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1.
Effect of Triacontanol on Chlamydomonas: II. Specific Activity of Ribulose-Bisphosphate Carboxylase/Oxygenase, Ribulose-Bisphosphate Concentration, and Characteristics of Photorespiration 总被引:1,自引:1,他引:0
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Increased photosynthetic CO2 assimilation by Chlamydomonas reinhardtii cells treated with triacontanol (TRIA) was not due to changes in glycolate excretion, CO2 compensation point, or the sensitivity of photosynthetic CO2 assimilation to O2. Kinetic analysis of TRIA-treated cells showed that the increase in photosynthetic CO2 assimilation was a result of an increase in the apparent Vmax for intact cells. The total activity of ribulose-P2 carboxylase/oxygenase was higher in cell lysates from TRIA-treated cells. However quantification of this enzyme concentration by binding of [14C]carboxyarabinitol-P2 did not show an increase in TRIA-treated cells. Thus, there was an increase in the specific activity of ribulose-P2 carboxylase/oxygenase extracted from Chlamydomonas cells treated with TRIA. TRIA alone had no effect on the activity of the enzyme in cell lysates from Chlamydomonas or purified from spinach (Spinacia oleracea L.) leaves.
The ribulose-P2 pool was 50 to 60% higher in cells treated with TRIA that were assayed for photosynthetic CO2 assimilation at high- and low-CO2. TRIA also increased ribulose-P2 levels in the absence of CO2 in the light with atmospheres of N2 or N2 with 21% O2.
相似文献2.
Changes of some photosynthetic properties of high-CO2 grown cells of Chlorella pyrenoidosa during adaptation to low-CO2 conditions have been investigated. The Km value of photosynthesis of the high-CO2 grown cells for dissolved inorganic carbon was 3.3 millimolar and decreased to 25 to 30 micromolar within 4 hours after transferring to air. In the presence of saturating CO2 concentrations the photosynthetic activity of the high-CO2 grown cells was 1.5 times as high as that of the low-CO2 grown cells. There was a significant rise of the photosynthetic activity during adaptation of the high-CO2 grown cells to air, followed by a steady decrease. The activity of ribulose 1,5-bisphosphate carboxylase/oxygenase in both the high- and low-CO2 grown cells was close to the photosynthetic activity of the cells. The concentration of ribulose 1,5-bisphosphate (RuBP) was higher in the low-CO2 adapting and low-CO2 grown cells than in the high-CO2 grown cells regardless of the photosynthetic rate. This seems to be due to an increased RuBP regeneration activity during adaptation followed by maintenance of the new higher concentration. The RuBP level always exceeded the concentration of ribulose 1,5-bisphosphate carboxylase/oxygenase RuBP binding sites in both the high- and low-CO2 grown cells at any dissolved inorganic carbon concentration. 相似文献
3.
Glycolate Excretion and the Oxygen to Carbon Dioxide Net Exchange Ratio during Photosynthesis in Chlamydomonas reinhardtii 总被引:9,自引:9,他引:0
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Chlamydomonas reinhardtii cells were grown in high (5% v/v) or low (0.03% v/v) CO2 concentration in air. O2 evolution, HCO3− assimilation, and glycolate excretion were measured in response to O2 and CO2 concentration. Both low- and high-CO2-grown cells excrete glycolate. In low-CO2-grown cells, however, glycolate excretion is observed only at much lower CO2 concentrations in the medium, as compared with high-CO2-adapted cells. It is postulated that the activity of the CO2-concentrating mechanism in low-CO2-grown cells is responsible for the different dependence of glycolate excretion on external CO2 concentration in low- versus high-CO2-adapted cells. 相似文献
4.
