EFFECTS OF TEMPERATURE ON CHRONIC HYPOXIA TOLERANCE IN THE NON-INDIGENOUS BROWN MUSSEL, PERNA PERNA (BIVALVIA: MYTILIDAE) FROM THE TEXAS GULF OF MEXICO

Effects of temperature (15°, 20° and 25°C), O₂ partialpressure (P_O2=0, 1, 2, 4, and 6 kPa), and individual size(12–79 mm shell length; SL) on survivorship of specimensof the non-indigenous, marine, brown mussel, Perna perna, fromTexas were investigated to assess its potential distributionin North America. Its hypoxia tolerance was temperature-dependent,survivorship being significantly extended at lower temperaturesunder all tested lethal P_O2. Incipient tolerated P_O2 was 4 and6 kPa at 15 and 20°C, respectively, with >50% mortalityoccurring at 25°C at all tested levels of hypoxia. P_O2 hadless of an effect on survival of hypoxia than temperature. At25°C, survivorship was not different over a P_O2 range of0–2 kPa and increased only at 4 and 6 kPa. Survivorshipwas size-dependent. Median survival times increased with increasingSL in anoxia and P_O2=1 kPa, but at 2, 4 and 6 kPa,smaller individuals survived longer than larger individuals.With tolerance levels similar to other estuarine bivalve species,P. perna should withstand hypoxia encountered in estuarine environments.Thus, its restriction to intertidal rocky shores may be dueto other parameters, particularly its relatively low temperaturetolerance. (Received 26 January 2004; accepted 31 March 2005)     

Microsatellite variation, repeat array length, and population history of Plasmodium vivax

A recent paper (Leclerc et al. 2004) described limited variationin dinucleotide microsatellites from Plasmodium vivax, suggestingvery recent bottlenecks or genome-wide selective events. Wedescribe patterns of variation in 11 dinucleotide microsatellitesin P. vivax populations from Colombia, India, and Thailand.We find abundant variation with heterozygosity of 0.64, 0.76,and 0.77, respectively, in the three countries. The discrepancybetween these two studies results is simply explained by thedifferences in the size of repeat arrays. The microsatellitesstudied by Leclerc et al. (2004) have very few repeats (median5.5, range 4–13) and so would not be expected to be variable.Plasmodium vivax microsatellites show comparable levels of variationto those in Plasmodium falciparum when repeat array length istaken into account and provide no support for recent bottlenecksor widespread selective purging     

棉铃虫田间种群Bt毒素Cry1Ac抗性基因频率的估算

采用改进的F₁筛查法检测了2005年采自华北地区的棉铃虫Helicoverpa armigera (Hübner)田间种群对Bt毒素Cry1Ac的抗性基因频率。2005年从河南安阳和河北沧县转Bt基因抗虫棉上采集二代棉铃虫卵,在室内用人工饲料饲养至2龄幼虫,用1 μg/cm² 的Cry1Ac活化毒素进行初筛,将初筛存活成虫与室内筛选的GYBT抗性品系成虫进行单对杂交,并用区分剂量(2.5 μg/cm²)对F₁代进行检测。经检测,2005年河南安阳棉铃虫种群和河北沧县棉 铃虫种群对Cry1Ac抗性基因频率基本一致,分别为1.4×10^-3和1.5×10^-3。用毒素涂表法测定了2004、2005年采自河南安阳、河北高阳、河北沧县、新疆阿克苏和新疆沙湾棉铃虫田间种群对Cry1Ac活化毒素的敏感性水平,结果表明华北棉区与新疆内陆棉区棉铃虫种群对Cry1Ac的敏感性存在一定的地区性差异（<8倍）。总体上,我国华北棉区棉铃虫种群对Cry1Ac还未产生明显抗性,抗性基因频率处于正常水平。棉铃虫对转Bt基因抗虫棉的抗性风险依然存在,需要尽快启动全国性的早期抗性检测和预警工作。     

Horizontal distribution of Thetys vagina Tilesius (Tunicata, Thaliacea) in the Japan Sea during spring 2004

The occurrence of the salp Thetys vagina was observed in theJapan Sea during spring 2004. Catches up to 187 kg wet weight(WW) per 2.18 x 10⁵ m³ (equal to 0.9 g WW m^–3) were collectedwith 10-m diameter surface-water otter trawl nets. The horizontaldistribution indicated that the high biomass was related tothe area with high chlorophyll a (Chl a) concentration, whichwas located around the subarctic front with the warm TsushimaCurrent. Five prey taxa were identified from the gut contentsof individuals from the high Chl a area. The diatom Coscinodiscusspp. (13–55 µm in diameter) dominated numerically.Another significant prey was the large diatom Coscinodiscuswailesii (219–313 µm) that is an indicator of thespring bloom in this area. The mass occurrence of T. vaginathus appears related to phytoplankton availability, though themechanisms remain uncertain.     

