Transnodal Transport of 14C in Nitella flexilis: I. TANDEM CELLS WITHOUT APPLIED PRESSURE GRADIENTS

Using NaH¹⁴CO₃ (0·01-0·03 mol m^–3) fed to5·0 mm of Nitella flexilis in artificial pond water at22–25°C, we have found that uptake in 5 min or in1 h varies with the streaming rate of the fed cell and is reducedby anoxia over the uptake position. We have also found thatthe %¹⁴C transported across the node between two internodalcells in tandem is highly sensitive to the streaming rate ineach cell, to the physiological state of the cells (summer versuswinter), to the method of feeding (5 min versus 1 h) and tocovering the node, particularly with winter cells or summercells preconditioned for 3 h in the dark and run in the dark.Transnodal transport by plasmodesmata is sensitive to anoxiaand seems to be at least partly active. Key words: Node, plasmodesmata, anoxia, active transport, influx     

Influence of Cytoplasmic Streaming and Turgor Pressure Gradient on the Transnodal Transport of Rubidium and Electrical Conductance in Chara corallina

In order to study the transnodal transport of Rb⁺ in internodalcells of Chara corallina, a low-temperature loading system wasestablished to separate the loading process from the transportprocess. Tandem cells, consisting of internode-node-internode,were isolated from algal plants. Treatment of a single internodewith 100 mM RbCl at 5°C for 30 min caused an accumulationof 43 mM Rb⁺ in the cytoplasm of this cell (= source cell),but no Rb⁺ was found in the other internode (= sink cell) ofthe tandem cells. In 40 min after a return to 25°C, about12% of the Rb⁺ loaded in the source cell was transported intothe sink cell. The apparent transnodal permeability of Rb⁺ wascalculated to be 4.6 x 10^–7 m.s^–1. Under the assumptionthat the total cross-sectional area of plasmodesmata occupies10% of the nodal area, the diffusion coefficient of RbCl throughplasmodesmata was calculated to be 2.3 x 10^–11 m².s^–1which is about 1% of the free diffusion coefficient in water(2 x 10^–9m².s^–1). The transnodal transport of Rb⁺ was intimately correlated withthe rate of cytoplasmic streaming. The rate of streaming inboth the source and sink cells was varied either by treatingthe cells with cytochalasin B (CB) or by lowering the temperature.The transport rate correlated with the streaming rate irrespectiveof the method used. Since the level of ATP was not influencedby CB or low temperature, the transnodal transport is assumedto be the result of passive diffusion process through plasmodesmata. A turgor pressure gradient across the node decreased both thenodal electrical conductance and the transnodal transport ofRb⁺. By contrast, the exposure of both internodal cells to asolution of sorbitol had no effect on either of them. A turgorpressure gradient of 240 mOsm decreased the transport of Rb⁺in the first hour to 3% of the control, while it decreased thenodal conductance to about 50%. The increase in the electricalresistance occurred on the junction side between the node andthe internode that was treated with sorbitol. Cytochalasin Ehad no effect on the nodal electrical resistance. It is assumedthat plasmodesmata are equipped with a valve-like mechanismwhich is sensitive to the gradient of turgor pressure acrossthe node and is not regulated by an actomyosin system. (Received February 15, 1989; Accepted April 20, 1989)     

Transnodal Transport of 14C in Nitella flexilis: III. FURTHER STUDIES ON DISSOLVED INORGANIC CARBON MOVEMENTS IN TANDEM CELLS

