Pumpkin (Cucurbita sp.) seed globulin IV. Terminal sequences of the acidic and basic peptide chains and identification of a pyroglutamyl peptide chain

Pumpkin seed globulin is composed of heterogeneous polypeptidechains, acidic and chains and basic ₁ and ₂ chains (12). This study showed that the basicchains had similar N-terminal sequences, Gly-Leu-Asp-Glu-Thr-Ile-for the ₁ chain and Gly-Leu-Glu-Glu-Thr-Ile- for ₂. On the contrary,the N-terminal sequences of the acidic and chains were dissimilar, Ile-Gln-Gly-Tyr- for the chain and no N-terminal residue for the chain, according to routine terminal analysis. Pyrrolidonylpeptidase digestion of the chain and its thermolysin digestion followed by Edman degradationsrevealed that the N-terminal sequence of the chain was < Glu-Ile-Glu-Gln-Gln-Glu-Pro(Trp,Ser)-. The N-terminal sequences and the C-terminal residuesindicated that the acidic and chains were more heterogeneous than the basic ₁ and ₂ chains.A preliminary study on the degradation of storage globulin isalso presented. (Received November 9, 1979; )     

Effects of blue light deficiency on acclimation of light energy partitioning in PSII and CO2 assimilation capacity to high irradiance in spinach leaves

Blue light effects on the acclimation of energy partitioningcharacteristics in PSII and CO₂ assimilation capacity in spinachto high growth irradiance were investigated. Plants were grownhydroponically in different light treatments that were a combinationof two light qualities and two irradiances, i.e. white lightand blue-deficient light at photosynthetic photon flux densities(PPFDs) of 100 and 500 µmol m^–2 s^–1. The CO₂assimilation rate, the quantum efficiency of PSII (PSII) andthermal dissipation activity / in young, fully expanded leaves were measured under 1,600 µmol m^–2 s^–1white light. The CO₂ assimilation rate and PSII were higher,while / was lower in plants grown under high irradiancethan in plants grown under low irradiance. These responses wereobserved irrespective of the presence or absence of blue lightduring growth. The extent of the increase in the CO₂ assimilationrate and PSII and the decrease in / by high growth irradiance was smaller under blue light-deficient conditions. These resultsindicate that blue light helps to boost the acclimation responsesof energy partitioning in PSII and CO₂ assimilation to highirradiance. Similarly, leaf N, Cyt f and Chl contents per unitleaf area increased by high growth irradiance, and the extentof the increment in leaf N, Cyt f and Chl was smaller underblue light-deficient conditions. Regression analysis showedthat the differences in energy partitioning in PSII and CO₂assimilation between plants grown under high white light andhigh blue-deficient light were closely related to the differencein leaf N.     

Differential rates of inhibition of N2 fixation by sustained low concentrations of NH4+ and NO3- in northern ecotypes of white clover (Trifolium repens L.)

An experimental study in flowing solution culture compared threeNorwegian ecotypes (from Saerheim, Pasvik and Bod) and a commercialcultivar (Ac51) of white clover (Trifolium repens L.) and demonstrateddifferences with respect to the rate and intensity with whichN₂ fixation was affected when or were supplied at 20 mmol m^–3 over 14 d. Plants were nodulated and N₂ fixation wasestablished over 17 d prior to supplying mineral N, with shoottemperature 25/15 C day/night and root temperature adjustedprogressively to 12C. Control plants received no mineral Nthroughout, and did not grow as rapidly as those supplied with or . Mineral N generally depressed the total N₂ fixation per plantrelative to control plants, with two exceptions. The effectof on N₂ fixation was moresevere than that of and, over the 14 d, -fed plants fixed more N₂ than the comparable -fed plants. Interpolated daily rates of N₂ fixation per plant andnodule dry wts were used to calculate specific rates of N₂ fixation.These showed that (1) addition of either or initially stimulated fixation relative to control plants and to mineral N uptake;(2) this stimulation was greatest and was delayed by 1-2 d in-fed plants; and (3) nutrition sustained higher residualrates of N₂ fixation after 8 d compared with nutrition, under which fixation all but ceased after10 d in three of the genotypes. Ecotype Bode showed by far themost severe induced depression of N₂ fixation. Key words: N₂ fixation, nitrate, ammonium, white clover, northern ecotypes     

