共查询到20条相似文献,搜索用时 15 毫秒
1.
Carbon dioxide (CO 2) and its hydration product bicarbonate (HCO 3‐) are essential molecules in various physiological processes of all living organisms. The reversible interconversion between CO 2 and HCO 3‐ is in equilibrium. This reaction is slow without catalyst, but can be rapidly facilitated by Zn 2+‐metalloenzymes named carbonic anhydrases (CAs). To gain an insight into the function of multiple clades of fungal CA, we chose to investigate the filamentous fungi Aspergillus fumigatus and A. nidulans. We identified four and two CAs in A. fumigatus and A. nidulans, respectively, named cafA‐D and canA‐B. The cafA and cafB genes are constitutively, strongly expressed whereas cafC and cafD genes are weakly expressed but CO 2‐inducible. Heterologous expression of the A. fumigatus cafB, and A. nidulans canA and canB genes completely rescued the high CO 2‐requiring phenotype of a Saccharomyces cerevisiaeΔ nce103 mutant. Only the Δ cafAΔ cafB and Δ canB deletion mutants were unable to grow at 0.033% CO 2, of which growth defects can be restored by high CO 2. Defects in the CAs can affect Aspergilli conidiation. Furthermore, A. fumigatusΔ cafA, Δ cafB, Δ cafC, Δ cafD and Δ cafAΔ cafB mutant strains are fully virulent in a low‐dose murine infection. 相似文献
2.
The effects of increasing the heterocyst-to-vegetative cell ratio on the nitrogenase-based photobiological hydrogen production by the filamentous heterocyst-forming cyanobacterium Anabaena sp. PCC 7120 were studied. Using the uptake hydrogenase-disrupted mutant (ΔHup) as the parent, a deletion-insertion mutant (PN1) was created in patN, known to be involved in heterocyst pattern formation and leading to multiple singular heterocysts (MSH) in Nostoc punctiforme strain ATCC 29133. The PN1 strain showed heterocyst differentiation but failed to grow in medium free of combined-nitrogen; however, a spontaneous mutant (PN22) was obtained on prolonged incubation of PN1 liquid cultures and was able to grow robustly on N2. The disruption of patN was confirmed in both PN1 and PN22 by PCR and whole genome resequencing. Under combined-nitrogen limitation, the percentage of heterocysts to total cells in the PN22 filaments was 13–15 and 16–18% under air and 1% CO2-enriched air, respectively, in contrast to the parent ΔHup which formed 6.5–11 and 9.7–13% heterocysts in these conditions. The PN22 strain exhibited a MSH phenotype, normal diazotrophic growth, and higher H2 productivity at high cell concentrations, and was less susceptible to photoinhibition by strong light than the parent ΔHup strain, resulting in greater light energy utilization efficiency in H2 production on a per unit area basis under high light conditions. The increase in MSH frequency shown here appears to be a viable strategy for enhancing H2 productivity by outdoor cultures of cyanobacteria in high-light environments. 相似文献
3.
The filamentous, heterocyst‐forming cyanobacteria are multicellular organisms in which two different cell types, the CO 2‐fixing vegetative cells and the N 2‐fixing heterocysts, exchange nutrients and regulators. In Anabaena sp. strain PCC 7120, inactivation of sepJ or genes in the fraC operon ( fraC, fraD and fraE) produce filament fragmentation. SepJ, FraC and FraD are cytoplasmic membrane proteins located in the filament's intercellular septa that are needed for intercellular exchange of the fluorescent tracer calcein (622 Da). Transmission electron microscopy showed an alteration in the heterocyst cytoplasmic membrane at the vegetative cell‐heterocyst septa in Δ fraC and Δ fraD mutants. Immunogold labelling of FraD confirmed its localization in the intercellular septa and clearly showed the presence of part of the protein between the cytoplasmic membranes of the adjacent cells. This localization seemed to be affected in the Δ fraC mutant but was not impaired in a Δ sepJ mutant. Intercellular transfer of a smaller fluorescent tracer, 5‐carboxyfluorescein (374 Da), was largely impaired in Δ fraC, Δ fraD and double Δ fraC‐Δ fraD mutants, but much less in the Δ sepJ mutant. These results show the existence in the Anabaena filaments of a FraC/FraD‐dependent intercellular molecular exchange that does not require SepJ. 相似文献
4.
