The Effects of Temperature on 86Rb Uptake by Two Species of Chlamydomonas (Chlorophyta, Chlorophyceae)

⁸⁶Rb uptake was examined in two species of unicellular greenalgae, Chlamydomonas nivalis isolated from snow, and a cellwall-less mutant of the temperate freshwater Chlamydomonas reinhardii.In C. reinhardii cells grown at 20°C and cooled rapidlyto 0°C, ⁸⁶Rb uptake was abolished. Cells cooled rapidlyto –5°C in the absence of ice accumulated ⁸⁶Rb veryrapidly but the time course of this uptake suggested non-selectiveaccumulation through a damaged plasmalemma. Cells grown at 8°Cwere viable, able to divide and motile; they showed no signsof cold-shock and ⁸⁶Rb uptake, albeit slow, was measurable at–5°C in the absence of extracellular ice. Cells ofC. nivalis grown at 20°C were damaged at sub-zero temperaturesalthough they did show an enhanced ⁸⁶Rb uptake at 0°C. Cellsgrown at 5°C were able to accumulate ⁸⁶Rb from media undercooledto -5°C in the absence of extracellular ice, and again showedenhanced uptake at 0°C. The process of acclimation to lowtemperature appears to differ in the two species. Key words: Chlamydomonas, temperature, ⁸⁶Rb uptake, membrane     

Nitrogen dynamics in lower Narragansett Bay, Rhode Island. I. Uptake by size-fractionated phytoplankton populations

The contribution of nanoplankton (< 10 µm fraction)to winter – spring (1977 – 78) and summer (1978,1979) phytoplankton nitrogen dynamics in lower NarragansettBay was estimated from ammonium, nitrate and urea uptake ratesmeasured by ¹⁵N tracer methods. During the winter – spring,an average of 80% of chlorophyll a and nitrogen uptake was associatedwith phytoplankton retained by a 10 µm screen. In contrast,means of 51 – 58% of the summer chlorophyll a standingcrops and 64 – 70% of nitrogen uptake were associatedwith cells passing a 10 µm screen. Specific uptake ratesof winter – spring nanoplankton populations were consistentlylower than those of the total population. Specific uptake ratesof fractionated and unfractionated summer populations were notsignificantly different. Ammonium uptake averaged between 50and 67% of the total nitrogen uptake for both the total populationand the < 10µm fraction. The total population and the10 µm fraction displayed similar preferences for individualnitrogen species. Though composed of smaller cells, flagellatedominated nanoplankton assemblages may not necessarily takeup nitrogen at faster rates than diatom dominated assemblagesof larger phytoplankters in natural populations. ¹Present address: Australian Institute of Marine Science, P.M.B.No. 3, Townsville M.S.O., Qld. 4810, Australia     

Effects of some Cyclic 'Crown' Polyethers on Potassium Uptake, Efflux and Transport in Excised Root Segments and Whole Seedlings

The ionophores benzo-18-crown-6 (18-C-6), t-butylbenzo-18-crown-6(TBB) and di-t-butyldibenzo-30-crown-10 (30-C-10) were testedfor their effects on potassium ion absorption in onion rootsegments, and in wheat and mung bean seedlings. Potassium uptake,efflux and transport were progressively reduced in onion rootsegments and seedlings by 18-C-6 over the range 0.1–1.0mM. The effects of TBB (up to 0.3 mM) were more severe but otherwisegenerally similar to those of 18-C-6 in seedlings. Both ionophoresreduced growth, and at the highest concentrations, resultedin root potassium ion content falling below initial values after48 h treatment. The effects of 30-C-10 were evident at muchlower concentrations, inhibition of net potassium uptake occurringabove 10^–4 M. Between 10^–4 and 10^–4 M 30-C-10,however, a modest but significant stimulation of potassium uptakewas observed in onion roots and seedlings; growth of seedlingswas largely unaffected. The reductions in potassium absorptionwere attributed to the promotion, by the ionophores, of facilitateddiffusion down the electrochemical diffusion gradient, counteringthe efficiency of the potassium ion influx pump. Stimulationof uptake at certain concentrations of 30-C-10 was consideredmore likely to be due to an inhibition of passive potassiumefflux, rather than a stimulation of active influx. The importanceof stability constants, bonding and lipophilicity, in determiningthe relative effectiveness of the ionophores, is discussed. Allium cepa L, onion, Triticum aestivum L, wheat, Phaseolus aureus L, mung bean, cyclic ‘crown’ polyethers, potassium fluxes, ion transport     

