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1.
The theory and practice of applying the thermodynamics of irreversibleprocesses to mass-flow theories is presented. Onsager coefficientswere measured on cut and uncut phloem and cut xylem strandsof Heracleum muntegazzimum. In 0.3 N sucrose + 1 mN KC1 theyare as follows. In phloem, LEE = 5 ? 104 mho cm1,LpE = 9 ? 106 cm3 s1 cm2 volt1 cm,and LPP = 0.16 cm3 s1 cm2 (J cm3)1cm. In uncut phloem strands LEE is about 1 ? 103 mhocm1. In xylem in 2 x 103 N KCI, Lpp = 50 to 225,LPE = 2 ? 104, and LEE = 4 ? 103. The measurementsare tentative since the blockage of the sieve plates is an interferingfactor, but if they are valid they lead to the conclusion thatneither a pressure-flow nor an electro-kinetic mechanism envisaginga long distance current pathway can be the majormotive force for transport in mature phloem. Measurementsof biopotentials along conducting but laterally detached phloembundles of Heracleum suggest, nevertheless, that there may bea small electro-osmotic component of at least 0.1 mV cm1endogenous in the phloem. 相似文献
2.
Journal of Plankton Research, 11, 12731295, 1989. The values of P/U0 (Table I) and fluid velocity used to calculatethe energy required for sieving (pp. 12891290) and severalequations (footnote b of Table I; p. 1290, lines 34)are incorrect. The corrected table appears below: Table I. Filter setule measurements (mean and within specimenstandard deviation) of the gnathobases for the cladocerans studiedaGnathobaseof trunklimb number. bP = 8µU0/(b(1 21nt + 1/6(t2) - 1/144(t4))), whereP = pressure drop in dyn cm2, =3.1416, U0 = fluid velocityin cm s1, b = distance between setule centres in cm,t = ( x setule diameter)/b and µ = 0.0101 dyn s1cm2. 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 cm2 (with fluid velocity of 0.07 cms1) allocates only 2171 ergs h1 to filtrationof a total energy expenditure of 104 ergs h1 [filtrationenergy (ergs h1) = area (cm2) x pressure drop (dyn cm2)x 3600 (s h1) x 1/0.2 (efficiency of conversion of biochemicalinto mechanical work); total energy (ergs h1) = respiration(0.05 µl O2 ind1 h1 consumed; Gophen, 1976)x conversion factor (2 x 105 ergs µl1 O2). Withan estimated 0.034 mm2 in filter area, fluid velocity of 0.041cm s1 and respiration of 1.8 x 104 ergs h1 (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 s1for Ceriodaphnia, 0.2 cm s1 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 s1 for Ceriodaphnia and 0.041 cm s1 forBosmina) was determined from the maximum clearance rate/filterarea. The amended energy expenditures, although higher, do notrefute the sieve model of particle collection. 相似文献
3.
Five inbred strains (129/J, BALB/cByJ, C3HeB/FeJ, C57BI/6J andDBA/2J) were examined with two-bottle (48 h) preference ratiotesting across concentrations of sodium saccharin (3 x 104M, 103 M, 3 x 103 M and 102 M), d-phenylalanine(103 M, 102 M and 101 M), and l-glutamine(102 M, 3 x 102 M, 101 M and 3 x 101M). Three consistent groupings of strains were observed acrosssubstances and concentrations:
- C57BI/6J (preference at low andhigh concentrations);
- BALB/cByJ and C3HeB/FeJ (preferenceat high concentrations);
- 129/J and DBA/2J (preference at highconcentration for sodiumsaccharin and indifference to d-phenylalanineand l-glutamine).
4.
