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1.
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 m3) 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 m3valine inhibited sucrose uptake by 25%. At 500 mol m3sucrose, 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 m3 (these concentrations are non-saturatingwith respect to sucrose uptake), a constant 1.8% of the sucrosetaken up was respired. The Km of the concentration-dependentsucrose oxidation (44±6 mol m3) agreed reasonablywell with that for sucrose uptake (29±6 mol m3).When the external sucrose concentration was increased from 100to 600 mol m3, 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 相似文献
2.
Mobilization of Endosperm Reserves and Uptake of Sucrose and Valine by the Cotyledons of Euphorbia lathyris L. 总被引:1,自引:0,他引:1
Upon germination, the endosperm triacylglycerols and proteinswere converted to sucrose and amino acids. During early postgerminativegrowth, the rate of sucrose and amino acid production exceededthe rate of uptake by the cotyledons. As a result, the levelsof total amino acid and sucrose in the endosperm increased;maximum levels were reached at 7 d and 10 d after imbibition(DAI), respectively. Intact seedlings were used to measure thedevelopment of valine, arginine, glutamic acid, and sucroseuptake rate throughout the course of endosperm depletion. Maximumamino acid uptake rates were measured at around 9 DAI, the highestuptake rate for sucrose was obtained at 12 DAI (just beforedepletion of the endosperm). The daily increase of sucrose andamino acid uptake could be manipulated, by replacing the endospermwith a pre-incubation solution during 1 d. The increase in sucroseuptake in vitro was equal to that measured with intact seedlingswhen the cotyledons were pre-incubated in 10 mol m3 sucrose.Higher sucrose concentrations reduced the increase of sucroseuptake; at 300 mol m3 sucrose (corresponding to the meanendosperm sucrose concentration) sucrose uptake after pre-incubationwas even lower than before. This reduction was largely counteractedwhen the pre-incubation solution was supplemented with minerals.The development of the valine uptake was hardly affected bysucrose, but was inhibited by several amino acids. Key words: Euphorbia lathyris seedling, sucrose uptake, amino acid uptake, reserve mobilization 相似文献
3.
The Interaction of Genotype, Explant and Media on the Regeneration of Shoots from Complex Explants of Brassica napus L. 总被引:7,自引:0,他引:7
The relative importance of explant type, genotype and growthregulator regime in the determination of shoot regenerationfrequencies from complex explants of Brassica napus L. has beenevaluated. Cotyledon, hypocotyl and stem sections taken fromone spring (Westar) and three winter (Ariana, Cobra, Libravo)varieties of B. napus were cultured on three different growthregulator regimes, 0.5 mg dm3 NAA + 2.0mg dm3BAP, 0.5 mg dm3 NAA + 4.0mg dm3 BAP and 1.0mgdm3 NAA + 4.0mg dm3 BAP. The most significanteffects on shoot regeneration were due to explant type and variety.The regeneration from stem segments was not only two to threetimes higher than from hypocotyls or cotyledons, in all varieties,but the response was also more uniform across the varieties.The explant effect accounted for 4495% of the regenerationresponse. In contrast, the contribution of growth regulatorregime was negligible. Although the growth regulator regimeas an independent effect was unimportant, regeneration fromboth Ariana and Libravo was significantly affected by the interactionof genotype with growth regulator regime. The importance ofboth the high shoot regeneration frequency from stem segmentsand the relative uniformity of response across the four testedgenotypes is discussed with respect to the potential benefitsof using this explant source in Agrobacterium-based transformationexperiments. Key words: Brassica napus, regeneration, genotype, tissue culture, complex explant 相似文献
4.