Reply to: European barn swallows use melanin pigments to color their feathers brown

McGraw et al. (2004) have recently presented evidence that barnswallow (Hirundo rustica) feathers from the forehead and throatdo not     

What hypothesis tests are not: a reply to Johnson

We are sorry that Johnson's pleasure at reading our recent paper(Colegrave and Ruxton, 2003) was so short-lived. Johnson (2005)is correct that the definition of the P value that we use inthe paper is incorrect, and we are grateful     

Sex-ratio differences in Mnium hornum Hedw. and M. undulatum Sw. in relation to spore germination and vegetative regeneration

As Mnium undulatum was shown to be homosporous, it was concludedthat neither male nor female derived an advantage from sporesize that might be related to the observed excess of femaleplants. The rate of germination was greater at 20 °C thanat 10 °C in M. hornum and M. undulatum, and was also reducedin short days (7.25 hours) at both temperatures. Spores of M.undulatum germinated more slowly than those of M. hornum undereach of the environmental regimes used. Isolated spores of M.undulatum showed a ratio of 1: 4.1 compared with 1: 0.89 inM. hornum. The excess of female plants of M. undulatum thathad been established by the end of germination, was maintainedamongst the first protonemal buds produced (1: 3.5), whereasan excess of male M. hornum was observed in the first protonemalbuds (1: 0.45). Frost reduced the rate of germination in M.undulatum, but unlike desiccation did not affect the final percentage.Male and female were amongst the spores which survived desiccationat 10 °C. Regeneration of detached leaves occurred more rapidly in M.undulatum than in M. hornum, and no difference between maleand female was detected. It was found that frost prior to orduring regeneration did not produce long-term harmful effectsin M. undulatum. None of the young male gametophytes producedby regeneration from leaves survived desiccation, compared with77 per cent of similarly produced female gametophytes.     

Water-Relations Parameters of the Phloem. Determinations of Volumetric Elastic Modulus and Membrane Conductivity using an Applied Force Method and Shrinkage and Swelling of Tissues in Solutions at Differing Osmotic Pressure

Water-relations parameters were measured on sections of secondaryphloem from red oak (Quercus borealis michx. f.) and white ash(Fraxinus americana var. biltmoreana [Beadle] J. Wright) usinga linear displacement transducer. Changes in tissue thicknessin response to changes in the osmotic pressure of the bathingsolution were used to calculate the volumetric elastic modulusplus osmotic pressure (_v + ) of the tissue, and an applied forcemethod was used to estimate the time constant for water equilibration(T). The hydraulic conductivity of the cell membranes (L_p) wascalculated utilizing _v + and r values. The time-dependent behaviour of the tissue was much more complexthan originally expected. A correction for a time-dependentprocess that we call ‘drift’ was required to obtainnumbers for _v + . Furthermore, _v + was calculated on two assumptionsin order to relate changes in tissue dimensions to sieve elementparameters. In the first case, a lower limit for _v + of thesieve elements was determined by attributing all changes intissue dimensions to these cells. For red oak the average _v+ on this assumption is 72 bars. Assuming that all cell typeswere equally responsible for the changes in tissue dimensionsresulted in an _v + value of 192 bars for oak. If _v + and rare the same for all cells in the tissue, L_p for the sieve elementsof oak is 9.6 x 10^–8 cm s^–1 bar^–1. Exudationfrom the sieve elements of white ash during excision of thephloem led to artificially high values of _v + for that species. Quercus borealis michx. f., Fraxinus americana var, biltmoreana (Beadle) J. Wright, red oak, white ash, water relations, phloem, volumetric elastic modulus, membrane hydraulic conductivity     

Reply to Horizons Article 'Some ideas about the role of lipids in the life cycle of Calanus finmarchicus' Irigoien (2004): II

Recently, Irigoien (Irigoien, 2004) suggested a conceptual modelof the role of lipids in the life cycle of the marine copepodCalanus finmarchicus. As he pointed out, lipids accumulatedbefore     

