共查询到20条相似文献,搜索用时 31 毫秒
1.
Root growth of 7-d-old wheat (Triticum aestivum cv. Gamenya)seedlings was impaired at dissolved O2 concentrations of 0.01and 0.055 mol m3 O2, while growth at 0.115 mol m3O2 was the same as that in continuously aerated controls (0.26mol m3 O2). Oxygen uptake by apical (02 mm), expanding (24mm) and expanded (1012 mm) tissues of the roots decreasedbelow 0.16, 0.09 and 0.05 mol m3 O2, respectively. Thishierarchy is consistent with the metabolic rates of these tissues.There was a small (c. 9%) inhibition of O2 uptake and some netsynthesis of ethanol and alanine in root apices at 0.115 molm3 O2. Significant amounts of anaerobic end-productsaccumulated at 0.055 mol m3 O2 and even more so at 0.01mol m3 O2, indicating that oxidative phosphorylationwas strongly inhibited. Net alanine synthesis increased in fully expanded (1016mm) tissues exposed to <0.0030.01 mol m3 O2,and this increase was accompanied either by a proportionallysmaller increase in the concentration of other free amino acidsor by a net decrease in free amino acid levels excluding alanine.This suggests that alanine was synthesized as an end-productof anaerobic catabolism and did not accumulate simply becauseof decreased net protein synthesis. Comparing the carbon flow to CO2, ethanol, lactate and alaninein roots at 0.01 mol m3 O2 with carbon loss as CO2 inaerated roots suggests that carbon flow to products of metabolismwas not greatly enhanced due to O2 deficiency. This infers,but does not prove that, in wheat, generation of energy duringperiods of O2 deficiency is not enhanced due to a Pasteur effect. Key words: Anaerobic, fermentation, oxygen, wheat 相似文献
2.
Atwell, B. J. and Green way, H. 1987. The relationship betweengrowth and oxygen uptake in hypoxic rice seedlings.J.exp. Bot. 38: 454465. Rice seedlings (Oryza saliva L.) were grown in the dark forup to 4 d in solutions containing various concentrations ofO2. Compared with seedlings grown at 0·250 mol O2 m3,the dry weight of the growing seedling was 14% lower at 0·110mol O2 m3 and 60% lower at 0 mol O2 m3. Decreasesin fresh weight were similar but not identical to decreasesin dry weight, possibly because leaf growth was suppressed evenabove 0·110 mol O2 m3. Oxygen deficiency inhibitedroot growth more severely than coleoptile growth. Coleoptiles from seedlings grown in aerated solution were exposedto an atmosphere of pure N2 for 30 min. Anoxia caused a declinein ATP content and energy charge, suggestive of decreased oxidativephosphorylation. It is not clear whether the decline in oxidativephosphorylation was solely responsible for impaired growth inhypoxia. In seedlings growing at O2 concentrations less than 0·110mol O2 m3, significant amounts of ethanol were synthesized.The rate of O2 uptake decreased markedly below 0·06 molO2 m3; this was presumably near the external O2 concentrationat which oxidative phosphorylation became limited by the supplyof O2. The stage of development of the seedlings appeared toinfluence O2 uptake, possibly through changes in conductanceof the tissue to O2. Uncouplers were used to confirm that thecritical O2 concentration was dependent on O2 diffusion ratherthan enzyme kinetics. Impaired growth above 0·110 molO2 m3 may have been due to a decreased activity of oxygenasesof relatively low affinity for O2, which in turn altered cellmetabolism. Key words: Growth, oxygen uptake, rice seedlings, hypoxia 相似文献
3.