Photoinhibition of Glucose Uptake in Chlorella

In colorless mutant cells of Chlorella vulgaris (M125), endogenousrespiration in the dark was not affected by 30-min preilluminationwith white light (9,000 mW?m^–2), while exogenous respirationof glucose or fructose was inhibited significantly by the sametreatment in air, but not under N₂. This light effect on exogenousrespiration was accompanied by an inhibition of hexose uptake. When autotrophically grown wild-type cells of Chlorella vulgaris(211-11h) were incubated in glucose medium with DCMU, lightalso greatly inhibited glucose uptake and growth. Blue lightwas very effective, while red light had only a slight effect.This photoinhibitory effect was also observed in algal cellsthat had been grown in a glucose-containing medium in the dark. Using SDS-gel electrophoresis, a new protein peak with a molecularweight of 35–40 kDa was detected in plasma membrane-richcell wall fractions when Chlorella vulgaris (211-11h) cellswere transferred to a glucose-containing medium. This peak disappearedafter the algal cells were returned to the glucose-free medium.These findings suggest that this protein includes the hexose-carrierprotein. Blue light significantly inhibited the formation ofthis protein during incubation in a glucose-containing medium. ¹ Present address: Laboratory of Chemistry, Faculty of PharmaceuticalSciences, Teikyo University, Sagamiko, Kanagawa 199-01, Japan. (Received July 31, 1986; Accepted March 12, 1987)     

Effects of Sucrose Concentration on the Photosynthetic Ability of Rose Shoots In Vitro

Reducing the concentration of sucrose in the culture mediumover successive subcultures has been tested as a method forincreasing the ability of rose shoots grown in vitro (Rosa cvsIceberg and Peace) to take up CO₂. Shoots maintained on ‘constant’10, 20 and 40 g I^–1 sucrose showed decreased levels ofCO² uptake at higher sucrose concentrations, although cv. Peacegrew least at 10 g l^–1 and showed correspondingly lowamounts of CO₂ uptake compared with 20 and 40 g l^–1. Bothcultivars died when sucrose was omitted from the medium. Assucrose concentration was reduced in the medium, so CO₂ uptakeof shoots initially cultured on 20 and 40 g l^–1 sucrosewas found to increase, although a concentration of 10 gl ^–1sucrose seemed to be limiting, below which the growth and chlorophylllevels of shoots declined. Rosa hybrid, rose, shoot culture in vitro, photosynthetic ability, sucrose, infra-red gas analysis     

Phosphate Uptake in the Cyanobacterium Synechococcus R-2 PCC 7942

Phosphate uptake rates in Synechococcus R-2 in BG-11 media (anitrate-based medium, not phosphate limited) were measured usingcells grown semi-continuously and in continuous culture. Netuptake of phosphate is proportional to external concentration.Growing cells at pH_o 10 have a net uptake rate of about 600pmol m^–2 s^–1 phosphate, but the isotopic flux for³²P phosphate was about 4 nmol m^–2 s^–1. There appearsto be a constitutive over-capacity for phosphate uptake. TheK_m and V_max, of the saturable component were not significantlydifferent at pH_o 7.5 and 10, hence the transport system probablyrecognizes both H₂PO^–₄and HPO^2–₄. The intracellularinorganic phosphate concentration is about 3 to 10 mol m^–3,but there is an intracellular polyphosphate store of about 400mol m^–3. Intracellular inorganic phosphate is 25 to 50kJ mol^–1 from electrochemical equilibrium in both thelight and dark and at pH_o 7.5 and 10. Phosphate uptake is veryslow in the dark ( 100 pmol m^–2 s^–1) and is light-activated(pH_o 7.51.3 nmol m^–2 s^–1, pH_o 10600 pmol m^–2s^–1). Uptake has an irreversible requirement for Mg²⁺in the medium. Uptake in the light is strongly Na⁺-dependent.Phosphate uptake was negatively electrogenic (net negative chargetaken up when transporting phosphate) at pH_o 7.5, but positivelyelectrogenic at pH_o 10. This seems to exclude a sodium motiveforce driven mechanism. An ATP-driven phosphate uptake mechanismneeds to have a stoichiometry of one phosphate taken up perATP (1 PO_{4 in}/ATP) to be thermodynamically possible under allthe conditions tested in the present study. (Received June 16, 1997; Accepted September 4, 1997)     

