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1.
In the field, photosynthesis of Acer saccharum seedlings was rarely light saturated, even though light saturation occurs at about 100 mol quanta m-2 s-1 photosynthetic photon flux density (PPFD). PPFD during more than 75% of the daylight period was 50 mol m-2 s-1 or less. At these low PPFD's there is a marked interaction of PPFD with the initial slope (CE) of the CO2 response. At PPFD-saturation CE was 0.018 mol m-2 s-1/(l/l). The apparent quantum efficiency (incident PPFD) at saturating CO2 was 0.05–0.08 mol/mol. and PPFD-saturated CO2 exchange was 6–8 mol m-2 s-1. The ratio of internal CO2 concentration to external (C i /C a ) was 0.7 to 0.8 except during sunflecks when it decreased to 0.5. The decrease in C i /C a during sunflecks was the result of the slow response of stomates to increased PPFD compared to the response of net photosynthesis. An empirical model, which included the above parameters was used to simulate the measured CO2 exchange rate for portions of two days. Parameter values for the model were determined in experiments separate from the daily time courses being sumulated. Analysis of the field data, partly through the use of simulations, indicate that the elimination of sunflecks would reduce net carbon gain by 5–10%.List of symbols A measured photosynthetic rate under any set of conditions (mol m-2 s-1) - A m (atm) measured photosynthetic rate at saturating PPFD, 350 l/l CO2 and 21% (v/v) O2 (mol m-2 s-1) - C constant in equation of Smith (1937, 1938) - C a CO2 concentration in the air (l/l) - C i CO2 concentration in the intercellular air space (l/l) - C i /* C i corrected for CO2 compensation point, i.e., C i -I *, (l/l) - CE initial slope of the CO2 response of photosynthesis (mol m-2 s-1/(l/l)) - CEM CE at PPFD saturation - E transpiration rate (mmol m-2 s-1) - F predicted photosynthetic rate (mol m-2 s-1) - G leaf conductance to H2O (mol m-2 s-1) - I photosynthetic photon flux density (mol m-2 s-1) - N number of data points - P m predicted photosynthetic rate at saturating CO2 and given PPFD (mol m-2 s-1) - P ml predicted photosynthetic rate at saturating CO2 and PPFD (mol m-2 s-1) - R d residual respiratory rate (mol m-2 s-1) - T a air temperature (°C) - T l leaf temperature (°C) - V reaction velocity in equation of Smith (1937, 1938) - V max saturated reaction velocity in equation of Smith (1937, 1938) - VPA vapor pressure of water in the air (mbar/bar) - VPD vapor pressure difference between leaf and air (mbar/bar) - X substrate concentration in equation of Smith (1937, 1938) - initial slope of the PPFD response of photosynthesis at saturating CO2 (mol CO2/mol quanta) - (atm) initial slope of the PPFD response of photosynthesis at 340 l/l CO2 and 21% (v/v) O2 (mol CO2/mol quanta) - I * CO2 compensation point after correction for residual respiration (l/l) - PPFD compensation point (mol m-2 s-1)  相似文献   

2.
Dry weight and Relative Growth Rate of Lemna gibba were significantly increased by CO2 enrichment up to 6000 l CO2 l–1. This high CO2 optimum for growth is probably due to the presence of nonfunctional stomata. The response to high CO2 was less or absent following four days growth in 2% O2. The Leaf Area Ratio decreased in response to CO2 enrichment as a result of an increase in dry weight per frond. Photosynthetic rate was increased by CO2 enrichment up to 1500 l CO2 l–1 during measurement, showing only small increases with further CO2 enrichment up to 5000 l CO2 l–1 at a photon flux density of 210 mol m–2 s–1 and small decreases at 2000 mol m–1 s–1. The actual rate of photosynthesis of those plants cultivated at high CO2 levels, however, was less than the air grown plants. The response of photosynthesis to O2 indicated that the enhancement of growth and photosynthesis by CO2 enrichment was a result of decreased photorespiration. Plants cultivated in low O2 produced abnormal morphological features and after a short time showed a reduction in growth.  相似文献   

