The utility of far‐infrared illumination in oxygenation dynamics as measured with near‐infrared spectroscopy

Near‐infrared spectroscopy (NIRS) is a noninvasive method for measuring the oxygenation in muscle and other tissues in vivo. For quantitative NIRS measurement of oxygenation dynamics, the vessel‐occlusion test was usually applied as physiological intervention. There are several drawbacks of the vessel‐occlusion method that include skin contact, uncomfortable and microcirculation block of patients. Thus, we propose the far‐infrared (FIR) illumination as a new physiological intervention method in this paper. Our preliminary result shows a linear correlation of oxygenation dynamic signals between FIR illumination and arterial‐occlusion test (AOT) that implies the FIR illumination could be applied for hemodynamic response measurement in clinical diagnosis. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Redistribution of intestinal microcirculatory oxygenation during acute hemodilution in pigs.

Acute normovolemic hemodilution (ANH) compromizes intestinal microcirculatory oxygenation; however, the underlying mechanisms are incompletely understood. We hypothesized that contributors herein include redistribution of oxygen away from the intestines and shunting of oxygen within the intestines. The latter may be due to the impaired ability of erythrocytes to off-load oxygen within the microcirculation, thus yielding low tissue/plasma Po(2) but elevated microcirculatory hemoglobin oxygen (HbO(2)) saturations. Alternatively, oxygen shunting may also be due to reduced erythrocyte deformability, hindering the ability of erythrocytes to enter capillaries. Anesthetized pigs underwent ANH (20, 40, 60, and 90 ml/kg hydroxyethyl starch; ANH group: n = 10; controls: n = 5). We measured systemic and mesenteric perfusion. Microvascular intestinal oxygenation was measured independently by remission spectrophotometry [microcirculatory HbO(2) saturation (muHbO(2))] and palladium-porphyrin phosphorescence quenching [microcirculatory oxygen pressure in plasma/tissue (muPo(2))]. Microcirculatory oxygen shunting was assessed as the disparity between mucosal and mesenteric venous HbO(2) saturation (HbO(2)-gap). Erythrocyte deformability was measured as shear stress-induced cell elongation (LORCA difractometer). ANH reduced hemoglobin concentration from 8.1 to 2.2 g/dl. Relative mesenteric perfusion decreased (decreased mesenteric/systemic perfusion fraction). A paralleled reduction occurred in mucosal muHbO(2) (68 +/- 2 to 41 +/- 3%) and muPo(2) (28 +/- 1 to 17 +/- 1 Torr). Thus the proposed constellation indicative for oxygen off-load deficits (sustained muHbO(2) at decreased muPo(2)) did not develop. A twofold increase in the HbO(2)-gap indicated increasing intestinal microcirculatory oxygen shunting. Significant impairment in erythrocyte deformability developed during ANH. We conclude that reduced intestinal oxygenation during ANH is, in addition to redistribution of oxygen delivery away from the intestines, associated with oxygen shunting within the intestines. This shunting appears to be not primarily caused by oxygen off-load deficit but rather by oxygen/erythrocytes bypassing capillaries, wherein a potential contributor is impaired erythrocyte deformability.     

Protein–cofactor binding and ultrafast electron transfer in riboflavin binding protein under the spatial confinement of nanoscopic reverse micelles