Occurrence of viable photoautotrophic picoplankton in the aphotic zone of Lake Biwa, Japan 总被引:1,自引:0,他引:1
Eguchi Mitsuru; Oketa Takemi; Miyamoto Nobukazu; Maeda Hiroto; Kawai Akira 《Journal of plankton research》1996,18(4):539-550
The distribution and abundance of photoautotrophic picoplankton(PPP. Synechococcus group) in the aphotic bottom sediments ofLake Biwa were investigated by direct counting and viable counting(most probable number, MPN) methods. In the surface layer ofbottom sediments (01 cm). where large PPP blooms occurredin the past 5 years, >105 cells cm3 of PPP were foundto be viable throughout the year. Furthermore, the density ofPPP deposited on the sediment surface (00.1 cm) was oneorder of magnitude higher (MPN = 1.3 x 106 cells cm3.direct count = 9.9 x 106 cells cm3) than that of bulkedsurface sediments (01 cm). Even in the deeper layer (1314cm) of bottom mud, viable PPP were still found (101 cells cm1.In winter, viable PPP in the aphotic bottom sediments were 104105times greater per Unit volume than those in the euphotic lakewater. Since the aphotic bottom sediments have high levels ofPPP, as well as high growth potential (high ratio of viablecount/total direct count), they are likely to seed PPP bloomsin the North Basin of Lake Biwa. 相似文献
5.
A Study of the Exudation of Excised Maize Roots after Removal of the Epidermis and Outer Cortex 总被引:1,自引:1,他引:0
The fluid exudation rates and the ionic composition of the exudatesof isolated maize roots were compared with those of similarroots from which the epidermal and outer cortical cells hadbeen removed. The results indicate that in low ionic strengthmedia the salt fluxes into the exudation stream are severaltimes larger in the control than in the treated roots. As theionic strength of the bathing medium increases to 10 mM KClor greater, the salt fluxes become equal. A mechanism to accountfor this behaviour is discussed. The values of Lp, the hydraulic conductivity of the roots toradial water flow, are 0.26 x 106 cm sec1 atm1for treated and 0.14 x 106 cm sec1 atm1for control roots, but a statistical technicality precludeda significance test on this apparent difference. The kinetics of tritiated water exchange from external mediumto the exudation fluid in both control and treated roots werenot significantly different. The entry of labelled water seemsto be achieved by the fluid exudation rate in both cases; thusthe barrier to water movement to the exudate compartment remainsintact after removal of the epidermis. 相似文献
6.
The Water Relations of Young Olive Trees in a Mediterranean Winter: Measurements of Evaporation from Leaves and Water Conduction in Wood 总被引:1,自引:0,他引:1
We report measurements of evaporation rate, leaf resistanceto evaporation and water conduction in the stems of young olivetrees (Olea europea L.) growing in Messina, Italy, during thewinter and early spring. We have measured what Zimmermann callsleaf specific conductivity (LSC) of stem segmentsexcised from olive trees. The LSC is a measure of the specifichydraulic conductivity of stem segments normalized per unitarea of leaves supplied by the stem segment rather than perunit area of sapwood cross-sectional area. We find that theLSC's of primary stems were the largest followed in magnitudeby the LSC's of secondary stems and tertiary stems. Under winterand early spring conditions the maximum evaporative flux fromCoratina and Nocellara varieties of olive trees is about 2.6x 105 kg 81 m2. From this and the LSC measurementswe calculate that the pressure gradients needed to maintainthis rate of evaporation in the steady state is 65 kPa m1in primary stems, 170 kPa m1 in secondary stems and 560kPa m1 in tertiary stems. Olive, Olea europea L, evaporation, leaf specific conductivity, hydraulic conductivity, leaf resistance 相似文献
7.
