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1.
Protoplasts were prepared from Ulva fasciata Delile, and their photosynthetic performance was measured and compared with that of thalli discs. These protoplasts maintained maximal rates of photosynthesis as high as those of thalli (up to 300 μmol O2·mg chlorophyll?1·h?1) for several hours after preparation and were therefore considered suitable for kinetic studies of inorganic carbon utilization. The photosynthetic K1/2(inorganic carbon) at pH 6.1 was 3.8 μM and increased to 67, 158, and 1410 μM at the pH values 7.0, 7.9, and 8.9, respectively. Compared with these protoplasts, thalli had a much lower affinity for CO2 but approximately the same affinity for HCO3?. Comparisons between rates of photosynthesis and the spontaneous dehydration of HCO3? (at 50 μM inorganic carbon) revealed that photosynthesis of both protoplasts (which lacked apparent activity of extracellular/surface-bound carbonic anhydrase) and thalli (which were only 25% inhibited by the external carbonic anhydrase inhibitor acetazolamide) could not be supported by CO2 formation in the medium at the higher pH values, indicating HCO3? uptake. Since both protoplasts and thalli were sensitive to 4,4′-diisothiocyanostilbene-2,2′-disulfonate, we suggest that HCO3? transport was facilitated by the membrane-located anion exchange protein recently reported to function in certain Ulva thalli. These findings suggest that the presence of a cell wall may constitute a diffusion barrier for CO2, but not for HCO3?, utilization under natural seawater conditions. 相似文献
2.
The bloom‐forming cyanobacterium Microcystis aeruginosa (Kütz.) Kütz. 854 was cultured with 1.05 W · m?2 ultraviolet‐B radiation (UVBR) for 3 h every day, and the CO2‐concentrating mechanism (CCM) within this species as well as effects of UVBR on its operation were investigated. Microcystis aeruginosa 854 possessed at least three inorganic carbon transport systems and could utilize external HCO3? and CO2 for its photosynthesis. The maximum photosynthetic rate was approximately the same, but the apparent affinity for dissolved inorganic carbon was significantly decreased from 74.7 μmol · L?1 in the control to 34.7 μmol · L?1 in UVBR‐treated cells. At 150 μmol · L?1 KHCO3 and pH 8.0, Na+‐dependent HCO3? transport contributed 43.4%–40.2% to the photosynthesis in the control and 34.5%–31.9% in UVBR‐treated cells. However, the contribution of Na+‐independent HCO3? transport increased from 8.7% in the control to 18.3% in UVBR‐treated cells. The contribution of CO2‐uptake systems showed little difference: 47.9%–51.0% in the control and 49.8%–47.2% in UVBR‐treated cells. Thus, the rate of total inorganic carbon uptake was only marginally affected, although UVBR had a differential effect on various inorganic carbon transporters. However, the number of carboxysomes in UVBR‐treated cells was significantly decreased compared to that in the control. 相似文献
3.
Affinity, capacity and oxygen sensitivity of two different mechanisms for bicarbonate utilization in Ulva lactuca L. (Chlorophyta) 总被引:1,自引:0,他引:1
Ulva lactuca, collected on the west coast of Sweden at the end of May, was able to utilize the HCO3 ? pool of seawater only through extracellular dehydration via carbonic anhydrase, followed by uptake of the CO2 formed. A decrease in the CO2 supply via this mechanism resulted in the gradual development of an additional method of HCO3 ? utilization, namely a direct uptake of HCO3 ? . Photosynthesis could then be supported by either a ‘HCO3 ? dehydration mechanism’ or a ‘HCO3 ? uptake mechanism’. Through selective inhibition of either of these mechanisms, the physiological properties of the other could be assessed. These properties suggest that the HCO3 ? uptake mechanism of U. lactuca is important under conditions when low concentrations of inorganic C, high pH and high external O2 concentrations would limit photosynthesis supported by the HCO3 ? dehydration mechanism. Such conditions may occur during intense irradiation of the alga in rockpools or in shallow bays with low rates of water exchange. The results are discussed in relation to a possible coupling between mechanisms for inorganic C acquisition and cell structure (or even morphology) of green macroalgae. They also illustrate some necessary precautions when using Michaelis–Menten kinetics for estimations of Vmax and K1/2 values. 相似文献
4.