3.
Elevated CO2 (ambient + 35 Pa) increased shoot dry mass production in Avena fatua by 68% at maturity. This increase in shoot biomass was paralleled by an 81% increase in average net CO2 uptake (A) per unit of leaf area and a 65% increase in average A at the ecosystem level per unit of ground area. Elevated CO2 also increased ecosystem A per unit of biomass. However, the products of total leaf area and light-saturated leaf A divided by the ground surface area over time appeared to lie on a single response curve for both CO2 treatments. The approximate slope of the response suggests that the integrated light saturated capacity for leaf photosynthesis is 10-fold greater than the ecosystem rate. Ecosystem respiration (night) per unit of ground area, which includes soil and plant respiration, ranged from-20 (at day 19) to-18 (at day 40) mol m-2 s-1 for both elevated and ambient CO2 Avena. Ecosystem below-ground respiration at the time of seedling emergence was -10 mol m-2 s-1, while that occuring after shoot removal at the termination of the experiment ranged from -5 to-6 mol m-2 s-1. Hence, no significant differences between elevated and ambient CO2 treatments were found in any respiration measure on a ground area basis, though ecosystem respiration on a shoot biomass basis was clearly reduced by elevated CO2. Significant differences existed between leaf and ecosystem water flux. In general, leaf transpiration (E) decreased over the course of the experiment, possibly in response to leaf aging, while ecosystem rates of evapotranspiration (ET) remained constant, probably because falling leaf rates were offset by an increasing total leaf biomass. Transpiration was lower in plants grown at elevated CO2, though variation was high because of variability in leaf age and ambient light conditions and differences were not significant. In contrast, ecosystem evapotranspiration (ET) was significantly decreased by elevated CO2 on 5 out of 8 measurement dates. Photosynthetic water use efficiencies (A/E at the leaf level, A/ET at the ecosystem level) were increased by elevated CO2. Increases were due to both increased A at leaf and ecosystem level and decreased leaf E and ecosystem ET.  相似文献   

4.
Summary Two methods were compared for estimating of Gibberella fujikuroi grown with different proportions of glucose and starch. They were, =Ln2 (Vr/Le) on Petri dish (Vr= rate of tip extension and Le= mean hyphal length) and, 2=d (LnX)/dt in stirred fermenter. Values of 1 and 2 were in close agreement with each other.  相似文献   

5.
Strawberry (Fragaria ananassaDuch. cv. Fengxiang) plantlets were cultured under two in vitroenvironments for rooting, and then acclimatized under two ex vitroirradiance conditions. At the end of rooting stage plant height, fresh weight and specific leaf area of T1-plants grown under high sucrose concentration (3 sucrose), low photosynthetic photon flux density (30 mol m–2 s–1) and normal CO2 concentration (350–400 l l–1) were significantly higher than those of T2-plantlets grown under low sucrose concentration (0.5), high photosynthetic photon flux density (90 mol m–2 s–1) and elevated CO2 concentration (700–800 l l–1). But T2-plantlets had higher net photosynthetic rate (Pn), effective photochemical quantum yield of PSII (PSII), effective photosynthetic electron transport rate (ETR), photochemical quenching (qP) and ratio of chlorophyll fluorescence yield decrease (Rfd). After transfer, higher irradiance obviously promoted the growth of plantlets and was beneficial for the development of photosynthetic functions during acclimatization. T2-plantlets had higher fresh weight, leaf area, PSII and ETR under higher ex vitroirradiance condition.  相似文献   