FLEURAT-LESSARD P.; ROBLIN G.; BONMORT J.; BESSE C. 《Journal of experimental botany》1988,39(2):209-221
Fleurat-Lessard, P., Roblin, G., Bonmort, J. and Besse, C. 1988.Effects of colchicine, vinblastine, cytochalasin B and phalloidinon the seismonastic movement of Mimosa pudica leaf and on motorcell ultrastructure.J. exp. Bot. 39: 209221. Colchicine at 1 x 103 mol dm3 does not affectthe seismonastic movement of Mimosa pudica leaves but disruptsmicrotubules in motor cells. Vinblastine at 5 x 103 moldm3 does not affect this movement and partly disruptsmicrotubules. Vinblastine at 1 x 104 mol dm3 alwaysdisrupts microtubules, even after a 12 h reversibility whenthe movement is restored. These drugs, applied at the same respectiveconcentrations, do not alter cytoplasmic and vacuolar fibrils.Cytochalasin B and phalloidin alter the seismonastic movementof Mimosa leaves when applied at concentrations of 1.25 x 103and 2.4 x 104 mol dm3 respectively. These drugs,used at the same respective concentrations, also affect themotor cell structure and, in particular, modify the arrangementand the structure of the fibrils but they do not destroy themicrotubules. These data suggest that microtubules are not directly involvedin the seismonastic reaction whereas fibrils, formed by thin(3.0 nm wide) filaments, may be implicated in this reaction. Key words: Colchicine, cytochalasin B, phalloidin, Mimosa pudica, motor cells, vinblastine 相似文献
8.
Effective Thickness and Resistance of the Air Boundary Layer Adjacent to Spherical Plant Parts 总被引:5,自引:0,他引:5
Using existing heat transfer data a rather simple expressionis developed for the effective thickness of the boundary layerof air adjacent to spheres. The calculated boundary layer thicknessagreed fairly well with that determined for water vapour diffusionfrom a wet spherical surface 5.90 cm in diameter for wind velocitiesfrom 10 to 1000 cm s1. At a turbulence intensity representativeof field conditions (0.5), the measured boundary layer thicknessaveraged 11 per cent less than for a relatively low turbulenceintensity of 0.01. For wind velocities up to 100 cm s1,the resistance of the boundary layer for water vapour diffusionwas actually greater than the resistance of the basidiocarpsof Lycoperdon perlatum, L. polymorphum, and Scleroderma australe.The tissue resistance for water vapour movement from the fruitingbodies of other members of the Basidiomycetes was also low (below10 s cm1), while the resistance of 20 different sphericalfruits ranged from 30 to over 5000 s cm1. The thicknessof the air boundary layer for spheres can depend on the squareroot of a characteristic dimension divided by the wind velocity,as has already been shown for cylindrical and flat plant material. 相似文献
9.
Grazing and ingestion rates of laboratory-born Thalia democraticaaggregates and Dolioletta gegenbauri gonozooids, phorozooidsand oozooids were determined while fed Isochrysis galbana (45µm diameter) alone or in combination with Peridinium trochoideum(1618 µm diameter) at concentrations of 0.150.70mm3 x 11. Grazing rates (ml x zooid1 x 24 h 1)ranged from 10 to 355, and at zooid weights greater than 5 µgcarbon were in order oozooid > gonozooid > aggregate.Grazing rates increased exponentially with increasing zooidweight. Weight-specific grazing rates (ml x µgC1x 24 h1) were independent of the four-fold initial foodconcentration. Mean weight-specific grazing rates increasedlinearly with increasing zooid weight for the aggregates andoozooids, but gonozooid mean rates were independent of zooidweight. Aggregate and gonozooid ingestion rates (106 µm3x zooid1 x 24 h1) ranged from 4 to 134 while oozooidrates ranged from 3 to 67. All ingestion rates were independentof the initial food concentration but increased linearly withincreasing zooid weight at similar rates. All mean weight-specificingestion rates (ml x µgC1 x 24 h1) wereindependent of zooid weight. The mean aggregate daily ration(µgC ingested x µg body C1) was 59% and themean doliolid ration was 132%. Field studies indicate that normalconcentrations of D. gegenbauri in the Georgia Bight clear theirresident water volume (1 m3) in about 4 months, but that highlyconcentrated, swarm populations which occur along thermohalinefronts clear their resident water volume in less than 1 day.
