Compensatory changes in Photosystem II electron turnover rates protect photosynthesis from photoinhibition

Exposure of algae or higher plants to bright light can result in a photoinhibitory reduction in the number of functional PS II reaction centers (n) and a consequential decrease in the maximum quantum yield of photosynthesis. However, we found that light-saturated photosynthetic rates (P_max) in natural phytoplankton assemblages sampled from the south Pacific ocean were not reduced despite photoinhibitory decreases in n of up to 52%. This striking insensitivity of P_max to photoinhibition resulted from reciprocal increases in electron turnover ( )through the remaining functional PS II centers. Similar insensitivity of P_max was also observed in low light adapted cultures of Thalassiosira weissflogii (a marine diatom), but not in high light adapted cells where P_max decreased in proportion to n. This differential sensitivity to decreases in n occurred because was close to the maximum achievable rate in the high light adapted cells, whereas was initially low in the low light adapted cells and could thus increase in response to decreases in n. Our results indicate that decreases in plant productivity are not necessarily commensurate with photoinhibition, but rather will only occur if decreases in n are sufficient to maximize or incident irradiance becomes subsaturating.     

Optimal age at sexual maturity of sympatric and experimentally allopatric cutthroat trout and Dolly Varden charr

Summary Reproductive potentials of transplanted curthroat trout (Salmo clarki) and Dolly Varden charr (Salvelinus malma) and of their donor stocks were estimated from life history data. We found good agreement between observed and predicted age at maturity in all populations, and cannot reject the hypothesis that the fish matured at the age maximizing the overall lifetime reproductive potential ( ). Our estimates were insensitive to probable variations in female fecundity, adult mortalityrate and maximum body length. Small changes in either juvenile mortality-rate or individual growth-rate had marked effects on the estimations, as did changes in the Malthusian parameter (r). Three alternative mechanistic explanations of how age at maturity is determined could be rejected. We suggest that fish are able to adjust the maturity age non-genetically to changes in growth-rate, and that temporal variations in juvenile survival-rate allow coexistence of genotypes coding for different ages at maturity at the same growth-rate.     

Pace of diffusion through membranes

Summary Although membranes are often viewed as barriers to diffusing particles, in many cases their presence does not slow down diffusion. Investigations of the transit time (mean diffusion time) for cases where the source and the target of diffusing particles are separated by various arrangements of membranes reveal the following facts: (i) The transit time is composed of the sum of the times to diffuse each of the membrane and aqueous regions separately and terms representing the time spent at the vicinity of the interfaces between these regions. (ii) In cases of one dimensional diffusion between aqueous and membranal phases, the transit time is governed by the parameter whereD _m andD _w are the diffusion coefficients in the membrane and water, respectively, and is the membrane/water partition coefficient of the particles. While the former ratio depends mostly on the viscosities of the two phases, the latter parameter is very strongly dependent on the identity of the particles. The diffusion from water to the membrane is faster than from the membrane to water whenever 1$$ " align="middle" border="0"> . The opposite is true when this parameter is smaller than 1. (iii) In case of one dimensional transmembranal diffusion, the transit time shows a minimum when wherel _w1 andl _w2 are the net diffusion distances in the aqueous phases on both sides of the membrane. In this case, if the diffusion proceeds through pores in the membrane, represents the fraction of membrane area that is occupied by the pores.The transit times for three dimensional diffusion into and from a spherical cell are also presented in a simple form. In addition, some of the relations between transit times and other measurable time parameters, such as the course of the decay of gradients and the time lag to establish steady states, are discussed briefly.The conclusions emerging from this analysis, together with the simple expressions for the transit times can make these investigation useful for the understanding of diffusion in systems containing natural or artificial membranes.     