Alexei Solovchenko Olga Gorelova Irina Selyakh Larisa Semenova Olga Chivkunova Olga Baulina Elena Lobakova 《Marine biotechnology (New York, N.Y.)》2014,16(5):495-501
A novel chlorophyte Desmodesmus sp. 3Dp86E-1 isolated from a White Sea hydroid Dynamena pumila was cultivated at CO2 levels from atmospheric (the ‘low-CO2’ conditions) to pure carbon dioxide (the 5, 20, and 100 % CO2 conditions) under high (480 μE/(m2 s) PAR) light. After 7 days of cultivation, the ‘100 % CO2’ (but not 5 or 20 % CO2) cells possessed ca. four times higher chlorophyll content per dry weight (DW) unit than the low-CO2 culture. The rate of CO2 fixation under 100 % CO2 comprised ca. 1.5 L/day per L culture volume. After a lag period which depended on the CO2 level, biomass accumulation and volumetric fatty acid (FA) content of the Desmodesmus sp. 3Dp86E-1 bubbled with CO2-enriched gas mixtures increased and was comparable to that of the culture continuously bubbled with air. Under the low-to-moderate CO2 conditions, the FA percentage of the algal cells increased (to 40 % DW) whereas under high-CO2 conditions, FA percentage did not exceed 15 % DW. A strong increase in oleate (18:1) proportion of total FA at the expense of linolenate (18:3) was recorded in the ‘100 % CO2’ cells. Electron microscopy and pulse–amplitude-modulated chlorophyll fluorescence investigation revealed no damage to or significant downregulation of the photosynthetic apparatus in ‘100 % CO2’ cells grown at the high-PAR irradiance. Possible mechanisms of high-CO2 tolerance of Desmodesmus sp. 3Dp86E-1 are discussed in view of its symbiotic origin and possible application for CO2 biomitigation. 相似文献
5.
A simple model of photosynthetic CO2 assimilation in Chlamydomonas has been developed in order to evaluate whether a CO2-concentrating system could explain the photosynthetic characteristics of this alga (high apparent affinity for CO2, low photorespiration, little O2 inhibition of photosynthesis, and low CO2 compensation concentration). Similarly, the model was developed to evaluate whether the proposed defects in the CO2-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 CO2, 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 CO2 diffusion or reversal of HCO
3
-
transport. Published values for kinetic parameters were used where possible. The model accurately reproduced the CO2-response curves of photosynthesis for wild-type Chlamydomonas, the two mutants defective in the CO2-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 CO2-concentrating system. These calculations indicate that the system may be no more energy-costly than C4 photosynthesis.Abbreviations Chl
chlorophyll
- RuBPC/O
ribulose 1,5-bisphosphate carboxylase-oxygenase
- CA
carbonic anhydrase 相似文献
6.
Unicellular algae grown under low-CO2 conditions (0.03% CO2) have developed a means of concentrating CO2 at the site of ribulose-1,5-bisphosphate carboxylase/oxygenase. Cells with the CO2-concentrating mechanism (CCM) acquire the ability to accumulate inorganic carbon to a level higher than that obtained by simple diffusion. To identify proteins which are involved in the organization of the CCM, cells of Scenedesumus obliquus and Chlorella vulgaris grown in high CO2 (5% CO2 in air) were transferred to low-CO2 (0.03%) conditions in the presence of 35SO inf4 sup2? and, thereafter, polypeptides labeled with 35S were detected. Under low-CO2 conditions the inducton of 36-, 39-, 94- and 110- to 116kDa polypeptides were particularly observed in S. obliquus and 16-, 19-, 27-, 36-, 38- and 45-kDa polypeptides were induced in C. vulgaris. Western blots with antibodies raised against 37-kDa subunits of the periplasmic carbonic anhydrase (CA) of Chlamydomonas reinhardtii showed immunoreactive bands with the 39-kDa polypeptide in the whole-cell homogenates from S. obliquus and with 36 and 38-kDa polypeptides in both high- and low-CO2grown cells of C. vulgaris. Anti-pea-chloroplast CA antibodies cross-reacted with a single polypeptide of 30 kDa in the whole-cell homogenates but not with thylakoid membranes. The CA activity was associated with soluble and membrane-bound fractions, except thylakoid membranes. 相似文献
7.
Photosynthetic characteristics of photoautotrophically grown tobacco callus cells 总被引:3,自引:3,他引:0
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Haploid callus cells of tobacco (Nicotiana tabacum) were grown photoautotrophically on a solid agar medium in the absence of sucrose in Petri plates in an atmosphere of 1% or 3% CO2 in air. The averages of dry weight increases for four to five consecutive passages were 2.3- to 3.6-fold per 3-week passage for different subclones. Photosynthetic 14CO2 assimilation was maximum at about 1% CO2 with half-maximal rates obtained at 0.2% CO2. At saturating CO2 concentration the average rate of CO2 fixation was about 5 μmole per gram fresh weight per hour or about 125 μmole per mg of chlorophyll per hour. 相似文献
8.
