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1.
Photosynthesis of Ivy Leaves (Hedera helix) after Heat Stress I. CO2 -Gas Exchange and Diffusion Resistances 总被引:1,自引:0,他引:1
HELMUT BAUER 《Physiologia plantarum》1978,44(4):400-406
For an analysis of the inhibition of the photosynthetic CO2-uptake after heat stress attached leaves of Hedera helix L. were heat-stressed for 30 min at various temperatures. Subsequently their photosynthetic CO2-uptake, transpiration, respiration in light and darkness, and CO2-compensation concentration were measured under optimal conditions. After heat stress the stomatal resistance increased only corresponding to the raised CO2-concentration inside the leaves (due to the reduced CO2-uptake). The physical resistance between the mesophyll cell walls and the chloroplasts remained unchanged after heat stress. A non-stomatal inhibition of the CO2-uptake is indicated by a strong increase of the CO2-compensation concentration after heat stress. This is hardly due to a stimulation of the respiration in light, as the CO2-evolution into CO2-free air in light was even reduced. Therefore, it must be concluded that the photosynthetic process itself is impaired after heat stress. 相似文献
2.
Summary Measurements of gas exchange, xylem tension and nocturnal malate synthesis were conducted with well-watered and droughted plants of Kalanchoë uniflora. Corresponding results were obtained with plants grown in 9 h and 12 h photoperiods. In well-watered plants, 50 to 90% of total CO2-uptake occurred during the light period. Nocturnal CO2-uptake and malate synthesis were higher and respiration rate was lower in old leaves (leaf pairs 6 to 10) compared to young leaves (leaf pairs 1 to 5). Within four days of drought distinct physiological changes occurred. Gas exchange during the light period decreased and CO2-uptake during the dark period increased. Nocturnal malate synthesis significantly increased in young leaves.Respiration rate decreased during periods of drought, this decrease being more pronounced in young leaves compared to old leaves. Restriction of gas exchange during the light period resulted in a decrease of transpiration ratio from more than 100 to about 20. The difference between osmotic pressure and xylem tension decreased in young leaves, indicating a reduction in bulk leaf turgor-pressure.We conclude that both the CAM-enhancement in young leaves and the decrease of respiration rate are responsible for the increase of nocturnal CO2-uptake during water stress. During short drought periods, which frequently occur in humid habitats, the observed physiological changes result in a marked reduction of water loss while net CO2-uptake is maintained. This might be relevant for plant growth in the natural habitat.Abbreviations LP
light period
- DP
dark period
- CAM
crassulacean acid metabolism 相似文献
3.
CO(2) and O(2) Exchanges in the CAM Plant Ananas comosus (L.) Merr: Determination of Total and Malate-Decorboxylation-Dependent CO(2)-Assimilation Rates; Study of Light O(2)-Uptake
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Photosynthesis and light O2-uptake of the aerial portion of the CAM plant Ananas comosus (L.) merr. were studied by CO2 and O2 gas exchange measurements. The amount of CO2 which was fixed during a complete day-night cycle was equal to the amount of total net O2 evolved. This finding justifies the assumption that in each time interval of the light period, the difference between the rates of net O2-evolution and of net light atmospheric CO2-uptake give the rates of malate-decarboxylation-dependent CO2 assimilation. Based upon this hypothesis, the following photosynthetic characteristics were observed: (a) From the onset of the light to midphase IV of CAM, the photosynthetic quotient (net O2 evolved/net CO2 fixed) was higher than 1. This indicates that malate-decarboxylation supplied CO2 for the photosynthetic carbon reduction cycle during this period. (b) In phase III and early phase IV, the rate of CO2 assimilation deduced from net O2-evolution was 3 times higher than the maximum rate of atmospheric CO2-fixation during phase IV. A conceivable explanation for this stimulation of photosynthesis is that the intracellular CO2-concentration was high because of malate decarboxylation. (c) During the final hours of the light period, the photosynthetic quotient decreased below 1. This may be the result of CO2-fixation by phosphoenolpyruvate-carboxylase activity and malate accumulation. Based upon this hypothesis, the gas exchange data indicates that at least 50% of the CO2 fixed during the last hour of the light period was stored as malate. Light O2-uptake determined with 18O2 showed two remarkable characteristics: from the onset of the light until midphase IV the rate of O2-uptake increased progressively; during the following part of the light period, the rate of O2-uptake was 3.5 times higher than the maximum rate of CO2-uptake. When malate decarboxylation was reduced or suppressed after a night in a CO2-free atmosphere or in continuous illumination, the rate of O2-uptake was higher than in the control. This supports the hypothesis that the low rate of O2-uptake in the first part of the light period is due to the inhibition of photorespiration by increased intracellular CO2 concentration because of malate decarboxylation. In view of the law of gas diffusion and the kinetic properties of the ribulose-1,5-bisphosphate carboxylase/oxygenase, O2 and CO2 gas exchange suggest that at the end of the light period the intracellular CO2 concentration was very low. We propose that the high ratio of O2-uptake/CO2-fixation is principally caused by the stimulation of photorespiration during this period. 相似文献
4.