Yield stress threshold (Y) and volumetric extensibility () arethe rheological properties that appear to control root growth.In this study they were measured in wheat roots by means ofparallel measurement of the growth rate (r) of intact wheatroots and of the turgor pressures (P) of individual cells withinthe expansion zone. Growth and turgor pressure were manipulatedby immersion in graded osmoticum (mannitol) solutions. Turgorwas measured with a pressure probe and growth rate by visualobservation. The influence of various growth conditions on Yand was investigated; (a) At 27 °C.In 0.5 mol m3 CaCl2 r, P, Y and were20.7±4.6 µm min1, 0.77±0.05 MPa,0.07±0.03 MPa and 26±1.9 µm min1MPa1 (expressed as increase in length), respectively.Following 24 h growth in 10 mol m3 KC1 these parametersbecame 12.3±3.5 µm min1, 0.72±0.04MPa, 0.13±0.01 MPa and 21±0.7 µm min1MPa1. After 24 h osmotic adjustment in 150 mol m3mannitol/0.5 mol m3 CaCl2 r= 19.6±4.2 µmmin1, P = 0.68±0.05 MPa and Y and were 0.07±0.04MPa and 30±0.2 µm min1 MPa01, respectively.After 24 h growth in 350 mol m3 mannitol/0.5 mol m3CaCl2 r= 13.3±4.1 µm min1, P= 0.58±0.07MPa, Y=0.12±0.01 MPa and ø 32±0.2 tim min1MPa1. During osmotic adjustment in 200 mol m3mannitol/0.5 mol m3 CaCl2, with or without KCl, the recoveryof growth rate corresponded to turgor pressure recovery (t1/2approximately 3 h). (b) At 15 °C. Lowered temperature dramatically influencedthe growth parameters which became r= 8.3±2.8 um min1,P=0.78 MPa, r=<0.2 MPa and =15±0.1 µm min1MPa1. Therefore, Y and are influenced by 10 mol m3 K+ ionsand low temperature. In each case the effective pressure forgrowth (P-Y) was large indicating that small fluctuations ofsoil water potential will not stop root elongation. Key words: Yield threshold, cell wall extensibility, wheat root growth, temperature, turgor pressur 相似文献
5.
X-Ray Microanalysis and Ultrastructural Studies of Cell Compartments of Dunaliella parva 总被引:1,自引:0,他引:1
HAJIBAGHERI M. A.; GILMOUR D. J.; COLLINS J. C.; FLOWERS T. J. 《Journal of experimental botany》1986,37(11):1725-1732
Hajibagheri, M. A., Gilmour, D. J., Collins, J. C. and Flowers,T. J. 1986. X-ray microanalysis and ultrastructural studiesof cell compartments of Dunaliella parva. -J. exp. Bot. 37:17251732. Ultrastructural studies of the unicellular green alga Dunaliellaparva showed the presence of cytoplasmic vacuoles. X-ray microanalysiswas performed on sections of cells which had been freeze substitutedin acetone. It was found that the concentrations of both Naand Cl were much higher in the vacuoles than in the cytoplasm.When cells were grown in 0·4 kmol m3 NaCl theNa and Cl concentrations in the vacuoles were 349 and 283 molm 3 respectively, whilst cytoplasmic Na and Cl concentrationswere 37 and 26 mol m3. Corresponding values for cellsgrown in 1·5 kmol m3 NaCl were 392 mol m3Na and 325 mol m3 Cl in the vacuoles and 36 mol m3Na and 30 mol m3 Cl in the cytoplasm. Immediately afterexposure to an increase in external salinity Na and Q concentrationsincreased in both vacuoles and cytoplasm. The results are discussedwith reference to compartmental models for the ionic relationsof Dunaiiella. Key words: X-ray microanalysis, ultrastructural studies, Dunaliella parva 相似文献
6.