Effects of Low Concentration of Ozone, Singly, and in Combination with Sulphur Dioxide on Net Photosynthesis Rates of Vicia faba L. 总被引:3,自引:0,他引:3
Net photosynthesis rates (PN) of Viciafaba plants were measuredin chambers containing either clean air or air containing between50 and 300 parts 109 ozone (O3) with or without 40 parts10 9 SO2. Exposure to O3 concentrations greater than 50 parts 109 for periods of 4 h resulted in reductions in PN with greaterreductions at higher concentrations. After exposure ceased,recovery of pre-exposure PN depended on O3 concentration. Exposureto less than 90. 100 parts 10 9 was followed by completerecovery after 20 h whereas 200-300 parts 10 9 resultedin visible injury and irreversible depression of PN. The additionof 40 parts 10 9 SO2 to O3 significantly decreased Psbut the effect of SO2 declined with increasing O3. The additionof SO2 had no significant affect on recovery patterns. It is postulated that Vicia faba plants are able to toleratethe absorption of O, up to a threshold above which progressivedecreases in PN occur due to effects on photosynthetic processes.The slow and sometimes incompletely reversible effects of O3on PN indicate cellular differences in the injury mechanismand repair capacity compared with the action of SO2 alone. Lowconcentrations of O3 with SO2 result in additive injury to PNsuggesting independent action of the pollutants, but the reductionin SO2 action with increasing O3 indicates a limit for potentialphysiological injury More the onset of visible injury. 相似文献
4.
We have examined the long-term effects of NO3 concentrationson NO3 (15NO3) fluxes and cellular pool sizesin roots of intact 30-d-old wheat (Triticum aestivum cv. Courtot)grown hydroponically. Compartmental analysis was performed understeady-state conditions at five different levels of NO3concentration (from 0.1 up to 5 mol m3 taking into accountmetabolism and secretion into the xylem (Devienne et al., 1994).Nitrate and reduced nitrogen levels in the tissues were largelyindependent of external NO3 concentration although below1.5 mol m3 NO3; concentration limited plant growth.In the chamber, marked diurnal variations in net uptake occurredand, in the light, higher NO3 concentrations yieldedhigher NO3 uptake rates. After transfer of the plantsto the laboratory, the increase in net uptake linked to elevationof NO3; concentrations was even larger (from 0.1 to 8.8µmolh1 g1 FW) as a result of a marked increase (x1011) in the unidirectional influx at the plasmalemmawhile NO3 efflux was less enhanced (x 45). Underthese conditions, influx into the vacuole was also higher (x24) while efflux from the vacuole was little affected(x 13). NO3 concentrations within the cell compartmentswere estimated under the clas sical assumptions. The vacuolarconcentration was a little modified by NO3 availabilitywhereas that in the cytosol increased from about 10 mol m3to about 20 mol m3 indicating that (1) the absolute valuefor the cytosol was high and (2) it displayed only a small increasedespite very large changes in NO3 fluxes. NO3distribution within the cells did not seem to involve an activeaccumulation of NO3 in the vacuole. Key words: Wheat, ion transport, nitrate, 15N, compartmentation 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.
The use of chlorate as an analogue for NO3 during nitrateuptake into Chara corallina cells has been investigated. NO3inhibits 36C1O3 influx into Chara over the concentrationrange 01000 mmol m3. Lineweaver-Burke plots ofthe data are characteristic of competitive inhibition by NO3in the low concentration range (0300 mmol m3 ClO3)and apparent KINO3 is 140 mmol m3 which is of a similarorder of magnitude as apparent KmCIO3- 180 mmol m3. Athigher substrate concentrations the inhibition by NO3was not characteristic of competitive or uncompetitive inhibition. 36C1O3/NO3 influx was dependent on K+ and Ca2+in the external medium and inhibited by FCCP. NO3 pretreatmentor N starvation increased subsequent 36C1O3/NO3influx into Chara. A comparison between rates of net NO3uptake and 36C1O3/NO3 influx supported the previoushypothesis that NO3 efflux is an important componentin the determination of overall uptake rates. Key words: Nitrate, Chara, 36CIO3 相似文献
7.