Stephen C. Maberly Lucy A. Ball John A. Raven Dieter Sültemeyer 《Journal of phycology》2009,45(5):1052-1061
Twelve species, representing 12 families of the chrysophytes sensu lato, were tested for their ability to take up inorganic carbon. Using the pH‐drift technique, CO2 compensation points generally varied between 1 and 20 μmol · L?1 with a mean concentration of 5 μmol · L?1. Neither pH nor alkalinity affected the CO2 compensation point. The concentration of oxygen had a relatively minor effect on CO2‐uptake kinetics, and the mean CO2 compensation point calculated from the kinetic curves was 3.6 μmol · L?1 at 10–15 kPa starting oxygen partial pressure and 3.8 μmol · L?1 at atmospheric starting oxygen partial pressure (21 kPa). Similarly, uptake kinetics were not affected by alkalinity, and hence concentration of bicarbonate. Membrane inlet mass spectrometry (MIMS) in the presence and absence of acetazolamide suggested that external carbonic anhydrase in Dinobryon sertularia Ehrenb. and Synura petersenii Korschikov was either very low or absent. Rates of net HCO3? uptake were very low (~5% of oxygen evolution) using MIMS and decreased rather than increased with increasing HCO3? concentration, suggesting that it was not a real uptake. The CO2 compensation points determined by MIMS for CO2 uptake and oxygen evolution were similar to those determined in pH‐drift and were >1 μmol · L?1. Overall, the results suggest that chrysophytes as a group lack a carbon‐concentrating mechanism (CCM), or an ability to make use of bicarbonate as an alternative source of inorganic carbon. The possible evolutionary and ecological consequences of this are briefly discussed. 相似文献
5.
The green marine macroalga Ulva lactuca L. was found to be able to utilize HCO3? from sea water in two ways. When grown in flowing natural sea water at 16°C under constant dim irradiance, photosynthesis at pH8.4 was suppressed by acetazolamide but unaffected by 4,4′-diisothiocyanostilbene-2,2′-disulphonate. These responses indicate that photosynthetic HCO3? utilization was via extracellular carbonic anhydrase (CA) -mediated dehydration followed by CO2 uptake. The algae were therefore described as being in a ‘CA state’. If treated for more than 10 h in a sea water flow-through system at pH9.8, these thalli became insensitive to acetazolamide but sensitive to 4,4′-diisothiocyanostilbene-2,2′-disulphonate. This suggests the involvement of an anion exchanger (AE) in the direct uptake of HCO3?, and these plants were accordingly described as being in an ‘AE state’. Such thalli showed an approximately 10-fold higher apparent affinity for HCO3? (at pH9.4) than those in the ‘CA state’, while thalli of both states showed a very high apparent affinity for CO2. These results suggest that the two modes of HCO3? utilization constitute two ways in which inorganic carbon may enter the Ulva lactuca cells, with the direct entry of HCO3?, characterizing the ‘AE state’, being inducible and possibly functioning as a complementary uptake system at high external pH values (e.g. under conditions conducive to high photosynthetic rates). Both mechanisms of entry appear to be connected to concentrating CO2 inside the cell, probably via a separate mechanism operating intracellularly. 相似文献
6.
