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1.
Phosphorus deficiency was induced in sugar beet plants ( Beta vulgaris L. var. F5855441), cultured hydroponically under standardized environmental conditions, by removal of phosphorus from the nutrient supply at the ten leaf stage 28 days after germination. CO 2 and water vapor exchange rates of individual attached leaves were determined at intervals after P cutoff. Leaves grown with an adequate nutrient supply attained net rates of photosynthetic CO 2 fixation of 125 ng CO 2 cm −2 sec −1 at saturating irradiance, 25 C, and an ambient CO 2 concentration of about 250 μl l −1. After P cutoff, leaf phosphorus concentrations decreased as did net rates of photosynthetic CO 2 uptake, photorespiratory evolution of CO 2 into CO 2-free air, and dark respiration, so that 30 days after cutoff these rates were about one-third of the control rates. The decrease in photosynthetic rates during the first 15 days after cutoff was associated with increased mesophyll resistance ( rm) which increased from 2.4 to 4.9 sec cm −1, while from 15 to 30 days there was an increase in leaf (mainly stomatal) diffusion resistance ( rl′) from 0.3 to 0.9 sec cm −1, as well as further increases in rm to 8.5 sec cm −1. Leaf diffusion resistance ( rl′) was increased greatly by low P at low but not at high irradiance, rl′ for plants at low P reaching values as high as 9 sec cm −1. 相似文献
2.
The effects of Mg deficiency on the photosynthesis and respiration of sugar beets ( Beta vulgaris L. cv. F58-554H1) were studied by withholding Mg from the culture solution and by following changes in CO 2 and water vapor exchange of attached leaves. Leaf blade Mg concentration decreased from about 1200 to less than 200 meq kg −1 dry matter without change in the rate of photosynthetic CO 2 uptake per unit leaf area, while from 200 to 50 meq kg −1 the rate decreased to one-third. Rates of photorespiratory evolution of CO 2 into CO 2-free air responded to Mg like those of photosynthetic CO 2 uptake, the rates decreasing to one-half, below 200 meq kg −1. Respiratory CO 2 evolution in the dark increased almost 2-fold in low Mg leaves. Magnesium deficiency had less effect on leaf (mainly stomatal) diffusion resistance (r 1) than on mesophyll resistance (r m); in Mg-deficient plants r m increased from 2.9 to 7.1 sec cm −1, whereas r 1 became significantly greater than the control value only in the most severe instances of Mg deficiency. 相似文献
3.
Whole-plant diurnal C exchange analysis provided a noninvasive estimation of daily net C gain in transgenic tobacco ( Nicotiana tabacum L.) plants deficient in leaf cytosolic pyruvate kinase (PK c−). PK c− plants cultivated under a low light intensity (100 μmol m −2 s −1) were previously shown to exhibit markedly reduced root growth, as well as delayed shoot and flower development when compared with plants having wild-type levels of PK c (PK c+). PK c− and PK c+ source leaves showed a similar net C gain, photosynthesis over a range of light intensities, and a capacity to export newly fixed 14CO 2 during photosynthesis. However, during growth under low light the nighttime, export of previously fixed 14CO 2 by fully expanded PK c− leaves was 40% lower, whereas concurrent respiratory 14CO 2 evolution was 40% higher than that of PK c+ leaves. This provides a rationale for the reduced root growth of the PK c− plants grown at low irradiance. Leaf photosynthetic and export characteristics in PK c− and PK c+ plants raised in a greenhouse during winter months resembled those of plants grown in chambers at low irradiance. The data suggest that PK c in source leaves has a critical role in regulating nighttime respiration particularly when the available pool of photoassimilates for export and leaf respiratory processes are low. 相似文献
4.
Carbonyl sulfide (COS), a substrate for carbonic anhydrase, inhibited alkalization of the medium, O 2 evolution, dissolved inorganic carbon accumulation, and photosynthetic CO 2 fixation at pH 7 or higher by five species of unicellular green algae that had been air-adapted for forming a CO 2-concentrating process. This COS inhibition can be attributed to inhibition of external HCO 3− conversion to CO 2 and OH − by the carbonic anhydrase component of an active CO 2 pump. At a low pH of 5 to 6, COS stimulated O 2 evolution during photosynthesis by algae with low CO 2 in the media without alkalization of the media. This is attributed to some COS hydrolysis by carbonic anhydrase to CO 2. Although COS had less effect on HCO 3− accumulation at pH 9 by a HCO 3− pump in Scenedesmus, COS reduced O 2 evolution probably by inhibiting internal carbonic anhydrases. Because COS is hydrolyzed to CO 2 and H 2S, its inhibition of the CO 2 pump activity and photosynthesis is not accurate, when measured by O 2 evolution, by NaH 14CO 3 accumulation, or by 14CO 2 fixation. 相似文献
5.