Reduced15N-nitrogen Transport Through Arbuscular Mycorrhizal Hyphae to Triticum aestivum L. Supplied with Ammonium vs. Nitrate Nutrition

This study compared the influence of or nutrition on the contribution of extraradical hyphae of the arbuscular mycorrhizal fungusGlomus mosseae(Nicol. and Gerd.) Gerd. and Trappe (BEG 107)to or uptake byTriticum aestivum L. ‘Hano’(summer wheat) with sufficient or insufficient N supply in semi-hydroponicculture. Roots and root-distant hyphae were spatially separatedin compartmentalized pots. Although -fed plants supplied with sufficient N had higher N concentrationsthan their -fed counterparts, this did not favourably affect colonization rates, hyphal lengthdensities or¹⁵N amounts transported via hyphae to the plants.Ammonium supply did not result in higher P or reduced carbohydrateconcentrations in the plants, so these factors could not explainthe reduced hyphal lengths. It was concluded that the effectof supply on hyphal length may be related to the reduced root growth and/or a direct effectof on hyphal growth. Plant N deficiency reduced the percentage root length colonized, hyphallength, total¹⁵N uptake by hyphae and dry weight of both - and -fed mycorrhizal plants. This was more obvious for -fed plants because plant biomass and hyphal lengthsof -fed plants were relatively low in mycorrhizal plants irrespective of the N concentrationsupplied. Copyright 2001 Annals of Botany Company Ammonium, arbuscular mycorrhiza, Glomus mosseae, nitrate, nitrogen uptake,¹⁵N studies, Triticum aestivum, wheat     

Intra- and intergeneric mating behaviour of ascosporogenous yeasts I. Quantitative analysis of sexual agglutination

When respective opposite mating types of the heterothallic yeastsare mixed, remarkable sexual agglutination occurs. This is consideredto be indispensable for the subsequent cell fusion and karyogamy.Based on the Duysens's findings (1956) that the heterogeneousdistribution or localization of pigment in particles causedto flatten their absorption spectrum, we developed the followingequation to express the intensity of agglutination: I/flattening coefficient (designated agglutination index, A.I.) expresses mean value of aggregateradii as a parameter to express agglutination intensity. TheA.I. is easily measurable with a spectrophotometer. The bestfit of k with the experimental values was calculated with acomputer. The other parameter to express the intensity of agglutination,mean cell number per aggregate (N?), was roughly estimated bythe equation, The analysis of this parameter supported the above relationship between A.I.and . The approximations of the relationship between A.I. and are also presented and their validity is discussed. ¹ A part of this work was reported in Japanese in Ref. (24). (Received June 9, 1978; )     

Nitrate Transport Characteristics in Hordeum vulgare L. Seedlings using Three Different Tracer Techniques

Deane-Drummond, C. E. and Thayer, J.R. 1986. Nitrate transportcharacteristics in Hordeum vulgare L. seedlings using threedifferent tracer techniques.—J. exp. Bot. 37: 429–439. and have been used to investigate various properties of nitrate uptake and translocation intoHordeum vulgare L seedlings. Short term / influx into seed lings grown in CaSO⁴ was stimulated by after a lag of 2 h. The apparent kinetics of shortterm / influx over the concentration range 0?0–0?7mol m fitted Michaelis-Menten equations The apparent V_max didnot change when seedlings were used that had been pretreatedin 10 or 100 mmol m^–3 and V^max=3.77 and 3?56µmol g^–1 fr. wt. h^–1respectively. The apparent Michaelis constants were also similarand K_m=0?47 and 0?45 mol m^–3 respectively. Longer term pulse chase experiments with the heavy isotope ¹⁵Nhave shown that feeding roots with resulted in the preferential appearance of ¹⁵N labelled aminoacids in the xylem sap. Pulse chase experiments with the radioisotope¹³N have shown that feeding shoots with resulted in a radial pattern of distnbution of labelin the leaf veins, which can be detected using autoradiography. The limitations and advantages of all three techniques are comparedby reference to other known experimental data. Key words: ³⁶Chlorate, ¹³nitrate, ¹⁵nitrate, Hordeum vulgare     

