EFFECT OF BODY SIZE ON THE RESPIRATION OF CERITHIDEA (CERITHIDEOPSILLA) CINGULATA (GMELIN, 1790) AND CERITHIUM CORALIUM KIENER, 1841

The effect of body size on the oxygen consumption and metabolicrate of Cerithidea (Cerithideopsilla) cingulata (Gmelin, 1790)andCerithium coralium Kiener, 1841 was studied at a constant temperatureof 25°C. An exponential relationship has been observed inboth animals. Oxygen consumption showed a positive linear correlationwith a ‘b’ value of 0.6518 in C. cingulata and 0.7667in C. coralium. A negative linear correlation was obtained forthe metabolic rate with a (b-1) value of –0.3482 in C.cingulata and –0.2333 in C. coralium.     

Respiratory rates in the cladoceran Ceriodaphnia dubia in Lake Rotongaio, a monomictic lake

The experimentally measured oxygen consumption rate by the cladoceran,Ceriodaphnia dubia, showed a linear increase between 5 and 20°C.Oxygen consumption rates of C. dubia were estimated in situfrom respiratory electron transport system (ETS) activity inLake Rotongaio during summer stratification and winter mixing.Oxygen consumption was 0.002 µl O₂ animal^–1 h^–1in the hypolimnion and 0.076 µl O₂ animal^–1 h^–1in the epilimnion during stratification. Implications of respiredoxygen for metabolic carbon requirements are discussed.     

Vertical distribution of zooplankton respiration in relation to the intense oxygen minimum zones in two British Columbia fjords

The vertical distribution of zooplankton respiration rate asestimated from respiratory enzyme activity (ETS activity) ispresented in relation to the intense oxygen deficient zonesof two British Columbia fjords. In both inlets the maximum zooplanktonrespiration rate was often found immediately above the oxygendeficient zone. Also there was a complete lack of zooplanktonrespiration (due to a complete lack of zooplankton) in waterswith dissolved oxygen concentrations less than about 5 µg-atomst^–1. Thus, in these inlets it appears that waters containingless than 5 µg-atoms 0 t^–1 act as a barrier to zooplanktonmigration. The significance of this barrier is indicated bycalculations that show zooplankton respiration in the layerimmediately above the oxygen deficient zone to be quantitativelyimportant in the formation and stabilization of the oxygen deficientzone. ¹Contribution No. 564 from the Fisheries Research Institute,University of Washington.     

Transport of Oxygen by the Blood of the Land Crab, Gecarcinus lateralis

Parameters relating to transport of oxygen were measured inthe pericardial blood and venous outflow from the first walkingleg of Gecarcinus lateralis. O₂-equilibrium curves of the hemocyaninof G. lateralis were found to be sigmoid and, at 27°C andpH 7.45, to have a half-saturation pressure of about 17 mm Hgoxygen. Average partial pressures of oxygen as measured by O₂-electrodewere 32 mm Hg in pericardial blood and 9 mm Hg in the venoussamples. Analysis of the O₂-content in corresponding samplesby the Van Slyke technique revealed an average of 2.17 volumes% O₂-capacity for whole blood, 1.45 volumes % for pericardialblood, and 0.61 volumes % for venous blood. Estimates basedon the Van Slyke analyses indicated an average pO₂ of 29 and14 mm Hg in pericardial and venous samples, respectively. Thesefigures agree fairly well with those obtained by means of O₂-electrodes.Of the oxygen carried to the tissues, about 94% is carried asoxyhemocyanin and about 6% is carried in physical solution.As the blood passes through the gills, the hemocyanin, on anaverage, becomes 80–85% saturated with oxygen and returnedfrom the tissues 18–45% saturated with oxygen. These resultsindicate that the blood of G. lateralis has a higher O₂-capacitythan the blood of most other decapod crustaceans for which similarinformation is available. In addition, the blood of G. lateralistransports more oxygen to the tissues per unit volume than doother crustacean bloods.     