Fragments of maize leaves were incubated at controlled temperatureand irradiance either on distilled water or on one of threeconcentrations of cytokinin (101, 102 and 103mol m3). The effects of zeatin or kinetin on stomatalaperture were determined by stripping abaxial epidermis fromthe fragments after incubation and immediately measuring stomatalapertures under the microscope. At each cytokinin concentrationleaf pieces were incubated at 5 or 350 µmol mol1CO2 with or without ABA (101 mol m3). At 5.0 µmolmol1 CO2 increasing the concentrations of zeatin hada negligible effect upon stomatal aperture. When air containing350 umol mol1 CO2 was bubbled through the incubationsolutions, apertures of stomata incubated on water were morethan halved. Increasing cytokinin concentrations reduced theeffect of CO2 on stomata and incubation on 101 mol m3zeatin completely removed any CO2 response. The addition ofABA restored the effect of CO2, even at the highest cytokininconcentration. Key words: Maize, CO2 response, ABA, Cytokinins 相似文献
8.
This paper reports the effects of low O2 concentration (001,0055, and 0.115mol m3) in nutrient solutions onK+/Na+ selectivity of growing and mature root tissues of 6-to 8-d-old, intact, wheat (Triticum aestivum cv. Gamenya) seedlings. Increases in anaerobic catabolism and decreases in O2 uptake,K+ uptake and K+/Na+ selectivity were all more pronounced and/oroccurred at higher external O2 concentrations in the apex (02mm) than in the expanding tissues (24 mm); these growingtissues were, in turn, more affected than the expanded tissuesof the roots (412 mm). Selectivity for K+ over Na+ in roots and shoots was particularlysensitive to O2 deficiency. For example, in apical tissues (02mm) K + /Na+ selectivity was already reduced at 0.115 mol m3O2, yet at this O2 concentration there was no effect on eithergrowth or (K+/Na+) uptake. Upon transfer from 0.01 to 0.26 mol m3 O2, a detailedstudy of the 12 mm root tips showed that 70% of these tips regainedhigh (K+ + Na+) concentrations and K+/Na+ ratios. In contrast,there was no recovery in the remaining 30% of the 12 mm roottips. Net K+ transport to the shoots during the period afterre-aeration was negative for the population as a whole. Theseverity of these effects supports the view that the root tipsand the stele were more susceptible to O2 deficiency than wasthe cortex of the fully-developed root tissues. Key words: Hypoxia, K+/Na+ selectivity, expanded and expanding tissues 相似文献
9.
Effects of a Range of O2 Concentrations on Porosity of Barley Roots and on their Sugar and Protein Concentrations 总被引:1,自引:0,他引:1
Barley was grown at a range of oxygen concentrations (0.59mg l1), in nutrient solutions. Growth of both shootsand seminal roots was restricted by O2 concentrations lowerthan 23 mg l1) but nodal root growth was not. Root porosities were increased even at those O2 concentrationswhich did not restrict growth, and were inversely proportionalto the protein levels of the roots. Sugar concentrations increasedappreciably only at those O2 concentrations which also restrictedgrowth. Hordeum vulgare L., barley, root porosity, sugar, protein, oxygen concentration 相似文献
10.
L-Leucine Transport in Isolated Protoplasts of Vinca Suspension Culture: Characterization of Uptake 总被引:1,自引:0,他引:1
The uptake of L-leucine into Vinca protoplasts was studied undervarious conditions. The uptake was highly pH-dependent, withthe optimal pH between 3.0 and 4.0. The uptake was also energydependent, since azide, 2,4-dinitrophenol (DNP), carbonyl cyanidem-chlorophenyl hydrazone (CCCP), and iodoacetate inhibited theuptake. Oligomycin, N,N'-dicycIohexyI carbodiimide (DCCD) andvanadate, but not ouabain, inhibited the uptake, suggestingthat ATPase for H+ electrogenic extrusion was necessary to theuptake of L-leucine. The uptake showed stereospecificity, butwas partially inhibited by other L-amino acids. A kinetic studyof the uptake showed that the uptake was multiphasic with threesaturable phases and one unsaturable phase which occurred atconcentrations of L-leucine over 1 mM. The Km values of thethree affinity sites were 1.4 x 103 M, 1.3 x 104M, 4.3 x 105 M; the maximum velocity values were 3.3x 108, 4.5 x 109, 1.8 x 109 mol/10 min/4x 106 cells. (Received April 18, 1981; Accepted August 25, 1981) 相似文献
11.
