Transport of 14C-lableled indoleacetic acid in Vicia root segments

IAA transport in Vicia root segments was investigated for comparisonwith that in intact roots. Lanolin paste (1-mm-wide ring) oragar blocks (3?3?1.5mm), both containing IAA-2-¹⁴C were appliedto the surface or a cut end of the root segments, respectively;transported ¹⁴C was collected in receiver agar blocks placedon the cut end of the segments. When lanolin paste was appliedto 5-mm segments, basipetal transport of IAA predominated overacropetal transport. When agar blocks were applied to 1- and2-mm segments, the same was true; in longer segments (3 and5 mm long), however, basipetal movement occurred predominantlyat first but was surpassed by acropetal movement after 2–3hr. Among the segments tested (regions 2–4, 4–6and 8–10 mm from the tip), the most apical one showedthe distinctest predominancy of basipetal movement. The velocitiesof the acropetal and basipetal movement of the ¹⁴C were estimatedat 3–3.8 and 8–12 mm/hr, respectively. Autoradiographicstudy and the experiment in which wire was inserted longitudinallythrough the central part of the segments showed that basipetalmovement occurred mainly through the outer part of the rootsand acropetal movement mainly through the central cylinder.The present results were compatible with those obtained previouslywith intact roots. Some properties of polar movement, such asits specificity, inhibition by TIBA, and dependency on terneprature are described. (Received March 22, 1978; )     

Auxin Transport in Secondary Tissues1

Auxin transport was investigated in excised stem segments ofNicotiana tabacum L. by the agar block technique using [1-¹⁴C]indol-3yl-acetic acid (IAA). The ability of the stems to transportauxin basipetally increased as secondary development proceeded;by contrast the ability of the pith to transport auxin declinedwith age. By separation of the stem tissues it was shown thatthe great majority of auxin transport took place in cells associatedwith the internal phloem and in cells close to the cambium;in both cases similar velocities of transport were found (c.5.0 mm h^–1 at 22°C). The effects of osmotic gradientson auxin transport through the internal phloem were investigated.IAA was found by chromatography to account for practically allthe radioactivity in receiver blocks and other extracts of stemsegments. The significance of these results is discussed.     

Effects of algal concentration, bacterial size and water chemistry on the ingestion of natural bacteria by cladocerans

Journal of Plankton Research, 11, 1273–1295, 1989. The values of P/U⁰ (Table I) and fluid velocity used to calculatethe energy required for sieving (pp. 1289–1290) and severalequations (footnote b of Table I; p. 1290, lines 3–4)are incorrect. The corrected table appears below: Table I. Filter setule measurements (mean and within specimenstandard deviation) of the gnathobases for the cladocerans studied^aGnathobaseof trunklimb number. ^bP = 8µU₀/(b(1 – 21nt + 1/6(t²) - 1/144(t⁴))), whereP = pressure drop in dyn cm^–2, =3.1416, U₀ = fluid velocityin cm s^–1, b = distance between setule centres in cm,t = ( x setule diameter)/b and µ = 0.0101 dyn s^–1cm^–2. Formula from Jørgensen (1983). The text (p. 1289, line 19 to p. 1290, line 10) should read: organism. Using a similar argument, a 0.5 mm Ceriodaphnia witha filter area of 0.025 mm² (Ganf and Shiel, 1985) and pressuredrop P = 2757 dyn cm^–2 (with fluid velocity of 0.07 cms^–1) allocates only 2171 ergs h^–1 to filtrationof a total energy expenditure of 10⁴ ergs h^–1 [filtrationenergy (ergs h^–1) = area (cm²) x pressure drop (dyn cm^–2)x 3600 (s h^–1) x 1/0.2 (efficiency of conversion of biochemicalinto mechanical work); total energy (ergs h^–1) = respiration(0.05 µl O₂ ind^–1 h^–1 consumed; Gophen, 1976)x conversion factor (2 x 10⁵ ergs µl^–1 O₂). Withan estimated 0.034 mm² in filter area, fluid velocity of 0.041cm s^–1 and respiration of 1.8 x 10⁴ ergs h^–1 (calculatedfrom Porter and McDonough, 1984), a 0.5 mm Bosmina uses <4%of its metabolism to overcome filter resistance. The velocities used in the original examples (0.4 cm s^–1for Ceriodaphnia, 0.2 cm s^–1 for Bosmina) were derivedfrom literature values of appendage beat rate and estimatesof the distance travelled by the appendages during each beatcycle. This approach unnecessarily assumes that all water movedpasses through the filter. In the new calculations, the flowacross the filter needed for food to be collected by sieving(0.07 cm s^–1 for Ceriodaphnia and 0.041 cm s^–1 forBosmina) was determined from the maximum clearance rate/filterarea. The amended energy expenditures, although higher, do notrefute the sieve model of particle collection.     