A comparison of net and gross rates of oxygen production as a function of light intensity in some natural plankton populations and in a Synechococcus culture

In vitrorates of gross and net oxygen production were measuredas a function of light intensity in some plankton communitiescollected from Bedford Basin, Nova Scotia, and in a monoclonalculture of Synechococcus. The rate of gross oxygen productionwas measured by a technique in which the stable oxygen isotope,¹⁸O, serves as a photosynthetic tracer Net oxygen productionwas measured by automated Winkler technique. The rate of communityrespiration in the light was then determined by the differencebetween gross and net rates of oxygen production. In the naturalpopulations examined, neither gross nor net oxygen productionrates were significantly inhibited at the highest light intensitymeasured (500–800 µE m^–2 s^–1) In a samplein which the dark respiration rate was small relative to themaximal rate of production [P_max;sensu Platt et al (1980) JMar. Res., 38, 687–701] the rates of ‘light’respiration were 3 times greater. In two other communities,with high rates of dark respiration relative to P_maxthe ratesof ‘light’ respiration were closer to rates of darkrespiration. In the Synechococcus clone, both gross and netoxygen production rates were inhibited at high light intensities.Rates of ‘light’ respiration were found to varyas a function of light intensity. The greatest rates of respirationwere measured in samples incubated at light intensities thatwere just saturating (100 µE m^–2 s^–1). Therates of ¹⁴C production were also measured as a function oflight intensity The photosynthetic quotients, based on ¹⁴C productionrates and gross oxygen production rates, average 1 9     

The Effect of Hypoxia and Sulphide on Culture-Grown Wetland and Non-Wetland Plants: II. METABOLIC AND PHYSIOLOGICAL CHANGES

Pearson, J. and Havill, D. C. 1988. The effect of hypoxia andsulphide on culture-grown wetland and non-wetland plants. II.Metabolic and physiological changes.—J. exp. Bot. 39:431–439. Two non-wetland (Agropyron pungens, Hordeum vulgare) and fivewetland species (Oryza sativa, Aster tripolium, three Salicorniaspp.) were grown in aerated, unaerated and sulphide-treatedculture solution. Changes in the activity of alcohol dehydrogenase(ADH) and cytochrome oxidase (COase) in the roots were measured.In the non-wetland species, treatment with hypoxia or sulphideincreased ADH activity by 900–1 800%, whereas COase activitydecreased by 80–92% of the aerated control. In the wetlandspecies, except S. europaea which was not affected, hypoxiaincreased ADH activity by 350–550%, while COase activitywas little affected. Generally, when treated with sulphide theactivity of ADH increased to about 750% in most of the wetlandspecies, but increases as low as 175% (S. europaea) and as highas 1400% (S.fragilis) were recorded. The effect of sulphideon the COase activity in the wetland plants was not as markedas in the non-wetland plants. The Salicornia spp. were the leastaffected by the sulphide treatment and they also had intrinsicallyhigher levels of COase activity than the other species sampled.Of the wetland plants the Salicornia species had the lowestvalue for root aerenchyma, 3–6%. Therefore, there wasno correlation between the possession of aerenchyma and thephysiological changes measured. Measurement of malate, lactateand ethanol in roots of the first four species listed abovegave no evidence for alternative anaerobic fermentation pathways.While in the flood-intolerant species, high ADH activities werenot able to maintain the energy charge. It is suggested thatmaintenance of relatively high COase activity in wetland plantsmay help to ‘scavenge’ any available oxygen withinroots and thus help reduce energy loss. Key words: Cytochrome oxidase, alcohol dehydrogenase, metabolic adaptation     

Root Hydraulic Conductivity of Two Cactus Species in Relation to Root Age, Temperature, and Soil Water Status