Stephen C. Maberly 《Journal of phycology》1990,26(3):439-449
Thirty-five species of marine macroalgae were tested for their ability to remove inorganic carbon from seawater using the pH-drift technique. Six of these species, all Rhodophyta, were unable to use HCO3–. The remaining species exhibited a range in ability to use HCO3– and deplete inorganic carbon (Cτ); the three most effective species, all Chlorophyta, raised the pH to over 10.50, depleted the concentration of CO2 effectively to zero, and depleted the concentration of Cτ to less than 50% of that at air-equilibrium. In contrast, the six species restricted to CO2 did not raise the pH above 9.0 at a CO2 concentration of about 1.5 μmol · L-1 and depleted the concentration of Cτ to about 80% of that at air-equilibrium. Ability to raise pH and deplete Cτ was linked to the habitat in which the species grew. Five of the six species which lack the ability to use HCO3– grow subtidally in relatively low light beneath a canopy of larger Phaeophyta. None of these species grow in rockpools where carbon-depletion may occur. Species from rockpools were all effective at removing inorganic carbon. Competition for Cτ may be one of the factors that determines species composition in rockpools. There was a species-specific difference between the calculated concentration of Cτ at the end of a pH-drift experiment and that measured directly. Most, but not all, species with the ability to generate high pH-values showed a lower than calculated final concentration of Cτ consistent with precipitation of CaCO3. A number of Rhodophyta with no, or a limited, ability to use HCO3– showed the opposite response, with final concentrations of Cτ exceeding that calculated from the pH. Calculations based on the maximum gross rate of production of CO2 from HCO3– in the absence of external carbonic anhydrase confirmed the results of the pH-drift experiments by demonstrating HCO3– -use in Monostroma fuscum (Post et Rupr.) Wittr. And Ulva lactuca L. and the lack of this ability in Lomentaria articulate (Huds.) Lyngb. Rates of net photosynthesis at air-equilibrium were greater than 95% of those at 2.3 mmol Cτ· L-1 for many of the species which were able to use HCO3–, but on average only 72% for the six species restricted to CO2. 相似文献
7.
SUMMARY.
- 1 Rates of photosynthetic oxygen evolution by Callitriche cophocarpa and Ranunculus peltatus in stream were measured on live occasions during the light period on 2 days at ambient light and ambient inorganic carbon, ambient light and saturating inorganic carbon, saturating light and ambient inorganic carbon, saturating light and saturating inorganic carbon and air-equilibrium inorganic carbon and ambient light.
- 2 Despite an ambient CO2 concentration of about 220 μm , which is about ten times air-equilibrium, the concentration of inorganic carbon was more limiting than light on all the occasions that rates were measured. On average, rates of photosynthesis at ambient concentrations of CO2 were about 130 and 425 μmol O2 g?1 DW h?1 for C. cophocarpa and R. peltatus, respectively. These rates as a percentage of carbon saturated rates were only about 35% for C. cophocarpa and about 60% for R. peltatus. Ambient rates as a percentage of light saturated rates were about 80% for C. cophocarpa and about 95% for R. peltatus. Only in early morning and late evening where the photon irradiance was below 160 μmol m?2 s?1 was there evidence for slight light limitation.
- 3 Based on results from pH-drift experiments and from rates of photosynthesis as a function of CO2 concentration in the presence and absence of HCO3?, C. cophocarpa was unable, but R. peltatus able to use HCO3? at an ambient HCO3? concentration of about 0·84 mm . The greater rates of photosynthesis at ambient CO2 concentration and the lesser limitation by inorganic carbon shown by R. peltatus compared to C. cophocarpa was the result of HCO3?-use as laboratory experiments showed that R. peltatus performed similarly to C. cophocarpa if the HCO3? concentration was reduced to 60 μm .
8.
Physiological properties of photosynthesis were determined in the marine diatom, Phaeodactylum tricornutum UTEX640, during acclimation from 5% CO2 to air and related to H2CO3 dissociation kinetics and equilibria in artificial seawater. The concentration of dissolved inorganic carbon at half maximum rate of photosynthesis (K0·5[DIC]) value in high CO2‐grown cells was 1009 mmol m ? 3 but was reduced three‐fold by the addition of bovine carbonic anhydrase (CA), whereas in air‐grown cells K0·5[DIC] was 71 mmol m ? 3, irrespective of the presence of CA. The maximum rate of photosynthesis (Pmax) values varied between 300 and 500 μ mol O2 mg Chl ? 1 h ? 1 regardless of growth pCO2. Bicarbonate dehydration kinetics in artificial seawater were re‐examined to evaluate the direct HCO3 ? uptake as a substrate for photosynthesis. The uncatalysed CO2 formation rate in artificial seawater of 31·65°/oo of salinity at pH 8·2 and 25 °C was found to be 0·6 mmol m ? 3 min ? 1 at 100 mmol m ? 3 DIC, which is 53·5 and 7·3 times slower than the rates of photosynthesis exhibited in air‐ and high CO2‐grown cells, respectively. These data indicate that even high CO2‐grown cells of P. tricornutum can take up both CO2 and HCO3 ? as substrates for photosynthesis and HCO3 ? use improves dramatically when the cells are grown in air. Detailed time courses were obtained of changes in affinity for DIC during the acclimation of high CO2‐grown cells to air. The development of high‐affinity photosynthesis started after a 2–5 h lag period, followed by a steady increase over the next 15 h. This acclimation time course is the slowest to be described so far. High CO2‐grown cells were transferred to controlled DIC conditions, at which the concentrations of each DIC species could be defined, and were allowed to acclimate for more than 36 h. The K0·5[DIC] values in acclimated cells appeared to be correlated only with [CO2(aq)] in the medium but not to HCO3 ? , CO32 ? , total [DIC] or the pH of the medium and indicate that the critical signal regulating the affinity of cells for DIC in the marine diatom, P. tricornutum, is [CO2(aq)] in the medium. 相似文献
9.
