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1.
Summary Elodea canadensis grows over a wide range of inorganic carbon, nutrient, and light conditions in lakes and streams. Affinity for HCO 3 - use during photosynthesis ranged from strong to weak in Elodea collected from seven localities with different HCO 3 - and CO2 concentrations. The response to HCO 3 - was also very plastic in plants grown in the laboratory at high HCO 3 - concentrations and CO2 concentrations varying from 14.8 to 2,200 M. Bicarbonate affinity was markedly reduced with increasing CO2 concentrations in the growth medium so that ultimately HCO 3 - use was not detectable. High CO2 concentrations also decreased CO2 affinity and induced high CO2 compensation points (360M CO2) and tenfold higher half-saturation values (800 M CO2).The variable HCO 3 - affinity is probably environmentally based. Elodea is a recently introduced species in Denmark, where it reproduces only vegetatively, leaving little opportunity for genetic variation. More important, local populations in the same water system had different HCO 3 - affinities, and a similar variation was created by exposing one plant collection to different laboratory conditions.Bicarbonate use enabled Elodea to photosynthesize rapidly in waters of high alkalinity and enhanced the carbon-extracting capacity by maintaining photosynthesis above pH 10. On the other hand, use of HCO 3 - represents an investment in transport apparatus and energy which is probably not profitable when CO2 is high and HCO 3 - is low. This explanation is supported by the findings that HCO 3 - affinity was low in field populations where HCO 3 - was low (0.5 and 0.9 m M) or CO2 was locally high, and that HCO 3 - affinity was suppressed in the laboratory by high CO2 concentrations.Abbreviations DIC dissolved inorganic carbon (CO2+ HCO 3 - +CO 3 - ) - CO2 compensation point - K 1/2 apparent halfsaturation constant - PHCO 3 interpolated photosynthesis in pure HCO 3 - and zero CO2 - Pmax photosynthetic rate under carbon and light saturation  相似文献   

2.
Kübler  Janet E.  Raven  John A. 《Hydrobiologia》1996,326(1):401-406
Palmaria palmata, which is able to use HCO inf3 sup– as a carbon source for photosynthesis, and Lomentaria articulata, which is dependent on diffusive uptake of dissolved CO2, were grown under constant light and light with sunflecks designed to model wave-induced fluctuations of near-shore underwater light. Both species exhibited significantly increased stable carbon isotope discrimination (more negative values of 13C relative to PDB) when grown with sunflecks. More negative 13C values were associated with decreased growth rate of P. palmata but not of L. articulata. The contrasting effects of sunflecks on the carbon-use characteristics of the two species are discussed in terms of the energetic cost of HCO inf3 sup– use and the susceptibility of CO2 diffusion-dependent species to photoinhibition.  相似文献   

3.
Developing tumors induced by Agrobacterium tumefaciens, strain C58, on stems of Ricinus communis L. var. gibsonii cv. Carmencita were shown to be strong metabolic sinks for sucrose and amino acids, thus causing higher nutrient demand in the host plant. However, NO3 uptake and, to a lesser extent, also H2PO4 uptake were strongly inhibited. Correspondingly, NO3 concentration was lower in tumorised than in the control plants. NO3 reductase activity was the same in both plant types, but it was completely suppressed in the tumors. The electrical membrane potential difference of root cells was unaffected in tumorised plants when soil-grown, but significantly lowered when grown hydroponically. Consistent with the low NO3 uptake rate, NO3 -dependent membrane depolarisation at the onset of NO3 /2H+-cotransport was nearly zero. In the phloem sap, sucrose and amino acid concentrations were considerably lower in tumorised than in control plants, and lower below than above the tumor. The qualitative pattern of amino acids of the phloem sap of stems was almost the same in tumorised and control plants. It is concluded that neither the overall amino acid concentration nor special amino acids nor ammonium in the transport phloem suppress NO3 uptake in the roots. Aminocyclopropane-carboxylate, the precursor of ethylene, which is produced in the tumors in high amounts, was low in the stems and the same in both plant types. Thus, ACC and ethylene were ruled out as directly interfering with nutrient uptake in the roots. Root morphology was strongly affected during tumor development. Root fresh weight decreased to 50% of the controls and lateral root development was almost completely prevented. This suggests that the high tumor ethylene production, together with an increasing concentration of phenolic compounds, severely inhibits the basipetal auxin flow to the roots. Auxin accumulation and retention was confirmed by specifically enhanced expression of the auxin-responsive promoter of the soybean gene GH3:GUS in tumors induced in transgenic Trifolium repens L. Hence, root development is poorer and anion uptake inhibited in tumorised plants. This may be aggravated by abscisic acid accumulation in the tumor and its basipetal export into the roots. Moreover, sucrose depletion of the sieve tubes leads to energy shortage at the root level for maintaining energy-dependent anion uptake.  相似文献   