The effects of root age, temperature, and soil water statuson root hydraulic conductivity (L_P) were investigated for twocactus species, Ferocactus acanthodes and Opuntia ficus-indica.The volumetric flux density of water was measured for excisedroot segments, either using negative hydrostatic pressures appliedto the proximal end or using reverse flow of water from theroot to the soil. For both species, L_P at 20 ?C increased withroot age, average values reaching a maximum of 3.9 ? 10^–7m s^–1 MPa^–1 for F. acanthodes and 5.2 ? 10^–7m s^–1 MPa^–1 for O.ficus-indica at 11 to 17 weeksof age; L_P subsequently declined with increasing root age forboth species. L_P was maximal at a temperature of about 10 ?Cfor the youngest roots (1–3 weeks), this optimum shiftingto 40 ?C for 8-week-old roots of both species. For older roots(up to 1.5-years-old), L_P increased with temperature from 0?C to 50 ?C, with a Q₁₀ of 1.3 between 20 ?C and 30 ?C. At asoil water potential (_soil) of –0.016 MPa, root L_P wasindependent of the direction of water flow for both species.Depending on root age, L_P declined 45- to 500-fold for F. acanthodesand 90- to 800-fold for O.ficus-indica as _soil was reduced from–0.016 to –1.06 MPa, consistent with a rectifier-likebehaviour with respect to water movement between soil and roots.Incorporation of such responses into water uptake models shouldlead to a better understanding of root function. Key words: Ferocactus acanthodes, Opuntia ficus-indica, water potential, tension, reverse flow     

The ecology of the Calanus ponticus population in the deeper layer of its concentration in the Black Sea

The layer of daytime concentration of Calanus ponticus (VC andVI C) performing daily vertical migrations and the layer of‘winter stock’ aggregation are confined to the depthof maximal gradient of the main pycnocline under an unusuallysharp oxycline. The concentration layer thickness ranges from2 to 20–30 m and the Calanus concentration in it is >250ind. m^–3, sometimes being 3500 ind. m^–3 and evenmore. The population in the concentration layer is divided intotwo ecological groups: I, feeding and migrating specimens ofcopepodite stages V and VI, their body lipid contents being25–60 µg min.^–1; and II, non-feeding and non-migratingspecimens of copepodite stage V, their body lipid contents being100–150 µg ind.^–1. The relationship with oxygenconcentration was studied in both ecogroups. The experimentsshow that specimens of ecogroup II can exit at an oxygen concentrationof 0.06 ml 1^–1, but at such concentration falling intoanabiosis. They die at 0.04 ml O₂ 1^–1. Estimates of respirationof the group II specimens (‘winter stock’) showthat lipids they store are sufficient for 7 months' survival.Depth of Calanus concentration is determined by water densityrather than concentration of oxygen.     

The Effect of Sugar Supply Rate on Photosynthetic Development of Ocimum basilicum (Sweet Basil) Cells in Continuous Culture

The fructose supply rate to continuous cultures of Ocimum basilicumL. cells was changed in two ways. The concentration of fructosein the medium feed was diminished or the dilution rate was increasedin fructose-limiting conditions. When fructose in the feed wasdecreased, whilst maintaining constant dilution rate (0.87 µ_max),the specific rate of chlorophyll production increased—thebiomass became greener. Actual photosynthesis rate (dry biomass^–1)measured in the steady state conditions also increased. When fructose supply rate was increased by increasing the dilutionrate, the specific rate of chlorophyll production and actualphotosynthesis rate (dry biomass^–1) increased until acritical dilution rate (0.64 µ_max) was reached, thereafterdecreasing. The potential photosynthesis rate was measured on samples ofcells supplied with additional photons. This was inversely relatedto dilution rate. It seemed possible that the concentration of residual fructoseoutside the cells was related to specific growth rate but probablynot according to the Monod model. The specific production ofchlorophyll may be regulated by the intracellular concentrationof a catabolite of fructose, possibly glucose. Results suggestthat the specific production rate of chlorophyll was inhibitedwhen glucose concentration in the cells was above a thresholdof about 1.2% dry biomass. The degree of inhibition was a functionof glucose concentration above this threshold. Key words: Continuous culture, Photosynthesis, Greening, Ocimum basilicum     