1Current address: MacLaren Plansearch Ltd., P.O.Box 13250, sta.A.,St.John's, Nfld. A1B 4A5 相似文献
10.
Population structure and swarm formation of the cyclopoid copepod Dioithona oculata near mangrove cays 总被引:1,自引:0,他引:1
The cyclopoid copepod Dioithona oculata forms swarms in water>30 on deep among prop roots of red mangroves (Rhizophoramangle) which fringe protected areas of two lagoonal cays, TwinCays, Belize. During 7 of 8 months surveyed by in situ observation,swarms were present but differed in size from small cylindricalswarms (510 cm diameter) to bands extending up to 1200m Swarms were never observed at night Swarms formed at dawnwhen light intensities reached an average value of 13.82 (logioquanta cmAbstract. s1) and dispersed at dusk atsimilar intensities Swarms observed in June formed earlier anddispersed later in the day than swarms observed in January,their swarming behavior followed seasonal changes in light intensityMean dioithonan density in swarms (10 ml1) was much higherthan the mean density (0 15 ml1) of non-swarming dioithonansaround mangrove prop roots. In open water 35 m away fromthe mangroves, mean dioithonan density was 7 9 x 105ml1 during the day, and 2 68 x103 ml1 at nightSwarms were composed predominantly of adults and copepodid stagesIV and V, although younger copepodid stages could be presentNauplii were never present. The average copepodid stagefor all 95 swarms sampled was 5 3, where 6 0 represents a swarmwith only adults In open water 35 m away from the mangroves,the youngest copepodids (stage one) dominated the dioithonanpopulation during the day. At night when swarms dispersed toopen waters, average copepodid stage was higher (3 5) comparedwith the day value (1.2) in open waters. Although densitiesin swarms were higher in June than January, average copepodidstage in June was higher (5 6) than that in January (4.9). Ahigher percentage of adults were females during June than January.Therefore higher densities did not result from increases ofsmaller stages in swarms, but perhaps changes in behavior orpopulation structure. 相似文献
11.
An attempt has been made to separate constituents of marineseston samples: inorganic material, detritus and the algal species,by density gradient centrifugation, without affecting the physiologicalstate of the algae. A relatively inert gradient material, consistingof Percoll, salt and sucrose, was composed. Since the densitiesof detritus and algae as well as those of different algal speciesoften overlapped, only 10 of the 100 samples processed in thecourse of the year showed a reasonable separation. However,an enrichment with respect to one or more species was oftenachieved. Densities of eleven species of marine diatoms andof one dinoflagellate have been determined at different timesof the year. For eight diatom species and for the dinoflagellatethe following specific density ranges were established: Bidduiphiaaurita: 1.181.23 g cm3, Biddulphia sinensis: 1.031.08g cm3, Cerataulina bergonii: 1.031.06 g cm3,Ditylum brightwellii: 1.071.13 g cm3, Rhizosoleniadelicatula: 1.041.09 g cm3, Skeletonema costatum:1.121.17 g cm3, Streptotheca thamensis: 1.041.10g cm3 , Thalassiosira rotula: 1.051.10 g cm3,Peridinium sp.: 1.081.12 g cm3. No seasonal variationin density was demonstrated. Gradients of different compositiondid not influence density measurements. 相似文献
12.