In this contribution, we study the effect of confinement on the ultrafast electron transfer (ET) dynamics of riboflavin binding protein (RBP) to the bound cofactor riboflavin (Rf, vitamin B2), an important metabolic process, in anionic sodium bis(2‐ethylhexyl) sulfosuccinate reverse micelles (AOT‐RMs) of various hydration levels. Notably, in addition to excluded volume effect, various nonspecific interactions like ionic charge of the confining surface can influence the biochemical reactions in the confined environment of the cell. To this end, we have also studied the ET dynamics of RBP–Rf complex under the confinement of a cationic hexadecyltrimethylammonium bromide (CTAB) RMs with similar water pool size to the anionic AOT‐RMs towards simulating equal restricted volume effect. It has been found that the spatial confinement of RBP in the AOT‐RM of w₀ = 10 leads to the loss of its tertiary structure and hence vitamin binding capacity. Although, RBP regains its binding capacity and tertiary structure in AOT‐RMs of w₀ ≥20 due to its complete hydration, the ultrafast ET from RBP to Rf merely occurs in such systems. However, to our surprise, the ET process is found to occur in cationic CTAB‐RMs of similar volume restriction. It is found that under the spatial confinement of anionic AOT‐RM, the isoalloxazine ring of Rf is improperly placed in the protein nanospace so that ET between RBP and Rf is not permitted. This anomaly in the binding behaviour of Rf to RBP in AOT‐RMs is believed to be the influence of repulsive potential of the anionic AOT‐RM surface to the protein. Our finding thus suggests that under similar size restriction, both the hydration and surface charge of the confining volume could have major implication in the intraprotein ET dynamics in real cellular environments. Copyright © 2013 John Wiley & Sons, Ltd.     

Extraction of monoclonal antibodies (IgG1) using anionic and anionic/nonionic reverse micelles

Purification schemes for antibody production based on affinity chromatography are trying to keep pace with increases in cell culture expression levels and many current research initiatives are focused on finding alternatives to chromatography for the purification of Monoclonal antibodies (MAbs). In this article, we have investigated an alternative separation technique based on liquid–liquid extraction called the reverse micellar extraction. We extracted MAb (IgG1) using reverse micelles of an anionic surfactant, sodium bis 2‐ethyl‐hexyl sulfosuccinate (AOT) and a combination of anionic (AOT) and nonionic surfactants (Brij‐30, Tween‐85, Span‐85) using isooctane as the solvent system. The extraction efficiency of IgG1 was studied by varying parameters, such as pH of the aqueous phase, cation concentration, and type and surfactant concentration. Using the AOT/Isooctane reverse micellar system, we could achieve good overall extraction of IgG1 (between 80 and 90%), but only 30% of the bioactivity of IgG1 could be recovered at the end of the extraction by using its binding to affinity chromatography columns as a surrogate measure of activity. As anionic surfactants were suspected as being one of the reasons for the reduced activity, we decided to combine a nonionic surfactant with an anionic surfactant and then study its effect on the extraction efficiency and bioactivity. The best results were obtained using an AOT/Brij‐30/Isooctane reverse micellar system, which gave an overall extraction above 90 and 59% overall activity recovery. An AOT/Tween‐85/Isooctane reverse micellar system gave an overall extraction of between 75 and 80% and overall activity recovery of around 40–45%. The results showed that the activity recovery of IgG1 can be significantly enhanced using different surfactant combination systems, and if the recovery of IgG1 can be further enhanced, the technique shows considerable promise for the downstream purification of MAbs. © 2010 American Institute of Chemical Engineers Biotechnol. Prog., 2010     

Microvascular and mitochondrial PO2 simultaneously measured by oxygen‐dependent delayed luminescence

Measurement of tissue oxygenation is a complex task and various techniques have led to a wide range of tissue PO₂ values and contradictory results. Tissue is compartmentalized in microcirculation, interstitium and intracellular space and current techniques are biased towards a certain compartment. Simultaneous oxygen measurements in various compartments might be of great benefit for our understanding of determinants of tissue oxygenation. Here we report simultaneous measurement of microvascular PO₂ (μPO₂) and mitochondrial PO₂ (mitoPO₂) in rats. The μPO₂ measurements are based on oxygen‐dependent quenching of phosphorescence of the near‐infrared phosphor Oxyphor G2. The mitoPO₂ measurements are based on oxygen‐dependent quenching of delayed fluorescence of protoporphyrin IX (PpIX). Favorable spectral properties of these porphyrins allow simultaneous measurement of the delayed luminescence lifetimes. A dedicated fiber‐based time‐domain setup consisting of a tunable pulsed laser, 2 red‐sensitive gated photomultiplier tubes and a simultaneous sampling data‐acquisition system is described in detail. The absence of cross talk between the channels is shown and the feasibility of simultaneous μPO₂ and mitoPO₂ measurements is demonstrated in rat liver in vivo. It is anticipated that this novel approach will greatly contribute to our understanding of tissue oxygenation in physiological and pathological circumstances. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Ischaemia‐related cell damage in extracorporeal preserved tissue – new findings with a novel perfusion model