Strength, skeletal muscle composition, and enzyme activity in multiple sclerosis

Kent-Braun, J. A., A. V. Ng, M. Castro, M. W. Weiner, D. Gelinas, G. A. Dudley, and R. G. Miller. Strength, skeletal musclecomposition and enzyme activity in multiple sclerosis. J. Appl. Physiol. 83(6):1998-2004, 1997.This study examined functional, biochemical, andmorphological characteristics of skeletal muscle in nine multiplesclerosis (MS) patients and eight healthy controls in an effort toascertain whether intramuscular adaptations could account for excessivefatigue in this disease. Analyses of biopsies of the tibialis anteriormuscle showed that there were fewer type I fibers (66 ± 6 vs. 76 ± 6%), and that fibers of all types were smaller (average26%) and had lower succinic dehydrogenase (SDH; average40%) and SDH/-glycerol-phosphate dehydrogenase (GPDH) butnot GPDH activities in MS vs. control subjects, suggesting that musclein this disease is smaller and relies more on anaerobic thanaerobic-oxidative energy supply than does muscle of healthyindividuals. Maximal voluntary isometric force fordorsiflexion was associated with both average fiber cross-sectionalarea (r = 0.71, P = 0.005) and muscle fat-free cross-sectional area by magnetic resonance imaging(r = 0.80, P < 0.001). Physical activity,assessed by accelerometer, was associated with average fiber SDH/GPDH(r = 0.78, P = 0.008). There was a tendency forsymptomatic fatigue to be inversely associated with average fiber SDHactivity (r = 0.57,P = 0.068). The results of thisstudy suggest that the inherent characteristics of skeletal musclefibers per se and of skeletal muscle as a whole are altered in thedirection of disuse in MS. They also suggest that changes in skeletalmuscle in MS may significantly affect function.

     

Water Relations of Tropical Epiphytes: II. PERFORMANCE DURING DROUGHTING

Relative water content R, water potential and leaf diffusiveconductance C₅ were monitored while five tropical epiphyteswere subjected to an extended period of drought. The speciesstudied were: ferns Pyrrosia adnascens (Forst.) Ching and Pyrrosiaangustata (Sw.) Ching, family Polypodiaceae; orchids: Eria velutinaLindl., Dendrobium tortile Lindl. and Dendrobium crumenatumSw. The ferns reached zero turgor rapidly and after only small declinesin relative water content (R) and . Beyond this point stomatalmovement seemed strongly suppressed, but the leaves continuedto lose water vapour until very low values of R were reached.Nevertheless, on re-watering water potential (), R and diffusiveconductance (C₅) returned to pre-stress levels within 3 d. The orchids showed a more gradual decline in R and , stomatalactivity was not so strongly suppressed, and night opening ofstomata was observed under stress. The relationship between and R was found for each species,curves being fitted to the data points by non-linear regression.From these analyses it was concluded that these species hadvery dilute cell sap, and consequently the change in for agiven decline in R was smaller than for most other species recordedin the literature. Key words: Orchid, Fern, Drought, Relative water content, Diffusive conductance, Water potential     

A Transient Stimulation of Net Photosynthesis of Rye Leaves by {alpha}-Hydroxy-2-pyridinemethanesulphonic Acid ({alpha}-HPMS) due to Inhibition of Photorespiratory CO2 Release

The effects of -hydroxy-2-pyridinemethanesulphonic acid (-HPMS)upon net photosynthesis (P_n, the CO₂ compensation point (),post-lower illumination burst of CO₂ (PLIB) and post-lower temperatureburst of CO₂ (PLTB) in detached rye (Secale cereale L.) leaveswere investigated. At low concentrations ( 0.5 mol m^–3),-HPMS initially stimulated P_n and decreased the magnitude ofboth PLIB and PLTB. The decreased at all concentrations of-HPMS (0.05–5.0 mol m^–3. The effects of -HPMS onP_n and were time-dependent and, after a few minutes, the P_nwas inhibited while values increased considerably. At a higherconcentration (5.0 mol m ^–3), the transient effects of-HPMS were shorter () or not observed at all (P_n. Both PLIBand PLTB, when expressed in relation to P_n, increased at higherlevels of this compound. Similar data with respect to the effectsof -HPMS on PLIB and PLTB were found for leaves of dandelion(Taraxacum officinale L.). The results suggest that -HPMS may stimulate P_n by inhibitingphotorespiration, as originally suggested by Zelitch (1966),but only at low concentrations and over a short time span. Thedecrease of PLIB and PLTB values at low -HPMS levels is consistentwith these processes being a residual activity of the glycolatepathway. Key words: CO₂ compensation point, -hydroxy-2-pyridinemethanesulphonic acid, photorespiration, photosynthesis     