Atwell, B. J. and Greenway, H. 1987. Carbohydrate metabolismof rice seedlings grown in oxygen deficient solution.J.exp. Bot. 38: 466478. Rice seedlings (Oryza sativa L.) were grown in the dark forup to 4 d in solutions containing various concentrations ofO2. The rate of depletion of the endosperm was most rapid inaerated solution (0·25 mol O2 m3), largely dueto the inhibition of growth of seedlings at very low O2 concentrations.Earlier suggestions that there is a deficit of sugars for growthand energy generation in O2 deficient coleoptiles were tested. Coleoptiles, shaking in aerated solution, respired about one-thirdof the endogenous sugars to CO2 and incorporated the rest intostructural compounds. In contrast, the proportion of carbonwhich went to growth in anoxia was very low. Consistent withthese results, endogenous sugar levels were generally highestat low O2 concentrations. Even so, coleoptiles grown and testedas low as 0·03 mol O2 m3 showed appreciable metabolismof exogenous 14C-glucose to CO2, soluble and insoluble compounds,suggesting that a minimal O2 supply was sufficient to sustainsome growth. Furthermore, glucose feeding caused little or norise in O2 uptake or tissue sugar levels. Similarly, the specificactivity of the evolved CO2 was not markedly different in coleoptilesgrowing at 0·03 and 0·25 mol O2 m3 Further evidence was obtained to show that endogenous substrateswere adequate for growth and respiration at both low and highO2 concentrations. Exogenous glucose and malate did not stimulateO2 uptake at any stage of growth in aerated coleoptiles. Therewas sufficient endogenous substrate to sustain a 3545%rise in O2 uptake induced by uncoupling and enrichment withO2. Exogenous glucose did not stimulate growth of intact seedlingsat any O2 concentration. Key words: Rice seedlings, carbohydrate metabolism, oxygen deficient solution 相似文献
12.
KARGIOLAKI HARIKLIA; OSBORNE DAPHNE J.; THOMPSON FRANK B. 《Journal of experimental botany》1991,42(9):1189-1198
Differences in premature leaf abscission and in visible steminjury in genetic lines of poplar followed continuous fumigationswith air pollutant levels of SO2 (90100 nl l1)and O3 (7080 nl l1) either separately or together.The clones used were: Populus deltoides var. missiouriensisMarsh., P. nigra cv. italicd L., and the hybridsP. nigra cv. italica xP. deltoides (He-X/3) andP. nigra cv.italica x P. nigra cv. Serres(He-K/7). While most leaf abscission occurred within 20 d fromthe start of fumigation, stem lesions (intumescences), appearedonly after 72 d. Their anatomical characteristics include theformation of lysigenous aerenchyma in the lower parts of theintumescence, the sloughing of superficial cells from the injuredarea, and the development of crystalline formations on the surfaceof the lesions. P. deltoides exhibited the least morphologicalresponse to the gases. Ethylene released from fumigated leaves was determined at thesame gas concentration of SO2 (100 nl l1), O3 (75 nll1) and their mixture. Leaves of P. deltoides consistentlyshowed the lowest ethylene production after the gas treatments.P. italica production was higher but was littlealtered by the treatments. The two hybrids He-X/3 and He-K/7showed the greatest increases in ethylene evolution with time.With He-K/7 exposed to the gas mixture the production of ethylenedecreased after the initial sharp rise during days 12,and reflected the considerable leaf damage observed after day3. The results suggest that sensitivity to air pollution, (as shownby leaf abscission and the formation of stem intumescences)can be correlated with the level of pollutant-induced ethyleneevolution from leaves. Initially high levels could induce abscission,whilst prolonged production could be responsible for intumescenceinitiation. The discussion proposes a series of events fromSO2 and/or O3 entry into the leaf and the physiological reasonsfor the clonal differences. Key words: Sulphur dioxide, ozone, ethylene, poplar, leaf abscission, stem lesions 相似文献
13.