Inorganic phosphorus (P i) and carbon (here, CO 2) potentially limit the photosynthesis of phytoplankton simultaneously (colimitation). A single P i limitation generally reduces photosynthesis, but the effect of a colimitation is not known. Therefore, photosynthesis was measured under P i‐limited conditions and high and low CO 2, and osmo‐mixotrophic (i.e., growth in the presence of glucose) conditions that result in colimiting conditions in some cases. The green alga Chlamydomonas acidophila Negoro was used as a model organism because low P i and CO 2 concentrations likely influence its photosynthetic rates in its natural environment. Results showed a decreasing maximum photosynthetic rate ( Pmax) and maximum quantum yield (Φ II) with increasing P i limitation. In addition, a P i limitation enhanced the relative contribution of dark respiration to Pmax ( Rd: Pmax) but did not influence the compensation light intensity. Pmax positively correlated with the cellular RUBISCO content. Osmo‐mixotrophic conditions resulted in similar Pmax, Φ II, and RUBISCO content as in high‐CO 2 cultures. The low‐CO 2 cultures were colimited by P i and CO 2 and had the highest Pmax, Φ II, and RUBISCO content. Colimiting conditions for P i and CO 2 in C. acidophila resulted in an enhanced mismatch between photosynthesis and growth rates compared to the effect of a single P i limitation. Primary productivity of colimited phytoplankton could thus be misinterpreted. 相似文献
5.
The availability of a complete genome database for the cyanobacterium Synechocystissp. PCC6803 (glucose-tolerant strain) has raised expectations that this organism would become a reference strain for work
aimed at understanding the CO 2-concentrating mechanism (CCM) in cyanobacteria. However, the amount of physiological data available has been relatively limited.
In this report we provide data on the relative contributions of net HCO 3
− uptake and CO 2 uptake under steady state photosynthetic conditions. Cells were compared after growth at high CO 2 (2% v/v in air) or limiting CO 2 conditions (20 ppm CO 2). Synechocystishas a very high dependence on net HCO 3
− uptake at low to medium concentrations of inorganic carbon (Ci). At high Ci concentrations net CO 2 uptake became more important but did not contribute more than 40% to the rate of photosynthetic O 2 evolution. The data also confirm that high Ci cells of Synechocystissp. PCC6803 possess a strong capacity for net HCO 3
− uptake under steady state photosynthetic conditions. Time course experiments show that induction of maximal Ci uptake capacity
on a shift from high CO 2 to low CO 2 conditions was near completion by four hours. By contrast, relaxation of the induced state on return of cells to high CO 2, takes in excess of 230 h. Experiments were conducted to determine if Synechocystissp. PCC6803 is able to exhibit a `fast induction' response under severe Ci limitation and whether glucose was capable of causing
a rapid inactivation in Ci uptake capacity. Clear evidence for either response was not found.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
6.