Nonautotrophic CO 2 metabolism in Opuntia echinocarpa roots was studied with techniques of manometry and radiometry. The roots were grown in a one-quarter strength nutrient solution for several days; the distal 2 cm was used for physiological studies. The roots assimilated significant quantities of 14CO 2 and appeared to show a crassulacean-type acid metabolism with respect to quality and quantity. Most of the 14C activity was associated with the distal portion of the elongating root indicating correlation with metabolic activity. The 14CO 2 assimilation was comparable to a crassulacean leaf succulent, but 3 times greater than that found for stem tissue of the same Opuntia species. The rates of O2 and CO2 exchange and estimated CO2 fixation were 180, 123, and 57 μl/g per hour. A respiratory quotient of 0.66 was found. The products of 14CO2 fixation were similar in most respects to reported experiments with leaf succulents. Equilibration of the predominant malic acid with isocitric, succinic, and fumaric acids was not evident. The latter observation was interpreted as metabolic isolation of the fixation products rather than poor citric acid cycle activity. A rapid turnover of the fixed 14CO2 was measured by following decarboxlyation kinetics and by product analysis after a postincubation period. The first order rate constant for the steady state release was 4.4 × 10−3 min−1 with a half-time of 157.5 minutes. Amino acids decayed at a more rapid rate than organic acids. 相似文献
6.
Young bell pepper ( Capsicum annuum L.) plants grown in nutrient solution were gradually acclimated to 50, 100, or 150 moles per cubic meter NaCl, and photosynthetic rates of individual attached leaves were measured on several occasions during the salinization period at external CO 2 concentrations ranging from approximately 70 to 1900 micromoles per mole air. Net CO 2 assimilation (A) was plotted against computed leaf internal CO 2 concentration (C i), and the initial slope of this A-C i curve was used as a measure of photosynthetic ability. During the 10 to 14 days after salinization began, leaves from plants exposed to 50 moles per cubic meter NaCl showed little change in photosynthetic ability, whereas those treated to 100 or 150 moles per cubic meter NaCl had up to 85% inhibition, with increase in CO 2 compensation point. Leaves appeared healthy, and leaf chlorophyll content showed only a 14% reduction at the highest salinity levels. Partial stomatal closure occurred with salinization, but reductions in photosynthesis were primarily nonstomatal in origin. Photosynthetic ability was inversely related to the concentration of either Na + or Cl − in the leaf laminas sampled at the end of the experimental period. However, the concentration of Cl − expressed on a tissue water basis was greater, exceeding 300 moles per cubic meter, and Cl − was more closely associated (R 2 = 0.926) with the inhibition of photosynthetic ability. Leaf turgor was not reduced by salinization and leaf osmotic potential decreased to a slightly greater extent than the osmotic potential decreases of the nutrient solutions. Concentration of accumulated Na + and Cl − (on a tissue water basis) accounted quantitatively for maintenance of leaf osmotic balance, assuming that these ions were sequestered in the vacuoles. 相似文献
7.
When studying active CO 2 and HCO 3− transport by cyanobacteria, it is often useful to be able to inhibit concomitant CO 2 fixation. We have found that glycolaldehyde was an efficient inhibitor of photosynthetic CO 2 fixation in Synechococcus UTEX 625. Glycolaldehyde did not inhibit inorganic carbon accumulation due to either active CO 2 or HCO 3− transport. When glycolaldehyde (10 millimolar) was added to rapidly photosynthesizing cells, CO 2 fixation was stopped within 15 seconds. The quenching of chlorophyll a fluorescence remained high (≤ 82% control) when CO 2 fixation was completely blocked by glycolaldehyde. This quenching was relieved upon the addition of a glucose oxidase oxygentrap. This is consistent with our previous finding that q-quenching in the absence of CO 2 fixation was due to O 2 photoreduction. Photosynthetic CO 2 fixation was also inhibited by d,l,-glyceraldehyde but a sixfold higher concentration was required. Glycolaldehyde acted much more rapidly than iodoacetamide (15 seconds versus 300 seconds) and did not cause the onset of net O 2 evolution often observed with iodoacetamide. Glycolaldehyde will be a useful inhibitor when it is required to study CO 2 and HCO 3− transport without the complication of concomitant CO 2 fixation. 相似文献
8.