De Rueda P. Muoz; allardo M.G; Matilla A.J.; Sanchez-Calle I.M. 《Journal of experimental botany》1995,46(6):695-700
For a deeper understanding of the germination of chickpea(Cicer arietinum) seeds, which is dependent upon ethylene synthesis,a crude extract containing authentic ACC oxidase (ACCO) activitywas isolated in soluble form from the embryonic axes of seedsgerminated for 24 h. Under our optimal assay conditions (200mM HEPES at pH 7.0, 4µM FeS04, 6 mM Naascorbate,1 mM ACC, 20% 02, 3% CO2 , and 10%glycerol) this enzyme was5fold more active than under the conditions we used initiallyin the present work. The enzyme has the following Km: 28 µMfor ACC (approximately 4fold less than in vivo), 1.2%for O2 (in the presence of an optimal CO2 concentration of 3%),and 1% for CO2 in the presence of O2 (20%). The enzyme is inhibitedby phenanthroline (PNT) (specific chelating agent of ferrousion), and competitively inhibited (K1, =0.5 mM) by 2aminoisobutyricacid (AIB), and the enzymatic activity was not detectable inthe absence of CO2. Under optimal assay conditions, the enzymehas two optimum temperatures (28 C and 35 C) and is inhibitedby divalent metal cations (Zn2+> CO2+>Ni2+>Cu2+>Mn2+>Mg2+) and by salicylic acid, propylgallate, carbonyl cyanidemchlorophenyl hydrazone (CCCP), dinitrophenol (DNP),and Nabenzoate. The in vitro ACCO activity which we recoveredin soluble form is equivalent to approximately 8085%of the apparent activity evaluated in vivo. Key words: ACC oxidase, Cicer arietinum, ethylene, germination, seeds 相似文献
14.
Epidermal strips from either well-watered or water-stressedplants of Commelina communis L. were subjected to a range ofABA concentrations (106103 mol m3)in the presence (330 parts 106 in air) or virtual absence(3 parts 106 in air) of CO2. The stomatal response toCO2 was greater in epidermis from water-stressed plants, althoughthere was a distinct CO2 response in epidermis from well-wateredplants. Additions of ABA via the incubation medium had littleeffect on the relative CO2 response. Stomata responded to ABAboth in the presence and virtual absence of CO2, but the relativeresponse to ABA was greatest in the high CO2 treatment. Whenwell-watered plants were sprayed with a 101 mol m3ABA solution 1 d prior to use, the stomatal response of detachedepidermis to both CO2 and ABA was very similar to that of epidermisdetached from water-stressed leaves. It is hypothesized thata prolonged exposure to ABA is necessary before there is anymodification of the CO2 response of stomata. 相似文献
15.
Measuring the Canopy Net Photosynthesis of Glasshouse Crops 总被引:3,自引:0,他引:3
HAND D. W.; CLARK G.; HANNAH M.A; THORNLEY J. H. M.; WILSON J. WARREN 《Journal of experimental botany》1992,43(3):375-381
A null balance method is described for measuring net photosynthesisof mature canopies of cucumber and other protected crops overperiods of 10 min in a single-span glasshouse (c. 9m x 18m inarea). Accuracy of control of the CO2 concentration in the greenhouseatmosphere is within ±10 vpm of the normal ambient level(c. 350 vpm). The amounts of CO2 used in canopy net photosynthesisare measured with linear mass flowmeters accurate to within±0.80g. The total errors incurred in measuring canopynet photosynthesis at an ambient CO2 level are estimated tobe of the order of ± 1·2% in bright light (350W m2, PAR)and ±3·6% in dull light (100W m2, PAR). Measurements of the rates of net photosynthesis of a maturecanopy of a cucumber crop were made at near-ambient CO2 concentrationsover a range (0350 W m2) of natural light fluxdensities. A model of light absorption and photosynthesis applicableto row crops was used to obtain a net photosynthesis versuslight response curve for the cucumber crop. At a light fluxdensity of 350 W m2 the fitted value of canopy net photosynthesiswas 2.65 mg CO2 m2s1 (equivalent to over 95 kgCO2 ha1h1). The results are discussed in relationto the need for CO2 supplements to avoid depletion in both ventilatedand unventilated glasshouses during late spring and summer. Key words: Glasshouse crops, cucumber, measurement, canopy photosynthesis, light, CO2 相似文献
16.
