Active Transport of Inorganic Carbon Increases the Rate of O(2) Photoreduction by the Cyanobacterium Synechococcus UTEX 625

Chlorophyll a fluorescence of Synechococcus UTEX 625 was quenched during the transport of inorganic carbon, even when CO₂ fixation was inhibited by iodoacetamide. Measurements with a pulse modulation fluorometer showed that at least 75% of the quenching was due to oxidation of Q_a, the primary acceptor of photosystem II. Mass spectrometry revealed that transport of inorganic carbon increased the rate of O₂ photoreduction. Hence, O₂ could serve as an electron acceptor to allow oxidation of Q_a even in the absence of CO₂ fixation.     

Influence of bio-optical parameter variability on the reflectance peak position in the red band of algal bloom waters

On the basis of field measurements, the quantitatively different relationships of peak position in the red band of the remote sensing reflectance vs. Chl concentration are found in the bloom waters of the diatom Skeletonema costatum and the dinoflagellate Prorocentrum donghaiense in coastal areas of the East China Sea. Model simulations of remote sensing reflectance, R_rs, accounting for the influence of variations in the bio-optical parameters such as chlorophyll fluorescence quantum efficiency, Φ, and specific absorption coefficient, a_ph^⁎, are carried out to analyze the characteristics of this spectral peak. The strong effect of fluorescence on the magnitude of R_rs results in the inhibition of the shift of the peak to longer wavelengths, increasing Φ enhances this effect. Increasing a_ph^⁎, specifically in the red-wavelength band, causes a sharper shift in the red peak position by decreasing the effect of the fluorescence. The dominant parameter governing the slope of the shift is a_ph^⁎. The analysis indicates that the higher a_ph^⁎ of S. costatum in the red region is primarily responsible for the much higher slope of the peak shift than for that of P. donghaiense. We show that the relationship between the peak position and Chl concentration may be useful for discriminating S. costatum blooms from those due to P. donghaiense, although information about chlorophyll fluorescence quantum efficiency should be included. Finally, we show that using the band ratio R_rs(708 nm)/R_rs(665 nm) instead of Chl in the relationship with peak position can be useful for the practical identification of S. costatum blooms from hyperspectral measurements of remote sensing reflectance.     

First results obtained with a sweeping pulsed radar reflectometer in the Globus-M tokamak

A weeping pulsed radar reflectometer designed for measuring the spatial electron density distribution in the Globus-M spherical tokamak with a minor plasma radius of a=24 cm, a major radius of R=36 cm, a toroidal field of B _T=0.5 T, a plasma current of I _p=200 kA, and an average density of n=(3–10)×10¹³ cm^?3 is described. The reflectometer operation is based on the reflection of microwaves with a carrier frequency f from a plasma layer with the critical density n=(0.0111f)², where n is the electron density in units of 10¹⁴ cm^?3 and f is the microwave frequency in GHz. By simultaneously probing the plasma at different frequencies, it is possible to recover the electron density profile. Microwave pulses with different frequencies are obtained by frequency sweeping. To increase the range of measured densities, channels with fixed frequencies are also used; as a result, the instrument has eleven frequency channels: a 19.5-GHz channel, eight channels in the 26-to 40-GHz frequency range, a 51.5-GHz channel, and a 60-GHz channel, which corresponds to eleven points in the density profile: 0.47×10¹³ cm^?3, eight points in the (0.8–1.95)×10¹³-cm^?3 range, 3.27×10¹³ cm^?3, and 4.5×10¹³ cm^?3. The reflectometer allows detailed measurements of the density profile with a time resolution of several tens of microseconds, which can be useful, in particular, in studying the processes related to the formation of an internal transport barrier in plasma. The first results obtained using this reflectometer in the Globus-M tokamak under various operating conditions are discussed.     

