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1.
Increase in fluence rates of white light over the range of 5to 80 µmol m2 s1 brought about a correspondingincrease in amounts of anthocyanin production in shoots of Zeamays L. seedlings. Roots also exhibited a similar relationshipbetween increased fluence rate and increased anthocyanin productionover the range of 5 to 40 µmol m2 s1 whereasfluence rates above 40 µmol m2 s1 broughtabout decreases in anthocyanin production. Rates of productionand amounts of accumulation of anthocyanin in both shoots androots were found to vary with the age of the seedlings at thetime of exposure to light. Age, fluence rates, anthocyanin, seedlings, Zea mays 相似文献
2.
Effects of variations in light intensity on diel patterns ofgrowth, respiration and organic release of Skeletonema costatum(Grev.) Cleve in a cyclostat were evaluated. Light intensitywas either constant during the tight period at levels from 1500to 15 µEm2 s1 or fluctuated throughout thelight period from 500 to 10 µEm2 s1 at ratesof either 1 or 12 cycles day1. Periodicity in cell divisionwas observed only at light intensities of 130 Em2 s1and was decreased under diurnally varying tight. Under all lightconditions carbon and pigment growth were maximal during thelight period but well coupled throughout the 24 h period. Carbonassimilation during the dark period varied from 19 to 34% oftotal daily production and was a linear function of growth rate.Respiratory activity during the light period increased relativeto total daily respiration as growth rate increased. The increasein night-time carbon assimilation with growth rate interactedwith night-time respiration through the refixation of respiredcarbon, thus, influencing the pattern of respiratory loss ofcarbon. Rates of organic release (Ec) were maximal during thelight period and did variations consistently increased withtight intensity. Fluctuating light increased Ec relative toconstant light. Net growth efficiency was maximal at 130 µEm2s1 when cell division periodicity was greatest. Underother light conditions relatively higher rates of cell divisionoccorred at night and cell division periodicity was reducedas well as net growth efficiency. Cellular chemical fractionationindicated that under high or variable light conditions fixedcarbon was stored during the tight period for subsequent synthesisof protein and pigments, and division at night. Such an uncouplingof photosynthesis and other growth parameters resulted in greatermetabolic costs to the cell.
1Present address: Marine Biology, Lamont Doherty GeologicalObservatory, Palisades, NY 10964, USA 相似文献
3.
Environmental Effects on the Diurnal Accumulation of 45Ca by Young Fruit and Leaves of Tomato Plants 总被引:1,自引:0,他引:1
Diurnal uptake and distribution of 45Ca in young fruiting tomatoplants were assessed 12 or 24 h after 45Ca was applied to thenutrient solution at the beginning of either the light (12 h)or the dark (12 h) period. During the experiment, the salinityof the nutrient solution (measured as electrical conductivity,EC) was either 2·5 or 17 mS cm1 and the relativehumidity (measured as vapour pressure deficit, VPD) was either0·2 or 0·6 kPa The uptake of 45Ca by a tomato plant over 12 h was higher inthe light than in the dark but the difference was less at lowhumidity. More 45Ca was transported from the roots to the shootin the light than in the dark. More than half of the 45Ca inthe shoot was accumulated by the stem; the proportion of 45Cain the stem was greater in the dark and was further enhancedby high humidity to more than 80% of the 45Ca in the shoot.The accumulation of 45Ca by the fruit truss in the dark wasgreater than in the light in all experimental conditions. Underlow humidity the accumulation of 45Ca by young leaves was similarin both light and dark. In high humidity there was considerablyless accumulation of 45Ca by the young leaves in the dark The uptake of 45Ca continued over 24 h but the transport of45Ca to individual organs in the second 12 h period was affectedby both light and humidity. Some of the 45Ca accumulated byyoung leaves and fruit in the second period appears to havebeen derived from 45Ca released from the xylem wall along thetransport pathway in the stem The roles of root pressure and transpiration in the diurnalaccumulation of calcium in young fruit and leaves are discussed Calcium, diurnal translocation, tomato, young fruit and leaves 相似文献
4.