This research examined the hypothesis that as cacti evolve tothe leafless condition, the stem epidermis and cortex becomemore leaflike and more compatible with a photosynthetic role.All cacti in the relict genus Pereskia have non-succulent stemsand broad, thin leaves. All members of the derived subfamilyCactoideae are leafless, having an expanded cortexthat is the plant's only photosynthetic tissue. In Pereskia,leaves have a high stomatal density (mean: 50.7 stomata mm2in the lower epidermis, 38.1 mm2 in the upper epidermis),but stems have low stomatal densities (mean: 11.3 mm 2, threeof the species have none). Stems of Cactoideae have a high stomataldensity (mean: 31.1 mm2, all species have stomata). Theouter cortex cells of stems of Cactoideae occur in columns,forming a palisade cortex similar to a leaf palisade parenchyma.In this palisade cortex, the fraction of tissue volume availablefor gas diffusion has a mean volume of 12.9%, which is identicalto that of Pereskia leaf palisade parenchyma. Pereskia stemcortex is much less aerenchymatous (mean: 5.3% of cortex volume).Cactoideae palisade cortex has a high internal surface density(0.0207 cm2 cm2 which is higher than in Pereskia stemcortex (0.0150 cm2 cm3) but not as high as Pereskia leafpalisade parenchyma (0.0396 cm2 cm3). Pereskia stem cortexhas no cortical bundles, but Cactoideae cortexes have extensivenetworks of collateral vascular bundles that resemble leaf veins. Cactaceae, cactus, intercellular space, stomatal density, internal surface/volume, evolution 相似文献
13.
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
14.
Studies on the Movement of Water Through Apple Trees 总被引:12,自引:0,他引:12
Resistances to the flow of water through young potted appletrees were estimated by measuring the transpiration rate oftrees with and without root systems. Root system resistanceswere obtained by difference. Whole-plant resistances were ofthe order 10 x 1013 Pa s m3 and there was some evidencethat root resistances (Rr) varied with transpiration rate; theratio Rr:Rx (where Rx is resistance to water flow in the stemsystem) altered from 2:1 at relatively high transpiration ratesto 1:1 at lower rates. The trunk of a 9-year-old orchard tree (trunk diameter {smalltilde}7 cm, height {small tilde}2.5 m) was cut under water andestimates of the flow resistances in this tree were obtained.These were much lower than the resistances to flow in the pottedtrees. Capacitance (defined as the change in stored water content perunit change in plant water potential) values were calculatedfor the small trees and the large tree from measurements ofweight and water potential changes after the trees were removedfrom water. They were very similar on a weight basis (approx.2.0 x 108 kg kg1 Pa1). Leaf capacitancevalues ({small tilde}1 x 108 kg Pa1 m2)were also obtained. Stomatal conductances decreased with water potential and increasedwith short-wave radiation, but the relationships were not definitive.Estimates of boundary layer conductance in a greenhouse (verylow wind speeds) were of the same order ({small tilde}5 mm s1)as values obtained previously. 相似文献
15.
The Effect of Root Temperature on Growth and Uptake of Ammonium and Nitrate by Brassica napus L. in Flowing Solution Culture: I. GROWTH 总被引:1,自引:0,他引:1
Macduff, J. H., Hopper, M. J. and Wild, A. 1987. The effectof root temperature on growth and uptake of ammonium and nitrateby Brassica napus L. in flowing solution culture. I. Growth.J.exp. Bot. 38: 4252 Oilseed rape (Brassica napus L. cv. Bien venu) was grown for49 d in flowing nutrient solution at pH 6?0 with root temperaturedecrementally reduced from 20?C to 5?C; and then exposed todifferent root temperatures (3, 5, 7, 9, 11, 13,17 or 25?C)held constant for 14 d. The air temperature was 20/15?C day/nightand nitrogen was supplied automatically to maintain 10 mmolm3 NH4NO3 in solution. Total dry matter production wasexponential with time and similar at all root temperatures givinga specific growth rate of 0?0784 g g1 d1. Partitioningof dry matter was influenced by root temperature; shoot: rootratios increased during treatment at 17?C and 25?C but decreasedafter 5 d at 3?C and 5?C. The ratio of shoot specific growthrate: root specific growth rate increased with the ratio ofwater soluble carbohydrates (shoot: root). Concentrations ofwater soluble carbohydrates in shoot and root were inverselyrelated to root temperature; at 3, 5 and 7?C they increasedin stem + petioles throughout treatment, coinciding with a decreasein the weight of tissue water per unit dry matter. These resultssuggest that the accumulation of soluble carbohydrates at lowtemperature is the result of metabolic imbalance and of osmoticadjustment to water stress. Key words: Brassica napus, oilseed rape, root temperature, specific growth rate 相似文献
16.
