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1.
After alfalfa ( Medicago sativa) seedlings were exposed to approximately 0.7 microliter per liter SO 2 for 8 hours, elevated ethylene and ethane production was observed. Ethylene production peaked about 6 hours and returned to control levels by about 24 hours following the fumigation, while ethane production peaked about 36 hours and was still above control levels 48 hours after the fumigation. Light had an opposite effect upon the production of the two gases: ethane production rates were higher from plants held in light, whereas ethylene production rates were higher from those held in the dark. Peak ethylene and ethane production rates from SO 2-treated plants were about 10 and 4 to 5 times greater, respectively, than those of the control plants. Ethylene appeared to be formed primarily from stressed yet viable leaves and ethane from visibly damaged leaves. The different time courses and light requirements for ethylene and ethane production suggest that these two gases were formed via different mechanisms. Light appears to have a dual role. It enhances SO 2-induced cellular damage and plays a role for repairs. 相似文献
2.
Tillandsia usneoides L. is a favorite model plant for investigating ethylene biosynthesis because no soil is needed for cultivation (important
for long-term measurements) and small plants and different clones are available. We investigated the endogenous production
of ethylene in relation to temperature, light, daylength and CO 2 concentration. Using a novel and most sensitive technique to measure ethylene, laser-driven photoacoustic spectroscopy, real-time
online measurements were performed. Since T. usneoides is a crassulacean acid metabolism (CAM) plant and does not take up CO 2 during the day we could show that ethylene production is strictly light dependent and does not follow any endogenous rhythm.
In contrast to reports on other plants, CO 2 concentration did not influence the production of ethylene by T. usneoides. However, high ethylene production was obtained after application of 1-aminoacyclopropane-1-carboxylic acid (ACC).
Received: 10 September 1997 / Accepted: 27 November 1997 相似文献
3.
Internal ethylene concentration, ability to convert 1-amino-cyclopropane-1-carboxylic acid (ACC) to ethylene (ethylene-forming enzyme [EFE] activity) and ACC content in the peel of apples ( Malus domestica Borkh., cv Golden Delicious) increased only slightly during fruit maturation on the tree. Treatment of immature apples with 100 microliters ethylene per liter for 24 hours increased EFE activity in the peel tissue, but did not induce an increase in ethylene production. This ability of apple peel tissue to respond to ethylene with elevated EFE activity increased exponentially during maturation on the tree. After harvest of mature preclimacteric apples previously treated with aminoethoxyvinyl-glycine, 0.05 microliter per liter ethylene did not immediately cause a rapid increase of development in EFE activity in peel tissue. However, 0.5 microliter per liter ethylene and higher concentrations did. The ethylene concentration for half-maximal promotion of EFE development was estimated to be approximately 0.9 microliter per liter. CO 2 partially inhibited the rapid increase of ethylene-promoted development of EFE activity. It is suggested that ethylene-promoted CO 2 production is involved in the regulation of autocatalytic ethylene production in apples. 相似文献
4.
Since CO 2 is known to stimulate ethylene production by promoting the conversion of 1-aminocyclopropane-1-carboxylic acid (ACC) to ethylene, the effect of CO 2 on the activity and the development of the ethylene forming enzyme (EFE) was studied in tobacco ( Nicotiana tabacum L. cv Havana 425 and Xanthi) leaf discs. In addition to previous observations that EFE activity is dependent on CO 2 concentration and is saturable with 2% CO 2, present data show two saturation curves at 2% and 10% CO 2. Promotion of EFE development was dependent also on CO 2 concentration (saturated at 2% CO 2) and duration (maximum at 24 in the dark), and was abolished by 20 micromolar cycloheximide. Application of exogenous ethylene (20 microliters per liter) or light treatment further increased the CO 2-enhanced development of EFE, implying that these two factors can also affect EFE development via interaction with CO 2. The results suggest that CO 2 exerts its stimulatory effect on the conversion of ACC to ethylene by enhancing not only the activity but also the synthesis of EFE in leaf discs. 相似文献
5.
The effect of light on the rate of ethylene production was monitored using two different techniques—leaf segments incubated in closed flasks versus intact plants in a flow-through open system. Three different plants were used, viz sunflower ( Helianthus annuus), tomato ( Lycopersicon esculentum), and soybean ( Glycine max). Experiments were conducted both in the presence and absence of 1-aminocyclopropane-1-carboxylic acid (ACC). The results obtained indicate that, in all three species studied, light strongly inhibits ethylene production when cut leaf segments are incubated in the presence of ACC in closed flasks. When ethylene measurements are made with ACC-sprayed intact plants using a continuous flow system, the effect of light on ethylene production is only marginal. In leaf segments of sunflower and soybean incubated only in distilled H2O in closed flasks, light promotes ethylene production. In tomato, there is no difference between the rate of ethylene production between light and darkness under such conditions. When measurements are made with intact plants in a continuous flow system, the rate of ethylene production is almost identical in light and darkness, in the three plants studied. It is concluded that the effect of light on cut leaf segments incubated in the presence of ACC in closed flasks can be attributed to the techniques used for these measurements. Light has little effect on ethylene production by intact plants in an open system. 相似文献
6.