The puhrinule of the terminal leaflet in the trifoliate leafof bean (Phaseolus vulgaris L.) responds to its continuous exposureto directional overhead light by increasing the elevation ofits attached lamina. Blue light drives this response, but theeffectiveness of unfiltered white light equalled, or exceededthe effectiveness of blue light at equivalent irradiances (200800µmol m2 s1). Adding red light to blue lightenhanced the initial rate of response, and increased its steady-state.These effects of red light increased with irradiance. Adding200800 µmol m2 s1 red light to 50µmol m2 s1 blue light was more effectivein enhancing the initial rate of response than adding blue lightat equivalent irradiances, whereas added blue light was moreeffective in increasing the steady-state. In continuous bluelight the initial (maximal) angular velocity of laminar reorientation,as well as the eventual steady-state of the response increasedlinearly with log PFD (up to 800 µmol m2s2).Laminar reorientation also took place in continuous red lightby itself, and the angular velocity of the response was initiallyhigh, then became considerably slower. The initial phase wasapparently independent of irradiance up to PFD 100 µmolm2 s1 but increased progressively with log PFDat higher irradiances. During the second phase, the rate increasedlinearly with irradiance, becoming saturated at PFD 200 µmolm2 s1. Key words: Phaseolus, phototropism, pulvinule, spectral dependence, trifoliate leaf movements 相似文献
5.
The effect of a dark period at very low partial pressures ofoxygen (104101mm. Hg) upon the subsequentphotosynthetic production of oxygen by Chlorella pyrenoidotawith saturating intensities of illumination has been investigated.With the lowest partial pressures of oxygen used the time courseof oxygen production separates into two phases; an initial burstfollowed by a subsequent rise to the final steady state. Theseparation of the two phases in time is greater the lower theconcentration of carbon dioxide and the longer the precedingdark period. The initial burst of oxygen as distinct from thesteady state production is not inhibited by 103 M. iodoacetamide.In contrast with the Hill reaction, as measuredafter addition of quinone, the initial burst of oxygen was inhibitedby p-chloromercuribenzoate 104M.). Concentrations ofsodium fluoride and of 2:4-DNP which had no effect on the steadystate of photosynthesis shortened the half-time for attainmentof the steady state so removing or obscuring the initial burst.The effect with fluoride was observed only if added at the beginningof the preceding dark period. It is suggested that the initial oxygen burst results from reductiveamination and carboxylation of keto acids present at the beginningof illumination. Iodoacetamide is assumed to inhibit steadystate photosynthesis by preventing reduction of phosphoglycericacid (PGA) to triose and hence its regeneration. It is assumednot to inhibit reductive amination or carboxylation. With longdark periods the initial burst is separated in time from thefinal acceleration to a steady state; this phase appearing asa decreased rate of production of oxygen may be also due toinhibition by fermentation products or to their conversion toamino acid without change in oxidation-reduction. The separationin time is minimized if fluoride or 2:4-dinitro-phenol is addedat the beginning of the dark period; both probably prevent accumulationof pyruvic acid during fermentation limiting the initial reactionsto the reduction of PGA. 相似文献
6.
Rooted cuttings of Kalanchoë blossfeldiana cv. Feuer Bluteand K. crenatum failed to show a net dark CO2 fixation whenraised in dilute nutrient solution. Dark CO2 fixation (CAM)in these plants was initiated either by increasing the soluteconcentration or lowering the water potential of the nutrientsolution by addition of mannitol (0.11 M and 0.25 M) and carbowax4000 (0.16 M and 0.3 M). Initiation was also brought about byspraying the leaves with B-9 (N,dimethylamino-succinamicacid,300mg11) or by addition of CCC (2 chloroethyl trimethylammonium chloride, 300 or 750 mg11) to the nutrient medium.Failure of CAM in dilute solution was suggested to be due tolack of accumulation of photosynthates in the leaves. Waterstress and growth retardants brought about reduction of monilizationand/or translocation thereby leading to accumulation of assimilatesin the leaves and to initiation of dark CO2 fixation. 相似文献
7.