4.
Summary The intracellular pH (pH i ) of tissue-cultured bovine lens epithelial cells was measured in small groups of 6 to 10 cells using the trapped fluorescent dye 2,7-bis-(2-,carboxyethyl)-5 (and 6)carboxyfluorescein (BCECF). When perifused at 35°C with artificial aqueous humour solution (AAH) containing 16 mM HCO 3 - and 5% CO2, pH 7.25, pH i was 7.19±0.02 (sem, n = 95). On removing HCO 3 - and CO2 there was an initial transient alkalinization followed by a fall in pH to a steady value of 6.97±0.03 (sem, n = 54). Addition of 0.25 mM 4,4-diisothiocyanatostilbene2, 2-disulfonic acid (DIDS) to AAH containing HCO 3 - and CO2 led to a rapid and pronounced fall in pH. Exposure to Na+-free AAH again led to a marked fall in pH i , but in this case the addition of DIDS did not produce a further fall. Substitution of the impermeant anion gluconate for Cl in the presence of HCO 3 - led to a rise in pH i , while substitution in the absence of HCO 3 - led to a fall in pH i . The above data indicate a significant role for a sodium-dependent Cl-HCO 3 - exchange mechanism in the regulation of pH i . Addition of 1 mM amiloride to control AAH in both the presence and absence of HCO 3 - led to a marked fall in pH i , indicating that a Na+/H+ exchange mechanism also has a significant role in the regulation of pH i . There is evidence for a lactic acid transport mechanism in bovine lens cells, as addition of lactate to the external medium produced a rapid fall in pH i . Larger changes in pH i were observed in control compared to HCO 3 - -free AAH and in the latter case a pronounced alkalinizing overshoot was obtained on removing external lactate. Tissue-cultured bovine lens cells thus possess at least three membrane transport mechanisms that are involved in pH regulation. The buffering capacity of the lens cells was measured by perturbing pH i with either NH 4 + or procaine. The values obtained were similar in both cases and the intrinsic buffering capacity measured in the absence of external HCO 3 - was 5 mm/pH unit (procaine). However, in the presence of HCO 3 - and CO2 the buffer capacity increases approximately fourfold, indicating that HCO 3 - is the principal intracellular buffer.We acknowledge financial support from the Wellcome Trust and the Humane Research Trust for this project. M.R. Williams was in receipt of a Science & Engineering Research Council studentship.  相似文献   