Using NaH ¹⁴CO₃ (0.1 to 3.0 mol m ^–3) fed to 5.0 mm ofan internodal cell of Nitella flexilis in artificial pond waterat pH 6.8 and 19–25 °C, we have found that the carbohydrates(lactose, xylose, mannose, galactoseand sucrose) are formedby photo-assimilation from ¹⁴C-DIC (dissolved organic carbon)in 1 h and are carried in the cytoplasm with amino acids (glutamineand alanine in particular) to the node attached to a tandeminternodal cell. These small sacchandes and some amino acidspassed, apparently unchanged, across the node into the sinkcell. Influx of DIC was highly sensitive to inhibitors of photosystemsI and II (at concentrations around 1.0 mol m^–3) and touncouplers of phosphorylation. Most influx inhibitors, exceptfor NaN₃, also reduced % transnodal transport. NH₄⁺ (1.0 to5.0 mol m^–3) appeared to reduce % transport in light (butnot in dark) with much less effect on influx. Dinitrophenoland Na citrate (at pH 8.2) also strongly reduced apparent %transport without altering cytoplasmic streaming rates. Someof the apparent reduction of transport could be due to an alterationof metabolism or of sequestering in the feed cell, but withNH₄⁺ the latter was not detectable. Our findings support thehypothesis that transnodal transport, including that via theplasmodesmata, is at least partly ‘active’ and requiresmetabolic energy to sustain it. Key words: Inhibitors, influx, plasmodesmata, nodal transport, ¹⁴C, ³⁶Cl     

Transnodal Transport of 14C in Nitella flexilis: II. TANDEM CELLS WITH APPLIED PRESSURE GRADIENTS

Using carefully standardized test conditions and tandem pairsof cells of Nitella flexilis, the influx of ¹⁴C (added as H¹⁴CO₃^–and transnodal transport were studied under various pressuregradients applied across the node up to P=± 2·5bar. When mannitol was used as the osmoticum, influx was foundto increase only when the mannitol solution was around the cellproximal to the feed. ¹⁴C was transported across the node tothe distal cell, probably as ¹⁴C-photosynthate products, evenagainst a pressure gradient of 2 bars or more, as was ³⁶Cl^–and ³²P. The % transported in general decreased with increasingP, whether assisted or opposed by added pressure. It was unchangedby the presence of mannitol at the node and was essentiallythe same whether the pressure gradient was produced by directpressure or by use of the osmoticum. Transnodal transport of¹⁴C products is almost certainly via plasmodesmata and appearsto be largely by an active mechanism. In absolute amounts itis the same whether the pressure gradient assists or opposesflow. Valving is evident at the node, increasing the resistanceto transport as the pressure gradient increases whether ¹⁴C(asHCO₃^–), ⁴²K⁺ (as KCl), ³⁶Cl^– (as NaCl) or ³²P (asNa₃PO₄) are used to detect it. The mechanism of movement ofK⁺ across the node differs from that of photosynthate products. Key words: Node, plasmodesmata, pressure gradients, active transport     

Rates of Axial Transport of 11C and 14C in Characean Cells: Faster than Visible Streaming?

Movements of ¹¹C and ¹⁴C in N. translucens occur at rates twoto five times greater than those of visually observed streaming.Like cytoplasmic streaming, longitudinal tracer movement isstopped reversibly by action potentials, irreversibly by N-ethylmaleimide(NEM) and is unaffected by colchicine (colch), suggesting thatboth processes share a common mechanism. Colchicine causes anincreased loading delay time. In both N. translucens and C. corallina the activity of ¹¹Cand ¹⁴C at the nodes shows a sharp discontinuity: it is lowon the feed side of the node and high at the node itself. Thissuggests that transport across plasmodesmata may be active. Key words: Axial-carbon transport, Cytoplasmic streaming, Carbon     

Intercellular Transport in Plants: I. THE RATE OF TRANSPORT OF CHLORIDE AND THE ELECTRIC RESISTANCE

