共查询到20条相似文献,搜索用时 15 毫秒
1.
Rates of CO 2 assimilation and steady state chlorophyll a fluorescence were measured simultaneously at different intercellular partial pressures of CO 2 in attached cotton ( Gossypium hirsutum L. cv Deltapine 16) leaves at 25°C. Electron transport activity for CO 2 assimilation plus photorespiration was calculated for these experiments. Under light saturating (1750 microeinsteins per square meter per second) and light limiting (700 microeinsteins per square meter per second) conditions there was a good correlation between fluorescence and the calculated electron transport activity at 19 and 200 millibars O 2, and between fluorescence and rates of CO 2 assimilation at 19 millibars but not 200 millibars O 2. The values of fluorescence measured at about 220 microbars intercellular CO 2 were not greatly affected by increasing O 2 from 19 to 800 millibars. Fluorescence increased with light intensity at any one intercellular CO 2 partial pressure. But the values obtained for fluorescence, expressed as a ratio of the maximum fluorescence obtained in DCMU-treated tissue, over the same range of CO 2 partial pressure at 500 microeinsteins per square meter per second were similar to those obtained at 1000 and 2000 microeinsteins per square meter per second. There were two phases in the observed correlation between fluorescence and calculated electron transport activity: an initial inverse relationship at low CO 2 partial pressures which reversed to a positive correlation at higher values of CO 2 partial pressures. Similar results were observed in the C 3 species Helianthus annuus L., Phaseolus vulgaris L., and Brassica chinensis. In all C 4 species ( Zea mays L., Sorghum bicolor L., Panicum maximum Jacq., Amaranthus edulis Speg., and Echinochloa frumentacea [Roxb.] Link) examined changes in fluorescence were directly correlated with changes in CO 2 assimilation rates. The nature and the extent to which Q (primary quencher) and high-energy state ( qE) quenching function in determining the steady state fluorescence obtained during photosynthesis in leaves is discussed. 相似文献
2.
Castor bean ( Ricinus communis L.) has a high photosynthetic capacity under high humidity and a pronounced sensitivity of photosynthesis to high water vapor pressure deficit (VPD). The sensitivity of photosynthesis to varying VPD was analyzed by measuring CO 2 assimilation, stomatal conductance ( gs), quantum yield of photosystem II ( II), and nonphotochemical quenching of chlorophyll fluorescence ( qN) under different VPD. Under both medium (1000) and high (1800 micromoles quanta per square meter per second) light intensities, CO 2 assimilation decreased as the VPD between the leaf and the air around the leaf increased. The gs initially dropped rapidly with increasing VPD and then showed a slower decrease above a VPD of 10 to 20 millibars. Over a temperature range from 20 to 40°C, CO 2 assimilation and gs were inhibited by high VPD (20 millibars). However, the rate of transpiration increased with increasing temperature at either low or high VPD due to an increase in gs. The relative inhibition of photosynthesis under photorespiring (atmospheric levels of CO 2 and O 2) versus nonphotorespiring (700 microbars CO 2 and 2% O 2) conditions was greater under high VPD (30 millibars) than under low VPD (3 millibars). Also, with increasing light intensity the relative inhibition of photosynthesis by O 2 increased under high VPD, but decreased under low VPD. The effect of high VPD on photosynthesis under various conditions could not be totally accounted for by the decrease in the intercellular CO 2 in the leaf (C i) where C i was estimated from gas exchange measurements. However, estimates of C i from measurements of II and qN suggest that the decrease in photosynthesis and increase in photorespiration under high VPD can be totally accounted for by stomatal closure and a decrease in C i. The results also suggest that nonuniform closure of stomata may occur in well-watered plants under high VPD, causing overestimates in the calculation of C i from gas exchange measurements. Under low VPD, 30°C, high light, and saturating CO 2, castor bean (C 3 tropical shrub) has a rate of photosynthesis (61 micromoles CO 2 per square meter per second) that is about 50% higher than that of tobacco (C 3) or maize (C 4) under the same conditions. The chlorophyll content, total soluble protein, and ribulose-1,5-bisphosphate carboxylase/oxygenase level on a leaf area basis were much higher in castor bean than in maize or tobacco, which accounts for its high rates of photosynthesis under low VPD. 相似文献
3.