Fluxes and concentrations of carbon dioxide and 13CO 2 provide information about ecosystem physiological processes and their response to environmental variation. The biophysical model, CANOAK, was adapted to compute concentration profiles and fluxes of 13CO 2 within and above a temperate deciduous forest (Walker Branch Watershed, Tennessee, USA). Modifications to the model are described and the ability of the new model ( CANISOTOPE) to simulate concentration profiles of 13CO 2, its flux density across the canopy–atmosphere interface and leaf‐level photosynthetic discrimination against 13CO 2 is demonstrated by comparison with field measurements. The model was used to investigate several aspects of carbon isotope exchange between a forest ecosystem and the atmosphere. During the 1998 growing season, the mean photosynthetic discrimination against 13CO 2, by the deciduous forest canopy (Δ canopy), was computed to be 22·4‰, but it varied between 18 and 27‰. On a diurnal basis, the greatest discrimination occurred during the early morning and late afternoon. On a seasonal time scale, the greatest diurnal range in Δ canopy occurred early and late in the growing season. Diurnal and seasonal variations in Δ canopy resulted from a strong dependence of Δ canopy on photosynthetically active radiation and vapour pressure deficit of air. Model calculations also revealed that the relationship between canopy‐scale water use efficiency (CO 2 assimilation/transpiration) and Δ canopy was positive due to complex feedbacks among fluxes, leaf temperature and vapour pressure deficit, a finding that is counter to what is predicted for leaves exposed to well‐mixed environments. 相似文献
7.
The small heat shock protein (sHSP) from Methanococcus jannaschii (Mj Hsp16.5) forms a monodisperse 24mer and each of its monomer contains two flexible N‐ and C‐terminals and a rigid α‐crystallin domain with an extruding β‐strand exchange loop. The minimal α‐crystallin domain with a β‐sandwich fold is conserved in sHSP family, while the presence of the β‐strand exchange loop is divergent. The function of the β‐strand exchange loop and the minimal α‐crystallin domain of Mj Hsp16.5 need further study. In the present study, we constructed two fragment‐deletion mutants of Mj Hsp16.5, one with both the N‐ and C‐terminals deleted (ΔNΔC) and the other with a further deletion of the β‐strand exchange loop (ΔNΔLΔC). ΔNΔC existed as a dimer in solution. In contrast, the minimal α‐crystallin domain ΔNΔLΔC became polydisperse in solution and exhibited more efficient chaperone‐like activities to prevent amorphous aggregation of insulin B chain and fibril formation of the amyloidogenic peptide dansyl‐SSTSAA‐W than the mutant ΔNΔC and the wild type did. The hydrophobic probe binding experiments indicated that ΔNΔLΔC exposed much more hydrophobic surface than ΔNΔC. Our study also demonstrated that Mj Hsp16.5 used different mechanisms for protecting different substrates. Though Mj Hsp16.5 formed stable complexes with substrates when preventing thermal aggregation, no complexes were detected when preventing aggregation under non‐heat‐shock conditions. Proteins 2014; 82:1156–1167. © 2013 Wiley Periodicals, Inc. 相似文献
8.
The Arctic is particularly sensitive to climate change, but the independent effects of increasing atmospheric CO 2 concentration ( pCO 2) and temperature on high‐latitude forests are poorly understood. Here, we present a new, annually resolved record of stable carbon isotope (δ 13C) data determined from Larix cajanderi tree cores collected from far northeastern Siberia in order to investigate the physiological response of these trees to regional warming. The tree‐ring record, which extends from 1912 through 1961 (50 years), targets early twentieth‐century warming (ETCW), a natural warming event in the 1920s to 1940s that was limited to Northern hemisphere high latitudes. Our data show that net carbon isotope fractionation (Δ 13C), decreased by 1.7‰ across the ETCW, which is consistent with increased water stress in response to climate warming and dryer soils. To investigate whether this signal is present across the northern boreal forest, we compiled published carbon isotope data from 14 high‐latitude sites within Europe, Asia, and North America. The resulting dataset covered the entire twentieth century and spanned both natural ETCW and anthropogenic Late Twentieth‐Century Warming (~0.7 °C per decade). After correcting for a ~1‰ increase in Δ 13C in response to twentieth century pCO 2 rise, a significant negative relationship ( r = ?0.53, P < 0.0001) between the average, annual Δ 13C values and regional annual temperature anomalies is observed, suggesting a strong control of temperature on the Δ 13C value of trees growing at high latitudes. We calculate a 17% increase in intrinsic water‐use efficiency within these forests across the twentieth century, of which approximately half is attributed to a decrease in stomatal conductance in order to conserve water in response to drying conditions, with the other half being attributed to increasing pCO 2. We conclude that annual tree‐ring records from northern high‐latitude forests record the effects of climate warming and pCO 2 rise across the twentieth century. 相似文献
9.