Tracy Lawson J.i.m. Craigon Ann-Marie Tulloch Colin R. Black Jeremy J. Colls Geoff Landon 《Journal of plant physiology》2001,158(3)
Potato plants (Solanum tuberosum L. cv. Bintje) were grown to maturity in open-top chambers under three carbon dioxide (CO2; ambient and 24 h d−1 seasonal mean concentrations of 550 and 680 μmol mol−1) and two ozone levels (O3; ambient and an 8 h d−1 seasonal mean of 50 nmol mol−1). Chlorophyll content, photosynthetic characteristics, and stomatal responses were determined to test the hypothesis that elevated atmospheric CO2 may alleviate the damaging influence of O3 by reducing uptake by the leaves. Elevated O3 had no detectable effect on photosynthetic characteristics, leaf conductance, or chlorophyll content, but did reduce SPAD values for leaf 15, the youngest leaf examined. Elevated CO2 also reduced SPAD values for leaf 15, but not for older leaves; destructive analysis confirmed that chlorophyll content was decreased. Leaf conductance was generally reduced by elevated CO2, and declined with time in the youngest leaves examined, as did assimilation rate (A). A generally increased under elevated CO2, particularly in the older leaves during the latter stages of the season, thereby increasing instantaneous transpiration efficiency. Exposure to elevated CO2 and/or O3 had no detectable effect on dark-adapted fluorescence, although the values decreased with time. Analysis of the relationships between assimilation rate and intercellular CO2 concentration and photosynthetically active photon flux density showed there was initially little treatment effect on CO2-saturated assimilation rates for leaf 15. However, the values for plants grown under 550 μmol mol−1 CO2 were subsequently greater than in the ambient and 680 μmol mol−1 treatments, although the beneficial influence of the former treatment declined sharply towards the end of the season. Light-saturated assimilation was consistently greater under elevated CO2, but decreased with time in all treatments. The values decreased sharply when leaves grown under elevated CO2 were measured under ambient CO2, but increased when leaves grown under ambient CO2 were examined under elevated CO2. The results obtained indicate that, although elevated CO2 initially increased assimilation and growth, these beneficial effects were not necessarily sustained to maturity as a result of photosynthetic acclimation and the induction of earlier senescence. 相似文献
9.
Martin H. Spalding 《Photosynthesis research》1990,24(3):245-252
The effect of photon flux density on inorganic carbon accumulation and photosynthetic CO2 assimilation was determined by CO2 exchange studies at three, limiting CO2 concentrations with a ca-1 mutant of Chlamydomonas reinhardiii. This mutant accumulates a large internal inorganic carbon pool in the light which apparently is unavailable for photosynthetic assimilation. Although steady-state photosynthetic CO2 assimilation did not respond to the varying photon flux densities because of CO2 limitation, components of inorganic-carbon accumulation were not clearly light saturated even at 1100 mol photons m-2 s-1, indicating a substantial energy requirement for inorganic carbon transport and accumulation. Steady-state photosynthetic CO2 assimilation responded to external CO2 concentrations but not to changing internal inorganic carbon concentrations, confirming that diffusion of CO2 into the cells supplies most of the CO2 for photosynthetic assimilation and that the internal inorganic carbon pool is essentially unavailable for photosynthetic assimilation. The estimated concentration of the internal inorganic carbon pool was found to be relatively insensitive to the external CO2 concentration over the small range tested, as would be expected if the concentration of this pool is limited by the internal to external inorganic carbon gradient. An attempt to use this CO2 exchange method to determine whether inorganic carbon accumulation and photosynthetic CO2 assimilation compete for energy at low photon flux densities proved inconclusive. 相似文献
10.