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     

Feeding of planktonic rotifers on ciliates: a method using natural ciliate assemblages labelled with fluorescent microparticles

A method was developed to allow direct measurements of predationexerted by metazooplankton on ciliates. The method relied onthe use of ciliates labelled with fluorescent microparticles(FMP). Optimal labelling conditions were determined with ciliatesfrom cultures (Tetrahymena pyriformis) and with natural ciliateassemblages sampled in a river. Labelled T. pyriformis wereused as tracer food to determine gut passage time (GPT) andingestion rates of the rotifer Brachionus calyciflorus in thelaboratory. Predation of metazooplankton from the lowland riverMeuse (Belgium) was determined by labelling natural assemblagesof ciliates and using them as tracer food for metazooplankterssampled in the river. Optimal labels of ciliates, i.e. sharpdistribution of FMP in cells, were obtained with short incubations(10 min) and low FMP concentrations (1 x 10⁵ mL^–1). GPTvaried between 30 and 45 min for B. calyciflorus and from 25up to >35 min for rotifers from the river. The ingestionrate of B. calyciflorus fed with T. pyriformis was 3.3 ±0.6 ciliate rot^–1 h^–1, i.e. 1.4 ± 0.3 ngCrot^–1 h^–1. Metazooplankton species for which theingestion of ciliates could be measured were the rotifers Keratellacochlearis, Euchlanis dilatata and Synchaeta spp. Ingestionrates measured ranged from 0.4 to 12.5 ngC rot^–1 h^–1.The method proposed proved to be useful in estimating the predationof microplankton on ciliates in semi- in situ conditions; infurther developments, labelled natural assemblages of ciliatescould be used for in situ incubations with the Haney chamber.     

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.     

Photosynthetic electron transport in Dunaliella tertiolecta (Chlorophyceae) measured by fast repetition rate fluorometry: relation to carbon assimilation

A comparison of photosynthesis-irradiance response curves (P–Eresponse curves) obtained through fast repetition rate (FRR)fluorometry and radiocarbon (¹⁴C) tracer method was made inthe chlorophyte, Dunaliella tertiolecta, grown under differentirradiance conditions. In FRR-based P–E response curveexperiments, actinic light provided by white light-emittingdiodes (LEDs) was increased gradually from 0 to 1500 µmolquanta m^–2 s^–1 and the rate of photosyntheticelectron transport was determined at each light level. Short-termexperiments (20 min) of ¹⁴C-based P–E response curvewere carried out with an improved photosynthetron, which containswhite LEDs as the light source. Irrespective of growth irradiance,the ratios of FRR to ¹⁴C-based initial slopes were almost uniform.The ratios of FRR- to ¹⁴C-based maximum rates were 25–36%higher than those of FRR- to ¹⁴C-based initial slopes. The relationshipbetween electron transport and carbon assimilation was non-linearwith increasing discrepancy towards high actinic light. Thisnon-linear relationship between FRR- and ¹⁴C-based estimatesis primarily due to the effect of physiological processes stimulatedat high levels of light, such as cyclic electron flow and theMehler reaction. The results of this study indicate that theFRR fluorometry can be used as a good indicator of photosyntheticrates from low to middle light levels, but becomes increasinglyquestionable as the maximum photosynthetic rate is approached.The degree to which this relationship is further affected bynutrient-status warrants investigation.     