Respiration and germination rates of tomato seeds at suboptimal temperatures and reduced water potentials

Suboptimal temperature (T) affects germination rates (reciprocalof time to radicle emergence) on a thermal time basis; thatis, the T in excess of a base or minimum temperature multipliedby the time to a given per cent germination [t_g) is a constant.Respiration rates are also sensitive to T, and proportionalrelationships are often found between respiration rates andgermination rates. Reduced water potential () delays seed germinationon a hydrotime basis (i.e. the in excess of a base water potentialmultiplied by t_g is a constant). It was tested whether respirationrates prior to radicle emergence vary in proportion to T and as expected from the thermal and hydrotime models. Respirationrates (C0₂ evolution) of cold-tolerant, rapidly germinating(PI 341988) and cold-sensitive, more slowly germinating (T5)tomato [Lycopersicon esculentum Mill.) seeds were evaluatedover a range of T and conditions. For both genotypes, respirationrates until the beginning of radicle emergence were relatedto T on a thermal time basis and increased approximately linearlywith above -2.0 MPa, consistent with the hydrotime model. Respirationrates were uniquely related to germination rates, regardlessof whether germination timing was affected by T, , or genotype.However, germination timing was unaffected when respirationrates were manipulated by varying 0₂ partial pressure. Thus,while both germination and respiration rates vary with T and consistent with thermal and hydrotime models of biologicaltime, respiration rates per se were not the limiting factorin germination timing of tomato seeds. Key words: Lycopersicon esculentum Mill., tomato, germination, respiration, temperature, water potential     

Responses of Soybean Leaf Angle, Photosynthesis and Stomatal Conductance to Leaf and Soil Water Potential

The hypothesis that soil water potential (_s) is better correlatedto heliotropic leaf orientation, photosaturated photosyntheticCO₂ assimilation and stomatal conductance during periods oflimited water availability than is bulk leaf water potential(₁) was examined in greenhouse-grown soybean (Glycine max) plants,submitted to a progressive drought. Paired plants were exposedto either 1000 or 100 µmol m^–2 s^–1 photonflux densities (PFD) for 45–60 mins. The higher irradianceinduced short-term decreases in ₁, due to increased transpiration,while _l in the plant exposed to low PFD did not decrease. Thesechanges in ₁ occurred independently of changes in soil waterstatus. Concurrent to the light treatments, a single attachedleaf from each of the two plants was isolated from the restof the plant by shading, and the pulvinus of its terminal leafletwas exposed to a perpendicular PFD of 500 µmol m–²S^–1. Leaf movement of this leaflet was recorded in responseto this light, until a stable leaflet angle was achieved. Valuesof _s and _l (before and after light treatment), and photosaturatedrates of photosynthesis and stomatal conductance, were thenmeasured on these leaves. Leaflet angle and gas exchange werebetter correlated with _s (r² = 0.50, 0.50 and 0.57 for angle,photosynthesis and conductance, respectively) than with _l especiallywhen _l was the result of short-term, high-light induced changesin leaf water status (r² = 0.36, 0.32 and 0.49, for the sameparameters). Leaflet angle was also correlated with stomatalconductance (r² = 0.61) and photosynthetic rate (r² = 0.60),suggesting a close association between leaf orientation, leafmetabolism and soil water availability. Glycine max (L.) Merr. cv. Essex, soybean, heliotropism, water potential, photosynthesis, stomatal conductance, solar tracking     

The Enzymic Decarboxylation of {gamma}-methyleneglutamic Acid by Plant Extracts

-Methyleneglutamic acid, an acidic amino-acid isolated fromgroundnut plants, was decarboxylated by enzymes present in extractsof Capsicum fruits, barley roots, and tulip leaves, and alsoby intact cells of Clostridium welchii S.R. I2. The amino-acidwas attacked in a similar manner to, but in all cases at a slowerrate than, l-glutamic acid. The nature of the enzyme responsiblefor the decarboxylation of -methyleneglutamic acid was furtherinvestigated using preparations from barley roots (which donot contain the amino-acid) and from tulip leaves (in whichthe amino-acid is normally present, together with larger amountsof its amide form, -methyleneglutamine). The effects of pH,inhibitors, and partial heat denaturation upon the enzyme systemspresent in the barley and tulip extracts indicated that a singleenzyme was responsible for the decarboxylation of both l-glutamicacid and -methyleneglutamic acid. Although the Cl. welchii rapidlydeamidated and then decarboxylated l-glutamine, -methyleneglutaminewas not attacked by the organism.     