An analysis of the physiological basis of commonality between diurnal patterns of NH4+, NO3- and K+ uptake by Phleum pratense and Festuca pratensis

Commonality in diurnal variation in net uptake of by the grasses Phleum pratense L. cv. Bodin (timothy),and Festuca pratensis Huds. cv. Salten (fescue) was evaluatedin flowing solution culture under a semi-natural light regime.Hourly uptake rates from constant 20 mmol m^–3 concentrationsof each ion were measured concurrently over 7 d, without physicaldisturbance. The light period was 11 h, natural light supplementedby constant artificial illumination, with a step-transitionto a 13 h dark period. Uptake of all three ions showed a broadlysimilar pattern of diurnal variation, rates increasing duringthe light period and decreasing during the darkness to a minimumwithin 2 h of the end of the dark period. The amplitude wasgreatest during high-irradiance days, and both proportionatelyand absolutely greater for (mean min:max uptake?0.24) than (min:max=0.41) or K⁺ (min:max?0.34). There were significantdifferences between and the other two ions whose behaviour coincided in almost all respects, in timing of maximum and minimumrates, and acceleration in uptake during the light period. Preferentialuptake of over increased sharply during the first half of the lightperiod; in relative terms uptake accelerated twice as fast as uptake. Fescue always absorbed more than but timothy showed a preference for during part of the dark period. The results are interpreted in terms ofthe hypothesis that diurnally fluctuating ‘sink-strength’for nutrients is the primary determinant of nutrient transportrates, although uptake may become temporarily uncoupled fromnutrient demand during periods of physiological stress or perturbation,such as towards the end of the dark period, during which uptakerates are determined by factors (e.g. carbohydrate supply) otherthan current nutrient demand. Key words: Ammonium, diurnal variation, Gramineae, ion uptake, nitrate, potassium, regulation     

Relative Uptake Rates of Inorganic Nutrients by NO3- and NH4+ Grown Ricinus communis and by two Plantago Species

Allen, S., Thomas, G. E. and Raven, J. A. 1986. Relative uptakerates of inorganic nutrients by and grown Ricinus communis and by two Plantago species.—J. exp. Bot. 37: 419–428. The relative rates of uptake and assimilation of C, N, P, S,Cl^–, K⁺ , Na⁺ Ca²⁺ and Mg²⁺ by and grown Ricinus conimunisand by NH₄NO₃- grown Plantago lanceolata and P. major were calculatedfrom data presented elsewhere. Results showed that for grown Ricinus the short term relativeuptake rates, for each nutrient X did not change significantly over the steady-state periodof exponential growth. The average gave , the mean relative uptake rate during exponential growth, for each nutrient. The amountof each nutrient taken up from a nutrient solution over a periodof time could, therefore, be calculated. For and -grown R. communis,the relative uptake rate of each nutrient was a constant fractionof the relative rate of carbon assimilation. It is suggestedthat this is typical of plants of cauline habit. For both Plantago spp., the relative rates of nitrogen uptakeand assimilation fell significantly during the exponential growthphase It is suggested that this could be a characteristic ofthe growth habit of the rosette plant. Key words: Relative uptake rates, Ricinus, Plantago, ammonium, nitrate, cauline, rosette     

Pumpkin (Cucurbita sp.) seed globulin V. Proteolytic activities involved in globulin degradation in ungerminated seeds

Two proteolytic activities I and II involved in the globulindegradation were detected in pumpkin seeds. Activity I, hydrolyzing and ß subunits of the globulin to form F_ß,was found in both dry seeds and cycloheximide-treated cotyledons,and decreased during germination. Activity II, hydrolyzing F_ßto produce small peptides and amino acids, was not observedin dry seeds but found in cycloheximide-treated cotyledons,increased up to 4 days, and gradually decreased during germination. Activity I gave limited hydrolytic products from the globulinand the chain, but not from F_ß, the chain and some animal proteins. It was inhibitedby EDTA. On the other hand, activity II hydrolyzed F_ßand the chain faster than the globulin, the chain and some animal proteins. It was inhibitedby EDTA and p-chloromer-curibenzoate, and activated by ß-mercaptoethanol,dithiothreitol and CoCl₂. Optimum pH's were at about 6.8 andat 6.0 to 6.8 for activities I and II, respectively. The degradation process of the globulin can be divided intotwo steps: the first step is the conversion of globulin to F_ßand the second step, F_ß to small peptides and aminoacids. (Received November 9, 1979; )     