Grazing rates of the freshwater ciliate Balanion planctonicum determined by flow cytometry

Feeding of Balanion planctonicum on the cryptomonad Rhodomonassp. was recorded in vivo at 2–3 min intervals by flowcytometry. Ingestion rates were 1.6–1.7 algal cells ciliate^–1h^–1. On average, 20–30 min elapsed between ingestionand egestion.     

Photosynthetic characteristics of Dinophysis norvegica Claparede & Lachmann, a red-tide dinoflagellate

The relationships between photosynthesis and photosyntheticphoton flux densities (PPFD, P-l) were studied during a red-tideof Dinophysis norvegica (July-August 1990) in Bedford Basin.Dinophysis norvegica, together with other dinoflagellates suchas Gonyaulax digitate, Ceratium tripos, contributed {small tilde}50%of the phytoplankton biomass that attained a maximum of 16.7µg Chla 1^– and 11.93 10⁶ total cells I^–1.The atomic ratios of carbon to nitrogen for D.norvegica rangedfrom 8.7 to 10.0. The photosynthetic characteristics of fractionatedphytoplankton (>30 µm) dominated by D.norvegica weresimilar to natural bloom assemblages: o (the initial slope ofthe P-l curves) ranged between 0.013 and 0.047 µg C [µgChla]^–1 h–1 [µmol m^– s^–1]^–1the maximum photosynthetic rate, p^B_m, between 0.66 and 1.85µg C [µghla]^–1 h^–1; l_k (the photoadaptationindex) from 14 to 69 µ,mol m^–2 s^–1. Carbonuptake rates of the isolated cells of D.norvegica (at 780 µmolm^–2 s^–1) ranged from 16 to 25 pg C cell^–1h^– and were lower than those for C.tripos, G.digitaleand some other dinoflagellates. The variation in carbon uptakerates of isolated cells of D.norvegica corresponded with P^B_mof the red-tide phytoplankton assemblages in the P-l experiments.Our study showed that D.norvegica, a toxigenic dinoflagellate,was the main contributor to the primary production in the bloom.     

Pyrosoma atlanticum (Tunicata, Thaliacea): grazing impact on phytoplankton standing stock and role in organic carbon flux

Pyrosomas are the large group of pelagic tunicates whose trophicrole in pelagic communities has not yet been sufficiently studied.We ran across a local area of high concentration of the mostwidespread and commonest species of pyrosomas, Pyrosoma atlanticum,450 miles off the Congo river mouth. The following was estimated:gut pigment content, defecation rate, organic carbon and pigmentcontent of fecal pellets, and sinking rate. Based on these dataand the measured number of pyrosomas colonies the grazing impacton phytoplankton and the fecal pellet flux were calculated.During the night swarms of 50–65 mm P.atlanticum removed53% of phytoplankton standing stock in the 0–10 m layer;sparsely distributed pyrosomas consumed only 4%. The grazingimpact in the 0–50 m layer was only 12.5 and <1% respectively.The fecal pellet flux resulting from nocturnal feeding of P.atlanticumwhile swarming made up 1.4–1.6 x 10⁶ pellets m^–210 h^–1 or 305–1035 mg C m^–2 10 h^–1 and1.4 x 10⁵ pellets m^–2 10 h^–1 or 87.4 mg C m^–210 h^–1 while non-swarming. Incubation experiments showedthe rapid degradation of fecal pellets at 23°C: the lossof pigment and carbon content was {small tilde}60–70%after 45 h. We believe that given the sinking rate of 70 m day^–1the main part of fecal material does not leave the upper watercolumn and is retained in the trophic web of the epipelagiclayer.     

