the vascular sensitivity to ATP was determined by wire myography on second-order mesenteric arteries. Finally, bone marrow samples were collected from the femurs to measure gene expression levels in the erythropoietic tissue. Our experimental design allowed us to examine the interactive effects of cold hypoxic environments on RBC phenotype, by untangling environmentally-induced plasticity from the signatures of adaptation that are unique to high-altitude natives. This work is providing a better understanding of how RBC function participates in matching cardiovascular O2 supply and demand in extreme hypoxia, which has important applications in animal and human health. This work was supported by a NSERC Canada Banting Postdoctoral Fellowship to TSH and a Discovery Grant to GRS. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Influence of hemoglobin-O2 affnity on aerobic capacity in deer mice

High-altitude hypoxia can constrain tissue O2 supply, and several high-altitude populations and species have evolved adaptations to overcome this challenge. Evolved increases in hemoglobin-O2 (Hb-O2) affnity are pervasive across high-altitude taxa, but the influence of such increases on aerobic capacity (maximal O2 consumption) in hypoxia remains contentious. The influence of Hb-O2 affnity on aerobic capacity in hypoxia could vary depending on other traits in the O2 transport pathway, but this possibility is poorly understood. We examined this issue in deer mice ( Peromyscus maniculatus), which is found from sea level to &gt;4300m altitude in the Rocky Mountains. Mice from populations native to high altitude and low altitude were born and raised to adulthood in captivity. Low-altitude mice (n=14) were acclimated to warm (25°C) normoxia, and high-altitude mice (n=14) were acclimated to cold (5°C) hypoxia (~12 kPa O2) for 6 weeks, creating two groups with very different capacities for O2 transport in hypoxia. Aerobic capacity for thermogenesis (VO2max) was then measured in hypoxia after each of three pharmacological treatments to manipulate Hb-O2 affnity: saline (control); efaproxiral, a negative allosteric regulator that decreases Hb-O2 affnity; and sodium cyanate, which covalently modifies Hb and increases Hb-O2 affnity. In control conditions, high-altitude mice had higher VO2max and arterial O2 saturation (SaO2) in hypoxia and higher Hb-O2 affnity (lower P50) than low-altitude mice. Efaproxiral reduced SaO2 and led to similar decreases in VO2max in both populations. Sodium cyanate increased SaO2 in hypoxia in both populations. However, this was only associated with an increase in VO2max in 7 of 14 high-altitude mice and 4 of 14 low-altitude mice. Our results suggest that Hb-O2 affnity may be optimal for aerobic capacity in hypoxia in high-altitude mice, and that reductions in Hb-O2 affnity reduce performance. Supported by NSERC of Canada. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

The gut microbiome regulates thermogenic performance in high-altitude deer mice

High altitude is one of the most extreme environments inhabited by endotherms, where cold temperatures demand high rates of thermogenesis to maintain body temperature (Tb) but hypoxia constrains aerobic metabolism. Recent findings suggest that the gut microbiome contributes to whole-body thermogenesis, but its significance for coping in cold environments remains poorly understood. We hypothesized that the gut microbiome contributes to adaptive increases in thermogenic performance in deer mice native to high altitude. Mice from populations native to high altitude and low altitude were born and raised to adulthood in common lab conditions. Adults from both populations were then acclimated to warm (25°C) normoxia or cold (5°C) hypoxia (12 kPa O2) for 6 weeks, and a subset of mice in each group were treated with antibiotics to disrupt the gut microbiome. Thermogenic endurance was then measured as the duration that Tb could be maintained during acute cold challenge. Antibiotic treatment strongly diminished thermogenic endurance in highlanders, but led to only minor reductions in thermogenic endurance in lowlanders. These differences could not be fully explained by impairments in aerobic heat production by host thermogenic tissues, because antibiotic treatment had only modest effects on cold-induced increases in O2 consumption rate and the abundance of UCP-1 protein and oxidative phosphorylation complexes in brown adipose tissue. Therefore, our findings suggest that the gut microbiome plays an increased role in regulating thermogenesis in high-altitude deer mice, and that changes in host-microbe interactions contribute to high-altitude adaptation. Funded by NSERC of Canada. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Controlled Atmosphere Storage and Sorbitol Dipping Minimize Chilling Injuries in ‘Palmer’ Mangoes