Leaves of C 3 plants which exhibit a normal O 2 inhibition of CO 2 fixation at less than saturating light intensity were found to exhibit O 2-insensitive photosynthesis at high light. This behavior was observed in Phaseolus vulgaris L., Xanthium strumarium L., and Scrophularia desertorum (Shaw.) Munz. O 2-insensitive photosynthesis has been reported in nine other C 3 species and usually occurred when the intercellular CO 2 pressure was about double the normal pressure. A lack of O 2 inhibition of photosynthesis was always accompanied by a failure of increased CO 2 pressure to stimulate photosynthesis to the expected degree. O 2-insensitive photosynthesis also occurred after plants had been water stressed. Under such conditions, however, photosynthesis became O 2 and CO 2 insensitive at physiological CO 2 pressures. Postillumination CO 2 exchange kinetics showed that O 2 and CO 2 insensitivity was not the result of elimination of photorespiration. It is proposed that O2 and CO2 insensitivity occurs when the concentration of phosphate in the chloroplast stroma cannot be both high enough to allow photophosphorylation and low enough to allow starch and sucrose synthesis at the rates required by the rest of the photosynthetic component processes. Under these conditions, the energy diverted to photorespiration does not adversely affect the potential for CO2 assimilation. 相似文献
4.
When leaflets of bean and leaves of other species of C 3 plants are illuminated in the absence of CO 2 and at low O 2 partial pressure, the capacity for CO 2 assimilation at saturating light and its efficiency at low light intensities are inhibited. This photoinhibition is dependent on leaflet age and period of illumination. In young leaflets and following short exposure to these photoinhibitory conditions, some recovery of CO 2 assimilation capacity is observed immediately after treatment. Following substantial (70 to 80%) photoinhibition of CO 2 assimilation, recovery in fully expanded leaflets is observed only after 48 hours in normal air. The photoinhibition is largely prevented by providing CO 2 at partial pressures equivalent to the CO 2 compensation point, or by >210 millibars O 2 which permits internal CO 2 production by photorespiration. If leaflets are illuminated in 60 microbars CO 2 and 210 millibars O 2 (the CO 2 compensation point in air), no photoinhibition is observed. Electron transport processes and fluorescence emission associated with photosystem II are inhibited in chloroplast thylakoids isolated from leaflets after illumination in zero CO 2 and 10 millibars O 2. These studies support the hypothesis that CO 2 recycling through photorespiration is one means of effectively dissipating excess photochemical energy when CO 2 supply to illuminated leaves is limited. 相似文献
5.
The postillumination transient of CO 2 exchange and its relation to photorespiration has been examined in leaf discs from tobacco ( Nicotiana tabacum) and maize ( Zea mays). Studies of the transients observed by infrared gas analysis at 1, 21, and 43% O 2 in an open system were extended using the nonsteady state model described previously (Peterson and Ferrandino 1984 Plant Physiol 76: 976-978). Cumulative CO 2 exchange equivalents ( i.e. nanomoles CO 2) versus time were derived from the analyzer responses of individual transients. In tobacco (C 3), subtraction of the time course of cumulative CO 2 exchange under photorespiratory conditions (21 or 43% O 2) from that obtained under nonphotorespiratory conditions (1% O 2) revealed the presence of an O 2-dependent and CO 2-reversible component within the first 60 seconds following darkening. This component was absent in maize (C 4) and at low external O 2:CO 2 ratios ( i.e. <100) in tobacco. The size of the component in tobacco increased with net photosynthesis as irradiance was increased and was positively associated with inhibition of net photosynthesis by O 2. This relatively simple and rapid method of analysis of the transient is introduced to eliminate some uncertainties associated with estimation of photorespiration based on the maximal rate of postillumination CO 2 evolution. This method also provides a useful and complementary tool for detecting variation in photorespiration. 相似文献
6.
