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1.
Ten seaweed species were surveyed for simultaneous photoevolution of hydrogen and oxygen. In an attempt to induce hydrogenase activity (as measured by hydrogen photoproduction) the seaweeds were maintained under anaerobiosis in CO 2-free seawater for varying lengths of time. Although oxygen evolution was observed in every alga studied, hydrogen evolution was not observed. One conclusion of this research is that, in contrast to the microscopic algae, there is not a single example of a macroscopic alga for which the photoevolution of hydrogen has been observed, in spite of the fact that there are now at least nine macroscopic algal species known for which hydrogenase activity has been reported (either by dark hydrogen evolution or light-activated hydrogen uptake). These results are in conflict with the conventional view that algal hydrogenase can catalyze a multiplicity of reactions, one of which is the photoproduction of molecular hydrogen. Two possible explanations for the lack of hydrogen photoproduction in macroscopic algae are presented. It is postulated that electron acceptors other than carbon dioxide can take up reducing equivalents from Photosystem I to the measurable exclusion of hydrogen photoproduction. Alternatively, the hydrogenase system in macroscopic algae may be primarily a hydrogen-uptake system with respect to light-activated reactions. A simple kinetic argument based on recent measurements of the photosynthetic turnover times of simultaneous light-activated hydrogen and oxygen production is presented that supports the second explanation. 相似文献
2.
Air-grown cells of Porphyridium purpurem contain appreciable carbonic-anhydrase activity, comparable to that in air-grown Chlamydomonas reinhardtii, but activity is repressed in CO 2-grown cells. Assay of carbonic-anhydrase activity in intact cells and cell extracts shows all activity to be intracellular in Porphyridium. Measurement of inorganic-carbon-dependent photosynthetic O 2 evolution shows that sodium ions increase the affinity of Porphyridium cells for HCO
3
-
. Acetazolamide and ethoxyzolamide were potent inhibitors of carbonic anhydrase in cell extracts but at pH 5.0 both acetazolamide and ethoxyzolamide had little effect upon the concentration of inorganic carbon required for the half-maximal rate of photosynthetic O 2 evolution (K 0.5[CO 2]). At pH 8.0, where HCO
3
-
is the predominant species of inorganic carbon, the K 0.5 (CO 2) was increased from 50 M to 950 M in the presence of ethoxyzolamide. It is concluded that in air-grown cells of Porphyridium. HCO
3
-
is transported across the plasmalemma and intracellular carbonic anhydrase increases the steady-state flux of CO 2 from inside the plasmalemma to ribulose-1,5-bisphosphate carboxylase-oxygenase by catalysing the interconversion of HCO
3
-
and CO 2 within the cell.Abbreviations AZ
acetazolamide
- EZ
ethoxyzolamide
- K 0.5[CO 2]
half-maximal rate of photosynthetic O 2 evolution 相似文献
3.
Air-grown cells of the marine diatom Phaeodactylum tricornutum showed only 10% of the carbonic-anhydrase activity of air-grown Chlamydomonas reinhardtii. Measurement of carbonic-anhydrase activity using intact cells and cell extracts showed all activity was intracellular in Phaeodactylum. Photosynthetic oxygen evolution at constant inorganic-carbon concentration but varying pH showed that exogenous CO 2 was poorly utilized by the cells. Sodium ions increased the affinity of Phaeodactylum for HCO
3
-
and even at high HCO
3
-
concentrations sodium ions enhanced HCO
3
-
utilization. The internal inorganic-carbon pool (HCO
3
-
+CO 2] was measured using a silicone-oil-layer centrifugal filtering technique. The internal [HCO
3
-
+CO 2] concentration never exceeded 15% of the external [HCO
3
-
+CO 2] concentration even at the lowest external concentrations tested. It is concluded that an internal accumulation of inorganic carbon relative to the external medium does not occur in P. tricornutum.Abbreviation Hepes
4-(2-hydroxyethyl)-1-piperazineethane-sulfonic acid 相似文献
4.