5.
Net O2 evolution, gross CO2 uptake and net HCO inf3 su– uptake during steady-state photosynthesis were investigated by a recently developed mass-spectrometric technique for disequilibrium flux analysis with cells of the marine cyanobacterium Synechococcus PCC7002 grown at different CO2 concentrations. Regardless of the CO2 concentration during growth, all cells had the capacity to transport both CO2 and HCO inf3 su– ; however, the activity of HCO inf3 su– transport was more than twofold higher than CO2 transport even in cyanobacteria grown at high concentration of inorganic carbon (Ci = CO2 + HCO inf3 su– ). In low-Ci cells, the affinities of CO2 and HCO inf3 su– transport for their substrates were about 5 (CO2 uptake) and 10 (HCO inf3 su– uptake) times higher than in high-Ci cells, while air-grown cells formed an intermediate state. For the same cells, the intracellular accumulated Ci pool reached 18, 32 and 55 mM in high-Ci, air-grown and low-Ci cells, respectively, when measured at 1 mM external Ci. Photosynthetic O2 evolution, maximal CO2 and HCO inf3 su– transport activities, and consequently their relative contribution to photosynthesis, were largely unaffected by the CO2 provided during growth. When the cells were adapted to freshwater medium, results similar to those for artificial seawater were obtained for all CO2 concentrations. Transport studies with high-Ci cells revealed that CO2 and HCO inf3 su– uptake were equally inhibited when CO2 fixation was reduced by the addition of glycolaldehyde. In contrast, in low-Ci cells steady-state CO2 transport was preferably reduced by the same inhibitor. The inhibitor of carbonic anhydrase ethoxyzolamide inhibited both CO2 and HCO inf3 su– uptake as well as O2 evolution in both cell types. In high-Ci cells, the degree of inhibition was similar for HCO inf3 su– transport and O2 evolution with 50% inhibition occurring at around 1 mM ethoxyzolamide. However, the uptake of CO2 was much more sensitive to the inhibitor than HCO inf3 su– transport, with an apparent I50 value of around 250 M ethoxyzolamide for CO2 uptake. The implications of our results are discussed with respect to Ci utilisation in the marine Synechococcus strain.Abbreviations Chl chlorophyll - Ci inorganic carbon (CO2 + HCO inf3 su– ) - CA carbonic anhydrase - CCM CO2-concentrating mechanism - EZA ethoxyzolamide - GA glycolaldehyde - K1/2 concentration required for half-maximal response - Rubisco ribulose-1,5,-bisphosphate carboxylase-oxygenase D.S. is a recipient of a research fellowship from the Deutsche Forschungsgemeinschaft (D.F.G.). In addition, we are grateful to Donald A. Bryant, Department of Molecular and Cell Biology and Center of Biomolecular Structure Function, Pennsylvania State University, USA, for sending us the wild-type strain of Synechococcus PCC7002.  相似文献   

6.
Summary Recent studies in hepatocytes indicate that Na+-coupled HCO 3 transport contributes importantly, to regulation of intracellular pH and membrane HCO 3 transport. However, the direction of net coupled Na+ and HCO 3 movement and the effect of HCO 3 on Na+ turnover and Na+/K+ pump activity are not known. In these studies, the effect of HCO 3 on Na+ influx and turnover were measured in primary rat hepatocyte cultures with22Na+, and [Na+] i was measured in single hepatocytes using the Na+-sensitive fluorochrome SBFI. Na+/K+ pump activity was measured in intact perfused rat liver and hepatocyte monolayers as Na+-dependent or ouabain-suppressible86Rb uptake, and was measured in single hepatocytes as the effect of transient pump inhibition by removal of extracellular K+ on membrane potential difference (PD) and [Na+] i . In hepatocyte monolayers, HCO 3 increased22Na+ entry and turnover rates by 50–65%, without measurably altering22Na+ pool size or cell volume, and HCO 3 also increased Na+/K+ pump activity by 70%. In single cells, exposure to HCO 3 produced an abrupt and sustained rise in [Na+] i , from 8 to 12mm. Na+/K+ pump activity assessed in single cells by PD excursions during transient K+ removal increased 2.5-fold in the presence of HCO 3 , and the rise in [Na+] i produced by inhibition of the Na+/K+ pump was similarly increased 2.5-fold in the presence of HCO 3 . In intact perfused rat liver, HCO 3 increased both Na+/K+ pump activity and O2 consumption. These findings indicate that, in hepatocytes, net coupled Na+ and HCO 3 movement is inward and represents a major determinant of Na+ influx and Na+/K+ pump activity. About half of hepatic Na+/K+ pump activity appears dedicated to recycling Na+ entering in conjunction with HCO 3 to maintain [Na+] i within the physiologic range.  相似文献   

