The pathophysiology of 'happy' hypoxemia in COVID-19

The novel coronavirus disease 2019 (COVID-19) pandemic is a global crisis, challenging healthcare systems worldwide. Many patients present with a remarkable disconnect in rest between profound hypoxemia yet without proportional signs of respiratory distress (i.e. happy hypoxemia) and rapid deterioration can occur. This particular clinical presentation in COVID-19 patients contrasts with the experience of physicians usually treating critically ill patients in respiratory failure and ensuring timely referral to the intensive care unit can, therefore, be challenging. A thorough understanding of the pathophysiological determinants of respiratory drive and hypoxemia may promote a more complete comprehension of a patient's clinical presentation and management. Preserved oxygen saturation despite low partial pressure of oxygen in arterial blood samples occur, due to leftward shift of the oxyhemoglobin dissociation curve induced by hypoxemia-driven hyperventilation as well as possible direct viral interactions with hemoglobin. Ventilation-perfusion mismatch, ranging from shunts to alveolar dead space ventilation, is the central hallmark and offers various therapeutic targets.

Factors associated with acute kidney injury in acute respiratory distress syndrome

Background

Acute kidney injury (AKI) is the most frequent extra-pulmonary organ failure in acute respiratory distress syndrome (ARDS). The objective of this study was to assess the factors associated with the development and severity of AKI in patients with ARDS.

Methods

This is a retrospective cohort study of ARDS patients without acute or chronic kidney disease prior to the onset of ARDS over a 7-year period (2010–2017). AKI and severity of AKI were defined according to the Kidney Disease Improving Global Outcomes 2012 guidelines.

Results

Of the 634 ARDS patients, 357 patients met study criteria. A total of 244 (68.3%) patients developed AKI after ARDS onset: 60 (24.6%) had stage I AKI, 66 (27%) had stage II AKI, and 118 (48.4%) had stage III AKI. The median time of AKI onset for stage I AKI was 2 days (interquartile range, 1.5–5.5) while stage II and III AKI was 4 days. On multivariable analysis, factors associated with development of AKI were age [subdistribution hazard ratio (SHR) 1.01, 95% confidence interval (CI) 1.00–1.02], SOFA score (SHR 1.16, 95%CI 1.12–1.21), a history of diabetes mellitus (DM) (SHR 1.42, 95%CI 1.07–1.89), and arterial pH on day 1 of ARDS (SHR per 0.1 units decrease was 1.18, 95%CI 1.05–1.32). In severity of AKI, stage I AKI was associated with age (SHR 1.03, 95%CI 1.01–1.05) and serum bicarbonate on day 1 of ARDS (SHR 1.07, 95%CI 1.02–1.13). Stage II AKI was associated with age (SHR 1.03, 95%CI 1.01–1.05), serum bicarbonate on day 1 (SHR 1.12, 95%CI 1.06–1.18), SOFA score (SHR 1.19, 95%CI 1.10–1.30), history of heart failure (SHR 3.71, 95%CI 1.63–8.46), and peak airway pressure (SHR 1.04, 95%CI 1.00–1.07). Stage III AKI was associated with a higher BMI (SHR 1.02, 95%CI 1.00–1.03), a history of DM (SHR 1.79, 95%CI 1.18–2.72), SOFA score (SHR 1.29, 95%CI 1.22–1.36), and arterial pH on day 1 (SHR per 0.1 units decrease was 1.25, 95%CI 1.05–1.49).

Conclusions

Age, a higher severity of illness, a history of diabetes, and acidosis were associated with development of AKI in ARDS patients. Severity of AKI was further associated with BMI, history of heart failure, and peak airway pressure.

Electronic supplementary material

The online version of this article (10.1186/s13613-019-0552-5) contains supplementary material, which is available to authorized users.

Leaf area accumulation helps juvenile evergreen trees tolerate shade in a temperate rainforest

Most knowledge of the physiological correlates of interspecific variation in shade tolerance derives from studies of first-year seedlings in artificial environments. The present study relates growth, allocation, foliage turnover, biomass distribution and gas exchange traits to low-light survival of large seedlings (20-100 cm tall) of eight temperate rainforest evergreens under field conditions. Taxa for which natural mortality was not observed in low light during the 14-month study are referred to here as "shade-tolerant" species, and those which did die in the shade are referred to as "light-demanding" species. In low light (2-5% canopy openness), shade-tolerant species had slightly lower light compensation points than light-demanders. Light-demanding species had more plastic aboveground allocation patterns, generally allocating proportionally less aboveground biomass to foliage production than shade-tolerant associates in high light (>10% canopy openness), but more in low light. Foliage turnover was generally much slower in shade-tolerant species (10-40% year^-1) than in light-demanding species (30-190%). As these differences in leaf retention outweighed variation in allocation, shade-tolerant species displayed higher leaf areas at all light levels. Furthermore, all shade-tolerant species gained leaf area in low light during the study period, whereas light-demanding taxa showed leaf area declines. Higher leaf area ratios, plus differences in light compensation points, indicate that large seedlings of shade-tolerant evergreens enjoy net carbon gain advantages over light-demanding associates in low light. However, minimal growth rate differences in low light imply higher storage allocation in shade-tolerant species. This study provides a rather different picture from that which has emerged from recent reviews of first-year seedling data, illustrating the long-term consequences of foliage turnover differences for biomass distribution, and suggesting that shade tolerance in juvenile evergreen trees is associated with a suite of traits which enhance net carbon gain, but not growth, in low light. Accumulation of a large foliage area through long leaf retention times is probably a key mechanism enhancing low-light carbon gain in evergreens.

