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1.
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
2.
Transpiration of Festuca arundinacea Schreb, strain S170, wasmeasured at two different wind speeds in a controlled-environmentwind tunnel. As a result of a wind increase from 1 m s1to 3.5 m s1 above the sward, transpiration graduallyincreased, especially at night-time. Similar effects were notedin three other grass species. The transpiration increase couldbe attributed to decreases in stomatal and cuticular resistances,as a result of leaf buffeting. 相似文献
3.
Shishido, Y., Challa, H. and Krupa, J. 1987. Effects of temperatureand light on the carbon budget of young cucumber plants studiedby steady-state feeding with 14CO°2J. exp. Bot. 38: 10441054. The effect of temperature on the fate of 14C assimilated insteady-state by the expanding third leaf of cucumber seedlingswas studied at irradiances of either 30 or 75 W m2 (PAR)with a daylength of 8 h. The irradiance did not affect the relativedistribution of 14C assimilated by the source leaf between growth,respiration and export. In the range 1530°C risesin temperature generally increased the proportion of carbonexported. The average rate of carbon exported during the nightwas about half the rate in the day. About 45% of the exportedcarbon was lost by respiration. The distribution pattern ofcarbon exported during the day differed considerably from thatof carbon exported during the night. The intensity of irradiance did not affect the proportion oflabelled carbon recovered from the roots. Thus the decreasedshoot/root ratio generally observed with increased irradianceis not directly controlled by carbohydrate supply. We found that the distribution patterns of exported 14C do notnecessarily represent the real carbon distribution, due to differencesin specific activity of imported carbon of individual organs.Consequently distribution patterns of 14C observed in experimentswith one source leaf have to be considered with caution. Key words: Carbon budget, 14C, 14C steady-state feeding, translocation, respiration, assimilate distribution, cucumber, temperature 相似文献
4.
PRANGE ROBERT K.; ORMROD DOUGLAS P.; PROCTOR JOHN T. A. 《Journal of experimental botany》1983,34(9):1108-1116
Experiments were conducted in a gas exchange system to examinethe effect of a water stress, induced by 200 kPa polyethyleneglycol (PEG), on carbon dioxide and water vapour flux, fronddiffusive resistance, intercellular carbon dioxide concentration,carbon dioxide residual resistance and frond water potentialin the ostrich fern (Matteuccia struthiopteris (L.) Todaro).Measurements were taken 1 d after the application of PEG. Themeasurements were made on young fronds (8 d old) and maturefronds (2024 d old) at PPFD's (Photosynthetic PhotonFlux Density) from 01400 µmol m22 s1.Water stress decreased the net photosynthesis rate in maturefronds at PPFD's of 210 µmol m2 s1 or greaterand increased the net photosynthesis rate below 210 µmolm2 s1 in young fronds. The increase in net photosynthesisin stressed young fronds was associated with a significant reductionin the dark respiration rate. Water stress and decreasing PPFD'sincreased frond diffusive resistance. Carbon dioxide concentrationin the intercellular spaces decreased with increasing frondage and PPFD's up to 200 µmol m2 s1. Theresidual resistance to carbon dioxide flux was not significantlyaffected by either frond age or water stress. Frond water potentialwas significantly lower in mature fronds than in young fronds. Key words: Matteuccia struthiopteris, Water relations, Photosynthesis, Dark respiration 相似文献
5.
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
6.
A semi-closed system to label with 14C and trace photoassimilatesunder steady state conditions is described. It was used to elucidatethe effects of night temperature on the carbon budget of tomato The third leaf kept at 25 °C in 8 h light of 36 W m1(PAR) assimilated 13·77 mg C . d1. By the endof the photoperiod, 46% of the carbon assimilate was exportedto the sinks, out of which 27% was respired and 19% was accumulatedin the sinks, respectively The plants were then kept in the dark for 16 h at 15, 20, 25and 30%C. The export in the night-time increased with nighttemperature, reaching 1827% of the carbon assimilated.Thus, the total export in a whole day amounted to 6372%of the carbon assimilated, out of which 35 and 42% were lostby respiration and 29 and 31% was accumulated in the sinks at15 and 30 °C, respectively. Thus, accumulation in the sinksdiffered little with night temperature, while that in the sourceleaf, and hence the total accumulation, decreased with increasingnight temperature The export started early in the morning and was much greaterin the light than in the dark. In addition, the day/night ratioof export was lower at higher night temperatures The percentage distribution of 14C-assimilates to the lowerparts decreased, while that to the upper parts increased withincreasing night temperature. The calculated respiratory lossin individual sinks seemed to correspond to the distributionpattern of 14C-assimilates Carbon budget, 14C, 14C steady state feeding, translocation, respiration, assimilate distribution, temperature, tomato 相似文献
7.