Detection and Quantification of Snow Algae with an Airborne Imaging Spectrometer

We describe spectral reflectance measurements of snow containing the snow alga Chlamydomonas nivalis and a model to retrieve snow algal concentrations from airborne imaging spectrometer data. Because cells of C. nivalis absorb at specific wavelengths in regions indicative of carotenoids (astaxanthin esters, lutein, β-carotene) and chlorophylls a and b, the spectral signature of snow containing C. nivalis is distinct from that of snow without algae. The spectral reflectance of snow containing C. nivalis is separable from that of snow without algae due to carotenoid absorption in the wavelength range from 0.4 to 0.58 μm and chlorophyll a and b absorption in the wavelength range from 0.6 to 0.7 μm. The integral of the scaled chlorophyll a and b absorption feature (I_0.68) varies with algal concentration (C_a). Using the relationship C_a = 81019.2 I_0.68 + 845.2, we inverted Airborne Visible Infrared Imaging Spectrometer reflectance data collected in the Tioga Pass region of the Sierra Nevada in California to determine algal concentration. For the 5.5-km² region imaged, the mean algal concentration was 1,306 cells ml⁻¹, the standard deviation was 1,740 cells ml⁻¹, and the coefficient of variation was 1.33. The retrieved spatial distribution was consistent with observations made in the field. From the spatial estimates of algal concentration, we calculated a total imaged algal biomass of 16.55 kg for the 0.495-km² snow-covered area, which gave an areal biomass concentration of 0.033 g/m².     

Reflectance Variation within the In-Chlorophyll Centre Waveband for Robust Retrieval of Leaf Chlorophyll Content

The in-chlorophyll centre waveband (ICCW) (640–680 nm) is the specific chlorophyll (Chl) absorption band, but the reflectance in this band has not been used as an optimal index for non-destructive determination of plant Chl content in recent decades. This study develops a new spectral index based solely on the ICCW for robust retrieval of leaf Chl content for the first time. A glasshouse experiment for solution-culture of one chlorophyll-deficient rice mutant and six wild types of rice genotypes was conducted, and the leaf reflectance (400–900 nm) was measured with a high spectral resolution (1 nm) spectrophotometer and the contents of chlorophyll a (Chla), chlorophyll b (Chlb) and chlorophyll a+b (Chlt) of the rice leaves were determined. It was found that the reflectance curves from 640 nm to 674 nm and from 675 nm to 680 nm of the low-chlorophyll mutant leaf were drastically steeper than that of the wild types in the ICCW. The new index based on the reflectance variation within ICCW, the difference of the first derivative sum within the ICCW (DFDS_ICCW), was highly sensitive (r = −0.77, n = 93, P<0.01) to Chlt while the mean reflectance (R_ICCW) in the ICCW became insensitive (r = −0.12, n = 93, P>0.05) to Chlt when the leaf Chlt was higher than 200 mg/m². The best equations of R-ICCW and DFDS_ICCW yielded an RMSE of 78.7, 32.9 and 107.3 mg/m², and an RMSE of 37.4, 16.0 and 45.3 mg/m⁻², respectively, for predicting Chla, Chlb and Chlt. The new index could rank in the top 10 for prediction of Chla and Chlt as compared with the 55 existing indices. Additionally, most of the 55 existing Chl-related VIs performed robustly or strongly in simultaneous prediction of leaf Chla, Chlb and Chlt.     

Comparative analyses of physiological assays and chlorophyll <Emphasis Type="Italic">a</Emphasis> variable fluorescence parameters: investigating the importance of phosphorus availability in oligotrophic and eutrophic freshwater systems

Diverse measurements of nutrient status indicators were used to test the severity of physiological phosphorus (P) limitation of phytoplankton among lake systems ranging from oligotrophic to eutrophic, based on P and chlorophyll a (Chl a) concentrations. Metabolic assays and particulate nutrient ratios were used to estimate nutrient status at sites located in Lake Erie, Lake Ontario and Lake Huron. Variable fluorescence ratios (F _v/F _m), relative electron transport rates and their response to irradiance were measured by the pulse-amplitude-modulated fluorometer. Under summer stratified conditions, P deficiency was strongest in the oligotrophic sites and nitrogen (N) status indicators and Chl a variable parameters revealed no severe N deficiency. Nutrient amendment assays showed positive associations with P additions and Chl a fluorescence parameters at P-deficient sites. In the most oligotrophic sites, N additions revealed a modest increase only detected by the Chl a fluorescence parameters. Phytoplankton communities were also associated with nutrient status, where chrysophytes and cryptophytes were important in P-deficient sites and cyanobacteria, phyrrophyta, and diatoms were prevalent in nutrient-rich sites. The results confirmed that Chl a fluorescence parameters can reveal P deficiency and indicate its severity among the range of trophic status in aquatic systems.     