A quantitative study has been made of the intercellular movementof chloride in Chara corallina, using pairs of joined internodalcells. One cell of the pair (cell 1) was exposed to a solutioncontaining ³⁶Cl; the distribution of this tracer between thecells was determined at the end of the uptake period. Of thechloride taken up, 0.29 was transported out of cell 1 for alluptake times from 1.8 to 22 ks and 0.57 was transported to thevacuole of cell 1, in experimental series I. In series II, thefraction transported out of cell 1 was 0.43 at 22 and 43 ks,but 0.17 at 600 s. These results represent a rate of transport of 4 to 60 pmols^–1, across an intercellular wall of area 1.5 x 10^–6m²; the wall has 0.03 to 0.04 of its area occupied by plasmodesmata.The estimate of transport rate is based on an attempt to determinethe specific activity of the cytoplasm of cell 1. The electricresistance of the node was found to be 47 m m². The observed transport rate can be explained by diffusion inthe plasmodesmata, without the need to postulate active processes.Diffusion in the plasmodesmata is slower than in free solutionby an ‘impediment factor’ of 7 to 700, dependingon the assumed chloride concentration of the ground-plasm. Ifthe plasmodesmata offer the major conducting path for electriccurrent, the electric impediment factor is 390. Chloride entersthe plasmodesmata from the same small kinetic compartment whichsupplies the flux to the vacuole, or from a smallintermediatecompartment.     

Intercellular Transport and Cytoplasmic Streaming in Chara hispida

The correlation between the velocities of cytoplasmic streamingand of translocation of ¹⁴C-photosynthate and ³²P-phosphateassociated radioactivity has been investigated in whole plantsof the green freshwater alga Chara hispida L. Tracer was suppliedto the plant's rhizoid system in a split-chamber. The velocityof cytoplasmic streaming of 52±3.3 µm s^–1compares with 57±10 µm s^–1 found for ¹⁴C-transportand 32±20 µm s^–1 found for ³²P-transport.There was no indication of intercellular translocation at avelocity faster than visible streaming. Cytochalasin B inhibitedthe translocation of ³²P and cytoplasmic streaming. CytochalasinB becomes fully effective in inhibiting streaming and transportafter an incubation time of at least 5 h. Key words: Chara hispida, Cytoplasmic streaming, Intercellular transport     

Intercellular Transport in Plants: II. CYCLOSIS AND THE RATE OF INTERCELLULAR TRANSPORT OF CHLORIDE IN CHARA

The effect of streaming speed on intercellular transport ofchloride has been studied using pairs of internodal cells ofChara. The rate of transport was measured by that fraction ofthe chloride that entered one internode which was transportedout of it into the cells of the node and the next internode.The speed of cytoplasmic streaming was altered by treating thefirst cell with cytochalasin B. The relative rate of intercellular transport depended markedlyon the streaming speed at all speeds up to those found in untreatedcells. The chloride influx into the treated cell did not dependon the streaming speed. It is concluded that the rate of intercellular transport oflow molecular weight solutes in Chara will be normally limitedby the rate at which cytoplasmic streaming brings solute tothe plasmodesmata, rather than by the diffusion permeabilityof the plasmodesmata. This conclusion may well apply to othercharophyte plants, and could in principle apply to higher plants.     

Reactivation of Cytoplasmic Streaming in a Tonoplast-Permeabilized Cell Model of Acetabularia

To find whether cytoplasmic streaming in Acetabularia is controlledby Ca²⁺, a tonoplast-permeabilized cell model was prepared usinga vacuolar perfusion technique. The cytoplasmic streaming remainedalmost normal after perfusion with EGTA medium (10 mM EGTA,40 mM PIPES, 5mM MgCl₂ and 800 mM sorbitol, pH 6.9), but stoppedwithin 10 min when saponin medium (EGTA medium plus 50 µg/mlsaponin, 50 µg/ml hexokinase and 5 mM glucose) was perfused.This model system was reactivated with a solution containing0.5 mM ATP and different concentrations of Ca²⁺ (reactivationmedium). With the reactivation medium at pCa 6–5, theresumed streaming lasted for about 10 min before the cytoplasmaggregated. At pCa 4–3, the streaming was observed onlyfor a few minutes because the cytoplasm aggregated quickly.At pCa 7, no reactivated movement was observed. Reactivationwas not induced in an ATP- or Mg²⁺-deficient medium even inthe presence of an adequate concentration of Ca²⁺, and was inhibitedby 50 µg/ml cytochalasin B or 1 mM N-ethylmaleimide. We concluded from these observations that the cytoplasmic streamingin Acetabularia is very likely to be driven by the actomyosinsystem in the presence of Mg-ATP and Ca²⁺ at pCa 6–5. (Received October 31, 1984; Accepted April 1, 1985)     