In earlier work the effects of light intensity over the range31 to 250 J cm2 day1 and carbon dioxide concentrationfrom 325 to 900 ppm with 8-h days at 18.3 °C and 16-h nightsat 15.6 °C were described. The present paper is concernedwith three further experiments with light levels up to 375 Jcm2 day1 (which corresponds to the daily totalin a glasshouse in southern England in early May or August andthe intensity is approximately that of mid-winter sunshine),carbon dioxide concentration up to 1500 ppm, and day temperaturesof 18.3 to 29.4 °C. Final plant weight was increased by light over the range 125375J cm2 day1 and by carbon dioxide over the range325900 ppm, with positive interaction between them; thisinteraction was increased by raising the temperature to 23.9°C and somewhat more at 29.4 °C day temperature. Leaf-arearatio and specific leaf area were reduced by increasing eitherlight or carbon dioxide but there was little effect of temperature.Leaf-weight ratios were uniform within experiments but therewere small consistent differences between one experiment andthe other two which also affected leaf-area ratios. Mean unit leaf rate was scarcely affected by day temperatureover the range investigated. There were the usual increasesdue to increased light and carbon dioxide concentration anda consistent difference in absolute value between one experimentand the other two. These differences in mean unit leaf rateare illustrated in detail in the ontogenetic trend of unit leafrate and plant size. Lower unit leaf rates were to a considerableextent compensated for by increased leaf-area ratios in theusual way. Despite the substantial differences in day temperature the specificwater contents (g water g dry weight1) differed little,showing in the majority of cases higher values in the highertemperature for otherwise similar treatment combinations. Flower development was somewhat delayed at 23.9 °C day temperature,and substantially so at 29.4 °C. Lateral branch length wasincreased at 23.9 °C and excessively so at 29.4 °C.This reveals quite clearly that a temperature optimum for vegetativegrowth may not be the optimum for flowering performance norproduce a desirable plant shape. Despite the marked effects of temperature on rate of flowerdevelopment, the relationship between flower development andthe ratio of flower to total weight was the same for all treatmentcombinations in all three experiments and coincident with thatreported earlier. Gasometric determinations indicated that respiratory loss bythe whole plant was a smaller proportion of net photosyntheticgain at a temperature of 29.4 °C than at 18.3 °C andwas likewise a smaller proportion at 1500 ppm carbon dioxidethan at 325 ppm. If photorespiration of leaves is assumed tobe as great as their dark respiration, the respiratory lossesare in the range of 3150 per cent of the gross gain.Greater rates of photorespiration would increase the proportionaterespiratory loss. 相似文献
8.
The specific respiration rates of nodulated root systems, ofnodules and of roots were determined during active nitrogenfixation in soya bean, navy bean, pea, lucerne, red clover andwhite clover, by measurements on whole plants before and afterthe removal of nodule populations. Similar measurements weremade on comparable populations of the six legumes, lacking nodulesbut receiving abundant nitrate-nitrogen, to determine the specificrespiration of their roots. All plants were grown in a controlled-environmentclimate which fostered rapid growth. The specific respiration rates of nodulated root systems ofthe three grain and three forage legumes during a 714-dayperiod of vegetative growth varied between 10 and 17 mg CO2g1 (dry weight) h1. This mean value consistedof two components: a specific root respiration rate of 69mg CO2 g1 h1 and a specific nodule respirationrate of 2246 mg CO2 g1 h1. Nodule respirationaccounted for 4270 per cent of nodulated root respiration;nodule weight accounted for 1240 per cent of nodulatedroot weight. The specific respiration rates of roots lackingnodules and utilizing nitrate nitrogen were generally 2030per cent greater than the equivalent rates of roots from nodulatedplants. The measured respiratory effluxes are discussed in thecontext of nitrogen nitrogen fixation, nitrate assimilation. Glycine max, Phaseolus vulgaris, Pisum sativum, Medicago sativa, Trifolium pratense, Trifolium repens, soya bean, navy bean, pea, lucerne, red clover, white clover, nodule respiration, root respiration, fixation, nitrate assimilation 相似文献
9.