Gender, mediterranean drought, and seasonality: photosystem II photochemistry in Pistacia lentiscus L.

In this work, photosystem II (PSII) photochemistry, leaf water potential, and pigment contents of male and female Pistacia lentiscus L. were investigated during a seasonal cycle at three different, arid locations: superior semiarid, inferior semiarid, and arid. The results showed that the gender, season, and the site conditions interacted to influence the quantum yield and pigment contents in P. lentiscus. Predawn leaf water status was determined only by the site and season. The annual patterns of PSII maximum quantum efficiency (F_v/F_m) were characterized by a suboptimal activity during the winter, especially, populations with the more negative water potential exhibited a lower chlorophyll (Chl) a content and chronic photoinhibition irrespective of a gender. We also demonstrated that both photochemical or nonphotochemical mechanisms were involved to avoid the photoinhibition and both of them depended on the season. This plasticity of photosynthetic machinery was accompanied by changes in carotenoids and Chl balance. In the spring, the female F_v/F_m ratio was significantly higher than in male individuals, when the sexual dimorphism occurred during the fruiting stage, regardless of site conditions. P. lentiscus sex-ratio in Mediterranean areas, where precipitations exceeded 500 mm, was potentially female-biased. Among the fluorescence parameters investigated, nonphotochemical quenching coefficient appeared as the most useful one and a correlation was found between Chl a content and F_v/F_m. These results suggest that functional ecology studies would be possible on a large scale through light reflectance analysis.     

Effects of phytoplankton species composition on absorption spectra and modeled hyperspectral reflectance

Understanding the spectral characteristics of remotely-sensed reflectance by different phytoplankton species can assist in the development of algorithms to identify various algal groups using satellite ocean color remote sensing. One of the main challenges is to separate the effect of species composition on the reflectance spectrum from other factors such as pigment concentration and particle size structure. Measuring the absorption spectra of nine different cultured algae, and estimating the reflectance of the different species, provides a useful approach to study the effects of species composition on the bio-optical properties. The results show that the absorption spectra of different species exhibit different spectral characteristics and that species composition can significantly change the absorption characteristics at four main peaks (438, 536, 600 and 650 nm). A ‘distance angle index’ was used to compare different phytoplankton species. Results indicate that this index can be used to identify species from the absorption spectra, using a database of standard absorption spectra of known species as reference. By taking into account the role of species composition in the phytoplankton absorption model, the performance of the model can be improved by up to 5%. A reflectance-species model is developed to estimate the remotely-sensed reflectance from the absorption spectra, and the reflectance of different phytoplankton species at the same chlorophyll-a concentration is compared, to understand effects of species composition on the reflectance spectra. Different phytoplankton species can cause up to 33% difference in the modeled reflectance at short wavelengths under the condition of the same chlorophyll-a concentration, and variations in the reflectance spectrum correspond to the colors of the algae. The standard deviation of the reflectance among different species shows that the variations from 400 to 450 nm are sensitive to species composition at low chlorophyll-a concentrations, whereas variations in the 510 to 550 nm range are more sensitive under high chlorophyll-a concentrations. For this reason, the green bands may be more suitable for estimating species composition from hyperspectral satellite data during bloom conditions, whereas the blue bands may be more helpful in detection of species under low chlorophyll-a concentrations. In this theoretical approach, variations in reflectance at the same chlorophyll-a concentration can be used to identify phytoplankton species. Another approach to identify phytoplankton species from remotely-sensed hyperspectral reflectance measurements would be to derive the absorption spectra of phytoplankton from the reflectance measurements, and compare these with a standard database of absorption spectra.     