Variation in Photorespiration in Lolium 总被引:1,自引:0,他引:1
The rate of photorespiration in several grass species was shownto be highly variable and dependent on the species, genotype,and conditions under which the plants were grown. Photorespiration,measured as oxygen uptake, was negligible in Cenchrus ciliarisand Paspalum dilatatum but significant in Lolium spp. and Festucaarundinacea. There were significant differences in the rateof photorespiration among plants within a Lolium populationof diverse origin and these differences were independent ofthe conditions under which the plants were grown. Among thetemperate grasses there was a significant correlation betweenphotorespiration and the CO2-compensation concentration andboth parameters were very low in P. dilatatum. Plants grownin day/night temperatures of 15/10 °C compared with 25/20°C had faster rates of dark respiration but slower ratesof light respiration when measured at the same temperature.Photorespiration was faster than dark respiration although differencesin respiration among plants in the light were not shown in thedark. 相似文献
5.
Preillumination of leaves of spinach, soybean and maize in theabsence of CO2 greatly enhanced the capacity for fixing CO2in an immediately following dark period. Lightenhanced darkCO2-fixation was further observed in isolated chloroplasts ofspinach and soybean. When isolated chloroplasts were illuminated,CO2-fixing capacity in the subsequent dark period increasedrapidly at first and later more slowly attaining a stationaryvalue in about 20 min. When the light was turned off at thisstage, the capacity decreased very rapidly becoming zero inabout 10 min. The magnitude of the enhanced dark fixation andits decay in the dark were not influenced by the presence orabsence of atmospheric oxygen. In both leaves and isolated chloroplasts,no significant change in oxygen (21%) occurred in distributionpatterns of radioactivity in products fixed by photosynthetic,or light-enhanced, dark, 14CO2-fixation. In preilluminated leaves14C was incorporated into sucrose in the subsequent dark period,indicating that the photosynthetic carbon reduction cycle isoperating in light-enhanced dark fixation in higher plants.
1Present address: Noda Institute for Scientific Research, Noda,Chiba Prefecture (Received August 10, 1970; ) 相似文献
6.