Nitrate Metabolism in Alfalfa Root Nodules under Water Stress

Three-month-old plants (vegetative stage) of alfalfa (Medicagosaliva L cv. Aragon) were supplied for one week with 1.0dm³(uniformly distributed) nutrient solutions containing 0 or 20mol m^–3 . One week after initiation of treatment, the plants were subjected to drought by withholding water. Bacteroidsand cytosol of nodules were obtained at different stages ofstress, and used for enzyme assays and for determination of, and . Proteins of bacteroids were more stable than cytosolic proteinswith respect to the detrimental effects of water stress and. Protein contents of bacteroids and cytosol were inversely related to proteolytic activitiesagainst azocasein in both nodule fractions. Specific nitrate reductase activity (NRA) and nitrite reductaseactivity (NiRA) of bacteroids from -treated plants were inhibited by c. 70% and 45%, respectively, as leafwater potential (_w) declined from –0.5 MPa (control) to–1.8 MPa. At still lower _w both activities began to increase:NRA was doubled, whereas NiRA only returned to its control level.Cytosolic NRA was strongly inhibited by drought, but the correspondingNiRA remained constant. Ammonia concentration in bacteroids and nodule cytosol keptbasically constant, whereas accumulated in the cytosol at severe stress, due to the activationof bacteroid nitrate reductase. Results indicate that nitrate and nitrite reductases of thebacteroids and the nodule cytosol act in different form: assimilatory,the cytosolic enzymes; and dissimilatory, the enzymes of bacteroidsat low _w The possibility that assimilation of also occurs in bacteroids at control or mild waterstress conditions is suggested. Key words: Assimilatory and dissimilatory reduction, bacteroids, Medicago saliva, nodule cytosol, water stress     

Intracellular pH Regulation in Ricinus communis Grown with Ammonium or Nitrate as N Source: The Role of Long Distance Transport

Allen, S. and Raven, J. A. 1987. Intracellular pH regulationin Ricinus communis grown with ammonium or nitrate as N source:the role of long distance transport.—J. exp. Bot. 38:580–596. Charge balance and intracellular pH regulation were studiedin Ricinus communis grown in water culture with 1–0 molm^–3 or l-0 mol m ^–3 as sole N source. Seedling and 70-d-old plant parts were analysed for total P, C, organic N and S, and ash alkalinity;xylem and phloem saps were analysed for mineral ion content,and amino acids, amides, and dicarboxylates. Excreted H⁺ andbase were also measured. It was shown that in -N plants, H ⁺ produced and excreted directly bythe roots accounted for all net —COOH produced in theplant, but not for cation uptake by net H⁺ exchange. IntracellularpH perturbation in the shoot was regulated partly by reduction and partly by the transportof OH^- -generating dicarboxylates in the xylem. Phloem sap hadthe capacity to transport organic N and carboxylates excessto shoot requirements back to the root. In -N plants, 60% of total reduction occurred in the root, and 70% of all OH^- produced by root and reduction was excreted directly as base. Very little —COO^–from root reduction was stored in the root: most was transported to the shoot as xylem dicarboxylateand stored in the shoot. Of the OH^- produced from shoot and reduction, 40% was stored as shoot carboxylate: the phloem saphad the capacity to transport the rest back to the roots whereit was excreted as base. Key words: Intracellular pH, ammonium nutrition, nitrate nutrition, xylem dicarboxylates, phloem dicarboxylates, charge balance     

The Effects of Habitat Geometry on Territorial Defense Costs: Intruder Pressure in Bounded Habitats

