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1.
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
2.
The metabolism of 14C-glycine (a substrate for photorespiration) was studied in the light and in darkness under natural CO 2 concentration (0.03%) in the leaves of ephemeroides Scilla sibirica Haw. and Ficaria verna Huds. at different developmental stages. Using one and the same sample, potential photosynthesis (at 1% CO 2), true photosynthesis (at 0.03% CO 2), and leaf respiratory capacity were measured by the radiometric and manometric methods, respectively. All measurements were performed at 15°C, an average temperature during ephemer growth. It was found that, in the white zone of the Scilla leaf, the rate of CO 2 evolution resulting from metabolization of exogenous 14C-glycine was similar in the light and in darkness. In the green zone of the Scilla leaf and in the green leaf of Ficaria, both 14C-glycine absorption and 14CO 2 evolution were lower in the light as compared with darkness, which is explained by CO 2 reassimilation. In all treatments of both plant species, a specific inhibitor of glycine decarboxylase complex (GDC), aminoacetonitrile (5 mM) suppressed CO 2 evolution by 20–40%. It was concluded that in ephemeroides mitochondrial GDC, responsible for CO 2 evolution in photorespiration, is formed at the earliest stage of leaf development. This indicates that photorespiration can occur simultaneously with the development of the leaf photosynthetic activity. On the basis of the assumption that carbon losses in the form of CO 2 evolved during photorespiration comprise 25% of true photosynthesis, it was calculated that, in ephemer leaves, the highest rates of photorespiration and photosynthesis were attained during flowering when the leaf area was the largest and the rate of dark respiration was reduced by 1.5–2.0 times. The highest rates of dark respiration were observed in the beginning of growth. In senescing leaves by the end of the plant vegetation, potential photosynthesis and true photosynthesis were reduced, whereas dark respiration remained essentially unchanged. It is concluded that the high rates of potential and true photosynthesis are characteristic of ephemeroides when they complete their short developmental program in early spring (at 15°C); theoretically, photorespiration also occurs at a high rate during this period, when this process provides for a defense against the threat of photoinhibition at low temperature and high insolation. 相似文献
3.
The hypothesis that net photosynthesis is diminished in many plant species because of a high rate of CO 2 evolution in the light has been tested further. High rates of CO 2 output in CO 2-free air in comparison with dark respiration were found in Chlamydomonas reinhardi, wheat leaves, tomato leaves, and to a lesser extent in Chlorella pyrenoidosa by means of the 14C-photorespiration assay. In tobacco leaves high photorespiration was characteristic of a standard variety, Havana Seed, and a possibly still higher rate was found in a yellow heterozygous mutant, JWB Mutant. However, the dark homozygous sibling of the latter, JWB Wild, had a low photorespiration for the tobacco species. The relative rates of photorespiration were in the same sequence when measured by the 14CO 2 released in normal air from leaf disks supplied with glycolate-1- 14C in the light. As would be predicted by the hypothesis, the maximal net rate of photosynthesis at 300 ppm of CO2 in the air in JWB Wild leaves was greater (24%) than in Havana Seed, while JWB Mutant had less CO2 uptake than the standard variety (21%). At 550 ppm of CO2 the differences in net photosynthesis were not as great between the 2 siblings as at 200 ppm. The relative leaf expansion rates of seedlings of the 3 tobacco varieties in a greenhouse had the same relationship as their rates of CO2 assimilation. Thus within the tobacco species, as in a comparison between tobacco and maize, low photorespiratory CO2 evolution was correlated with higher photosynthetic efficiency. Therefore it seems that increased CO2 uptake should be achieved by genetic interference with the process of photorespiration. 相似文献
4.
The rate of photorespiration of Douglas-fir seedlings was measured under different light intensities by: (1) extrapolating the curve for CO 2 uptake in relation to atmospheric CO 2 content to zero CO 2 content, and (2) measuring CO 2 evolution of the plants into a CO 2-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, CO 2 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 CO 2 evolution above dark respiration before it leveled off. The rate of CO 2 evolution was stimulated by increase in temperature at all light intensities. With the CO 2-free air method, CO 2 evolution in the light was less than dark respiration at all light intensities. 相似文献
5.
