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1.
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
2.
Oxygen inhibition of photosynthesis and CO 2 evolution during photorespiration were compared in high CO 2-grown and air-grown Chlorella pyrenoidosa, using the artificial leaf technique at pH 5.0. High CO 2 cells, in contrast to air-grown cells, exhibited a marked inhibition of photosynthesis by O 2, which appeared to be competitive and similar in magnitude to that in higher C 3 plants. With increasing time after transfer to air, the photosynthetic rate in high CO 2 cells increased while the O 2 effect declined. Photorespiration, measured as the difference between 14CO 2 and 12CO 2 uptake, was much greater and sensitive to O 2 in high CO 2 cells. Some CO 2 evolution was also present in air-grown algae; however, it did not appear to be sensitive to O 2. True photosynthesis was not affected by O 2 in either case. The data indicate that the difference between high CO 2 and air-grown algae could be attributed to the magnitude of CO 2 evolution. This conclusion is discussed with reference to the oxygenase reaction and the control of photorespiration in algae. 相似文献
3.
Carbonyl sulfide (COS), a substrate for carbonic anhydrase, inhibited alkalization of the medium, O 2 evolution, dissolved inorganic carbon accumulation, and photosynthetic CO 2 fixation at pH 7 or higher by five species of unicellular green algae that had been air-adapted for forming a CO 2-concentrating process. This COS inhibition can be attributed to inhibition of external HCO 3− conversion to CO 2 and OH − by the carbonic anhydrase component of an active CO 2 pump. At a low pH of 5 to 6, COS stimulated O 2 evolution during photosynthesis by algae with low CO 2 in the media without alkalization of the media. This is attributed to some COS hydrolysis by carbonic anhydrase to CO 2. Although COS had less effect on HCO 3− accumulation at pH 9 by a HCO 3− pump in Scenedesmus, COS reduced O 2 evolution probably by inhibiting internal carbonic anhydrases. Because COS is hydrolyzed to CO 2 and H 2S, its inhibition of the CO 2 pump activity and photosynthesis is not accurate, when measured by O 2 evolution, by NaH 14CO 3 accumulation, or by 14CO 2 fixation. 相似文献
4.
Preincubation of illuminated tobacco ( Nicotiana tabacum L.) leaf disks in glycidate (2,3-epoxypropionate) or glyoxylate inhibited photorespiration by about 40% as determined by the ratio of 14CO 2 evolved into CO 2-free air in light and in darkness. However, under identical preincubation conditions used for the light/dark 14C assays, the compounds failed to reduce photorespiration or stimulate net photosynthesis in tobacco leaf disks based on other CO 2 exchange parameters, including the CO 2 compensation concentration in 21% O 2, the inhibitory effect of 21% O 2 on net photosynthesis in 360 microliters per liter of CO 2 and the rate of net photosynthetic 14CO 2 uptake in air. The effects of both glycidate and glyoxylate on the 14C assay are inconsistent with other measures of photorespiratory CO2 exchange in tobacco leaf disks, and thus these data question the validity of the light to dark ratio of 14CO2 efflux as an assay for relative rates of photorespiration (Zelitch 1968, Plant Physiol 43: 1829-1837). The results of this study specifically indicate that neither glycidate nor glyoxylate reduces photorespiration or stimulates net photosynthesis by tobacco leaf disks under physiological conditions of pO2 and pCO2, contrary to previous reports. 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.