Equations have been developed which quantitatively predict the theoretical time-course of photosynthetic 14C incorporation when CO 2 or HCO 3− serves as the sole source of exogenous inorganic carbon taken up for fixation by cells during steady state photosynthesis. Comparison between the shape of theoretical (CO 2 or HCO 3−) and experimentally derived time-courses of 14C incorporation permits the identification of the major species of inorganic carbon which crosses the plasmalemma of photosynthetic cells and facilitates the detection of any combined contribution of CO 2 and HCO 3− transport to the supply of intracellular inorganic carbon. The ability to discriminate between CO 2 or HCO 3− uptake relies upon monitoring changes in the intracellular specific activity (by 14C fixation) which occur when the inorganic carbon, present in the suspending medium, is in a state of isotopic disequilibrium (JT Lehman 1978 J Phycol 14: 33-42). The presence of intracellular carbonic anhydrase or some other catalyst of the CO 2-HCO 3− interconversion reaction is required for quantitatively accurate predictions. Analysis of equations describing the rate of 14C incorporation provides two methods by which any contribution of HCO 3− ions to net photosynthetic carbon uptake can be estimated. 相似文献
9.
Effects of sulfur on photosynthesis in sugar beets ( Beta vulgaris L. cv. F58-554H1) were studied by inducing sulfur deficiency and determining changes in the photosynthesis of whole attached leaves and of isolated chloroplasts. The rates of photosynthetic CO 2 uptake by intact leaves, photoreduction of ferricyanide, cyclic and noncyclic photophosphorylation of isolated chloroplasts, and the rate of CO 2 assimilation by ribulose diphosphate carboxylase, decreased with decrease in total leaf sulfur from 2500 to about 500 μg g −1 dry weight. Sulfur deficiency reduced photosynthesis through an effect on chlorophyll content, which decreased linearly with leaf sulfur, and by decreasing the rate of photosynthesis per unit chlorophyll. There was only a small effect of sulfur deficiency on stomatal diffusion resistance to CO 2 until leaf sulfur decreased below 1000 μg g −1 when stomatal resistance became a more significant proportion of the total diffusion resistance to CO 2. Light respiration rates were positively correlated with photosynthesis rates and dark respiration was unchanged as leaf sulfur concentrations declined. 相似文献
10.
The effect of purified host-specific toxin from Bipolaris (Helminthosporium) maydis, race T, on dark or light-dependent CO 2 fixation was studied with thin (1 × 8 mm) corn ( Zea mays L.) leaf slices supplied H 14CO 3−. At 5 to 30 nanograms per milliliter (5 nanomolar), toxin significantly inhibited (20 to 40%) dark CO 2 fixation in susceptible (T) corn slices after either dark or light preincubations of 10-20 minutes. The same concentrations were effective to the same degree on photosynthesis, but the effect differed in that significant inhibition occurred after 25 minutes and only with light preincubation. Light preincubation without toxin did not shorten the time required for inhibition of photosynthesis after addition of toxin. Once photosynthetic inhibition was entrained, it was not reversed by subsequent periods of darkness. The results suggest the possibility that race T toxin affects two separate metabolic sites, and the data are discussed in view of currently held concepts of toxin action in susceptible tissue. 相似文献
11.