A controlled atmospheric-environment system (CAES) designed to sustain normal or hypobaric ambient growing conditions was developed, described, and evaluated for its effectiveness as a research tool capable of controlling ethylene-induced leaf senescence in intact plants of Phaseolus vulgaris L. Senescence was prematurely-induced in primary leaves by treatment with 30 parts per million ethephon. Ethephon-derived endogenous ethylene reached peak levels within 6 hours at 26°C. Total endogenous ethylene levels then temporarily stabilized at approximately 1.75 microliters per liter from 6 to 24 hours. Thereafter, a progressive rise in ethylene resulted from leaf tissue metabolism and release. Throughout the study, the endogenous ethylene content of ethephon-treated leaves was greater than that of nontreated leaves. Subjecting ethephon-treated leaves to atmospheres of 200 millibars, with O2 and CO2 compositions set to approximate normal atmospheric partial pressures, prevented chlorophyll loss. Alternately, subjecting ethephon-treated plants to 200 millibars of air only partially prevented chlorophyll loss. Hypobaric conditions (200 millibars), with O2 and CO2 at normal atmospheric availability, could be delayed until 48 hours after ethephon treatment and still prevent most leaf senescence. In conclusion, hypobaric conditions established and maintained within the CAES prevented ethylene-induced senescence (chlorosis) in intact plants, provided O2 and CO2 partial pressures were maintained at levels approximating normal ambient availability. An unexpected increase in endogenous ethylene was detected within nontreated control leaves 48 hours subsequent to relocation from winter greenhouse conditions (latitude, 42°00″ N) to the CAES operating at normal ambient pressure. The longer photoperiod and/or higher temperature utilized within the CAES are hypothesized to influence ethylene metabolism directly and growth-promotive processes (e.g. response thresholds) indirectly. 相似文献
7.
In well-watered plants of Welwitschia mirabilis, grown in the glass-house under high irradiance conditions, net CO 2 assimilation was almost exclusively observed during the daytime. The plants exhibited a very low potential for Crassulacean acid metabolism, which usually resulted in reduced rates of net CO 2 loss for several hours during the night. In leaves exposed to the diurnal changes in temperature and humidity typical of the natural habitats, CO 2 assimilation rates in the light were markedly depressed under conditions resembling those occurring during midday, when leaf temperatures and the leaf-air vapor pressure differences were high (36°C and 50 millibars bar −1, respectively). Studies on the relationship between CO 2 assimilation rate and intercellular CO 2 partial pressure at various temperatures and humidities showed that this decrease in CO 2 assimilation was largely due to stomatal closure. The increase in the limitation of photosynthesis by CO 2 diffusion, which is associated with the strong decline in stomatal conductance in Welwitschia exposed to midday conditions, may significantly contribute to the higher 13C content of Welwitschia compared to the majority of C 3 species. 相似文献
8.
Rates of CO 2 assimilation and leaf conductances to CO 2 transfer were measured in plants of Zea mays during a period of 14 days in which the plants were not rewatered, and leaf water potential decreased from −0.5 to −8.0 bar. At any given ambient partial pressure of CO 2, water stress reduced rate of assimilation and leaf conductance similarly, so that intercellular partial pressure of CO 2 remained almost constant. At normal ambient partial pressure of CO 2, the intercellular partial pressure of CO 2 was estimated to be 95 microbars. This is the same as had been estimated in plants of Zea mays grown with various levels of nitrogen supply, phosphate supply and irradiance, and in plants of Zea mays examined at different irradiances. After leaves of Phaseolus vulgaris L. and Eucalyptus pauciflora Sieb. ex Spreng had been exposed to high irradiance in an atmosphere of CO2-free N2 with 10 millibars O2, rates of assimilation and leaf conductances measured in standard conditions had decreased in similar proportions, so that intercellular partial pressure of CO2 remained almost unchanged. As the conductance of each epidermis that had not been directly irradiated had declined as much as that in the opposite, irradiated surface it was hypothesized that conductance may have been influenced by photoinhibition within the mesophyll tissue. 相似文献
9.