The photosynthetic linear electron transport rate in excess of that used for CO 2 reduction was evaluated in Sorghum bicolor Moench. [NADP-malic enzyme (ME)-type C 4 plant], Amaranthus cruentus L. (NAD-ME-type C 4 plant) and Helianthus annuus L. (C 3 plant) leaves at different CO 2 and O 2 concentrations. The electron transport rate ( J
F) was calculated from fluorescence using the light partitioning factor (relative PSII cross-section) determined under conditions
where excess electron transport was assumed to be negligible: low light intensities, 500 μmol CO 2 · mol −1 and 2% O 2. Under high light intensities there was a large excess of J
F/4 at 10–100% O 2 in the C 3 plant due to photorespiration, but very little in sorghum and somewhat more in amaranth, showing that photorespiration is
suppressed, more in the NADP-ME- and less in the NAD-ME-type species. It is concluded that when C 4 photosynthesis is limited by supply of atmospheric CO 2 to the C 4 cycle, the C 3 cycle becomes limited by regeneration of ribulose 1,5-bisphosphate (RuBP) which in turn limits RuBP oxygenase activity and
photorespiration. The rate of excess electron transport over that consumed for CO 2 fixation in C 4 plants was very sensitive to the presence of O 2 in the gas phase, rapidly increasing between 0.01 and 0.1% O 2, and at 2% O 2 it was about two-thirds of that at 21% O 2. This shows the importance of the Mehler O 2 reduction as an electron sink, compared with photorespiration in C 4 plants. However, the rate of the Mehler reaction is still too low to fully account for the extra ATP which is needed in C 4 photosynthesis.
Received: 8 November 1997 / Accepted: 26 December 1997 相似文献
6.
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
7.
Gas exchange and fluorescence measurements of attached leaves of water stressed bean, sunflower and maize plants were carried out at two light intensities (250 mol quanta m -2s -1 and 850 mol quanta m -2s -1). Besides the restriction of transpiration and CO 2 uptake, the dissipation of excess light energy was clearly reflected in the light and dark reactions of photosynthesis under stress conditions. Bean and maize plants preferentially use non-photochemical quenching for light energy dissipation. In sunflower plants, excess light energy gave rise to photochemical quenching. Autoradiography of leaves after photosynthesis in 14CO 2 demonstrated the occurrence of leaf patchiness in sunflower and maize but not in bean. The contribution of CO 2 recycling within the leaves to energy dissipation was investigated by studies in 2.5% oxygen to suppress photorespiration. The participation of different energy dissipating mechanisms to quanta comsumption on agriculturally relevant species is discussed.Abbreviations F o
minimal fluorescence
- F m
maximal fluorescence
- F p
peak fluorescence
- g
leaf conductance
- P N
net CO 2 uptake
- q N
coefficient of non-photochemical quenching
- q P
coefficient of photochemical quenching 相似文献
8.
Summary Ribulose diphosphate (RuDP) and (PEP) phosphoenolpyruvate carboxylase enzyme activities were studied in young, mature, and senescent Portulaca oleracea leaves. While the absolute amount of both the C 3 (RuDP) and C 4 (PEP) carboxylase is less in senescent leaves than in mature leaves, RuDP carboxylase activity is reduced to a lesser degree. In senescent leaves, PEP carboxylase activity equals 10% of that in mature tissue, but RuDP carboxylase is 27% of that in mature leaves. The same ontogenetic series was also used to determine photorespiration rates and responses to several gas treatments. Young and mature leaves were unaffected by changes in the light regime or oxygen concentrations, and exhibited typical C 4-plant light/dark 14CO 2 evolution ratios. Senescent leaves, on the other hand, have photorespiration ratios similar to C 3-plants. In addition, senescent leaves were affected by minus CO 2, 100% O 2 and N 2 in a manner expected of C 3-plants, but not C 4-plants. These results are discussed in terms of a relative increase in activity of the C 3 cycle in later developmental stages in this plant.Abbreviation RuDP
ribulose diphosphate
- PEP
phosphoenolpyruvate
- PGA
phosphoglyceric acid 相似文献
9.