Light-dependent O 2 exchange was measured in intact, isolated soybean ( Glycine max. var. Williams) cells using isotopically labeled O 2 and a mass spectrometer. The dependence of O 2 exchange on O 2 and CO 2 was investigated at high light in coupled and uncoupled cells. With coupled cells at high O 2, O 2 evolution followed similar kinetics at high and low CO 2. Steady-state rates of O 2 uptake were insignificant at high CO 2, but progressively increased with decreasing CO 2. At low CO 2, steady-state rates of O 2 uptake were 50% to 70% of the maximum CO 2-supported rates of O 2 evolution. These high rates of O 2 uptake exceeded the maximum rate of O 2 reduction determined in uncoupled cells, suggesting the occurrence of another light-induced O 2-uptake process ( i.e. photorespiration). Rates of O2 exchange in uncoupled cells were half-saturated at 7% to 8% O2. Initial rates (during induction) of O2 exchange in uninhibited cells were also half-saturated at 7% to 8% O2. In contrast, steady-state rates of O2 evolution and O2 uptake (at low CO2) were half-saturated at 18% to 20% O2. O2 uptake was significantly suppressed in the presence of nitrate, suggesting that nitrate and/or nitrite can compete with O2 for photoreductant. These results suggest that two mechanisms (O2 reduction and photorespiration) are responsible for the light-dependent O2 uptake observed in uninhibited cells under CO2-limiting conditions. The relative contribution of each process to the rate of O2 uptake appears to be dependent on the O2 level. At high O2 concentrations (≥40%), photorespiration is the major O2-consuming process. At lower (ambient) O2 concentrations (≤20%), O2 reduction accounts for a significant portion of the total light-dependent O2 uptake. 相似文献
7.
The submersed angiosperms Myriophyllum spicatum L. and Hydrilla verticillata (L.f.) Royal exhibited different photosynthetic pulse-chase labeling patterns. In Hydrilla, over 50% of the 14C was initially in malate and aspartate, but the fate of the malate depended upon the photorespiratory state of the plant. In low photorespiration Hydrilla, malate label decreased rapidly during an unlabeled chase, whereas labeling of sucrose and starch increased. In contrast, for high photorespiration Hydrilla, malate labeling continued to increase during a 2-hour chase. Thus, malate formation occurs in both photorespiratory states, but reduced photorespiration results when this malate is utilized in the light. Unlike Hydrilla, in low photorespiration Myriophyllum, 14C incorporation was via the Calvin cycle, and less than 10% was in C 4 acids. Ethoxyzolamide, a carbonic anhydrase inhibitor and a repressor of the low photorespiratory state, increased the label in glycolate, glycine, and serine of Myriophyllum. Isonicotinic acid hydrazide increased glycine labeling of low photorespiration Myriophyllum from 14 to 25%, and from 12 to 48% with high photorespiration plants. Similar trends were observed with Hydrilla. Increasing O2 increased the per cent [14C]glycine and the O2 inhibition of photosynthesis in Myriophyllum. In low photorespiration Myriophyllum, glycine labeling and O2 inhibition of photosynthesis were independent of the CO2 level, but in high photorespiration plants the O2 inhibition was competitively decreased by CO2. Thus, in low but not high photorespiration plants, glycine labeling and O2 inhibition appeared to be uncoupled from the external [O2]/[CO2] ratio. These data indicate that the low photorespiratory states of Hydrilla and Myriophyllum are mediated by different mechanisms, the former being C4-like, while the latter resembles that of low CO2-grown algae. Both may require carbonic anhydrase to enhance the use of inorganic carbon for reducing photorespiration. 相似文献
8.
The role of photorespiration in the foliar assimilation of nitrate (NO 3–) and carbon dioxide (CO 2) was investigated by measuring net CO 2 assimilation, net oxygen (O 2) evolution, and chlorophyll fluorescence in tomato leaves ( Lycopersicon esculentum). The plants were grown under ambient CO 2 with ammonium nitrate (NH 4NO 3) as the nitrogen source, and then exposed to a CO 2 concentration of either 360 or 700 µmol mol ?1, an O 2 concentration of 21 or 2%, and either NO 3– or NH 4+ as the sole nitrogen source. The elevated CO 2 concentration stimulated net CO 2 assimilation under 21% O 2 for both nitrogen treatments, but not under 2% O 2. Under ambient CO 2 and O 2 conditions (i.e. 360 µmol mol ?1 CO 2, 21% O 2), plants that received NO 3– had 11–13% higher rates of net O 2 evolution and electron transport rate (estimated from chlorophyll fluorescence) than plants that received NH 4+. Differences in net O 2 evolution and electron transport rate due to the nitrogen source were not observed at the elevated CO 2 concentration for the 21% O 2 treatment or at either CO 2 level for the 2% O 2 treatment. The assimilatory quotient ( AQ) from gas exchange, the ratio of net CO 2 assimilation to net O 2 evolution, indicated more NO 3– assimilation under ambient CO 2 and O 2 conditions than under the other treatments. When the AQ was derived from gross O 2 evolution rates estimated from chlorophyll fluorescence, no differences could be detected between the nitrogen treatments. The results suggest that short‐term exposure to elevated atmospheric CO 2 decreases NO 3– assimilation in tomato, and that photorespiration may help to support NO 3– assimilation. 相似文献
9.