Endogenous ethylene of Poa pratensis leaves infected by Bipolaris sorokiniana was evaluated as a factor in leaf chlorosis during pathogenesis. Detectable increases in endogenous ethylene of leaves of intact plants under normal ambient pressure occurred 12 hours after inoculation and was maximum at 48 hours; from 48 to 96 hours the ethylene progressively decreased. Necrotic lesions surrounded by chlorotic halos occurred on infected leaves between 24 and 48 hours. Midvein chlorosis interconnecting individual lesions and complete chlorosis of all tissues not directly affected by the lesions occurred between 72 and 96 hours, after maximum production of ethylene at 48 hours. The chlorophyll loss in infected leaves by 96 hours was 44% compared with controls. Subjecting inoculated leaves of intact plants to a controlled atmospheric-environmental system with an atmospheric pressure of 233 millibars and O2 and CO2 partial pressures adjusted to approximately that of normal ambient pressure during infection and disease development prevented most midvein chlorosis and complete chlorosis, but did not prevent necrotic lesion or chlorotic halo development. Under the hypobaric conditions, chlorophyll loss during disease development was reduced to 22% compared with controls at 96 hours. The observations suggest that ethylene may function late in pathogenesis of this host-pathogen interaction and is responsible for much of the chlorophyll loss after its maximum production at 48 hours. 相似文献
7.
The physiological site of ethylene action on CO 2 assimilation was investigated in intact plants of Glycine max L., using a whole-plant, open exposure system equipped witha remotely operated single-leaf cuvette. The objective of the study was met by investigating in control and ethylene-treated plants the (a) synchrony in response of CO 2 assimilation, stomatal conductance to water vapor, and substomatal CO 2 partial pressure; (b) response of CO 2 assimilation as a function of a range of substomatal CO 2 partial pressures; and (c) response of CO 2 assimilation as a function of a range of photon flux densities. After exposure to 410 micromoles per cubic meter of ethylene for 2.0 hours, CO 2 assimilation and stomatal conductance declined in synchrony, while substomatal CO 2 partial pressure remained unchanged until exposure times equaled and exceeded 3.0 hours. Because incipient changes in CO 2 assimilation occurred without a change in the CO 2 partial pressure in the leaf interior, it is concluded that both stomatal physiology and the chloroplast's CO 2 assimilatory capacity were initial sites of ethylene action. After 3.5 hours the effect of ethylene on stomatal conductance and CO 2 assimilation exhibited saturation kinetics, and the effect was substantially more pronounced for stomatal conductance than for CO 2 assimilation. Based on the response of CO 2 assimilation to a range of substomatal CO 2 partial pressures, ethylene did not affect either the CO 2 compensation point or carboxylation efficiency at subsaturating CO 2 partial pressures. Above-ambient supplies of CO 2 did not alleviate the diminished rates of CO 2 assimilation. In partitioning the limitations imposed on CO 2 assimilation in control and ethylene-treated plants, the stomatal component accounted for only 16 and 4%, respectively. The response of CO 2 assimilation to a range of photon flux densities suggests that ethylene reduced apparent quantum yield by nearly 50%. Thus, the pronounced decline in net photosynthetic CO 2 assimilation in the presence of ethylene was due more to a loss in the mesophyll tissue's intrinsic capacity to assimilate CO 2 than to a reduction in stomatal conductance. 相似文献
8.
The association of the level of ACC and the ethylene concentration in ripening apple fruit ( Malus sylvestris Mill, var. Ben Davis) was studied. Preclimacteric apple contained small amounts of ACC and ethylene. With the onset of the climacteric and a concomitant decrease in flesh firmness, the level of ACC and ethylene concentration both increased markedly. During the postclimacteric period, ethylene concentration started to decline, but the level of ACC continued to increase. Ethylene production and loss of flesh firmness of fruits during ripening were greatly suppressed by treatments with low O 2 (O 2 1–3%, CO 2 O%) or high CO 2 (CO 2 20–30%, O 2 15–20%) at the preclimacteric stage. However, after 4 weeks an accumulation of ACC was observed in treated fruits when control fruit was at the postclimacteric stage. Treatment of fruit with either low O 2 or high CO 2 at the climacteric stage resulted in a decrease of ethylene production. However, the ACC level in fruit treated with low O 2 was much higher than both control and high CO 2 treated fruit; it appears that low O 2 inhibits only the conversion of ACC to ethylene, resulting in an accumulation of ACC. Since CO 2 inhibits ethylene production but does not result in an accumulation of ACC, it appears that high CO 2 inhibits both the conversion of ACC to ethylene and the formation of ACC. 相似文献
9.