Comparison of the Disruption of Mitosis and Cell Plate Formation in Oat Roots by DCPA, Colchicine and Propham 总被引:1,自引:0,他引:1
Holmsen, J. D. and Hess, F. D. 1985. Comparison of the disruptionof mitosis and cell plate formation in oat roots by DCPA, colchicineand propham.J. exp. Bot. 36: 15041513. Concentrationsof DCPA, propham and colchicine were selected to cause from0% to greater than 60% inhibition of oat (Avena sativa L. Victory)root growth after 24 h exposure. Root growth progressively declinedas concentrations were raised from 1·0 to 5·6mmol m3 DCPA, 1·05·0 mmol m3propham, and 50500 mmol m3 colchicine. In additionto inhibiting root growth each mitotic disrupter caused theroot tips to swell to an extent dependent upon concentration.All three compounds effectively disrupted mitosis at concentrationsthat caused less than maximal root growth inhibition. Mitoticdisruption was manifest as a reduction in the number of normalmitotic figures and an increase in the number of condensed prophase,multipolar and anaphase bridge division figures. The frequencyof each type of division figure was different for each of thethree compounds. DCPA disrupted mitosis more effectively whencompared with propham and colchicine at concentrations whichcaused the same amount of root growth inhibition. Each mitoticdisrupter also induced the formation of aberrant cell walls.DCPA was the most effective at disrupting cell plate formation,whereas colchicine was least effective. These data suggest thatthe mechanism of action of DCPA is distinct from the mechanismof colchicine or propham Key words: Avena sativa L., mitotic disruption, DCPA, colchicine, propham 相似文献
7.
Developmental Responses to Drought and Abscisic Acid in Sunflower Roots: 2. MITOTIC ACTIVITY 总被引:1,自引:0,他引:1
ROBERTSON J. MASON; YEUNG EDWARD C.; REID DAVID M.; HUBICK KERRY T. 《Journal of experimental botany》1990,41(3):339-350
Mitotic activity was studied in the root apices of aeroponicallygrown sunflower seedlings (Helianthus annum L. var. RussianGiant) which were draughted or treated with abscisic acid (ABA)over a 7 d period. Labelling index (LI) and mitotic index (MI)were scored from autoradiographs of median longitudinal sectionsof [3H] methyl-thymidine treated root apices. Both drought stressand ABA-treatment (at a concentration of 102 mol m3inhibited DNA synthesis and mitosis within the first 6 h oftreatment. The depression of mitotic activity was first evidentin the proximal regions of the meristem (10001500 µmfrom the cap junction). This was followed by a general depressionof mitotic activity throughout the meristem which was, in turn,followed by a partial recovery of mitotic activity in the distalregions of the meristem. The beginning of this partial recoverywas concurrent with the activation of the quiescent centre (QC).Treatment with lower concentrations of ABA (103 mol m3and 104 mol m3) also inhibited mitotic activity.Exogenous supplements of sucrose to the plant did not alleviatethe inhibition of mitotic activity by drought or ABA. Thesefindings support the hypothesis that ABA mediates drought-inducedchanges in the primary development of sunflower roots. Key words: Abscisic acid, drought, mitotic activity 相似文献
8.
Nuclear volumes and cell areas were determined for seven regionsof the meristem of roots of Zea mays. Roots were fixed in 10per cent neutral buffered formalin, in 3 per cent glutaraldehydeor in acetic acid/alcohol; they were prepared as sections oralls were teased apart. Mean volumes of interphase nuclei weresimilar in all regions of the root except the vascular tissueof the stele. Mean nuclear volumes and the overall range ofvolumes were similar in sub-populations of cells with differentproportions of G1, S and G2 cells, e.g. in row I of root capinitials, whose cells lack a G1 phase, and in quiescent centrecells, which are mainly in G1. Nuclear volume does not appearto be closely correlated with DNA content. Nuclear volumes covereda 6 to 12-fold range within a meristem and even within specificregions, in which cells are part of the same cell lineages,there was a 4- to 9-fold range. Nuclear volumes were comparedin sister cells in rows I and II of the root cap initials. In10 per cent of the pairs, sister nuclei had identical volumes;the other pain had different volumes and mean difference was68 µm3. Mechanisms by which this variability could begenerated are discussed, particularly asymmetry, at mitoses,of factors that regulate nuclear growth. Zea mays L., nuclear volume, cell size, root mcristem, DNA content, mitosis 相似文献
9.