The sensitivity of photosynthesis to O 2 and CO 2 was measured in leaves from field grown plants of six species ( Phaseolus vulgaris, Capsicum annuum, Lycopersicon esculentum, Scrophularia desertorum, Cardaria draba, and Populus fremontii) from 5°C to 35°C using gas-exchange techniques. In all species but Phaseolus, photosynthesis was insensitive to O 2 in normal air below a species dependent temperature. CO 2 insensitivity occurred under the same conditions that resulted in O 2 insensitivity. A complete loss of O 2 sensitivity occurred up to 22°C in Lycopersicon but only up to 6°C in Scrophularia. In Lycopersicon and Populus, O 2 and CO 2 insensitivity occurred under conditions regularly encountered during the cooler portions of the day. Because O 2 insensitivity is an indicator of feedback limited photosynthesis, these results indicate that feedback limitations can play a role in determining the diurnal carbon gain in the field. At higher partial pressures of CO 2 the temperature at which O 2 insensitivity occurred was higher, indicating that feedback limitations in the field will become more important as the CO 2 concentration in the atmosphere increases. 相似文献
10.
Steady-state room temperature variable fluorescence from leaves was measured as a function of CO 2 pressure in Xanthium strumarium L. and Phaseolus vulgaris L. Measurements were made in a range of light intensities, at normal and low O 2 parital pressure and over a range of temperatures. At low CO 2 pressure fluorescence increased with increasing CO 2. At higher CO 2 pressure fluorescence usually decreased with increasing CO 2 but occasionally increased slightly. The transition CO 2 pressure between the responses could be changed by changing light, O 2 pressure, or temperature. This breakpoint in the fluorescence-CO 2 curve was a reliable indicator of the transition between ribulose 1,5-bisphosphate (RuBP) saturated assimilation and RuBP regeneration limited assimilation. The fluorescence signal was not a reliable indicator of O 2-insensitive assimilation in these C 3 species. 相似文献
11.
An open system associated with an infrared gas analyzer was employed to study transients in CO 2 exchange generated upon darkening preilluminated leaf discs of tobacco ( Nicotiana tabacum vars John Williams Broadleaf and Havana Seed). An empirical formula presented previously enabled prediction of the analyzer response under nonsteady state conditions as a function of time and of the leaf CO 2 exchange rate. A computer was used to evaluate parameters of the leaf CO 2 release rate to provide an estimate of the initial rate of postillumination CO 2 evolution and to produce maximal agreement between predicted and observed analyzer responses. In 21% O 2, the decline in rate of CO 2 evolution upon darkening followed first order kinetics. Initial rates of CO 2 evolution following darkening were relatively independent of the prior ambient CO 2 concentrations. However, rates of photorespiration expressed as a fraction of net photosynthesis declined rapidly with increasing external CO 2 concentration at 21% O 2. Under normal atmospheric conditions, photorespiration was 45 to 50% of the net CO 2 fixation rate at 32°C and high irradiance. The rapid initial CO 2 evolution observed upon darkening at 21% O 2 was absent in 3% O 2. Rates of photorespiration under normal atmospheric concentrations of CO 2 and O 2 as measured by the postillumination burst were highly dependent upon temperature (observed activation energy = 30.1 kilocalories per mole). The results are discussed with respect to previously published estimates of photorespiration in C 3 leaf tissue. 相似文献
12.