Lung morphometry: the link between structure and function

The study of the structural basis of gas exchange function in the lung depends on the availability of quantitative information that concerns the structures establishing contact between the air in the alveoli and the blood in the alveolar capillaries, which can be entered into physiological equations for predicting oxygen uptake. This information is provided by morphometric studies involving stereological methods and allows estimates of the pulmonary diffusing capacity of the human lung that agree, in experimental studies, with the maximal oxygen consumption. The basis for this "machine lung" structure lies in the complex design of the cells building an extensive air-blood barrier with minimal cell mass.

The Effects of Aging on Lung Structure and Function

Growth of the segment of the population older than 65 years has led to intensified interest in understanding the biology of aging. This article is focused on age-related alterations in lung structure that produce predictable changes in physiologic function, both at rest and during exercise. Increased insight into the physiology of the healthy aging lung should ultimately lead to improved methods of lung function assessment in the elderly (defined as those older than 65 years) as well as better understanding of the manifestations and possibly even the treatment of geriatric lung disease.

Aquaporins and membrane diffusion of CO2 in living organisms

BACKGROUND

Determination of CO2 diffusion rates in living cells revealed inconsistencies with existing models about the mechanisms of membrane gas transport. Mainly, these discrepancies exist in the determined CO2 diffusion rates of bio-membranes, which were orders of magnitudes below those for pure lipid bilayers or theoretical considerations as well as in the observation that membrane insertion of specific aquaporins was rescuing high CO2 transport rates. This effect was confirmed by functional aquaporin protein analysis in heterologous expression systems as well as in bacteria, plants and partly in mammals.

SCOPE OF REVIEW

This review summarizes the arguments in favor of and against aquaporin facilitated membrane diffusion of CO2 and reports about its importance for the physiology of living organisms.

MAJOR CONCLUSIONS

Most likely, the aquaporin tetramer forming an additional fifth pore is required for CO2 diffusion facilitation. Aquaporin tetramer formation, membrane integration and disintegration could provide a mechanism for regulation of cellular CO2 exchange. The physiological importance of aquaporin mediated CO2 membrane diffusion could be shown for plants and cyanobacteria and partly for mammals.

GENERAL SIGNIFICANCE

Taking the mentioned results into account, consequences for our current picture of cell membrane transport emerge. It appears that in some or many instances, membranes might not be as permeable as it was suggested by current bio-membrane models, opening an additional way of controlling the cellular influx or efflux of volatile substances like CO2. This article is part of a Special Issue entitled Aquaporins.

Omega-3 polyunsaturated fatty acids in critically ill patients with acute respiratory distress syndrome: A systematic review and meta-analysis

OBJECTIVE

Acute respiratory distress syndrome (ARDS) is characterized by an acute inflammatory response in the lung parenchyma leading to severe hypoxemia. Because of its anti-inflammatory and immunomodulatory properties, omega-3 polyunsaturated fatty acids (ω-3 PUFA) have been administered to ARDS patients, mostly by the enteral route, as immune-enhancing diets with eicosapentaenoic acid, γ-linolenic acid, and antioxidants. However, clinical benefits of ω-3 PUFAs in ARDS patients remain unclear because clinical trials have found conflicting results. Considering the most recent randomized controlled trials (RCTs) and recent change in administration strategies, the aim of this updated systematic review and meta-analysis was to evaluate clinical benefits of ω-3 PUFA administration on gas exchange and clinical outcomes in ARDS patients.

METHODS

We searched for RCTs conducted in intensive care unit (ICU) patients with ARDS comparing the administration of ω-3 PUFAs to placebo. The outcomes assessed were PaO2-to-FiO2 ratio evaluated early (3-4 d) and later (7-8 d), mortality, ICU and hospital length of stay (LOS), length of mechanical ventilation (MV), and infectious complications. Two independent reviewers assessed eligibility, risk of bias, and abstracted data. Data were pooled using a random effect model to estimate the relative risk or weighted mean difference (WMD).