We grew velvetleaf ( Abutilon theophrasti Medic.) and cotton ( Gossypium hirsutum L. var. Stoneville 213) at three irradiances and determined the photosynthetic responses of single leaves to a range of six irradiances from 90 to 2000 μeinsteins m −2sec −1. In air containing 21% O 2, velvetleaf and cotton grown at 750 μeinsteins m −2sec −1 had maximum photosynthetic rates of 18.4 and 21.9 mg of CO 2 dm −2hr −1, respectively. Maximum rates for leaves grown at 320 and 90 μeinsteins m −2sec −1 were 15.3 and 10.3 mg of CO 2 dm −2hr −1 in velvetleaf and 12 and 6.7 mg of CO 2 dm −2hr −1 in cotton, respectively. In 1 O 2, maximum photosynthetic rates were 1.5 to 2.3 times the rates in air containing 21% O 2, and plants grown at medium and high irradiance did not differ in rate. In both species, stomatal conductance was not significantly affected by growth irradiance. The differences in maximum photosynthetic rates were associated with differences in mesophyll conductance. Mesophyll conductance increased with growth irradiance and correlated positively with mesophyll thickness or volume per unit leaf area, chlorophyll content per unit area, and photosynthetic unit density per unit area. Thus, quantitative changes in the photosynthetic apparatus help account for photosynthetic adaptation to irradiance in both species. Net assimilation rates calculated for whole plants by mathematical growth analysis were closely correlated with single-leaf photosynthetic rates. 相似文献
12.
A model which predicts total photosynthetic electron flow from a linear regression of the relationship between corrected steady-state quantum yield and nonphotochemical quenching (E Weis, JA Berry [1987] Biochem Biophys Acta 894: 198-208) was formulated for N-limited cells of the green alga Selenastrum minutum. Unlike other models based on net CO 2 fixation, our model is based on total photosynthetic electron flow measured as gross O 2 evolution. This allowed for the prediction of total photosynthetic electron flow from water to both CO 2 fixation and NO 3−/NO 2− reduction. The linear regression equation predicting electron flow is of the form: J = I · Qq[0.4777-0.3282 QNP] (where J = gross photosynthetic electron flow, I = incident PAR, Qq = photochemical quenching, QNP = nonphotochemical quenching). During steady-state photosynthesis, over a range of irradiance, the model predicted a photosynthetic light saturation curve which was well correlated with that observed. Although developed under steady-state conditions, the model was tested during nonsteady-state photosynthesis induced by transient nitrogen assimilation. The model predicted transient rates of gross O 2 evolution which were in excellent agreement with the rates observed under a variety of conditions regardless of whether CO 2 or NO 3−/NO 2− served as the physiological electron acceptor. The fluorescence transients resulting from ammonium and nitrate assimilation are discussed with respect to metabolic demands for reductant and ATP. 相似文献
13.
Gas exchange measurements and leaf anatomy of 10 cassava cultivars were conducted to study the interrelationship between the relatively high photosynthetic rates and the factors limiting internal CO 2 diffusion. The internal mesophyll surface area per unit leaf surface area (A mes/A) and the intracellular components of CO 2 diffusion and fixation resistance (R cellCO 2) were determined. Among the group of cultivars tested net CO 2 exchange rates were 26±2.5 mol CO 2 m –2 s –1 in normal air and intense light and A mes/A ranged from 14 to 38. Estimated R cellCO 2 ranged from 4300 to 13,000 s m –1. The combined and compensating effects of A mes/A and R cellCO 2 accounted for both the high net photosynthetic rates (P n) and the lack of large differences in P n among cultivars. 相似文献
14.
The species of inorganic carbon (CO 2 or HCO 3−) taken up a source of substrate for photosynthetic fixation by isolated Asparagus sprengeri mesophyll cells is investigated. Discrimination between CO 2 or HCO 3− transport, during steady state photosynthesis, is achieved by monitoring the changes (by 14C fixation) which occur in the specific activity of the intracellular pool of inorganic carbon when the inorganic carbon present in the suspending medium is in a state of isotopic disequilibrium. Quantitative comparisons between theoretical (CO 2 or HCO 3− transport) and experimental time-courses of 14C incorporation, over the pH range of 5.2 to 7.5, indicate that the specific activity of extracellular CO 2, rather than HCO 3−, is the appropriate predictor of the intracellular specific activity. It is concluded, therefore, that CO 2 is the major source of exogenous inorganic carbon taken up by Asparagus cells. However, at high pH (8.5), a component of net DIC uptake may be attributable to HCO 3− transport, as the incorporation of 14C during isotopic disequilibrium exceeds the maximum possible incorporation predicted on the basis of CO 2 uptake alone. The contribution of HCO 3− to net inorganic carbon uptake (pH 8.5) is variable, ranging from 5 to 16%, but is independent of the extracellular HCO 3− concentration. The evidence for direct HCO 3− transport is subject to alternative explanations and must, therefore, be regarded as equivocal. Nonlinear regression analysis of the rate of 14C incorporation as a function of time indicates the presence of a small extracellular resistance to the diffusion of CO 2, which is partially alleviated by a high extracellular concentration of HCO 3−. 相似文献
15.
