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1.
The Effect of Methionine Sulphoximine on the Absorption of Ammonium by Maize and Barley Roots over Short Periods 总被引:4,自引:3,他引:1
Pre-treating intact, ammonium-grown plants of maize and barleywith the glutamine synthetase inhibitor, L-methionine sulphoximine(MSO), increased subsequent accumulation of 13N or 15N fromlabelled ammonium very markedlyup to 8-fold in extremecases. The phenonemon could not be satisfactorily explainedin terms of an effect of MSO on the cation-exchange propertiesof the root free space, because neither potassium (86Rb+) norsodium absorption was enhanced by MSO pretreatment, and rapidabsorption of ammonium continued for too long in relation tothe likely free-space content of a monovalent cation. Instead,the response is seen as a consequence of the enlargement ofthe cytoplasmic and vacuolar ammonium pools that occurs whenammonium assimilation is inhibited by MSO. The results, whichincluded comparisons between short-term and longer-term ratesof ammonium absorption, provide tentative evidence of rapidfluxes of ammonium through the plasma membrane. Key words: Cytoplasm, vacuole, flux, transport 相似文献
2.
The light-saturated growth rate of fully deuterated algae hasbeen found less than that of ordinary algae by a factor of threeto four. However, as compared to the net rate of photosynthesis,the Hill reaction rate indicates an unimpaired light reactionsystem. Analysis of cell extracts for amino acid content and14C-uptake studies indicate a decreased utilization of the productsof photosynthesis by deuterated algae, probably because of agenerally lowered protein metabolism. We conclude that in algaeD2O does not have a pronounced effect on the light reactionin photosynthesis.
1 Based on work performed under the auspices of the U. S. AtomicEnergy Commission.
2 Resident Research Associate, 196264.
3Present address: University of Illinois, Department of Pharmacy,Chicago, Illinois. 相似文献
3.
The effect of radiation from P32 on the growth and phosphateabsorption of barley seedlings was studied in water culture.Concentrations of carrier phosphate ranging from less than 001to 31 p.p.m. P were employed for varying periods. Between experiments wide variations occurred in the nature andextent of the effects of radiation. An increase in the proportionof the absorbed phosphate translocated to the shoots, and thereduction of root weight, were the most consistent symptoms.While severe injury was characterized by a reduction in bothgrowth and phosphate absorption, intermediate levels of P32on occasion caused increases in dry weight, in nutrient absorption,and in the development of lateral meristems. The interrelation of the observed effects of radiation is discussed;the reduced metabolic activity of root meristems is consideredto be the primary effect in the syndrome of radiation injury.Although injury is due to the accumulation of P32 in meristematicregions, no close correlation can be shown between its extentand the level of radiation received by the meristems. The inaccuracyof present methods for estimating the levels of radiation towhich tissues are exposed has complicated the investigationsof this subject. It appears, however, that the injurious levelof radiation may vary from under 10 to over 40 rep. per daywhen the treatment period is 5 to 7 days. If active accumulationof phosphate occurs, the meristems of plant roots may receivethis dosage when treated with more than 5 µ C. of P32per litre for periods of 6 days. The extent to which the effects of radiation may complicatethe interpretation of the results of plant physiological investigationsis considered. 相似文献
4.
In situ light measurements were used to obtain information oninherent and apparent optical properties. The average verticalattenuation coefficient Kd(ave) varied from 1.1 to 4.6 In unitsm1 During three periods the variation in Kd(ave) correlatedwith changes in chlorophyll a concentration and specific attenuationcoefficients Ks, of 0.013, 0.014 and 0.022 m2 mg Chl a1were calculated. Chlorophyll-specific diffuse absorption coefficients(A,) for these periods were 0.012. 0.013 and 0.017 m2 mg Chla1 and only varied significantly from estimates of Ksin the period when scattering was intense. Absorption coefficientsa(zmid) and scattering coefficients b(zmid) calculated for themid-point of the euphotic zone ranged between 0.45 and 2.9 mand 3.552.0 m respectively. Chlorophyll-specific absorptioncoefficients Ka, of 0.005, 0.006 and 0.007 m2 mg Chl a1and scattering coefficients Kb of 0.05. 0.09 and 0.191 m2 mgChl a1 were measured during the three periods. The highKb value occurred when gas-vacuolate cyanobactena were dominant.Algal photosynthesis and light absorption were related throughthe maximum quantum yield m which varied between 0.019 and 0.11mol C Einstein1 while average quantum yields a, variedbetween 0.006 and 0.024 with a mean of 0.013 mol C Einstein1A comparison of changes in the mean irradiance of the mixedzone and chlorophyll concentration indicated that growth waslight limited below 0.040.05 Einsteins absorbed mg Chla1 day1. 相似文献
5.