6.
Summary The effects of CO2 enrichment and water stress on gas exchange of Liquidambar styraciflua L. (sweetgum) and Pinus taeda L. (loblolly pine) seedlings were examined for individuals grown from seed under high (1000 mol·m-2·s-1) and low (250 mol·m-2·s-1) photosynthetic photon flux density at 350, 675 and 1000 l·l-1 CO2. At 8 weeks of age, half the seedlings in each CO2-irradiance treatment were subjected to a drying cycle which reduced plant water potential to about -2.5 MPa in the most stressed plants, while control plants remained well-watered (water potentials of -0.3 and -0.7 MPa for sweetgum and loblolly pine, respectively). During this stress cycle, whole seedling net photosynthesis, transpiration and stomatal conductance of plants from each CO2-irradiance-water treatment were measured under respective growth conditions.For both species, water stress effects on gas exchange were greatest under high irradiance conditions. Waterstressed plants had significantly lower photosynthesis rates than well-watered controls throughout most of the drying cycle, with the most severe inhibition occurring for low CO2, high irradiance-grown sweetgum seedlings. Carbon dioxide enrichment had little effect on gas exchange rates of either water-stressed or well-watered loblolly pine seedlings. In contrast, water stress effects were delayed for sweetgum seedlings grown at elevated CO2, particularly in the 1000 l·l-1 CO2, high irradiance treatment where net photosynthesis, transpiration and conductance of stressed plants were 60, 36 and 33% of respective control values at the end of the drying cycle. Development of internal plant water deficits was slower for stressed sweetgum seedlings grown at elevated CO2. As a result, these seedlings maintained higher photosynthetic rates over the drying cycle than stressed sweetgum seedlings grown at 350 l·l-1 CO2 and stressed loblolly pine seedlings grown at ambient and enriched CO2 levels. In addition, water-stressed sweetgum seedlings grown at elevated CO2 exhibited a substantial increase in water use efficiency.The results suggest that with the future increase in atmospheric CO2 concentration, sweetgum seedlings should tolerate longer exposure to low soil moisture, resulting in greater first year survival of seedlings on drier sites of abandoned fields in the North Carolina piedmont.  相似文献   

7.
Effects of elevated CO2 (700 L L–1) and a control (350 L L–1 CO2) on the productivity of a 3-year-old ryegrass/white clover pasture, and on soil biochemical properties, were investigated with turves of a Typic Endoaquept soil in growth chambers. Temperature treatments corresponding to average winter, spring, and summer conditions in the field were applied consecutively to all of the turves. An additional treatment, at 700 L L–1 CO2 and a temperature 6°C higher throughout than in the other treatments, was included.Under the same temperature conditions, overall herbage yields in the 700 L L–1 CO2 treatment were ca. 7% greater than in the control at the end of the summer period. Root mass (to ca 25 cm depth) in the 700 L L–1 CO2 treatment was then about 50% greater than in the control, but in the 700 L L–1 CO2+6°C treatment it was 6% lower than in the control. Based on decomposition results, herbage from the 700 L L–1+6°C treatment probably contained the highest proportion of readily decomposable components.Elevated CO2 had no consistent effect on soil total C and N, microbial C and N, or extractable C concentrations in any of the treatments. Under the same temperature conditions, it did, however, enhance soil respiration (CO2-C production) and invertase activity. The effects of elevated CO2 on rates of net N mineralization were less distinct, and the apparent availability of N for the sward was not affected. Under elevated CO2, soil in the higher-temperature treatment had a higher microbial C:N ratio; it also had a greater potential to degrade plant materials.Data interpretation was complicated by soil spatial variability and the moderately high background levels of organic matter and biochemical properties that are typical of New Zealand pasture soils. More rapid cycling of C under CO2 enrichment is, nevertheless, indicated. Futher long-term experiments are required to determine the overall effect of elevated CO2 on the soil C balance.  相似文献   