Analysis of Pressure-Volume Curves of Leaves of Rosa hybrida cv. Sonia

By analysing the relationship between inverse water potential(^–1), and relative water content (RWC) measured on leavesof roses (Rosa hybrida cv. Sonia), grown soilless, it was foundthat a non-linear (NL) model was better suited than a linearmodel to reproduce values observed in the non-turgid region.To explain this apparent curvature, it is assumed that a reductionof the non-osmotic water fraction (A_p) takes place when decreases.Osmotic potentials () measured on fresh and frozen leaf discstend to support this hypothesis. A method for exploiting PVcurves, which takes into account the variation of A_p, is described.It delivers values for the turgor pressure (_p), the relativeosmotic water content, and the mean bulk volumetric elasticitycoefficient, lower than those given by the linear model. Onthe other hand, it gives higher estimates for A_p and for . Whenapplying the traditional model to obtain estimates for waterrelations characteristics of rose leaves, and comparing resultsfrom two distinct salinity treatments (electrical conductivitiesof 1·8 mS cm^–1 and 3·8 mS cm^–1, respectively),one deduces a significant reduction of at turgor-loss in thehigh salinity treatment. The NL method is, in addition, ablesimultaneously to reveal a reduction of and a significant increasein _p at RWC=100% this proves that soilless–grown roseplants are able to osmoregulate when subjected to a constantand relatively high degree of salinity. Key words: Apoplastic water, non-linear regression, pressure-volume curves, tissue-water relations     

Mechanisms of Inhibition of Water Movement in Anaerobically Treated Roots of Zea mays L.

Changes in water flux (Jv) across detopped, 7-d-old, maize rootswere characterized during the initial 24 h of being made anoxicby exposure to an anaerobic nutrient solution. Suction (50 kPa)was applied to the xylem and samples of the xylem sap were collectedat intervals and the osmolality and ionic content were measured. Values of Jv through anoxic roots fell below those of aerobiccontrols 1 h after the equilibrium oxygen partial pressure inthe bathing medium dropped below 20 kPa (air = 20.6 kPa). Thereduction in Jv was due primarily to a nullification of thediurnal rhythm in hydraulic conductivity (Lp) that was measuredin aerobic roots. However, about one-quarter of the reductionin Jv could be accounted for by a smaller osmotic componentof the driving force () on water movement. The significance of changes in Jv in anoxic roots is discussedin terms of the reliability of estimates of Lp, the reflectioncoefficient () and . Key words: Anaerobiosis, hydraulic conductivity, osmotic potential, water     

In vivo chlorophyll forms in higher plants and algae sensitive to treatment with lutein

Lamella preparations of spinach, Chlorella, Phaeodactylum, Anabatnaand Porphyra were treated with a hydrophobic reagent, lutein,and the absorption and fluorescence spectra in the red regionbefore and after treatment were compared for changes causedby the treatment. Absorption spectra of all these preparationsunderwent the same spectral change, transformation of a bandat 684 nm into a band at 666 nm. The longer the maximum wavelengthof the red peak, the greater was the fractional absorbance decreaseat 684 nm. The content of C684 (the chlorophyll form responsiblefor the 684 nm band) in the lamellae was estimated from thefractional decreases as being progressively higher in the orderof Phaeodactylum, Porphyra, Anabatna, Chlorella and spinach.The fluorescence spectra at liquid nitrogen temperature beforetreatment showed two bands. The longer wavelength band was transformedby the treatment into a shorter wavelength band(s), as describedbelow, according to the maximum wavelengths: spinach, F735F695(or F686); Chlorella, F715F700 (or F686); Phaeodactylum, anunidentified componentF690; Anabaena, F732F685 (or F695); Porphyra,F726F683. These chlorophyll forms with fluorescence maxima between715 and 735 nm were, therefore, designated C684 based on absorptionspectrophotometry, and are considered to play a role in photosystemII. (Received August 15, 1972; )