Distinct types of carboxysomes were distinguished in Synechococcus PCC 7942: electron-clear, electron-intermediate, carboxysomes with internal electron-clear areas, typical electron-dense and bar-shaped carboxysomes. Immunogold location with antibodies against the Rubisco large subunit showed specific label in all carboxysomes. The positive correlation between electron-density, the density of immunogold label, and the percentage of labeled structures within each type support a model of carboxysome biogenesis whereby electron-clear evolve to electron-intermediate and then to electron-dense carboxysomes by the progressive sequestering of Rubisco molecules. Cells responded to limitation in CO 2 supply by increasing carboxysome frequency and the proportion of typical electron-dense carboxysomes, the extent of the response depending on the degree of limitation. The time course of carboxysome expression during transfers between different conditions of CO 2 supply indicated that, under our experimental conditions, there were different levels of response, depending on the degree of limitation. The first level occured at atmospheric levels of CO 2 and involved changes in the affinity of the CCM and in carboxysome, which occurred simultaneously. More severe limitation of CO 2 supply affected carboxysomes exclusively, without further improvement in the affinity of the CCM. 相似文献
10.
The low CO 2 concentration in seawater poses severe restrictions on photosynthesis, especially on those species with form II RUBISCO. We found that the potentially toxic dinoflagellate Protoceratium reticulatum Clap. et J. Lachm. possesses a form II RUBISCO. To cast some light on the mechanisms this organism undergoes to cope with low CO 2 availability, we compared cells grown at atmospheric (370 ppm) and high (5000 ppm) CO 2 concentrations, with respect to a number of physiological parameters related to dissolved inorganic carbon (DIC) acquisition and assimilation. The photosynthetic affinity for DIC was about one order of magnitude lower in cells cultivated at high [CO 2]. End‐point pH‐drift experiments suggest that P. reticulatum was not able to efficiently use HCO 3? under our growth conditions. Only internal carbonic anhydrase (CA) activity was detected, and its activity decreased by about 60% in cells cultured at high [CO 2]. Antibodies raised against a variety of algal CAs were used for Western blot analysis: P. reticulatum extracts only cross‐reacted with anti‐ß‐CA sera, and the amount of immunoreactive protein decreased in cells grown at high [CO 2]. No pyrenoids were observed under all growth conditions. Our data indicate that P. reticulatum has an inducible carbon‐concentrating mechanism (CCM) that operates in the absence of pyrenoids and with little intracellular CO 2 accumulation. Calculations on the impact of the CA activity to photosynthetic growth [CO 2] suggest that it is an essential component of the CCM of P. reticulatum and is necessary to sustain the photosynthetic rates observed at ambient CO 2. 相似文献
11.
The frequent production of the hepatotoxin microcystin (MC) and its impact on the lifestyle of bloom-forming cyanobacteria are poorly understood. Here, we report that MC interferes with the assembly and the subcellular localization of RubisCO, in Microcystis aeruginosa PCC7806. Immunofluorescence, electron microscopic and cellular fractionation studies revealed a pronounced heterogeneity in the subcellular localization of RubisCO. At high cell density, RubisCO particles are largely separate from carboxysomes in M. aeruginosa and relocate to the cytoplasmic membrane under high-light conditions. We hypothesize that the binding of MC to RubisCO promotes its membrane association and enables an extreme versatility of the enzyme. Steady-state levels of the RubisCO CO 2 fixation product 3-phosphoglycerate are significantly higher in the MC-producing wild type. We also detected noticeable amounts of the RubisCO oxygenase reaction product secreted into the medium that may support the mutual interaction of M. aeruginosa with its heterotrophic microbial community. 相似文献
12.
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
13.