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 CO 2 concentrations. The response to HCO
3
-
was also very plastic in plants grown in the laboratory at high HCO
3
-
concentrations and CO 2 concentrations varying from 14.8 to 2,200 M. Bicarbonate affinity was markedly reduced with increasing CO 2 concentrations in the growth medium so that ultimately HCO
3
-
use was not detectable. High CO 2 concentrations also decreased CO 2 affinity and induced high CO 2 compensation points (360 M CO 2) and tenfold higher half-saturation values (800 M CO 2).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 CO 2 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 CO 2 was locally high, and that HCO
3
-
affinity was suppressed in the laboratory by high CO 2 concentrations.Abbreviations DIC
dissolved inorganic carbon (CO 2+ HCO
3
-
+CO
3
-
)
-
CO 2 compensation point
-
K
1/2
apparent halfsaturation constant
- P HCO
3
–
interpolated photosynthesis in pure HCO
3
-
and zero CO 2
- P max
photosynthetic rate under carbon and light saturation 相似文献
5.
Inorganic-carbon transport was investigated in the eukaryotic marine microalgae Stichococcus minor, Nannochloropsis oculata and a Monallantus sp. Photosynthetic O 2 evolution at constant inorganic-carbon concentration but varying pH showed that S. minor had a greater capacity for CO 2 rather than HCO
3
–
utilization but for N. oculata and Monallantus HCO
3
–
was the preferred source of inorganic carbon. All three microalgae had a low affinity for CO 2 as shown by the measurement of inorganic-carbon-dependent photosynthetic O 2 evolution at pH 5.0. At pH 8.3, where HCO
3
–
is the predominant form of inorganic carbon, the concentration of inorganic carbon required for half-maximal rate of photosynthetic O 2 evolution [ K
0.5 (CO 2)] was 53 M for Monallantus sp. and 125 M for N. oculata, values compatible with HCO
3
–
transport. Neither extra- nor intracellular carbonic anhydrase was detected in these three microalgal species. It is concluded that these microalgae lack a specific transport system for CO 2 but that HCO
3
–
transport occurs in N. oculata and Monallantus, and in the absence of intracellular carbonic anhydrase the conversion of HCO
3
–
to CO 2 may be facilitated by the internal pH of the cell. 相似文献
6.
The hypothesis that net photosynthesis is diminished in many plant species because of a high rate of CO 2 evolution in the light has been tested further. High rates of CO 2 output in CO 2-free air in comparison with dark respiration were found in Chlamydomonas reinhardi, wheat leaves, tomato leaves, and to a lesser extent in Chlorella pyrenoidosa by means of the 14C-photorespiration assay. In tobacco leaves high photorespiration was characteristic of a standard variety, Havana Seed, and a possibly still higher rate was found in a yellow heterozygous mutant, JWB Mutant. However, the dark homozygous sibling of the latter, JWB Wild, had a low photorespiration for the tobacco species. The relative rates of photorespiration were in the same sequence when measured by the 14CO 2 released in normal air from leaf disks supplied with glycolate-1- 14C in the light. As would be predicted by the hypothesis, the maximal net rate of photosynthesis at 300 ppm of CO2 in the air in JWB Wild leaves was greater (24%) than in Havana Seed, while JWB Mutant had less CO2 uptake than the standard variety (21%). At 550 ppm of CO2 the differences in net photosynthesis were not as great between the 2 siblings as at 200 ppm. The relative leaf expansion rates of seedlings of the 3 tobacco varieties in a greenhouse had the same relationship as their rates of CO2 assimilation. Thus within the tobacco species, as in a comparison between tobacco and maize, low photorespiratory CO2 evolution was correlated with higher photosynthetic efficiency. Therefore it seems that increased CO2 uptake should be achieved by genetic interference with the process of photorespiration. 相似文献
7.
In Photosystem II preparations at low temperature we were able to generate and trap an intermediate state between the S 1 and S 2 states of the Kok scheme for photosynthetic oxygen evolution. Illumination of dark-adapted, oxygen-evolving Photosystem II preparations at 140 K produces a 320-G-wide EPR signal centered near g = 4.1 when observed at 10 K. This signal is superimposed on a 5-fold larger and somewhat narrower background signal; hence, it is best observed in difference spectra. Warming of illuminated samples to 190 K in the dark results in the disappearance of the light-induced g = 4.1 feature and the appearance of the multiline EPR signal associated with the S 2 state. Low-temperature illumination of samples prepared in the S 2 state does not produce the g = 4.1 signal. Inhibition of oxygen evolution by incubation of PS II preparations in 0.8 M NaCl buffer or by the addition of 400 μM NH 2OH prevents the formation of the g = 4.1 signal. Samples in which oxygen evolution is inhibited by replacement of Cl ? with F ? exhibit the g = 4.1 signal when illuminated at 140 K, but subsequent warming to 190 K neither depletes the amplitude of this signal nor produces the multiline signal. The broad signal at g = 4.1 is typical for a spin system in a rhombic environment, suggesting the involvement of non-heme Fe in photosynthetic oxygen evolution. 相似文献
8.