RESULTS

Twelve RCTs (n = 1280 patients) met our inclusion criteria. Omega-3 PUFAs administration was associated with a significant improvement in early PaO2-to-FiO2 ratio (WMD = 49.33; 95% confidence interval [CI] 20.88-77.78; P = 0.0007; I2 = 69%), which persisted at days 7 to 8 (WMD = 27.87; 95% CI 0.75-54.99; P = 0.04; I2 = 57%). There was a trend in those receiving ω-3 PUFA toward reduced ICU LOS (P = 0.08) and duration of MV (P = 0.06), whereas mortality, hospital LOS, and infectious complications remained unchanged. Continuous enteral infusion was associated with reduced mortality (P = 0.02), whereas analysis restricted to enteral administration either with or without bolus found improved early PaO2 and FiO2 (P = 0.001) and MV duration (P = 0.03). Trials at higher risk of bias had a significant reduction in mortality (P = 0.04), and improvement in late PaO2-to-FiO2 ratio (P = 0.003).

CONCLUSIONS

In critically ill patients with ARDS, ω-3 PUFAs in enteral immunomodulatory diets may be associated with an improvement in early and late PaO2-to-FiO2 ratio, and statistical trends exist for an improved ICU LOS and MV duration. Considering these results, administering ω-3 PUFAs appears a reasonable strategy in ARDS.

Triose phosphate utilization and beyond: from photosynthesis to end product synthesis

During photosynthesis, plants fix CO2 from the atmosphere onto ribulose-bisphosphate, producing 3-phosphoglycerate, which is reduced to triose phosphates (TPs). The TPs are then converted into the end products of photosynthesis. When a plant is photosynthesizing very quickly, it may not be possible to commit photosynthate to end products as fast as it is produced, causing a decrease in available phosphate and limiting the rate of photosynthesis to the rate of triose phosphate utilization (TPU). The occurrence of an observable TPU limitation is highly variable based on species and especially growth conditions, with TPU capacity seemingly regulated to be in slight excess of typical photosynthetic rates the plant might experience. The physiological effects of TPU limitation are discussed with an emphasis on interactions between the Calvin-Benson cycle and the light reactions. Methods for detecting TPU-limited data from gas exchange data are detailed and the impact on modeling of some physiological effects are shown. Special consideration is given to common misconceptions about TPU.

Control of breathing and the circulation in high-altitude mammals and birds

Hypoxia is an unremitting stressor at high altitudes that places a premium on oxygen transport by the respiratory and cardiovascular systems. Phenotypic plasticity and genotypic adaptation at various steps in the O2 cascade could help offset the effects of hypoxia on cellular O2 supply in high-altitude natives. In this review, we will discuss the unique mechanisms by which ventilation, cardiac output, and blood flow are controlled in high-altitude mammals and birds. Acclimatization to high altitudes leads to some changes in respiratory and cardiovascular control that increase O2 transport in hypoxia (e.g., ventilatory acclimatization to hypoxia). However, acclimatization or development in hypoxia can also modify cardiorespiratory control in ways that are maladaptive for O2 transport. Hypoxia responses that arose as short-term solutions to O2 deprivation (e.g., peripheral vasoconstriction) or regional variation in O2 levels in the lungs (i.e., hypoxic pulmonary vasoconstriction) are detrimental at in chronic high-altitude hypoxia. Evolved changes in cardiorespiratory control have arisen in many high-altitude taxa, including increases in effective ventilation, attenuation of hypoxic pulmonary vasoconstriction, and changes in catecholamine sensitivity of the heart and systemic vasculature. Parallel evolution of some of these changes in independent highland lineages supports their adaptive significance. Much less is known about the genomic bases and potential interactive effects of adaptation, acclimatization, developmental plasticity, and trans-generational epigenetic transfer on cardiorespiratory control. Future work to understand these various influences on breathing and circulation in high-altitude natives will help elucidate how complex physiological systems can be pushed to their limits to maintain cellular function in hypoxia.

The impact of arbuscular mycorrhizal fungi in mitigating salt-induced adverse effects in sweet basil (Ocimum basilicum L.)

Salinity is one of the serious abiotic stresses adversely affecting the majority of arable lands worldwide, limiting the crop productivity of most of the economically important crops. Sweet basil (Osmium basilicum) plants were grown in a non-saline soil (EC = 0.64 dS m^-1), in low saline soil (EC = 5 dS m^-1), and in a high saline soil (EC = 10 dS m^-1). There were differences between arbuscular mycorrhizal (Glomus deserticola) colonized plants (+AMF) and non-colonized plants (-AMF). Mycorrhiza mitigated the reduction of K, P and Ca uptake due to salinity. The balance between K/Na and between Ca/Na was improved in +AMF plants. Growth enhancement by mycorrhiza was independent from plant phosphorus content under high salinity levels. Different growth parameters, salt stress tolerance and accumulation of proline content were investigated, these results showed that the use of mycorrhizal inoculum (AMF) was able to enhance the productivity of sweet basil plants under salinity conditions. Mycorrhizal inoculation significantly increased chlorophyll content and water use efficiency under salinity stress. The sweet basil plants appeared to have high dependency on AMF which improved plant growth, photosynthetic efficiency, gas exchange and water use efficiency under salinity stress. In this study, there was evidence that colonization with AMF can alleviate the detrimental salinity stress influence on the growth and productivity of sweet basil plants.