Excised sporophytes of the moss Funaria hygrometrica Hedw. absorbexternally applied sugar through their basal haustorium. Influxof [3H]sucrose is inhibited by metabolic uncouplers, darkness,and by the photosynthetic inhibitor DCMU. The kinetics of uptakeof glucose and sucrose suggest a biphasic mechanism of absorption.Uptake of 3-O-methyl [3H]glucose shows no saturation characteristicsand a passive mechanism is indicated. Externally applied glucoseis rapidly converted to sucrose. Good retention of productsof short-term absorption and metabolism of [3H]glucose was achievedby freeze-substitution. Autoradiography showed dense and uniformlabelling of the transfer cells of the haustorium. Vmax valuesfor uptake of sucrose and glucose, expressed in terms of theweight and external surface area of haustorium, are considerablygreater than typical values from other plant systems. However,if the surface area amplification that is brought about by thedevelopment of wall ingrowths in the transfer cells is takeninto account, fluxes per unit area of plasma membrane are reducedinto the range of typical values. The hypothesis that the surfacearea amplification that characterizes transfer cells is relatedfunctionally to processes of solute transport is therefore supportedby the data. 相似文献
6.
The uptake of uniformly labelled L-glutamic acid-14C, glycine-14C,and L-proline-14C by carrot root tissue is inhibited by chloramphenicolat a concentration of 2 g./l. L-glutamic acid absorption isaffected to a much greater extent than is the uptake of theother two amino-acids. It is shown that the 14C from the labelledamino-acids is incorporated into protein of the carrot slices,and that the amount of incorporation from glycine and L-prolineis about six times as large as that from L-glutamic acid undercomparable conditions. Almost all the 14C detected in the proteinafter feeding labelled L-proline or glycine remains in the amino-acidsupplied; in the case of L-glutamic acid some of the label istransferred to other amino-acid residues, but most of it remainsin glutamic acid. Chloramphenicol is found to inhibit 14C-incorporationfrom L-proline and glycine in short-term, but not in long-term,experiments whereas incorporation from L-glutamic acid is inhibitedin both long- and short-term experiments. Chloramphenicol alsoinhibits incorporation of 14C from L-glutamic acid into proteinsof preparations of isolated subcellular particles from carrotroot tissue. Under some conditions, 14C incorporation into proteinproceeds for some time after the slices have been removed fromthe radioactive solution. Such incorporation is not inhibitedsignificantly by chloramphenicol when 14C-labelled L-prolineis supplied, but it is reduced by about 50 per cent. when glycineand L-glutamic acid are used. It is shown that chloramphenicolinhibits net protein synthesis in carrot root slices suspendedin aerated solutions. It is concluded that amino-acid incorporationinto the protein of carrot slices proceeds by at least two mechanisms,one of which is related to protein synthesis and is sensitiveto chloramphenicol and the other is unrelated to protein synthesisand insensitive to the drug. Most of the L-proline and glycineincorporation into carrot root tissue protein seems to occurby the chloramphenicol-insensitive mechanism while much of theL-glutamic acid-14C incorporation seems to take place by thechloramphenicol-sensitive one. 相似文献
7.
Zinc Absorption by Wheat Seedlings and the Nature of its Inhibition by Alkaline Earth Cations 总被引:4,自引:0,他引:4
The effects and interactions of the alkaline earth cations onZn2+ absorption were studied in. short-term experiments. Atlow concentrations of Zn2+ ( 2 µM), rates of Zn2+ absorptionwere linear even in the absence of Ca2+ or of other cations.At higher Zn2+ concentrations (5 and 10µm), rates werenot linear in the absence of other cations but became linearon addition of 250 µM or more of Ca2+, Mg2+, Sr2+, orBa2+. From 0.1 to 10µM Zn2+, all alkaline earth cations inhibitedabsorption in the order Mg2+ > Ba2+ Sr2+ = Ca2+. Increasingconcentrations of Ca2+ or of Mg2+ from 0 to 40 mM progressivelydepressed absorption from 1µM ZnCl2. Increasing Ca2+ orMg2+ from 40 to 100 mM had no further effect on absorption.Over both high and low ranges of Ca2+ or Mg2+ concentrations,the affinity of plant roots for Zn2+ and the responses of Zn2+absorption to temperature, H+, and Cu2+ were identical. At equalconcentrations over the whole concentration range, Mg2+ was30 per cent more effective than Ca2+ in inhibiting absorption.At concentrations below 40 mM, Ca2+ and Mg2+ competed with eachother in their inhibiting effects. At concentrations above 40mM, Ca2+ alleviated the extra inhibitory effects of Mg2+ insome unknown way. The alkaline earth cations inhibited Zn2+ absorption non-competitively.They depressed it to values which would limit vigorous plantgrowth. It is postulated that their effects are important inthe zinc nutrition of plants in soil and in solution cultures. 相似文献
8.