Two strains of marine Synechococcus possessed a much greater potential for photorespiration than other marine algae we have studied. This conclusion was based
on the following physiological and biochemical characteristics: a) a light-dependent O 2 inhibition of photosynthetic CO 2 assimilation at atmospheric O 2 concentrations. The degree of inhibition was dependent on the relative concentrations of dissolved O 2 and CO 2, being greatest at 100% O 2 with no extra bicarbonate added to the medium; b) actively photosynthesizing cells had high levels of ribulose-1,5-bisphosphate
carboxylase compared with phosphoenolpyruvate carboxylase; ribulose-1,5-bisphosphate oxygenase activities were three times
greater than ribulose-1,5-bisphosphate carboxylase activities; c) cells photosynthesizing in 21% O 2, showed significant 14C-labelling of phosphoglycolate and glycolate and the percentage of total carbon-14 incorporated into these two compounds
increased when the O 2 concentration was 100%; d) at 100% O 2, there was a post-illumination enhanced rate of O 2 consumption, which was three times greater than dark respiration, and the rate declined with increasing bicarbonate concentrations.
The inhibitory effect of O 2 on photosynthesis did not appear to be solely due to photorespiration, since O 2 inhibition of photosynthetic O 2 evolution was much greater than that of photosynthetic CO 2 assimilation. Also, O 2 inhibition of photosynthetic O 2 evolution declined only slightly with decreasing light intensities, while the inhibition of CO 2 assimilation declined rapidly with decreasing light intensity. 相似文献
10.
The relative magnitudes of ( a) CO 2 compensation concentration, ( b) zero CO 2 intercept of the CO 2 response curve, ( c) O 2 suppression of net photosynthesis, ( d) differential 12CO 2 and 14CO 2 uptake, and ( e) 14CO 2 efflux into CO 2-free air were determined in the dry bean ( Phaseolus vulgaris L.) varieties Michelite-62 (M-62) and Red Kidney (RK). In comparing the two varieties for each of the above processes, there were three categories of response, M-62 > RK, M-62 = RK, and M-62 < RK. Since these processes did not give the same relative difference for the two varieties being studied, it was concluded that these phenomena cannot validly be used to estimate the magnitude of photorespiration, although they do identify its presence. The results suggest that photorespiration is but one component of O 2 inhibition of net photosynthesis and that photorespiration itself has two or more component metabolic pathways. 相似文献
11.
The weedy species Parthenium hysterophorus (Asteraceae) possesses a Kranz-like leaf anatomy. The bundle sheath cells are thick-walled and contain numerous granal chloroplasts, prominent mitochondria, and peroxisomes, all largely arranged in a centripetal position. Both mesophyll and bundle sheath chloroplasts accumulate starch. P. hysterophorus exhibits reduced photorespiration as indicated by a moderately low CO 2 compensation concentration (20-25 microliters per liter at 30°C and 21% O 2) and by a reduced sensitivity of net photosynthesis to 21% O 2. In contrast, the related C 3 species P. incanum and P. argentatum (guayule) lack Kranz anatomy, have higher CO 2 compensation concentrations (about 55 microliters per liter), and show a greater inhibition of photosynthesis by 21% O 2. Furthermore, in P. hysterophorus the CO 2 compensation concentration is relatively less sensitive to changes in O 2 concentrations and shows a biphasic response to changing O 2, with a transition point at about 11% O 2. Based on these results, P. hysterophorus is classified as a C 3-C 4 intermediate. The activities of diagnostic enzymes of C 4 photosynthesis in P. hysterophorus were very low, comparable to those observed in the C 3 species P. incanum ( e.g. phosphoenolpyruvate carboxylase activity of 10-29 micromoles per milligram of chlorophyll per hour). Exposures of leaves of each species to 14CO 2 (for 8 seconds) in the light resulted in 3-phosphoglycerate and sugar phosphates being the predominant initial 14C products (77-84%), with ≤4% of the 14C-label in malate plus aspartate. These results indicate that in the C 3-C 4 intermediate P. hysterophorus, the reduction in leaf photorespiration cannot be attributed to C 4 photosynthesis. 相似文献
12.