Computer simulation models were used to explore the effect ofhabitat geometry on intruder pressure for territories in differentlocations within a patch of uniformly high quality habitat,for territories in patches of different shapes and sizes, andfor patches surrounded by different types of suboptimal habitats. In models in which the edges of the habitat patch are impermeable(hard-edged), intruders do not leave the central territorialhabitat, H, and intruder pressure is lower for territories onthe edge of H than for more centrally located territories. Averageintruder pressure for any given loop of territories (, for loop = i) is positively relatedto both the proportion of territories on the edge of the patch(ESR) and the average distance moved by intruders. In models in which the edges of H are permeable (soft-edged),intruders are able to move between H and the surrounding habitats,which were of two types: sinks (no intruders generated there)and reserves (a source of intruders). The presence of sinksdramatically reduces both and average intruder pressure over H () as compared to hard-edged habitats, and both and are negatively related to the proportion of territories on theedge of the patch (ESR). Conversely, and are positively related to ESR when the surrounding habitat acts as an intruder-reserve. Data from empirical studies of territorial species agree withmany of the direct and indirect qualitative predictions of thesemodels. The effects of habitat geometry on defense costs maybe important in many territorial species, and should be takeninto account in future studies.     

Plant response to nitrate starvation is determined by N storage capacity matched by nitrate uptake capacity in two Arabidopsis genotypes

In a low-input agricultural context, plants facing temporalnutrient deficiencies need to be efficient. By comparing theeffects of NO-starvation in two lines of Arabidopsis thaliana (RIL282 and 432 from the Bay-0xShahdarapopulation), this study aimed to screen the physiological mechanismsallowing one genotype to withstand NO-deprivation better than another and to rate the relative importance of processessuch as nitrate uptake, storage, and recycling. These two lines,chosen because of their contrasted shoot N contents for identicalshoot biomass under N-replete conditions, underwent a 10 d nitratestarvation after 28 d of culture at 5 mM NO. It was demonstrated that line 432 coped betterwith NO-starvation, producing higher shoot and root biomass and sustaining maximal growthfor a longer time. However, both lines exhibited similar featuresunder NO-starvation conditions. In particular, the nitrate pool underwent the same drastic andearly depletion, whereas the protein pool was increased to asimilar extent. Nitrate remobilization rate was identical too.It was proportional to nitrate content in both shoots and roots,but it was higher in roots. One difference emerged: line 432had a higher nitrate content at the beginning of the starvationphase. This suggests that to overcome NO-starvation, line 432 did not directly rely on theN pool composition, nor on nitrate remobilization efficiency,but on higher nitrate storage capacities prior to NO-starvation. Moreover, the higher resistanceof 432 corresponded to a higher nitrate uptake capacity anda 2–9-fold higher expression of AtNRT1.1, AtNRT2.1, andAtNRT2.4 genes, suggesting that the corresponding nitrate transportersmay be preferentially involved under fluctuating N supply conditions. Key words: Arabidopsis thaliana, genetic variability, N partitioning, N recycling, N use efficiency, nitrate deficiency, nitrate remobilization rate, nitrate transporter gene expression, nitrogen reserves, plant development Received 12 July 2007; Revised 21 November 2007 Accepted 17 December 2007     

Nitrate Reductase Activity of Photoautotrophic Suspension Culture Cells of Chenopodium rubrum is under the Hierarchical Regime of NO3-, NH4+ and Light

During batch culture of photoautotrophic cells of Chenopodiumrubrum under long-day illumination regime a growth phase ofthree weeks was followed by a stationary phase of another sixweeks. During the growth phase two thirds of the nitrate and85 percent of the in the medium were consumed. Uptake of both ions was only observed duringthe light period. Nitrate reductase (but none of the other enzymesof nitrate assimilation) exhibited pronounced diurnal fluctuationsabove a basic activity. Both the basic and the superimposeddiurnally oscillating activity slowly but continuously declinedand virtually disappeared in cultures older than seven weeks.The oscillations were due to light triggered protein synthesis.However, nitrate uptake from the medium or remobilization from the vacuole was a prerequisitefor the de-novo synthesis of NR, suggesting the requirementof a ‘metabolic pool’ of nitrate for the inductiveprocess. Uptake as well as remobilization of depended pivotally on the presence of comparativelyhigh concentrations of ammonium (20 mM) in the medium. (Received March 22, 1988; Accepted July 20, 1988)     