Effect of feedback contingencies on the control of occipital alpha

Ten color transparencies were presented 30 times each to ten normal adults in response to changes in their occipital-parietal EEG's. By means of a feedback paradigm, detected alphas caused each slide to flash and stay on as long as alpha persisted, and then to turn off when alpha attenuated, according to four different contingency conditions. For half of the feedback trials, stimulus presentation depended on alpha detection in only one hemisphere and was not influenced by changes in the simultaneously recorded contralateral EEG. For the other feedback trials, stimulus presentation was bilaterally contingent. These contingency configurations were compared with sham feedback, a noncontingent condition during which slide presentation was controlled by a prerecorded tape. For both alpha and no-alpha, the ratio of mean duration over standard error was used as a quantification of the EEG response to visual stimulation. It was assumed that larger ratios indicated increased control of the EEG. Compared with the sham condition, all feedback contingencies produced greater ratios, and hence, improved control of the EEG. The highest ratios were obtained during unilateral feedback from the EEG in which the occurrence of alpha elicited the visual stimulus. The results show that contingency between a visual stimulus and the EEG is an important parameter with regard to experimental control of the EEG.     

Respiratory evaporation in panting fowl: Partition between the respiratory and buccopharyngeal pumps

Summary Ventilation (V) and respiratory water loss were measured in domestic fowlGallus gallus subjected to raised environmental temperatures (33±2°C) and breathing air, 8% O₂ in N₂, 3% CO₂ in air or 5% CO₂ in air. Birds breathing air underwent an 18.6-fold increase in respiratory frequency and a 5-fold reduction in tidal volume and panting was accompanied by vigorous gular flutter. Hypoxic and hypercapnic birds breathed more slowly and deeply and gular flutter was strongly inhibited. The ratio was similar to that predicted on the basis of the measured ventilation assuming saturation of expired gas at measured gular mucosal temperature in hypoxic and hypercapnic birds but 54% greater than the predicted value in birds panting in air. It is concluded that the excess water loss during normal panting results from tidal airflow generated independently by the buccopharyngeal pump and that buccopharyngeal ventilation is equivalent to 54% of the respiratory ventilation.     

Laser light scattering determination of size and dispersity of synaptosomes and synaptic vesicles isolated from squid (Loligo pealei) optic lobes

Quasi-elastic laser light scattering has been used to investigate the size and dispersity of synaptosomes and synaptic vesicles isolated from optic lobes of the squid Loligo pealei. Synaptosomal fractions were highly polydisperse ( ) and the mean diameter ( ) ranged from 0.5–2.0 m. Size distribution histograms yielded two major components — smaller particles ( ) and a larger group of particles ( ). The heterogeneity of the synaptosomal particles detected in solution is in agreement with published data obtained using electron microscopy. Purified synaptic vesicle fractions also yielded complex particle size distribution data. A component with a mean diameter in the range 150–250 nm was detected, though a smaller particle ( ) dominated the scattering signal. This smaller particle closely resembles in size the electron lucent vesicles seen in the majority of squid optic lobe nerve terminals when examined by electron microscopy. Osmotically-induced shirnkage and swelling of the synptosomes was detected. Depolarization by veratridine (1.0×10^–4 M) did not result in a detectable change in the size of synaptosomal particles.     

13C spin relaxation measurements in RNA: Sensitivity and resolution improvement using spin-state selective correlation experiments

A set of new NMR pulse sequences has been designed for the measurement of ¹³C relaxation rate constants in RNA and DNA bases: the spin-lattice relaxation rate constant R(C_z), the spin-spin relaxation rate constant R(C₊), and the CSA-dipolar cross-correlated relaxation rate constant . The use of spin-state selective correlation techniques provides increased sensitivity and spectral resolution. Sensitivity optimised C-C filters are included in the pulse schemes for the suppression of signals originating from undesired carbon isotopomers. The experiments are applied to a 15% ¹³C-labelled 33-mer RNA–theophylline complex. The measured ratios indicate that ¹³C CSA tensors do not vary significantly for the same type of carbon (C₂, C₆, C₈), but that they differ from one type to another. In addition, conformational exchange effects in the RNA bases are detected as a change in the relaxation decay of the narrow ¹³C doublet component when varying the spacing of a CPMG pulse train. This new approach allows the detection of small exchange effects with a higher precision compared to conventional techniques.     