Rebecca E. Korb Peter J. Saville Andrew M. Johnston John A. Raven 《Journal of phycology》1997,33(3):433-440
The utilization of inorganic carbon by three species of marine diatom, Skeletonema costatum (Grev.) Cleve. Ditylum brightwellii (West) Grun., and Chaetoceros calcitrans Paulsen was investigated using an inorganic carbon isotopic disequilibnum technique and inorganic carbon dose-response curves. Stable carbon isotope data of the diatoms are also presented. Observed rates of photosynthetic oxygen evolution were greater than could be accounted for by the theoretical rate of CO2 supply from the uncatalyzed dehydration of HCO3? in the external medium, suggesting use of HCO3? as an inorganic carbon source. Data from the isotopic disequilibrium experiment demonstrate the use of both HCO3? and CO2 for photosynthesis. Carbon isotope discrimination values support the use of HCO3? by the diatoms. 相似文献
10.
Some physiological characteristics of photosynthetic inorganic carbon uptake have been examined in the marine diatoms Phaeodactylum tricornutum and Cyclotella sp. Both species demonstrated a high affinity for inorganic carbon in photosynthesis at pH7.5, having K1/2(CO2) in the range 1.0 to 4.0mmol m?3 and O2? and temperature-insensitive CO2 compensation concentrations in the range 10.8 to 17.6 cm3 m?3. Intracellular accumulation of inorganic carbon was found to occur in the light; at an external pH of 7.5 the concentration in P. tricornutum was twice, and that in Cyclotella 3.5 times, the concentration in the suspending medium. Carbonic anhydrase (CA) was detected in intact Cyclotella cells but not in P. tricornutum, although internal CA was detected in both species. The rates of photosynthesis at pH 8.0 of P. tricornutum cells and Cyclotella cells treated with 0.1 mol m?3 acetazolamide, a CA inhibitor, were 1.5- to 5-fold the rate of CO2 supply, indicating that both species have the capacity to take up HCO3? as a source of substrate for photosynthesis. No Na+ dependence for HCO3? could be detected in either species. These results indicate that these two marine diatoms have the capacity to accumulate inorganic carbon in the light as a consequence, in part, of the active uptake of bicarbonate. 相似文献
11.