8.
We studied the effects of atmospheric CO2 enrichment (280, 420 and 560 l CO2 l–1) and increased N deposition (0,30 and 90 kg ha–1 year–1) on the spruce-forest understory species Oxalis acetosella, Homogyne alpina and Rubus hirtus. Clones of these species formed the ground cover in nine 0.7 m2 model ecosystems with 5-year-old Picea abies trees (leaf area index of approx 2.2). Communities grew on natural forest soil in a simulated montane climate. Independently of N deposition, the rate of light-saturated net photosynthesis of leaves grown and measured at 420 l CO2 l–1 was higher in Oxalis and in Homogyne, but was not significantly different in Rubus compared to leaves grown and measured at the pre-industrial CO2 concentration of 280 l l–1. Remarkably, further CO2 enrichment to 560 l l–1 caused no additional increase of CO2 uptake. With increasing CO2 supply concentrations of non-structural carbohydrates in leaves increased and N concentrations decreased in all species, whereas N deposition had no significant effect on these traits. Above-ground biomass and leaf area production were not significantly affected by elevated CO2 in the more vigorously growing species O. acetosella and R. hirtus, but the slow growing H. alpina produced almost twice as much biomass and 50% more leaf area per plant under 420 l CO2 l–1 compared to 280 l l–1 (again no further stimulation at 560 l l–1). In contrast, increased N addition stimulated growth in Oxalis and Rubus but had no effect on Homogyne. In Oxalis (only) biomass per plant was positively correlated with microhabitat quantum flux density at low CO2, but not at high CO2 indicating carbon saturation. On the other hand, the less shade-tolerant Homogyne profited from CO2 enrichment at all understory light levels facilitating its spread into more shady micro-habitats under elevated CO2. These species-specific responses to CO2 and N deposition will affect community structure. The non-linear responses to elevated CO2 of several of the traits studied here suggest that the largest responses to rising atmospheric CO2 are under way now or have already occurred and possible future responses to further increases in CO2 concentration are likely to be much smaller in these understory species.  相似文献   

9.
Chloroplasts with high rates of photosynthetic O2 evolution (up to 120 mol O2· (mg Chl)-1·h-1 compared with 130 mol O2· (mg Chl)-1·h-1 of whole cells) were isolated from Chlamydomonas reinhardtii cells grown in high and low CO2 concentrations using autolysine-digitonin treatment. At 25° C and pH=7.8, no O2 uptake could be observed in the dark by high- and low-CO2 adapted chloroplasts. Light saturation of photosynthetic net oxygen evolution was reached at 800 mol photons·m-2·s-1 for high- and low-CO2 adapted chloroplasts, a value which was almost identical to that observed for whole cells. Dissolved inorganic carbon (DIC) saturation of photosynthesis was reached between 200–300 M for low-CO2 adapted chloroplasts, whereas high-CO2 adapted chloroplasts were not saturated even at 700 M DIC. The concentrations of DIC required to reach half-saturated rates of net O2 evolution (Km(DIC)) was 31.1 and 156 M DIC for low- and high-CO2 adapted chloroplasts, respectively. These results demonstrate that the CO2 concentration provided during growth influenced the photosynthetic characteristics at the whole cell as well as at the chloroplast level.Abbreviations Chl chlorophyll - DIC dissolved inorganic carbon - Km(DIC) coneentration of dissolved inorganic carbon required for the rate of half maximal net O2 evolution - PFR photon fluence rate - SPGM silicasol-PVP-gradient medium  相似文献   

10.
The effect of lead on the filtration rate of the zebra musselDreissena polymorpha was investigated, together with the accumulation of Pb in the soft tissues of the mussels. The NOEC-filtration was 116 g.l–1 (0,56 mol.l–1) and the EC50-filtration was 370 g.l–1 (1.79 mol.l–1). The NOEC-accumulation was the concentration found in the control water (1.4g.l–1). These experiments show that the EC50-filtration for Pb is similar to that for Cd, higher than that for Cu and lower than that for Zn. The water quality criteria for lead allow 25 g Pb.l–1 in surface water. This will not cause short-term effects. Long-term effects may, however, occur, since an accumulation of Pb as low as 16 g.l–1 was recorded in this study.  相似文献   