Using an open gas-exchange system, apparent photosynthesis, true photosynthesis (TPS), photorespiration (PR) and dark respiration of sunflower ( Helianthus annuus L.) leaves were determined at three temperatures and between 50 and 400 l/l external CO 2. The ratio of PR/TPS and the solubility ratio of O 2/CO 2 in the intercellular spaces both decreased with increasing CO 2. The rate of PR was not affected by the CO 2 concentration in the leaves and was independent of the solubility ratio of oxygen and CO 2 in the leaf cell. At photosynthesis-limiting concentrations of CO 2, the ratio of PR/TPS significantly increased from 18 to 30°C and the rate of PR increased from 4.3 mg CO 2 dm -2 h -1 at 18°C to 8.6 mg CO 2 dm -2 h -1 at 30°C. The specific activity of photorespired CO 2 was CO 2-dependent but temperature-independent, and the carbon traversing the glycolate pathway appeared to be derived both from recently fixed assimilate and from older reserve materials. It is concluded that PR as a percentage of TPS is affected by the concentrations of O 2 and CO 2 around the photosynthesizing cells, but the rate of PR may also be controlled by other factors.Abbreviations APS
apparent photosynthesis (net CO 2 uptake)
- PR
photorespiration (CO 2 evolution in light)
- RuBP
ribulose-1,5-bisphosphate
- TPS
true photosynthesis (true CO 2 uptake) 相似文献
10.
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
11.
An advanced radiogasometric method for the study of plant leaf CO 2 exchange is presented. The method enables determination of the rates of CO 2 fixation, photorespiration and respiration in the light under steady‐state photosynthesis and discrimination between primary and stored photosynthates as substrates of photorespiratory and respiratory decarboxylations. The method is based on the analysis of the time curves of 14CO 2 evolution from labeled primary and stored photosynthates in leaves previously exposed to 14CO 2. The molar rates of different decarboxylation reactions are calculated from the initial slopes of the curves taking into account the specific radioactivity of CO 2 fed to leaves and/or evolved from leaves. To estimate the contribution of primary and stored photosynthates, the measurements of 14CO 2 evolution are performed after feeding plant leaves for different periods with 14CO 2. Photorespiration and respiration are distinguished on the basis of data obtained from measurements of 14CO 2 evolution under normal (210 ml l −1) and low (15 ml l −1) concentrations of oxygen. A principally new method for the determination of the rate of intracellular refixation of respiratory CO 2 has been developed. The method is based on the measurements of 14CO 2 evolution from leaves into the medium of very high concentrations (30 ml l −1) of 12CO 2, where the probability of refixation of 14CO 2 evolved inside the cell is close to zero. The results obtained were comparable with the data derived from parallel refixation measurements by means of gasometric methods. As an example of application, the data on CO 2 exchange in leaves of two contrasting groups of C 3‐species, differing in the ability of starch accumulation, are presented. 相似文献
12.
Photosynthetic rate (P n) and the partitioning of noncyclic photosynthetic electron transport to photorespiration (J O) in seedlings of four subtropical woody plants growing at three light intensities were studied in the summer time by measurements of chlorophyll fluorescence and CO 2 exchange. Except Schima superba, an upper canopy tree species, the tree species Castanopsis fissa and two understory shrubs Psychotria rubra, Ardisia quinquegona had the highest P n at 36% of sunlight intensity. The total photosynthetic electron transport rate (J F) and the ratio of J O/J F were elevated in leaves under full sunlight. J O/J F ratio reached 0.5–0.6 and coincided with the increasing of oxygenation rate of Rubisco (V O), the activity of glycolate oxidase and photorespiration rate at full sunlight. It is suggested that an increasing partitioning proportion of photosynthetic electron transport to photorespiration might be one of the protective regulation mechanisms in forest plant under strong summer light and high temperature conditions. 相似文献
13.
Young leaves of tropical trees frequently appear red in color, with the redness disappearing as the leaves mature. During leaf expansion, plants may employ photoprotective mechanisms to cope with high light intensities; however, the variations in anthocyanin contents, nonphotochemical quenching (NPQ), and photorespiration during leaf expansion are poorly understood. Here, we investigated pigment contents, gas exchange, and chlorophyll (Chl) fluorescence in Woodfordia fruticosa leaves during their expansion. Young red leaves had significantly lower Chl content than that of expanding or mature leaves, but they accumulated significantly higher anthocyanins and dissipated more excited light energy through NPQ. As the leaves matured, net photosynthetic rate, total electron flow through PSII, and electron flow for ribulose-1,5-bisphosphate oxygenation gradually increased. Our results provided evidence that photorespiration is of fundamental importance in regulating the photosynthetic electron flow and CO 2 assimilation during leaf expansion. 相似文献
14.