T. MIMURA R. MÜLLER W. M. KAISER T. SHIMMEN K.-J. DIETZ 《Plant, cell & environment》1993,16(6):653-661
Carbon transport across the plasma membrane, and carbon fixation were measured in perfused Chara internodal cells. These parameters were measured in external media of pH 5·5 and pH 8·5, where CO2 and HCO3- are, respectively, the predominant carbon species in both light and dark conditions. Cells perfused with medium containing ATP could utilize both CO2 and HCO3- from the external medium in the light. Photosynthetic carbon fixation activity was always higher at pH 5·5 than at pH 8·5. When cells were perfused either with medium containing hexokinase and 2-deoxyglucose to deplete ATP from the cytosol (HK medium) or with medium containing vanadate, a specific inhibitor of the plasma membrane H+-ATPase (V medium), photosynthetic carbon fixation was strongly inhibited at both pH 5·5 and 8·5. Perfusion of cells with medium containing pyruvate kinase and phosphoenolpyruvate (PEP) to maximally activate the H+-ATPase (PK medium), stimulated the photosynthetic carbon fixation activities. Oxygen evolution of isolated chloroplasts and the carbon fixation of cells supplied 14C intracellularly were not inhibited by perfusion media containing either hexokinase and 2-deoxyglucose or vanadate. The results indicate that Chara cells possess CO2 and HCO3- transport systems energized by ATP and sensitive to vanadate in the light. In the dark, intact cells also fix carbon. By contrast, in cells perfused with medium containing ATP, no carbon fixation was detected in 1 mol m -3 total dissolved inorganic carbon (TDIC) at pH 8·5. By increasing TDIC to 10 mol m-3, dark fixation became detectable, although it was still lower than that of intact cells at 1mol m-3 TDIC. Addition of PEP or PEP and PEP carboxylase to the perfusion media significantly increased the dark-carbon fixation. Perfusion with vanadate had no effect on the dark-carbon fixation. 相似文献
12.
Microcystis aeruginosa Kütz. 7820 was cultured at 350 and 700 μL·L ? 1 CO2 to assess the impacts of doubled atmospheric CO2 concentration on this bloom‐forming cyanobacterium. Doubling of CO2 concentration in the airflow enhanced its growth by 52%–77%, with pH values decreased and dissolved inorganic carbon (DIC) increased in the medium. Photosynthetic efficiencies and dark respiratory rates expressed per unit chl a tended to increase with the doubling of CO2. However, saturating irradiances for photosynthesis and light‐saturated photosynthetic rates normalized to cell number tended to decrease with the increase of DIC in the medium. Doubling of CO2 concentration in the airflow had less effect on DIC‐saturated photosynthetic rates and apparent photosynthetic affinities for DIC. In the exponential phase, CO2 and HCO3 ? levels in the medium were higher than those required to saturate photosynthesis. Cultures with surface aeration were DIC limited in the stationary phase. The rate of CO2 dissolution into the liquid increased proportionally when CO2 in air was raised from 350 to 700 μL·L ? 1, thus increasing the availability of DIC in the medium and enhancing the rate of photosynthesis. Doubled CO2 could enhance CO2 dissolution, lower pH values, and influence the ionization fractions of various DIC species even when the photosynthesis was not DIC limited. Consequently, HCO3 ? concentrations in cultures were significantly higher than in controls, and the photosynthetic energy cost for the operation of CO2 concentrating mechanism might decrease. 相似文献
13.
Interactions of blue light and inorganic carbon supply in the control of light-saturated photosynthesis in brown algae 总被引:3,自引:2,他引:1
Photosynthetic capacities of five species of brown algae in red light were found to be strongly limited by the inorganic carbon supply of natural sea water. Under these conditions, pH 8·2 and dissolved inorganic carbon concentration (DIG) of 2·1 mol m?3, a short pulse of blue light was found to increase the subsequent rate of photosynthesis in saturating red light. The degree of blue light stimulation varied between species, ranging from an increase of over 200% of the original rate in Colpomenia peregrins to only 10% in Dictyota dichotoma. Increasing the DIG concentration of sea water by bicarbonate addition resulted in carbon saturation of photosynthesis in all five species. Blue light stimulation was greatly reduced at these higher DIG concentrations. The response in Laminaria digitata was examined in more detail by manipulation of pH and DIG to produce solutions with different concentrations of dissolved CO2. At a CO2 concentration typical of normal sea water (12·4 mmol m?3), blue light treatment increased photosynthetic rate by approximately 50%. Blue light stimulation was increased to over 150% at CO2 concentrations below that of sea water, whereas at concentrations above that of sea water, the effect was diminished. Therefore, the effect of blue light on photosynthetic capacity appears to involve an increase in the rate of supply of carbon dioxide to the plant. 相似文献
14.