Rates of photosynthetic O 2 evolution, for measuring K 0.5(CO 2 + HCO 3−) at pH 7, upon addition of 50 micromolar HCO 3− to air-adapted Chlamydomonas, Dunaliella, or Scenedesmus cells, were inhibited up to 90% by the addition of 1.5 to 4.0 millimolar salicylhydroxamic acid (SHAM) to the aqueous medium. The apparent K1(SHAM) for Chlamydomonas cells was about 2.5 millimolar, but due to low solubility in water effective concentrations would be lower. Salicylhydroxamic acid did not inhibit oxygen evolution or accumulation of bicarbonate by Scenedesmus cells between pH 8 to 11 or by isolated intact chloroplasts from Dunaliella. Thus, salicylhydroxamic acid appears to inhibit CO 2 uptake, whereas previous results indicate that vanadate inhibits bicarbonate uptake. These conclusions were confirmed by three test procedures with three air-adapted algae at pH 7. Salicylhydroxamic acid inhibited the cellular accumulation of dissolved inorganic carbon, the rate of photosynthetic O 2 evolution dependent on low levels of dissolved inorganic carbon (50 micromolar Na-HCO 3), and the rate of 14CO 2 fixation with 100 micromolar [ 14C] HCO 3−. Salicylhydroxamic acid inhibition of O 2 evolution and 14CO 2-fixation was reversed by higher levels of NaHCO 3. Thus, salicylhydroxamic acid inhibition was apparently not affecting steps of photosynthesis other than CO 2 accumulation. Although salicylhydroxamic acid is an inhibitor of alternative respiration in algae, it is not known whether the two processes are related. 相似文献
13.
A leaf disk assay for photorespiration has been developed based on the rate of release of recently fixed 14CO 2 in light in a rapid stream of CO 2-free air at 30° to 35°. In tobacco leaves (Havana Seed) photorespiration with this assay is 3 to 5 times greater than the 14CO 2 output in the dark. In maize, photorespiration is only 2% of that in tobacco. The importance of open leaf stomata, rapid flow rates of CO2-free air, elevated temperatures, and oxygen in the atmosphere in order to obtain release into the air of a larger portion of the 14CO2 evolved within the tissue in the light was established in tobacco. Photorespiration, but not dark respiration, was inhibited by α-hydroxy-2-pyridinemethanesulfonic acid, an inhibitor of glycolate oxidase, and by 3-(4-chlorophenyl)-1,1-dimethylurea (CMU), an inhibitor of photosynthetic electron transport, under conditions which did not affect the stomata. These experiments show that the substrates of photorespiration and dark respiration differ and also provide additional support for the role of glycolate as a major substrate of photorespiration. It was also shown that at 35° the quantity of 14CO2 released in the assay may represent only 33% of the gross 14CO2 evolved in the light, the remainder being recycled within the tissue. It was concluded that maize does not evolve appreciable quantities of CO2 in the light and that this largely accounts for the greater efficiency of net photosynthesis exhibited by maize. Hence low rates of photorespiration may be expected to be correlated with a high rate of CO2 uptake at the normal concentrations of CO2 found in air and at higher light intensities. 相似文献
14.
The dependence of the CO 2 compensation concentration on O 2 partial pressure and the dependence of differential uptake of 14CO 2 and 12CO 2 on CO 2 and O 2 partial pressures are analyzed in illuminated white clover ( Trifolium repens L.) leaves. The data show a deviation of the photosynthetic gas exchange from ribulose bisphosphate carboxylase oxygenase kinetics at 10°C but not at 30°C. This deviation is due to an effect of CO 2 partial pressure on the ratio of photosynthesis to photorespiration which can be explained if active inorganic carbon transport is assumed. 相似文献
15.