Field spectrometry: New methods to investigate epilithic micro-algae on rocky shores

The use of field reflectance spectrometry to detect and quantify chlorophyll-a in intertidal epilithic micro-algae is evaluated. Sandstone disks were placed into intertidal areas for different amounts of time to accumulate micro-algae. Field reflectance spectra (350-1050 nm) were acquired from each of the disks before and after they were collected from the intertidal zone. Pigments were extracted from the sandstone disks using methanol and chlorophyll-a concentration was determined spectrophotometrically. Other pigments were identified using High Performance Liquid Chromatography (HPLC). Different ratios of reflectance were tested. A ratio of reflectances at 750 and 670 nm (R₇₅₀ / R₆₇₀) had the tightest correlation with chlorophyll-a (R² = 0.93; SE = 1.14; P = < 0.001; n = 25). Data from the field were used to predict values of chlorophyll-a; predictions were strongly and linearly related to observed values (R² = 0.95; SE = 0.15; P < 0.001; n = 8). The average difference and average absolute difference between observed and predicted values of chlorophyll-a was 0.03 μg cm^− 2 (1.79% of the measured range) and 0.14 μg cm^− 2 (8.38% of the measured range), respectively.Absorptions due to chlorophylls a, b and c, carotenoids and the phycobiliproteins phycoerythrin, phycocyanin and allophycocyanin were identified. The techniques described here enable estimation of amounts of chlorophyll-a and the detection of several other pigments. Thus, investigations of microflora in studies of succession, biofilms or grazing in intertidal habitats can be enhanced by field spectrometry.     

Prediction of Secondary Ionization of the Phosphate Group in Phosphotyrosine Peptides

A computational approach, based on a continuum molecular electrostatics model, for the calculation of the pK_a values of secondary ionization of the phosphate group in phenyl phosphate derivatives is described. The method uses the ESP atomic charges of the mono-anionic and di-anionic forms of the ionizable phosphate group, computed with the use of the density functional method, and applies a new concept of the model group, being the reference state for the pK_a calculations. Both conformational flexibility and tautomeric degrees of freedom are taken into account in the calculations. The method was parameterized using experimentally available pK_a values of four derivatives of phenyl phosphates, and phosphotyrosine. Subsequently this parameterization was used to predict pK_a of the phosphate group in a short peptide Gly-Gly-Tyr(P)-Ala, and in a longer peptide consisting of 12 residues, the latter in water, and in a complex with a protein—phospholipase. The agreement between the computed and the experimental pK_a values is better than ±0.3 pH units for the optimized solute dielectric constant of 11–13. This approach is promising and its extension to other phospho-amino acids is in progress.     

Properties of pullulan-based blend films as affected by alginate content and relative humidity

Pullulan-sodium alginate blend films were prepared and characterized as a function of water activity (a_w). At low a_w, the incorporation of alginate into pullulan film increased the tensile strength and elastic modulus, but decreased the elongation at break of the composite films; the opposite trends were observed at elevated a_w. Above 0.43 a_w, water exerted a typical plasticization effect upon the biopolymer blends. As a_w increased from 0.23 to 0.43, an anti-plasticization effect was observed as tensile strength and elastic modulus increased. The glass transition temperature of all samples decreased substantially as aw increased from 0.23 to 0.84 due to the plasticization effect of water. Within this a_w range, one transition temperature was observed for all film specimens. The stretching vibration band of O-H was investigated using attenuated total reflection Fourier transform infrared spectroscopy to identify the various species of water interacting with the polysaccharide films.     