Guttation was used as a non-destructive way to study the flowof water and mineral ions from the roots and compared with parallelmeasurements of root exudation. Guttation of the leaves of barley seedlings depends on age andon the culture solution. Best rates of guttation were obtainedwith the primary leaves of 6- to 7-day-old seedlings grown onfull mineral nutrient solution. The growing leaf tissue becomessaturated with K+ below 1.5 mM K+ in the medium, whereas K+concentration in the guttated fluid still increases furtheras K+ concentration in the medium is raised. At 3 mM K+ averagevalues of guttation were 1.42.4 mm3 h1 per plantwith a K+ concentration of 1020 mM; for exuding plantsthe flow was 4.27.6 mm3 h1 per plant and K+ concentration3555 mM. Abscisic acid (ABA) at 106 to 104 M 02h after addition to the root medium increased volume flow ofguttation and exudation and the amount of K+ exported. Threeh after addition of ABA both volume and amount of K+ were reduced.There was an ABA-dependent increase in water permeability (Lp)of exuding roots shortly after ABA addition. Later Lp was decreasedby 35 per cent and salt export by 60 per cent suggesting aneffect of ABA on salt transport to the xylem apart from itseffect on Lp. Benzyladenine (5 x 108 to 105 M)and kinetin (5 x 106 M) progressively reduced volumeflow and K+ export in guttation and exudation and reduced Lp. Guttation showed a qualitatively similar response to phytohormonesas found here and elsewhere using exuding roots. Hordeum vulgare L., barley, guttation, abscisic acid, cytokinins, benzyl adenine, kinetin 相似文献
17.
Ca Fluxes and Membrane Potentials in Nitella translucens 总被引:4,自引:0,他引:4
The concentrations of Ca have been measured in the flowing cytoplasmand the vacuole of the single cells of Nitella translucens,the cells being immersed in an artificial pond Water (composition:NaCl, 1.0 mM; KCl, 0.1 mM; CaCl2, 0. mM). In the flowing cytoplasmthe total concentration is 8 mM and in the vacuole 12 mM. Measurementsof the electrical potential differences across the plasmalemmaand tonoplast membranes show that the cytoplasm is at a potentialof 134 mV with respect to the bathing medium and 24mV with respect to the vacuole. An attempt has been made tomeasure the tracer fluxes of Ca and it is shown that the cellsare not in flux equilibrium. The influx is 0.046 µµmoles cm2 sec1; the efflux was too small to measurewith any degree of accuracy. The observed potential differences across both membranes arecompared with the Nernst potentials for Ca. This analysis showsthat Ca is not in electrochemical equilibrium across eithermembrane and that the driving forces on Ca are directed fromthe bathing medium and the vacuole into the cytoplasm. It issuggested that there is no necessity for a metabolically drivenCa pump at the plasmalemma because the low cytoplasmic Ca contentcould be due to the low permeability of the plasmalemma; theGoldman flux equation gives a value of PCa = 4.3x108cm sec1. A Ca pump at the tonoplast appears to be necessaryto explain the steep electrochemical potential gradient fromthe vacuole to the cytoplasm. The efflux of Ca from the isolated cell wall has been measured.From these measurements it was possible to estimate the concentrationof indiffusible anions in the Donnan Free Space; the value obtainedwas 0.74 equiv. 1.1. 相似文献
18.