Pathways of Uptake and Accumulation of Sugars in Tomato Fruit

The route of sucrose unloading from the conducting tissue, theregulation of sucrose hydrolysis and the uptake and subsequentmetabolism of sugars were investigated in the rapidly growingtomato fruit. During the first two weeks of fruit enlargement, the vacuoleaccounted for more than 85% of the protoplast volume and theintercellular space accounted for 20% of the fruit placentaltissue. The plasmodesmatal frequency was highest between phloemparenchyma cells and lowest between phloem sieve cells and phloemparenchyma. The total invertase activity was about 8 µmolglucose g^–1 d. wt min^–1 during the rapid growingperiod and increased six-fold at ripening. The wall-bound invertaseaccounted for less than 11% of the total activity. Invertaseactivity increased with increasing sucrose concentrations (upto 50 mM) in the incubation medium, but decreased at higherconcentrations. Sucrose synthase activity could only be detectedwhen fruit was older than 19 d. The uptake and metabolism of sugars by fruit cells were investigatedby incubation of fruit slices with ¹⁴C-sugars for 3 h. The uptakeof sucrose increased with the sucrose concentration up to 200mM. The rate of glucose uptake and its conversion to the ethanol-insolublefraction were higher than those of sucrose. The uptake of sucrosedid not compete with that of glucose or vice versa, providedthe osmotic potential of the incubation solution was maintainedconstant. The uptake of sucrose was not inhibited by metabolicinhibitors such as PCMBS, CCCP, sodium azide or vanadate. TheATPase activity in the fruit tissue was low. These findings did not identify conclusively the mode of sucroseunloading. However, the uptake of sugars by fruit cells is non-specificand does not appear to require a membrane carrier or plasmalemmaATPase to provide energy for sucrose uptake. Fruit, invertase, Lycopersicon esculentum, phloem unloading, plasmodesmata, sucrose     

N2 Fixation and Nitrate Uptake by White Clover Swards in Response to Root Temperature in Flowing Solution Culture

Nodulated white clover plants (Trifolium repens L. cv. Huia)were grown as simulated swards for 71 d in flowing nutrientsolutions with roots at 11 C and shoots at 20/15 C, day/night,under natural illumination. Root temperatures were then changedto 3, 5, 7, 11, 13, 17 or 25 C and the total N₂, fixation over21 d was measured in the absence of a supply mineral N. Alltreatments were subsequently supplied with 10 mmol m^–2NO₂ ^– in the flowing solutions for 14 d, and the relativeuptake of N by N₂, fixation and NO₃ ^– uptake was compared.Net uptake of K⁺ was measured on a daily basis. Root temperature had little effect on root d. wt over the 35-dexperimental period, but shoot d. wt increased by a factor of3.5 between 3 and 25 C, with the sharpest increase occurringat 7–11 C. Shoot: root d. wt ratios increased from 25to 68 with increasing temperature at 7–25 C. N₂-fixationper plant (in the absence of NO₂ ^–) increased with roottemperature at 3–13C, but showed little change above13 C. The ratios of N₂ fixation: NO₂ ^– uptake over 14d (mol N: mol N) were 0.47–0.77 at 3–7 C, 092–154at 11–17 C, and 046 at 25 C, reflecting the dominanceof NO₃ ^– uptake over N₂ fixation at extremes of high andlow root temperature. The total uptake of N varied only slightlyat 11–25 –C (095–110 mmol N plant^–1),the decline in N₂ fixation as root temperature increased above11 C was compensated for by the increase in NO^– ₃ uptake.The % N in shoot dry matter declined with decreasing root temperature,from 32% at 13 C to 15% at 3 C. In contrast, concentrationsof N expressed on a shoot water content basis showed a modestdecrease with increasing temperature, from 345 mol m^–3at 3 C to 290 mol m^–3 at 25 C. Trifolium repens L, white clover, root temperature, N₂ fixation, potassium uptake, nitrate uptake, flowing solution culture     