Christopher D. Hepburn Daniel Pritchard Kim I. Currie Christina M. McGraw Keith A. Hunter Catriona L. Hurd 《Journal of phycology》2012,48(1):137-144
Ocean acidification (OA) is a reduction in oceanic pH due to increased absorption of anthropogenically produced CO2. This change alters the seawater concentrations of inorganic carbon species that are utilized by macroalgae for photosynthesis and calcification: CO2 and HCO3? increase; CO32? decreases. Two common methods of experimentally reducing seawater pH differentially alter other aspects of carbonate chemistry: the addition of CO2 gas mimics changes predicted due to OA, while the addition of HCl results in a comparatively lower [HCO3?]. We measured the short‐term photosynthetic responses of five macroalgal species with various carbon‐use strategies in one of three seawater pH treatments: pH 7.5 lowered by bubbling CO2 gas, pH 7.5 lowered by HCl, and ambient pH 7.9. There was no difference in photosynthetic rates between the CO2, HCl, or pH 7.9 treatments for any of the species examined. However, the ability of macroalgae to raise the pH of the surrounding seawater through carbon uptake was greatest in the pH 7.5 treatments. Modeling of pH change due to carbon assimilation indicated that macroalgal species that could utilize HCO3? increased their use of CO2 in the pH 7.5 treatments compared to pH 7.9 treatments. Species only capable of using CO2 did so exclusively in all treatments. Although CO2 is not likely to be limiting for photosynthesis for the macroalgal species examined, the diffusive uptake of CO2 is less energetically expensive than active HCO3? uptake, and so HCO3?‐using macroalgae may benefit in future seawater with elevated CO2. 相似文献
15.
Mass spectromelry has been used to investigate the uptake of CO2 by two marine diatoms, Phaeodactylum tricornutum and Cyclotella sp. The time course of CO2 formation in the dark after addition of 100 mmol m?3 dissolved inorganic carbon (DIC) to cell suspensions showed that external carbonic anhydrase (CA) was not present in cells of P. tricornutum but was present in Cyclotella sp. In the absence of external CA, or when it was inhibited by 5 mmol m?3 acetazolamide, cells of both species preincubated with 100 mmol m?3 DIG rapidly depleted almost all of the free CO2 (3·2mmol m?31 at pH7·5) from the suspending medium within seconds of illumination and prior to the onset of steady-state photosynthesis. Addition of bovine CA quickly restored the HCO3?–CO2 equilibrium in the medium, indicating that the initial depletion of CO2 resulted from the selective uptake of CO2 rather than uptake of all DIG species. Transfer of cells to the dark caused a rapid increase in the CO2 concentration in the medium, largely as a result of the efflux of unfixed inorganic carbon from the cells. The measured CO2 uptake rates for both species accounted for 50% of the total DIG uptake at HCO3?–CO2 equilibrium, indicating that HCOHCO3? was also being taken up. These results indicate that both Phaeodactylum tricornutum and Cyclotella sp. have the capacity to transport CO2 actively against concentration and pH gradients. 相似文献
16.
Abstract This paper describes a dynamic model for photosynthesis by an aquatic plant, Egeria densa. The model takes into account an HCO?3 pump, high diffusion resistances and PEP carboxylase, and develops a set of differential equations to form the time-dependent solutions for photosynthesis. The predicted changes in pH, [CO2]aq and total inorganic carbon are compared with experimental data and the model is found to describe the data. The model is then used to examine the effect of O2 on photosynthesis under these conditions, and shows that the increase in internal CO2 concentration due to the recycling of photorespiratory CO2 directly stimulates gross CO2 fixation and can more than compensate for the O2 inhibition of gross photosynthesis. The importance of the HCO?3 pump in O2 inhibition is also examined. The CO2 compensation point (where inorganic carbon influx and efflux are equal) is examined and the importance of the HCO?3 pump and PEP carboxylase in reducing the compensation concentration is discussed. The model was developed in order to study the photosynthesis of an aquatic weed, which will be reported in a later paper. 相似文献
17.