Sulphur dioxide inhibits noncyclic photophosphorylation in isolated envelope-free chloroplasts. This inhibition was shown to be reversible and competitive with phosphate, with an inhibitor constant of K i=0.8mM. The same inhibition characteristics were observed when phosphoglycerate (PGA)- or ribulose-1,5-bisphosphate (RuBP)-dependent oxygen evolution was examined in a reconstituted chloroplast system in the presence of SO
3
2-
. Using an ATP-regenerating system (phosphocreatine-creatine kinase), it was demonstrated that the inhibition of PGA-dependent oxygen evolution is solely the result of inhibited photophosphorylation. It is concluded that at low SO 2 and SO
3
2-
concentrations the inhibition of photophosphorylation is responsible for the inhibition of photosynthetic oxygen evolution.Abbreviations Chl
chlorophyll
- PGA
D-3-phosphoglyceric acid trisodium salt
- Pi
inorganic phosphate
- RuBP
D-ribulose-1,5-bisphosphoric acid tetrasodium salt 相似文献
9.
Summary Sunflower ( Helianthus annuus L.) leaf discs were exposed to 14CO 2 or 14CO 2 followed by 12CO 2 at 21% O 2 and three different CO 2 concentrations. After intervals of up to 15 min, the specific activity of some photosynthetic intermediates was determined. At all CO 2 concentrations, the specific activity of 3-phosphoglyceric acid (3-PGA) increased most rapidly and after 15 min of 14CO 2 feeding was 92% (967 ppm CO 2), 87% (400 ppm CO 2) and 53% (115 ppm CO 2) of CO 2 supplied to the assimilation chamber. The specific activity of glycine, serine and the photorespiratory CO 2 was similar at all CO 2 concentrations, in aggreement with their proposed close metabolic relationship in the glycolate pathway. However, the kinetics of serine and glycine labelling suggested that serine was not totally derived from glycine. Because the specific activity of these glycolate-pathway intermediates was very differnet from that of 3-PGA at all CO 2 concentrations, not all of the carbon traversing this pathway came directly from the Calvin cycle. The non-equilibration of the 3-PGA with the feeding gas reflects the recycling of C from the glycolate pathway into the photosynthetic reduction cycle. Measurements of the rates of CO 2 evolution in the light and estimates of the C flux through the glycolate pathway suggest that the photorespiratory activity was high and similar at 115 ppm CO 2 and 400 ppm CO 2 but inhibited at 967 ppm CO 2. 相似文献
10.
36Cl - was used to study the slow exchange of chloride at a binding site associated with Photosystem II (PS II). When PS II membranes were labeled with different concentrations of 36Cl -, saturation of binding at about I chloride/PS II was observed. The rate of binding showed a clear dependence on the concentration of chloride approaching a limiting value of about 3·10 -4 s -1 at high concentrations, similar to the rate of release of chloride from labeled membranes. These rates were close to that found earlier for the release of chloride from PS II membranes isolated from spinach grown on 36Cl -, which suggests that we are observing the same site for chloride binding. The similarity between the limiting rate of binding and the rate of release of chloride suggests that the exchange of chloride with the surrounding medium is controlled by an intramolecular process. The binding of chloride showed a pH-dependence with an apparent pK a of 7.5 and was very sensitive to the presence of the extrinsic polypeptides at the PS II donor side. The binding of chloride was competitively inhibited by a few other anions, notably Br - and NO 3
-. The slowly exchanging Cl - did not show any significant correlation with oxygen evolution rate or yield of EPR signals from the S 2 state. Our studies indicate that removal of the slowly exchanging chloride lowers the stability of PS II as indicated by the loss of oxygen evolution activity and S 2 state EPR signals.Abbreviations Chl
chlorophyll
- EPR
electron paramagnetic resonance
- Hepes
4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid
- Mes
4-morpholineethanesulfonic acid
- MWCO
molecular weight cut off
- PPBQ
phenyl- p-benzoquinone
- PS II
Photosystem II 相似文献
11.