Many aquatic algae induce a CO2-concentrating mechanism (CCM) associated with active inorganic carbon transport to maintain high photosynthetic affinity using dissolved inorganic carbon even in low-CO2 (LC) conditions. In the green alga Chlamydomonas reinhardtii, a Ca2+-binding protein CAS was identified as a novel factor regulating the expression of CCM-related proteins including bicarbonate transporters. Although previous studies revealed that CAS associates with the thylakoid membrane and changes its localization in response to CO2 and light availability, its detailed localization in the chloroplast has not been examined in vivo. In this study, high-resolution fluorescence images of CAS fused with a Chlamydomonas-adapted fluorescence protein, Clover, were obtained by using a sensitive hybrid detector and an image deconvolution method. In high-CO2 (5% v/v) conditions, the fluorescence signals of Clover displayed a mesh-like structure in the chloroplast and part of the signals discontinuously overlapped with chlorophyll autofluorescence. The fluorescence signals gathered inside the pyrenoid as a distinct wheel-like structure at 2 h after transfer to LC-light condition, and then localized to the center of the pyrenoid at 12 h. These results suggest that CAS could move in the chloroplast along the thylakoid membrane in response to lowering CO2 and gather inside the pyrenoid during the operation of the CCM. 相似文献
11.
Martin H. Spalding Christa Critchley Govindjee William L. Orgren 《Photosynthesis research》1984,5(2):169-176
Carbon dioxide concentration during growth is commonly not considered to be a factor influencing the photochemical properties of plants. It was observed that fluorescence induction in Chlamydomonas reinhardii cells grown at air levels of CO2 was both qualitatively and quantitatively different from that of cells grown at 5% CO2. In the two cell types, measured at equivalent chlorophyll and irradiance levels, the fluorescence intensity and the ratio of the levels of peak fluorescence (Fp) to that of the initial fluorescence (Fo) were much lower in the air-adapted than in the 5% CO2 adapted cells. The maximum fluorescence (Fmax) in the presence of diuron was also lower for air-adapted cells. Roughly twice the light input was required for the air-adapted cells to give a fluorescence induction transient and intensity equivalent to that of the 5% CO2-adapted cells. Similar properties were observed in several other unicellular green algae and in cyanobacteria. Chlamydomonas grown under variable CO2 concentrations exhibit significant differences in photosynthetic carbon metabolism and are presumed to have altered energy requirements. The observed variation in fluorescence induction may be due to changes in the properties of the thylakoid reactions (e.g. cyclic electron flow) of Chlamydomonas cells, which may, in turn, be due to a response to the altered energy requirements. 相似文献
12.
Ziyadin Ramazanov Pedro A. Sosa Margaret C. Henk Miguel Jiménez del Rio Juan Luis Gómez-Pinchetti Guillermo García Reina 《Planta》1995,195(4):519-524
In the green marine alga Dunaliella tertiolecta, a CO2-concentrating mechanism is induced when the cells are grown under low-CO2 conditions (0.03% CO2). To identify proteins induced under low-CO2 conditions the cells were labelled with 35SO4
2–, and seven polypeptides with molecular weights of 45, 47, 49, 55, 60, 68 and 100 kDa were detected. The induction of these polypeptides was observed when cells grown in high CO2 (5% CO2 in air) were switched to low CO2, but only while the cultures were growing in light. Immunoblot analysis of total cell protein against pea chloroplastic carbonic anhydrase polyclonal antibodies showed immunoreactive 30-kDa bands in both high- and low-CO2-grown cells and an aditional 49-kDa band exclusively in low-CO2-grown cells. The 30-kDa protein was shown to be located in the chloroplast. Western blot analysis of the plasmamembrane fraction against corn plasma-membrane AT-Pase polyclonal antibodies showed 60-kDa bands in both high- and low-CO2 cell types as well as an immunoreactive 100-kDa band occurring only in low-CO2-grown cells. These results suggest that there are two distinct forms of both carbonic anhydrase and plasma-membrane ATPase, and that one form of each of them can be regulated by the CO2 concentration.Abbreviations CA
carbonic anhydrase
- DIC
dissolved inorganic carbon (CO2+ HCO3
–)
- CCM
CO2-concentrating mechanism
- low CO2
air containing 0.03% CO2
- high CO2
air supplemented with 5% CO2 (v/v)
We thank Prof. John Coleman for providing antibodies raised against pea chloroplast CA, Dr. James V. Moroney for providing antibodies raised against the 37-kDa periplasmic carbonic anhydrase of CO2 Chlamydomonas reinhardtii, and Prof. Leonard T. Robert for a gift of corn plasma-membrane 100-kDa ATPase antibodies. We thank Dr. Jeanine Olsen (University of Groningen, the Netherlands) for style comments. This work was supported by the Institute Tecnológico de Canarias (Spain). 相似文献
13.