Root Aeration and Respiration in Young Mangrove Plants (Avicennia marina (Forsk.) Vierh.) 总被引:2,自引:0,他引:2
The roots of young plants of Avicennia marina (Forsk.) Vierh.grown under simulated tidal conditions were harvested so asto obtain the entire root system. The roots were subdividedand weighed and subsamples taken for manometric determinationof respiration rates at different temperatures. The supply capacityof the above-ground portion of the root system was determinedand the results compared in terms of supply and demand. Theoxygen consumption rate of the roots at 15°C was found tobe 1·69±0·07 µmol kg1 s1for cable roots and 3·27±0·12 µmolkg1 s1 for fine roots. The Q10 for respirationwas 2·55 for oxygen consumption in both fine and cableroots, and for carbon dioxide production was 2·66 forfine roots and 3·04 for cable roots. The respiratoryquotient varied with temperature but was less than unity. Concentrationdifferences of between 1·8 mol m3 and 3·4mol m3 between the inside of root and the air were sufficientto permit aeration of the root system by diffusion alone, andthe aerenchyma contained sufficient oxygen to maintain aerobicconditions while the roots were covered with water. The effectof tide and seasonal temperature change on gas exchange, togetherwith the possibility of some form of carbon dioxide fixationwithin the root, are examined and the implications of theseeffects on growth and development are discussed. Key words: Mangrove, root aeration, respiration, aerenchyma 相似文献
10.
SCHMITT ANDREAS K.; LEE HELEN S. J.; LUTTGE ULRICH 《Journal of experimental botany》1988,39(11):1581-1590
Gas exchange measurements were undertaken on 2-year-old plantsof Clusia rosea. The plants were shown to have the ability toswitch from C3-photosynthesis to CAM and vice versa regardlessof leaf age and, under some conditions, CO2 was taken up continuously,throughout the day and night. The light response was saturatedby 120 µmol m2 s1 typical of a shade plant. Gas exchange patterns in response to light, water and VPD wereexamined. All combinations of daytime and night-time CO2 uptakewere observed, with rates of CO2 uptake ranging from 2 to 11µmol m2 s1 depending upon water status andlight. Categorization of this plant asC3, CAM or an intermediateis impossible. Differing VPD affected the magnitude of changesfrom CAM to C3-photosynthesis (0 to 0.5 and 0 to 6.0 µmolm2 s1 CO2, respectively) when plants were watered.Under well-watered conditions, but not under water stress, highPPFD elicited changes from CAM to C3 gas exchange. This is unusualnot only for a shade plant but also for a plant with CAM. Itis of ecological importance for C. rosea, which may spend theearly years of its life as an epiphyte or in the forest understorey,to be able to maximize photosynthesis with minimal water loss. Key words: Clusia rosea, CAM, C3, stress 相似文献
11.
Root growth in chickpea (Cicer arietinum) has been studied fromthe early vegetative phase to the reproductive stage in orderto elucidate its growth and maintenance respiration and to quantifythe translocation of assimilates from shoot to root. A carbonbalance has been drawn for this purpose using the growth andrespiration data. The increase in the sieve tube cross-sectionalarea was also followed simultaneously. Plants growing in a nutrient culture medium were studied todetermine the relative growth rate (RGR) 560 d aftergermination. RGR declined from 113 to 41 mg d1 g1during the measurement period. Simultaneous with the RGR analysis,respiration rate was also measured using an oxygen electrode.The respiration rate declined as the plants aged and a drasticreduction was recorded following anthesis. The relationshipbetween RGR and respiration rate was used to extrapolate themaintenance respiration (m) and growth respiration (1/YEG).The respiration quotient (r.q.) of the roots was 1.2 and theQ10 in the range 2025 °C was 2·2. A carbon balance for the roots was constructed by subtractingthe carbon lost during respiration from that gained during growth.The roots were found to respire no less than 80% of the carbontranslocated. The increase in the cross-sectional area composed of sieve tubeswas measured near the root-shoot junction as the plants grew.Chickpea has storied sieve plates which simplifies these measurements.Their cross-sectional area increased during growth mainly becauseof an increase in sieve tube number. The diameter of individualsieve tubes remained constant. Specific mass transfer (SMT) values for seive tubes into theroots have been computed during various stages of growth. SMTvalues were relatively constant before anthesis (approx. 6·5g h1 cm2), but decreased following anthesis. Wedid not evaluate possible retranslocation from roots: any suchretranslocation would have the effect of increasing our SMTvalues. Chickpea, Cicer arietinum, legume, root, respiration, phloem, translocation, carbon balance, specific mass transfer, sieve-tube dimensions 相似文献
12.