Exploring the role of galectin 3 in kidney function: a genetic approach

Galectin 3 belongs to a family of glycoconjugate-binding proteinsthat participate in cellular homeostasis by modulating cellgrowth, adhesion, and signaling. We studied adult galectin 3null mutant (Gal 3–/–) and wild-type (WT) mice togain insights into the role of galectin 3 in the kidney. Byimmunofluorescence, galectin 3 was found in collecting duct(CD) principal and intercalated cells in some regions of thekidney, as well as in the thick ascending limbs at lower levels.Compared to WT mice, Gal 3–/– mice had ~11% fewerglomeruli (p < 0.04), associated with kidney hypertrophy(p < 0.006). In clearance experiments, urinary chloride excretionwas found to be higher in Gal 3–/– than in WT mice(p < 0.04), but there was no difference in urinary bicarbonateexcretion, in glomerular filtration, or urinary flow rates.Under chronic low sodium diet, Gal 3–/– mice hadlower extracellular fluid (ECF) volume than WT mice (p <0.05). Plasma aldosterone concentration was higher in Gal 3–/–than in WT mice (p < 0.04), which probably caused the observedincrease in -epithelial sodium channel (-ENaC) protein abundancein the mutant mice (p < 0.001). Chronic high sodium dietresulted paradoxically in lower blood pressure (p < 0.01)in Gal 3–/– than in WT. We conclude that Gal 3–/–mice have mild renal chloride loss, which causes chronic ECFvolume contraction and reduced blood pressure levels.     

Measurement of the Rates of Oxindole-3-Acetic Acid Turnover, and Indole-3-Acetic Acid Oxidation in Zea mays Seedlings

Nonhcbcl, H. M. 1986. Measurement of the rates of oxindole-3-aceticacid turnover and indole-3-acetic acid oxidation in Zea maysseedlings.—J. exp. Bat. 37: 1691–1697. Oxindole-3-acetic acid is the pnncipal catabolite of indole-3-aceticacid in Zea mays seedlings. In this paper measurements of theturnover of oxindole-3-acetic acid are presented and used tocalculate the rate of indole-3-acetic acid oxidation. [³H]Oxindolc-3-acetic acid was applied to the endosperm of Zeamays seedlings and allowed to equilibrate for 24 h before thestart of the experiment. The subsequent decrease in its specificactivity was used to calculate the turnover rate. The averagehalf-life of oxindole-3-acetic acid in the shoots was foundto be 30 h while that in the kernels had an average half-lifeof 35 h. Using previously published values of the pool sizesof oxindole-3-acetic acid in shoots and kernels from seedlingsof the same age and variety, and grown under the same conditions,the rate of indole-3-acetic acid oxidation was calculated tobe I-I pmol plant^–1 h^–1 in the shoots and 7·1pmol plant^–1 h^–1 in the kernels. Key words: Oxindole-3-acetic acid, indole-3-acetic acid, turnover, Zea mays     

The energetics of Calanus euxinus: locomotion, filtration of food and specific dynamic action

The effect of locomotor activity on respiration rate was studiedin the food-deprived copepod Calanus euxinus tethered to a forcesensor. The power generated by mouth appendages during cruisinglocomotion, with a frequency of 40 Hz, accounted for 0.026 and0.0031 W for metabolic and mechanical processes, respectively.To overcome total hydrodynamic drag during foraging with a meanswimming speed of 3.2 cm s^–1, the copepods need 0.4 x10^–3 W, equating to 1.3% of total metabolism. The lossesof mechanical energy for body propulsion amounted to 1.3 x 10^–3W, whilst the cost of feeding current generation run up to 1.8x 10^–3 W, or 58% of the total. Changing of locomotor activityand respiration rate during feeding was examined separatelyin tethered and free-swimming copepods. At algal concentrationof 300 µg C L^–1, the magnitude of specific dynamicaction (SDA) averaged 1.2 ± 0.44 nL O₂ µg C^–1h^–1 in copepodites V and females, with similar movingactivity before and during feeding. The contribution of SDAinto total metabolism varied from 23 to 85% in C. euxinus withlow activity level and constituted only 10% in active animals.In starved copepods, with low locomotor activity, feeding eventsstimulated the increase in frequency and total duration of locomotionwhich resulted in elevated energy expenditure enhancing the‘apparent SDA’.     