Photosynthetic 14C fixation by Characean cells in solutionsof high pH containing NaH14CO3 gave a measure of the abilityof these cells to take up bicarbonate (H14CO3). Whereascells of Nitella translucens from plants collected and thenstored in the laboratory absorbed bicarbonate at 11.5µµmoles cm2 sec1, rates of 38µµmoles cm2 sec1 were obtained withN. translucens cells from plants grown in the laboratory. Influxesof 56 µµmoles cm2 sec1 wereobtained with Chara australis, 38 µµmolescm2 sec1 with Nitellopsis obtusa, and 15µµmoles cm2 sec1 with Tolypella intricata.It is considered that these influxes represent the activityof a bicarbonate pump, which may be an electrogenic process. In solutions of lower pH, H14CO3 uptake would be maskedby rapid diffusion of 14CO2 into the cells: the four Characeanspecies fixed 14CO2 at maximum rates of 3040 µµmolescm2 sec1 (at 21° C). 相似文献
19.
Hydraulic and osmotic properties of spruce roots 总被引:9,自引:6,他引:3
Rdinger Marcus; Hallgren Stephen W.; Steudle Ernst; Schulze Ernst-Detlef 《Journal of experimental botany》1994,45(10):1413-1425
Hydraulic and osmotic properties of roots of 2-year-old Norwayspruce seedlings (Plcea abiea (L.) Karst) were investigatedusing different techniques (steady flow, pressure probe, andstop flow technique). Root pressures were measured using theroot pressure probe. Compared to roots of herbaceous plantsor deciduous trees, excised root systems of spruce did not developappreciable root pressure (-0.001 to 0.004 MPa or -10 to 40cm of water column). When hydrostatic pressure gradients wereused to drive water flows across the roots, hydraulic conductivities(Lpr) were determined in two types of experiments: (i) rootpressure relaxations (using the root pressure probe) and (ii)steady flow experiments (pneumatic pressures applied to theroot system or xylem or partial vacuum applied to the xylem).Root Lpr ranged between 0.2 and 8108m s1 MPa1(on average) depending on the conditions. In steady flow experiments,Lpr depended on the pressure applied (or on the flow acrossthe roots) and equalled (0.190.12) to (1.21.7)108m s1 MPa1 at pressures between 0.2 and 0.4 MPaand (1.51.3)108 m s1 MPa1 at appliedpressures between 0.8 and 1.0 MPa. When pressures or vacuumwere applied to the xylem, Lpr values were similar. The hydraulicconductivity measured during pressure relaxations (transientwater flows) was similar to that obtained at high pressures(and water flows). Although there was a considerable scatterin the data, there was a tendency of the hydraulic conductivityof the roots to decrease with increasing size of the root system.When osmotic gradients were used to drive water flows, Lpr valuesobtained with the root pressure probe were much smaller thanthose measured in the presence of hydrostatic gradients. Onaverage, a root Lpr=0.017108 was found for osmotic andLpr=6.4108 m s1 MPa1 in correspondinghydrostatic experiments, i.e. the two values differed by a factorwhich was as large as 380. The same hydraulic conductivity asthat obtained in osmotic experiments using the pressure probewas obtained by the 'stop flow techniquel. In this technique,the suction created by an osmoticum applied to the root wasbalanced by a vacuum applied to the xylem. Lpr values of rootsystems did not change significantly when measured for up to5 d. In osmotic experiments with different solutes (Na2S04,K2S04, Ca(NO3)2, mannitol), no passive uptake of solutes couldbe detected, i.e. the solute permeability was very low whichwas different from earlier findings on roots of herbs. Reflectioncoefficients of spruce roots (O were low for solutes for whichplant cell membranes exhibit values of virtually unity ( 相似文献
20.
Kinetin (4.7 x 105 M) and 6-benzyladenine (2.22 x 105M) were found to increase ca. 2-fold the putrescine contentin cotyledons of lettuce (Lactuca sativa L.) seedlings grownfor 3 days under fluorescent light. On the other hand, severalinorganic ions (K+, Na+, Ga++, Mg++) at a concentration of 3x 102 M reduced the putrescine content. The combinationof kinetin with one of several inorganic ions at the same levelmarkedly increased the spermine content, but the putrescinecontent decreased; calcium and magnesium ions were less effective.The physiological significance of these findings is discussed. (Received July 4, 1982; Accepted November 6, 1982) 相似文献