Assimilatory power was measured in ten C 3 species by means of a rapid-response gas exchange device as the total amount of CO 2 fixed in N 2-CO 2 atmosphere after switching the light off. Different steady-state levels of the assimilatory power were obtained by varying light intensity and O 2 and CO 2 concentrations during the preexposition periods in the leaf chamber. Within the limits of the linear part of the CO2 curve of photosynthesis in N2, the assimilatory power is constant, being sufficient for the assimilation of about 20 nanomoles CO2 per square centimeter leaf. The pool starts to decrease with the onset of the CO2 saturation of photosynthesis. Increase in O2 concentration from 0 to 100% at 350 microliters CO2 per liter produces a considerable decrease in the assimilatory power. The mesophyll conductance (M) was found to be proportional to the assimilatory power (A): M = mA. The most frequently occurring values of the proportionality constant (m) (called the specific efficiency of carboxylation) were concentrated between 0.03 and 0.04 centimeter per second per nanomole A per square centimeter but the measured extreme values were 0.01 and 0.06 centimeter per second per nanomole A per square centimeter. The specific rate of carboxylation (the rate per unit A) showed a hyperbolic dependence on CO2 conentration with the most frequent values of Km (CO2) ranging from 25 to 35 micromolar in the liquid phase of mesophyll cells (extremes 23 and 100 micromolar). It is concluded that the CO2− and light-saturated rate of photosynthesis is limited by the reactions of the formation of the assimilatory power and not by ribulose-1,5-bisphosphate carboxylase. O2 is a competitive consumer of the assimilatory power, and the inhibitory effect of O2 on photosynthesis is caused mainly by a decrease in the pool of the assimilatory power at high O2 concentrations. In intact leaves, the kinetic properties of ribulose-1,5-bisphosphate carboxylase seem to be variable. 相似文献
13.
The magnitude of the percentage inhibition of photosynthesis by atmospheric levels of O 2 in the C 3 species Solanum tuberosum L., Medicago sativa L., Phaseolus vulgaris L., Glycine max L., and Triticum aestivum L. increases in a similar manner with an increase in the apparent solubility ratio of O 2/CO 2 in the leaf over a range of solubility ratios from 25 to 45. The solubility ratio is based on calculated levels of O 2 and CO 2 in the intercellular spaces of leaves as derived from whole leaf measurements of photosynthesis and transpiration. The solubility ratio of O 2/CO 2 can be increased by increased leaf temperature under constant atmospheric levels of O 2 and CO 2 (since O 2 is relatively more soluble than CO 2 with increasing temperature); by increasing the relative levels of O 2/CO 2 in the atmosphere at a given leaf temperature, or by increased stomatal resistance. If the solubility ratio of O 2/CO 2 is kept constant, as leaf temperature is increased, by varying the levels of O 2 or CO 2 in the atmosphere, then the percentage inhibition of photosynthesis by O 2 is similar. The decreased solubility of CO 2 relative to O 2 (decreased CO 2/O 2 ratio) may be partly responsible for the increased percentage inhibition of photosynthesis by O 2 under atmospheric conditions with increasing temperature. 相似文献
14.
The specificity factor of Rubisco ( S f) was estimated in intact leaves from the carboxylation of ribulose-1,5-bisphosphate (RuBP) at various CO 2/O 2 ratios. As oxygenation is calculated by the difference of the 14CO 2 uptake by RuBP in the absence and presence of oxygen, it is important to choose the optimum CO 2/O 2 ratios. At high CO 2 concentration (1,000 cm 3 m ?3 and higher) oxygenation consumes less than 50% RuBP but the difference of concentrations of CO 2 at cell walls ( C w) and at the carboxylation centers ( C c) is 2?C5% and the influence of mesophyll resistance ( r md) is of minor importance. To accumulate large endogenous pool of RuBP, the leaves were preilluminated in the CO 2- and O 2-free gas environments for 8 to 10 s. Thereafter the light was switched off and the leaves were flushed with the gas containing different concentrations of 14CO 2 and O 2. The specificity factor of Rubisco was calculated from the amount of the tracer taken up under different 14CO 2/O 2 ratios by the exhaustion of the RuBP pool. Application of 14CO 2 allowed us to discriminate between the CO 2 uptake and the concurrent respiratory CO 2 release which proceeded at the expense of unlabelled intermediates. 相似文献
15.