Potassium-Ammonium Uptake Interactions in Tobacco Seedlings

Short-term (< 12 h) uptake experiments were conducted with6–7-week-old tobacco (Nicotiana tabacum L. cv. Ky 14)seedlings to determine absorption interactions between K⁺ andNH₄⁺. At equal solution concentrations (0.5 mol m^–3) netK⁺ uptake was inhibited 30–35% by NH₄⁺ and NH₄⁺ uptakewas decreased 9–24%. Removal of NH₄⁺ resulted in completerecovery in K⁺ uptake rate, but NH⁴⁺ uptake rate did not recoverwhen K⁺ was removed. In both cases, inhibition of the uptakerate of one cation saturated as the concentration of the othercation was increased up to 0.5 mol m^–3. The relative effectof K⁺-NH₄⁺ interactions was not altered when Cl- was replacedwith SO₄^2–, but the magnitudes of the uptake rates wereless in the absence of Cl-. The V_max for NH₄⁺ uptake was reducedfrom 128 to 105 µmol g^–1 dry wt. h^–1 in thepresence of 0.5 mol m^–3 K⁺ and the K_m for NH₄⁺ doubledfrom 12 to 27 mmol m^–3 in the presence of K⁺. The resultsof these K⁺-NH₄⁺ experiments are interpreted as mixed-noncompetitiveinteractions. However, an enhanced efflux of K⁺ coupled to NH₄⁺influx via an antiporter cannot be ruled out as contributingto the decrease in net K⁺ uptake. Key words: Nicotiana tabacum, K⁺, NH₄⁺, Uptake interactions     

Pyruvate Uptake by Mesophyll and Bundle Sheath Chloroplasts of a C4 Plant, Panicum miliaceum L.

Intact chloroplasts were isolated from mesophyll and bundlesheath protoplasts of a C₄ plant, Panicum miliaceum L., to measurethe uptake of [1-¹⁴C]pyruvate into their sorbitol-impermeablespaces at 4?C by the silicone oil filtering centrifugation method.When incubated in the dark, both chloroplasts showed similarslow kinetics of pyruvate uptake, and the equilibrium internalconcentrations were almost equal to the external levels. Whenincubated in the light, only mesophyll chloroplasts showed remarkableenhancement of the uptake, the internal concentration reaching10–30 times of the external level after 5 min incubation.The initial uptake rate of the mesophyll chloroplasts was enhancedabout ten fold by light and was saturated with increasing pyruvateconcentration; K_m and V_max were 0.2–0.4 mM and 20–40µmol(mg Chl)^–1 h^–1, respectively. The lightenhancement was abolished by DCMU and uncoupling reagents suchas carbonylcyanide-m-chlorophenylhydrazone and nigericin. Theseresults indicate the existence of a light-dependent pyruvatetransport system in the envelope of mesophyll chloroplasts ofP. miliaceum. The uptake activity of mesophyll chloroplastsboth in the light and the dark was inhibited by sulfhydryl reagentssuch as mersalyl and p-chloromercuriphenylsulfonate, but thebundle sheath activity was insensitive to the reagents. Thesefindings are further evidence for the differentiation of mesophylland bundle sheath chloroplasts of a C₄ plant with respect tometabolite transport. (Received July 3, 1986; Accepted October 8, 1986)     

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     

Active Uptake of CO2 by the Diatom Navicula pelliculosa

Mass spectrometry has been used to investigate the transportof CO₂ in the freshwater diatom Navicula pelliculosa. The timecourseof CO₂ formation in the dark after addition of 100 mmol m^–3dissolved inorganic carbon (DIC) to cell suspensions showedthat no external carbonic anhydrase (CA) was present in thesecells. Upon illumination, cells pre-incubated at pH 75 with100 mmol m^–3 DIC, removed almost all free CO₂ from themedium at an initial rate of 285 µmol CO₂ mg^–1Chl h^–1. Equilibrium between HCO₃^– and CO₂ in themedium occurred rapidly upon addition of bovine CA, showingthat CO₂ depletion resulted from a selective uptake of CO₂ ratherthan an uptake of all inorganic carbon species. However, photosyntheticO₂ evolution rate remained constant after CO₂ had been depletedfrom the medium indicating that photosynthesis is sustainedprimarily by active HCO₃^– uptake. Treatment of cells with2-iodoacetamide (83 mol m^–3) completely inhibited CO₂fixation but had little effect on CO₂ transport since initialrates of CO₂ depletion were about 81% that of untreated cells.Transfer of iodoacetamide-treated cells to the dark caused arapid increase in the CO₂ concentration in the medium largelydue to the efflux of the unfixed intracellular DIC pool whichwas found to be about 194 times the concentration of that inthe external medium. These results indicate that Navicula pelliculosaactively takes up molecular CO₂ against a concentration gradientby a process distinct from HCO₃^– transport. Key words: Dissolved inorganic carbon, carbonic anhydrase, bicarbonate transport, CO₂ transport, mass spectrometry     