Leaks and isotopic disequilibria represent potential errors and artefacts during combined measurements of gas exchange and carbon isotope discrimination (Δ). This paper presents new protocols to quantify, minimize, and correct such phenomena. We performed experiments with gradients of CO 2 concentration (up to ±250 μmol mol ?1) and δ 13C CO2 (34‰), between a clamp‐on leaf cuvette (LI‐6400) and surrounding air, to assess (1) leak coefficients for CO 2, 12CO 2, and 13CO 2 with the empty cuvette and with intact leaves of Holcus lanatus (C 3) or Sorghum bicolor (C 4) in the cuvette; and (2) isotopic disequilibria between net photosynthesis and dark respiration in light. Leak coefficients were virtually identical for 12CO 2 and 13CO 2, but ~8 times higher with leaves in the cuvette. Leaks generated errors on Δ up to 6‰ for H. lanatus and 2‰ for S. bicolor in full light; isotopic disequilibria produced similar variation of Δ. Leak errors in Δ in darkness were much larger due to small biological : leak flux ratios. Leak artefacts were fully corrected with leak coefficients determined on the same leaves as Δ measurements. Analysis of isotopic disequilibria enabled partitioning of net photosynthesis and dark respiration, and indicated inhibitions of dark respiration in full light ( H. lanatus: 14%, S. bicolor: 58%). 相似文献
14.
Summary Red algae have the highest known selectivity factor (S rel) for CO 2 over O 2 of ribulose bisphosphate carboxylase-oxygenase (RUBISCO). This allows the prediction that a red alga relying on diffusive supply of CO 2 to RUBISCO from air-equilibrated solution should have less O 2 inhibition of photosynthesis than would an otherwise similar non-red alga with a lower S rel of RUBISCO. Furthermore, RUBISCO shows an increased S rel values at low temperatures. The prediction that O 2inhibition of photosynthesis should be small for marine red algae relying on diffusive CO 2 entry growing in the North Sea with an annual temperature range of 4–16°C was tested in O 2 electrode experiments at 12°C. Phycodrys rubens and Plocamium cartilagineum, which rely on diffusive CO 2 entry showed, as predicted, only a small inhibition at lower inorganic C concentrations. Palmaria palmata, which has a CO 2 concentrating mechanism, had the expected negligible O 2 inhibition of photosynthesis at any inorganic C concentration except (non-significantly) for saturating inorganic C. 相似文献
15.
The objective of this study is to globally assess the effects of atmospheric nitrogen deposition and climate, associated with rising levels of atmospheric CO 2, on the variability of carbon isotope discrimination ( Δ13C), and intrinsic water‐use efficiency ( iWUE) of angiosperm and conifer tree species. Eighty‐nine long‐term isotope tree‐ring chronologies, representing 23 conifer and 13 angiosperm species for 53 sites worldwide, were extracted from the literature, and used to obtain long‐term time series of Δ13C and iWUE. Δ13C and iWUE were related to the increasing concentration of atmospheric CO 2 over the industrial period (1850–2000) and to the variation of simulated atmospheric nitrogen deposition and climatic variables over the period 1950–2000. We applied generalized additive models and linear mixed‐effects models to predict the effects of climatic variables and nitrogen deposition on Δ13C and iWUE. Results showed a declining Δ13C trend in the angiosperm and conifer species over the industrial period and a 16.1% increase of iWUE between 1850 and 2000, with no evidence that the increased rate was reduced at higher ambient CO 2 values. The temporal variation in Δ13C supported the hypothesis of an active plant mechanism that maintains a constant ratio between intercellular and ambient CO 2 concentrations. We defined linear mixed‐effects models that were effective to describe the variation of Δ13C and iWUE as a function of a set of environmental predictors, alternatively including annual rate ( Nrate) and long‐term cumulative ( Ncum) nitrogen deposition. No single climatic or atmospheric variable had a clearly predominant effect, however, Δ13C and iWUE showed complex dependent interactions between different covariates. A significant association of Nrate with iWUE and Δ13C was observed in conifers and in the angiosperms, and Ncum was the only independent term with a significant positive association with iWUE, although a multi‐factorial control was evident in conifers. 相似文献
16.