Environmental Influences on Carbon Recycling in a Terrestrial CAM Bromeliad, Bromelia humilis Jacq. 总被引:2,自引:0,他引:2
The effects of night-time temperature, leaf-to-air vapour pressuredeficit (VPD) and water stress on CO2 recycling in Bromeliahumilis Jacq. grown under two light and nitrogen regimes wereinvestigated. At night-time temperatures above 30°C, integratednet dark CO2 uptake was severely reduced and CO2 for malatesynthesis was mainly derived from dark respiration. At 35°C,up to 84% of the CO2 liberated by dark respiration was refixedinto malic acid. Below 30 °C only nitrogen deficient plantsshowed significant recycling. No significant differences wereobserved between high and low light grown plants in CO2 recycling.A doubling of leaf-to-air VPD from 7-46 Pa kPa1 to 15.49Pa kPa1 resulted in a 2- to 20-fold decrease in leafconductance and about 50 to 65% reduction in integrated darkCO2 uptake. However, about twice as much CO2 was recycled atthe higher VPD as in the lower. Ten days of water stress resultedin 80 to 100% recycling of respiratory CO2. Under high VPD andwater stress treatments, the amount of water potentially savedthrough recycling of CO2 reached 2- to 6-fold of the actualtranspiration. In general, nitrogen deficient plants had higherper cent recycling of respiratory CO2 in response to high night-timetemperature, increased VPD or water stress. The results emphasizethe ecological relevance of carbon recycling in CAM plants. Key words: Bromelia humilis, CAM, PPFD, dark respiration, temperature, VPD, water stress 相似文献
13.
Cuticular Conductance and the Humidity Response of Stomata 总被引:4,自引:0,他引:4
Meidner, H. 1986. Cuticular conductance and the humidity responseof stomata.J. exp. Bot. 37: 517525. Detailed measurements of cuticular vapour loss from leaves ofseveral species showed that cuticular conductance declined froman early morning maximum of 0?02 cm s1 to between 0?004and 0.005 cm scm s1 even in the absence of stomatal transpiration.Re-establishment of the maximum conductance occurred only ina humid atmosphere and when the xylem system was under pressure(simulated mild root pressure) Cuticular vapour loss alone is,therefore, unlikely to be the underlying mechanism of the humidityresponse of Stomata. Evidence for the existence of a humidity-sensing feed-forwardmechanism is discussed and it is shown that when detailed measurementsare made the humidity response is found to have two phases.This indicates a perturbation of the fine turgor balance betweenepidermat and guard cells that exists in a transpiring leaf.It is argued that the humidity response can be accounted forby reference to hydropassive movements which initiate a metabolicadjustment of the guard cells to altered evaporative demand. Key words: Cuticle, conductance, humidity, stomata, transpiration 相似文献
14.
Cultivated Agave mapisaga and A. salmiana can have an extremelyhigh above-ground dry-weight productivity of 40 Mg ha1yr1. To help understand the below-ground capabilitiesthat support the high above-ground productivity of these Crassulaceanacid metabolism plants, roots were studied in the laboratoryand in plantations near Mexico City. For approximately 15-year-oldplants, the lateral spread of roots from the plant base averaged1.3 m and the maximal root depth was 0.8 m, both considerablygreater than for desert succulents of the same age. Root andshoot growth occurred all year, although the increase in shootgrowth at the beginning of the wet season preceded the increasein growth of main roots. New lateral roots branching from themain roots were more common at the beginning of the wet season,which favoured water uptake with a minimal biomass investment,whereas growth of new main roots occurred later in the growingseason. The root: shoot dry weight ratio was extremely low,less than 0.07 for 6-year-old plants of both species, and decreasedwith plant age. The elongation rates of main roots and lateralroots were 10 to 17 mm d1, higher than for various desertsucculents but similar to elongation rates for roots of highlyproductive C3 and C4 agronomic species. The respiration rateof attached main roots was 32 µmol CO2 evolved kg1dry weight s1 at 4 weeks of age, that of lateral rootswas about 70% higher, and both rates decreased with root age.Such respiration rates are 4- to 5-fold higher than for Agavedeserti, but similar to rates for C3 and C4 agronomic species.The root hydraulic conductivity had a maximal value of 3 x 107ms1 MPa1 at 4 weeks of age, similar to A. deserti.The radial hydraulic conductivity from the root surface to thexylem decreased and the axial conductivity along the xylem increasedwith root age, again similar to A. deserti. Thus, although rootsof A. mapisaga and A. salmiana had hydraulic properties perunit length similar to those of a desert agave, their highergrowth rates, their higher respiration rates, and the greatersoil volume explored by their roots than for various desertsucculents apparently helped support their high above-groundbiomass productivity Key words: Crassulacean acid metabolism, productivity, root elongation rate, root system, water uptake 相似文献
15.