Tobacco plants ( Nicotiana tabacum) were kept in CO 2 free air for several days to investigate the effect of lack of electron acceptors on the photosynthetic electron transport
chain. CO 2 starvation resulted in a dramatic decrease in photosynthetic activity. Measurements of the electron transport activity in
thylakoid membranes showed that a loss of Photosystem II activity was mainly responsible for the observed decrease in photosynthetic
activity. In the absence of CO 2 the plastoquinone pool and the acceptor side of Photosystem I were highly reduced in the dark as shown by far-red light effects
on chlorophyll fluorescence and P700 absorption measurements. Reduction of the oxygen content of the CO 2 free air retarded photoinhibitory loss of photosynthetic activity and pigment degradation. Electron flow to oxygen seemed
not to be able to counteract the stress induced by severe CO 2 starvation. The data are discussed in terms of a donation of reducing equivalents from mitochondria to chloroplasts and a
reduction of the plastoquinone pool via the NAD(P)H-plastoquinone oxidoreductase during CO 2 starvation.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
12.
The light-induced oxidation of the accessory donor tyrosine-D (Y D) has been studied by measurements of the EPR Signal II slow at room temperature in the autotrophically and photoheterotrophically cultivated alga Chlamydobotrys stellata. After illumination and dark adaptation, Y D Signal II slow was observed only in autotrophic algae, i.e. under conditions of a linear photosynthetic electron transfer from water to NADP +. The addition of artificial electron acceptors phenyl-p-benzoquinone (PPQ) or dichloro-p-benzoquinone (DCQ) to the autotrophic cells caused an almost negligible increase of this signal. When photosynthetic electron flow and oxygen evolution were diminished by removal of the carbon source CO 2 and addition of acetate (photoheterotrophy), a pronounced Y D Signal II slow was seen only in presence of DCQ or PPQ. Several possibilities are discussed to explain the absence of Y D Signal II slow in photoheterotrophic Chl. stellata such as the existence of a cyclic PS II electron flow very effectively reducing P 680 and thereby preventing the possibility of Y D oxidation. Artificial electron acceptors withdraw electrons from this cycle thus keeping the primary quinone acceptor, Q A, oxidized and thereby diminishing the reduction of P 680
+ by cyclic PSII. This leads to the appearance of the Y D Signal II slow also in the photoheterotrophically grown algae.Abbreviations A-band-
thermoluminescence band associated with S 2Q A
- charge recombination
- DCQ-
2,5-dichlorobenzoquinone
- D 2-
structure protein of Photosystem II
- EPR-
electron paramagnetic resonance
- OEC-
oxygen evolving complex
- PPQ-
phenyl-p-benzoquinone
- PS II-
Photosystem II
- P 680-
reaction center of Photosystem II
- Q-band-
thermoluminescence band associated with S 2Q A
- charge recombination
- S i-
oxidation levels of the OEC
- Y D-
tyrosine-D accessory donor to P 680
- Y Z-
tyrosine-Z electron donor to P 680
Dedicated to Prof. Dr E. Schnepf/Heidelberg. 相似文献
13.
One of the most serious problems in obtaining estimates of the K
m
values for HCO
3
-
of phosphoenolpyruvate carboxylase (PEPCase; EC 4.1.1.31) by measurement of initial rates at varying HCO
3
-
is the impossibility of completely excluding any contaminating HCO
3
-
. A method is proposed which has no need for the careful control of HCO
3
-
/CO 2 contamination. The kinetic data are obtained by the evaluation of progress curves of HCO
3
-
consumption. The method is discussed and the K
m
values for HCO
3
-
of PEPCase from several C 4-species are presented.Abbreviations C 3, C 4
assimilated CO 2 initially found in 3-phosphoglycerate (C 3) or malate and aspartate (C 4)
- OAA
oxaloacetic acid
- PEP
phosphoenolpyruvate
- PEPCase
phosphoenolpyruvate carboxylase 相似文献
14.