Effects of light quality on the chloroplastic ultrastructure and photosynthetic characteristics of cucumber seedlings 总被引:4,自引:0,他引:4
To understand how light quality influences plant photosynthesis, we investigated chloroplastic ultrastructure, chlorophyll fluorescence and photosynthetic parameters, Rubisco and chlorophyll content and photosynthesis-related genes expression in cucumber seedlings exposed to different light qualities: white, red, blue, yellow and green lights with the same photosynthetic photon flux density of 100 μmol m?2 s?1. The results revealed that plant growth, CO2 assimilation rate and chlorophyll content were significantly reduced in the seedlings grown under red, blue, yellow and green lights as compared with those grown under white light, but each monochromatic light played its special role in regulating plant morphogenesis and photosynthesis. Seedling leaves were thickened and slightly curled; Rubisco biosynthesis, expression of the rca, rbcS and rbcL, the maximal photochemical efficiency of PSII (Fv/Fm) and quantum yield of PSII electron transport (ФPSII) were all increased in seedlings grown under blue light as compared with those grown under white light. Furthermore, the photosynthetic rate of seedlings grown under blue light was significantly increased, and leaf number and chlorophyll content of seedlings grown under red light were increased as compared with those exposed to other monochromatic lights. On the contrary, the seedlings grown under yellow and green lights were dwarf with the new leaves etiolated. Moreover, photosynthesis, Rubisco biosynthesis and relative gene expression were greatly decreased in seedlings grown under yellow and green light, but chloroplast structural features were less influenced. Interestingly, the Fv/Fm, ФPSII value and chlorophyll content of the seedlings grown under green light were much higher than those grown under yellow light. 相似文献
14.
Quantum requirements of photosynthetic oxygen evolution at 682 nm and fluorescence spectra at liquid nitrogen temperature (77 K), were investigated in Dunaliella tertiolecta, Chlamydomonas reinhardtii C-9, Chlorella vulgaris 11g, Chlorella vulgaris C3, and Chlorella pyrenoidosa 8b grown under low- and high-CO2 conditions. Dunaliella, Chlamydomonas and C. vulgaris 11g show higher quantum requirements and a higher ratio of F710–740/F680–695 fluorescence when grown under low-CO2 conditions, indicating a change in excitation energy distribution towards PS I. In C. pyrenoidosa the quantum requirement for low-CO2 grown cells is higher than in high-CO2 grown cells, but there was practically no change in the fluorescence ratio. In C. vulgaris C3, the quantum requirements of low- and high-CO2 grown cells are the same, but the fluorescence ratio is higher in high-CO2 grown cells than in low-CO2 grown cells. These results indicate that most of the low-CO2 grown cells require more PS I light than high-CO2 grown cells. It is possible that this energy is used for cyclic electron flow. In C. vulgaris C 3, a mechanism may exist for excitation energy distribution which leads to the same quantum requirements under low- and high-CO2 conditions. 相似文献
15.
Kristin Palmqvist Lars-Göran Sundblad Göran Samuelsson Erik Sundbom 《Photosynthesis research》1986,10(1-2):113-123
In experiments with the unicellular green algae Scenedesmus obliquus a correlation was found between the presence of the CO2-accumulating mechanism and the appearance of polyphasic luminescence decay kinetics. A potentiometric titration method was used to measure and calculate photosynthetic carbon uptake.Polyphasic luminescence decay kinetics was found when the algae showed photosynthetic characteristics typical of algae adapted to low-CO2 conditions. When high-CO2 grown algae were transferred to low-CO2 conditions they gradually developed polyphasic decay kinetics during the first 25–30 minutes. When low-CO2 grown algae were transferred to high-CO2 conditions the polyphasic decay kinetics disappeared. To account for these results a working hypothesis is presented on the basis of the energy requirement for a CO2-accumulating mechanism. 相似文献
16.