Effect of calcium ions on electron transfer between hemes <Emphasis Type="Italic">a</Emphasis> and <Emphasis Type="Italic">a</Emphasis><Subscript>3</Subscript> in cytochrome <Emphasis Type="Italic">c</Emphasis> oxidase

Kinetics of the reduction of the hemes in cytochrome c oxidase in the presence of high concentration of ruthenium(III)hexaammine chloride was examined using a stopped-flow spectrophotometer. Upon mixing of the oxidized enzyme with dithionite and Ru(NH₃) ₆ ³⁺ , three well-resolved phases were observed: heme a reduction reaching completion within a few milliseconds is followed by two slow phases of heme a ₃ reduction. The difference spectrum of heme a ₃ reduction in the visible region is characterized by a maximum at ～612 nm, rather than at 603 nm as was believed earlier. It is shown that in the case of bovine heart cytochrome c oxidase containing a special cation-binding site in which reversible binding of calcium ion occurs, heme a ₃ reduction is slowed down by low concentrations of Ca²⁺. The effect is absent in the case of the bacterial cytochrome oxidase in which the cation-binding site contains a tightly bound Ca²⁺ ion. The data corroborate the inhibition of the cytochrome oxidase enzymatic activity by Ca²⁺ ions discovered earlier and indicate that the cation affects intramolecular electron transfer.     

Temperature dependence of growth,development, and photosynthesis in maize under elevated CO2

Global atmospheric carbon dioxide concentrations (C_a) are rising. As a consequence, recent climate models have projected that global surface air temperature may increase 1.4–5.8 °C with the doubling of C_a by the end of the century. Because, changes in C_a and temperature are likely to occur concomitantly, it is important to evaluate how the temperature dependence of key physiological processes are affected by rising C_a in major crop plants including maize (Zea mays L.), a globally important grain crop with C₄ photosynthetic pathway. We investigated the temperature responses of photosynthesis, growth, and development of maize plants grown at five temperature regimes ranging from 19/13 to 38.5/32.5 °C under current (370 μmol mol⁻¹) and doubled (750 μmol mol⁻¹) C_a throughout the vegetative stages using sunlit controlled environmental chambers in order to test if the temperature dependence of these processes was altered by elevated C_a. Leaf and canopy photosynthetic rates, C₄ enzyme activities, leaf appearance rates, above ground biomass accumulation and leaf area were measured. We then applied temperature response functions (e.g., Arrhenius and Beta distribution models) to fit the measured data in order to provide parameter estimates of the temperature dependence for modeling photosynthesis and development at current and elevated C_a in maize. Biomass, leaf area, leaf appearance rate, and photosynthesis measured at growth C_a was not changed in response to CO₂ enrichment. Carboxylation efficiency and the activities of C₄ enzymes were reduced with CO₂ enrichment indicating possible photosynthetic acclimation of the C₄ cycle. All measured parameters responded to growth temperatures. Leaf appearance rate and leaf photosynthesis showed curvilinear response with optimal temperatures near 32 and 34 °C, respectively. Total above ground biomass and leaf area were negatively correlated with growth temperature. The dependence of leaf appearance rate, biomass, leaf area, leaf and canopy photosynthesis, and C₄ enzyme activities on growth temperatures was comparable between current and elevated C_a. The results of this study suggest that the temperature effects on growth, development, and photosynthesis may remain unchanged in elevated C_a compared with current C_a in maize.     

Analysis of the Heat Stress Induced Quenching of Variable Chlorophyll a Fluorescence in Beet Spinach Leaves: Possible Accumulation of Oxidized Quencher P680+ under High Illumination