Quantum yields were measured for CO 2 fixation by sunflower ( Helianthus annuus L.) leaves having various water potentials and for dichlorophenolindophenol photoreduction by chloroplasts isolated from similar leaves having various water potentials. In red radiation, the quantum yield for CO 2 was 0.076 for an attached sunflower leaf at a water potential of −3 to −4 bars but was 0.020 for the same leaf at −15.3 bars. After recovery to a water potential of −5 bars, the quantum yield rose to 0.060. Soybean ( Glycine max L. [Merr.]) leaves behaved similarly. Chloroplasts from a sunflower leaf with a water potential of −3.6 bars had a quantum yield for 4 equivalents of 0.079, but when tissue from the same leaf had a water potential of −14.8 bars, the quantum yield of the chloroplasts decreased to 0.028. The decrease could not be attributed to differences in rates of respiration by the leaves or the chlorophyll content or absorption spectrum of the leaves and chloroplasts. 相似文献
16.
The supply of photosynthates by leaves for reproductive development in cotton ( Gossypium hirsutum L.) has been extensively studied. However, the contribution of assimilates derived from the fruiting forms themselves is inconclusive. Field experiments were conducted to document the photosynthetic and respiratory activity of cotton leaves, bracts, and capsule walls from anthesis to fruit maturity. Bracts achieved peak photosynthetic rates of 2.1 micromoles per square meter per second compared with 16.5 micromoles per square meter per second for the subtending leaf. However, unlike the subtending leaf, the bracts did not show a dramatic decline in photosynthesis with increased age, nor was their photosynthesis as sensitive as leaves to low light and water-deficit stress. The capsule wall was only a minor site of 14CO 2 fixation from the ambient atmosphere. Dark respiration by the developing fruit averaged −18.7 micromoles per square meter per second for 6 days after anthesis and declined to −2.7 micromoles per square meter per second after 40 days. Respiratory loss of CO 2 was maximal at −158 micromoles CO 2 per fruit per hour at 20 days anthesis. Diurnal patterns of dark respiration for the fruit were age dependent and closely correlated with stomatal conductance of the capsule wall. Stomata on the capsule wall of young fruit were functional, but lost this capacity with increasing age. Labeled 14CO 2 injected into the fruit interior was rapidly assimilated by the capsule wall in the light but not in the dark, while fiber and seed together fixed significant amounts of 14CO 2 in both the light and dark. These data suggest that cotton fruiting forms, although sites of significant respiratory CO 2 loss, do serve a vital role in the recycling of internal CO 2 and therein, function as important sources of assimilate for reproductive development. 相似文献
17.
The aim of this study was to determine how Chondrus crispus, a marine red macroalga, acquires the inorganic carbon (C i) it utilizes for photosynthetic carbon fixation. Analyses of C i uptake were done using silicone oil centrifugation (using multicellular fragments of thallus), infrared gas analysis, and gas chromatography. Inhibitors of carbonic anhydrase (CA), the band 3 anion exchange protein and Na +/K + exchange were used in the study. It was found that: (a) C. crispus does not accumulate C i internally above the concentration attainable by diffusion; (b) the initial C i fixtion rate of C. crispus fragments saturates at approximately 3 to 4 millimolar C i; (c) CA is involved in carbon uptake; its involvement is greatest at high HCO 3− and low CO 2 concentration, suggesting its participation in the dehydration of HCO 3− to CO 2; (d) C. crispus has an intermediate C i compensation point; and (e) no evidence of any active or facilitated mechanism for the transport of HCO 3− was detected. These data support the view that photosynthetic C i uptake does not involve active transport. Rather, CO 2, derived from HCO 3− catalyzed by external CA, passively diffuses across the plasma membrane of C. crispus. Intracellular CA also enhances the fixation of carbon in C. crispus. 相似文献
18.