Effect of Chilling Temperatures on the Protoplasmic Streaming of Plants from Different Climates

A microscope mount was designed so that specimen temperaturescould be monitored and controlled without impairing phase contrastoptics and used to measure rates of protoplasmic streaming between0 and 25 ?C in trichome cells of Lycopersicon esculentum, Lycopersiconhirsutum, Citrullus vulgaris, Tradescantia albiflora, Digitalispurpurea, and Veronica persica. Between 10 and 20 ?C the rates of streaming varied from 2–6µm s^–1 depending on the temperature, and differencesbetween the species were small. The temperature coefficientof streaming rates was found to increase as the temperaturewas lowered so that the plot of log rate against temperaturehad a steeper slope at the lower temperatures. The largest temperature cofficients were for the warmth-requiringL. esculentum (tomato) and C. vulgaris (water melon), and thesmallest for the temperate-zone plants V. persica (speedwell)and D. purpurea (foxglove). The changes in rate always occurredover a range of temperature; no ‘critical temperature’wasobserved below which streaming abruptly stopped and above whichit was active, although the amount of streaming as well as therate decreased as the lowest temperatures were approached. The temperatures experienced by the specimens during the experimentdid not affect the recovery of normal streaming rates betweenabout 10 and 20 ?C. In a population of a wild tomato, Lycopersicon hirsutum Humb.and Bonpl., collected from different altitudes in Peru and Ecuador,i.e. from locations of different environmental temperature,the rate of protoplasmic streaming at 5 ?C was greatest in thevarieties collected from the highest altitudes. The resultssuggest that streaming rates correlate with genetic adaptationto low temperature in the species examined.     

Impaired trafficking of choline transporter-like protein-1 at plasma membrane and inhibition of choline transport in THP-1 monocyte-derived macrophages

The present study investigates choline transport processes and regulation of choline transporter-like protein-1 (CTL1) in human THP-1 monocytic cells and phorbol myristate 13-acetate (PMA)-differentiated macrophages. Choline uptake is saturable and therefore protein-mediated in both cell types, but its transport characteristics change soon after treatments with PMA. The maximal rate of choline uptake intrinsic to monocytic cells is greatly diminished in differentiated macrophages as demonstrated by alterations in V_max values from 1,973 ± 118 to 380 ± 18 nmol·mg^–1·min^–1, when the binding affinity did not change significantly (K_m values 56 ± 8 and 53 ± 6 µM, respectively). Treatments with hemicholinim-3 effectively inhibit most of the choline uptake, establishing that a choline-specific transport protein rather than a general transporter is responsible for the observed kinetic parameters. mRNA screening for the expression of various transporters reveals that CTL1 is the most plausible candidate that possesses the described kinetic and inhibitory properties. Fluorescence-activated cell sorting analyses at various times after PMA treatments further demonstrate that the disappearance of CTL1 protein from the cell surface follows the same trend as the reduction in choline uptake. Importantly, the loss of functional CTL1 from the cell surface occurs without significant changes in total CTL1 protein or its mRNA level indicating that an impaired CTL1 trafficking is the key contributing factor to the reduced choline uptake, subsequent to the PMA-induced THP-1 differentiation to macrophages. protein trafficking     

Photoinhibition and light-induced cyclic electron transport in ndhB(-) and psaE(-) mutants of Synechocystis sp. PCC 6803