Tissue undergoing free transfer in transplant or reconstructive surgery always is at high risk of ischaemia‐related cell damage. This study aims at assessing different procedures using an extracorporeal perfusion and oxygenation system to investigate the expression of hypoxia inducible factor (HIF)‐1‐α as marker for hypoxia and of the pro‐apoptotic protein Caspase‐3 in skeletal muscle to elucidate potential improvements in tissue conservation. Twenty‐four porcine rectus abdominis muscles were assigned to five different groups and examined after they had been extracorporeally preserved for 60 min. time. Group I was left untreated (control), group II was perfused with a cardioplegic solution, group III was flushed with 10 ml of a cardioplegic solution and then left untreated. Group IV and V were perfused and oxygenated with either an isotone crystalloid solution or a cardioplegic solution. Among others, immunohistochemistry (Caspase‐3 and HIF‐1‐α) of muscle samples was performed. Furthermore, oxygen partial pressure in the perfusate at the arterial and venous branch was measured. Expression of Caspase‐3 after 60 min. was reduced in all groups compared to the control group. Furthermore, all groups (except group III) expressed less HIF‐1‐α than the control group. Oxygenation leads to higher oxygen levels at the venous branch compared to groups without oxygenation. Using an extracorporeal perfusion and oxygenation system cell damage could be reduced as indicated by stabilized expressions of Caspase‐3 and HIF‐1‐α for 60 min. of tissue preservation. Complete depletion of oxygen at the venous branch can be prevented by oxygenation of the perfusate with ambient air.     

Effects of compression on muscle tissue oxygenation at the onset of exercise

The effects of compression on gastrocnemius medialis muscle oxygenation and hemodynamics during a short-term dynamic exercise was investigated in a sample of 15 male subjects (mean ± SD; age 25.8 ± 4.9 years; mass 70.6 ± 4.3 kg). Elastic compression sleeves were used to apply multiple levels of compression to the calf muscles during exercise, and noncompressive garments were used for the control condition. Tissue hemoglobin oxygen saturation was measured as the relative "tissue oxygen index" (TOI) with a near-infrared spectrometer. The recovery of TOI during exercise was determined from the slope of oxygenation recovery in a nonoccluded situation. The TOI recovery rate during the first 2 minutes of the exercise was 24% higher (p = 0.042) for the compression condition than for the control condition. A significant correlation (r = 0.61, p = 0.012) between the level of compression and the tissue oxygenation recovery during exercise was observed. Muscle energy use was determined from the rate of decline of TOI immediately upon arterial occlusion during early exercise. Muscle energy use measured during the occluded situation was not significantly influenced by compression. Based on these results, it was concluded that compression induced changes in tissue blood flow and perfusion appear to result in improved oxygenation during short-term exercise. Assuming that increased muscle oxygen availability positively influences performance, compression of muscles may enhance performance especially in sports that require repeated short bouts of exercise.     

Correlations between 31P-NMR spectroscopy and tissue O2 tension measurements in a murine fibrosarcoma

Size-dependent changes in therapeutically relevant and interrelated metabolic parameters of a murine fibrosarcoma (FSaII) were investigated in vivo using conscious (unanesthetized) animals and tumor sizes less than or equal to 2% of body weight. Tumor pH and bioenergetics were evaluated by 31P nuclear magnetic resonance spectroscopy (31P-MRS), and tumor tissue oxygen tension (pO2) distribution was examined using O2-sensitive needle electrodes. During growth FSaII tumors showed a progressive loss of phosphocreatine (PCr) and nucleoside triphosphate (NTP) with increasing inorganic phosphate (Pi) and phosphomonoester (PME) signals. Ratios for PCr/Pi, PME/Pi, NTP/Pi, and phosphodiester/inorganic phosphate (PDE/Pi) as well as pH determined by 31P-NMR (pHNMR) and the mean tissue pO2 progressively declined as the tumors increased in size. The only relevant ratio increasing with tumor growth was PME/NTP. When the mean tissue pO2 value was plotted against pHNMR, NTP/Pi, PCr/Pi, PME/Pi, and PDE/Pi for tumor groups of similar mean volumes, a highly significant positive correlation was observed. There was a negative correlation between mean tumor tissue pO2 values and PME/NTP. From these results we concluded that 31P-MRS can detect changes in tumor bioenergetics brought about by changes in tumor oxygenation. Furthermore, the close correlation between oxygenation and energy status suggests that the microcirculation in FSaII tumors yields an O2-limited energy metabolism. Finally, a correlation between the proportion of pO2 readings between 0 and 2.5 mmHg and the radiobiologically hypoxic cell fraction in FSaII tumors was observed. The latter finding might be of particular importance for radiation therapy.     