11.
The magnitude of the proton motive force (p) and its constituents, the electrical () and chemical potential (-ZpH), were established for chemostat cultures of a protease-producing, relaxed (rel ) variant and a not protease-producing, stringent (rel +) variant of an industrial strain ofBacillus licheniformis (respectively referred to as the A- and the B-type). For both types, an inverse relation of p with the specific growth rate was found. The calculated intracellular pH (pHin) was not constant but inversely related to . This change in pHin might be related to regulatory functions of metabolism but a regulatory role for pHin itself could not be envisaged. Measurement of the adenylate energy charge (EC) showed a direct relation with for glucose-limited chemostat cultures; in nitrogen-limited chemostat cultures, the EC showed an approximately constant value at low and an increased value at higher . For both limitations, the ATP/ADP ratio was directly related to .The phosphorylation potential (G'p) was invariant with . From the values for G'p and p, a variable H+/ATP-stoichiometry was inferred: H+/ATP=1.83+0.52µ, so that at a given H+/O-ratio of four (4), the apparent P/O-ratio (inferred from regression analysis) showed a decline of 2.16 to 1.87 for =0 to max (we discuss how more than half of this decline will be independent of any change in internal cell-volume). We propose that the constancy of G'p and the decrease in the efficiency of energy-conservation (P/O-value) with increasing are a way in which the cells try to cope with an apparent less than perfect coordination between anabolism and catabolism to keep up the highest possible with a minimum loss of growth-efficiency. Protease production in nitrogen-limited cultures as compared to glucose-limited cultures, and the difference between the A- and B-type, could not be explained by a different energy-status of the cells.Abbreviations CCCP carbonylcyanide-p-trichloromethoxyphenylhydrazone - DW dry weight of biomass - F Faraday's constant, 96.6 J/(mV × mol) - Fo chemostat outflow-rate (ml/h) - FCCP carbonylcyanide-p-trifluoromethoxyphenylhydrazone - G'p phosphorylation potential, the Gibbs energy change for ATP-synthesis from ADP and Pi - G'0p standard Gibbs energy change at specified conditions - H+/ATP number of protons translocated through - ATP synthase in synthesis of one ATP - H+/O protons translocated during transfer of 2 electrons from substrate to oxygen - specific growth rate (1/h) - H+ transmembrane electrochemical proton potential, J/mol - Mb molar weight (147.6 g/mol) of bacteria with general cell formula C6.0H10.8O3.0N1.2 - pHout,in extracellular, intracellular pH - Pi (intracellular) inorganic phosphate - p proton motive force, mV - pH transmembrane pH-difference - transmembrane electrical potential, mV - P/O number of ADP phosphorylated to ATP upon reduction of one O2– to H2O by two electrons transferred through the electron transfer chain - P/O (H+/O) × (H+/ATP)–1 - P/OF, P/ON P/O with the two electrons donated by resp. (NADH + H+) and FADH - q specific rate of consumption or production (mol/g DW × h) - rel +,rel stringent, relaxed genotype - R universal gas constant, 8.36 J/(mol × degree) - T absolute temperature - TPMP+ triphenylmethylphosphonium ion - TPP+ tetraphenyl phosphonium ion - Y growth yield, g DW/mol - Z conversion constant=61.8 mV for 310 K (37 °C) - ZpH transmembrane proton potential or chemical potential, mV  相似文献   

12.
Lower concentrations of CuSO4 (25–75 M) in the MS medium supplemented with 0.1 mg l–1 IAA+5.0 mg l–1 Kn+500 mg l–1 CH+10 mg l–1 Cyst hyd enhanced the growth of regenerants of Dioscorea bulbifera L. CuSO4 (75 M) induced an appreciable diosgenin yield in the regenerants compared to those obtained on media without Cu. The presence of Cu thus seems to stimulate diosgenin production. The regenerants also differentiated bulbils on lower concentrations of Cu. At CuSO4 (100 M), however, cultures showed poor growth as well as a low diosgenin yield. Increased proline and protein contents were recorded in cultures grown on Cu-enriched media.  相似文献   

13.
The activities and kinetics of the enzymes G6PDH (glucose-6-phosphate dehydrogenase) and 6PGDH (6-phosphogluconate dehydrogenase) from the mesophilic cyanobacterium Synechococcus 6307 and the thermophilic cyanobacterium Synechococcus 6716 are studied in relation to temperature. In Synechococcus 6307 the apparent K m's are for G6PDH: 80M (substrate) and 20M (NADP+); for 6PGDH: 90M (substrate) and 25M (NADP+). In Synechococcus 6716 the apparent K m's are for G6PDH: 550M (substrate) and 30M (NADP+); for 6PGDH: 40M (substrate) and 10M (NADP+). None of the K m's is influenced by the growth temperature and only the K m's of G6PDH for G6P are influenced by the assay temperature in both organisms. The idea that, in general, thermophilic enzymes possess a lower affinity for their substrates and co-enzymes than mesophilic enzymes is challenged.Although ATP, ribulose-1,5-bisphosphate, NADPH and pH can all influence the activities of G6PDH and 6PGDH to a certain extent (without any difference between the mesophilic and the thermophilic strain), they cannot be responsible for the total deactivation of the enzyme activities observed in the light, thus blocking the pentose phosphate pathway.Abbreviations G6PDH glucose-6-phosphate, dehydrogenase - 6PGDH 6-phosphogluconate dehydrogenase - G6P glucose-6-phosphate - 6PG 6-phosphogluconate - RUDP ribulose-1,5-bisphosphate - Tricine N-Tris (hydroxymethyl)-methylglycine  相似文献   