Kinetic, thermodynamic, and structural properties of the aminoglycoside N3‐acetyltransferase‐VIa (AAC‐VIa) are determined. Among the aminoglycoside N3‐acetyltransferases, AAC‐VIa has one of the most limited substrate profiles. Kinetic studies showed that only five aminoglycosides are substrates for this enzyme with a range of fourfold difference in kcat values. Larger differences in KM (~40‐fold) resulted in ~30‐fold variation in kcat/ KM. Binding of aminoglycosides to AAC‐VIa was enthalpically favored and entropically disfavored with a net result of favorable Gibbs energy (Δ G < 0). A net deprotonation of the enzyme, ligand, or both accompanied the formation of binary and ternary complexes. This is opposite of what was observed with several other aminoglycoside N3‐acetyltransferases, where ligand binding causes more protonation. The change in heat capacity (ΔCp) was different in H 2O and D 2O for the binary enzyme–sisomicin complex but remained the same in both solvents for the ternary enzyme–CoASH–sisomicin complex. Unlike, most other aminoglycoside‐modifying enzymes, the values of ΔCp were within the expected range of protein‐carbohydrate interactions. Solution behavior of AAC‐VIa was also different from the more promiscuous aminoglycoside N3‐acetyltransferases and showed a monomer‐dimer equilibrium as detected by analytical ultracentrifugation (AUC). Binding of ligands shifted the enzyme to monomeric state. Data also showed that polar interactions were the most dominant factor in dimer formation. Overall, thermodynamics of ligand‐protein interactions and differences in protein behavior in solution provide few clues on the limited substrate profile of this enzyme despite its >55% sequence similarity to the highly promiscuous aminoglycoside N3‐acetyltransferase. Proteins 2017; 85:1258–1265. © 2017 Wiley Periodicals, Inc. 相似文献
17.
The photosynthetic efficiency of the CO 2‐concentrating mechanism in two forms of single‐cell C 4 photosynthesis in the family Chenopodiaceae was characterized. The Bienertioid‐type single‐cell C 4 uses peripheral and central cytoplasmic compartments ( Bienertia sinuspersici), while the Borszczowioid single‐cell C 4 uses distal and proximal compartments of the cell ( Suaeda aralocaspica). C 4 photosynthesis within a single‐cell raises questions about the efficiency of this type of CO 2‐concentrating mechanism compared with the Kranz‐type. We used measurements of leaf CO 2 isotope exchange (Δ 13C) to compare the efficiency of the single‐cell and Kranz‐type forms of C 4 photosynthesis under various temperature and light conditions. Comparisons were made between the single‐cell C 4 and a sister Kranz form, S. eltonica[NAD malic enzyme (NAD ME) type], and with Flaveria bidentis[NADP malic enzyme (NADP‐ME) type with Kranz Atriplicoid anatomy]. There were similar levels of Δ 13C discrimination and CO 2 leakiness ( ?) in the single‐cell species compared with the Kranz‐type. Increasing leaf temperature (25 to 30 °C) and light intensity caused a decrease in Δ 13C and ? across all C 4 types. Notably, B. sinuspersici had higher Δ 13C and ? than S. aralocaspica under lower light. These results demonstrate that rates of photosynthesis and efficiency of the CO 2‐concentrating mechanisms in single‐cell C 4 plants are similar to those in Kranz‐type. 相似文献
18.