Using a manometric method, photosynthetic oxygen evolution and 14CO 2 fixation have been determined for leaf tissue of Triticum aestivum L., Hordeum vulgare L., Phaseolus vulgaris L., and Lemna minor L. Approximately similar values in the range 0.2 to 0.4 millimoles grams fresh weight −1 hour −1 were obtained for both gases. In tissue subjected to vacuum infiltration, O 2 evolution and 14CO 2 fixation were barely measurable. It is considered that the elimination of photosynthetic gas exchange results from a decreased supply of CO 2 to the chloroplasts. Chopping wheat laminae also leads to a reduction in photosynthetic gas exchange, slices 1 millimeter or less giving only 10 to 20% of the value for whole tissue. Respiration is unaffected by either treatment. Carbonic anhydrase did not improve photosynthetic gas exchange in infiltrated tissue. The use of sliced or vacuum-infiltrated leaf tissue in photosynthetic studies is discussed. 相似文献
16.
Reduced photorespiration has been reported in Panicum milioides on the basis of lower CO 2 compensation concentrations than in C 3 species, lower CO 2 evolution in the light, and less response of apparent photosynthesis to O 2 concentration. The lower response to O 2 in P. milioides could be due to reduced O 2 competition with CO 2 for reaction with ribulose 1,5-bisphosphate, to a reduced loss of CO 2, or to an initial fixation of CO 2 by phosphoenolpyruvate carboxylase. Experiments were carried out with Panicum maximum Jacq., a C 4 species having no apparent photorespiration; tall fescue ( Festuca arundinacea Schreb.), a C 3 species; P. milioides Nees ex Trin.; and Panicum schenckii Hack. The latter two species are closely related and have low photorespiration rates. CO 2 exchange was measured at five CO 2 concentrations ranging from 0 to 260 microliters per liter at both 2 and 21% O 2. Mesophyll conductance or carboxylation efficiency was estimated by plotting substomatal CO 2 concentrations against apparent photosynthesis. In the C 4 species P. maximum, mesophyll conductance was 0.96 centimeters per second and was unaffected by O 2 concentration. At 21% O 2 mesophyll conductance of tall fescue was decreased 32% below the value at 2% O 2. Decreases in mesophyll conductance at 21% O 2 for P. milioides and P. schenckii were similar to that for tall fescue. On the other hand, loss of CO 2 in CO 2-free air, estimated by extrapolating the CO 2 response curve to zero CO 2, was increased from 1.8 to 6.5 milligrams per square decimeter per hour in tall fescue as O 2 was raised from 2-21%. Loss of CO 2 was less than 1 milligram per square decimeter per hour for P. milioides and P. schenckii and was unaffected by O 2. The results suggest that the reduced O 2 response in P. milioides and P. schenckii is due to a lower loss of CO 2 in the light rather than less inhibition of carboxylation by O 2, since the decrease in carboxylation efficiency at 21% O 2 was similar for P. milioides, P. schenckii, and tall fescue. The inhibition of apparent photosynthesis by 21% O 2 in these three species at low light intensities was similar at 31 to 36% which also indicates similar O 2 effects on carboxylation. Apparent photosynthesis at high light intensity was inhibited less by 21% O 2 in P. milioides (16.8%) and P. schenckii (23.8%) than in tall fescue (28.4%). This lower inhibition in the Panicum species may have been due to a higher degree of recycling of photorespired CO 2 in these species than in tall fescue. 相似文献
17.