Our previous studies have shown that ‘Palmer’ mangoes immersed in solutions containing 2.5% sorbitol and stored under a controlled atmosphere (CA) at 8 °C for 30 days had fewer symptoms of a chilling injury. However, there is no information regarding the effectiveness of sorbitol treatment in other atmospheres and/or in combination with lower temperatures. Thus, the objective of this study was to assess the impact of dipping ‘Palmer’ mangoes in 0.1% and 2.5% (w/v) sorbitol solutions and storing the fruit under a CA without atmosphere modification (21 kPa O2 + 0.03 kPa CO2) at 8 °C/95% relative humidity (RH) or with 5 kPa O2 + 5 kPa CO2 at 4 °C/95% RH for 28 days. The fruits were evaluated periodically for chilling injuries, quality, and oxidative metabolism. A chilling injury (CI) was correlated with increased fresh weight loss (FWL) and changes in the color of the epicarp (Lpeel, h°peel, and Cpeel) and mesocarp (L*pulp). Lipid peroxidation (LPpulp and LPpeel) and the hydrogen peroxide content (H2O2peel and H2O2pulp) were associated with the development of a CI, particularly after being transferred to ambient. The treatment with 2.5% sorbitol was more effective in minimizing the chilling injury symptoms and did not compromise the fruit quality, especially when it was stored at 4 °C in association with a CA containing 5 kPa O2 + 5 kPa CO2. This treatment reduced lipid peroxidation and increased the activities of the superoxide dismutase (SOD) and ascorbate peroxidase (APX) enzymes in the epicarp and mesocarp, providing greater cold tolerance. The use of 2.5% sorbitol has been identified as the most efficacious approach for mitigating the adverse impacts of chilling injuries, preserving the fruit quality, and enhancing oxidative metabolism, even at lower temperatures. Thus, this treatment represents a viable alternative for managing chilling injuries in mangoes.

Highland deer mice support increased thermogenesis in response to chronic cold hypoxia by shifting uptake of circulating fatty acids from muscles to brown adipose tissue.

During maximal cold challenge (cold-induced V̇O2,max) in hypoxia, highland deer mice (Peromyscus maniculatus) show higher rates of circulatory fatty acid delivery compared with lowland deer mice. Fatty acid delivery also increases with acclimation to cold hypoxia (CH) and probably plays a major role in supporting the high rates of thermogenesis observed in highland deer mice. However, it is unknown which tissues take up these fatty acids and their relative contribution to thermogenesis. The goal of this study was to determine the uptake of circulating fatty acids into 24 different tissues during hypoxic cold-induced V̇O2,max, by using [1-14C]2-bromopalmitic acid. To uncover evolved and environment-induced changes in fatty acid uptake, we compared lab-born and -raised highland and lowland deer mice, acclimated to either thermoneutral (30°C, 21 kPa O2) or CH (5°C, 12 kPa O2) conditions. During hypoxic cold-induced V̇O2,max, CH-acclimated highlanders decreased muscle fatty acid uptake and increased uptake into brown adipose tissue (BAT) relative to thermoneutral highlanders, a response that was absent in lowlanders. CH acclimation was also associated with increased activities of enzymes citrate synthase and β-hydroxyacyl-CoA dehydrogenase in the BAT of highlanders, and higher levels of fatty acid translocase CD36 (FAT/CD36) in both populations. This is the first study to show that cold-induced fatty acid uptake is distributed across a wide range of tissues. Highland deer mice show plasticity in this fatty acid distribution in response to chronic cold hypoxia, and combined with higher rates of tissue delivery, this contributes to their survival in the cold high alpine environment.

Water film-mediated photocatalytic oxidation of oxalate on TiO2

Water films on minerals under humid environment can be photocatalytic hotspots when exposed to sunlight or artificial sources of ultraviolet (and visible) radiation. In this study, we resolved the water film-mediated photocatalysis of oxalate adsorbed on TiO2 using in situ infrared spectroscopy. We found that 0.5 to 4 monolayer- (ML) thick water films enhanced the photodecomposition rates of oxalate under 21 kPa O2. We explained this through the combined actions of direct hole transfer, ligand-to-metal-charge transfer, as well as the production of hydroxyl radicals and reactive oxygen species. Rates were, however, substantially slower in the absence of O2 because charge recombination, together with water film-mediated charge localization, disrupted hole transfer and hydroxyl radical production. Our work adds insight into the impact of humidity on controlling important photocatalytic processes in nature (drying soils, atmospheric aerosols), and technology (water and air treatment).

Evolved changes in phenotype across skeletal muscles in deer mice native to high altitude.