The CO 2 exchange of several species of fresh water and marine algae was measured in the laboratory to determine whether photorespiration occurs in these organisms. The algae were positioned as thin layers on filter paper and the CO 2 exchange determined in an open gas exchange system. In either 21 or 1% O 2 there was little difference between 14CO 2 and 12CO 2 uptake. Apparent photosynthesis was the same in 2, 21, or 50% O 2. The compensation points of all algae were less than 10 μl 1 −1. CO 2 or 14CO 2 evolution into CO 2-free air in the light was always less than the corresponding evolution in darkness. These observations are inconsistent with the proposal that photorespiration exists in these algae. 相似文献
15.
In order to measure CO 2 exchange reactions by leaves using isotopes of CO 2, it is necessary to know precisely the discrimination against 14CO 2 by leaves. Earlier determinations of discrimination are at variance, and may be inaccurate because of assumptions made about the rate of photorespiration. Maize leaves evolve little or no CO 2 in light, and so provide suitable material for this measurement. Discrimination against 14CO 2 in photosynthesis by maize leaves is almost precisely the same as in CO 2 absorption by NaOH solution, amounting to 2.1 and 2.0% respectively. The agreement between these values and their close approximation to the relative rates of diffusion of 12CO 2 and 14CO 2, calculated from Graham's law, shows that diffusion into the leaf is primarily responsible for discrimination against 14CO 2 in photosynthesis. 相似文献
16.
Sugar maple ( Acer saccharum Marsh.) seedlings were grown in a nursery for three years in 13, 25, 45 and 100 per cent of full daylight. During the third year of growth, the rates of their apparent photosynthesis and respiration were measured periodically with an infra-red gas analyzer at various light intensities and normal CO 2 concentration. In addition, the rates of apparent photosynthesis of a single attached leaf of the same seedlings were measured at saturating light intensity, hut varying CO 2 concentrations. An increase in the light intensity in which seedlings were grown had no effect on their height or mean leaf area, hut resulted in thicker leaves, an increase in the total leaf area per seedling due to an increase in the number of leaves, an increase in the dry weight especially of roots and a decrease in the chlorophyll content of leaves. Throughout the growing season seedlings grown in full daylight, as compared with those grown in lower light intensities, had the lowest rates of apparent photosynthesis measured at standard conditions (21,600 lux light intensity and 300 ul/l of CO 2), when this was expressed per unit leaf area, hut the highest rates on a per seedling basis. Thus dry matter production attained at the end of the growing season correlated positively with the photosynthetic rate per seedling, but not per unit leaf area. The rates of apparent photosynthesis of seedlings grown at lower light intensities were more responsive to changes in light intensity or CO 2 concentration than those of seedlings grown in full daylight intensity. 相似文献
17.
Using a mass-spectrometric 16O 2/ 18O 2-isotope technique, we compared the nature and the relative importance of oxygen exchange in photomixotrophic (PM) and photoautotrophic (PA) suspensions of Euphorbia characias L. with those in intact leaves of the same species. Young and mature leaves, dividing and nondividing cell suspensions were characterized in short-term experiments. On chlorophyll basis, the gross photosynthetic activities at CO 2 saturating concentration of PA and PM suspensions varied little from those of leaves. On dry weight basis, gross photosynthesis of PA suspensions was equal to that of leaves because of their similar chlorophyll content. This was not the case in PM suspensions where gross photosynthesis was lower and largely varied during the growth cycle. The CO 2 compensation point of PA cells (155-265 parts per million) was much higher than that of leaves (50-80 ppm). Oxygen uptakes were analyzed in terms of mitochondrial respiration, photorespiration and light stimulation of oxygen uptake (LSOU), often identified to Mehlertype reactions. In PA and PM suspensions, mitochondrial respiration rates were higher than in leaves by a factor of 1.5 to 4.5. In PM suspensions, photorespiration and LSOU were observed only in nondividing cells. Photorespiration and LSOU rates were comparable in PA suspensions and leaves. Our results demonstrate that photorespiration of PA suspensions has not been affected by the 2% CO 2 concentration imposed during 2 years of culture. 相似文献
18.