14.
Isolated embryos ofKarwinskia humboldtiana were cultured in vitro. The growth of embryos and development to plantlets on woody plant medium supplemented with indole-3-acetic acid 6.10-2 mol l–1, gibberellic acid (GA3) 3.10-2 mol l–1, and 6-benzylaminopurine (BA) 2 mol l–1 was obtained. Multiplication of shoots and rooting of excised shoots has been achieved. Callus formation on modified Murashige-Skoog medium supplemented with 1-naphthaleneacetic acid 10 mol l–1, GA3 14 mol l–1, and kinetin 5 mol l–1 on hypocotyls, or on root cultures on medium supplemented with 2.4-dichlorophenoxyacetic acid 10 mol l–1 and BA 10 mol l–1 was induced.Abbreviations BA 6-benzylaminopurine - 2,4-d 2,4-dichlorophenoxyacetic acid - GA3 gibberellic acid - IAA indole-3-acetic acid - NAA 1-naphthaleneacetic acid - TEM transmission electron microscopy  相似文献   

15.
W. Hüsemann  A. Plohr  W. Barz 《Protoplasma》1979,100(1):101-112
Summary Cell suspension cultures ofChenopodium rubrum have been grown for more than 2 years photoautotrophically with CO2 as sole carbon source. Average increase in fresh weight is appr. 600% within 14 days. The chlorophyll content of photoautotrophic cells (200 g/g fresh weight) is much higher than of photomixotrophic cells (50 g/g fresh weight). The photosynthetic activity of the cells (190 moles CO2×mg–1 chlorophyllXh–1) is comparable to the values found with intact leaves. As shown by short-term14CO2 photosynthesis, both, the photomixotrophic and the photoautotrophic cell suspension cultures assimilate CO2 predominantly via the Calvin pathway.Major differences were found with cells from either exponential or stationary phase of growth with regard to differential labelling of 3-phosphoglyceric acid, malate, sucrose and glucose/fructose.In vitro measurements of carboxylation reactions only partially corroborate our findings with14CO2 incorporation. The ratio of ribulosebisphosphate to phosphoenolpyruvate carboxylase activity is 4.7 for leaves of C.rubrum, 1.2 for photoautotrophic cells during stationary growth and 0.5 for cells during exponential growth phase, however, 0.18 was found for photomixotrophic cells. Though the14CO2 incorporation into 3-phosphoglyceric acid is clearly higher than into malate, thein vitro activity of phosphoenolpyruvatecarboxylase is 2–6 fold higher than that of ribulosebisphosphate carboxylase. We postulate that anaplerotic reactions of the tricarboxylic acid cycle are involved in the regulation of phosphoenolpyruvate carboxylase.Abbreviations 2,4-D didilorophenoxyacetic acid - EDTA ethylene-diamine-tetraacetic acid - fr. w. fresh weight - HEPES N-2-hydroxyethylpiperazine-N-2-ethanesulfonic acid - PGA 3-phosphoglyceric acid - PPO 2,5-diphenyloxazole - PEP phosphoenolpyruvate - RuBP nbulosebisphosphate  相似文献   