Intraoperative multispectral and hyperspectral label‐free imaging: A systematic review of in vivo clinical studies

Multispectral and hyperspectral imaging (HSI) are emerging optical imaging techniques with the potential to transform the way surgery is performed but it is not clear whether current systems are capable of delivering real‐time tissue characterization and surgical guidance. We conducted a systematic review of surgical in vivo label‐free multispectral and HSI systems that have been assessed intraoperatively in adult patients, published over a 10‐year period to May 2018. We analysed 14 studies including 8 different HSI systems. Current in‐vivo HSI systems generate an intraoperative tissue oxygenation map or enable tumour detection. Intraoperative tissue oxygenation measurements may help to predict those patients at risk of postoperative complications and in‐vivo intraoperative tissue characterization may be performed with high specificity and sensitivity. All systems utilized a line‐scanning or wavelength‐scanning method but the spectral range and number of spectral bands employed varied significantly between studies and according to the system's clinical aim. The time to acquire a hyperspectral cube dataset ranged between 5 and 30 seconds. No safety concerns were reported in any studies. A small number of studies have demonstrated the capabilities of intraoperative in‐vivo label‐free HSI but further work is needed to fully integrate it into the current surgical workflow.      

Decrease of transport of some polyols in sickle cells

This paper reports the results of kinetic studies on the inward net-flux of small non-electrolytes (ethylene glycol, glycerol and erythritol) in sickle cells as compared to normal erythrocytes. Net transport rates were evaluated by turbidimetric measurements for ethylene glycol and glycerol and by hematocrit monitoring for erythritol. A 2-fold and 4-fold reduction in the permeability coefficient for ethylene glycol and glycerol, respectively, were found in sickle cells as compared to normal erythrocytes. In contrast, no significant changes in erythritol transport kinetics were observed. The dependence of glycerol permeability on temperature, pH and oxygenation is the same in both types of cells. A significant correlation was observed between glycerol permeability and cell density only for sickle cells. The results indicate that irreversible modifications of membrane proteins, responsible for the glycerol and ethylene glycol transport, do occur in sickle cells.     

A modular NIRS system for clinical measurement of impaired skeletal muscle oxygenation.

Near-infrared spectrometry (NIRS) is a well-known method used to measure in vivo tissue oxygenation and hemodynamics. This method is used to derive relative measures of hemoglobin (Hb) + myoglobin (Mb) oxygenation and total Hb (tHb) accumulation from measurements of optical attenuation at discrete wavelengths. We present the design and validation of a new NIRS oxygenation analyzer for the measurement of muscle oxygenation kinetics. This design optimizes optical sensitivity and detector wavelength flexibility while minimizing component and construction costs. Using in vitro validations, we demonstrate 1) general optical linearity, 2) system stability, and 3) measurement accuracy for isolated Hb. Using in vivo validations, we demonstrate 1) expected oxygenation changes during ischemia and reactive hyperemia, 2) expected oxygenation changes during muscle exercise, 3) a close correlation between changes in oxyhemoglobin and oxymyoglobin and changes in deoxyhemoglobin and deoxymyoglobin and limb volume by venous occlusion plethysmography, and 4) a minimal contribution from movement artifact on the detected signals. We also demonstrate the ability of this system to detect abnormal patterns of tissue oxygenation in a well-characterized patient with a deficiency of skeletal muscle coenzyme Q(10). We conclude that this is a valid system design for the precise, accurate, and sensitive detection of changes in bulk skeletal muscle oxygenation, can be constructed economically, and can be used diagnostically in patients with disorders of skeletal muscle energy metabolism.     