A variant corn callus line derived from callus which originatedfrom etiolated leaves of Illinois High Oil corn (Zea mays L.)has been identified. The variant corn callus line had increasedlipid content concomitant with increased acetyl-CoA carboxylaseactivity and altered biotin-con-taining protein patterns relativeto the wild type callus. The variant callus line also had alteredfatty acid composition concomitant with decreased oleate desaturaseactivity compared to the wild type callus. The altered variantcorn callus line has been designated High Oil Callus (HOC).
1Part of a dissertation submitted by Y.C.H. to the Universityof Illinois in partial fulfillment of the Ph.D. degree. Thispaper reports results of research only and the research wassupported in part by the University of Illinois, College ofAgriculture Fellowship awarded to Y.C.H. Mention of a trademark,proprietary product, or vendor does not constitute a guaranteeor warranty of the product (Received September 18, 1990; Accepted May 21, 1991) 相似文献
9.
An optical emission spectrographic method was used to studythe distribution and accumulation of nanogram quantities of15N in leaves and roots of individual rice plants. Gaseous nitrogenthat was prepared from plant samples, not weighing more than100 µg, was trapped in an electrodeless tube. The excess15N was determined by exciting the gas with a high frequencygenerator, then measuring the light intensities of the molecularbandheads at 2977, 2983 and 2989 ?. For leaves that contained4 atom % 15N the precision obtained was ?1.33%. A comparisonof emission and mass spectrographic 15N values were obtainedwith a number of second leaves of rice plants that were grownunder similar environmental conditions. The 15N contents obtainedat a 2 atom % level by the 2 methods were in reasonable agreement.
1Permanent address: University of Tokyo, Dept. of Agr. Chem.,Japan.
2Permanent address: Argonne National Lab., Argonne, Illinois,U. S. A. (Received April 2, 1969; ) 相似文献
10.
The in vivo data presented here are strong evidence for theinvolvement of citrate cleavage enzyme in lipid synthesis indeveloping soybean cotyledons. The incorporation of 14C fromcitrate into crude lipid fraction in vivo had a pH optimum of4.5; was linear with time; had a temperature optimum of 35?C;and was inhibited by ()-hydroxycitrate. The point ofcitrate cleavage was between carbons 3 and 4 of the citratemolecule and therefore 14C was incorporated into crude lipidfraction from citrate-5-14C but not citrate-1-14C or citrate-6-14C.
1 Cooperative investigations of the Agricultural Research Service,U.S. Department of Agriculture, and the Illinois AgriculturalExperiment Station.
2 This research represents partial fulfillment of the Ph.D.requirements of Daniel R. Nelson. Presently at Monsanto AgriculturalProducts Co., St. Louis, MO 63141, U.S.A. (Received September 20, 1976; ) 相似文献
11.
Two RNases, designated WL-RNase I and II, were separated fromextracts of senescing wheat leaves. WL-RNase II, but not WL-RNaseI, was inhibited by EDTA. A period of time was necessary forthe full effect of EDTA to be observed. Zinc ions abolishedthe EDTA effect.
1Most of the data are taken from a Ph. D. Thesis submitted tothe University of London by L. SODEK. A portion of the workwas cooperative between the University of Illinois and the U.S.Dept. of Agriculture. Mention of a trademark or proprietaryproduct does not constitute a guarantee or warranty of the productby the U.S. Dept. of Agriculture, and does not imply its approvalto the exclusion of other products that may also be suitable
2Research Chemist, Crops Research Division, Agricultural ResearchService, United States Department of Agriculture (Received October 3, 1969; ) 相似文献
12.