The effects of osmotically induced water deficits on the metabolismof aged beetroot and potato discs were investigated. In thispaper the tissue-water relationships in two osmotica, mannitol,and Carbowax 1540, are described. Tissues in equilibrium with Carbowax solutions had lower freshweights than those in isotonic mannitol solutions, particularlyat water potentials below 0.7 J g1 with potatoand 2.0J g with beetroot. Potato discs killedby freezing and thawing lost water to Carbowax but not to mannitolsolutions. The extra effectiveness of Carbowax solutions inlowering fresh weight was attributed to an osmotic effect acrossthe cell wall. Carbowax was found to penetrate plasmolysed potatotissue, however, at a rate of about 3.0 mg (g fresh weight)1h. The extent to which water uptake occured on retransfer to waterwas unaffected by the nature of the soulte used, but dependon the degree of dehydration. The following phases were clearlydefined: (1) recovery to the fresh weight at full turgor, whenthe water potential of potato tissue was not reduced below 0.5J g and of beetroot below 1.2 J g1; (2)a declining degree of recovery with decreasing water potentialover the ranges 0.5 to 1.0 J g1 and 1.2to 3.0 J g1 for potato and beetroot, respectively,and (3)in potato, the absence of recovery of fresh weight followingreduction of the water potential below 1.0 J g1. 相似文献
16.
Single clonal plants of white clover (Trifolium repens L) grownfrom explants in a Perlite rooting medium, and dependent fornitrogen on N2 fixation in root nodules, were grown for severalweeks in controlled environments which provided two regimesof CO2, and temperature 23/18 °C day/night temperaturesat 680 µmol mol1 CO2, (C680), and 20/15 °Cday/night temperatures at 340 µmol mol1 CO2 (C340)After 34 weeks of growth, when the plants were acclimatedto the environmental regimes, leaf and whole-plant photosynthesisand respiration were measured using conventional infra-red gasanalysis techniques Elevated CO2 and temperature increased ratesof photosynthesis of young, fully expanded leaves at the growthirradiance by 1729%, despite decreased stomatal conductancesand transpiration rates Water use efficiency (mol CO2 mol H2O1)was also significantly increased Plants acclimated to elevatedCO2, and temperature exhibited rates of leaf photosynthesisvery similar to those of C340 leaves instantaneouslyexposed to the C680 regime However, leaves developed in theC680 regime photosynthesised less rapidly than C340 leaves whenboth were exposed to a normal CO2, and temperature environmentIn measurements where irradiance was varied, the enhancementof photosynthesis in elevated CO2 at 23 °C increased graduallyfrom approx 10 % at 100 µmol m1 s1 to >27 % at 1170 µmol m2 s1 In parallel, wateruse efficiency increased by 2040 % at 315 µmolm2 s1 In parallel, water use efficiency increasedby 2040 % at 315 µmol m2 s1 In parallel,water use efficiency increased by 2040 % at 315 µmolm2 s1 In parallel, water use efficiency increasedby 2040 % at 315 µmol m2 s1 to approx100 % at the highest irradiance Elevated CO2, and temperatureincreased whole-plant photosynthesis by > 40 %, when expressedin terms of shoot surface area or shoot weight No effects ofelevated CO2 and temperature on rate of tissue respiration,either during growth or measurement, were established for singleleaves or for whole plants Dependence on N2, fixation in rootnodules appeared to have no detrimental effect on photosyntheticperformance in elevated CO2, and temperature Trifolium repens, white clover, photosynthesis, respiration, elevated CO2, elevated temperature, water use efficiency, N2 fixation 相似文献
17.