L-Leucine Transport in Isolated Protoplasts of Vinca Suspension Culture: Characterization of Uptake

The uptake of L-leucine into Vinca protoplasts was studied undervarious conditions. The uptake was highly pH-dependent, withthe optimal pH between 3.0 and 4.0. The uptake was also energydependent, since azide, 2,4-dinitrophenol (DNP), carbonyl cyanidem-chlorophenyl hydrazone (CCCP), and iodoacetate inhibited theuptake. Oligomycin, N,N'-dicycIohexyI carbodiimide (DCCD) andvanadate, but not ouabain, inhibited the uptake, suggestingthat ATPase for H⁺ electrogenic extrusion was necessary to theuptake of L-leucine. The uptake showed stereospecificity, butwas partially inhibited by other L-amino acids. A kinetic studyof the uptake showed that the uptake was multiphasic with threesaturable phases and one unsaturable phase which occurred atconcentrations of L-leucine over 1 mM. The K_m values of thethree affinity sites were 1.4 x 10^–3 M, 1.3 x 10^–4M, 4.3 x 10^–5 M; the maximum velocity values were 3.3x 10^–8, 4.5 x 10^–9, 1.8 x 10_–9 mol/10 min/4x 10⁶ cells. (Received April 18, 1981; Accepted August 25, 1981)     

Persistence of the Potassium Uptake Rhythm in the Presence of Exogenous Sucrose in Lemna gibba G3

The potassium uptake rhythm in a flow medium culture of Lemnagibba G3 persisted in darkness for 3 days, when the flow mediumcontained sucrose (1%). The rhythm was damped out after thatin darkness but it persisted longer when the plants were keptunder continuous weak light (80 lux). The rhythm was not dampedout when a daily light pulse (4,200 lux for 15 min) was applied.A single light pulse (4,200 lux for 15 min) at hour 48 of theprolonged dark period caused the rhythm to start again. DCMU(1 µM) slightly reduced the amplitude of the rhythm butdid not nullify the effect of the inserted light pulse. (Received September 16, 1981; Accepted February 2, 1982)     

Characterization of regulatory mechanisms and states of human organic cation transporter 2

Polyspecific organic cation transporters (OCTs) have a large substrate binding pocket with different interaction domains. To determine whether OCT regulation is substrate specific, suitable fluorescent organic cations were selected by comparing their uptake in wild-type (WT) human embryonic kidney (HEK)-293 cells and in HEK-293 cells stably transfected with hOCT2. N-amidino-3,5-diamino-6-chloropyrazine-carboxamide (amiloride) and 4-[4-(dimethylamino)-styryl]-N-methylpyridinium (ASP) showed concentration-dependent uptake in hOCT2 at 37°C. After subtraction of unspecific uptake determined in WT at 37°C or in hOCT2 at 8°C saturable specific uptake of both substrates was measured. K_m values of hOCT2-mediated uptake of 95 µM amiloride and 24 µM ASP were calculated. Inhibition of amiloride and ASP uptake by several organic cations was also measured [IC₅₀ (in µM) for amiloride and ASP, respectively, tetraethylammonium (TEA) 98 and 30, cimetidine 14 and 26, and tetrapentylammonium (TPA) 7 and 2]. Amiloride and ASP uptake were significantly reduced by inhibition of Ca²⁺/CaM complex (–55 ± 5%, n = 10 and –63 ± 2%, n = 15, for amiloride and ASP, respectively) and stimulation of PKC (–54 ± 5%, n = 14, and –31 ± 6%, n = 26) and PKA (–16 ± 5%, n = 16, and –18 ± 4%, n = 40), and they were increased by inhibition of phosphatidylinositol 3-kinase (+28 ± 6%, n = 8, and +55 ± 17%, n = 16). Inhibition of Ca²⁺/CaM complex resulted in a significant decrease of V_max (160–99 photons/s) that can be explained in part by a reduction of the membrane-associated hOCT2 (–22 ± 6%, n = 9) as determined using FACScan flow cytometry. The data indicate that saturable transport by hOCT2 can be measured by the fluorescent substrates amiloride and ASP and that transport activity for both substrates is regulated similarly. Inhibition of the Ca²⁺/CaM complex causes changes in transport capacity via hOCT2 trafficking. organic cation transport; fluorescence measurement; 4-[4-(dimethylamino)-styryl]-n-methylpyridinium; amiloride     