Auxin Transport in Roots: V. EFFECTS OF TEMPERATURE ON THE MOVEMENT OF IAA IN ZEA ROOTS

The effects of temperature on the polar movement of IAA through6-mm and 12-mm segments of Zea mays roots have been investigatedover the range from 1 to 50°C. At all temperatures an acropetal polar movement of IAA predominated,although at low temperatures and at 50°C the 6-mm segmentsshowed a transient basipetal polarity, before the persistentacropetal polarity developed. At 1°C the differences betweenacropetal and basipetal movement of IAA were less distinct thanat the other temperatures. There is, however, a marked metabolically-dependentacropetal movement of IAA through the tissues at 1°C, becausewhen the segments were deprived of oxygen the acropetal movementwas severely reduced while the basipetal movement was reducedto a smaller extent. At 1°C and at 5°C there was alwaysa persistent basipetal polarity of IAA movement through 6-mmand 12-mm segments under anaerobic conditions. The velocity of acropetal movement (mm h^–1) was the samethrough the 6-mm and the 12-mm segments and was markedly affectedby temperature. It increased from 1°C to a maximum valueof 8 mm h^–1 at 31°C and then decreased again at 40and 50°C. The velocity of basipetal movement could be assessedonly at 1 and 5°C at which temperatures it was greater thanthe velocity of acropetal movement, and virtually independentof segment length. The acropetal flux of IAA (cpm h^–1) was much less through12-mm segments than through 6-mm segments. For both lengthsof segment, however, the flux showed a complex relationshipwith ambient temperature, increasing from 1°C to a maximumat 10–15°C, declining to a minimum value at 31°Cand then rising again at 40 and 50°C. The basipetal fluxof IAA could be astimated only at 1 and 5°C at which itwas very much smaller than the acropetal flux. The amount of IAA in the receiver blocks increased linearlywith time at the lower temperatures. At temperatures withinthe range 15°C to about 31°C, however, the amount ofIAA in the receiver blocks began to decline if the transportperiods exceeded a certain length. The time at which this declinein the IAA in the receiver block began was related to the ambienttemperature. Chromatographic analysis indicated one radioactive substancein receiver blocks at the apical end of segments supplied withIAA-1-¹⁴C at the basal end after transport periods of 6 h at25°C, and 72 h at 5°C. The Rf of this substance wasclosely similar to that of the radioactive IAA supplied in thedonor blocks.     

RNA Synthesis in Phaseolus Chloroplasts: I. RIBONUCLEIC ACID SYNTHESIS IN CHLOROPLAST PREPARATIONS FROM PHASEOLUS VULGARIS L. LEAVES AND SOLUBILIZATION OF THE RNA POLYMERASE

Chloroplast preparations from the young primary leaves of Phaseolusvulgaris L. cv. Canadian Wonder carry out the DNA-dependentincorporation of UTP into RNA at rates between 8 and 14 pmolUTP µg^–1 chlorophyll h^–1. It is estimatedthat 90% of the activity was localized in the chloroplasts.The incorporation proceeded for between 20 and 30 min at 35°C. The maximum rates of RNA synthesis were attained atpH 8.3, in the presence of 15 mM MgCl₂. Chloroplasts were alsoactive, to a lesser extent, with 1.5 mM MnCl₂. The simultaneouspresence of MnCl₂ and MgCl₂ resulted in inhibition of activity.Nuclear material prepared from young P. vulgaris leaves incorporatedUTP at a rate of about 12 pmol UTP µg^–1 DNA h^–1.On a chloroplast (Tritonsoluble) DNA basis chloroplast activitywas over 40-fold that of nuclei. Methods of solubilizing chloroplastRNA polymerase were explored. Yields of over 75% were achieved,but methods suitable for one species were not always successfulwhen applied to another. The highest yields of the P. vulgarisenzyme were obtained using EDTA and KCl. All methods resultedin solubilization of DNA. RNA synthesis by the soluble P. vulgarisenzyme proceeded for more than 40 min at 35 °C.     