16.
To assess the long-term effect of increased CO2 and temperature on plants possessing the C3 photosynthetic pathway, Chenopodium album plants were grown at one of three treatment conditions: (1) 23 °C mean day temperature and a mean ambient partial pressure of CO2 equal to 350 bar; (2) 34 °C and 350 bar CO2; and (3) 34 °C and 750 bar CO2. No effect of the growth treatments was observed on the CO2 reponse of photosynthesis, the temperature response of photosynthesis, the content of Ribulose-1,5-bisphosphate carboxylase (Rubisco), or the activity of whole chain electron transport when measurements were made under identical conditions. This indicated a lack of photosynthetic acclimation in C. album to the range of temperature and CO2 used in the growth treatments. Plants from every treatment exhibited similar interactions between temperature and CO2 on photosynthetic activity. At low CO2 (< 300 bar), an increase in temperature from 25 to 35 °C was inhibitory for photosynthesis, while at elevated CO2 (> 400 bar), the same increase in temperature enhanced photosynthesis by up to 40%. In turn, the stimulation of photosynthesis by CO2 enrichment increased as temperature increased. Rubisco capacity was the primary limitation on photosynthetic activity at low CO2 (195 bar). As a consequence, the temperature response of A was relatively flat, reflecting a low temperature response of Rubisco at CO2 levels below its km for CO2. At elevated CO2 (750 bar), the temperature response of electron transport appeared to control the temperature dependency of photosynthesis above 18 °C. These results indicate that increasing CO2 and temperature could substantially enhance the carbon gain potential in tropical and subtropical habitats, unless feedbacks at the whole plant or ecosystem level limit the long-term response of photosynthesis to an increase in CO2 and temperature.Abbreviations A net CO2 assimilation rate - C a ambient partial pressure of CO2 - C i intercellular partial pressure of CO2 - Rubisco Ribulose-1,5-bisphosphate carboxylase - VPD vapor pressure difference between leaf and air  相似文献   

17.
G. Röderer  H. -D. Reiss 《Protoplasma》1988,144(2-3):101-109
Summary Pollen tubes ofLilium longiflorum growingin vitro were treated for 1 h with inorganic lead (Pb) and with triethyl lead (TriEL) and studied by light and electron microscopy. Pb was considerably more toxic in relation to inhibition of pollen tube growth (EC50=6 M Pb) than was TriEL (EC50=60 M TriEL). On the other hand, at almost the entire concentration range tested (25-500 M) TriEL caused aberrant tubes and tube swellings. Pb did not cause tube swellings, even at highly growth-impairing concentrations. Pb (60 M) predominantly affected the ultrastructure of the growing cell walls without impairing the distribution of the cell organelles in the tube tips. In contrast, 50 and 100 M TriEL did not visibly influence cell wall ultrastructure but it severely damaged dictyosomes; 100 M TriEL also disturbed the original order of cell organelles in the tube tips. Cortical microtubules were selectively and completely destructed by TriEL at concentrations (50 M) where no effect on polar organization of the tube tips occurred but they remained unimpaired by 60 M Pb, indicating selective and effective interaction of TriEL with these cell organelles.Abbreviations EC50 effective lead concentration causing 50% inhibition of pollen tube growth - MTs microtubules - Pb inorganic lead - TriAL trialkyl lead - TriEL triethyl lead  相似文献   

18.
Midbrain slices containing the dorsal and medial raphe nuclei were prepared from rat brain in order to study serotonergic-GABAergic interaction. The slices were loaded with either [3H] serotonin or [3H]GABA, superfused and the electrically induced efflux of radioactivity was determined. The GABAA receptor agonist muscimol (3 to 30 M) and the GABAB receptor agonist baclofen (30 and 100 M) inhibited [3H]serotonin and [3H]GABA release. These effects of muscimol were reversed by the GABAA antagonists bicuculline (100 M). The GABAB antagonist phaclofen (100 M) also antagonized the baclofen-induced inhibition of [3H]serotonin and [3H]GABA release. Phaclofen by itself increased [3H]serotonin release but it did not alter [3H]GABA overflow. Muscimol (10 M) and baclofen (100 M) also inhibited [3H]serotonin release after depletion of GABAergic neurons by isoniazid pretreatment. These findings indicate the presence of postsynaptic GABAA and GABAB receptors located on serotonergic neurons. The 5-HT1A receptor agonist 8-OH-DPAT (0.01 to 1 M) and the 5-HT1B receptor agonist CGS-12066A (0.01 to 1 M) inhibited the electrically stimulated [3H]serotonin and [3H]GABA release. The 5-HT1A antagonist WAY-100135 (1 M) was without effect on [3H]serotonin and [3H]GABA efflux by itself but it reversed the 8-OH-DPAT-induced transmitter release inhibition. During KCl (22 mM)-induced depolarization, tetrodotoxin (1 M) did not alter the inhibitory effect of CGS-12066A (1 M) on [3H]GABA release, it did blocked, however, the ability of 8-OH-DPAT (1 M) to reduce [3H]GABA efflux. After depletion of raphe serotonin neurons by p-chlorophenylalanine pretreatment, CGS-12066A (1 M) still inhibited [3H]GABA release whereas in serotonin-depleted slices, 8-OH-DPAT (1 M) was without effect on the release. We conclude that reciprocal influence exists between serotonergic projection neurons and the GABAergic interneurons or afferents in the raphe nuclei and these interactions may be mediated by 5-HT1A/B and GABAA/B receptors. Both synaptic and non-synaptic neurotransmission may be operative in the 5-HTergic-GABAergic reciprocal interaction which may serve as a local tuning in the neural connection between cerebral cortex and midbrain raphe nuclei.  相似文献   