The Effects of Light Intensity and External Potassium Level on Root/Shoot Ratio and Rates of Potassium Uptake in Perennial Ryegrass (Lolium perenne L.)

Loliun perenne L. (cv.S. 23) was grown on vermiculite in winterin a heated greenhouse for 8 weeks under factorial combinationsof two potassium regimes (nominally 6 parts/10⁶ and 156 parts/10⁶in Hewitt's solution) and three densities of artificially supplementedvisible radiation flux (36.1, 7.3, and 2.2 W m^–2). Growthand potassium uptake were studied through the calculation ofvarious growth functions from fitted curves. There was little effect of potassium treatment but the experimentalmaterial responded markedly to light. Leaf-area ratio in thethree treatments showed extreme plasticity in increasing from2–3 x 10^–2 through 6 x 10^–2 to 8–9 x10^–2 m² g^–1 as light intensity decreased. Correspondingdecreases in unit leaf rate, however, caused over-all reductionsin relative growth rate. Specific absorption rates for potassium (A_K, dry-weight basis)were strongly reduced at the lower light intensities but alsodisplayed complex ontogenetic drifts. Values of the allometricconstant, k (the ratio of root and shoot relative growth rates),decreased from c. 0.7 at 36.1 W m^–2 through c. 0.3 at7.3 W m^–2 to a value not significantly different fromzero (P < 0.05) at 2.2 W m^–2. In material grown under the two higher light intensities a constantinverse relationship was found between the mass ratio of rootand shoot and the corresponding activity ratio. The resultsconform to this model: Mass ratio = –0.001+45.0 (1/activityratio) where activity ratio is expressed as specific absorptionrate for potassium (in µg g root^–1 h^–1)/unitshoot rate (rate of increase of whole-plant dry weight per unitshoot dry weight, in mg g shoot^–1 h^–1). The implicationsof this relationship are discussed.     

Uptake and Accumulation of Inorganic Carbon by a Freshwater Diatom

Colman, B. and Rotatore, C. 1988. Uptake and accumulation ofinorganic carbon by a freshwater diatom.—J. exp Bot 39:1025–1032. The mechanism of uptake of inorganic carbon and its accumulationhas been studied in the freshwater diatom Navicula pelliculosa.No external carbonic anhydrase could be detected, although itwas detected in cell extracts. The rate of photosynthetic O₂evolution, in media in the range pH 7.5–8.5, exceededthe calculated rate of CO₂ supply 2- to 5-fold, indicating thatHCO^–₃ was taken up by the cells. At an external pH of7.5, the internal pH, measured by ¹⁴C-dimethyloxazolidine-2,4-dione distribution between the cells and the medium, was pH7.6 in the light and pH 7.4 in the dark. Accumulation of inorganiccarbon was determined by the silicone oil centrifugation methodand inorganic carbon pools of 23.5 mol m^–3 were found,a concentration 21.6-fold that in the external medium. The resultsindicate an active accumulation of inorganic carbon againstpH and concentration gradients in this diatom, probably by activeHCO^–₃ uptake. Key words: Bicarbonate transport, carbon dioxide, carbonic anhydrase, CO₂ affinity, CO₂ concentrating mechanism, internal pH, Navicula pelliculosa     