Breathing pattern and growth: comparative aspects

Summary The resting oxygen consumption and breathing pattern of nine newborn and adult species (ranging in body size from mouse to human) have been compared on the basis of data collected from the literature. Minute ventilation is similarly linked to at both ages, the percent of extracted as O₂ about 2.2. Tidal volume/kg is an interspecies constant in newborns and adults, approximately 8 ml/kg. Breathing frequency decreases with the increase in size in a different way at the two ages: large species have newborns breathing at rates 2–3 times above the corresponding adults' values, while in the small species newborns and adults breathe at almost the same rate. Therefore the newborns of the smallest species have both and below the expected values, implying a greater inability to cope with the external demands than newborns of larger species. Several considerations indicate that in the smallest newborns the mechanical properties of the respiratory system could be a constraint to resting ventilations larger than observed. It is therefore possible that their low is the cause, and not the effect, of the relatively small .     

Interrelationship of static mechanical factors and anatomical structure in lung evolution

Summary The inflation curves in 8 reptilian and in 2 avian lungs are sigmoid in comparison with the complex curve in the rat. Compliance is greatest in the lungs of those reptiles possessing well developed, membranous lung regions, and is similar to the extremely high compliance of avian air sacs. The body-weight standardized compliance of mammalian lungs is 1 to 2 orders of magnitude lower than that in reptilian lungs or in avian air sacs. Comparison of breathing pattern, elastic work of breathing and ventilatory rate indicates that a low-work strategy predominates in reptiles and in birds, which are obligatory rib breathers. Mammals can sustain a work rate per unit ventilation rate some 10 times greater than that of other groups because of efficient diaphragm breathing. The evolutionary implications of static mechanics for lung structure are discussed.Supported by grants Du 50/3 and 50/4 from the Deutsche Forschungsgemeinschaft     

Identification and assay of pyrethrins in Chrysanthemum cinerariefolium calli

Summary Callus from four clones of Chrysanthemum cinerariaefolium have been investigated for pyrethrins biosynthesis. Calli from disc-flowers, bud-flowers, stems and leaves of clone HY D were cultivated. Best growth was obtained by initiating the culture on Murashige and Skoog medium containing 3% sucrose, 1% agar, 4 ppm -naphtoxy acetic acid (ANA) and 0.4 ppm 6- benzyl aminopurine (BAP) for 28 d, then transfering explants on i.e. at the beginning of the stationnary phase. Disc-flowers calli from two high-producers clones (HY C and HY D) and two low-producers clones (SY A and SY B) were also cultivated. Pyrethrin amounts found in callus cells showed a direct relationship between parental clone synthesis ability and callus cell production. Selection of high-producers clones is thus essential for optimisation of pyrethrin synthesis.     

Biologische reisestudien in südamerika.

Ohne ZusammenfassungAufzeichnungen vom ersten Standlager Lapango der vom Autor geleiteten Deutschen Chacoexpedition, etwa südl. Breite und westl. Länge, September 1925.     

Studies on the behaviour of Oscinella frit L. (Diptera) adults of the panicle generation

Evidence from direct observations in the oatfield and from catches in various traps shows that Oscinella frit adults of the panicle generation, emerging in the oatfield, have a high level of migratory activity.

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Zusammenfassung Direkte Beobachtungen in einem erntereifen Haferfeld wiesen auf eine hohe Abflug-intensität der Vollkerfe der Rispengeneration von Oscinella frit hin. In der untersuchten Periode lag dieser Höhepunkt morgens, ungefähr Stunden nach Sonnenaufgang. Direkte Beobachtungen ergaben weiterhin, daß bei diesem Flug die Fliegen von Luftströmungen in horizontaler und senkrechter Richtung vom Feld weggetragen werden. Daß bei guten Wetterverhältnissen ein großer Anteil der Population abwandert, wurde durch aufeinanderfolgende Schätzungen der vorhandenen und der ausschlüpfenden Individuen im Haferfeld bestätigt sowie durch die rings um das Haferfeld aufgestellten, wassergefüllten Fallen. Es zeigte sich ferner, daß die große Mehrzahl von Oscinella frit am frühen Morgen aus den Puparien schlüpft und daß die Paarung nicht vor der Mitte des Vormittags stattfindet, womit die Angaben von Riggert (1935) bestätigt werden. Es wurde beobachtet, daß sich die Fliegen im Haferfeld von Honigtautropfen der Blattläuse und von verfaultem Pflanzengewebe ernähren. Sämtliche Stufen der Vorflugreifeperiode (teneral period), die bei 20° C 3–4 Stunden dauert, werden beschrieben.