The role of Cl in the reactivation of O2 evolution inphotosystem II (PS II) particles derived from spinach chloroplastswas studied in the presence of various salts. Multivalent ion(especially anion) salts were found to strongly suppress thereactivation of O2 evolution by Cl in the Cl-depletedPS II particles in a competitive manner. The effectiveness ofanions in the suppression of Cl-supported O2 evolutionwas in the order of trivalent>divalent>monovalent ones.Multivalent anions similarly suppressed O2 evolution in theuntreated PS II particles under low and moderate Cl concentrations.pH dependence of the Cl-affinity (Km) value for Cl)was also studied. Within the pH range 5.5 to 8 the Km valuebecame higher as the pH of the medium increased. These resultssuggest that the membrane surface in the vicinity of the Claction site is net positively charged and attracts Clelectrostatically, and that the site is almost freely accessibleto various anions. The origin and role of the local net positivedomain and the role of peripheral proteins are discussed. (Received May 27, 1985; Accepted October 8, 1985) 相似文献
17.
GEHL KATHARINA A.; COOK CATHERINE M.; COLMAN BRIAN 《Journal of experimental botany》1987,38(7):1203-1210
The carbon dioxide compensation point of the unicellular greenalga, Chloretla saccharophila, was determined in aqueous mediumby a gas chromatographic method. Compensation points decreasedmarkedly from 63 cm3 m3 at an external pH of 4.0 to 3.2cm3 m3 at pH 8.0 and were not affected by the O2 concentrationof the medium. The calculated CO2 concentration required tosupport the half-maximum photosynthetic rate of the algal cellsranged from 6.0 mmol m3 at an external pH of 60 to 1.5mmol m3 at pH 8.0 and these values were not affectedby O2 concentration. The Km(CO2) of nbulose-l,5-bisphosphatecarboxylase isolated from cells grown either at pH 4.0 or pH8.0 was determined to be 64 mmol m3. These results indicatethat loss of CO2 by photorespiration does not occur in C. saccharophilacells at acid pH and the disparity between the apparent affinityfor CO2 of the intact cells and that of the carboxylase indicatesthe operation of a CO2 concentrating mechanismin this alga at acid pH. Key words: Acidophilic alga, bicarbonate transport, Chlorella saccharophila, compensation point, CO2 affinity, PH, RuBP carboxylase 相似文献
18.
Millhouse, J. and Strother, S. 1987. Further characteristicsof salt-dependent bicarbonate use by the seagrass Zostera muelleri.J.exp. Bot. 38: 10551068. The contribution of HCO3to photosynthetic O2 evolutionin the seagrass Zostera muelleri Irmisch ex Aschers. increasedwith increasing salinity of the bathing seawater when the inorganiccarbon concentration was kept constant. K1/2 (seawater salts)for HCO3 -dependent photosynthesis was 66% of seawatersalinity. Both short- and long-term pretreatment at low salinitiesstimulated photosynthesis in full strength seawater. Twentyfour hours pre-incubation of seagrass plants in 3·0 molm3 NaHCO3 resulted in increased photosynthesis at allsalinities, apparently due to stimulation of HCO3 use(K1/2 (seawater salts) = 26%). Vmax (HCO3) was not affectedby low salinity pretreatment. The kinetics of HCO3 stimulationby the major seawater cations was investigated. Ca2+ was themost effective cation with the highest Vmax (HCO3) andwith K1/2(Ca2+) = 14 mol m3. Mg2+ was also very effectiveat less than 50 mol m3 but higher concentrations wereinhibitory. This inhibition cannot be accounted for solely byprecipitation of MgCO3. Na+ and K+ were both capable of stimulatingHCO3 use. Stimulation was in two distinct parts. Up to500 mol m3, both citrate and chloride salts gave similarresults (K1/2(Na+) 81 mol m3, Vmax(HCO3) 0·26µmol O2 mg1 chl min1), but use of citratesalts above 500 mol m2 caused a second stimulation ofHCO3 use (K1/2(Na+) 830 mol m3, Vmax(HCO3)0·68 µmol O2 mg1 chl min1). Vmax(HCO3)for the second-phase Na+ or K+ stimulation was of the same orderas for Ca2+-stimulated HCO3 use. To further characterizesalt-dependent HCO3 use, the sensitivity of photosynthesisto Tris and TES buffers was investigated. The effects of Trisappear to be due to the action of Tris+ causing stimulationof HCO3 -dependent photosynthesis in the absence of salt,but inhibition of HCO3 use in saline media. TES has noeffect on photosynthesis. External carbonic anhydrase, althoughimplicated in salt-dependent HCO3 use in Z. muelleri,could not be detected in whole leaves. Key words: Zostera muelleri, HCO3 use, salinity 相似文献
19.