The increase in net photosynthesis in M 4 progeny of an O 2-resistant tobacco ( Nicotiana tabacum) mutant relative to wild-type plants at 21 and 42% O 2 has been confirmed and further investigated. Self-pollination of an M 3 mutant produced M 4 progeny segregating high catalase phenotypes (average 40% greater than wild type) at a frequency of about 60%. The high catalase phenotype cosegregated precisely with O 2-resistant photosynthesis. About 25% of the F 1 progeny of reciprocal crosses between the same M 3 mutant and wild type had high catalase activity, whether the mutant was used as the maternal or paternal parent, indicating nuclear inheritance. In high-catalase mutants the activity of NADH-hydroxypyruvate reductase, another peroxisomal enzyme, was the same as wild type. The mutants released 15% less photorespiratory CO 2 as a percent of net photosynthesis in CO 2-free 21% O 2 and 36% less in CO 2-free 42% O 2 compared with wild type. The mutant leaf tissue also released less 14CO 2 per [1- 14C]glycolate metabolized than wild type in normal air, consistent with less photorespiration in the mutant. The O 2-resistant photosynthesis appears to be caused by a decrease in photorespiration especially under conditions of high O 2 where the stoichiometry of CO 2 release per glycolate metabolized is expected to be enhanced. The higher catalase activity in the mutant may decrease the nonenzymatic peroxidation of keto-acids such as hydroxypyruvate and glyoxylate by photorespiratory H 2O 2. 相似文献
18.
A normal appearing plant with a low rate of photorespiration (ratio of 14CO 2 released light/dark = 1.6) was found in an unselected tobacco ( Nicotiana tabacum) cultivar. The plant was self-pollinated, and further selections were made on several successive generations. Excised leaves from the progeny of the selections were examined for photorespiration and net CO 2 assimilation in normal air during photosynthesis. Similar measurements were made of plants derived from selfed parents with high rates of photorespiration (ratio of 14CO 2 released light/dark = 3.0 or greater). Efficient photosynthetic plants (greater than 22.0 mg of CO 2 dm −2 hr −1) with low rates of photorespiration produced a larger proportion of efficient progeny (about 25%) than did selfing inefficient plants (about 6%), but this proportion did not increase in successive generations. 相似文献
19.
Dry weight and Relative Growth Rate of Lemna gibba were significantly increased by CO 2 enrichment up to 6000 l CO 2 l –1. This high CO 2 optimum for growth is probably due to the presence of nonfunctional stomata. The response to high CO 2 was less or absent following four days growth in 2% O 2. The Leaf Area Ratio decreased in response to CO 2 enrichment as a result of an increase in dry weight per frond. Photosynthetic rate was increased by CO 2 enrichment up to 1500 l CO 2 l –1 during measurement, showing only small increases with further CO 2 enrichment up to 5000 l CO 2 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 CO 2 levels, however, was less than the air grown plants. The response of photosynthesis to O 2 indicated that the enhancement of growth and photosynthesis by CO 2 enrichment was a result of decreased photorespiration. Plants cultivated in low O 2 produced abnormal morphological features and after a short time showed a reduction in growth. 相似文献
20.
Plants were obtained with novel O 2-resistant photosynthetic characteristics. At low CO 2 (250-350 μL CO 2 L −1) and 30°C when O 2 was increased from 1% to 21% to 42%, the ratio of net CO 2 uptake in O 2-resistant whole plants or leaf discs compared to wild type increased progressively, and this was not related to stomatal opening. Dihaploid plantlets regenerated from anther culture were initially screened and selected for O 2-resistant growth in 42% O 2/160 μL CO 2 L −1 and 0.18% of the plantlets showed O 2-resistant photosynthesis. About 30% of the progeny (6 of 19 plants) of the first selfing of a fertile plant derived from a resistant dihaploid plant had O 2-resistant photosynthesis, and after a second selfing this increased to 50% (6 of 12 plants). In 21% O 2 and low CO 2, net photosynthesis of the resistant plants was about 15% greater on a leaf area basis than wild type. Net photosynthesis was compared in leaf discs at 30 and 38°C in 21% O 2, and at the higher temperature O 2-resistant plants showed still greater photosynthesis than wild type. The results suggest that the O 2-resistant photosynthesis described here is associated with a decreased stoichiometry of CO 2 release under conditions of rapid photorespiration. This view was supported by the finding that leaves of O 2-resistant plants averaged 40% greater catalase activity than wild type. 相似文献
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