Melatonin enhances drought resistance by regulating leaf stomatal behaviour, root growth and catalase activity in two contrasting rapeseed (Brassica napus L.) genotypes

Two contrasting rapeseed (Brassica napus L.) genotypes, Qinyou 8 (drought-sensitive) and Q2 (drought-tolerant), were studied under drought stress with or without pretreatment with melatonin to (i) explore whether melatonin enhances drought resistance by regulating root growth and (ii) determine the relationship between the belowground and aboveground responses to melatonin under drought stress. Results show that the light-saturated rate of photosynthesis (P_n), stomatal conductance (g_s), water use efficiency (WUE) and chlorophyll content were decreased by drought for Qinyou 8, whereas drought only decreased P_n and chlorophyll content for Q2. Drought decreased actual photochemical efficiency in saturated light (F_v'/F_m'), actual photochemical efficiency (PhiPSⅡ), quenching of photochemical efficiency (qL) and electron transport rate (ETR) in Qinyou 8. However drought only decreased F_v'/F_m' and qL in Q2. Drought increased malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) contents in the roots of both genotypes. Melatonin had no significant additional effects on root guaiacol peroxidase (POD) and superoxide dismutase (SOD) activities, but enhanced root catalase (CAT) activity of droughted plants further. Melatonin promoted taproot and lateral root growth under drought stress. Melatonin also promoted stomatal opening resulting in enhanced photosynthesis in the two genotypes. The two mechanisms induced by melatonin synergistically enhance drought resistance of rapeseed as indicated by enhanced gas exchange parameters under melatonin pretreatment. The findings provide evidence for a physiological role of melatonin in improving drought resistance, especially in belowground parts.

Comparative ecophysiology of five species of Sedum (Crassulaceae) under well-watered and drought-stressed conditions

Gas exchange patterns, diurnal malic acid fluctuations, and stable carbon isotope ratios of five species of Sedum were investigated to assess the ecophysiological characteristics of three different photosynthetic pathways under well-watered and drought-stressed conditions. All five species have succulent leaves and stems and were examined under identical environmental conditions. When well-watered, Sedum integrifolium (Raf.) Nels. and S. ternatum Michx. displayed C₃ photosynthesis, S. telephioides Michx. and S. nuttallianum Raf. exhibited CAM-cycling, and S. wrightii A. Gray showed CAM. When grown under a less frequent watering regime, S. integrifolium and S. ternatum exhibited CAM-cycling, whereas S. telephioides and S. nuttallianum displayed CAM-cycling simultaneously with low-level CAM. Sedum wrightii retained its CAM mode of photosynthesis. In general, leaf δ¹³C values reflected these variations in photosynthetic pathways. While all values of water-use efficiency (WUE) were greater than those reported for most C₃ and C₄ species, no correlation of malic acid accumulation in the CAM and CAM-cycling (including low-level CAM) species with increased WUE was found. Sedum wrightii (CAM) had the highest WUE value at night, yet its 24-h WUE was not different from S. ternatum when the latter was in the C₃ mode. Thus, relative water-use efficiencies of these species of Sedum were not predictable based on photosynthetic pathways alone.

Phyto-management of chromium contaminated soils through sunflower under exogenously applied 5-aminolevulinic acid

Soil contamination with heavy metals is threatening the food security around the globe. Chromium (Cr) contamination results in poor quality and reduction in yield of crops. The present research was performed to figure out the Cr toxicity in sunflower and the ameliorative role of 5-aminolevulinic acid (ALA) as a plant growth regulator. The sunflower (FH-614) was grown under increasing concentration of Cr (0, 5, 10 and 20mgkg^-1) alone and/or in combination with 5-ALA (0, 10 and 20mgL^-1). Results showed that Cr suppressed the overall growth, biomass, gas exchange attributes and chlorophyll content of sunflower plants. Moreover, lower levels of Cr (5 and 10mgkg^-1) increased the production of reactive oxygen species (ROS) and electrolyte leakage (EL) along with the activities of antioxidant enzymes i.e., superoxide dismutase (SOD), guaiacole peroxidase (POD), ascorbate (APX), catalase (CAT). But at higher concentration of Cr (20mgkg^-1), the activities of these enzymes presented a declining trend. However, the addition of 5-ALA significantly alleviated the Cr-induced toxicity in sunflower plant and enhanced the plant growth and biomass parameters along with increased chlorophyll content, gas exchange attributes, soluble proteins and soil plant analysis development (SPAD) values by scavenging the ROS and lowering down the EL. The 5-ALA also enhanced the activities of antioxidant enzymes at all levels of Cr. The increase in Cr concentration in all plant parts such as leaf, root and stem was directly proportional to the Cr concentration in soil. The application of 5-ALA further enhanced the uptake of Cr and its concentration in the plants. To understand this variation in response of plants to 5-ALA, detailed studies are required on plant biochemistry and genetic modifications.