Cramer M.D.; Schierholt A.; Wang Y.Z.; Lips S.H. 《Journal of experimental botany》1995,46(10):1569-1577
In hydroponically grown Lycopersicon esculentum (L.) Mill. cv.F144 the site of NO3 reduction and assimilation withinthe plant was shifted from the shoot to the root by salinity.Uptake of NO3 from the root solution was strongly inhibitedby salinization. Consequently, NO3 concentrations inthe leaf, stem and root tissues as well as the nitrate reductaseactivities of the leaves were lower in salinized than in controlplants. Lower NO3, but higher reduced-N, concentrationswere observed in the xylem sap as a result of the enhanced participationof the root in NO3 reduction in salinized plants. Lowerstem K+ concentrations and leaf malate concentrations were foundin salinized compared to control plants which indicates reducedfunctioning of the K+shuttle in the salinized plants. Incorporation of inorganic carbon by the root was determinedby supplying a pulse of NaH14CO3 followed by extraction andseparation of the labelled products on ion exchange resins.The rate of H14CO3 incorporation was c. 2-fold higherin control than in salinized plants. In salinized plants theproducts of H14CO3 incorporation within the roots werediverted into amino acids, while the control plants divertedrelatively more 14C into organic acids. Products of inorganiccarbon incorporation in the roots of salinized plants providean anaplerotic source of carbon for assimilation of reducedNO3 into amino acids, while in control plants the productswere predominantly organic acids as part of mechanisms to maintainionic balance in the cells and in the xylem sap. Key words: Tomato, nitrate, PEPc, respiration, salinity 相似文献
18.
Sources of Inorganic Carbon Acquired through CAM in Littorella uniflora (L.) Aschers 总被引:1,自引:0,他引:1
Madsen, T. V. 1987. Sources of inorganic carbon acquired throughCAM in Littorella uniflora (L.) Aschers.J. exp. Bot.38: 367377. The CO2 dynamics of the lacunal air and the relative contributionof external and internal CO2 sources to dark CO2 assimilationwas examined in the submerged aquatic CAM species Littorellauniflora (L.) Aschers. Refixation of internal CO2, released by dark respiration, constitutedabout 3035% of the total dark CO2 assimilation. At aCO2 concentration of 0·2 mol m3 around the leavesthe external CO2 uptake through the roots increased from 45%of the total CO2 uptake at 0·7 mol m3 CO2 to 100%at 1·6 mol m3 and 3·1 mol m3 CO2around the roots. The negligible importance of leaf CO2 uptakeat high CO2 concentrations around the roots was the result ofa causative high CO2 concentration in the leaf lacunae. The CO2 permeability of Littorella leaves was high relativeto root permeability. This has at least two ecological implications:(1) it enhances the potential diffusive release of CO2 fromthe sediment C02-pool via the lacunal system of the plants.This loss of CO2, however, was found to be greatly reduced byCAM activity of the plants. (2) The high permeability of theleaf surface to CO2 exchange allows the plants to assimilateCO2 from the water surrounding the leaves when the concentrationis high, i.e. during extensive epiphyte dark respiration. Thus,CAM tends to facilitate retension of a high CO2 pool in thesediment-plant system and at the same time allows the plantsto exploit the water column CO2 source when it is abundant.This result is in accordance with the general idea that CAMin aquatics constitute a carbon conserving mechanism. Key words: Aquatic macrophytes, dark CO2 assimilation, inorganic carbon sources 相似文献
19.
Environmental Factors Affecting the Loss of Carbon from the Roots of Wheat and Barley Seedlings 总被引:6,自引:0,他引:6
The amounts of carbon released into soil from roots of wheatand barley seedlings grown under three environmental conditionsfor 3 weeks with shoots in constant specific activity 14CO2are reported. This carbon loss was measured as respired 14CO2from both the root and the accompanying microbial populationand as root derived 14C-labelled organic C compounds in thesoil. With a 16 h photoperiod, growth at 15 ?C constant or 18?C day/14 ?C night gave a loss of 3340% of the totalnet fixed carbon (defined as 14C retained in the plant plus14C lost from the root). The proportion of 14C translocatedto the roots that was released into the soil did not changewith temperature, so carbon distribution within the plant musthave changed. With a 12 h photoperiod and a temperature regimeof 18 ?C/14 ?C carbon loss from the roots was decreased to 1725%of the total fixed carbon. Key words: Cereals, Roots, Carbon loss 相似文献
20.
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