Erythrocyte-associated transients in PO2 revealed in capillaries of rat mesentery

Mathematical models have predicted the existence of Po(2) gradients between erythrocytes in capillaries in the usual case where plasma contributes substantial resistance to oxygen diffusion. According to theoretical predictions, these gradients could be detected as rapid Po(2) fluctuations (erythrocyte-associated transients, EATs) along the capillary. However, verification of a model and correct choice of its parameters can be made only on the basis of direct experimental measurements. We used phosphorescence quenching microscopy to measure Po(2) in 52 capillaries of rat mesentery to obtain plasma Po(2) values 100 times/s at a given point along a capillary. A 532-nm laser generated 10-micros pulses of light, concentrated by a x100 objective, onto a spot 0.9 microm in diameter. The presence of erythrocytes in the excitation region was detected on the basis of phosphorescence amplitude (PA), proportional to the amount of plasma encountered by the laser beam, and on the basis of the intensity of transmitted laser light (LT), detected by a photodiode placed under the capillary. The data revealed correlated waveforms in PA, LT, and Po(2) in capillaries. The magnitude of the Po(2) gradients between erythrocytes and plasma was correlated with average capillary Po(2). EATs in Po(2) were more readily detected in capillaries with relatively low oxygenation. The correlation coefficients between PA and Po(2) for the half of the capillaries (n = 26) below the median Po(2) (mean Po(2) = 17 mmHg; R = -0.72) was higher than that for the other half (mean Po(2) = 39 mmHg; R = -0.38). These results support the theoretical predictions of EATs and plasma Po(2) gradients in capillaries.     

Protein extraction by Winsor‐III microemulsion systems

Proteins (bovine serum albumin (BSA), α‐chymotrypsin, cytochrome c, and lysozyme) were extracted from 0.5 to 2.0 g L^?1 aqueous solution by adding an equal volume of isooctane solution that contained a surfactant mixture (Aerosol‐OT, or AOT, and a 1,3‐dioxolane (or cyclic ketal) alkyl ethoxylate, CK‐2,13‐E_5.6), producing a three‐phase (Winsor‐III) microemulsion with a middle, bicontinuous microemulsion, phase highly concentrated in protein (5–13 g L^?1) and small in volume (12–20% of entire volume). Greater than 90% forward extraction was achieved within a few minutes. Robust W‐III microemulsion systems were formulated at 40°C, or at 25°C by including a surfactant with shorter ethoxylate length, CK‐2,13‐E₃, or 1.5% NaCl (aq). Successful forward extraction correlated with high partitioning of AOT in the middle phase (>95%). The driving force for forward extraction was mainly electrostatic attractions imposed by the anionic surfactant AOT, with the exception of BSA at high ionic strength, which interacted via hydrophobic interactions. Through use of aqueous stripping solutions of high ionic strength (5.0 wt %) and/or pH 12.0 (to negate the electrostatic attractive driving force), cytochrome c and α‐chymotrypsin were back extracted from the middle phase at >75% by mass, with the specific activity of recovered α‐chymotrypsin being >90% of its original value. © 2011 American Institute of Chemical Engineers Biotechnol. Prog., 2011     