Eiko Morita Toshihiko Abe Mikio Tsuzuki Shoko Fujiwara Norihiro Sato Aiko Hirata Kintake Sonoike Hisayoshi Nozaki 《Planta》1998,204(3):269-276
Physiological and morphological characteristics related to the CO2-concentrating mechanism (CCM) were examined in several species of the free-living, unicellular volvocalean genus Chloromonas (Chlorophyta), which differs morphologically from the genus Chlamydomonas only by lacking pyrenoids. The absence of pyrenoids in the chloroplasts of Chloromonas (Cr.) rosae UTEX 1337, Cr. serbinowii UTEX 492, Cr.␣clatharata UTEX 1970, Cr. rosae SAG 26.90, and Cr. palmelloides SAG 32.86 was confirmed by light and electron microscopy. In addition, immunogold electron microscopy demonstrated that ribulose-1,5-bisphosphate
carboxylase/oxygenase (Rubisco; EC 4.1.1.39) molecules were distributed almost evenly throughout the chloroplasts in all five
Chloromonas strains. However, Chloromonas exhibited two types of physiological characteristics related to the CCM depending on the species or strains examined. Chloromonas rosae UTEX 1337 and Cr. serbinowii had high photosynthetic affinities for CO2 in cells grown in culture medium bubbled with air (low-CO2 cells), compared with those grown in medium bubbled with 5% CO2 (high-CO2 cells), indicating the presence of the low-CO2-inducible CCM. In addition, these two Chloromonas strains exhibited low-CO2-inducible carbonic anhydrase (CA; EC 4.2.1.1) activity and seemed to have small intracellular inorganic carbon pools. Therefore,
it appears that Cr. rosae UTEX 1337 and Cr. serbinowii possess the CCM as in pyrenoid-containing microalgae such as Chlamydomonas reinhardtii. By contrast, Cr. clatharata, Cr. rosae SAG 26.90 and Cr. palmelloides showed low photosynthetic affinities for CO2 when grown under both CO2 conditions. Moreover, these three strains exhibited an apparent absence of intracellular inorganic carbon pools and lacked
low-CO2-inducible CA activity. Thus, Cr. clatharata, Cr. rosae SAG 26.90 and Cr. palmelloides, like other pyrenoid-less algae (lichen photobionts) reported previously, seem to lack the CCM. The present study is the
first demonstration of the CCM in pyrenoid-less algae, indicating that pyrenoids or accumulation of Rubisco in the chloroplasts
are not always essential for the CCM in algae. Focusing on this type of CCM in pyrenoid-less algae, the physiological and
evolutionary significance of pyrenoid absence is discussed.
Received: 1 May 1997 / Accepted: 11 September 1997 相似文献
17.
Mass spectrometric measurements of dissolved free 13CO2 were used to monitor CO2 uptake by air grown (low CO2) cells and protoplasts from the green alga Chlamydomonas reinhardtii. In the presence of 50 micromolar dissolved inorganic carbon and light, protoplasts which had been washed free of external carbonic anhydrase reduced the 13CO2 concentration in the medium to close to zero. Similar results were obtained with low CO2 cells treated with 50 micromolar acetazolamide. Addition of carbonic anhydrase to protoplasts after the period of rapid CO2 uptake revealed that the removal of CO2 from the medium in the light was due to selective and active CO2 transport rather than uptake of total dissolved inorganic carbon. In the light, low CO2 cells and protoplasts incubated with carbonic anhydrase took up CO2 at an apparently low rate which reflected the uptake of total dissolved inorganic carbon. No net CO2 uptake occurred in the dark. Measurement of chlorophyll a fluorescence yield with low CO2 cells and washed protoplasts showed that variable fluorescence was mainly influenced by energy quenching which was reciprocally related to photosynthetic activity with its highest value at the CO2 compensation point. During the linear uptake of CO2, low CO2 cells and protoplasts incubated with carbonic anhydrase showed similar rates of net O2 evolution (102 and 108 micromoles per milligram of chlorophyll per hour, respectively). The rate of net O2 evolution (83 micromoles per milligram of chlorophyll per hour) with washed protoplasts was 20 to 30% lower during the period of rapid CO2 uptake and decreased to a still lower value of 46 micromoles per milligram of chlorophyll per hour when most of the free CO2 had been removed from the medium. The addition of carbonic anhydrase at this point resulted in more than a doubling of the rate of O2 evolution. These results show low CO2 cells of Chlamydomonas are able to transport both CO2 and HCO3− but CO2 is preferentially removed from the medium. The external carbonic anhydrase is important in the supply to the cells of free CO2 from the dehydration of HCO3−. 相似文献
18.