The interactive effects of irradiance and O 2 and CO 2 levels on the quantum yields of photosystems I and II have been studied under steady-state conditions at 25°C in leaf tissue of tobacco ( Nicotiana tabacum). Assessment of radiant energy utilization in photosystem II was based on changes in chlorophyll fluorescence yield excited by a weak measuring beam of modulated red light. Independent estimates of photosystem I quantum yield were based on the light-dark in vivo absorbance change at 830 nanometers, the absorption band of P700 +. Normal ( i.e. 20.5%, v/v) levels of O 2 generally enhanced photosystem II quantum yield relative to that measured under 1.6% O 2 as the irradiance approached saturation. Photorespiration is suspected to mediate such positive effects of O 2 through increases in the availability of CO 2 and recycling of orthophosphate. Conversely, at low intercellular CO 2 concentrations, 41.2% O 2 was associated with lower photosystem II quantum yield compared with that observed at 20.5% O 2. Inhibitory effects of 41.2% O 2 may occur in response to negative feedback on photosystem II arising from a build-up in the thylakoid proton gradient during electron transport to O 2. Covariation between quantum yields of photosystems I and II was not affected by concentrations of either O 2 or CO 2. The dependence of quantum yield of electron transport to CO 2 measured by gas exchange upon photosystem II quantum yield as determined by fluorescence was unaffected by CO 2 concentration. 相似文献
16.
Kinetic properties of soybean net photosynthetic CO 2 fixation and of the carboxylase and oxygenase activities of purified soybean ( Glycine max [L.] Merr.) ribulose 1, 5-diphosphate carboxylase (EC 4.1.1.39) were examined as functions of temperature, CO 2 concentration, and O 2 concentration. With leaves, O 2 inhibition of net photosynthetic CO 2 fixation increased when the ambient leaf temperature was increased. The increased inhibition of CO 2 fixation at higher temperatures was caused by a reduced affinity of the leaf for CO 2 and an increased affinity of the leaf for O 2. With purified ribulose 1,5-diphosphate carboxylase, O 2 inhibition of CO 2 incorporation and the ratio of oxygenase activity to carboxylase activity increased with increased temperature. The increased O 2 sensitivity of the enzyme at higher temperature was caused by a reduced affinity of the enzyme for CO 2 and a slightly increased affinity of the enzyme for O 2. The similarity of the effect of temperature on the affinity of intact leaves and of ribulose 1,5-diphosphate carboxylase for CO 2 and O 2 provides further evidence that the carboxylase regulates the O 2 response of photosynthetic CO 2 fixation in soybean leaves. Based on results reported here and in the literature, a scheme outlining the stoichiometry between CO 2 and O 2 fixation in vivo is proposed. 相似文献
17.
Photorespiration in Chlorella pyrenoidosa Chick. was assayed by measuring 18O-labeled intermediates of the glycolate pathway. Glycolate, glycine, serine, and excreted glycolate were isolated and analyzed on a gas chromatograph/mass spectrometer to determine isotopic enrichment. Rates of glycolate synthesis were determined from 18O-labeling kinetics of the intermediates, pool sizes, derived rate equations, and nonlinear regression techniques. Glycolate synthesis was higher in high CO 2-grown cells than in air-grown cells when both were assayed under the same O 2 and CO 2 concentrations. Synthesis of glycolate, for both types of cells, was stimulated by high O 2 levels and inhibited by high CO 2 levels. Glycolate synthesis in 1.5% CO 2-grown Chlorella, when exposed to a 0.035% CO 2 atmosphere, increased from about 41 to 86 nanomoles per milligram chlorophyll per minute when the O 2 concentration was increased from 21% to 40%. Glycolate synthesis in air-grown cells increased from 2 to 6 nanomoles per milligram chlorophyll per minute under the same gas levels. Synthesis was undetectable when either the O 2 concentration was lowered to 2% or the CO 2 concentration was raised to 1.5%. Glycolate excretion was also sensitive to O 2 and CO 2 concentrations in 1.5% CO 2-grown cells and the glycolate that was excreted was 18O-labeled. Air-grown cells did not excrete glycolate under any experimental condition. Indirect evidence indicated that glycolate may be excreted as a lactone in Chlorella. Photorespiratory 18O-labeling kinetics were determined for Pavlova lutheri, which unlike Chlorella and higher plants did not directly synthesize glycine and serine from glycolate. This alga did excrete a significant proportion of newly synthesized glycolate into the media. 相似文献
18.