Responses of tomato leaves in a greenhouse to light and CO2 were examined at the transient stage at the end of winter, when both photoperiod and irradiance gradually increase. Additionally, CO2 fluxes were calculated for a greenhouse without supplementary lighting and without CO2 enrichment based on CO2 sinks (plant photosynthesis) and CO2 sources (plant and substrate respiration). In January, tomato leaves in the greenhouse showed low photosynthesis with a maximum assimilation of 6–8 μmol CO2 m−2 s−1, a quantum yield of 0.06 μmol CO2 μmol−1 photosynthetic active radiation (PAR) and a low light compensation point of 26 μmol PAR m−2 s−1, a combination which classifies them as shade leaves. In February, tomato leaves increased their light compensation point to 39 μmol PAR m−2 s−1 and quantum yield to 0.08, the former indicating the adaptation to increased irradiance and photoperiod. These tomato leaves increased their transpiration from 0.4 to 0.9 in January to ∼2 mmol H2O m−2 s−1 in February. Both photosynthesis and transpiration were primarily limited by light but neither by stomatal conductivity nor by CO2. In January, light response of photosynthesis, dark respiration and transpiration were negligibly affected by increasing CO2 concentrations from 600 to 900 ppm CO2 under low light conditions, indicating no benefit of CO2 enrichment unless light intensity increased. In February, tomato leaves were photoinhibited at inherent greenhouse CO2 concentrations on the first sunny day; this photoinhibition was further enhanced by an increased CO2 concentration of 1000 ppm. CO2 fluxes in the greenhouse appeared strongly dependent on solar radiation. After exceeding the light compensation point in the morning, greenhouse CO2 concentrations decreased by 58 or by 110 ppm CO2 h−1 on a sunny day in January or February and by 23 ppm on overcast days in both months. Calculated per overall tomato canopy, plant photosynthesis contributed 42–50% to the morning CO2 depletion in the greenhouse. Dark respiration of tomato leaves was ∼2 μmol CO2 m−2 s−1 in January and ∼3 μmol CO2 m−2 s−1 in February. This dark respiration resulted in rises of 15 and 17 ppm CO2 h−1 at night in the greenhouse compartment and was identified as primary source of CO2. Respiration of the substrate used to grow the plants, which produced 7.3 ppm CO2 h−1, was identified as secondary source of CO2. The combined plant and substrate respiration resulted in peaks of up to 900 ppm CO2 in the greenhouse before dawn. 相似文献
7.
Simultaneous measurements of CO2 uptake, transpiration rate, and chlorophyll a fluorescence in leaf strips of C4 plants during the induction phase of photosynthesis are described. The timecourse of CO2 fixation is biphasic with the initial phase occurring within the first 1 to 5 min and the secondary phase consisting of a slow rise to the steady-state rate of photosynthesis. Transpiration rate follows the CO2-fixation timecourse closely but the intercellular CO2 concentration never falls below saturation for C4 plants. Chlorophyll a fluorescence quenching occurs exclusively during the initial fast phase of the CO2-fixation timecourse. The effect of duration of dark pretreatment of leaves on these parameters and the effects of light intensity and CO2 concentration are examined. These results are discussed with respect to the C4 cycle and photochemical and non-photochemical chlorophyll fluorescence quenching.Abbreviations IRGA
infra-red gas analyser
- NADP-ME, NAD-ME and PEP-CK
the three groups of C4 plants utilising the enzymes NADP-malic enzyme, NAD-malic enzyme and phosphoenolpyruvate carboxykinase, respectively, for C4-acid decarboxylation
- PEP
phosphoenolpyruvate
- 3-PGA
3-phosphoglyceric acid 相似文献
8.
Influence of light intensity at different temperatures on rate of respiration of douglas-fir seedlings 总被引:1,自引:1,他引:0
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Brix H 《Plant physiology》1968,43(3):389-393
The rate of photorespiration of Douglas-fir seedlings was measured under different light intensities by: (1) extrapolating the curve for CO2 uptake in relation to atmospheric CO2 content to zero CO2 content, and (2) measuring CO2 evolution of the plants into a CO2-free airstream. Different results, obtained from these techniques, were believed to be caused by a severe restriction of the photosynthetic activity when the latter was used. With the first method, CO2 evolution was lower than the dark respiration rate at low light intensity. For all temperatures studied (6°, 20°, 28°) a further increase in light intensity raised the CO2 evolution above dark respiration before it leveled off. The rate of CO2 evolution was stimulated by increase in temperature at all light intensities. With the CO2-free air method, CO2 evolution in the light was less than dark respiration at all light intensities. 相似文献
9.