The CO2 compensation point at 25 °C and 250 µEinsteinsm2 s1 wasmeasured for 27 bryo-phyte species, andwas found to be in the range of 45160 µl CO2 I1air. Under the same conditions Zea mays gave a value of 11 µlI1 and Horde um vulgare 76 µI1. The rate of loss of photosyntheticallyfixed 14CO2 in the light and dark in six bryophytes (three mosses,two leafy liverworts, one thalloid liverwort) was determinedin CO2-free air and 100% O2. The rate of 14CO2 evolution inthe light was less than that in the dark in CL2-free air, butin 100% O2 the rate in the light increased, so that in all butthe leafy liverworts it was greater than that in the dark. Raisingthe temperature tended to increase the rate of 14CO2 evolutioninto CO2-free air both in the light and dark, so that the light/dark(L/D) ratio did not greatly vary. The lower rate of loss of14CO2 in the light compared tothe dark could be due to partialinhibition of dark respiration reactions in thelight, a low rate of glycolate synthesis and oxidation, or partialreassimilation of the 14CO2 produced, or a combination of someor all of these factors. 相似文献
8.
High population densities of germinating rice seedlings in initiallyair-saturated sealed aquatic environments exhibited dseedling growth consisting solely of coleoptile emergence inlight and dark environments. Residual oxygen tensions of 1723%of the initially air-saturated water containing the dseedlings were evident after 15 d in both the light and dark.Coleoptiles of all d seedlings were stark white in appearance,lacked protochlorophyllide, and contained proplastids and amyloplasts,there being no evidence of normal etioplast development in thelight or dark and no chloroplast development in the light. Thus,complete environmental anoxia was observed to be unnecessaryfor inhibiting normal chloroplast photomorphogenesis in coleoptilesof light-germinated rice seedlings. Increasing the oxygen tensionsof the 15-d-old aquatic environments of light- and dark-germinatedd seedlings placed in the light resulted in normal chloroplastphotomorphogenesis in coleoptiles, shoots, and roots. Key words: Oryza sativa, environmental anoxia, chloroplast photomorphogenesis, rice coleoptiles 相似文献
9.
The effects of a number of growth-promoting and growth-inhibitingsubstances, including two fungal toxins, were studied on theextension of segments of etiolated tomato seedling hypocotyls.The bioassay was sensitive to small quantities of NaF, coumarinand 2, 4-DNP and inhibition was observed at all concentrations.2, 4-DNP or Iodoacetate stimulated growth at concentrationsbetween 1? 104 and 5 ? 106M. or 1 ? 106and 1 ? 107M. respectively. Inhibitor experiments inbuffered nutrient solution were approximately 10 per cent. moresensitive than those in deionized water. By means of paper partition chromatography small quantitiesof two fungal toxins, fusaric and alternaric acid were chromatographedand bioassayed. The effect of fussric acid (5, n-butyI picolinicacid) on hypocoty1 growth was detected at concentrations aslow as 1 ? 105M. Experiments with recongnized growth-promoting substances showedthat Kinetin inhibited growth at concentrations up to 1 ?108M.in both light and dark. IAA inhibited growth up to 1 ? 106M.At 1 ? 107 and 1 ? 108 only small increases occurredwith IAA and the effect of light was negligible. Gibberellicacid (GA2)stimulated growth at concentrations from 103to 107M. and significant increases up to 17 per cent.were recorded in the light. Since the light induced inhibitionwas only partly restored, the existence of some other naturallight sensitive growth substance is suggested. The value ofthe bioassay as a method for estimating natural growth-inhibitingand growth-promoting substances is discussed. 相似文献
10.
This paper describes how different wavelengths of light regulatespore germination in the fern Ceratopteris richardii. This speciesdoes not exhibit any dark germination. Maximum photosensitivityof the spores is reached 7 to 10 d after imbibition. An increasein the red light fluence above the threshold fluence of 1016quanta.m2 leads to a corresponding increase in germination.In sequential irradiation experiments, farred light can reversethis red light-mediated germination to the level observed withthe far-red light control. Blue light fluences above 1020 quanta.m2can also block the germination response to red light. Moreover,this antagonistic effect of blue light is not reversed by subsequentirradiation with red light. It is therefore concluded that phytochromeand a distinct blue light photoreceptor control C. richardiispore germination. These interpretations are entirely consistentwith the published literature on other fern genera. (Received November 28, 1986; Accepted April 6, 1987) 相似文献
11.