Absorption and distribution of K+ by two ryegrass genotypesfrom steady-state supplies at low external concentrations werefollowed through periods of NO3 deprivation and afterdefoliation. Electron microprobe analysis was also used to examineK+ concentrations across the root cortex and the effects onvacuolar/cytoplasmic K+ concentrations in the cortex. In manyrespects, the two genotypes behaved in a similar way. Totalquantities of K+ absorbed were less than 50% of those previouslyrecorded for NO3, and NO3 deprivation slightlyreduced cumulative K+ uptake. Unit absorption rates (K) declinedwith time in the control plants, and removal of NO3 resultedin a progressive decline in K, with an initial rapid responsewhich was independent of any effects of growth. In one genotypeabsorption rates did not recover but gradually did so in theother. Defoliation reduced K only slightly for 6 d, thereafterK, increased almost linearly so that values for plants withsustained NO3 supply were 2 ? those of entire plants.There was no evidence of an oscillatory cycle of K+ unit absorptionrates of the kind previously shown for NO3 during therecovery periods. Concentrations of K+ on both a dry matterand tissue water basis remained within a narrow range irrespectiveof treatment or time. The immediate decline in K+ unit absorption rate after NO3withdrawal indicated that at least a proportion of their uptakeswere coupled. Calculated values for the length of the diffusivepathway indicated that the primary site of absorption into thesymplasm was either the epidermis or the outermost corticalcell. This was supported by evidence from the electron microprobeanalysis which indicated a strong gradient of K+ concentrationswhich declined from outer to inner cortex and was much steeperin plants with a sustained NO3 supply. Concentrationsin the cytoplasm of most cortical cells were generally greaterthan in the vacuoles: this difference was greater in low N plants.The changes in K+ in the cortex were related to the role ofK+ in the transport of NO3 in the xylem and effects onrecycling to the roots in the phloem. Key words: Cytoplasm, defoliation, diffusion, electron probe X-ray microanalysis, Lolium, nitrate, potassium, S.E.M.,, unit absorption, vacuole 相似文献
13.
The role of citrate and the citrate cleavage enzyme in lipidsynthesis in developing soybean cotyledons (Glycine max L. Merr.var. Harosoy 63) was investigated. The activity of the enzymewas inhibited by () hydroxycitrate, which is a specificinhibitor of citrate cleavage by this enzyme. Incorporationof label from citrate-1-14C and -5-14C indicated that the citratemolecule is cleaved between carbons 3 and 4. Acetyl CoA-14Cand oxaloacetate-14C phenylhydrazone were isolated as productsof the citrate cleavage reaction. The production of oxaloacetate-14C-phenylhdrazonefrom citrate-6-14C was carried out using a nucleotide free enzymepreparation and did not require the addition of ATP or CoA.Therefore it would appear that the citrate cleavage reactionis not CoA dependent in developing soybean seeds. Incorporationof pyruvate-2-14C into the crude lipid fraction was shown torequire both the particulate and soluble fractions. Apparentlyin soybeans, as in animal systems, pyruvate is oxidized by thepyruvate dehydrogenase complex and the acetyl CoA formed condenseswith oxaloacetate to produce citrate in the mitochondria. Citrateis then transported out of the mitochondria to the cytosol whereit is cleaved to form acetyl CoA for lipid synthesis.
1 Cooperative investigations of the Agricultural Research Service,U.S. Department of Agriculture, and Illinois Agricultural ExperimentStation.
2 This research represents partial fulfillment of the Ph. D.requirements of Daniel R. Nelson. Presently at Monsanto AgriculturalProducts Co., St. Louis, MO 63141, U.S.A. (Received January 12, 1977; ) 相似文献
14.
The relevance of nongenomic pathways to regulation of epithelial function by aldosterone is poorly understood. Recently, we demonstrated that aldosterone inhibits transepithelial HCO3 absorption in the renal medullary thick ascending limb (MTAL) through a nongenomic pathway. Here, we examined the transport mechanism(s) responsible for this regulation, focusing on Na+/H+ exchangers (NHE). In the MTAL, apical NHE3 mediates H+ secretion necessary for HCO3 absorption; basolateral NHE1 influences HCO3 absorption by regulating apical NHE3 activity. In microperfused rat MTALs, the addition of 1 nM aldosterone rapidly decreased HCO3 absorption by 30%. This inhibition was unaffected by three maneuvers that inhibit basolateral Na+/H+ exchange and was preserved in MTALs from NHE1 knockout mice, ruling out the involvement of NHE1. In contrast, exposure to aldosterone for 15 min caused a 30% decrease in apical Na+/H+ exchange activity over the intracellular pH range from 6.5 to 7.7, due to a decrease in Vmax. Inhibition of HCO3 absorption by aldosterone was not affected by 0.1 mM lumen Zn2+ or 1 mM lumen DIDS, arguing against the involvement of an apical H+ conductance or apical K+-HCO3 cotransport. These results demonstrate that aldosterone inhibits HCO3 absorption in the MTAL through inhibition of apical NHE3, and identify NHE3 as a target for nongenomic regulation by aldosterone. Aldosterone may influence a broad range of epithelial transport functions important for extracellular fluid volume and acid-base homeostasis through direct regulation of this exchanger. thick ascending limb; acid-base transport; epithelial Na+ transport; kidney 相似文献
15.