Heterotrophic activity in macroalgae has been little studied, but the red macroalga Grateloupia doryphora is known to grow in light at a higher rate in a glycerol-containing medium than in seawater. The effects of 0·1 M exogenous glycerol in seawater (SW90-gly) on the respiration rate of G. doryphora and the role played by light were investigated. The algae pretreated for 2 h in the light and in SW90-gly evolved oxygen and fixed carbon dioxide (H14CO3 ?), but also evolved radioactive 14CO2 from [14C]glycerol. The rate of oxygen evolution was lower than that of samples in seawater, due to a high respiration rate and/or a partial inhibition of photosynthesis induced by glycerol. In contrast, the rate of inorganic carbon fixation was higher in SW90-gly than in control samples in seawater, suggesting that non-photosynthetic patterns were operating. In darkness, after pretreatment in the light in SW90-gly, samples showed a high oxygen uptake rate just after the light was turned off. Twenty minutes of darkness were enough to decrease this high respiration rate to that of samples in seawater. The oxygen uptake observed in all experiments with glycerol was mitochondrial as it was inhibited by potassium cyanide and salicylhydroxamic acid (SHAM). Pretreatment of samples in the light in SW90-gly with the photosynthetic inhibitor DCMU did not inhibit ensuing dark respiration, thus providing evidence for a non-photosynthetic effect of the light. The highest dark respiration rate was observed after the samples were pretreated in monochromatic blue light in glycerol-containing media. 相似文献
10.
Effect of oxygen on photosynthesis, photorespiration and respiration in detached leaves. I. Soybean 总被引:52,自引:47,他引:5
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The effect of O2 on the CO2 exchange of detached soybean leaves was measured with a Clark oxygen electrode and infrared carbon dioxide analysers in both open and closed systems.
The rate of apparent photosynthesis was inhibited by O2 while the steady rate of respiration after a few minutes in the dark was not affected. Part of the inhibition of apparent photosynthesis was shown to be a result of increased photorespiration. This stimulation of photorespiration by O2 was manifested by an increase in the CO2 compensation point.
The differential effects of O2 on dark respiration (no effect) and photorespiration (stimulation) indicated that these were 2 different processes.
Moreover the extrapolation of the CO2 compensation point to zero at zero O2 indicated that dark respiration was suppressed in the light at least at zero O2 concentration.
相似文献11.
Carbon exchange rates of shoots required to utilize available acetylene reduction capacity in soybean and alfalfa root nodules 总被引:3,自引:3,他引:0
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The CO2-exchange rate required to make full use of available N2-fixation capacity, measured as acetylene reduction, was determined in soybean and alfalfa. Carbohydrates of root systems were depleted during a 40-hour dark treatment; then plants were exposed to a 24-hour light period during which different CO2-exchange rates were maintained with various CO2 concentrations. In three- and four-week-old soybeans and four-week-old alfalfa plants, acetylene-reduction capacity was used fully with CO2-exchange rates as low as 10 milligrams CO2 per plant per hour. In six-week-old alfalfa plants, however, acetylene reduction rates increased linearly, and apparent N2-fixation capacity was not used fully when CO2-exchange rates were higher than 40 milligrams CO2 per plant per hour. Under the conditions established, the energy cost of N2 fixation, measured as Δ(respiration of roots + nodules)/Δacetylene reduction over dark-treatment values, was 0.453 milligrams CO2 per micromole C2H4 for all rates of acetylene reduction and for both ages of soybean and alfalfa plants. Thus, root-plus-nodule respiration was not promoted by higher rates of apparent photosynthesis after C2H2-reduction capacity became saturated, and all available capacity for apparent N2 fixation had the same energy requirement. 相似文献
12.