The cold and hypoxic conditions at high altitude necessitate high metabolic O2 demands to support thermogenesis while hypoxia reduces O2 availability. Skeletal muscles play key roles in thermogenesis, but our appreciation of muscle plasticity and adaptation at high altitude has been hindered by past emphasis on only a small number of muscles. We examined this issue in deer mice (Peromyscus maniculatus). Mice derived from both high-altitude and low-altitude populations were born and raised in captivity and then acclimated as adults to normoxia or hypobaric hypoxia (12 kPa O2 for 6-8 wk). Maximal activities of citrate synthase (CS), cytochrome c oxidase (COX), β-hydroxyacyl-CoA dehydrogenase (HOAD), hexokinase (HK), pyruvate kinase (PK), and lactate dehydrogenase (LDH) were measured in 20 muscles involved in shivering, locomotion, body posture, ventilation, and mastication. Principal components analysis revealed an overall difference in muscle phenotype between populations but no effect of hypoxia acclimation. High-altitude mice had greater activities of mitochondrial enzymes and/or lower activities of PK or LDH across many (but not all) respiratory, limb, core and mastication muscles compared with low-altitude mice. In contrast, chronic hypoxia had very few effects across muscles. Further examination of CS in the gastrocnemius showed that population differences in enzyme activity stemmed from differences in protein abundance and mRNA expression but not from population differences in CS amino acid sequence. Overall, our results suggest that evolved increases in oxidative capacity across many skeletal muscles, at least partially driven by differences in transcriptional regulation, may contribute to high-altitude adaptation in deer mice.NEW & NOTEWORTHY Most previous studies of muscle plasticity and adaptation in high-altitude environments have focused on a very limited number of skeletal muscles. Comparing high-altitude versus low-altitude populations of deer mice, we show that a large number of muscles involved in shivering, locomotion, body posture, ventilation, and mastication exhibit greater mitochondrial enzyme activities in the high-altitude population. Therefore, evolved increases in mitochondrial oxidative capacity across skeletal muscles contribute to high-altitude adaptation.

Dynamic controlled atmosphere monitored by respiratory quotient as a new method to store pears: Effect on the volatile compounds profile and general quality

Pears (Pyrus communis) are climacteric fruit that require storage under appropriate conditions to extend availability and delay ripening. This study evaluated the production of volatile organic compounds (VOCs) and the physicochemical quality of ‘Santa Maria’ and ‘Rocha’ pears after storage in a controlled atmosphere (CA) or dynamic controlled atmosphere (DCA), monitored by respiratory quotient (RQ). The pears, harvested from an orchard in São Joaquim (Santa Catarina State), were stored at − 0.5 °C in CA (2.0 kPa O2) and DCA with RQ levels of 1.1, 1.2, 1.3, and 1.4, all under 1.0 kPa CO2. ‘Santa Maria’ pears were stored for four months, and ‘Rocha’ pears for six months, followed by seven days at 20 °C before quality analysis. Storage of ‘Santa Maria’ pears in CA resulted in fruit with a more yellow skin color, lower flesh firmness, and higher ethylene production, while ‘Rocha’ pears in CA retained higher flesh firmness and produced less ethylene at 4 and 7 days at 20 °C compared to DCA conditions. Storage conditions did not significantly affect soluble solids and acidity. In ‘Rocha’ pears, DCA, regardless of RQ, suppressed the production of butyl acetate, hexyl acetate, pentyl acetate, methyl acetate, and propyl acetate, while in ‘Santa Maria’ pears, esters such as butyl acetate and hexyl acetate were less affected. In conclusion, no significant differences were found between the DCA-RQ levels evaluated in this research in maintaining physicochemical quality and VOCs production. However, DCA suppressed VOCs production in both ‘Santa Maria’ and ‘Rocha’ pears compared with CA storage.