     

Feedback delay and amplitude threshold and control of the occipital EEG

Six normal adults looked at 12 color transparencies that were presented 30 times each in response to the occurrence of alpha in the occipital EEG and that were not presented when no-alpha occurred. The time delay between the occurrence of recorded EEG alpha and the feedback stimulus was systematically varied, as was the threshold value of alpha amplitude required for feedback stimulus to occur. As time delay increased, the replicative reliability of the temporal association between alpha and the visual stimulus decreased. The measures of the EEG response were: the mean durations of alpha and of no-alpha durations ; an estimate of random scatter or variability in a single trial (S _e ); and the ratio of these , which is the reciprocal of the coefficient of variation. The latter ratio defines control of the EEG response. Control was greatest for the minimum feedback delay (.25 sec) and a feedback threshold of 25% of the maximum peak alpha amplitude recorded under a prior eyes-closed. resting condition. Control of the EEG decreased as time delays increased and at lower and higher feedback thresholds. It was proposed that the measurement of control for various combinations of values of relevant experimental parameters could be used to select that combination which gave the best control. This optimum combination of values of parameters could be chosen for astandardized method.This research was supported in its entirety by the Veterans Administration Medical Research Program.     

Dynamics of cardiorespiratory function in Standardbred horses during different intensities of constant-load exercise

Summary Six Standardbred horses were used to evaluate the time course of pulmonary gas exchange, ventilation, heart rate (HR) and acid base balance during different intensities of constant-load treadmill exercise. Horses were exercised at approximately 50%, 75% and 100% maximum oxygen uptake ( max) for 5 min and measurements taken every 30 s throughout exercise. At all work rates, the minute ventilation, respiratory frequency and tidal volume reached steady state values by 60 s of exercise. At 100% max, the oxygen consumption ( ) increased to mean values of approximately 130 ml/kg·min, which represents a 40-fold increase above resting . At the low and moderate work rates, showed no significant change from 30 s to 300 s of exercise. At the high work rate, the mean at 30 s was 80% of the value at 300 s. The HR showed no significant change over time at the moderate work rate but differing responses at the low and high work rates. At the low work rate, the mean HR decreased from 188 beats/min at 30 s to 172 beats/min at 300 s exercise, whereas at the high work rate the mean HR increased from 204 beats/min at 30 s to 221 beats/min at 300 s exercise. No changes in acid base status occurred during exercise at the low work rate. At the moderate work rate, a mild metabolic acidosis occurred which was nonprogressive with time, whereas the high work rate resulted in a progressive metabolic acidosis with a base deficit of 16 mmol/l by 300 s exercise. It is concluded that the kinetics of gas exchange during exercise are more rapid in the horse than in man, despite the relatively greater change in in the horse when going from rest to high intensity exercise.Symbols and abbreviations E minute ventilation - V _T tidal volume - oxygen uptake - carbon dioxide output - oxygen pulse - ventilatory equivalent for oxygen - ventilatory equivalent for carbon dioxide - R respiratory exchange ratio - HR heart rate - SBC standard bicarbonate - STPD standard temperature and pressure dry - BTPS body temperature and pressure saturated - arterial oxygen content - arteriovenous oxygen content difference - Rf respiratory frequency     

Graphic analysis of codon usage strategy in 1490 human proteins

The frequencies of bases A (adenine), C (cytosine), G (guanine), and T (thymine) occurring in codon positioni, denoted bya _i ,c _i ,g _i , andt _i , respectively (i=1, 2, 3), have been calculated and diagrammatized for the 1490 human proteins in the codon usage table for primate genes compiled recently. Based on the characteristic graphs thus obtained, an overall picture of codon base distribution has been provided, and the relevant biological implication discussed. For the first codon position, it is shown in most cases that G is the most dominant base, and that the relationshipg ₁>a ₁>c ₁>t ₁ generally holds true. For the second codon position, A is generally the most dominant base and G is the one with the least occurrence frequently, with the relationship ofa ₂>t ₂>c ₂>g ₂. As to the third codon position, the values ofg ₃+c ₃ vary from 0.27 to 1, roughly keeping the relationship ofc ₃>g ₃>a ₃=t ₃ for the majority of cases. Interestingly, if the average frequencies for bases A, C, G, and T are defined as , respectively, we find that is valid almost without exception. Such a characteristic inequality might reflect some inherent rule of codon usage, although its biological implications is unclear. An important advantage by introducing graphic methods is to make it possible to catch essential features from a huge amount of data by a direct and intuitive examination. The method used here allows one to see means and variances, and also spot outliers. This is particularly useful for finding and classifying similarity patterns and relationships in data sets of long sequences, such as DNA coding sequences. The current method also holds a great potential for the study of molecular evolution from the viewpoint of genetic code whose data have been accumulated rapidly and are to continue growth at a much faster pace.On sabbatical leave from Department of Physics, Tianjin University, Tianjin, China.     