Effect of changes in shoot carbon-exchange rate on soybean root nodule activity 总被引:7,自引:3,他引:4
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The effect of short- and long-term changes in shoot carbon-exchange rate (CER) on soybean (Glycine max [L.] Merr.) root nodule activity was assessed to determine whether increases in photosynthate production produce a direct enhancement of symbiotic N2 fixation. Shoot CER, root + nodule respiration, and apparent N2 fixation (acetylene reduction) were measured on intact soybean plants grown at 700 microeinsteins per meter per second, with constant root temperature and a 14/10-hour light/dark cycle. There was no diurnal variation of root + nodule respiration or apparent N2 fixation in plants assayed weekly from 14 to 43 days after planting. However, if plants remained in darkness following their normal dark period, a significant decline in apparent N2 fixation was measured within 4 hours, and decreasing CO2 concentration from 320 to 90 microliters CO2 per liter produced diurnal changes in root nodule activity. Increasing shoot CER by 87, 84, and 76% in 2-, 3-, and 4-week-old plants, respectively, by raising the CO2 concentration around the shoot from 320 to 1,000 microliters CO2 per liter, had no effect on root + nodule respiration or acetylene-reduction rates during the first 10 hours of the increased CER treatment. When the CO2-enrichment treatment was extended in 3-week-old plants, the only measured parameter that differed significantly after 3 days was shoot CER. After 5 days of continuous CO2 enrichment, root + nodule respiration and acetylene reduction increased, but such changes reflected an increase in root nodule mass rather than greater specific root nodule activity. The results show that on a 24-hour basis the process of symbiotic N2 fixation in soybean plants grown under controlled environmental conditions functioned at maximum capacity and was not limited by shoot CER. Whether N2-fixation capacity was limited by photosynthate movement to root nodules or by saturation of metabolic processes in root nodules is not known. 相似文献
13.
Muhlenbergia sobolifera (Muhl.) Trin., a C4 grass, occurs in understory habitats in the northeastern United States. Plants of M. sobolifera were grown at 23 and 30°C at 150 and 700 μmol photons m−2 s−1. The photosynthetic CO2 compensation point, maximum CO2 assimilation, dark respiration and the absorbed quantum use efficiency (QUE) were measured at 23 and 30°C at 2 and 20% O2. Photosynthetic CO2 compensation points ranged from 4 to 14mm3 dm−3 CO2 and showed limited O2 sensitivity. The mean photosynthetic CO2 compensation point of plants grown at 30°C (4·5 mm3 dm−3) was 57% lower and 80% less inhibited by O2 than that of plants grown at 23°C. Photosynthesis was similarly affected by growth temperature, with 70% more O2 inhibition in plants grown at 23°C; suppression over all treatments ranging from 2 to 11%. Unlike typical C4 species, plants of M. sobolifera from both temperature regimes exhibited higher CO2 assimilation rates when grown at low light. Growth temperature and light also affected QUE; plants grown at low light and 23°C had the highest value (0·068 mol CO2/mol quanta). Measurement temperature and growth light regime significantly affected dark respiration; however, O2 did not affect QUE or dark respiration under any growth or measurement conditions. The results indicate that M. sobolifera is adapted to low PPFD, and that complete suppression of photorespiration is dependent upon high growth temperature. 相似文献
14.
Two year old sweet chestnut seedlings (Castanea sativa Mill) were grown in pots at ambient (350 µmol·mol–1) and double (700 µmol·mol–1) atmospheric CO2 concentration in constantly ventilated greenhouses during entire growing seasons. CO2 enrichment caused either no significant change or a decrease in shoot response, depending on yearly weather conditions. Similarly, leaf area was either reduced or unchanged under elevated CO2. However, when grown under controlled conditions in a growth chamber, leaf area was enlarged with elevated CO2.The CO2 exchanges of whole plants were measured during the growing season. In elevated CO2, net photosynthetic rate was maximum in May and then decreased, reaching the level of the control at the end of the season. End of night dark respiration of enriched plants was significantly lower than that of control plants; this difference decreased with time and became negligible in the fall. The original CO2 level acted instantaneously on the respiration rate: a double concentration in CO2 decreased the respiration of control plants and a reduced concentration enhanced the respiration of enriched plants. The carbon balance of a chestnut seedling may then be modified in elevated CO2 by increased carbon inputs and decreased carbon outputs. 相似文献
15.