Growth, water and nitrogen relations in grassland model ecosystems of the semi-arid Negev of Israel exposed to elevated CO2

Are ecosystems in dry regions particularly responsive to atmospheric CO₂ enrichment? We studied responses of semi-arid grassland assemblages from the northern Negev (Israel) to CO₂ concentrations representative of the pre-industrial era, and early and mid to late 21st century (280, 440, and 600 µl l^-1, respectively). Communities of 32 mostly annual species were grown for a full season in large containers (ca 400 kg each) on native soil and under a simulated winter climate of the northern Negev. Ecosystem water relations were monitored weekly by wheeling containers onto a large electronic freight balance. Evapotranspiration was lower and soil water content was higher at elevated atmospheric CO₂. Deep soil drainage was increased, thus reducing the amount of applied rainwater that was effectively captured by the model ecosystems at elevated CO₂. At peak season, midday net ecosystem CO₂ exchange increased with rising CO₂ concentration, whereas nighttime exchange was not significantly affected. Aboveground biomass was 7% greater at 440 µl l^-1 and 17% greater at 600 µl l^-1 compared to 280 µl l^-1 CO₂. Reproductive output at the end of the season was increased by 10% and 24% at the two elevated CO₂ concentrations. Shoot nitrogen concentration was slightly reduced (significantly for grasses), but the total plant nitrogen pool reflected the biomass gain and was increased. While some responses, such as water savings and plant nitrogen pool, were more pronounced across the higher (440-600 µl l^-1) than across the lower CO₂ (280-440 µl l^-1) interval, total plant biomass (above- plus belowground) was already CO₂ saturated at 440 µl l^-1 (14% increase over biomass at 280 µl l^-1). Surprisingly, the biomass, reproduction, and nitrogen responses at the community level were largely caused by a single legume species (Onobrychis crista-galli), with the other five legume species contributing less, and most grasses, non-leguminous forbs, and geophytes hardly responding to elevated CO₂. Overall, responses were relatively small, despite the fact that we compared elevated to pre-industrial concentrations of CO₂. This contrasts with our original assumption that ecosystems in seasonally dry regions will be particularly responsive to elevated CO₂. Impacts of CO₂ enrichment on soil moisture depletion and biomass production in semi-arid ecosystems will largely depend on the net effect of reduced water use (evapotranspiration) versus increased water loss (deep drainage and runoff), and on the presence of certain species. In this case, 1 out of 32 species was responsible for most of the effects at the community level.

Foliar application of nanoparticles mitigates the chilling effect on photosynthesis and photoprotection in sugarcane

Chilling is one of the main abiotic stresses that adversely affect the productivity of sugarcane, in marginal tropical regions where chilling incidence occurs with seasonal changes. However, nanoparticles (NPs) have been tested as a mitigation strategy against diverse abiotic stresses. In this study, NPs such as silicon dioxide (nSiO₂; 5-15 nm), zinc oxide (nZnO; <100 nm), selenium (nSe; 100 mesh), graphene (graphene nanoribbons [GNRs] alkyl functionalized; 2-15 μm × 40-250 nm) were applied as foliar sprays on sugarcane leaves to understand the amelioration effect of NPs against negative impact of chilling stress on photosynthesis and photoprotection. To this end, seedlings of moderately chilling tolerant sugarcane variety Guitang 49 was used for current study and spilt plot was used as statistical design. The changes in the level chilling tolerance after the application of NPs on Guitang 49 were compared with tolerance level of chilling tolerant variety Guitang 28. NPs treatments reduced the adverse effects of chilling by maintaining the maximum photochemical efficiency of PSII (F_v/F_m), maximum photo-oxidizable PSI (P_m), and photosynthetic gas exchange. Furthermore, application of NPs increased the content of light harvesting pigments (chlorophylls and cartinoids) in NPs treated seedlings. Higher carotenoid accumulation in leaves of NPs treated seedlings enhanced the nonphotochemical quenching (NPQ) of PSII. Among the NPs, nSiO₂ showed higher amelioration effects and it can be used alone or in combination with other NPs to mitigate chilling stress in sugarcane.