7.
Clegg  S.  Gobran  G. R. 《Plant and Soil》1995,168(1):173-178
The impact of two constant non-toxic levels of Al stress (0.2 and 0.4 mM) on growth and 32P uptake capacity on sub-optimal (P-limited) Betula pendula seedlings grown in sand culture was examined.Seedling growth was under optimum controlled conditions in a growth chamber where nutrient additions were made at a predetermined relative addition rate (RA) of 10% day-1. Three treatment groups of seedlings 0, 0.2 and 0.4 mM Al were harvested at 15, 29 and 42 days. The excised roots were exposed to a 32P-labelled solution for 15 minutes to measure their capacity for P uptake. Growth was determined by weighing the roots, stems and leaves of the seedlings.Growth data showed that relative growth rate (RG) should equal the RA of P the most limiting nutrient, which was supplied at P/N 3% instead of an optimal 15%. Therefore, Ingestad's theory can also be used succesfully in sand culture and this may be particularly important for future studies of root and rhizosphere exudates. Low levels of Al (< 0.2 mM) in combination with low P supply significantly lowered the RG of the birch seedlings by further reducing P supply. However, previous studies of birch seedling growth and nutrient uptake using Ingestad's solution culture technique with optimumal P supply did not show any effect of Al on growth untill the Al was in excess of 3 mM. Aluminium was not directly toxic to the plants and therefore roots could respond to the 32P bioassay.  相似文献   

8.
Summary Unidirectional 22Na+ and 36Cl fluxes were determined in short-circuited, stripped rumen mucosa from sheep by using the Ussing chamber technique. In both CO2/HCO 3 -containing and CO2/HCO 3 -free solutions, replacement of gluconate by short-chain fatty acids (SCFA, 39 mM) significantly enhanced mucosal-toserosal Na+ absorption without affecting the Cl transport in the same direction. Short-chain fatty acid stimulation of Na+ transport was at least partly independent of Cl and could almost completely be abolished by 1 mM mucosal amiloride, while stimulation of Na+ transport was enhanced by lowering the mucosal pH from 7.3 to 6.5. Similar to the SCFA action, raising the PCO2 in the mucosal bathing solution led to an increase in the amiloride-sensitive mucosal-to-serosal Na+ flux. Along with its effect on sodium transport, raising the PCO2 also stimulated chloride transport. The results are best explained by a model in which undissociated SCFA and/or CO2 permeate the cell membrane and produce a raise in intracellular H+ concentration. This stimulates an apical Na+/H+ exchange, leading to increased Na+ transport. The stimulatory effect of CO2 on Cl transport is probably mediated by a Cl/HCO 3 exchange mechanism in the apical membrane. Binding of SCFA anions to that exchange as described for the rat distal colon (Binder and Mehta 1989) probably does not play a major role in the rumen.Abbreviations DIDS 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid - G t transepithelial conductance (mS·cm-2) - HSCFA undissociated short-chain fatty acids - J ms mucosal-to-serosal flux (Eq · cm-2 · h-1) - J net net flux (Eq · cm-2 · h-1) - J sm serosal-to-mucosal flux (Eq · cm-2 · h-1) - PD transepithelial potential difference (mV) - SCFA dissociated short-chain fatty acids - SCFA short-chain fatty acids  相似文献   

9.
Little information is known on what the magnitude of nitrogen (N) processed by ectomycorrhizal (ECM) fungal species in the field. In a common garden experiment performed in a northern California oak woodland, we investigated transfer of nitrogen applied as 15NH4 or 15NO3 from leaves to ectomycorrhizal roots of three oak species, Quercus agrifolia, Q. douglasii, and Q. garryana. Oak seedlings formed five common ectomycorrhizal morphotypes on root tips. Mycorrhizal tips were more enriched in 15N than fine roots. N transfer was greater to the less common morphotypes than to the more common types. 15N transfer from leaves to roots was greater when , not , was supplied. 15N transfer to roots was greater in seedlings of Q. agrifolia than in Q. douglasii and Q. garryana. Differential N transfer to ectomycorrhizal root tips suggests that ectomycorrhizal morphotypes can influence flows of N from leaves to roots and that mycorrhizal diversity may influence the total N requirement of plants.  相似文献   