Determination of phenol using an enhanced chemiluminescent assay

Enhanced chemiluminescence (ECL) describes the phenomenon of increased light output in the luminol oxidation reaction catalysed by horseradish peroxidase (HRP) in the presence of certain compounds, such as para‐iodophenol. In this work, the effects of phenol on the para‐iodophenol‐enhanced HRP‐catalysed chemiluninescent reaction intensity in an aqueous buffer (Tris–HCl buffer, pH 8.5) and in a surfactant–water–octane mixture were compared. Preincubation of HRP at low phenol concentrations stimulated the chemiluminescent intensity in the assay performed in an aqueous buffer, but did not have significant effect in the sodium bis(2‐ethylhexyl)sulphosuccinate) (Aerosol OT, AOT) applied system. It was also observed that HRP preincubation with phenol concentration higher than 0.003 mg/mL produced an inhibitory effect on the enzyme activity for both assay systems. Only an inhibitory effect of phenol on the chemiluminescent intensity in the surfactant system in octane (as organic solvent) was observed. Three assays were developed to determine phenol concentration in water and in an organic solvent mixture. The detection limits were 0.006, 0.003 and 0.0005 mg/mL, respectively, for the buffer‐containing system, the AOT‐applied system with phenol standard solutions in water and for the AOT‐applied system with phenol standard solutions in octane. Copyright © 2002 John Wiley & Sons, Ltd.     

Effect of oxygen consumption by measuring method on PO2 transients associated with the passage of erythrocytes in capillaries of rat mesentery

Mathematical models have predicted the existence of Po(2) gradients between erythrocytes in capillaries in the usual case where plasma contributes substantial resistance to oxygen diffusion. According to theoretical predictions, these gradients could be detected as rapid Po(2) fluctuations (erythrocyte-associated transients, EATs) along the capillary. However, verification of a model and correct choice of its parameters can be made only on the basis of direct experimental measurements. We used phosphorescence quenching microscopy to measure Po(2) in 52 capillaries of rat mesentery to obtain plasma Po(2) values 100 times/s at a given point along a capillary. A 532-nm laser generated 10-mus pulses of light, concentrated by a x100 objective, onto a spot 0.9 mum in diameter. The presence of erythrocytes in the excitation region was detected on the basis of phosphorescence amplitude (PA), proportional to the amount of plasma encountered by the laser beam, and on the basis of the intensity of transmitted laser light (LT), detected by a photodiode placed under the capillary. The data revealed correlated waveforms in PA, LT, and Po(2) in capillaries. The magnitude of the Po(2) gradients between erythrocytes and plasma was correlated with average capillary Po(2). EATs in Po(2) were more readily detected in capillaries with relatively low oxygenation. The correlation coefficients between PA and Po(2) for the half of the capillaries (n = 26) below the median Po(2) (mean Po(2) = 17 mmHg; R = -0.72) was higher than that for the other half (mean Po(2) = 39 mmHg; R = -0.38). These results support the theoretical predictions of EATs and plasma Po(2) gradients in capillaries.     

Cerebral oxygenation is highly sensitive to blood pressure variability in sick preterm infants

Objectives

The significance of blood pressure variability (BPV) for cerebral oxygenation in extremely preterm infants has not been explored, though BPV may well be associated with end organ injury. We hypothesized that increased BPV in sick preterm infants, by exceeding the cerebral autoregulatory capacity, is associated with cerebral oxygenation changes which closely follow the blood pressure fluctuations. We assessed the autoregulatory capacity in the early postnatal period, by determining the correlation between BPV (mmHg²) and coherence of mean arterial blood pressure (MABP mmHg) and cerebral oxygenation (tissue oxygenation index, TOI %).

Study Design

Thirty-two preterm infants of mean gestational age of 26.3 (±1.5) weeks were studied on the first 3 postnatal days. Spectral analysis (Coherence and transfer-function gain analysis) was used to calculate coherence of MABP and TOI; BPV was quantified using power spectral density of MABP.

Results

Overall, maximum Coherence showed a trend for positive correlation with BPV (n = 32, p = 0.06). Infants identified as clinically unstable with documented brain injury (n = 7) had high Coherence values at low BPV. Separate analysis of stable infants (excluding the 7 critically ill infants) revealed a significant association between maximum Coherence and BPV (n = 25, p = 0.006).

Conclusions

Fluctuation in cerebral oxygenation is closely associated with increased BPV in preterm infants undergoing intensive care. Moreover, in the critically sick preterm infant, blood pressure-dependent variations in cerebral oxygenation occur even with relatively lower BPV, suggesting they have severely impaired autoregulation, and placing them at greater vulnerability to cerebral injury arising from blood pressure fluctuations.     