Modification of the data-processing method for the turbidimetric bioassay of nisin

The data processing method of the turbidimetric bioassay of nisin was modified to facilitate its industrial application. The influence of the initial indicator concentration was minimized by a redefined specific dose of the bacteriocin as the quotient between the titer of the added bacteriocin and the initial population density of the indicator in the suspension. It was found that d _c = 0.125 μg ml⁻¹ was the critical dose of nisin that can cause a complete inhibition of the indicator, Pediococcus acidilactici UL5, with an initial OD of 0.135. To eliminate the interference of the cell debris, an equation, , exploiting d _c, was formulated to obtain the intrinsic survival proportion. The use of the specific dose of the bacteriocin and the intrinsic survival proportion as parameters of the dose/response curve greatly enhanced its repeatability and feasibility. A dual-dosage approach was developed to further simplify the conventional standard dose/response curve method.     

The threshold of perception of angular acceleration as a function of duration

The threshold for rotation about the yaw axis was determined for constant acceleration stimuli as a function of their duration in the range from 3 to 25 s. From the torsion-swing model the following theoretical equation can be derived: 1 $$a_{{\text{thr}}} = {C \mathord{\left/ {\vphantom {C {\left[ {1 - \exp \left( { - {{t_s } \mathord{\left/ {\vphantom {{t_s } {\tau _1 }}} \right. \kern-\nulldelimiterspace} {\tau _1 }}} \right)} \right]}}} \right. \kern-\nulldelimiterspace} {\left[ {1 - \exp \left( { - {{t_s } \mathord{\left/ {\vphantom {{t_s } {\tau _1 }}} \right. \kern-\nulldelimiterspace} {\tau _1 }}} \right)} \right]}}$$ , where a _thr=acceleration amplitude at threshold, t _s =duration of the acceleration, τ₁=time constant, C=threshold for very long stimuli. According to this formula the Mulder product (i.e. the product of the threshold acceleration amplitude and the duration of the stimulus) is constant for durations up to 0.3 τ₁. The best fit of this theoretical function to the somatosensory data is found for τ₁=14.5 s, and C=0.22⁰/s ². The time within the Mulder product is constant (about 5s) is doubtless due to the mechanics of the semicircular canals. For the oculogyral data a lower value of τ₁ is found. We do not have any explanation for this lower value.     

High groundwater nitrate concentrations inhibit eutrophication of sulphate-rich freshwater wetlands

During the last 60 years, pollution of the groundwater with has greatly increased in many parts of Europe, as a consequence of excessive use of manure and synthetic fertilisers. Monitoring of groundwater-fed wetlands indicated that sediments with high concentrations had the lowest Fe and concentrations in the pore water. A comparison of two restored open water fens, differing in supply via the groundwater, indicated that the redox potential and the sulphate ( ) reduction rate were lower when the groundwater contained not only but also high concentrations. The lower reduction rates in the -rich open water fen were associated with lower concentrations and the presence of plant species characteristic of clear water. In contrast, the higher reduction rates in the -poor open water fen were associated with very high concentrations and massive development of plant species characteristic of eutrophic environments. Investigations at -rich seepage sites in black alder carrs, showed that high concentrations in the pore water caused chlorosis in the alder carr vegetation, due to lower availability of Fe in the pore water and less Fe uptake by the plants. Experimental desiccation of sediments proved that the -rich seepage sites contained no oxidisable FeS _x , contrary to -poor locations, which became acidified and mobilised extremely high amounts of due to FeS _x oxidation. A laboratory experiment showed that addition to sediments led to reduced releases of Fe, and S^2–, very likely due to the oxidation of reduced Fe and S compounds. Overall, the results confirmed that is an energetically more favourable electron acceptor in anaerobic sediments than Fe and , and that high loads function as a redox buffer, preventing reduction of Fe and . Limited reduction prevents S^2– -mediated mobilisation of from Fe- complexes. At a higher redox potential, reduced Fe, including FeS _x , was oxidised, increasing the content of Fe(III) capable of binding . This prevented increased availability and the concomitant massive development of plant species characteristic of eutrophic environments.     