Effect of preheating of beet spinach leaves on chlorophyll a fluorescence yield was analyzed with the help of additional high intensity illumination pulses using a pulse modulated fluorometer. Preheating at mildly elevated temperature (35–45°C) causes a shift in the redox state of secondary donor of photosystem II, possibly due to uncoupling of phosphorylation because of thermal induced membrane disorganization and associated alkalinization of intra thylakoid space. Also, at these preheating temperatures, a rise in photosystem I catalyzed electron transfer has been shown to occur. These two effects induce rapid quenching of Chi a fluorescence, which drops even in the presence of actinic light, below the level of initial fluorescence (F_o′ monitored by the weak modulated probing light. Preheating of leaf segments induces an increase in fluorescence in the presence of dluron, which blocks electron flow between two photosystems, and thus this increases in fluorescence yield (F_o′ as monitored by weak modulated light, is not solely due to disorganization of light harvesting Chi-protein complex but also due to a shift in the redox equilibrium of the donor at the oxidizing side of photosystem II resulting in rapid reduction of Q_A the stable primary acceptor of photosystem II. In 50°C preheated DCMU treated samples, the fluorescence yield increases in weak modulated light and it approaches that of maximal steady state (F_max) level. At preheating temperature of 48°–50°C, the inactivation of enzymes in the reducing side of photosystem I, causes an impairment of the reoxidation of QA and under this condition, a strong illumination causes quenching of Chi a fluorescence. This quenching seems to arise because of accumulation of the P680⁺, the oxidized physiological donor of photosystem which is a quencher of Chi a fluorescence. This quenching depended on the pulse intensity and duration which saturates P680⁺ accumulation and is greatly manifested when water oxidation complex is damaged.     

Carboxyl pKa Values and Acid Denaturation of BBL

The protein BBL undergoes structural transitions and acid denaturation between pH 1.2 and 8.0. Using NMR spectroscopy, we measured the pK_a values of all the carboxylic residues in this pH range. We employed ¹³C direct-detection two-dimensional IPAP (in-phase antiphase) CACO NMR spectroscopy to monitor the ionization state of different carboxylic groups and demonstrated its advantages over other NMR techniques in measuring pK_a values of carboxylic residues. The two residues Glu161 and Asp162 had significantly lowered pK_a values, showing that these residues are involved in a network of stabilizing electrostatic interactions, as is His166. The other carboxylates had unperturbed values. The pH dependence of the free energy of denaturation was described quantitatively by the ionizations of those three residues of perturbed pK_a, and, using thermodynamic cycles, we could calculate their pK_as in the native and denatured states as well as the equilibrium constants for denaturation of the different protonation states. We also measured ¹³C^α chemical shifts of individual residues as a function of pH. These shifts sense structural transitions rather than ionizations, and they titrated with pH consistent with the change in equilibrium constant for denaturation. Kinetic measurements of the folding of BBL E161Q indicated that, at pH 7, the stabilizing interactions with Glu161 are formed mainly in the transition state. We also found that local interactions still exist in the acid-denatured state of BBL, which attenuate somewhat the flexibility of the acid-denatured state.     

Studying the vegetation response to simulated leakage of sequestered CO2 using spectral vegetation indices

Measurement of spectral reflectance provides a fast and nondestructive method of stress detection in vegetation. In this shallow subsurface CO₂ release experiment to simulate CO₂ leakage of geologically sequestered CO₂, the radiometric responses of plants to elevated soil CO₂ concentration were monitored using a spectroradiometer. Spectral responses included increased reflectance in the visible spectral region and decreased reflectance in the near-infrared region and thus an altered spectral pattern of vegetation. Visible responses of vegetation include purple discoloration and eventual death of leaves at sites where the soil CO₂ concentration was very high. Derivative analysis identified two features (minimum and maximum) in the 575–580 nm and 720–723 nm spectral regions. The normalized difference first derivative index (NFDI) was defined based on the spectral derivative at the two bands. Four vegetation indices were analyzed with the accumulated soil CO₂ concentration to assess the accumulated impact of high soil CO₂ concentration on vegetation. Results show that with increased soil CO₂ concentration due to the surface CO₂ leakage, (1) the structural independent pigment index (SIPI) increased, indicating a high carotenoid to chlorophyll ratio; (2) the chlorophyll normalized difference vegetation index (Chl NDI) decreased, suggesting a decrease in chlorophyll content with time; (3) pigment specific simple ratios (both PSSRa and PSSRb) were reduced for stressed vegetation compared to that at the control site, indicating a reduction in both chlorophyll a and chlorophyll b; and (4) NFDI was low where plants were stressed. Changes in NFDI during the experiment were 36% and 1% for stressed and control plants, respectively. All four indices were found to be sensitive to stress in vegetation induced by high soil CO₂ concentration.     