The influence of the summer pruning on ‘Fuji’ apples storage under controlled atmosphere

This study aimed to evaluate the effect of the summer pruning time in ‘Fuji’ apple trees on the quality of fruit at harvest and after storage in controlled atmosphere with extremely low O2 (CA-ELO) (0.5 kPa O2). The treatments evaluated were summer pruning in December, January, and February, in addition to a control treatment (without summer pruning). The experiment was carried out in the 2018/2019 and 2019/2020 growing seasons. The fruit were evaluated at harvest and after eight months of CA-ELO (0.5 kPa O2 + &lt;0.5 kPa CO2/1.5 ± 0.2°C/92 ± 2% RH) storage, at chamber opening, and after 7 days of shelf-life at 23 ± 3°C and 60 ± 5% RH. The quality of the fruit was evaluated through of soluble solids, flesh firmness, titratable acidity, fruit color, and physiological disorder incidence (sunburn and flesh browning), in addition to enzymatic activity and concentration of functional compounds. There was no significant effect of the summer pruning time on fruit flesh firmness, soluble solids, titratable acidity, and rot incidence after storage under CA-ELO plus 7 days of shelf life. Summer pruning in February resulted in fruit with higher peel red color development, which in general contains a higher concentration of functional compounds at harvest (total phenolic compounds and total antioxidant activity), and lower flesh browning incidence in ‘Fuji’ apples stored under CA-ELO. The nitrogen (N) concentration and nitrogen/calcium ratio (N/Ca) in the second growing season were lower in fruit from plants pruned in February, compared to no summer pruning or earlier pruning. The superoxide dismutase and peroxidase enzyme activity were lower in fruit from treatments with summer pruning in January and February, whereas the polyphenol oxidase enzyme activity was lower when summer pruning was conducted in February.

Quality Characteristics, Sensory Profiles and Ethylene Production of Stored ‘Abate Fetel’ Pears Sorted at Harvest by Time-Resolved Reflectance Spectroscopy

Time-resolved reflectance spectroscopy (TRS), a nondestructive technique, can help the industry to provide high-quality fruit to encourage pear consumption. The absorption coefficient measured by TRS at 670 nm (μa670) represents a maturity index for pear fruit, with less mature pears high μa670 and more mature low μa670. The aim of this work was to study the quality characteristics, the sensory profiles and the ethylene production of ‘Abate Fetel’ pears sorted at harvest in different TRS maturity classes and stored in different atmospheres. At harvest, 540 pears were measured by TRS for μa670, ranked by μa670 in three maturity classes (less-LeM, medium-MeM and more-MoM mature) and randomized in nine samples according to 1-MCP treatment (treated, control), storage time (4–6 months) and atmosphere (air-NA; CA: 8–12 kPa O2, 1 kPa CO2). Fruits were examined at harvest and after 7 days of poststorage shelf life for skin color, firmness, soluble solids, acidity and ethylene production and were submitted to sensory analysis. At harvest and after storage, MoM pears were less green and showed a higher SSC content than LeM ones. After storage, MoM pears produced less ethylene and were perceived to be firmer (especially in 1-MCP-treated pears), more astringent and less juicy (when stored for 6 months) than LeM ones.

Monitoring low O2 stress in apples – What we can learn from chlorophyll fluorescence and respiratory characteristics

Dynamic controlled atmosphere (DCA) is becoming a storage method of choice for apple producers seeking to store long-term. There is limited prior work comparing DCA monitoring chlorophyll fluorescence yield (DCA-CF) and respiratory characteristics (DCA-RQ), particularly for the popular UK-grown apple cultivars ‘Gala’ and ‘Braeburn’. However, these techniques can give an insight into the physiological response of apples to low O2 storage, which could help to design more efficient and sustainable storage regimes. In this study the chlorophyll fluorescence (CF) and respiratory quotient (RQ) responses of ‘Gala’ and ‘Braeburn’ are compared in typical and exaggerated DCA conditions. Results show that not only do the two techniques differ in their detection of low O2 stress but the two cultivars studied also differ noticeably in their behaviour. CF increase was confirmed to be a reaction to a stress signal from inside the fruit. Respiration rate curves were found to reflect the internal structure of the fruit, with ‘Gala’’s more homogeneous tissues and greater gas permeability resulting in a strongly bimodal O2 consumption rate where the change in rate hypothetically corresponds with the majority of the fruit tissue switching to anaerobic respiration at the same time. CF and RQ showed noticeable differences between cultivars, agreeing with previous observations that ‘Braeburn’ is less tolerant of low O2 and elevated CO2 than ‘Gala’ (CF Lower O2 Limit (LOL) for Braeburn of approximately 0.75 kPa O2 relative to 0.5 kPa O2 for Gala). Additionally, the CF and RQ responses indicated different LOLs for ‘Gala’, at approximately 0.5 kPa O2 for CF and 0.25 kPa O2 for RQ. Elevated CO2 depressed both the CF and RQ response, with a strong depressive effect on the rate of CO2 evolution but little effect on the rate of O2 consumption.