A simple model of photosynthetic CO 2 assimilation in Chlamydomonas has been developed in order to evaluate whether a CO 2-concentrating system could explain the photosynthetic characteristics of this alga (high apparent affinity for CO 2, low photorespiration, little O 2 inhibition of photosynthesis, and low CO 2 compensation concentration). Similarly, the model was developed to evaluate whether the proposed defects in the CO 2-concentrating system of two Chlamydomonas mutants were consistent with their observed photosynthetic characteristics. The model treats a Chlamydomonas cell as a single compartment with two carbon inputs: passive diffusion of CO 2, and active transport of HCO
3
-
. Internal inorganic carbon was considered to have two potential fates: assimilation to fixed carbon via ribulose 1,5-bisphosphate carboxylase-oxygenase or exiting the cell by either passive CO 2 diffusion or reversal of HCO
3
-
transport. Published values for kinetic parameters were used where possible. The model accurately reproduced the CO 2-response curves of photosynthesis for wild-type Chlamydomonas, the two mutants defective in the CO 2-concentrating system, and a double mutant constructed by crossing these two mutants. The model also predicts steady-state internal inorganic-carbon concentrations in reasonable agreement with measured values in all four cases. Carbon dioxide compensation concentrations for wild-type Chlamydomonas were accurately predicted by the model and those predicted for the mutants were in qualitative agreement with measured values. The model also allowed calculation of approximate energy costs of the CO 2-concentrating system. These calculations indicate that the system may be no more energy-costly than C 4 photosynthesis.Abbreviations Chl
chlorophyll
- RuBPC/O
ribulose 1,5-bisphosphate carboxylase-oxygenase
- CA
carbonic anhydrase 相似文献
15.
Stably sustained continuous production of hydrogen with high molar yield was achieved through a combination of dark fermentative hydrogen evolution by Chlamydomonas sp. strain MGA161 and hydrogen photoevolution by a marine photosynthetic bacterium W-1S in an alternating light-dark cycle as a model of the day-night cycle. The newly isolated strain W-1S could use acetic acid and ethanol excreted by strain MGA161 as electron donors for hydrogen photoevolution. The fermentation broth of strain MGA161 stimulated the hydrogen photoproduction of strain W-1S. This alga-bacterial combination had a high conversion yield of 8 mol H 2/mol of glucose of starch, with the possibility of improvement up to 10.5. 相似文献
16.
The photosynthetic apparatus of some plant species appears to be well-protected from direct damage from UV-B radiation. Leaf optical properties of these species apparently minimizes exposure of sensitive targets to UV-B radiation. However, damage by UV-B radiation to Photosystem II and Rubisco has also been reported. Secondary effects of this damage may include reductions in photosynthetic capacity, RuBP regeneration and quantum yield. Furthermore, UV-B radiation may decrease the penetration of PAR, reduce photosynthetic and accessory pigments, impair stomatal function and alter canopy morphology, and thus indirectly retard photosynthetic carbon assimilation. Subsequently, UV-B radiation may limit productivity in many plant species. In addition to variability in sensitivity to UV-B radiation, the effects of UV-B radiation are further confounded by other environmental factors such as CO 2, temperature, light and water or nutrient availability. Therefore, we need a better understanding of the mechanisms of tolerance to UV-B radiation and of the interaction between UV-B and other environmental factors in order to adequately assess the probable consequences of a change in solar radiation.Abbreviations A max
light and CO 2 saturated rate of oxygen evolution
- Ci
internal CO 2 concentration
- F v/F m
ratio of variable to total fluorescence yield
- PAR
photosynthetically active radiation (400–700 nm)
- PS II
Photosystem II
- app
apparent quantum yield of photosynthesis
- SLW
specific leaf weight
- UV-B
ultraviolet-B radiation between 290–320 nm 相似文献
17.