The uptake of phosphate by aged beetroot discs was examinedunder a range of water deficits which were induced osmoticallywith mannitol or polyethylene glycol At low water potentialsthe absorption of labelled phosphate was enhanced when the ambientconcentration of phosphate was high (103 M) and the timefor absorption was short (30 mm): this occurred even when themetabolism was inhibited (by the water deficit), as indicatedby lowered oxygen consumption and incorporation of 33P intohexose-phosphate, phosphoglycenc acid, a liquid fraction, anda precipitate consisting mainly of cell walls. The Q10 of theuptake process approached unity at these low water potentials.Accompanying the enhanced uptake there was an increase in leakageof previously absorbed phosphate. It is postulated that thestimulation in uptake of phosphate in low osmotic potentialswas due to an increase in permeability Over long periods (6 h) uptake was inhibited by treatment atlow osmotic potentials. This is interpreted in terms of inhibitionof a metabolic component of phosphate uptake. 相似文献
16.
Dark uptake of inorganic 14C by offshore plankton was measuredat two depths at 36 stations in the Atlantic Ocean from 52°Sto 26°N, mainly along 30°W. The samples were incubatedfor 2 h with and without inhibition of biological activity withHgCl2. In addition, six time course experiments were performed.The mean dark uptake rate varied from 0.68 to 4.82 (µmolC m3 h1 over the transect and showed a significantpositive relationship with chlorophyll a. The dark uptake wasusually >5% of the maximum photosynthetic capacity (Pm),and higher values relative to Pm were associated with low valuesof Pm and not with high absolute dark values. A linear relationshipbetween dark uptake and Pm was found with a background value(y-axis intercept) of 0.51 (µmol C m3 h1and a slope of 0.77% of Pm. A major fraction of the dark signal,6680% of the total signal, persisted in bottles treatedwith HgCl2, indicating that most of the dark signal was independentof biological activity. Time course experiments showed a lineardark uptake with time for the first hours, whereafter the uptakeceased. At stations with low concentrations of inorganic nitrogen[>1 (µmol (NH4++NO3)], a second stage was observedafter 38 h, probably due to an increase in bacterialactivity. The results suggest three mechanisms for the darkvalue in short-term incubations in oligotrophic waters. A backgroundvalue independent of biomass and incubation time which was thedominant part of the dark signal in samples with very low phytoplanktonbiomass (>0.3 p-g Chi a 1"). Another important part was residualsof 14C associated with plankton, probably adsorbed to compoundsinside the cells. This fraction was dominant in short-term incubationsat chlorophyll concentrations >0.3 p.g Chi a H. Active uptakeby living cells (total minus HgCl2 uptake) wasonly a minor part of the dark signal in short-term incubations,but dominated at longer incubation time (>39 h), probablydriven by an increase in bacterial activity. A significant enhancementof the non-photosynthetic uptake of 14C was observed in light,probably associated with a carbon-concentrating mechanism inphytoplankton or light stimulation of ß-carboxylationactivity. The results strongly suggest that dark values shouldbe subtracted from the light uptake. This correction is particularlyimportant when photosynthetic rates are low, e.g. at low lightor in short-term incubations where a time-zero background becomesa significant part of the total uptake in light.
Present address: National Environmental Research Institute,Department of Marine Ecology and Microbiology, Frederiksborgvej399, PO Box 358, DK-4000 Roskilde, Denmark 相似文献
17.