Soybean [Glycine max (L.) Merrill] seeds and cotyledons weregrown in an in vitro culture system to investigate the relationshipsbetween cell expansion (net water uptake by the seed) and drymatter accumulation. Seeds or cotyledons grown in a completenutrient medium containing 200 mol m3 sucrose continueddry matter accumulation for up to 16 d after in planta seedsreached physiological maturity (maximum seed dry weight). Seedor cotyledon water content increased throughout the cultureperiod and the water concentration remained above 600 g kg1fresh weight. These data indicate that the cessation of seeddry matter accumulation is controlled by the physiological environmentof the seed and is not a pre-determined seed characteristic.Adding 600 mol m3 mannitol to the medium caused a decreasein seed water content and concentration. Seeds in this mediumstopped accumulating dry matter at a water concentration ofapproximately 550 g kg1. The data suggest that dry matteraccumulation by soybean seeds can continue only as long as thereis a net uptake of water to drive cell expansion. In the absenceof a net water uptake, continued dry matter accumulation causesdesiccation which triggers maturation. Key words: Glycine max (L.) Merrill, solution culture, duration of seed growth, water content, dry matter accumulation 相似文献
10.
Effect of Sink-Source Manipulations on the Photosynthetic Rate and Carbohydrate Content of Cucumber Cotyledons 总被引:1,自引:0,他引:1
MAYORAL MARIA LUISA; PLAUT ZVI; REINHOLD LEONORA 《Journal of experimental botany》1985,36(10):1551-1558
Mayoral, M. L., Plaut, Z. and Reinhold, L. 1985. Effect of sink-sourcemanipulations on the photosynthetic rate and carbohydrate contentof cucumber cotyledons.-J. exp. Bot. 36 15511558. The photosynthetic rate of cucumber cotyledons (Cucumis sativuscv. Dahla) reached a maximum value of 12 mg dm2 h1,10 d after emergence. In 12-d-old seedlings removal of one cotyledondoubled the CO2 fixation rate of the other, as observed 3 dafter treatment. When the primary leaf was removed, the photosyntheticrate of the cotyledons was decreased by 33%. At this stage ofgrowth elimination of the roots as a sink for assimilates bygirdling the hypocotyl affected neither the photosynthetic ratenor the carbohydrate content of the cotyledons. By contrast,in 18-d-old seedlings removal of the first leaf brought abouta 42% increase in the photosynthetic rate of the cotyledons.The simultaneous removal of the first leaf and one cotyledondoubled the rate of CO2 fixation of the remaining cotyledon.Girdling the hypocotyl lowered the photosynthetic rate of thecotyledons by 73%. In both 12- and 18-d-old seedlings a decreaseor increase in the sink-source ratio was correlated with anincrease or a decrease respectively in the carbohydrate contentof the cotyledons. The stomatal resistance of the cotyledonswas not affected by any of the treatments. The effect of sink-sourcemanipulations on photosynthesis and on the level of carbohydratespresent in the cotyledons was more evident in those seedlingsgrowing under high light intensity (580 µE m2 s1),than in those exposed to 300 µE m2 s1 Key words: Sink-source relationship, cotyledons, photosynthesis 相似文献
11.