10.
Guo  S.  Brück  H.  Sattelmacher  B. 《Plant and Soil》2002,239(2):267-275
In order to investigate the effect of N form on dry matter (DM) formation and water uptake rate, French bean (Phaseolus vulgaris L. `Sotaxa') plants were grown with a split-root system. Three treatments were compared: sole nitrate (NO 3) supply (NN), sole ammonium (NH+ 4) supply (AA) and spatially separated supply of NO 3 and NH+ 4 (NA). The pH of the nutrient solutions was kept constant at 6.3 using a pH-stat system. 9 days after onset of the treatments, NN plants had higher root (36%) and shoot dry matter (11%) than AA plants. N form drastically influenced partitioning of assimilates: in the NA treatment, the root half exposed to NO 3 revealed a 170% higher DM than the root half exposed to NH+ 4. N form affected stable carbon-isotope discrimination () of leaf tissue. In leaves of plants which were supplied with NH+ 4 (AA; NA) was significantly more negative (–29.4, –29.6) than in NN treatment (–28.2). We explain this effect by differences in stomatal conductance. We suppose that the significantly less negative of root tissue under NH+ 4 supply is most probably related to higher PEP-case activity. The water uptake rate was higher in NN than in AA grown plants. This effect was found in both, short- and long-term experiments. In case of NA plants, the water uptake in the root part being exposed to NO 3 was 104% higher than in those receiving NH+ 4. At least in the case of the NA treatment we can exclude shoot growth effects as being responsible for differences in water uptake. We therefore assume that differences in root hydraulic conductivity are responsible for the observed effects.  相似文献   

11.
Gorissen  A.  Cotrufo  M.F. 《Plant and Soil》2000,224(1):75-84
Leaf and root tissue of Lolium perenne L., Agrostis capillaris L. and Festuca ovina L. grown under ambient (350 μl l-1 CO2) and elevated (700 μl l-1) CO2 in a continuously 14C-labelled atmosphere and at two soil N levels, were incubated at 14°C for 222 days. Decomposition of leaf and root tissue grown in the low N treatment was not affected by elevated [CO2], whereas decomposition in the high N treatment was significantly reduced by 7% after 222 days. Despite the increased C/N ratio (g g-1) of tissue cultivated at elevated [CO2] when compared with the corresponding ambient tissue, there was no significant correlation between initial C/N ratio and 14C respired. This finding suggests that the CO2-induced changes in decomposition rates do not occur via CO2-induced changes in C/N ratios of plant materials. We combined the decomposition data with data on 14C uptake and allocation for the same plants, and give evidence that elevated [CO2] has the potential to increase soil C stores in grassland via increasing C uptake and shifting C allocation towards the roots, with an inherent slower decomposition rate than the leaves. An overall increase of 15% in 14C remaining after 222 days was estimated for the combined tissues, i.e., the whole plants; the leaves made a much smaller contribution to the C remaining (+6%) than the roots (+26%). This shows the importance of clarifying the contribution of roots and leaves with respect to the question whether grassland soils act as a sink or source for atmospheric CO2. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

12.
A global survey of carbon isotope discrimination in plants from high altitude   总被引:55,自引:0,他引:55  
Summary Carbon 13/12 isotope ratios have been determined from leaves of a hundred C3 plant species (or ecotypes) from all major mountain ranges of the globe, avoiding drought stressed areas. A general increase in 13C content was found with increasing altitude, i.e. overall discrimination against the heavy isotope is reduced at high elevation. The steepest decline of discrimination is observed in taxa typically ranging to highest elevations (e.g. the genus Ranunculus). Mean 13C for all samples collected between 2500 and 5600 m altitude is-26.15 compared to the lowland average of-28.80 (P<0.001). Forbs from highest elevations reach-24. According to theory of 13C discrimination this indicates decreasing relative limitation of carbon uptake by carboxylation. In other words, we estimate that the ratio of internal to external partial pressure of CO2 (p i /p a )in leaves of high elevation plants is lower than in leaves of low altitude. These results confirm recent gas exchange analyses in high and low elevation plants.  相似文献   