In oxygenic photosynthetic organisms, excluding angiosperms, flavodiiron proteins (FDPs) catalyze light‐dependent reduction of O 2 to H 2O. This alleviates electron pressure on the photosynthetic apparatus and protects it from photodamage. In Synechocystis sp. PCC 6803, four FDP isoforms function as hetero‐oligomers of Flv1 and Flv3 and/or Flv2 and Flv4. An alternative electron transport pathway mediated by the NAD(P)H dehydrogenase‐like complex (NDH‐1) also contributes to redox hemostasis and the photoprotection of photosynthesis. Four NDH‐1 types have been characterized in cyanobacteria: NDH‐1 1 and NDH‐1 2, which function in respiration; and NDH‐1 3 and NDH‐1 4, which function in CO 2 uptake. All four types are involved in cyclic electron transport. Along with single FDP mutants (? flv1 and Δ flv3) and the double NDH‐1 mutants (? d1d2, which is deficient in NDH‐1 1,2 and ? d3d4, which is deficient in NDH‐1 3,4), we studied triple mutants lacking one of Flv1 or Flv3, and NDH‐1 1,2 or NDH‐1 3,4. We show that the presence of either Flv1/3 or NDH‐1 1,2, but not NDH‐1 3,4, is indispensable for survival during changes in growth conditions from high CO 2/moderate light to low CO 2/high light. Our results show functional redundancy between FDPs and NDH‐1 1,2 under the studied conditions. We suggest that ferredoxin probably functions as a primary electron donor to both Flv1/3 and NDH‐1 1,2, allowing their functions to be dynamically coordinated for efficient oxidation of photosystem I and for photoprotection under variable CO 2 and light availability. 相似文献
19.
Many eukaryotic green algae possess biophysical carbon‐concentrating mechanisms (CCMs) that enhance photosynthetic efficiency and thus permit high growth rates at low CO 2 concentrations. They are thus an attractive option for improving productivity in higher plants. In this study, the intracellular locations of ten CCM components in the unicellular green alga Chlamydomonas reinhardtii were confirmed. When expressed in tobacco, all of these components except chloroplastic carbonic anhydrases CAH3 and CAH6 had the same intracellular locations as in Chlamydomonas. CAH6 could be directed to the chloroplast by fusion to an Arabidopsis chloroplast transit peptide. Similarly, the putative inorganic carbon (Ci) transporter LCI1 was directed to the chloroplast from its native location on the plasma membrane. CCP1 and CCP2 proteins, putative Ci transporters previously reported to be in the chloroplast envelope, localized to mitochondria in both Chlamydomonas and tobacco, suggesting that the algal CCM model requires expansion to include a role for mitochondria. For the Ci transporters LCIA and HLA3, membrane location and Ci transport capacity were confirmed by heterologous expression and H 14CO 3‐ uptake assays in Xenopus oocytes. Both were expressed in Arabidopsis resulting in growth comparable with that of wild‐type plants. We conclude that CCM components from Chlamydomonas can be expressed both transiently (in tobacco) and stably (in Arabidopsis) and retargeted to appropriate locations in higher plant cells. As expression of individual Ci transporters did not enhance Arabidopsis growth, stacking of further CCM components will probably be required to achieve a significant increase in photosynthetic efficiency in this species. 相似文献
20.
Plants of the crassulacean acid metabolism (CAM) species Plectranthus marrubioides (Lamiaceae) were subjected to short- and long-term changes in air humidity in controlled-environment experiments. Stomata of well-watered individuals of this all-cell leaf-succulent taxon responded directly, quickly and reversibly to variations of the water vapour gradient between leaf and air (Δ w). Mean night-time leaf conductance to water vapour decreased curvilinearly with increasing Δ w but linearly with lowered relative air humidity. Stomatal response was generally independent of the prevailing temperature and was not linked to CO 2 uptake rates. Therefore, net night-time carbon gain, nocturnal malic acid accumulation and, thus, relative carbon recycling were not influenced by changes in air humidity in the temperature range tested. Mean nocturnal molar water use efficiency, however, decreased with decreasing air humidity because of the increased transpirational water loss. If watering was repeatedly withheld for several days during the experiments, employing a temperature regime of 35/30°C day and night, stomatal conductance became low enough to inhibit CO 2 uptake, but only at the highest Δ w. The results suggest that drought stress was necessary to increase responsiveness of plants to the point where CAM was also inhibited by decreases in air humidity. 相似文献
|