The Absorption and Distribution of Strontium in Plants: I. PRELIMINARY STUDIES IN WATER CULTURE 总被引:2,自引:1,他引:1
The absorption and distribution of strontium in barley plantshas been studied, in water culture, both in the presence andabsence of calcium. Tracer methods have been employed. When no other bivalent ions were present in the external solutionthe absorption of strontium was proportional to the concentrationover a wide concentration range (106 to 101 m.equiv./l.).In the presence of calcium, however, absorption was reducedand appeared to be dependent on the total concentration of calciumplus strontium rather than on that of 8trontlum alone. The translocationof stron tium from the root to the shoot increased as the externalconcentration of both ions was raised. In plants of low initialcalcium status the rate of translocation of strontium was markedlyreduced, apparently because of its retention at or near theroot surface. Autoradiographs of plants treated with labelled strontium for24 hours at different stages of growth and grown subsequentlyfor varying periods of time in unlabelled nutrient solutionsshowed that very little redistribution of strontium occurredwithin the plant. Leaves which developed after treatment inthe labelled solutions contained little or no strontium evenwhen the concentration in the older leaves was very high. Strontiumwas initially retained in the nodes of the stems, but the greatestaccumulation was later found to be in the leaves which had beengrowing most actively at the time of absorption. 相似文献
18.
Modeling cell volume regulation in nonexcitable cells: the roles of the Na+ pump and of cotransport systems 总被引:1,自引:0,他引:1
Hernandez Julio A.; Cristina Ernesto 《American journal of physiology. Cell physiology》1998,275(4):C1067
The purpose of this study is to contribute to understanding therole ofNa+-K+-ATPaseand of ionic cotransporters in the regulation of cell volume, byemploying a model that describes the rates of change of theintracellular concentrations ofNa+,K+, andCl, of the cell volume, andof the membrane potential. In most previous models of dynamic cellularphenomena,Na+-K+-ATPaseis incorporated via phenomenological formulations; the enzyme isincorporated here via an explicit kinetic scheme. Another feature ofthe present model is the capability to perform short-term cell volumeregulation mediated by cotransporters of KCl and NaCl. The model isemployed to perform numerical simulations for a "typical" nonpolarized animal cell. Basically, the results are consistent withthe view that the Na+ pump mainlyplays a long-term role in the maintenance of the electrochemicalgradients of Na+ andK+ and that short-term cell volumeregulation is achieved via passive transport, exemplified in this caseby the cotransport of KCl and NaCl. 相似文献
19.
Sodium absorption by bean-leaf slices from o·1 mM 22NaCldepends on metabolic energy, but is not enhanced by light. Lightalso does not effect the ATP content of the tissue. Inhibitorsof energy metabolism which decrease the ATP content also inhibit22Na+ absorption. In darkness, anoxia severely affects the ATPcontent as well as 22Na+ absorption; illumination restores bothto almost normal values. 相似文献
20.
Vertical profiles of temperature, the flux density and spectralcomposition of irradiance and the vertical distribution of Oscillatoriabourrellyi were measured in the North and South Basins of Windermerein the English Lake District At the population maximum (814m) the photon flux was 0.314 µmol m2 s1with the waveband 512580 nm contributing 5460%of the photosyn-thetically active irradiance. Samples of O.bourrcllyitaken concurrently from 0 and 12 m were analysed to determinethe absorption properties of the populations and the phycoerythrin-relatedfluorescence of individual filaments. The 12 m populations weredistinguished from the surface populations by higher beam absorptioncoefficients at all wavelengths throughout the visible spectrum.These differences were accentuated when the absorption characteristicswere calculated using in situ irradiance profiles. The deeperpopulations consistently absorbed a greater fraction of theavailable irradiance than the shallow populations. This wasdue to an overall increase in the total pigment per cell ratherthan the differential synthesis of phycobiliprotein pigments.These observations were confirmed by both laboratory and fieldexperiments using cultures of O. bourrellyi In these experimentslow white light was sufficient to induce the synthesis of bothphycoerythnn and phycocyanin as well as chlorophyll Mean individualfilament fluorescence also distinguished populations from differentdepths These measurements further demonstrated that filamentswithin a population located at a discrete depth have a widerange of fluorescence. This variation increased with decreasinglight intensity and suggests that phycoerythrin could be usedas a cellular marker to determine the provenance of individualfilaments The benefits of photo-adaptation in O.bourreUyi areanalysed in relation to the variable underwater light climateof Windermere, UK Their ecological significance for this algaduring periods of intense but intermittent stratification ina nutrient-limited environment are discussed. The ecologicalimplications of both intra- and inter-specific variations inthe absorption properties of phytoplankton are discussed inrelation to the use of simple community or populations meansas the data entry points for models of photosynthetic production. 相似文献