In studies of Trifolium repens nitrogen nutrition, the controlof nutrient solution pH using dipolar buffers, was evaluatedin tube culture under sterile conditions. Five buffers; MES,ADA, ACES, BES and MOPS with pK2s (20 °C) of 6.15, 6.60,6.90, 7.15 and 7.20 respectively, at a concentration of 2.0mol m3, were provided to inoculated Trifolium repensgrowing in nutrient solution containing 7.13 mol m3 nitrogenas (NH4)2SO4. Initial pH of each solution was adjusted to theappropriate buffer pK2 Two buffers, ADA and ACES completelyinhibited plant growth. The remaining buffers had little effectin limiting pH change, although plant dry matter was higherand nodule numbers lower in the presence of these buffers. MESand MOPS were supplied to nutrient solutions with and without7.13 mol m3 (NH4)2SO4, at concentrations ranging from012 mol m3. MES at 9 mol m3 and 12 molm3 reduced growth of plants reliant on the symbiosisfor providing nitrogen. The provision of MES to plants providedwith NH4+ significantly increased plant yield and reduced nodulenumber at all concentrations. MOPS did not affect plant yieldor nodule number. The use of dipolar buffers in legume nitrogennutrition studies is considered in terms of buffering capacity,and the side effects on plant growth and symbiotic development. Key words: Ammonium, Dipolar buffer, Nitrogen nutrition, pH control, Symbiosis, Trifolium repens 相似文献
20.
Knight, S. L. and Mitchell, C. A. 1988. Effects of CO2 and photosyntheticphoton flux on yield, gas exchange and growth rate of Lactucasativa L. Waldmanns Green'.J. exp. Bot.39: 317328. Enrichment of CO2 to 46 mmol m3 (1 000 mm3 dm3)at a moderate photosynthetic photon flux (PPF) of 450 µmolm2 s1 stimulated fresh and dry weight gain oflettuce leaves 39% to 75% relative to plants at 16 mmol m3CO2 (350 mm3 dm3). Relative growth rate (RGR) was stimulatedonly during the first several days of exponential growth. ElevatingCO2 above 46 mmol m3 at moderate PPF had no further benefit.However, high PPF of 880900 µmol m2 s1gave further, substantial increases in growth, RGR, net assimilationrate (NAR) and photosynthetic rate (Pn), but a decrease in leafarea ratio (LAR), at 46 or 69 mmol m3 (1000 or 1500 mm3dm3) CO2, the differences being greater at the higherCO2 level. Enrichment of CO2 to a supraoptimal level of 92 mmolm3 (2000 mm3 dm3) at high PPF increased leaf areaand LAR, decreased specific leaf weight, NAR and Pn and hadno effect on leaf, stem and root dry weight or RGR relativeto plants grown at 69 mmol m3 CO2 after 8 d of treatment.The results of the study indicate that leaf lettuce growth ismost responsive to a combination of high PPF and CO2 enrichmentto 69 mmol m3 for several days at the onset of exponentialgrowth, after which optimizing resources might be conserved. Key words: Photosynthesis, relative growth rate, CO2 enrichment 相似文献