A transient CO 2 burst is exhibited by irradiated leaves of the C 3 plant geranium ( Pelargonium X hortorum, Bailey) after the irradiance is quickly lowered. The light CO 2 burst appears to be related to photorespiration because of its irradiance dependency and its sensitivity to other environmental components such as CO 2 and O 2 concentration. The term post-lower-irradiance CO 2 burst or PLIB is used to describe the phenomenon. The PLIB appears to be a quantitative measurement of photorespiration with intact geranium leaves. The PLIB has been observed with intact leaves of other C 3 plants but not with C 4 leaves. Therefore, it is proposed that, after maximizing intact leaf photosynthetic rates and leaf chamber gas measuring conditions, photorespiration can be measured with intact C 3 leaves such as geranium as a transient post-lower-irradiance CO 2 burst. 相似文献
19.
Diurnal changes in photosynthetic gas exchange and chlorophyll fluorescence were measured under full sunlight to reveal diffusional and non‐diffusional limitations to diurnal assimilation in leaves of Arisaema heterophyllum Blume plants grown either in a riparian forest understorey (shade leaves) or in an adjacent deforested open site (sun leaves). Midday depressions of assimilation rate ( A) and leaf conductance of water vapour were remarkably deeper in shade leaves than in sun leaves. To evaluate the diffusional (i.e. stomatal and leaf internal) limitation to assimilation, we used an index [1– A/ A350], in which A350 is A at a chloroplast CO 2 concentration of 350 μ mol mol ? 1. A350 was estimated from the electron transport rate ( JT), determined fluorometrically, and the specificity factor of Rubisco ( S), determined by gas exchange techniques. In sun leaves under saturating light, the index obtained after the ‘peak’ of diurnal assimilation was 70% greater than that obtained before the ‘peak’, but in shade leaves, it was only 20% greater. The photochemical efficiency of photosystem II ( Δ F/ Fm ′ ) and thus JT was considerably lower in shade leaves than in sun leaves, especially after the ‘peak’. In shade leaves but not in sun leaves, A at a photosynthetically active photon flux density (PPFD) > 500 μ mol m ? 2 s ? 1 depended positively on JT throughout the day. Electron flows used by the carboxylation and oxygenation ( JO) of RuBP were estimated from A and JT. In sun leaves, the JO/ JT ratio was significantly higher after the ‘peak’, but little difference was found in shade leaves. Photorespiratory CO 2 efflux in the absence of atmospheric CO 2 was about three times higher in sun leaves than in shade leaves. We attribute the midday depression of assimilation in sun leaves to the increased rate of photorespiration caused by stomatal closure, and that in shade leaves to severe photoinhibition. Thus, for sun leaves, increased capacities for photorespiration and non‐photochemical quenching are essential to avoid photoinhibitory damage and to tolerate high leaf temperatures and water stress under excess light. The increased Rubisco content in sun leaves, which has been recognized as raising photosynthetic assimilation capacity, also contributes to increase in the capacity for photorespiration. 相似文献
20.
The effects of oxygen concentration and light intensity on the rates of apparent photosynthesis, true photosynthesis, photorespiration and dark respiration of detached spruce twigs were determined by means of an infra-red carbon dioxide analyzer (IRCA). A closed circuit system IRCA was filled with either 1 per cent of oxygen in nitrogen, air (21 % O 2) or pure oxygen (100 % O 2). Two light intensities 30 × 10 3 erg · cm ?2· s ?1 and 120 × 10 3 erg · cm ?2· s ?1 were applied. It has been found that the inhibitory effect of high concentration of oxygen on the apparent photosynthesis was mainly a result of a stimulation of the rate of CO 2 production in light (photorespiration). In the atmosphere of 100 % O 2, photorespiration accounts for 66–80 per cent of total CO 2 uptake (true photosynthesis). Owing to a strong acceleration of photorespiration by high oxygen concentrations, the rate of true photosynthesis calculated as the sum of apparent photosynthesis and photorespiration was by several times less inhibited by oxygen than the rate of apparent photosynthesis. The rates of dark respiration were essentially unaffected by the oxygen concentrations used in the experiments. An increase in the intensity of light from 30 × 10 3 erg · cm ?3· s ?1 to 120 · 10 3 erg · cm ?2· s ?1 enhanced the rate of photorespiration in the atmospheres of 21 and 100 % oxygen but not in 1 % O 2. The rate of apparent photosynthesis, however, was little affected by light intensity in an atmosphere of 1 % oxygen. 相似文献
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