In continuous cultures of Chlorella fusca under steady state conditions, the CO2-fixation rate, the ATP-level, the apparent rate of photophosphorylation as calculated from the changes in the ATP-level during light to dark or dark to light transients and the energy charge were measured at various environmental conditions. During growth the energy charge was around 0.64. CO2-assimilation and the apparent ATP-synthesis were strongly dependant on light intensity, however the ATP-level was independant on it. Since the rates of apparent ATP-synthesis and of the CO2-fixation do not seem to be strictly correlated in a logic way when environmental factors are changed and furthermore the stoichiometry of 3 ATP necessary per CO2 fixed was never achieved, the described method frequently used for procaryotes to determine the in vivo rate of phosphorylation does not give valid results in highly compartimented eukaryotic cells. 相似文献
16.
K. W. Brown 《Physiologia plantarum》1969,22(3):620-637
A model is proposed for the relationship between net photosynthetic rate (N) and light Intensity at a given concentration of CO2 in the air ([CO2]a). The model provides a prediction of the sum of the diffusion resistances (Σr), the capacity (K) of the leaf to fix CO2, the concentration of CO2 at the point of photosynthesis ([CO2]g), and the respiration rate (R). The model fits the available data well and provides a frame work by which future research may be guided. The calculated values of [CO2]g decreased from [CO2]g at the compensation point to a nearly constant value at high tight intensities. [CO2]g high light infensitit-s range from 32 to 144 μ/l (volume) depending on the species. When these values of [CO2]g, are used in the diffusion equation, the resulting levels of the mesophyll resistance (rm) are lower than those calculated by using the assumptions that [CO2]g equals zero. The plants which had (he higher photosynthetic rates at a given light intensity and [CO2]a had grealer values of [CO2]g than those with lower photo-synthetic rates. The calculated rates of respiration of wheat leaves were twice as high as those measured in the dark. This suggests that the light respiration rate may be twice as great as the dark respiration rate at the same temperature. The calculated values of K demonstrate variability within and between species. The maximum N was independent of K. A relationship between K and the maximum quantum efficiency, at constant levels of [CO2]g, was demonstrated in several species. The Σr was inversely related to the maximum rate of photosynthesis for the species investigated. The values of rm calculated for cotton were inversely related to [CO2]a suggesting that the transfer of [CO2] in the cell may involve a concentration dependent chemical reaction in addition to or rather than a physical diffusion process. 相似文献
17.
Prechilling of Xanthium strumarium L. Reduces Net Photosynthesis and, Independently, Stomatal Conductance, While Sensitizing the Stomata to CO(2) 总被引:8,自引:8,他引:0
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Greenhouse-grown plants of Xanthium strumarium L. were exposed in a growth cabinet to 10 C during days and 5 C during nights for periods of up to 120 hours. Subsequently, CO2 exchange, transpiration, and leaf temperature were measured on attached leaves and in leaf sections at 25 or 30 C, 19 C dew point of the air, 61 milliwatts per square centimeter irradiance, and CO2 concentrations between 0 and 1000 microliters per liter ambient air. Net photosynthesis and stomatal conductance decreased and dark respiration increased with increasing duration of prechilling. The reduction in net photosynthesis was not a consequence of decreased stomatal conductance because the intercellular CO2 concentration in prechilled leaves was equal to or greater than that in greenhouse-grown controls. The intercellular CO2 concentration at which one-half maximum net photosynthesis occurred remained the same in prechilled leaves and controls (175 to 190 microliters per liter). Stomata of the control plants responded to changes in the CO2 concentration of the air only slightly. Prechilling for 24 hours or more sensitized stomata to CO2; they responded to changes in CO2 concentration in the range from 100 to 1000 microliters per liter. 相似文献
18.