The kinetics of the postillumination reduction of P700 + which reflects the rate constant for plastoquinol (PQH 2) oxidation was recorded in sunflower leaves at different photon absorption densities (PAD), CO 2 and O 2 concentrations. The P700 oxidation state was calculated from the leaf transmittance at 830 nm logged at 50 s intervals. The P700 + dark reduction kinetics were fitted with two exponents with time constants of 6.5 and about 45 ms at atmospheric CO 2 and O 2 concentrations. The time constant of the fast component, which is the major contributor to the linear electron transport rate (ETR), did not change over the range of PADs of 14.5 to 134 nmol cm -2 s -1 in 21% O 2, but it increased up to 40 ms under severe limitation of ETR at low O 2 and CO 2. The acceptor side of Photosystem I (PS I) became reduced in correlation with the downregulation of the PQH 2 oxidation rate constant. It is concluded that thylakoid pH-related downregulation of the PQH 2 oxidation rate constant (photosynthetic control) is not present under normal atmospheric conditions but appears under severe limitation of the availability of electron acceptors. The measured range of photosynthetic control fits with the maximum variation of ETR under natural stress in C 3 plants. Increasing the carboxylase/oxygenase specificity would lead to higher reduction of the PS I acceptor side under stress.Abbreviations Cyt b
6
f
cytochrome b
6
f complex
- C w
cell-wall CO 2 concentration, M
- ETR
electron transport rate
- Fd
ferredoxin
- FNR
ferredoxin-NADP reductase
- FRL
far-red light
- PC
plastocyanin
- PAD
photon absorption density nmol cm -2 s -1
- PFD
photon flux density nmol cm -2 s -1
- PS I
Photosystem I complex
- PQ
plastoquinon
- PQH 2
plastoquinol
- PS II
Photosystem II complex
- P700
Photosystem I donor pigment, reduced
- S830
830 nm signal (D830, difference of S830 from the dark level)
- WL
white light
- Y l
maximum quantum yield of PS I electron transport, rel. un 相似文献
18.
By increasing water use efficiency and carbon assimilation, increasing atmospheric CO 2 concentrations could potentially improve plant productivity and growth at high salinities. To assess the effect of elevated CO 2 on the salinity response of a woody halophyte, we grew seedlings of the mangrove Avicennia germinans under a combination of five salinity treatments [from 5 to 65 parts per thousand (ppt)] and three CO 2 concentrations (280, 400 and 800 ppm). We measured survivorship, growth rate, photosynthetic gas exchange, root architecture and foliar nutrient and ion concentrations. The salinity optima for growth shifted higher with increasing concentrations of CO 2, from 0 ppt at 280 ppm to 35 ppt at 800 ppm. At optimal salinity conditions, carbon assimilation rates were significantly higher under elevated CO 2 concentrations. However, at salinities above the salinity optima, salinity had an expected negative effect on mangrove growth and carbon assimilation, which was not alleviated by elevated CO 2, despite a significant improvement in photosynthetic water use efficiency. This is likely due to non‐stomatal limitations to growth at high salinities, as indicated by our measurements of foliar ion concentrations that show a displacement of K + by Na + at elevated salinities that is not affected by CO 2. The observed shift in the optimal salinity for growth with increasing CO 2 concentrations changes the fundamental niche of this species and could have significant effects on future mangrove distribution patterns and interspecific interactions. 相似文献
20.
In the cyanobacterium Synechococcus UTEX 625, the extent of expression of carboxysomes appeared dependent on the level of inorganic carbon (CO 2+HCO
inf3
sup-
) in the growth medium. In cells grown under 5% CO 2 and in those bubbled with air, carboxysomes were present in low numbers (<2 · longitudinal section -1) and were distributed in an apparently random manner throughout the centroplasm. In contrast, cells grown in standing culture and those bubbled with 30 l CO 2 · 1 -1 possessed many carboxysomes (>8 · longitudinal section -1). Moreover, carboxysomes in these cells were usually positioned near the cell periphery, aligned along the interface between the centroplasm and the photosynthetic thylakoids. This arrangement of carboxysomes coincided with the full induction of the HCO
inf3
sup-
transport system that is involved in concentrating inorganic carbon within the cells for subsequent use in photosynthesis. Immunolocalization studies indicate that the Calvin cycle enzyme ribulose bisphosphate carboxylase was predominantly carboxysome-localized, regardless of the inorganic carbon concentration of the growth medium, while phosphoribulokinase was confined to the thylakoid region. It is postulated that the peripheral arrangement of carboxysomes may provide for more efficient photosynthetic utilization of the internal inorganic carbon pool in cells from cultures where carbon resources are limiting.Abbreviations Chl
chlorophyll
- DIC
dissolved inorganic carbon (CO 2+HCO
inf3
sup-
+CO
inf3
sup2-
)
- PRK
phosphoribulokinase
- RuBP
ribulose 1,5-bisphosphate
- Rubisco LS
large subunit of ribulose 1,5-bisphosphate carboxylase/oxygenase 相似文献
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