Models for Cutaneous Gas Exchange and Transport

SYNOPSIS. Models suited for quantitative analysis of cutaneousgas exchange and transport with particular emphasis on diffusionlimitation are discussed. I. The diffusive transfer of gasesbetween body and environment can be compared to diffusion acrossa homogeneous flat tissue sheet characterized by a diffusionconductance or diffusing capacity (D). II. A flat barrier separatingthe medium from blood flow is a widely useful model. The characteristic parameter is theratio , where rß is the effective solubility of the gas in blood. A high value means predominant perfusionlimitation; low signifies diffusion limitation. III. In some conditions, as in still wateror at body-soil contact, a considerable diffusion resistancein the medium may become important. IV. Unequal distributionof D to may strongly reduce gas exchange efficiency. V. Diffusive arteriovenous shuntingof gases may lead to additional reduction of gas exchange efficiency.VI. The parallel arrangement of skin circulation with respectto tissue circulation (in contrast to the arrangement in seriespresent in fish gills and in tetrapod lungs) leads to mixingof arterialized with venous blood and reduced efficiency ofblood flow in gas transport.     

Nitrate transport in Zea mays cell suspension cultures: the effect of solution composition and cell age

Nitrate transport characteristics of an amino acid-grown Zeamays P3377 cell culture line were studied. Age (days after subculturing)of the cells was shown to have a significant effect on transport; older stationary phasecultures did not absorb nitrate from the medium as rapidly asyounger growing cultures. Solution composition had a pronouncedimpact on induction of accelerated nitrate transport and transportrates. Maximum uptake rates required fresh culture media ratherthan simple solutions. Differences in ionic strength among uptakesolutions of equal concentration were shown to affect the apparent uptake rates by changing theactivity coefficient of . The uptake kinetics were established by following uptake for 24h in a wide range of nitrate concentrations. Uptake patternsof cells in solutions ranging from 0.02 to 2 mM were as typicallyreported for plants. The kinetic constants for the Zea mayscell suspension cultures concurred with reports of other solution-culturedcells. When cells were placed in solutions containing greater than 2 mM, uptake patternssuggested a significant passive uptake component. Passive diffusionof was estimated by Nernst analysis and indicated to be an important component of nitrateuptake in maize cell suspension cultures grown in the absenceof nitrate then transferred into nitrate-containing media. Key words: Cell suspension culture, nitrate, passive uptake, Zea mays     

Stage of development is an important determinant in the effect of nitrate on photoassimilate (13C) partitioning in chicory (Cichorium intybus)

The effect of nitrogen supply to chicory plants on carbon partitioningbetween shoot, root and tuberized root was studied at differentstages of vegetative growth, using long-term ¹³CO₂ labelling-chaseexperiments. This approach was complemented by measurement ofstorage carbohydrates and activities of enzymes involved inroot sucrose metabolism (sucrose-sucrose fructosyl transferase(SST), sucrose synthase, invertase). In both young and matureplants, low resulted in a 30–35% decrease in ¹³C assimilation. However, the partitioningof ¹³C between shoot and root was affected differently at differentstages of development. In young plants, in which carbohydrateswere being used for structural root and shoot growth, neither¹³C shoot/¹³C root ratio nor root activities of the above enzymeswere modified by supply. In contrast, in mature plants storing large amounts of carbohydratesas fructan in the tuberized root, low caused the ratio to decrease from 0.6 to 0.2, despiteunchanged net flux of ¹³C from shoot to root. The extractableactivity of SST was elevated in mature plants, compared to youngplants, at both low and high , consistent with its role in fructan synthesis. However, matureplants grown at low exhibited SST activity double that of plants grown at high . From these results, it is concluded that the observeddecrease in shoot/root dry weight ratio at low supply is caused by increased utilization of carbohydratesfor storage due to elevated root SST activity. Key words: Chicory, nitrate, ¹³C, shoot/root ratio, fructans, SST     