Characterization of Photosynthetic 14Carbon Assimilation by Potamogeton lucens L.

Photosynthetic assimilation of exogenous ¹⁴CO₂ and H¹⁴CO₃^–by the aquatic angiosperm Potamogeton lucens L. is reported.Equivalent maximum rates of assimilation (1.5 µmol s^–1m^–2) were obtained in the presence of saturating levelsof ¹⁴CO₂ (1.0 mol m^–3, pH 5.3) or H¹⁴CO₃^– (1.5 molm^–3, pH, 9.2). Under subsaturating ¹⁴CO₂ levels, bothgaseous diffusion and H¹⁴CO₃^– transport were shown tooperate simultaneously, such that maximal photosynthetic rateswere established. An induction lag of approximately 3 min was observed when exogenous¹⁴CO₂ was assimilated. A longer lag of approximately 12 minwas required, however, before linear assimilation rates wereestablished when H¹⁴CO₃ acted as the carbon source. The light-activatedH¹⁴CO₃^– transport system was found to be quite labile.A brief (5 min) dark treatment returned the system to the inactivestate. Bicarbonate transport was shown to be competitively inhibitedby CO₃^2–ions. The possibility is discussed that this formof inhibition may be common to many HCO₃^– assimilators. Preliminary polar cation transport studies (from lower to upperleaf surface) indicated an almost exact one to one relationshipbetween the rates of Na⁺ influx and efflux and H¹⁴CO₃^–assimilation. The possible relationship(s) between these transportprocesses and the requirement for electrical neutrality is brieflydiscussed.     

ERRATA

p. 1284. Fig. 1, values on the ordinate (Leaf extension rate,mm h^–1): scale should be moved down so that zero lieson the x-axis ... LER = 3.2 {1 – exp [–4 (S – 0.41)]}...     

The influence of temperature and light on the upper limit of Microcystis aeruginosa production in a hypertrophic reservoir

Primary production was measured for 7 years, using the in situ¹⁴C-method in hypertrophic Hartbeespoort Dam, South Africa,to examine the influence of light and water temperature on theupper limit of Microcystis aeruginosa production. Water temperaturesvaried from 11 to >25°C and chlorophyll concentrationsreached 6500 mg m^–3. The maximum volumetric rate of production(A_max) was 12->8800 mg C m^–3 h^–1 with areal productions(A) of 69->3300 mg C m^–2 h^–1 for euphotic zonedepths of <0.5–8.4 m. The intrinsic parameters of phytoplanktonproduction (, A_max/B, I_k) indicated that the phytoplankton populationwas adapted to high light levels. Both A_max/B and I_k were correlatedwith temperature. Under optimal conditions, , the theoreticalupper limit of A, was calculated to be 2.8 g Cm^–2 h^–1,while the measured rate was 2.5 g Cm^–2 h^–1. Measuredareal rates exceeding were overestimated due to methodologicalproblems when working with Microcystis scums. Light and watertemperature interacted to yield high production rates: watertemperature through its direct effect on photosynthetic ratesand indirectly in the formation of diurnal mixed layers; lightindirectly through water temperature and directly through itsattenuation and induction of light-adapted physiology in Microcystis.     

