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41.
42.
For maximal rates of CO2 assimilation in isolated intact spinach chloroplasts the generation of the adequate NADPH/ATP ratio is achieved either by cyclic electron flow around photosystem I or by linear electron transport to oxaloacetate, nitrite or oxygen (Mehler-reaction). The interrelationships between these poising mechanisms turn out to be strictly hierarchical. In the presence of antimycin A, an inhibitor of ferredoxin-dependent cyclic electron transport, the reduction of both, oxaloacetate and nitrite, but not that of oxygen restores CO2 fixation. When oxaloacetate and nitrite are added at low concentrations simultaneously during steady-state CO2 fixation, the reduction of nitrite is clearly preferred over the reduction of oxaloacetate, but CO2 fixation is not influenced. Nitrite reduction is not decreased upon addition of oxaloacetate, but vice versa. This is due to the regulation of NADP-malate dehydrogenase activation by electron pressure via the ferredoxin/thioredoxin system on the one hand, and by the NADPH/(NADP+NADPH) ratio (anabolic reduction charge, ARC) on the other hand. Thus the closing of the malate valve prevents drainage of reducing equivalents from the chloroplast (1) when a low ARC indicates a high demand for NADPH in the stroma and (2) when nitrite reduction reduces the electron pressure at ferredoxin. The malate valve is opened when cyclic electron transport is inhibited by antimycin A. Under these conditions the rate of malate formation is higher than in the absence of the inhibitor even in the presence of oxaloacetate, thus indicating that the regulation of the malate valve functions at various redox states of the acceptor side of Photosystem I.Abbreviations ARC
anabolic reduction charge (NADPH/(NADP+NADPH))
- Chl
chlorophyll
- DTT
dithiothreitol; Fd-ferredoxin
- NADP-MDH
NADP-malate dehydrogenase
- OAA
oxaloacetate
- PS
photosystem
- qN
non-photochemical quenching
- qP
photochemical quenching
- E
quantum efficiency of PS II
Dedicated to Prof. Dr. Hans Walter Heldt on the occasion of his 60th birthday. 相似文献
43.
Physiological effects of five months exposure to low concentrations of O3 and NH3 on Douglas fir (Pseudotsuga menziesii) 总被引:2,自引:0,他引:2
Three years old seedlings of Douglas fir (Pseudotsuga menziesii) were exposed lo filtered air, O3 (day and night concentrations of 78 and 30 μgm?3: respectively). NH3 (54 μg m?3) and to a mixture of NH3+O3 (day and night concentrations of 49 + 83 and 49 + 44 μg m?3 respectively), for 5 months in fumigation chambers. Both gas exchange and chlorophyll fluorescence were measured on shoots which had sprouted at the beginning of the exposure period. After 4. 8, 10 and 20 weeks of exposure, light response curves of electron transport rate (J) were determined, in which J was deduced from chlorophyll fluorescence. Net CO2 assimiialion was measured at maximum light intensity of 560) μmol m?2 S?1 (Pn.560). After 8 and 10 weeks of exposure also light response curves of CO2 assimilation were assessed. Shoots exposed to O3 showed a reduction in net CO2 assimilation as compared to the control shoots during the entire exposure period. The reduction was related lo a lower chlorophyll content and a lower electron transport rate, whereas no effect on quantum yield efficiency (qy) was observed. In contrast, shoots exposed to NH3 showed a positive effect on photosynthesis. Shoots exposed to NH3. + O3 showed a rapid increase in Pn.560, in the period between 4 and 8 weeks to a level equal of that of the NH3-treatment. After this period a decline in Pn.560 was observed. After 10 weeks of exposure shoots exposed to O3 showed an increased transpiration rate in the dark as compared to the control shoots. In addition, water use efficiency (WUE) declined as a result of an increase in leaf conductance. Both observations indicate that the stomatal apparatus was affected by O3. A high transpiration rate in the dark was also found for shoots esposed to NHX. However, shoots exposed to NH3+ O3 showed neither an effect on WUE, nor an effect on transpiration rate in the dark. The possibility that NH3 delayed the O3 induced effects on photosynthesis and stomatal conductance is discussed. 相似文献
44.