Inoculation with arbuscular mycorrhizal fungi alleviates harmful effects of drought stress on damask rose

This study was conducted to examine the role of arbuscular mycorrhiza fungi (AMF) in alleviating the adverse effects of drought stress on damask rose (Rosa damascena Mill.) plants. Four levels of drought stress (100, 75, 50, and 25% FC) were examined on mycorrhizal and non-mycorrhizal plants in pots filled with sterilized soil. Our results showed that increasing drought stress level decreased all growth parameters, nutrient contents, gas exchange parameters, and water relations indicators. Under different levels of drought stress, mycorrhizal colonization significantly increased all studied parameters. P n, g s, and E of the mycorrhizal plants was higher than those of non-mycorrhizal plants under different levels of drought stress. The increase in those rates was proportional the level of the mycorrhizal colonization in the roots of these plants. Majority of growth, nutrition, water status and photosynthetic parameters had a great dependency on the mycorrhizal colonization under all levels of drought stress. The results obtained in this study provide a clear evidence that AMF colonization can enhance growth, flower quality and adaptation of rose plants under different drought stress levels, particularly at high level of drought stress via improving their water relations and photosynthetic status. It could be concluded that colonization with AMF could help plants to tolerate the harmful effects caused by drought stress in arid and semi-arid regions.

QTLs for stomatal and photosynthetic traits related to salinity tolerance in barley

BACKGROUND

Stomata regulate photosynthesis and transpiration, and these processes are critical for plant responses to abiotic stresses such as salinity. A barley double haploid population with 108 lines derived from a cross between CM72 (salt-tolerant) and Gairdner (salt-sensitive) was used to detect quantitative trait loci (QTLs) associated with stomatal and photosynthetic traits related to salinity tolerance.

RESULTS

A total of 11 significant QTLs (LOD > 3.0) and 11 tentative QTLs (2.5 < LOD < 3.0) were identified. These QTLs are distributed on all the seven chromosomes, except 5H and explain 9.5-17.3% of the phenotypic variation. QTLs for biomass, intercellular CO2 concentration, transpiration rate and stomatal conductance under control conditions co-localised together. A QTL for biomass also co-located with one for transpiration rate under salinity stress. A linkage was found between stomatal pore area and gas exchange. A QTL for salinity tolerance also co-localised with QTLs for grain yield and biomass on chromosome 3H. Based on the draft barley genome, the candidate genes for salinity tolerance at this locus are proposed.

CONCLUSIONS

The lack of major QTLs for gas exchange and stomatal traits under control and saline conditions indicates a complex relationship between salinity and leaf gas exchange due to the fact that these complex quantitative traits are under the control of multiple genes.

Particulate matter on foliage of Betula pendula, Quercus robur, and Tilia cordata: deposition and ecophysiology

Trees in urban and industrial areas significantly help to limit the amount of particulate matter (PM) suspended in the air, but PM has a negative impact on their life. The amount of PM gathered on leaves depends on quantity, size, and morphology of leaves and can also be increased by the presence of epicuticular waxes, in which PM can become stuck or immersed. In this study, we determined the ability of PM to accumulate on leaves in relation to the species of tree and PM source. We tested saplings of three common European tree species (Betula pendula, Quercus robur, and Tilia cordata) by experimentally polluting them with PM from different sources (cement, construction, and roadside PM), and then assessing the effects of PM on plant growth and ecophysiology. In all studied species, we have found two types of PM accumulation: a layer on the leaf surface and an in-wax layer. Results showed that the studied species accumulate PM on their leaf blade, reducing the efficiency of its photosynthetic apparatus, which in a broader sense can be considered a reduction in the plants' normal functioning. Saplings of Q. robur suffered the least, whereas B. pendula (especially photosynthetic rate and conductivity) and T. cordata (especially increase in leader shoot length) exhibited greater negative effects. The foliage of B. pendula collected the most PM, followed by Q. robur, and then T. cordata, regardless of the dust's source. All tested species showed a tendency for higher wax production when growing under PM pollution stress. We believe that, potentially, B. pendula best enhances the quality of the PM-contaminated environment; however, faster leaf fall, reduced productivity, and worse quality of wood should be considered in urban forest management.

Chlorophyll, anthocyanin, and gas exchange changes assessed by spectroradiometry in Fragaria chiloensis under salt stress

Chlorophyll and anthocyanin contents provide a valuable indicator of the status of a plant's physiology, but to be more widely utilized it needs to be assessed easily and non-destructively. This is particularly evident in terms of assessing and exploiting germplasm for plant-breeding programs. We report, for the first time, experiments with Fragaria chiloensis (L.) Duch. and the estimation of the effects of response to salinity stress (0, 30, and 60 mmol NaCl/L) in terms of these pigments content and gas exchange. It is shown that both pigments (which interestingly, themselves show a high correlation) give a good indication of stress response. Both pigments can be accurately predicted using spectral reflectance indices (SRI); however, the accuracy of the predictions was slightly improved using multilinear regression analysis models and genetic algorithm analysis. Specifically for chlorophyll content, unlike other species, the use of published SRI gave better indications of stress response than Normalized Difference Vegetation Index. The effect of salt on gas exchange is only evident at the highest concentration and some SRI gave better prediction performance than the known Photochemical Reflectance Index. This information will therefore be useful for identifying tolerant genotypes to salt stress for incorporation in breeding programs.