13.
Vascular smooth muscle intracellular pH is maintained by the Na+/H+ and Cl/HCO 3 antiporters. The Na+/H+ exchanger is a major route of H+ extrusion in most eukaryotic cells and is present in vascular smooth muscle cells in a similar capacity. It extrudes H into the extracellular space in exchange for Na+. The Cl/HCO 3 exchanger plays an analogous role to lower the pH of vascular smooth muscle cells when increases in intracellular pH occur. Its activity has also been demonstrated in A7r5 and A10 vascular smooth muscle cells. The Na+/H+ exchanger is regulated by a number of agents which act through inositol trisphosphate/diacylglycerol, to stimulate the antiporter. Calcium-calmodulin dependent protein kinase may also activate the antiporter in vivo. Phosphorylation of the Cl/HCO 3 exchanger has also been observed but its physiological role is not known. Both these antiporters exist in the plasma membrane as integral proteins with free acidic cytoplasmic termini. These regions may be important in sensing changes in intracellular pH, to which these antiporters respond.Abbreviations CaM Calmodulin - DCCD Dicylohexyl-Carbodiimide - DG Diacylglycerol - DIDS-4 4-Diisthiocyanostilbene-2,2-Disulfonic Acid - IP3 Inositol Trisphosphate - PKC protein Kinase C - SITS-4 4-Acetamido-4-Isothiocyanstilbene-2,2-Disulfonate - VSMC Vascular Smooth Muscle Cell  相似文献   

14.
Summary This paper presents a study of the mechanisms of Cl transport through the brush border membranes of the posterior part of the intestine in the freshwater trout, Oncorhynchus mykiss. The mechanisms for Cl transport in the posterior intestine are distinct from those in the middle intestine; an inwardly directed pH gradient stimulates Cl uptake by bursh border membrane vesicles, indicating a Cl/OH exchange. A pH-regulated Cl conductance is present, which is not activated at normal intracellular pH. Cl uptake is stimulated by an outwardly directed HCO 3 gradient revealing the presence of a Cl/HCO 3 exchange but, conversely, Cl is not exchanged against SO 4 2- . In addition, carbonic anhydrase activities have been detected in both the intracellular and extracellular leaflets of the bursh border membranes which favour the establishment of a bicarbonate gradient. A model of Cl transport mechanisms through the brush-border membranes of the posterior intestine of the freshwater trout is proposed.Abbreviations BBM brush border membrane - CA carbonic anhydrase - EGTA ethylene-bis(oxyethylenenitrilo)tetra-acetic acid - FW fresh water - Hepes N-2-hydroxy-ethyl-piperazine-N'-2-ethanesulphonic acid - Mes 2-(N-morpholino)ethane sulphonic acid - SITS 4-acetamido-4-isothiocyanostilbene-2,2-disulphonic acid - TEA triethanolamine - TMA tetramethylammonium - TRIS tris(hydroxymethyl)aminomethane  相似文献   

15.
A number of plants were tested for their ability to bind ethylene and the number of binding sites present in each was calculated. Primary leaves of laboratory-grown beans (Phaseolus vulgaris) bound 140 dpm/g fwt (1794 dpm/g dry wt) when exposed to 1.0 Ci/1 of [14C]ethylene (110 ci/mol). Phytotron-grown leaves were less succulent but only bound 90 dpm/g fwt (1046 dpm/g dry wt). Bean roots bound 30 dpm/g fwt. Citrus and Ligustrum bound 207 and 240 dpm/g fwt, respectively. The time required to achieve equilibrium of leaves with the gas phase was 15 min for bean, 30 min for Citrus, and 30–60 min for Ligustrum. The time for 1/2 of the bound ethylene to diffuse out of the leaves was 20 min for bean, 10 min for Citrus, and 30 min for Ligustrum. The amount of ethylene needed to occupy 1/2 of the binding sites was obtained from Scatchard plots. This value (Kd) was 0.2 l/1 for bean, 0.15 for Citrus, and 0.31 for Ligustrum. The quantity of binding sites in the tissues was 2.0×10-9 mol of binding sites/kg tissue for bean leaves, 5.7×10-9 for Citrus leaves, and 6.8×10-9 for Ligustrum. Pretreatment with indoleacetic acid (IAA), ehtylene, and cycloheximide (1 mg/1) had little effect on the level of ethylene-binding sites in Citrus.Contribution from the Department of Biochemistry, School of Agriculture and Life Sciences and School of Physical and Mathematical Sciences, North Carolina State University. Paper No. 8445 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh, North Carolina 27695-7601.North Carolina-Israel exchange Scholar for 1981 at the Department of Biochemistry, North Carolina State University Raleigh, North Carolina, USA  相似文献   