Rates of photosynthetic O 2 evolution, for measuring K 0.5(CO 2 + HCO 3−) at pH 7, upon addition of 50 micromolar HCO 3− to air-adapted Chlamydomonas, Dunaliella, or Scenedesmus cells, were inhibited up to 90% by the addition of 1.5 to 4.0 millimolar salicylhydroxamic acid (SHAM) to the aqueous medium. The apparent K1(SHAM) for Chlamydomonas cells was about 2.5 millimolar, but due to low solubility in water effective concentrations would be lower. Salicylhydroxamic acid did not inhibit oxygen evolution or accumulation of bicarbonate by Scenedesmus cells between pH 8 to 11 or by isolated intact chloroplasts from Dunaliella. Thus, salicylhydroxamic acid appears to inhibit CO 2 uptake, whereas previous results indicate that vanadate inhibits bicarbonate uptake. These conclusions were confirmed by three test procedures with three air-adapted algae at pH 7. Salicylhydroxamic acid inhibited the cellular accumulation of dissolved inorganic carbon, the rate of photosynthetic O 2 evolution dependent on low levels of dissolved inorganic carbon (50 micromolar Na-HCO 3), and the rate of 14CO 2 fixation with 100 micromolar [ 14C] HCO 3−. Salicylhydroxamic acid inhibition of O 2 evolution and 14CO 2-fixation was reversed by higher levels of NaHCO 3. Thus, salicylhydroxamic acid inhibition was apparently not affecting steps of photosynthesis other than CO 2 accumulation. Although salicylhydroxamic acid is an inhibitor of alternative respiration in algae, it is not known whether the two processes are related. 相似文献
19.
We used a pale-green maize ( Zea mays L.) mutant that fails to accumulate ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) to test the working hypothesis that the regulatory phosphorylation of C 4 phospho enolpyruvate carboxylase (PEPC) by its Ca 2+-insensitive protein-serine/threonine kinase (PEPC kinase) in the C 4 mesophyll cytosol depends on cross-talk with a functional Calvin cycle in the bundle sheath. Wild-type (W22) and bundle sheath defective2-mutable1 ( bsd2-m1) seeds were grown in a controlled environment chamber at 100 to 130 μmol m −2 s −1 photosynthetic photon flux density, and leaf tissue was harvested 11 d after sowing, following exposure to various light intensities. Immunoblot analysis showed no major difference in the amount of polypeptide present for several mesophyll- and bundle-sheath-specific photosynthetic enzymes apart from Rubisco, which was either completely absent or very much reduced in the mutant. Similarly, leaf net CO 2-exchange analysis and in vitro radiometric Rubisco assays showed that no appreciable carbon fixation was occurring in the mutant. In contrast, the sensitivity of PEPC to malate inhibition in bsd2-m1 leaves decreased significantly with an increase in light intensity, and there was a concomitant increase in PEPC kinase activity, similar to that seen in wild-type leaf tissue. Thus, although bsd2-m1 mutant plants lack an operative Calvin cycle, light activation of PEPC kinase and its target enzyme are not grossly perturbed. 相似文献
20.
Nostoc punctiforme ATCC 29133 is a nitrogen-fixing, heterocystous cyanobacterium of symbiotic origin. During nitrogen fixation, it produces molecular hydrogen (H 2), which is recaptured by an uptake hydrogenase. Gas exchange in cultures of N. punctiforme ATCC 29133 and its hydrogenase-free mutant strain NHM5 was studied. Exchange of O 2, CO 2, N 2, and H 2 was followed simultaneously with a mass spectrometer in cultures grown under nitrogen-fixing conditions. Isotopic tracing was used to separate evolution and uptake of CO 2 and O 2. The amount of H 2 produced per molecule of N 2 fixed was found to vary with light conditions, high light giving a greater increase in H 2 production than N 2 fixation. The ratio under low light and high light was approximately 1.4 and 6.1 molecules of H 2 produced per molecule of N 2 fixed, respectively. Incubation under high light for a longer time, until the culture was depleted of CO 2, caused a decrease in the nitrogen fixation rate. At the same time, hydrogen production in the hydrogenase-deficient strain was increased from an initial rate of approximately 6 μmol (mg of chlorophyll a) −1 h −1 to 9 μmol (mg of chlorophyll a) −1 h −1 after about 50 min. A light-stimulated hydrogen-deuterium exchange activity stemming from the nitrogenase was observed in the two strains. The present findings are important for understanding this nitrogenase-based system, aiming at photobiological hydrogen production, as we have identified the conditions under which the energy flow through the nitrogenase can be directed towards hydrogen production rather than nitrogen fixation. 相似文献
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