Dependence of muscle VO2 on blood flow dynamics at onset of forearm exercise

Hughson, R. L., J. K. Shoemaker, M. E. Tschakovsky, and J. M. Kowalchuk. Dependence muscle ofO₂on blood flow dynamics at the onset of forearm exercise.J. Appl. Physiol. 81(4):1619-1626, 1996.The hypothesis that the rate of increase inmuscle O₂ uptake (O_{2 mus})at the onset of exercise is influenced by muscle blood flow was testedduring forearm exercise with the arm either above or below heart levelto modify perfusion pressure. Ten young men exercised at a power of~2.2 W, and five of these subjects also worked at 1.4 W. Blood flowto the forearm was calculated from the product of blood velocity andcross-sectional area obtained with Doppler techniques. Venous blood wassampled from a deep forearm vein to determineO₂ extraction. The rate ofincrease inO_{2 mus}and blood flow was assessed from the mean response time (MRT), which isthe time to achieve ~63% increase from baseline to steady state. Inthe arm below heart position during the 2.2-W exercise, blood flow andO_{2 mus}both increased, with a MRT of ~30 s. With the arm above the heart atthis power, the MRTs for blood flow [79.8 ± 15.7 (SE)s] and O_{2 mus}(50.2 ± 4.0 s) were both significantly slower. Consistent withthese findings were the greater increases in venous plasma lactateconcentration over resting values in the above heart position (2.8 ± 0.4 mmol/l) than in the below heart position (0.9 ± 0.2 mmol/l). At the lower power, both blood flow andO_{2 mus}also increased more rapidly with the arm below compared with above theheart. These data support the hypothesis that changes in blood flow atthe onset of exercise have a direct effect on oxidative metabolismthrough alterations in O₂transport.

     

Anatomy, physiology and biochemistry of root nodules of Sprint-2 Fix-, a symbiotically defective mutant of pea (Pisum sativum L.)

A plant-determined pea mutant Sprint-2 Fix^– and the parentalline Sprint-2 were compared for selected physiological and biochemicalparameters. The Fix^– mutation prevented differentiationof Rhizobium leguminosarum bacteria into bacteroids and producedlarge, white, non-fixing nodules. These lacked nitrogenase-linkedrespiration, but had a background rate of CO₂ evolution similarto the normal Fix⁺ nodules. The cortical structure of the ineffectivenodules suggests the existence of an oxygen diffusion barrierand this was supported by a low oxygen concentration in thecentral region (0.5–3.0%), measured using an O₂ sensitivemicro-electrode. Sucrose and starch contents were similar innormal and ineffective nodules while ononitol content was about15 times lower in the Fix^– nodules. The distribution ofstarch was also different in the two nodule types. The activitiesof glutamine synthetase (GS), sucrose synthase (SS), phosphoenolpyruvatecarboxylase (PEPC) and alanine pyruvate aminotransferase (APAT)were markedly higher in Fix⁺ nodules while the activities ofpyruvate decarboxylase (PDC), alcohol dehydrogenase (ADH) andglutamate dehydrogenase (GDH) were higher in Fix^– nodules.The data from immunodetection of host nodule proteins confirmedthe reduced levels of sucrose synthase and the almost completeabsence of glutamine synthetase and leghaemoglobin in mutantnodules. There was no significant difference in the amount ofnitrogenase component 1 extracted from the microsymbiont ofnormal and ineffective nodules, but component 2 was hardly detectablein the Fix^– mutant. Key words: Pisum sativum, Fix^– mutant, nodules     

Separation of Different Cell Types by Rotating Electric Fields

A new method is proposed for separating different cell typesby application of a rotating electric field technique. Plasmamembrane electrical properties and cell size are critical parametersfor cell separation. A suitable chamber is described and thetheoretical and experimental aspects of cell movement are presented.Kalancho? daigremontiana mesophyll protoplasts traveled witha velocity of about 3–7 µm/s on the agar surfaceat a field strength of 3.5?10³ V/m. (Received April 17, 1985; Accepted September 3, 1985)     

Hemodynamic and metabolic responses of the working heart in relation to the oxygen carrying capacity of the perfusion medium

Hemodynamic and metabolic adaptations of isolated working heart perfused alternatively with normal or low oxygen carrying capacity medium were studied in an experimental model. A step change in arterial oxygen content (1.75 to 15.3 ml O2/100 ml) was followed by a decrease in coronary flow, an increase in aortic flow, external work, myocardial oxygen consumption and efficiency, respectively. Metabolic investigations (steady state values) showed the activities of both glycolysis and the Krebs cycle to increase with the oxygen carrying capacity of the perfusion medium. Within the limits of these aerobic conditions, most of the cardiac changes were reversible. The use of reconstituted blood provides physiological conditions of oxygenation, allows a dynamic equilibrium between oxygen supply and oxygen requirements and maintains a near physiological regulation between cardiac dynamic and metabolic functions. These conclusions stress the importance of optimal O2 carrying capacity of perfusion medium in metabolic studies on isolated working heart.     