A growth analysis was made of ultraviolet-B (UV-B)-sensitive (Poinsett) and insensitive (Ashley) cultivars of Cucuumis satives L. grown in growth chambers at 600 μmol m−2 s−1 of photosynthetic photon flux (PPF) provided by red- and far-red-deficient metal halide (MH) or blue- and UV-A-deficient high pressure sodium/deluxe f HPS/DX) lamps. Plants were irradiated 6 h daiiy with 0.2 f-UV-B) or 18.2 C+UV-B) kJ m−2 day−1 of biologically effective UV-B for 8 or 15 days from time of seeding. In general, plants given supplemental UV-B for 15 days showed lower leaf area ratio (LARs, and higher specific leaf mass (SLM) mean relative growth rate (MRGR) and net assimilation rate (NAR) than that of control plants, but they showed no difference in leaf mass ratio (LMR), Plants grown under HPS/DX lamps vs MH lamps showed higher SLM and NAR. lower LAR and LMR. hut no difference in MRGR. LMR was the only growth parameter affected by cultivar: at 15 days, it was slightly greater in Poinsett than in Ashley. There were no interactive effects of UV-B. PPF source or cultivar on any of the growth parameters determined, indicating that the choice of either HPS/DX or MH lamps should not affect growth response to UV-B radiation. This was true even though leaves of UV-B-irradiated plants grown under HPS/DX lamps have been shown to have greater chlorosis than those grown under MH lamps. 相似文献
45.
46.
The decline and disappearance of Littorella uniflora from oligotrophic waters which have become eutrophic has been associated with shading or reduced CO2 supply. However NO
inf3
sup–
concentrations can reach very high levels (100–2000 mmol m–3 compared with <1–3 in oligotrophic habitats). To investigate the impact of NO
inf3
sup–
loading alone, plants were grown under three NO
inf3
sup–
regimes (very low, near-natural and high). The interactive effects of NO
inf3
sup–
and photon flux density (low and high regimes) on N assimilation and accumulation, CO2 concentrating mechanisms, C3 photosynthesis and growth were also examined. The results were unexpected. Increased NO
inf3
sup–
supply had very little effect on photosynthetic capacity, crassulacean acid metabolism (CAM) or lacunal CO2 concentrations ([CO2]i), although there was considerable plasticity with respect to light regime. In contrast, increased NO
inf3
sup–
supply resulted in a marked accumulation of NO
inf3
sup–
, free amino acids and soluble protein in shoots and roots (up to 25 mol m–3, 30 mol m–3 and 9 mg g–1 fresh weight respectively in roots), while fresh weight and relative growth rate were reduced. Total N content even under the very low NO
inf3
sup–
regime (1.6–2.3%) was mid-range for aquatic and terrestrial species (and 3.1–4.3% under the high NO
inf3
sup–
regime). These findings, together with field data, suggest that L. uniflora is not growth limited by low NO
inf3
sup–
supply in natural oligotophic habitats, due not to an efficient photosynthetic nitrogen use but to a slow growth rate, a low N requirement and to the use of storage to avoid N stress. However the increased NO
inf3
sup–
concentrations in eutrophic environments seem likely have detrimental effects on the long-term survival of L. uniflora, possibly as a consequence of N accumulation. 相似文献
47.
Gas exchange and dry-weight production in Opuntia ficus-indica, a CAM species cultivated worldwide for its fruit and cladodes, were studied in 370 and 750 μmol mol−1 CO2 at three photosynthetic photon flux densities (PPFD: 5, 13 and 20 mol m−2 d−1). Elevated CO2 and PPFD enhanced the growth of basal cladodes and roots during the 12-week study. A rise in the PPFD increased the growth of daughter cladodes; elevated CO2 enhanced the growth of first-daughter cladodes but decreased the growth of the second-daughter cladodes produced on them. CO2 enrichment enhanced daily net CO2 uptake during the initial 8 weeks after planting for both basal and first-daughter cladodes. Water vapour conductance was 9 to 15% lower in 750 than in 370 μmol mol−1 CO2. Cladode chlorophyll content was lower in elevated CO2 and at higher PPFD. Soluble sugar and starch contents increased with time and were higher in elevated CO2 and at higher PPFD. The total plant nitrogen content was lower in elevated CO2. The effect of elevated CO2 on net CO2 uptake disappeared at 12 weeks after planting, possibly due to acclimation or feedback inhibition, which in turn could reflect decreases in the sink strength of roots. Despite this decreased effect on net CO2 uptake, the total plant dry weight at 12 weeks averaged 32% higher in 750 than in 370 μmol mol−1 CO2. Averaged for the two CO2 treatments, the total plant dry weight increased by 66% from low to medium PPFD and by 37% from medium to high PPFD. 相似文献
48.