Working with what you’ve got: Changes in thermal preference and behavior in mice with or without nesting material

In laboratories mice are typically housed at ambient temperatures (T_a) of 20-24 °C, which are below their average preferred T_a of ≈30 °C. Adjusting laboratory T_a is not a solution because preferences differ depending on activity, time of the day, and gender. We tested the hypothesis that providing mice with nesting material will allow behavioral thermoregulation and reduce aversion to colder T_a. We housed C57BL/6J mice with and without nesting material in a set of 3 connected cages, each maintained at a different T_a (20, 25, or 30 °C). Mice were confined in and given free access to the T_a options to determine if thermotaxis or nest building was the primary mode of behavioral thermoregulation. As predicted, nesting material reduced aversion to 20 °C but the overall preference, in both treatments, was still 30 °C. Inactive and nesting behaviors were more likely to be seen in contact with nesting material while active behaviors were more likely to be observed when not in contact. Nest quality increased with decreasing T_a when mice could not use thermotaxis but nest quality was uncorrelated with T_a when thermotaxis was possible. Males decreased nest quality with increasing temperatures but females showed no correlation. We conclude that nesting material does not alter thermal preferences for 30 °C when thermotaxis is possible, indicating thermotaxis as the primary mode of behavioral thermoregulation. However, when thermotaxis is not possible, mice adjust nest shape depending on the T_a. Nesting material appears to partially compensate for cooler T_a and is especially important when mice are inactive. Therefore, nesting material may be a solution to the mismatch between laboratory T_a and mouse thermal preferences.     

Non-invasive monitoring of photosynthetic activity and water content in forest lichens by spectral reflectance data and RGB colors from photographs

There is a need for non-invasive monitoring of temporal and spatial variation in hydration and photosynthetic activity of red-listed poikilohydric autotrophs. Here, we simultaneously recorded kinetics in RGB-colors (photos), reflectance spectra, water content, maximal (F_V/F_M), and effective quantum yield of PSII (Φ_PSII) during desiccation in foliose lichens differing in cortical characteristics and photobionts. The spectral absorbance peaks of chlorophyll a, phycocyanin, and phycoerythrin were clearly displayed at high hydration levels. Brightness and total RGB colors of the lichens strongly increased during desiccation. The normalized difference vegetation index (NDVI) efficiently estimated hydration level and Φ_PSII – a proxy for lichen photosynthesis – in all species, including threatened old forest lichens. Color and reflectance indices based on green wavelengths gave good estimates of water content in cephalo- and chlorolichens, but not in cyanolichens with a wider range of photosynthetic pigments. Due to species-specific characteristics, species-wise calibration is essential for non-invasive assessments of lichen functioning.     

Red blood cell membrane water permeability increases with length of ex vivo storage

Water transport across the red blood cell (RBC) membrane is an essential cell function that needs to be preserved during ex vivo storage. Progressive biochemical depletion during storage can result in significant conformational and compositional changes to the membrane. Characterizing the changes to RBC water permeability can help in evaluating the quality of stored blood products and aid in the development of improved methods for the cryopreservation of red blood cells. This study aimed to characterize the water permeability (L_p), osmotically inactive fraction (b), and Arrhenius activation energy (E_a) at defined storage time-points throughout storage and to correlate the observed results with other in vitro RBC quality parameters. RBCs were collected from age- and sex-matched blood donors. A stopped flow spectrophotometer was used to determine L_p and b by monitoring changes in hemoglobin autofluorescence when RBCs were exposed to anisotonic solutions. Experimental values of L_p were characterized at three different temperatures (4, 20 and 37 °C) to determine the E_a. Results showed that L_p, b, and E_a of stored RBCs significantly increase by day 21 of storage. Degradation of the RBC membrane with length of storage was seen as an increase in hemolysis and supernatant potassium, and a decrease in deformability, mean corpuscular hemoglobin concentration and supernatant sodium. RBC osmotic characteristics were shown to change with storage and correlate with changes in RBC membrane quality metrics. Monitoring water parameters is a predictor of membrane damage and loss of membrane integrity in ex vivo stored RBCs.