The ndhB^– and psaE^– mutants of the cyanobacteriumSynechocystis sp. PCC 6803 are partly deficient in PSI-drivencyclic electron transport. We compared photoinhibition in thesemutants to the wild type to test the hypothesis that PSI cyclicelectron transport protects against photoinhibition. Photoinhibitorytreatment greatly accelerated PSI cyclic electron transportin the wild type and also in both the mutants. The psaE^–mutant showed rates of PSI cyclic electron transport similarto the wild type under all conditions tested. The ndhB^–mutant showed much lower rates of PSI cyclic electron transportthan the wild type following brief dark adaptation but exceededwild type rates after exposure to photoinhibitory light. Thewild type and both mutants showed similar rates of photoinhibitiondamage and photoinhibition repair at PSII. Photoinhibition atPSI was much slower than at PSII and was also similar betweenthe wild type and both mutants, despite the known instabilityof PSI in the psaE^– mutant. We conclude that photoinhibitorylight induces sufficient PSI-driven cyclic electron transportin both the ndhB^– and psaE^– mutants to fulfill anyrole that cyclic electron transport plays in protection againstphotoinhibition. ⁴ Corresponding author: E-mail, sherbert@uwyo.edu; Fax, +1-307-766-2851;Phone, +1-307-766-4353.     

The Polarity of Movement of Endogenously Produced IAA in Relation to a Gravity Perception Mechanism

The polarity of radioactive IAA transport in segments of theleaf sheath base of Avena fatua L. is reversed upon their inversionthrough 180° transport towards the apex being greater thantowards the base. Changes in rates of transport leading to thisreversal can be detected within 10–20 min, correlatingwith the timing of statolith movements from the base to theapex of statocyte cells and conforming to a proposed model forthe gravity control of auxin transport. Transport of H³-trytophan-derived H³-IAA was found to undergosimilar changes in polarity upon re-orientation as did exogenouslyapplied H³ or C¹⁴ IAA. It is concluded that the proposed modelalso relates to the movement of endogenously produced IAA.     

Intracellular Ca2+ Concentration and Cytoplasmic Streaming in Vallisneria Mesophyll Cells

Intracellular Ca²⁺ concentration regulating the cytoplasmicstreaming in Vallisneria mesophyll cells was estimated. Theleaf segment was cut open at the middle of the mesophyll celllayers and the exposed mesophyll cells were treated with testsolutions of various Ca²⁺ concentrations in the dark. This allowedA23187 [GenBank] , a calcium ionophore, to exert its full effect on thecell membrane. The streaming was induced or maintained in solutions which containedCa²⁺ at lower than 10^–6M. However, Ca²⁺ at concentrationshigher than 10^–5M had a definite, inhibitory effect. Theinduction and cessation of streaming could be repeated by alternatelychanging the solutions. (Received March 14, 1986; Accepted May 15, 1986)     

Fluid transport by human nonpigmented ciliary epithelial layers in culture: a homeostatic role for aquaporin-1

We report for thefirst time that cultured nonpigmented human ciliary epithelial (NPE)cell layers transport fluid. Cells were grown to confluence onpermeable membrane inserts, and fluid transport across the resultingcell layers was determined by volume clamp at 37°C. These cell layerstranslocated fluid from the apical to the basal side at a steady rateof 3.6 µl · h¹ · cm²(n = 4) for 8 h. This fluid movement wasindependent of hydrostatic pressure and was completely inhibited by 1 mM ouabain, suggesting it arose from fluid transport. Mercuricchloride, a nonspecific but potent blocker ofHg²⁺-sensitive aquaporins, and aquaporin-1 antisenseoligonucleotides both partially inhibited fluid transport across thecell layers, which suggests that water channels have a role in NPE cellhomeostasis. In addition, these results suggest that of the two ciliaryepithelial layers in tandem, the NPE layer by itself can transportfluid. This cultured layer, therefore, constitutes an interesting model that may be useful for physiological and pharmacologicalcharacterization of ciliary epithelial fluid secretion.