Tada Kuninao; Pithakpol Santiwat; Yano Rumiko; Montani Shigeru 《Journal of plankton research》2000,22(6):1203-1211
The carbon and nitrogen content of Noctiluca scintillans cellsfrom the Seto Inland Sea, Japan was investigated in order toestimate its biomass in natural samples. The carbon contentof N.scintillans ranged from 123 to 627 ng C cell1 witha mean value of 353 ng C cell1, or 1.12 to 2.67 fg Cµm3 with a mean value of 1.98 fg C µm3.The nitrogen content ranged from 36.0 to 232 ng N cell1with a mean value of 131 ng N cell1, or 0.499 to 0.910fg N µm3 with a mean value of 0.694 fg N µm3.Total cell carbon and nitrogen increased but the carbon andnitrogen per cell volume decreased with increasing cell volume.The C/N ratio of the cells ranged from 2.3 to 4.4, which wasrelatively low compared with the Redfield ratio. The carbonand nitrogen content was extremely low (91.2 ng C cell1,41.8 ng N cell1) for starved cells, whereas it was extremelyhigh (528 ng C cell1, 205 ng N cell1) for cellswhich had ingested the large diatom, Coscinodiscus wailesii.Our results suggest that the carbon and nitrogen content ofN.scintillans varies depending on its physiological conditionand the type of food that it has recently consumed. 相似文献
12.
Light, temperature and nitrogen as interacting factors affecting diel vertical migrations of dinoflagellates in culture 总被引:11,自引:0,他引:11
Diel vertical migrations of the marine dinoflagellates Gonyaulaxpolyedra Stein and Ceratium furca (Ehr.) Clap, et Lachm. werefollowed in a laboratory tube (2.02 m x 0.25 m) under a 12:12hlight:dark cycle. The effects of temperature stratification,two levels of surface irradiance and nitrogen depletion on patternsof vertical migrations were examined. At temperatures between2226°C with small temperature gradients, both speciesmigrated at a rate of 0.7 1.0 m h1. Steeper thermoclines(ca. 0.8°C 0.1 m1) with temperatures below ca. 20°Ccaused a marked decrease in swimming speed which resulted inaccumulations of cells in these thermocline regions. Under conditionsof nutrient sufficiency both algae migrated into the surfacelayers at irradiance values of over 1000 µE m2s1. Increasing nitrogen depletion caused the downwardmigration of both algae to commence progressively earlier inthe day and before the end of the light period. The earlierdownward migrations enabled a more complete descent throughthe thermocline. Nitrogen depleted cells of Gonyaulax continuedto undertake vertical migrations but avoided high irradiancesthus forming subsurface maxima at irradiance levels close to150 µE m2 s1. Ceratium cells which exhaustedboth inorganic nitrogen and phosphorus ceased to migrate accompaniedby a large change in cellular fluorescence. 相似文献
13.
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 I1.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 h1 [µmol m s1]1the maximum photosynthetic rate, pBm, between 0.66 and 1.85µg C [µghla]1 h1; lk (the photoadaptationindex) from 14 to 69 µ,mol m2 s1. Carbonuptake rates of the isolated cells of D.norvegica (at 780 µmolm2 s1) ranged from 16 to 25 pg C cell1h 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 PBmof 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. 相似文献
14.
Fluxes of diatoms in the Dona Paula Bay, west coast of India 总被引:2,自引:0,他引:2
Sediment traps were deployed at a station in the Dona PaulaBay to collect sedimenting particles at weekly intervals fromNovember to May during 19951997. Sedimented particleswere analysed for total diatom flux, chlorophyll a (Chl a) andparticulate organic carbon (POC). The highest diatom flux wasrecorded in AprilMay for both the years. Fluxes of diatomsvaried from0.6 x 104 cells m2 day1 (November 1995)to 121.47 x 104 cells m2 day1 (December 1996).In all, 19 diatom genera were identified in the sedimented material.Navicula, Nitzschia, Pleurosigma, Licmophora, Coscinodiscus,Rhizosolenia and Surirella were the most abundant genera inthe sedimented material throughout the sampling period. Meanflux of POC and diatom carbon was 251 and 0.39 mg C m2day1, respectively. The diatom carbon accounted for 0.15%of the POC flux. Mass flux of diatoms showed significant negativecorrelation with the concentration of nitrate and phosphate.This suggests that the nutrient concentration played an importantrole in influencing the sedimentation of diatoms at this coastalstation. 相似文献
15.