16.
The exudation of certain organic anions and protons by roots which may affect solubility of metals and P and uptake by plants, is affected by nitrogen form and pH. The objective of this work was to study exudation of carboxylates and H+/OH by tomato plants in response to NH4/NO3 ratio and pH in nutrient solution. Four NH4/(NH4+NO3) ratios (R= 0, 0.33, 0.67 and 1) and constant vs. variable solution pH treatments were investigated. The sum of the exudation rates of all carboxylates tended to decline with increasing R, particularly tri- and dicarboxylates. The molar fraction of the exuded tri- and dicarboxylates, averaged over all treatments and plant ages, increased in the order tartarate 2%), malate (6%), succinate (15%), citrate (26%) and fumarate (46%). At R=1 the solution pH dropped from 5.2 to 3 and at R=0 increased to 8. The R corresponding to the pH stat of tomato plant was 0.3. For the constant solution pH treatment, the effect of solution pH on carboxylate exudation rate was small as compared to the effect of R. The exudation of citrate and H+ efflux which were initiated when NO3 and NH4 uptake rates per plant exceeded certain threshold values, increased with plant age.  相似文献   

17.
The C4 grass Echinochloa polystachya, which forms dense and extensive monotypic stands on the Varzea floodplains of the Amazon region, provides the most productive natural higher plant communities known. The seasonal cycle of growth of this plant is closely linked to the annual rise and fall of water level over the floodplain surface. Diurnal cycles of leaf photosynthesis and transpiration were measured at monthly intervals, in parallel with measurements of leaf area index, canopy light interception and biomass. By artificial manipulation of the light flux incident on leaves in the field light-response curves of photosynthesis at the top and near to the base of the canopy were generated. Fitted light-response curves of CO2 uptake were combined with information of leaf area index, incident light and light penetration of the canopy to estimate canopy rates of photosynthesis. Throughout the period in which the floodplains were submerged photosynthetic rates of CO2 uptake (A) for the emergent leaves were high with a mean of c. 30 mol m-2 s-1 at mid-day and occasional values of 40 mol m-2 s-1. During the brief dry phase, when the floodplain surface is uncovered, there was a significant depression of A, with mid-day mean values of c. 17 mol m-2 s-1. This corresponded with a c. 50% decrease in stomatal conductance, and a c. 35% depression in the ratio of the leaf inter-cellular to external CO2 concentration (c i/c a). During the dry phase, a midday depression of rates of CO2 assimilation was observed. The lowest leaf area index (F) was c. 2 in November–December, when the flood plain was dry, and again in May, when the rising floodwaters were submerging leaves faster than they were replaced. The maximum F of c. 5 was in August when the floodwaters were receding rapidly. Canopy light interception efficiency varied from 0.90 to 0.98. Calculated rates of canopy photosynthesis exceeded 18 mol C m-2 mo-1 throughout the period of flooding, with a peak of 37 mol C m-2 mo-1 in August, but declined to 13 mol C m-2 mo-1 in November during the dry phase. Estimated uptake of carbon by the canopy from the atmosphere, over 12 months, was 3.57 kg C m-2. This was insufficient to account for the 3.99 kg C m-2 of net primary production, measured simultaneously by destructive harvesting. It is postulated that this discrepancy might be accounted for by internal diffusion of CO2 from the CO2-rich waters and sediments via the roots and stems to the sites of assimilation in the leaves.  相似文献   