Measurement of pulmonary blood flow by fractal analysis of flow heterogeneity in isolated canine lungs

Barman, Scott A., Laryssa L. McCloud, John D. Catravas, andIna C. Ehrhart. Measurement of pulmonary blood flow by fractalanalysis of flow heterogeneity in isolated canine lungs. J. Appl. Physiol. 81(5):2039-2045, 1996.Regional heterogeneity of lung blood flow can bemeasured by analyzing the relative dispersion (RD) of mass(weight)-flow data. Numerous studies have shown that pulmonary bloodflow is fractal in nature, a phenomenon that can be characterized bythe fractal dimension and the RD for the smallest realizable volumeelement (piece size). Although information exists for theapplicability of fractal analysis to pulmonary blood flow in wholeanimal models, little is known in isolated organs. Therefore, thepresent study was done to determine the effect of blood flow rate onthe distribution of pulmonary blood flow in the isolated blood-perfusedcanine lung lobe by using fractal analysis. Four different radiolabeledmicrospheres (¹⁴¹Ce,⁹⁵Nb,⁸⁵Sr, and⁵¹Cr), each 15 µm in diameter,were injected into the pulmonary lobar artery of isolated canine lunglobes (n = 5) perfused at fourdifferent flow rates ( flow1 = 0.42 ± 0.02 l/min;flow2 = 1.12 ± 0.07 l/min;flow 3 = 2.25 ± 0.17 l/min; flow 4 = 2.59 ± 0.17 l/min), and the pulmonary blood flow distribution was measured. Theresults of the present study indicate that under isogravimetric bloodflow conditions, all regions of horizontally perfused isolated lunglobes received blood flow that was preferentially distributed to themost distal caudal regions of the lobe. Regional pulmonary blood flowin the isolated perfused canine lobe was heterogeneous and fractal innature, as measured by the RD. As flow rates increased, fractal dimension values (averaging 1.22 ± 0.08) remained constant, whereas RD decreased, reflecting more homogeneous blood flowdistribution. At any given blood flow rate, high-flow areas of the lobereceived a proportionally larger amount of regional flow, suggestingthat the degree of pulmonary vascular recruitment may also be spatially related.

     

Anther Culture of Lolium temulentum, Festuca pratensis and Lolium x Festuca Hybrids. I. Influence of Pretreatment, Culture Medium and Culture Incubation Conditions on Callus Production and Differentiation

This study was conducted with Lolium temulentum, Festuca pratensis,and the two hybrids L. multiflorum x F. pratensis ‘Elmet’and L. perenne x F. pratensis ‘Prior’. In a comparisonof various durations (7–42 d) of pretreatment at 4 or7 °C the highest yield of microspore-derived callus of L.temulentum was obtained after pretreatment of spikes at 7 °Cfor 28 d, conditions which also proved optimal for panicle pretreatmentwith F. pratensis. For ‘Elmet’, durations of 21–42d were optimal, and for ‘Prior’ the responses tendedto decline with increasing duration. In L. temulentum addition of charcoal (1–2 g l^–1)to medium containing 2, 4-D and KN wa     

Effects of elevated CO2 concentrations on three montane grass species: III. Source leaf metabolism and whole plant carbon partitioning