Delhon Patricia; Gojon Alain; Tillard Pascal; Passama Lucien 《Journal of experimental botany》1995,46(10):1585-1594
The effect of light on NO3 utilization was investigatedin non-nodulated soybean (Clycine max L. Merr., cv. Kingsoy)plants during a 14/10 h light/dark period at a constant temperatureof 26C. A 3050% decrease of net NO3 uptake ratewas observed 26 h after the lights were turned off. Thiswas specifically due to an inhibition of NO3 influx asmeasured by 15N incorporation during 5 min. The absolute valuesof NO3 efflux depended on whether the labelling protocolinvolved manipulation of the plants or not, but were not affectedby illumination of the shoots. Darkness had an even more markedeffect in lowering the reduction of 15NO3 in both rootsand shoots, as well as xylem transport of 15NO3 and reduced15N. Concurrently with this slowing down of transport and metabolicprocesses, accumulations of NO3 and Asn were significantlystimulated in roots during the dark period. These data are discussedin view of the hypothesis that darkness adversely affects NO3uptake through specific feedback control, in response to alterationsin the later steps of N utilization which are more directlydependent on light. Key words: Glycine max, light/dark cycles, nitrate uptake, nitrate reduction 相似文献
12.
We report that growth of Dunaliella salina at either 13°C/150µmol m2s1 or 30°C/2,500 µmol m2s1 results in the accumulation of comparable levels ofcarotenoids and the zeaxanthin-binding protein, Cbr. We concludethat carotenoid and Cbr abundance in this green alga respondto changes in PSII excitation pressure ratherthan to high light per se. (Received September 19, 1996; Accepted November 20, 1996) 相似文献
13.
Delhon Patricia; Gojon Alain; Tillard Pascal; Passama Lucien 《Journal of experimental botany》1995,46(10):1595-1602
Experiments were performed with soybean plants to test the hypothesisthat the inhibition of NO3 uptake in darkness is dueto feedback control by NO3 and/or Asn accumulating inthe roots. Xylem export of N compounds was shown to depend onwater flux in both excised root systems and 15N-labelled intactplants, suggesting that the shortage of transpiration in darknessmay be responsible for the retention of NO3 and Asn inthe roots. This was verified in experiments where the light/darkpattern of transpiration was modulated in intact plants by changingthe relative humidity of the atmosphere. Any decrease of transpirationat night was associated with a concurrent stimulation of NO3and Asn accumulations in the roots. However, the light/darkrhythmicity of NO3 uptake was only marginally affectedby these treatments, and thusappeared quite independent fromtranspiration and root NO3 or Asn levels. Typically,the maintainance of a constant transpiration during the day/nightcycle did not suppress the inhibition of NO3 uptake indarkness, whereas it almost prevented the dark increase in rootNO3 and Asn contents. These data strongly support theconclusion that the effect of light on NO3 uptake isnot mediated by changes in translocation and accumulation ofN compounds. Key words: Glycine max, light/dark, cycles, nitrate uptake, transpiration, transport of N compounds, accumulation of N compounds 相似文献
14.
RAJASEKHAR V. K.; GUHA-MUKHERJEE SIPRA; SOPORY SUDHIR K. 《Journal of experimental botany》1983,34(11):1444-1454
In 5-d-old etiolated seedlings of Sorghum bicolor, 12 h of darknessafter 5 min in red light eliminated a lag before the accumulationof chlorophylls in subsequent continuous white light. Increasingthe dark period to 24 h and 36 h, increased the rate of chlorophyllaccumulation in the later stages of greening. Exogenous -aminolevulinicacid neither completely removed the lag, nor increased the rateof chlorophyll accumulation. Cycloheximide (25 µg ml1)and 6-methyl purine (5.0 µg ml1), given continuouslyor only until the 12 h dark period following the red light irradiation,restored the lag and decreased the rate of chlorophyll accumulation.D-threo-chloramphenicol (400µg ml1) also decreasedthe rate of chlorophyll accumulation but did not restore thelag. Addition of these inhibitors even 12 h after red lightirradiation decreased the rate of chlorophyll accumulation.Rifampicin (Rifamycin SV, 400 µg ml1) did not havesuch effects. Key words: Chlorophylls, Phytochrome, -Aminolevulinic acid, Sorghum bicolor 相似文献
15.