Influence of sunflecks on the δ 13 C of Adenocaulon bicolor plants occurring in contrasting forest understory microsites

Leaf characteristics and carbon isotope ratios (δ¹³C) of Adenocaulon bicolor were examined in the understory of a redwood forest along a gradient of microsites that differed in the amount of direct (sunfleck) photon flux density. Comparisons were made between plants that had been shaded from sunflecks with shadow bands but still received diffuse light, and adjacent plants that received both sunflecks and diffuse light. The δ¹³C of the shaded plants were 1.2‰ lower than predicted from the intercellular CO₂ pressure (p_i), probably because of recycling of respired CO₂ in the understory. Plants receiving sunflecks had higher δ¹³C values because assimilation during sunflecks occurred at a lower p_i than assimilation in diffuse light. The amount that their δ¹³C was higher was positively correlated with predicted direct photon flux density received by a plant. Leaf weight per unit area increased with increasing PFD. Although plants receiving sunflecks had greater leaf weights per unit area and photosynthetic capacities than those under shadow bands, there was no apparent acclimation of photosynthetic capacity to the differences in PFD among the microsites.

Incorporating Lung Diffusing Capacity for Carbon Monoxide in Clinical Decision Making in Chest Medicine

Lung diffusing capacity for carbon monoxide (Dlco) remains the only noninvasive pulmonary function test to provide an integrated picture of gas exchange efficiency in human lungs. Due to its critical dependence on the accessible "alveolar" volume (Va), there remains substantial misunderstanding on the interpretation of Dlco and the diffusion coefficient (Dlco/Va ratio, Kco). This article presents the physiologic and methodologic foundations of Dlco measurement. A clinically friendly approach for Dlco interpretation that takes those caveats into consideration is outlined. The clinical scenarios in which Dlco can effectively assist the chest physician are discussed and illustrative clinical cases are presented.

NaCl-induced physiological and biochemical adaptative mechanisms in the ornamental Myrtus communis L. plants

Physiological and biochemical changes in Myrtus communis L. plants after being subjected to different solutions of NaCl (44, and 88 mM) for up to 30 days (Phase I) and after recovery from the salinity period (Phase II) were studied. Myrtle plants showed salinity tolerance by displaying a series of adaptative mechanisms to cope with salt-stress, including controlled ion homeostasis, the increase in root/shoot ratio, the reduction of water potentials and stomatal conductance to limit water loss. In addition, they displayed different strategies to protect the photosynthetic machinery, including limiting toxic ion accumulation in leaves, increase in chlorophyll content, and changes in chlorophyll fluorescence parameters, leaf anatomy and increases in catalase activity. Anatomical modifications in leaves, including a decrease in spongy parenchyma and increased intercellular spaces, allow CO2 diffusion in a situation of reduced stomatal aperture. In spite of all these changes, salinity produced oxidative stress in myrtle plants as monitored by increases in oxidative stress parameter values. The post-recovery period is perceived as a new stress situation, as observed through effects on plant growth and alterations in non-photochemical quenching parameters and lipid peroxidation values.

Responses of leaf gas exchange attributes, photosynthetic pigments and antioxidant enzymes in NaCl-stressed cotton (Gossypium hirsutum L.) seedlings to exogenous glycine betaine and salicylic acid

BACKGROUND

Application of exogenous glycine betaine (GB) and exogenous salicylic acid (SA) mitigates the adverse effects of salinity. Foliar spraying with exogenous GB or SA alleviates salt stress in plants by increasing leaf gas exchange and stimulating antioxidant enzyme activity. The effects of foliar application of exogenous GB and SA on the physiology and biochemistry of cotton seedlings subjected to salt stress remain unclear.

RESULTS

Results showed that salt stress of 150 mM NaCl significantly reduced leaf gas exchange and chlorophyll fluorescence and decreased photosynthetic pigment quantities and leaf relative water content. Foliar spray concentrations of 5.0 mM exogenous GB and 1.0 mM exogenous SA promoted gas exchange and fluorescence in cotton seedlings, increased quantities of chlorophyll pigments, and stimulated the antioxidant enzyme activity. The foliar spray also increased leaf relative water content and endogenous GB and SA content in comparison with the salt-stressed only control. Despite the salt-induced increase in antioxidant enzyme content, exogenous GB and SA in experimental concentrations significantly increased the activity of glutathione reductase, ascorbate peroxidase, superoxide dismutase, catalase and peroxidase, and decreased malondialdehyde content under salt stress. Across all experimental foliar spray GB and SA concentrations, the photochemical efficiency of photosystem II (FV/FM) reached a peak at a concentration of 5.0 mM GB. The net photosynthetic rate (Pn) and FV/FM were positively correlated with chlorophyll a and chlorophyll b content in response to foliar spraying of exogenous GB and SA under salt stress.