Agrostis capillaris L.⁵, Festuca vivipara L. and Poaalpina L.were grown in outdoor open-top chambers at either ambient (340 3µmol mol^–1) or elevated (6804µmol mol^–1)concentrations of atmospheric carbon dioxide (CO₂) for periodsfrom 79–189 d. Photosynthetic capacity of source leaves of plants grown atboth ambient and elevated CO₂ concentrations was measured atsaturating light and 5% CO₂. Dark respiration of leaves wasmeasured using a liquid phase oxygen electrode with the buffersolution in equilibrium with air (21% O₂, 0.034% CO₂). Photo-syntheticcapacity of P. alpina was reduced by growth at 680 µmolmol^–1 CO₂ by 105 d, and that of F. vivipara was reducedat 65 d and 189 d after CO₂ enrichment began, suggesting down-regulationor acclimation. Dark respiration of successive leaf blades ofall three species was unaltered by growth at 680 relative to340 µmol mol^–1 CO₂. In F. vivipara, leaf respirationrate was markedly lower at 189 d than at either 0 d or 65 d,irrespective of growth CO₂ concentration. There was a significantlylower total non-structural carbohydrate (TNC) concentrationin the leaf blades and leaf sheaths of A. capillaris grown at680µmol mol^–1 CO₂. TNC of roots of A. capillariswas unaltered by CO₂ treatment. TNC concentration was increasedin both leaves and sheaths of P. alpina and F. vivipara after105 d and 65 d growth, respectively. A 4-fold increase in thewater-soluble fraction (fructan) in P. alpina and in all carbohydratefractions in F. vivipara accounted for the increased TNC content. In F. vivipara the relationship between leaf photosyn-theticcapacity and leaf carbohydrate concentration was such that therewas a strong positive correlation between photosynthetic capacityand total leaf N concentration (expressed on a per unit structuraldry weight basis), and total nitrogen concentration of successivemature leaves reduced with time. Multiple regression of leafphotosynthetic capacity upon leaf nitrogen and carbohydrateconcentrations further confirmed that leaf photosynthetic capacitywas mainly determined by leaf N concentration. In P. alpina,leaf photosynthetic capacity was mainly determined by leaf CHOconcentration. Thus there is evidence for down-regulation ofphotosynthetic capacity in P. alpina resulting from increasedcarbohydrate accumulation in source leaves. Leaf dark respiration and total N concentration were positivelycorrelated in P. alpina and F. vivipara. Leaf dark respirationand soluble carbohydrate concentration of source leaves werepositively correlated in A. capillaris. Changes in source leafphotosynthetic capacity and carbohydrate concentration of plantsgrown at ambient or elevated CO₂ are discussed in relation toplant growth, nutrient relations and availability of sinks forcarbon. Key words: Elevated CO₂, Climate change, grasses, carbohydrate partitioning, photosynthesis, respiration     

Photoadaptation in Antarctic phytopfankton: variations in growth rate, chemical composition and P versus I curves

The response of phytoplankton to variations in the light regimewas studied during the VULCAN and ACDA cruises in the Antarctic.Unenriched batch cultures of 12–19 days' duration reachedchl concentrations of 10–50 µg^–1 and exhibitedexponential growth rates, with the maximal rate being 0.41 doubl,day^–1. Ice edge algae exhibited maximum growth rates atphoton flux densities (PFD) of 30–100 µE m^–2S^–1and the growth rate was reduced by about 30% at 500–1000µE m^–2S^–1 The chl/C ratio ranged between 0.004and 0.018, with the lowest ratios at PFDs above 500 µEm^–2S^–1 chl/C ratios were also below maximum at PFDsbelow 40–50 µE m^–2S^–1 The C:N:P ratioswere close to the Redfield ratios; the Si/C ratio averaged 0.16(atoms), and the ATP/C ratio averaged from 0.0024 to 0.0050in different culture senes. When thawed after having been frozenfor 10 days, shade-adapted cultures were in a much better conditionthan sun-adapted ones. P versus I data showed that the maximumassimilation number varied from 0.75 to 4.4 µg C (µgchl)^–1h^–1. It varied inversely with the chl/C ratio;therefore the maximum carbon turnover rate varied little betweensamples (0.024/0.035 h^–1). Low biomass communities exhibitedrelatively high values for (the initial slope of P versus Icurves), low values for 1_sat (160–330 µE m^–2S^–1),and they were susceptible to photoinhibition. In contrast, communitiesdominated by Odontella weissflogii exhibited low values for, a high value for I_sat (560 µE m^–2S^–1 andthey tolerated high PFDs. The photo-adaptational status of thephytoplankton in natural water samples is discussed relativeto the profile of water column stability and mixing processes.