CO(2) Concentrating Mechanism of C(4) Photosynthesis: Permeability of Isolated Bundle Sheath Cells to Inorganic Carbon 总被引:2,自引:2,他引:0
Diffusion of inorganic carbon into isolated bundle sheath cells from a variety of C4 species was characterized by coupling inward diffusion of CO2 to photosynthetic carbon assimilation. The average permeability coefficient for CO2 (PCO2) for five representatives from the three decarboxylation types was approximately 20 micromoles per minute per milligram chlorophyll per millimolar, on a leaf chlorophyll basis. The average value for the NAD-ME species Panicum miliaceum (10 determinations) was 26 with a standard deviation of 6 micromoles per minute per milligram chlorophyll per millimolar, on a leaf chlorophyll basis. A PCO2 of at least 500 micromoles per minute per milligram chlorophyll per millimolar was determined for cells isolated from the C3 plant Xanthium strumarium. It is concluded that bundle sheath cells are one to two orders of magnitude less permeable to CO2 than C3 photosynthetic cells. These data also suggest that CO2 diffusion in bundle sheath cells may be made up of two components, one involving an apoplastic path and the other a symplastic (plasmodesmatal) path, each contributing approximately equally. 相似文献
19.
When grown photoautotrophically at air levels of CO2, Chlamydomonas reinhardii possesses a system involving active transport of inorganic carbon which increases the intracellular CO2 concentration considerably above ambient, thereby stimulating photosynthetic CO2 assimilation. In previous investigations, two mutant strains of this unicellular green alga deficient in some component of this CO2-concentrating system were recovered as strains requiring high levels of CO2 to support photoautotrophic growth. One of the mutants, ca-1-12-1C, is a leaky (nonstringent) CO2-requiring strain deficient in carbonic anhydrase (EC 4.2.1.1) activity, while the other, pmp-1-16-5K, is a stringent CO2-requiring strain deficient in inorganic carbon transport. In the present study a double mutant (ca pmp) was constructed to investigate the physiological and biochemical interaction of the two mutations. The two mutations are unlinked and inherited in a Mendelian fashion. The double mutant was found to have a leaky CO2-requiring phenotype, indicating that the mutation ca-1 overcomes the stringent CO2-requirement conferred by the mutation pmp-1. Several physiological characteristics of the double mutant were very similar to the carbonic-anhydrase-deficient mutant, including high CO2 compensation concentration, photosynthetic CO2 response curve, and deficiency of carbonic-anhydrase activity. However, the labeling pattern of metabolites during photosynthesis in 14CO2 was more like that of the bicarbonatetransport-deficient mutant, and accumulation of internal inorganic carbon was intermediate between that of the two original mutants. These data indicate a previously unsuspected complexity in the Chlamydomonas CO2-concentrating system. 相似文献
20.
Demonstration of Both a Photosynthetic and a Nonphotosynthetic CO(2) Requirement for NH(4) Assimilation in the Green Alga Selenastrum minutum 总被引:1,自引:1,他引:0
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Nitrogen-limited and nitrogen-sufficient cell cultures of Selenastrum minutum (Naeg.) Collins (Chlorophyta) were used to investigate the dependence of NH4+ assimilation on exogenous CO2. N-sufficient cells were only able to assimilate NH4+ maximally in the presence of CO2 and light. Inhibition of photosynthesis with 3-(3,4-dichlorophenyl)-1,1-dimethylurea, diuron also inhibited NH4+ assimilation. These results indicate that NH4+ assimilation by N-sufficient cells exhibited a strict requirement for photosynthetic CO2 fixation. N-limited cells assimilated NH4+ both in the dark and in the light in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea, diuron, indicating that photosynthetic CO2 fixation was not required for NH4+ assimilation. Using CO2 removal techniques reported previously in the literature, we were unable to demonstrate CO2-dependent NH4+ assimilation in N-limited cells. However, employing more stringent CO2 removal techniques we were able to show a CO2 dependence of NH4+ assimilation in both the light and dark, which was independent of photosynthesis. The results indicate two independent CO2 requirements for NH4+ assimilation. The first is as a substrate for photosynthetic CO2 fixation, whereas the second is a nonphoto-synthetic requirement, presumably as a substrate for the anaplerotic reaction catalyzed by phosphoenolpyruvate carboxylase. 相似文献