Tatsuo Omata Xanja Andriesse Atsushi Hirano 《Molecular & general genetics : MGG》1993,236(2-3):193-202
Summary The nrtA gene, which has been proposed to be involved in nitrate transport of Synechococcus sp. PCC7942 (Anacystis nidulans R2), was mapped at 3.9 kb upstream of the nitrate reductase gene, narB. Three closely linked genes (designated nrtB, nrtC, and nrtD), which encode proteins of 279, 659, and 274 amino acids, respectively, were found between the nrtA and narB genes. NrtB is a hydrophobic protein having structural similarity to the integral membrane components of bacterial transport systems that are dependent on periplasmic substrate-binding proteins. The N-terminal portion of NrtC (amino acid residues 1–254) and NrtD are 58% identical to each other in their amino acid sequences, and resemble the ATP-binding components of binding protein-dependent transport systems. The C-terminal portion of NrtC is 30% identical to NrtA. Mutants constructed by interrupting each of nrtB and nrtC were unable to grow on nitrate, and the nrtD mutant required high concentration of nitrate for growth. The rate of nitrate-dependent O2 evolution (photosynthetic O2 evolution coupled to nitrate reduction) in wild-type cells measured in the presence of l-methionine d,l-sulfoximine and glycolaldehyde showed a dual-phase relationship with nitrate concentration. It followed saturation kinetics up to 10 mM nitrate (the concentration required for half-saturation = 1 M), and the reaction rate then increased above the saturation level of the first phase as the nitrate concentration increased. The high-affinity phase of nitrate-dependent O2 evolution was absent in the nrtD mutant. The results suggest that there are two independent mechanisms of nitrate uptake and that the nrtB-nrtC-nrtD cluster encodes a high-affinity nitrate transport system. 相似文献
49.
Mutant plants defective in the assimilation of nitrate can be selected by their resistance to the herbicide chlorate. In Arabidopsis thaliana, mutations at any one of nine distinct loci confer chlorate resistance. Only one of the CHL genes, CHL3, has been shown genetically to be a nitrate reductase (NR) structural gene (NIA2) even though two NR genes (NIA1 and NIA2) have been cloned from the Arabidopsis genome. Plants in which the NIA2 gene has been deleted retain only 10% of the wildtype shoot NR activity and grow normally with nitrate as the sole nitrogen source. Using mutagenized seeds from the NIA2 deletion mutant and a modified chlorate selection protocol, we have identified the first mutation in the NIA1 NR structural gene. nia1, nia2 double mutants have only 0.5% of wild-type shoot NR activity and display very poor growth on media with nitrate as the only form of nitrogen. The nial-1 mutation is a single nucleotide substitution that converts an alanine to a threonine in a highly conserved region of the molybdenum cofactor-binding domain of the NR protein. These results show that the NIA1 gene encodes a functional NR protein that contributes to the assimilation of nitrate in Arabidopsis. 相似文献
50.
S. Abarzua R. Altenburger R. Callies L.-H. Grimme A. Mayer D. Leibfritz U. Schiewer 《Physiologia plantarum》1993,89(3):659-663
Over a period of several days, rhythmic changes in extracellular NH+ 4 concentration take place in cultures of the cyanobacterium Microcystis firma (Bré et Lenorm.) Schmidle, strain Gromov/St. Petersb. 398, under conditions of restricted CO2 supply and light/dark alternation. The changes are enhanced by nitrate supply. Among the various processes generating intracellular NH+ 4 (NH4 4 uptake, NO− 3 reduction, protein and amino acid degradation, photorespiration), NO− 3 reduction appears as the one most important. This can be concluded from experiments with and without nitrate and/or ammonium in the medium. In the presence of saturating CO2 , continuous light, or continuous darkness, rhythmic NH+4 4 oscillations are not induced. Studies of the incorporation of NH+ 4 nitrogen by in vivo 15 N-NMR show that if CO2 is supplied, 15 N is accumulated in several components with the following time course: in the first hour in Gln (δ), in the second hour in the α-amino groups of most nonbranched amino acids, in the third hour in γ-aminobutyric acid (GABA), Orn (δ) and Lys (ε), and in the sixth hour in Ala. Carbon limitation, however, results in accumulation of label in the amide nitrogen of glutamine only. 相似文献