Mode of photosynthesis in Mesembryanthemum crystallinum changesfrom C3 to Crassulacean acid metabolism (CAM) when the plantswere stressed with high salinity. [14C]Pyruvate uptake for 30s into intact chloroplasts isolated from leaves of the CAM modeof M. crystallinum was enhanced more than 5-fold in the lightcompared with that in the dark. The stromal concentration ofpyruvate in the light reached to more than 2.5 times of themedium. In contrast, little or no pyruvate uptake occurred inchloroplasts from C3 leaves in either light or dark condition.The initial uptake rate (10 s incubation at 4°C) into theCAM chloroplasts in the light was about 3-fold higher than therate in the dark. Km and Vmax of the initial uptake in the lightwere 0.54 mM and 8.5 µmol (mg Chl)1 h1 respectively.These suggest that pyruvate was actively incorporated into theCAM chloroplasts against its concentration gradient across theenvelope in the light. When hydroponically grown M. crystallinumwere stressed by 350 mM NaCl, the capacity of chloroplasts forpyruvate uptake was induced in 6 d corresponding to the inductionof the activities of PEP-carboxylase and NAD(P)+-malic enzymesin response to salt stress. (Received October 12, 1995; Accepted January 19, 1996) 相似文献
16.
Effects of Light on Degradation of Chlorophyll and Proteins during Senescence of Detached Rice Leaves 总被引:4,自引:0,他引:4
Okada Katsuhiko; Inoue Yasunori; Satoh Kazuhiko; Katoh Sakae 《Plant & cell physiology》1992,33(8):1183-1191
Regulatory effects of light on senescence of rice leaves wereinvestigated by measuring degradation of chlorophyll and proteinsin leaf segments which had been kept in the dark or under illuminationwith light of different intensities and colors. When leaveshad been left in total darkness for three days at 30°C,there was an initial long lag that lasted for one whole dayand then chlorophyll was rapidly degraded in the second andthird days. Breakdown of chlorophyll was strongly retarded bycontinuous illumination with white light of intensity as lowas 0.5 µmol photons m2 s1 but the effectof light decreased at intensities above 10 µmol photonsm2 s2. The initial lag and subsequent degradationof chlorophyll in the dark were little affected by illuminationwith red or far red light at the beginning of dark treatment.However, a brief illumination with red light at the end of thefirst and/or second day significantly suppressed degradationof chlorophyll during subsequent dark periods and the effectof red light was nullified by a short irradiation with far redlight. Thus, degradation of chlorophyll is regulated by phytochrome.Thylakoid membrane proteins and soluble proteins were also largelydegraded during three days in the dark. Degradation of membraneproteins such as the apoproteins of light-harvesting chlorophylla/b proteins of photosystem II and chlorophyll a-binding proteinsof reaction center complexes showed a long lag and was stronglysuppressed by illumination with weak white light. Thus, theloss of chlorophyll can be correlated with degradation of chlorophyll-carryingmembrane proteins. By contrast, light had only a weak protectingeffect on soluble proteins and ribulose-1,5-bisphosphate carboxylase/oxygenaserapidly disappeared under illumination with weak white light.Thus, breakdown of thylakoid membrane and soluble proteins aredifferently regulated by light. Artifacts which would be introducedby detachment of leaves were also discussed.
1 Present address: Department of Applied Biology, Faculty ofScience and Technology, Science University of Tokyo, Yamazaki,Noda-shi, Chiba, 278 Japan.
2 Present address: Department of Life Science, Faculty of Science,Himeji Institute of Technology, Harima Science Park City, Hyogo,678-12 Japan. 相似文献
17.
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
18.
Grande Karen D.; Bender Michael L.; Irwin Brian; Platt Trevor 《Journal of plankton research》1991,13(1):1-16
In vitrorates of gross and net oxygen production were measuredas a function of light intensity in some plankton communitiescollected from Bedford Basin, Nova Scotia, and in a monoclonalculture of Synechococcus. The rate of gross oxygen productionwas measured by a technique in which the stable oxygen isotope,18O, serves as a photosynthetic tracer Net oxygen productionwas measured by automated Winkler technique. The rate of communityrespiration in the light was then determined by the differencebetween gross and net rates of oxygen production. In the naturalpopulations examined, neither gross nor net oxygen productionrates were significantly inhibited at the highest light intensitymeasured (500800 µE m2 s1) In a samplein which the dark respiration rate was small relative to themaximal rate of production [Pmax;sensu Platt et al (1980) JMar. Res., 38, 687701] the rates of lightrespiration were 3 times greater. In two other communities,with high rates of dark respiration relative to Pmaxthe ratesof light respiration were closer to rates of darkrespiration. In the Synechococcus clone, both gross and netoxygen production rates were inhibited at high light intensities.Rates of light respiration were found to varyas a function of light intensity. The greatest rates of respirationwere measured in samples incubated at light intensities thatwere just saturating (100 µE m2 s1). Therates of 14C production were also measured as a function oflight intensity The photosynthetic quotients, based on 14C productionrates and gross oxygen production rates, average 1 9 相似文献
19.