The Uptake of Gaseous Ammonia by the Leaves of Italian Ryegrass

Lockyer, D. R. and Whitehead, D. C. 1986. The uptake of gaseousammonia by the leaves of Italian ryegrass.—J. exp. Bot.37: 919–927. Plants of Italian ryegrass (Lolium multiflorum Lam.) grown insoil with two rates of added ¹⁵N-labelled nitrate were exposed,in chambers, for 40 d to NH₃ in the air at concentrations of16, 118 and 520 µg m^–3. At the highest concentrationof NH₃, this source provided 47?3% of the total nitrogen inplants grown with the lower rate of nitrate addition (100mgN kg^–1 dry soil) and 35?2% with the higher rate (200mgN kg^–1 dry soil) At the intermediate concentration ofNH₃, the contributions to total plant N were 19?6% and 10?8%,respectively, at low and high nitrate while, at the lowest concentrationof NH₃, they were 5?1% and 32%. Most of the N derived from theNH₃ remained in the leaves, but some was transported to theroots. The amount of N derived from the NH³ that was presentin the leaves was not reduced by washing the leaves in waterat pH 5?0 before harvesting, indicating that the N was assimilatedby the plant and not adsorbed superficially. Rates of uptakeof NH₃ per unit leaf area ranged from 1?7 µg dm^–2h^–1 at a concentration of 16 µg m^–3 to 29?0µg dm^–2 h^–1 at a concentration of 520 µgm^–3 and with the lower rate of nitrate addition. Increasingthe supply of nitrate to the roots slightly reduced the rateof uptake of NH₃ per unit leaf area. Uptake of N from the higherrate of nitrate was reduced at the highest concentration ofNH₃ in the air. Key words: Ammonia, nitrogen, leaf sorption, Lolium multiflorum     

The Effect of Sucrose Supply on the Energization of Amino Acid Uptake by Cotyledons of Euphorbia lathyris L

The cotyledons of Euphorbia lathyris L. take up sucrose andamino acids from the endosperm. The interaction between theuptake of sucrose and that of amino acids by cotyledons of intactseedlings was investigated. Sucrose (100 mol m^–3) reducedvaline uptake to 75% of the control rate; the active uptakecomponent of valine uptake was reduced from 45 to 25 % of thetotal uptake rate. In a reverse experiment, 100 mol m^–3valine inhibited sucrose uptake by 25%. At 500 mol m^–3sucrose, valine uptake was completely restored to the controlrate, whereas high valine concentrations failed to restore sucroseuptake. The stimulation of valine uptake by sucrose is linkedto the role of sucrose as a primary respiratory substrate. Whenthe cotyledons were bathed in sucrose concentrations rangingfrom 0 to 100 mol m^–3 (these concentrations are non-saturatingwith respect to sucrose uptake), a constant 1.8% of the sucrosetaken up was respired. The K_m of the concentration-dependentsucrose oxidation (44±6 mol m^–3) agreed reasonablywell with that for sucrose uptake (29±6 mol m^–3).When the external sucrose concentration was increased from 100to 600 mol m^–3, the sucrose uptake increased by 30% again,while sucrose oxidation was increased by 300%. This increasewas not due to an increased engagement of the alternative (cyanide-resistant)pathway for respiration. Alternative pathway, Euphorbia lathyris L., fermentation, seedling, sucrose uptake, valine uptake     

Uptake of 13C and 15N (ammonium, nitrate and urea) by Microcystis in Lake Kasumigaura

The uptake rate of carbon and nitrogen (ammonium, nitrate andurea) by the Microcystis predominating among phytoplankton wasinvestigated in the summer of 1984 in Takahamaira Bay of LakeKasumigaura. The V_max values of Microcystis for nitrate (0.025–0.046h^–1) and ammonium (0.15–0.17 h^–1) were considerablyhigher than other natural phytoplankton. The ammonium, nitrateand urea uptake by Microcystis was light dependent and was notinhibited with nigh light intensity. The K₁ values were farlower than the I_k values. The carbon uptake was not influencedby nitrogen enrichment. Microcystis accelerated the uptake rateby changing V_max/K _s value when nitrogen versus carbon contentin cells declined. Nitrate was scarcely existent in TakahamairiBay during the summer, when Microcystis usually used ammoniumas the nitrogen source. However, the standing stock of ammoniumin the water was far lower than the daily ammonium uptake rates.Therefore, the ammonium in this water had to be supplied becauseof its rapid turn-over time (–0.7–2.6 h).