19.
Summary Accumulation of silver is reported for growing and non-growing populations of Citrobacter intermedius B6. In non-growing cultures a maximum uptake of 4.35% (w/w) was observed at an initial silver concentration of 2111.2 mol Ag+ l-1. In contrast the maximum uptake of silver by growing bacteria was 2.81% (w/w) at an effective concentration of silver of 217.8 mol·l-1. Silver accumulation rates in both resting (460 mol Ag+ g-1 per hour) and continuously grown (41 mol Ag+ g-1 per hour) bacteria are higher than previously reported. Cell fractionation and electron microscopy of continuously grown bacteria indicated that accumulation of silver was associated with the cell envelope, in the form of dense deposits of macromolecular proportions. This observation discounts simple surface adsorption as the process of accumulation in growing cultures.  相似文献   

20.
Chlorophyll (Chl) a and Chl b contents, rate of CO2 gas exchange, quenching coefficients of chlorophyll fluorescence, and endogenous phytohormones have been studied in primary leaves of barley seedlings cultivated under blue (BL) or red (RL) light. Photon flux densities (PFD) were between 0.3 and 12 mol m-2 s-1. Plants grown at PFD of 0.3 mol m-2 s-1 demonstrated in BL tenfold and in RL threefold decreased Chl content compared to plants grown at 12 mol m-2 s-1. Chl a/b ratio increased from 2.3–2.5 to 4.4–4.5 in BL, not in RL, following the decrease in PFD at plant cultivation from 12 to 0.3 mol m-2 s-1. Plants cultivated at weak BL demonstrated severalfold decreased rate of photosynthetic CO2 uptake, whereas decrease in PFD of RL from 12 to 0.3 mol m-2 s-1 caused only 20% de cline in the rate of photosynthesis. Decrease in PFD during a plant cultivation reduced the maximum quantum yield of photosynthesis in BL, not in RL leaves. Light response curves of non-photochemical and photochemical quenching of chlorophyll fluorescence calculated on the basis of absorbed quanta were not affected by PFD of RL during plant cultivation. On the contrary, both non-photochemical quenching and accumulation of QA -, reduced primary acceptor of Photosystem II, occurred at lower amounts of absorbed quanta in leaves of BL plants grown at 0.3 than at 12 mol m-2 s-1. Two photoregulatory reactions were suggested to exert the light control of the development of photosynthetic apparatus in the range of low PFDs. The photoregulatory reaction saturating by very low PFDs of RL was supposed to be mediated by phytochrome. Phytochrome was proposed to enhance (as related to other pigment-protein complexes of thylakoids) the accu mulation of chlorophyll- b-binding light-harvesting complex of Photosystem II (LHC II). It acts independently of the pigment mediating the second photoregulatory reaction, as evidenced by the results of experiments with plant growth under mixed blue plus red light. The contents of cytokinins and indole-3-acetic acid in a leaf were not significantly affected by either light quality and PFD thus indicating those phytohormones not to be involved into photoregulatory processes.  相似文献   

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