The Diurnal Pattern of Nitrate Uptake and Reduction by Spinach (Spinacia oleracea L.) 总被引:2,自引:0,他引:2
Spinach plants were grown in bowls of aerated nutrient solutionin a controlled environment chamber for 24 h, and harvestedevery 3·5-5 h to record their growth, nitrate and wateruptake, and plant nitrate concentration. Twelve such experimentsare described, either with a 14/10 h dark/light regime, or continuouslight or darkness. The irradiance was either 110, 320, or 510µmol m-2 s-1 (PPFD). All these regimes began at the endof the light period of a 14/10 h dark/light regime (510 µmolm-2 s-1) lasting approximately 2 weeks. Nitrate uptake rate per g of dry weight of plant continued almostunabated at about 17 µmol h-1 through the initial 14-hdark period, and then fell away sharply if the light was notrestored, but increased slightly when it was. With continuouslight at 510 µmol m-2 s-1, uptake rate rose steadily forthe first 24 h of light, and then fell sharply for about 6 h.Shoot nitrate concentration increased about three-fold in thedark phase, and declined in the light at a rate which was positivelyrelated to the irradiance. Root nitrate concentration was severaltimes higher than that of the shoot: its diurnal change wassmaller (relative to the mean) than that of the shoot. Nitratereduction occurred to a small extent in the dark, and increasedrapidly as soon as the lights came on, to remain at a roughlyconstant rate (related to the irradiance) throughout the lightphase. Dry matter increase in the light was related to irradiance,but with little increase above 320 µmol m-2 s-1. Respiratoryweight loss in the dark was not detectable. Rate of fresh weightincrease was approximately constant throughout light and darkperiods. The results compare quite well with the predictions of a simplesimulation model, based on the pump/leak principle.Copyright1994, 1999 Academic Press Spinacia oleracea, nitrate, uptake, reduction, influx, efflux, diurnal, regulation, model, simulation 相似文献
20.
The effects of light/dark on anion fluxes in isolated guardcells of Commelina communis L. have been studied, using 82Brand 36Cl. Transfer of open guard cells from light to dark hasno effect on the 82Br influx, but produces a marked transientstimulation of 82Br or 36Cl efflux, similar to the effect ofsuch transfer on the 86Rb fluxes, and to the effects on both86Rb and 82Br fluxes of adding ABA. On return of guard cellsto light, after the transient, there is a further reductionin Cl/Br efflux. It is argued that control of a specific processof ion extrusion is important in regulating the ability of guardcells to stay open. In three out of four batches of steady-statetissue labelled with 82Br, the plasmalemma fluxes were highenough, relative to the tonoplast fluxes, for the efflux kineticsto be separable into two exponential components, allowing estimationof bromide contents in cytoplasm and vacuole (Qc and Qv), andfluxes at plasmalemma and tonoplast. With opening in light,Qc increased by 3.9 ± 0.4 pmol mm2 µm1and Qy by 5.2 ± 0.6 pmol mm2 µm1(change in content per mm2 of epidermis perµm change inaperture). Using rough estimates for the volumes of cytoplasmand vacuole these figures suggest that at 6.1 µm in thedark the concentrations were about 63 mol m3 in the cytoplasmand 35 mol m3 in the vacuole, rising to about 185 molm3 in the cytoplasm and 125 mol m3 in the vacuole,at 16.7 µm aperture in light. Neither increase can providean adequate increase in salt concentration to account for theosmotic change required, and some solute other than potassiumsalt must also be involved. In one experiment with 82Br andin the only experiment with 36Cl the plasmalemma flux was lower,and not high enough relative to the tonoplast flux to allowseparation of two phases in the efflux curves, and calculationof cytoplasmic and vacuolar contents and fluxes. The effectsof transfer from light to dark were, nevertheless, similar inboth types of tissue. Key words: Commelina communis L., Light/dark effects, Anion fluxes, Guard cells 相似文献