The development of a medium for studying aluminium toxicityin plant cell cultures is described. To prevent the precipitationof Al added to the standard cell culture medium, it was necessaryto lower the phosphate concentration from 1250 mmol m3to10 mmol m3, and the pH from 5.8 to 4-0. Two additionalmodifications were the use of unchelated iron and a reductionin the calcium concentration from 3.0 mol m3 to 0.1 molm3. Since the gelling properties of agar are inhibitedat pH 4.0, cells were cultured on filter paper supported bypolyurethane foam sturated with liquid medium. The only limitationto the growth of plated Nicotiana plumbaginifolia Viv. cellson the modified medium was the reduced phosphate concentration.This was partly overcome by preloading the cellswith phosphate prior to each experiment. In addition, the filterpaper with adhering cells was transferred to fresh medium everysecond day to replenish phosphate, and to re-establish the initialpH of4.0 (which otherwise drifts upward). With the modifiedmedium, Al toxicity was observed in plated N. plumbaginifoliacells at both 200 mmol m3 and 400 mmol m3 Al.There was no toxicity at these Al concentrations when the normalphosphate concentration or pH were restored to the modifiedmedium. Partial alleviation of Al toxicity occurred with restorationof the normal calcium concentration or chelated iron. Chelationof Al with citrate or EDTA also mitigated Al toxicity. In additonto Al toxicity, the modified medium should also prove usefulfor studying other metal toxicities in plant cell culture. Key words: Al toxicity, Cell culture, Nicotiana plumbaginifolia 相似文献
16.
Flicker, M. D. and Willmer, C. M. 1986. Vanadate sensitive ATPaseand phosphatase activity in guard cell protoplasts of Commelina.J.exp. Bot. 38: 642648. Phosphatase activity was measured in extracts of guard cellprotoplasts of Commelina communis L. using the artificial substratep-nitrophenylphosphate. A pH optimum of 5.8 to 6.3 was determined.Ammonium molybdate (Ol mol m3) and sodium vanadate (10mol m3) gave almost complete inhibition of phosphataseactivity at pH 60. ATPase assays were, therefore, conductedin the presence of 02 mol m 3 molybdate and vanadatewas used as a specific inhibitor of plasmamembrane ATPase activity.Vanadate sensitive ATPase activity showed a pH optimum of 6.6and activity was stimulated by KC1. These properties are characteristicof plasmamembrane proton pumping ATPases in other systems andsuggest that proton extrusion in guard cells could be mediatedby a similar enzyme. The maximum ATPase activity is sufficientto account for all the proton flux observed during the stomatalopening response. Key words: ATPase, Commelina, guard cell protoplasts, phosphatase, vanadate 相似文献
17.
Density and distribution of bacterioplankton and planktonic ciliates in the Bering Sea and North Pacific 总被引:3,自引:0,他引:3
The total number of planktonic bacteria in the upper mixed layerof the Bering Sea during the late spring-early summer periodranged between 1 and {small tilde}4 x 106 ml1 (biomass1040mg C m3). In the northern Pacific, along 47526N,the corresponding characteristics of the bacterioplankton densityin the upper mixed water layer were: total number 12x 106 cells ml1 and biomass 1546mg C m3Below the thermocline at 50100 m, the density of bacterioplanktonrapidly decreased. At 300 m depth, it stabilized at 0.10.2x 106 cells ml1. The integrated biomass of bacterioplanktonin the open Bering Sea ranged between 1.2 and 3.6 g C m2(wet biomass 618 g m2) Its production per dayvaried from 2 to 23 mg C m3 days1 in the upper0100 m. The numerical abundance of planktonic ciliatesin this layer was estimated to be from 3 to l0 x 103 cells l1,and in the northern Pacific from 0.4 to 4.5 x 103 l2.Their populations were dominated by naked forms of Strombidium,Strombilidium and Tontonia. In some shelf areas, up to 40% ofthe total ciliate population was represented by the symbioticciliate Mesodinium rubrum. The data on the integrated biomassof basic groups of planktonic microheterotrophs are also presented,and their importance in the trophic relationships in pelagiccommunities of subarctic seas is discussed. 相似文献
18.