18.
Mass spectrometric measurements of 16O2 and 18O2 isotopes were used to compare the rates of gross O2 evolution (E0), O2 uptake (U0) and net O2 evolution (NET) in relation to different concentrations of dissolved inorganic carbon (DIC) by Chlamydomonas reinhardtii cells grown in air (air-grown), in air enriched with 5% CO2 (CO2-grown) and by cells grown in 5% CO2 and then adapted to air for 6h (air-adapted).At a photon fluence rate (PFR) saturating for photosynthesis (700 mol photons m-2 s-1), pH=7.0 and 28°C, U0 equalled E0 at the DIC compensation point which was 10M DIC for CO2-grown and zero for air-grown cells. Both E0 and U0 were strongly dependent on DIC and reached DIC saturation at 480 M and 70 M for CO2-grown and air-grown algae respectively. U0 increased from DIC compensation to DIC saturation. The U0 values were about 40 (CO2-grown), 165 (air-adapted) and 60 mol O2 mg Chl-1 h-1 (air-grown). Above DIC compensation the U0/E0 ratios of air-adapted and air-grown algae were always higher than those of CO2-grown cells. These differences in O2 exchange between CO2- and air-grown algae seem to be inducable since air-adapted algae respond similarly to air-grown cells.For all algae, the rates of dark respiratory O2 uptake measured 5 min after darkening were considerably lower than the rates of O2 uptake just before darkening. The contribution of dark respiration, photorespiration and the Mehler reaction to U0 is discussed and the energy requirement of the inducable CO2/HCO3 - concentrating mechanism present in air-adapted and air-grown C. reinhardtii cells is considered.Abbreviations DIC dissolved inorganic carbon - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - E0 rate of photosynthetic gross O2 evolution - PCO photosynthetic carbon oxidation - PFR photon fluence rate - PS I photosystem I - PS II photosystem II - U0 rate of O2 uptake in the light - MS mass spectrometer  相似文献   

19.
It is generally assumed that plant assimilation constitutes the major sink for anthropogenic Nitrate NO 3 deposited in temperate forests because plant growth is usually limited by nitrogen (N) availability. Nevertheless, plants are known to vary widely in their capacity for NO 3 uptake and assimilation, and few studies have directly measured these parameters for overstory trees. Using a combination of field and greenhouse experiments, we studied the N nutrition of Acer saccharum Marsh. in four northern hardwood forests receiving experimental NO 3 additions equivalent to 30 kg N ha–1 year–1. We measured leaf and fine-root nitrate reductase activity (NRA) of overstory trees using an in vivo assay and used 15N to determine the kinetic parameters of NO 3 uptake by excised fine roots. In two greenhouse experiments, we measured leaf and root NRA in A. saccharum seedlings fertilized with 0–3.5 g NO 3 –N m–2 and determined the kinetic parameters of NO 3 and NH 4 + uptake in excised roots of seedlings. In both overstory trees and seedlings, rates of leaf and fine root NRA were substantially lower than previously reported rates for most woody plants and showed no response to NO 3 fertilization (range = non-detectable to 33 nmol NO 2 g–1 h–1). Maximal rates of NO 3 uptake in overstory trees also were low, ranging from 0.2 to 1.0 mol g–1 h–1. In seedlings, the mean V max for NO 3 uptake in fine roots (1 mol g–1 h–1) was approximately 30 times lower than the V max for NH 4 + uptake (33 mol g–1 h–1). Our results suggest that A. saccharum satisfies its N demand through rapid NH 4 + uptake and may have a limited capacity to serve as a direct sink for atmospheric additions of NO 3 .  相似文献   

20.
Internodal and whorl (branch) cells of the green alga,Chara corallina Klein ex Willd., em. R.D.W., were studied with the extracellular vibrating probe for measuring transmembrane ion currents, and with an extracellular pH microprobe for measuring the surface pH profile. Bands of positive inward current (OH- efflux) 1–3 mm wide were separated by wider bands of outward current (HCO 3 - influx) along the length of the cell. The measured peaks of inward current ranged from 20 to 60 A cm-2 (98 m from the cell surface) which would correspond to a surface ionic flux of 270–800 pmol cm-2 s-1. The peaks of outward current (HCO 3 - influx) ranged from 10 to 30 A cm-2 which would correspond to a surface ionic flux of 140–400 pmol cm-2 s-1. The inward current bands matched the regions of surface alkalinity very well. The outward current (HCO 3 - influx) was reduced at least 10-fold in low-HCO 3 - medium, with a commensurate readjustment in the strength and pattern of inward current (OH- efflux). (Although these experiments involved a manipulation of the external pH, it is felt that the main adjustment in current patterns was in response to the reduction in exogenous HCO 3 - ). The presence of the vibrating probe perturbed the inward current region when vibrating with a 26-m amplitude, but this perturbation was eliminated when a 7-m amplitude was used. The perturbation was usually observed as a reduction in the number of inward current peaks with an increase (approximate doubling) in the amplitudes of the one or two remaining peaks. Both the inward and outward currents were light-dependent, falling off within seconds of light removal.  相似文献   

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