     

Interactions of NH4+ and L-glutamate with NO3- transport processes of non-mycorrhizal Fagus sylvatica roots

The processes of NO₃^– uptake and transport and the effectsof NH₄⁺ or L-glutamate on these processes were investigatedwith excised non-mycorrhizal beech (Fagus sylvatica L.) roots.NO₃^– net uptake followed uniphasic Michaelis-Menten kineticsin a concentration range of 10µM to 1 mM with an apparentK_m of 9.2 µM and a V_max of 366 nmol g^–1 FW h^–1.NH₄⁺, when present in excess to NO₃^–, or 10 mM L-glutamateinhibited the net uptake of NO₃^– Apparently, part of NO₃^–taken up was loaded into the xylem. Relative xylem loading ofNO₃^– ranged from 3.21.6 to 6.45.1% of NO₃^– netuptake. It was not affected by treatment with NH₄⁺ or L-glutamate.¹⁶N/¹³N double labelling experiments showed that NO₃^–efflux from roots increased with increasing influx of NO₃^–and, therefore, declined if influx was reduced by NH₄⁺ or L-glutamateexposure. From these results it is concluded that NO₃^–net uptake by non-mycorrhizal beech roots is reduced by NH₄⁺or L-glutamate at the level of influx and not at the level ofefflux. Key words: Nitrate transport, net uptake, influx, efflux, ammonium, Fagus, Fagaceae     

Are Mistletoes Shade Plants? CO2Assimilation and Chlorophyll Fluorescence of Temperate Mistletoes and their Hosts

Mistletoes usually have slower rates of photosynthesis thantheir hosts. This study examines CO₂assimilation, chlorophyllfluorescence and the chlorophyll content of temperate host–parasitepairs (nine hosts parasitized by Ileostylus micranthus and Carpodetusserratus parasitized by Tupeia antarctica). The hosts of I.micranthus had higher mean annual CO₂assimilation (3.59 ±0.41 µmol m^-2 s^-1) than I. micranthus(2.42 ± 0.20µmol m^-2 s^-1), and C. serratus(2.41 ± 0.43 µmolm^-2 s^-1) showed higher CO₂assimilation than T. antarctica(0.67± 0.64 µmol m^-2 s^-1). Hosts saturated at significantlyhigher electron transport rates (ETR) and light levels thanmistletoes. The positive relationship between CO₂assimilationand electron transport suggests that the lower CO₂assimilationrates in mistletoes are a consequence of lower electron transportrates. When photosynthetic rates, ETR and chlorophyll a /b ratioswere adjusted for photosynthetically active radiation, hostsdid not have significantly higher CO₂assimilation (3.21 ±0.37 µmol m^-2 s^-1) than mistletoes (2.54 ± 0.41µmol m^-2 s^-1), but still had significantly higher ETRand chlorophyll a / b ratios. The electron transport rates,saturating light and chlorophyll a / b ratios of sun leavesfrom mistletoes were similar to host shade leaves. These responsesindicate that in comparison with their hosts, mistletoe leaveshave the photosynthetic characteristics of the leaves of shadeplants. Copyright 2000 Annals of Botany Company CO₂assimilation, photosynthetic active radiation (PAR), chlorophyll fluorescence, electron transport rate (ETR), photochemical quenching (q_p), non-photochemical quenching (q_n), sun and shade leaves, chlorophyll content, Ileostylus micranthus, Tupeia antarctica, New Zealand     

Transport and Fixation of Inorganic Carbon during Photosynthesis of Anabaena Grown under Ordinary Air. I. Active Species of Inorganic Carbon Utilized for Photosynthesis