Low O 2 conditions were obtained by flowing N 2 through the solution in which the tomato plants ( Lycopersicon esculentum Mill cv Heinz 1350) were growing. Time course experiments revealed that low O 2 treatments stimulated 1-aminocyclopropane-1-carboxylate (ACC) synthase production in the roots and leaves. After the initiation of low O 2 conditions, ACC synthase activity and ACC content in the roots increased and reached a peak after 12 and 20 hours, respectively. The conversion of ACC to ethylene in the roots was inhibited by low levels of O 2, and ACC was apparently transported to the leaves where it was converted to ethylene. ACC synthase activity in the leaves was also stimulated by low O 2 treatment to the roots, reaching a peak after 24 hours. ACC synthase levels were enhanced by cobalt chloride and aminooxyacetic acid (AOA), although they inhibited ethylene production. Cobalt chloride enhanced ACC synthase only in combination with low O 2 conditions in the roots. Under aeration, AOA stimulated ACC synthase activity in both the roots and leaves. However, in combination with low O 2 conditions, AOA caused a stimulation in ACC synthase activity in the leaves and no effect in the roots. 相似文献
19.
Two silver birch ( Betula pendula Roth) clones K1659 and V5952 were grown in open‐top chambers over 3 years (age 7–9 years). The treatments were increased CO 2 concentration (+CO 2, 72 Pa), increased O 3 concentration (+O 3, 2 × ambient O 3 with seasonal AOT40 up to 28 p.p.m. h) and in combination (+CO 2 + O 3). Thirty‐seven photosynthetic parameters were measured in the laboratory immediately after excising leaves using a computer‐operated routine of gas exchange and optical measurements. In control leaves the photosynthetic parameters were close to the values widely used in a model (Farquhar, von Caemmerer and Berry, Planta 149, 78–90, 1980). The distribution of chlorophyll between photosystem II and photosystem I, intrinsic quantum yield of electron transport, uncoupled turnover rate of Cyt b 6f, Rubisco specificity and Km (CO 2) were not influenced by treatments. Net photosynthetic rate responded to +CO 2 with a mean increase of 17% in both clones. Dry weight of leaves increased, whereas protein, especially Rubisco content and the related photosynthetic parameters decreased. Averaged over 3 years, eight and 17 mechanistically independent parameters were significantly influenced by the elevated CO 2 in clones K1659 and V5952, respectively. The elevated O 3 caused a significant decrease in the average photosynthetic rate of clone V5952, but not of clone K1659. The treatment caused changes in one parameter of clone K1659 and in 11 parameters of clone V5952. Results of the combined treatment indicated that +O 3 had less effect in the presence of +CO 2 than alone. Interestingly, changes in the same photosynthetic parameters were observed in chamberless grown trees of clone V5952 as under +O 3 treatment in chambers, but this was not observed for clone K1659. These results suggest that during chronic fumigation, at concentrations below the threshold of visible leaf injuries, ozone influenced the photosynthetic parameters as a general stress factor, in a similar manner to weather conditions that were more stressful outside the chambers. According to this hypothesis, the sensitivity of a species or a clone to ozone is expected to depend on the growth conditions: the plant is less sensitive to ozone if the conditions are close to optimal and it is more sensitive to ozone under conditions of stress. 相似文献
20.
Evolution of O 2 by illuminated intact detached leaves from barley ( Hordeum vulgare L. cv Athos) and pea ( Pisum sativum L. cv Lincoln) in a CO 2-saturating atmosphere was enhanced when KNO 3 (1-2.5 millimolar) had been previously supplied through the transpiration stream. The extra O 2 evolution observed after feeding KNO 3 increased with the light intensity, being maximal at near saturating photon flux densities and resulting in no changes in the initial slope of the O 2 versus light-intensity curve. No stimulation of O 2 evolution was otherwise observed after feeding KCl or NH 4Cl. The data indicate that nitrate assimilation uses photosynthetically generated reductant and stimulates the rate of non-cyclic electron flow by acting as a second electron-accepting assimilatory process in addition to CO 2 fixation. 相似文献
|