The Titrimetric Assay of OH- and HCO3- Excreted by Ricinus Cultivated on NO3--containing Nutrient Media: The Influence of Ionic Strength, End Point pH and CO2 Supersaturation

Allen, S. and Allen, C. R. 1987. The titrimetric assay of OH^–and excreted by Ricinus cultivatedon -containing nutrient media: the influence of ionic strength, end point pH and CO² supersaturation.–J. exp. Bot. 38: 607–617. When spent -containing nutrient media were titrated to the starting pH of 6.5 the titre wasequivalent to 50%orless of the base (i.e. ) excreted. Calculation of the total amount of baseexcreted could only be made from data obtained by titrationto pH 4–5. An accurate calculation of the amount of baserequired the inclusion of activity coefficients, estimated fromionic strength, in the calculations. Spent nutrient media contained from four to ten times the concentrationof CO₂ predicted from equilibrium values. It is probable that is very slow. Key words: Ricinus, nitrate-N nutrient medium, base excretion, ionic activity coefficients, carbon dioxide supersaturation     

Respiratory Response to Periodic Emergence in Intertidal Molluscs

SYNOPSIS: The ratio of aerial: aquatic was computed for species of intertidal molluscs.This ratio was <1 for sub- and lower littoral species suggestingpartial anaerobiosis in air and >1 for high littoral archeogastropodssuggesting high metabolic demands in air. ratios were near unity for meso- and neogastropodspecies regardless of zonation. Littoral fringe mesogastropodshad ratios <1 reflecting reduced activity on emergence. Amajor gastropod adaptation to increasing emergence is reductionof ctenidium surface area and formation of a mantle cavity lung.Mid- and high littoral pulmonates with both a mantle cavitylung and secondary gills have ratios near unity. In contrast, littoral fringe pulmonates withoutsecondary gills are partially anaerobic in water. Emerged lowand mid-littoral bivalves close the valves, are almost entirelyanaerobic, have ratios 0.14:1and conserve energy by greatly reducing metabolic demand inair. In contrast, emerged high littoral bivalves remain aerobicby periodic gaping and mantle cavity ventilation. Such behaviorssupport an aerobic metabolism while minimizing evaporative waterloss. Aerial gas exchange prevents anaerobic end-product accumulationand, with a reduction in energy demand, allows efficient energystore utilization during prolonged emergence.     

Interaction of Benzoquinones with QA- and QB- in Oxygen-Evolving Photosystem II Particles from the Thermophilic Cyanobacterium Synechococcus elongatus

The interactions of benzoquinones with the reduced forms ofthe bound plastoquinone acceptors, Q_A and Q_B, were studied withoxygen-evolving photosystem II (PS II) particles from the thermophiliccyanobacterium Synechococcus elongatus, which largely lack poolplastoquinone molecules [Takahashi and Katoh (1986) Biochim.Biophys. Acta 845: 183]. Oxygen evolution in the presence ofvarious electron acceptors was determined and flash-inducedchanges in absorbance in the blue region were analyzed in termsof difference spectra, dependence on the concentration of benzoquinoneand on temperature, and sensitivity to 3-(3,4-dichlorophenyl)-1,1-dimethylurea(DCMU). The more hydrophobic the quinone molecule, the higherwas the rate of oxygen evolution, and the maximum rate of 3,000µmoles O₂.(mg chlorophyll)^–1.h^–1 was recordedin the presence of phenyl- and dichloro-p-benzoquinones. DCMUinhibited oxygen evolution by more than 95%. However, spectrophotometricstudies revealed that, even though electrons were transferredto benzoquinones predominantly via the direct oxidation of by added benzoquinones occurred in such a way as to indicate thatabout 40% of PS II reaction centers were not associated withfunctional Q_B sites. was very stable in the presence of ferricyanide. However, benzoquinonesinduced the slow oxidation of . The characteristics of the benzoquinone reductioin in thePS II preparation is discussed. ¹Present address: Department of Life Sciences, Faculty of Science,Himeji Institute of Technology, Shosha 2167, Himejishi, Hyogo-ken,671-22 Japan (Received May 8, 1990; Accepted August 14, 1990)