CONCLUSIONS

We concluded, from our results, that concentrations of 5.0 mM GB or 1.0 mM SA are optimal choices for mitigating NaCl-induced damage in cotton seedlings because they promote leaf photosynthesis, increase quantities of photosynthetic pigments, and stimulate antioxidant enzyme activity. Among, 5.0 mM GB and 1.0 mM SA, the best performance in enhancing endogenous GB and SA concentrations was obtained with the foliar application of 1.0 mM SA under salt stress.

High-throughput field phenotyping using hyperspectral reflectance and partial least squares regression (PLSR) reveals genetic modifications to photosynthetic capacity

Spectroscopy is becoming an increasingly powerful tool to alleviate the challenges of traditional measurements of key plant traits at the leaf, canopy, and ecosystem scales. Spectroscopic methods often rely on statistical approaches to reduce data redundancy and enhance useful prediction of physiological traits. Given the mechanistic uncertainty of spectroscopic techniques, genetic modification of plant biochemical pathways may affect reflectance spectra causing predictive models to lose power. The objectives of this research were to assess over two separate years, whether a predictive model can represent natural and imposed variation in leaf photosynthetic potential for different crop cultivars and genetically modified plants, to assess the interannual capabilities of a partial least square regression (PLSR) model, and to determine whether leaf N is a dominant driver of photosynthesis in PLSR models. In 2016, a PLSR analysis of reflectance spectra coupled with gas exchange data was used to build predictive models for photosynthetic parameters including maximum carboxylation rate of Rubisco (V _c,max ), maximum electron transport rate (J _max ) and percentage leaf nitrogen ([N]). The model was developed for wild type and genetically modified plants that represent a wide range of photosynthetic capacities. Results show that hyperspectral reflectance accurately predicted V _c,max, J _max and [N] for all plants measured in 2016. Applying these PLSR models to plants grown in 2017 resulted in a strong predictive ability relative to gas exchange measurements for V _c,max, but not for J _max, and not for genotypes unique to 2017. Building a new model including data collected in 2017 resulted in more robust predictions, with R² increases of 17% for V _c,max . and 13% J _max . Plants generally have a positive correlation between leaf nitrogen and photosynthesis, however, tobacco with reduced Rubisco (SSuD) had significantly higher [N] despite much lower V _c,max. The PLSR model was able to accurately predict both lower V _c,max and higher leaf [N] for this genotype suggesting that the spectral based estimates of V _c,max and leaf nitrogen [N] are independent. These results suggest that the PLSR model can be applied across years, but only to genotypes used to build the model and that the actual mechanism measured with the PLSR technique is not directly related to leaf [N]. The success of the leaf-scale analysis suggests that similar approaches may be successful at the canopy and ecosystem scales but to use these methods across years and between genotypes at any scale, application of accurately populated physical based models based on radiative transfer principles may be required.

ECCO2R therapy in the ICU: consensus of a European round table meeting

Background

With recent advances in technology, patients with acute respiratory distress syndrome (ARDS) and severe acute exacerbations of chronic obstructive pulmonary disease (ae-COPD) could benefit from extracorporeal CO₂ removal (ECCO₂R). However, current evidence in these indications is limited. A European ECCO₂R Expert Round Table Meeting was convened to further explore the potential for this treatment approach.

Methods

A modified Delphi-based method was used to collate European experts’ views to better understand how ECCO₂R therapy is applied, identify how patients are selected and how treatment decisions are made, as well as to identify any points of consensus.

Results

Fourteen participants were selected based on known clinical expertise in critical care and in providing respiratory support with ECCO₂R or extracorporeal membrane oxygenation. ARDS was considered the primary indication for ECCO₂R therapy (n = 7), while 3 participants considered ae-COPD the primary indication. The group agreed that the primary treatment goal of ECCO₂R therapy in patients with ARDS was to apply ultra-protective lung ventilation via managing CO₂ levels. Driving pressure (≥ 14 cmH₂O) followed by plateau pressure (P_plat; ≥ 25 cmH₂O) was considered the most important criteria for ECCO₂R initiation. Key treatment targets for patients with ARDS undergoing ECCO₂R included pH (> 7.30), respiratory rate (< 25 or < 20 breaths/min), driving pressure (< 14 cmH₂O) and P_plat (< 25 cmH₂O). In ae-COPD, there was consensus that, in patients at risk of non-invasive ventilation (NIV) failure, no decrease in PaCO₂ and no decrease in respiratory rate were key criteria for initiating ECCO₂R therapy. Key treatment targets in ae-COPD were patient comfort, pH (> 7.30–7.35), respiratory rate (< 20–25 breaths/min), decrease of PaCO₂ (by 10–20%), weaning from NIV, decrease in HCO₃⁻ and maintaining haemodynamic stability. Consensus was reached on weaning protocols for both indications. Anticoagulation with intravenous unfractionated heparin was the strategy preferred by the group.

Conclusions

Insights from this group of experienced physicians suggest that ECCO₂R therapy may be an effective supportive treatment for adults with ARDS or ae-COPD. Further evidence from randomised clinical trials and/or high-quality prospective studies is needed to better guide decision making.