Measurements of 14C Incorporation by Illuminated Intact Leaves of Coffee Plants from Gas Mixtures Containing 14CO2

A study was made of the incorporation of ¹⁴C by intact leavesof Coffea arabica (cultivars Mundo Novo, Catuai, 1130–13,and H 6586–2) and Coffea canephora (cultivar Guarini)supplied with gas mixtures containing ¹⁴CO₂ under controlledconditions. Samples of the leaves were combusted and the ¹⁴Cin the CO₂ produced measured using a liquid scintillation counter.The results were used to estimate photosynthetic rates. Theeffects of changing the partial pressures of O₂ and CO₂ on thephotosynthetic rate were studied and estimates made of the CO₂compensation point and photorespiration. The data obtained show differences between the mean net photosyntheticrates of the C. arabica cultivars (6·14 mg CO₂ dm^–2h^–1) and the mean rate for the C. canephora cultivar (3·96mg CO₂ dm^–2 h^–1). The cultivar of the latter speciesphotorespired more rapidly than the cultivar Catuai of C. arabica.Rates of photosynthesis in coffee measured using the ¹⁴CO₂ methodwere similar to rates obtained by others using an infrared gasanalyser. The ¹⁴CO₂ method proved to be reliable for photosyntheticmeasurements and the apparatus is suitable for use in fieldconditions.     

Auxin, transport and growth in intact roots of Vicia faba

Transport of IAA applied to the intact root of Vicia seedlingswas investigated in relation to root growth. The root was treatedat 3–4, 4–5 or 7–8 mm from the tip with anarrow ring of lanolin paste containing IAA or IAA-2-¹⁴C ingrowth or transport experiments, respectively. The growth processalong the root axis was examined in every 1-mm part from thetip at 30 min, 1 or 4 hr intervals. The elongation zone of thecontrol root was 1–9 mm from the tip. IAA treatment broughtabout no significant change in the growth of the region apicalto the treated site, whereas distinct inhibition of growth occurredin the region basal to the treated site within 1 hr. The transportof radioactivity was observed in both acropetal and basipetaldirections within 1 hr, but the latter predominated for 8 hror more; the nearer to the tip the treatment site, the longerthe predominance lasted. The velocities of acropetal and basipetaltransport were estimated at about 4 and 8 mm/hr, respectively.Autoradiographs of transverse section of roots showed that basipetaltransport occurred mainly through the outer part of the root,whereas acropetal transport occurred mainly through the innerpart, the central cylinder. It may be concluded that the basipetallytransported IAA which passed through the outer part of the rootinhibited the elongation of the intact root. (Received November 25, 1975; )     

Reversal of the Polarity of IAA Transport in the Leaf Sheath Base of Echinochloa colonum

The transport of [2-¹⁴C]IAA and its derived products has beeninvestigated in segments of the leaf sheath base of Echinochloacolonum. Segments orientated vertically in the normal uprightposition transport ¹⁴C basipetally at rates approximately 10times higher that acropetally. In horizontal segments the basipetalrates are lower, being only 1–4 times higher than acropetalrates. Segments orientated vertically in the inverted positiontransport ¹⁴C basipetally at approximately 1/10 of the acropetalrate. ¹⁴C in the receiver discs from vertically orientated segmentswas found to be present predominantly as [2-¹⁴C]IAA and itsderived metabolite. The levels of each of these compounds from upright and invertedvertical segments followed the same pattern as that of theirtotal ¹⁴C content.     

Ammonium release by zooplankton in suspensions of heat-killed algae and an evaluation of the flow-cell method

The maximum excretion rate of NH₄ (39 nmol mg dry wt^–1h^–1) was directly measured for Daphnia pulex by measuringNH₄ accumulation in bottles containing D. pulex and dense, satiatingsuspensions of heat-killed algae. Ammonium release rates inthe algal suspensions were compared to those of individual animalsremoved from the suspension and placed in flow cells. Ammoniumrelease rate, R (nmol mg dry wt^–1 h^–1). in the flowcell decreased very rapidly with time, t (min), after removalaccording to the relation R = 26 + 25e^–0.16t. Ammoniumexcretion obtained by the flow cell method after extrapolationto time zero was not significantly different from that obtainedin the bottles. The considerable experiment-to-experiment variationin NH₄ excretion was in large part correlated (r² = 0.73) withthe feeding rate on the algae.