Can CO2 assimilation in maize leaves be predicted accurately from chlorophyll fluorescence analysis?

Analysis is made of the energetics of CO₂ fixation, the photochemical quantum requirement per CO₂ fixed, and sinks for utilising reductive power in the C₄ plant maize. CO₂ assimilation is the primary sink for energy derived from photochemistry, whereas photorespiration and nitrogen assimilation are relatively small sinks, particularly in developed leaves. Measurement of O₂ exchange by mass spectrometry and CO₂ exchange by infrared gas analysis under varying levels of CO₂ indicate that there is a very close relationship between the true rate of O₂ evolution from PS II and the net rate of CO₂ fixation. Consideration is given to measurements of the quantum yields of PS II ( _{PS II}) from fluorescence analysis and of CO₂ assimilation ( ) in maize over a wide range of conditions. The ratio was found to remain reasonably constant (ca. 12) over a range of physiological conditions in developed leaves, with varying temperature, CO₂ concentrations, light intensities (from 5% to 100% of full sunlight), and following photoinhibition under high light and low temperature. A simple model for predicting CO₂ assimilation from fluorescence parameters is presented and evaluated. It is concluded that under a wide range of conditions fluorescence parameters can be used to predict accurately and rapidly CO₂ assimilation rates in maize.     

Suitability of the shaking flask for oxygen supply to microbiological cultures

Due of its simplicity the shaking flask is used in serial studies, e.g. in the screening for secondary metabolites or in the optimization of fermentation processes. Experimental investigations in these small bioreactors are often the first step in developing a large-scale fermentation process.Movement of the flask should produce sufficient mixing, supply of oxygen, and removal of carbon dioxide. In the case of fluids with low or moderate viscosity, gas transport is the most important aspect. This publication summarizes data necessary to calculate the gas transport. These data are derived from the consideration of the gas diffusions through the cotton plug as well as from the substance transport between the gas and liquid phases. As a result suitable fermentation conditions can be selected. Finally, the performance limits of the shaking flask are illustrated using the example of the oxygen supply in a Streptomyces tendae fermentation.List of Symbols A _s Cross section of plug - A Surface area of liquid in flask - a A/V _F specific phase interface area - c Concentration - c ^* Saturation concentration - c Plug diffusion term - D Widest diameter of flask - Diffusion coefficients in multicomponent gas mix tures - Diffusion coefficients in binary gas mixtures - Diffusion coefficient of oxygen in the liquid - d Diameter of neck of flask - e Eccentricity - G Volume-based mass flow - G _m Maximum volume-based mass flow - g Acceleration due to gravity - h Height coordinate - ¯H Mean height of plug - Hy p _i/c ^*, Henry constant - K Consistency index - k D _xy/D _xz, Ratio of diffusion coefficients in binary gas mixtures - k _M Monod constant - k _L a Mass transport coefficient: gas/liquid - M Molecular weight - m Flow exponent - n Speed of shaking - p Pressure - p _i Partial pressure of gas component i - q Area-based flow of volume - R , respiration ratio - Sc , Schmidt number - T Absolute temperature - V Flask volume - V _F Volume of liquid in flask - w Velocity of the Stefan flow - x, y, z Ratios of the partial pressures of the gases O₂, CO₂, N₂ - Rate of shear - Dynamic viscosity of the liquid - Kinematic viscosity of the liquid - Density of the liquid - _x, Density of O₂ gas - Surface tension Indices 0 State in gas volume of shaking flask - 1 State in outside air - G Gas volume - x, y, z O₂, CO₂, N₂