Hydrococcus brazieri and Arthritica semen on a sandflat at Coodanup,Peel Inlet, Western Australia, accounted for 89.5% of totalmollusc numbers. The mean density of H. brazieri was 9487 m2and A. semen averaged 8105 m2. H. brazieri grew at 0.5mm month1 and reached maturity in 4 months; A. semengrew at 0.3 mm month1 and reached maturity in 6 months.Somatic production in the Peel-Harvey estuarine system was estimatedto be 0.5 g m2yr1for H. brazieri and 4.1 g m2yr1for A. semen. The positions of these two species in the estuarinefoodweb is discussed. (Received 26 June 1981; 相似文献
19.
Summer coastal zooplankton biomass and copepod community structure near the Italian Terra Nova Base (Terra Nova Bay, Ross Sea, Antarctica) 总被引:7,自引:0,他引:7
Pane Luigi; Feletti Mirvana; Francomacaro Barbara; Mariottini Gian Luigi 《Journal of plankton research》2004,26(12):1479-1488
The structure of the zooplankton biotic community and of copepodpopulation in the coastal area of Terra Nova Bay (Ross Sea,Antarctica) was investigated during the 10th Italian AntarcticExpedition (1994/1995). Zooplankton biotic community consistedmainly of pteropods (Limacina helicina and Clione antarctica),Cyclopoid (Oithona similis), Poecilostomatoid (Oncaea curvata)and Calanoid (Ctenocalanus vanus, Paraeuchaeta antarctica, Metridiagerlachei and Stephos longipes) copepods, ostracods, larvalpolychaetes and larval euphausiids. Zooplankton abundance rangedfrom 48.1 ind m3 to 5968.9 ind m3, and copepodabundance ranged from 45.2 ind m3 to 3965.3 ind m3.The highest peak of zooplankton abundance was observed between25 m and the surface and was mainly due to the contributionof O. similis, O. curvata and C. vanus. Zooplankton biomassranged from 5.28 mg m3 to 13.04 mg m3 dry weight;the maximum value was observed between 25 m and the surface.Total lipid content varied from 216.44 to 460.73 mg g1dry weight. 相似文献
20.
The Nuclear Endoreduplication Cycle in Metaxylem Cells of Primary Roots of Zea mays L. 总被引:2,自引:0,他引:2
The nuclear DNA content of metaxylem cells in roots of Zea mayscv. Golden Bantam reaches 16C or 32C by successive rounds ofDNA endoreduplication. Each phase of endoreduplication (endo-S)is separated by a non-DNA synthetic phase (endo-G). These phasesseem to occur in zones at fixed distances from the root tip.The duration of the phases in two of the endoreduplication cycles(4C8C, 8C16C) has been estimated in two ways.The first makes use of the rate of movement of cells throughthe positions along the root where the different phases of thecycle are occurring, the second uses labelling with methyl-[3H]thymidineand autoradiography. Both methods indicate that the endo-S phaseswhich cause the nuclear DNA content to rise from 4C to 8C andfrom 8C to 16C last 810 h, and that the intervening endo-Gphase lasts 812 h. DNA endoreduplication keeps pace withthe increase of nuclear volume; cell volume increases at a morerapid rate, however. Comparison of the endoreduplication cyclein the metaxylem with the mitotic cycle in the adjoining filesof parenchyma cells shows that the mitotic cells complete theircycle more slowly. DNA synthesis, endoreduplication cycle, mitotic cycle, root apex, Zea mays 相似文献