Amram Eshel 《Journal of experimental marine biology and ecology》1983,70(1):99-106
The photosynthetic capacity of submerged Ulva sp. when utilizing CO2 and HCO?3 as exogenous carbon forms has been investigated and compared with ambient carbon concentrations in sea water. Saturating concentrations of HCO? 3 and CO2 were 1200 and 100 μM, respectively at saturating light, and photosynthetic rates under such conditions averaged 700 μmolO2·gDW?1 ·h?1. The HCO?3 concentration of sea water (≈2500μM), was thus found to be saturating for photosynthesis of Ulva. At the CO2 concentration of sea water (≈ 10 μM), the contribution of this carbon form to photosynthesis could be 27% at the most. Under conditions of slow water movement, the relative importance of CO2 utilization would probably be minimized in favour of HCO?3 utilization. It is concluded that HCO?3 uptake is not limiting photosynthesis for Ulva under natural conditions. 相似文献
18.
HCO3? utilization by the marine microalga Nannochloropsis oculata was investigated using a pH drift technique in a closed system. Light-dependent alkalization of the medium resulted in a final pH of 10.5, confirming substantial HCO3? use by this alga. Alkalinity remained constant throughout the pH drift. Measurement of dissolved inorganic carbon (DIC) or the uptake of H14CO3? showed that nearly 50% of the total DIC remained external to the plasma membrane on completion of a pH drift. The rate of light-driven alkalization was inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) and thus was dependent on photosynthesis. Light-driven alkalization was not inhibited by a membrane-impermeable inhibitor of carbonic anhydrase (CA), dcxtran-bound sulphonamide (DBS), indicating that external CA was not involved in HCO3? utilization. The anion-cxchangc inhibitor 4′,4′-diisothiocyanostilbene-2,2-disulphonic acid (DIDS) completely inhibited light-driven alkalization of the medium and H14CO3? uptake, providing unequivocal support for a direct uptake of H14CO3?. Chloride ions were essential for DIC-dependent photosynthetic oxygen evolution, suggesting that bicarbonate transport occurs by HCO3?/CI? exchange. 相似文献
19.
Carbon uptake in the green macroalga Cladophora glomerata (L.) Kütz. from the brackish Baltic Sea was studied by recording changes in pH, alkalinity, and inorganic carbon concentration of the seawater medium during photosynthesis. The use of specific inhibitors identified three uptake mechanisms: 1) dehydration of HCO3 ? into CO2 by periplasmic carbonic anhydrase, followed by diffusion of CO2 into the cell; 2) direct uptake of HCO3 ? via a 4,4′‐diisothiocyanato‐stilbene‐2,2′‐disulfonate‐sensitive mechanism; and 3) uptake of inorganic carbon by the involvement of a vanadate‐sensitive P‐type H + ‐ATPase (proton pump). A decrease in the alkalinity of the seawater medium during carbon uptake, except when treated with vanadate, indicated a net uptake of the ionic species contributing to alkalinity (i.e. HCO3 ? , CO32 ? , and OH ? ) from the medium, where OH ? influx is equivalent to H + efflux. This would suggest that the proton pump is involved in HCO3 ? transport. We also show that the proton pump can be induced by carbon limitation. The inducibility of carbon uptake in C. glomerata may partly explain why this species is so successful in the upper littoral zone of the Baltic Sea. Usually, carbon limitation is not a problem in the upper littoral of the sea. However, it may occur frequently within dense Cladophora belts with high photosynthetic rates that create high pH and low carbon concentrations in the alga's microenvironment. 相似文献
20.
CO2 uptake and transport in leaf mesophyll cells 总被引:1,自引:3,他引:1
Abstract The acquisition of inorganic carbon for photosynthetic assimilation by leaf mesophyll cells and chloroplasts is discussed with particular reference to membrane permeation of CO2 and HCO?3. Experimental evidence indicates that at the apoplast pH normally experienced by leaf mesophyll cells (pH 6–7) CO2 is the principal species of inorganic carbon taken up. Uptake of HCO?3 may also occur under certain circumstances (i.e. pH 8.5), but its contribution to the net flux of inorganic carbon is small and HCO?3 uptake does not function as a CO2-concentrating mechanism. Similarly, CO2 rather than HCO?3 appears to be the species of inorganic carbon which permeates the chloroplast envelope. In contrast to many C3 aquatic plants and C4 plants, C3 terrestrial plants lack specialized mechanisms for the acquisition and transport of inorganic carbon from the intercellular environment to the site of photosynthetic carboxylation, but rely upon the diffusive uptake of CO2. 相似文献