Inorganic carbon transport during photosynthesis of cyanobacteriumAnabaena variabilis grown under ordinary air was investigatedby supplying ¹⁴CO₂ or H¹⁴CO₃^– solution to three differentstrains. Both CO₂ and HCO₃^– were accumulated within thealgal cells. In the cell suspension from which dissolved inorganiccarbon had been depleted by pre-illumination, CO₂ was transportedand accumulated faster than HCO₃^–. When the concentrationof HCO₃^– injected into the cell suspension of A. variabilisM3 was 25 times as high as that of CO2 (the expected ratio atequilibrium at pH 7.8), the initial rates of fixation of bothinorganic carbon species were practically the same. On the otherhand, when ¹⁴CO₂ or H¹⁴CO₃^– was added under steady statephotosynthetic conditions, both carbon species were transportedat similar rates. The ratio of fixed to transported carbon measuredafter the initial 5 s was only 23–27% regardless of thecarbon species supplied. This percentage is much lower thanthat reported for Chlorella cells. ¹ To whom reprint requests should be addressed (Received June 30, 1986; Accepted December 16, 1986)     

Biomass, feeding and production of Noctiluca scintillans in the Seto Inland Sea, Japan

The abundance and biomass of the large heterotrophic dinoflagellateNoctiluca scintillans, together with the changes in its potentialprey items, were monitored in the Seto Inland Sea, Japan, duringsummer 1997 (17 July-11 August). Growth and grazing rates ofNscintillans fed natural plankton populations were also measuredeight and seven times, respectively, during the survey period.The abundance and biomass of N scintillans averaged over thewater column (19 m) were in the range 1–345 cells 1^–1(temporalaverage = 93 cell1^–1) and 0.1–49.6 µg C l^–1(temporalaverage = 13.8 µg C l^–1; three times higher thanthat of calanoid copepods during the same period). Noctilucascintillans populations followed the changes in phytoplankton:N.scintillans biomass was increasing during the period of diatomblooms and was at a plateau or decreasing during periods oflow chlorophyll a. The growth rates of N.scintillans (µ)were also consistent with the wax and wane of the N.scintillanspopulation: N.scintillans showed highest growth rates duringdiatom blooms. A simple relationship between µ and chlorophylla concentration was established, and the production of N.scintillanswas estimated using this relationship and the measured biomass.The estimated production averaged over the water column wasin the range >0.1–5.2 µg C l^–1 day^–1(temporalaverage = 1.4 µg C l^–1 day^–1; 64% of the productionof calanoid copepods during the same period). Diatom clearancerates by N.scintillans were in the range 0.10–0.35 mlcell^–1 day^–1, and the phytoplankton population clearanceby N.scintillans was >12% day^–1. Thus, although thefeeding pressure of N.scintillans on phytoplankton standingstock was low, N.scintillans was an important member of themesozooplank-ton in terms of biomass and production in the SetoInland Sea during summer.     

A study of feeding in predacious ciliates using prey ciliates labeled with fluorescent microspheres

Feeding in predacious estuarine ciliates was investigated ina series of laboratory experiments using a new method of preylabeling which facilitates microscopic indentification of ingestedprey items. Ingestion rates of Mesodinium pulex, Euplotes vannusand E.woodruffi were estimated using the appearance, insidethe predator, of bacteriovorous ciliates (Metanophrys sp., Cyclidiumsp.and Pleuronema sp ) labeled with fluorescent microspheres. Preyremain motile and have presumably unaltered surface characteristics.Ingestion rates of log-growth phase predators increased withprey density. Mesodinium pulex ingested 0 15–0.32 cellsh^–1 over a prey concentration of 60–2300 ml^–1.Maximum ingestion rates of E. woodruffi and E. vannus were 4.5and 3.4 cells h^–1 respectively, estimated at prey abundancesof 75 and 172 cells ml^–1 respectively. Comparisons offeeding rates on prey of different sizes, and the effects ofstarvation, indicated that ingestion is likely limited by differentfactors in ‘raptorial’ (M pulex) and ‘filterfeeding’ (Euplotes spp.) predators.