Activity regulation and physiological impacts of maize C4-specific phosphoenolpyruvate carboxylase overproduced in transgenic rice plants 总被引:6,自引:0,他引:6
Fukayama H Hatch MD Tamai T Tsuchida H Sudoh S Furbank RT Miyao M 《Photosynthesis research》2003,77(2-3):227-239
Phosphoenolpyruvate carboxylase (PEPC) was overproduced in the leaves of rice plants by introducing the intact maize C4-specific PEPC gene. Maize PEPC in transgenic rice leaves underwent activity regulation through protein phosphorylation in
a manner similar to endogenous rice PEPC but contrary to that occurring in maize leaves, being downregulated in the light
and upregulated in the dark. Compared with untransformed rice, the level of the substrate for PEPC (phosphoenolpyruvate) was slightly lower and the product (oxaloacetate) was slightly higher in transgenic rice, suggesting that maize
PEPC was functioning even though it remained dephosphorylated and less active in the light. 14CO2 labeling experiments indicated that maize PEPC did not contribute significantly to the photosynthetic CO2 fixation of transgenic rice plants. Rather, it slightly lowered the CO2 assimilation rate. This effect was ascribable to the stimulation of respiration in the light, which was more marked at lower
O2 concentrations. It was concluded that overproduction of PEPC does not directly affect photosynthesis significantly but it
suppresses photosynthesis indirectly by stimulating respiration in the light. We also found that while the steady-state stomatal
aperture remained unaffected over a wide range of humidity, the stomatal opening under non-steady-state conditions was destabilized
in transgenic rice.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
19.
Photorespiration and Glycolate Metabolism: A Re-examination and Correlation of Some Previous Studies 总被引:11,自引:8,他引:3
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Some previous studies of photorespiration and glycolate oxidation were re-examined and correlated by infra-red CO2 analysis. Data about rate of photosynthesis and oxygen sensitivity indicated that complete inhibition of photosynthesis with 3-(3,4-dichlorophenyl)-1,1 dimethyl urea (DCMU) allowed dark respiration to continue in the light. Photorespiration was also inhibited. The oxygen sensitivity of glycolate-stimulated CO2 production was found to be compatible with the proposal that glycolate is a substrate of photorespiration. Both `in vivo' and `in vitro' studies of the alga Nitella flexilis have revealed a pathway of glycolate oxidation similar to that of higher plants. DCMU inhibition of photosynthesis by Nitella gave results similar to those for the monocotyledons tested. Under very low light intensity, carbon dioxide compensation in corn was measurable but was not sensitive to high oxygen concentration. It appears that the lack of photorespiration in this plant is not the end result of efficient internal recycling of CO2 to photosynthesis. 相似文献
20.
Rates of carbon transport from a single mature tomato leaf inthe light period (day transport) and the dark period (nighttransport) were estimated from the rate of carbon fixation inthe light period, the rate of respiration in the dark periodand the changes in carbon contents over these two periods. Plantswere grown initially at 40 W m2 light intensity witheither 350 vpm (nonenriched plants) or 1000 vpm CO2 (enrichedplants). Various light flux densities or CO2 concentrationswere then applied to the experimental leaves in the light periodduring the experiment When leaves were temporarily exposed to contrasting light fluxdensities both day transport and night transport were linearlyrelated to the rate of carbon fixation. If leaves were shadedbelow the light compensation point for up to five days, or transferredto contrasting CO2 concentrations for up to ten days, the linearrelationship between carbon fixation and carbon transport nolonger held. During acclimatization, therate of wbon fixationwas simply related to thecurrent light flux density and CO2concentration, but the rate of carbon transport changed withtime. Day and night transports responded differently to changesin environment: night transport was more related to the contentof reserve, particularly starch, than to the rate of concurrentwbon fixation. It is concluded that the rate of carbon transport of a maturetomato leaf in a single photoperiod is regulated not merelyby the rate of concurrent carbon fixation but by the contentof reserve in the leaf. The latter results from previous cumulativewbon fixation and carbon transport. As a result of changingthe rate of carbon transport, a balance of carbon input andoutput was achieved within 10 days of acclimatization in a maturetomato leaf. 相似文献