Remote photonic sensing of cerebral hemodynamic changes via temporal spatial analysis of acoustic vibrations

A novel photonic method for remote monitoring of task‐related hemodynamic changes in human brain activation is presented. Physiological processes associated with neural activity, such as nano‐vibrations due to blood flow and tissue oxygenation in the brain, are detected by remote sensing of nano‐acoustic vibrations using temporal spatial analysis of defocused self‐interference random patterns. Temporal nanometric changes of the speckle pattern due to visual task‐induced hemodynamic responses were tracked by this method. Reversing visual checkerboard stimulation alternated with rest epochs, and responsive signals were identified in occipital lobe using near‐infrared spectroscopy. Temporal vibrations associated with these hemodynamic response functions were observed using three different approaches: (a) single spot illumination at active and control areas simultaneously, (b) subspots cross‐correlation‐based analysis, and (c) multiwavelength measurement using a magnitude‐squared wavelet coherence function. Findings show remote sensing of task‐specific neural activity in the human brain.     

Recruitment rates exhibit high elasticity and high temporal variation in populations of a short-lived perennial herb

Empirical studies for different life histories have shown an inverse relationship between elasticity (i.e. the proportional contribution to population growth rate) and temporal variation in vital rates. It is accepted that this relationship indicates the effect of selective pressures in reducing variation in those life‐history traits with a major impact on fitness. In this paper, we sought to determine whether changes in environmental conditions affect the relationship between elasticity of vital rates and their temporal variation, and whether vital rates with simultaneously large elasticity and temporal variation might represent a characteristic life‐history strategy. We used demographic data on 13 populations of the short‐lived Hypericum cumulicola over 5–6 years, in three time‐since‐fire classes. For each population of each time‐since‐fire, we computed the mean matrix over years and its respective elasticity matrix, and the coefficients of variation in matrix entries over study years as an estimate of temporal variability. We found that mean elasticity negatively significantly correlated with temporal variation in vital rates in populations (overall eight out of 13) included in each time‐since‐fire. However, seedling recruitment exhibited both high elasticity and high temporal variation in almost all study populations. These results indicated that (1) the general relationship between elasticity and temporal variation in vital rates was not modified by environmental changes due to time‐since‐fire, and (2) high elasticity and high temporal variation in seedling recruitment in H. cumulicola is a particular trait of the species' life history. After seed survival in the soil seed bank, seedling recruitment represents the most important life‐history trait influencing H. cumulicola population growth rate (and fitness). The high temporal variability in seedling recruitment suggests that this trait is determined by environmental cues, leading to an increase in population size and subsequent replenishment of the seed bank in favorable years.     

Effects of ozone on zinc and cadmium accumulation in wheat – dose–response functions and relationship with protein,grain yield,and harvest index

Response functions for the effect of ozone on cadmium (Cd) (toxic to humans) and zinc (Zn) (essential nutrient for plants and humans) in wheat grain were derived for the first time. Data from four open‐top chamber (OTC) experiments with field‐grown wheat, performed in southwest Sweden, were used. Ozone exposure was expressed as the phytotoxic ozone dose above a threshold of 6 nmol/m² per sec (POD₆), and AOT40. Grain Zn concentration was significantly enhanced by ozone, while Zn yield was not affected. The positive ozone effect on grain Zn concentration was almost twice as large as the corresponding effect on grain protein concentration, most likely as a result of nitrogen availability being more limiting than Zn availability. Cd concentration was unaffected by ozone, but Cd yield was significantly negatively affected. For the variables studied, correlation was stronger with POD₆ than AOT40, but in several cases, for example, for Zn concentration and Cd yield, there was practically no difference in the performance between the two exposure indices. From the literature, it is obvious that ozone has important adverse effects on wheat yield and certain quality traits. As shown in this study, there are also examples of ozone leading to improved quality, for example, in terms of enhanced Zn concentration of wheat grain. While OTC enclosure did not affect Zn accumulation in wheat grain, Cd accumulation was significantly positively affected, most likely through transpiration being enhanced by the OTC environment, promoting Cd uptake and transport through the plant.