Summary Ethylene inhibits hook opening in the bean hypocotyl and at high concentrations induces closure of the hook. Indoleacetic acid and 2,4-dichlorophenoxyacetic acid, whose inhibitory effect on hook opening resembles that of ethylene, stimulate ethylene production from the hook tissue, and this ethylene production is physiologically active in inhibiting hook opening. It is concluded that the inhibition of opening by auxin is due at least in a major part to auxin-induced ethylene production by the hook tissue.Carbon dioxide promotes hook opening, apparently by antagonizing the action of endogenous ethylene. The concentration of respiratory CO 2 in the internal gas space of the hook tissue is high enough to play a role in the regulation of hook opening.Red light causes a decrease in ethylene production and an increase in CO 2 evolution from the hook tissue. These effects are partially reversible by far-red light. It is concluded that both ethylene and CO 2 serve as natural growth regulators which mediate the hypocotyl hook-opening response to light in bean seedlings. 相似文献
10.
We have characterized the stimulation of ethylene production by galactose in tomatoes ( Lycopersicon esculentum Mill.). The effect of concentration was studied by infiltrating 0, 4, 40, 100, 200, 400, or 800 micrograms galactose for each gram of fresh fruit weight into mature green `Rutgers' fruit. Both 400 and 800 micrograms per gram fresh weight consistently stimulated a transient increase in ethylene approximately 25 hours after infiltration; the lower concentrations did not. Carbon dioxide evolution of fruit infiltrated with 400 to 800 micrograms per gram fresh weight was greater than that of lower concentrations. The ripening mutants, rin and nor, also showed the transient increase in ethylene and elevated CO 2 evolution by 400 micrograms per gram fresh weight galactose. 1-Aminocyclopropane-1-carboxylic acid (ACC) content and ACC-synthase activity increased concurrently with ethylene production. However, galactose did not stimulate ACC-synthase activity in vitro. The infiltrated galactose in pericarp tissue was rapidly metabolized, decreasing to endogenous levels within 50 hours. Infiltrated galacturonic acid, dulcitol, and mannose stimulated transient increases in ethylene production similar to that of galactose. The following sugars produced no response: sucrose, fructose, glucose, rhamnose, arabinose, xylose, raffinose, lactose, and sorbitol. 相似文献
11.
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
12.
The mechanism of light-inhibited ethylene production in excised rice ( Oryza sativa L.) and tobacco ( Nicotiana tabacum L.) leaves was examined. In segments of rice leaves light substantially inhibited the endogenous ethylene production, but when CO 2 was added into the incubation flask, the rate of endogenous ethylene production in the light increased markedly, to a level which was even higher than that produced in the dark. Carbon dioxide, however, had no appreciable effect of leaf segments incubated in the dark. The endogenous level of 1-aminocyclopropane-1-carboxylic acid (ACC), the immediate precursor of ethylene, was not significantly affected by lightdark or CO 2 treatment, indicating that dark treatment or CO 2exerted its effect by promoting the conversion of ACC to ethylene. This conclusion was supported by the observations that the rate of conversion of exogenously applied ACC to ethylene was similarly inhibited by light, and this inhibition was relieved in the presence of CO 2. Similar results were obtained with tobacco leaf discs. The concentrations of CO 2 giving half-maximal activity was about 0.06%, which was only slightly above the ambient level of 0.03%. The modulation of ACC conversion to ethylene by CO 2 or light in detached leaves of both rice and tobacco was rapid and fully reversible, indicating that CO 2 regulates the activity, but not the synthesis, of the enzyme converting ACC to ethylene. Our results indicate that light inhibition of ethylene production in detached leaves is mediated through the internal level of CO 2, which directly modulates the activity of the enzyme converting ACC to ethylene.Abbreviation ACC
1-aminocyclopropane-1-carboxylic acid
Recipient of a Republic of China National Science Council Fellowship 相似文献
13.
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 N 2 fixation. Shoot CER, root + nodule respiration, and apparent N 2 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 N 2 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 N 2 fixation was measured within 4 hours, and decreasing CO 2 concentration from 320 to 90 microliters CO 2 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 CO 2 concentration around the shoot from 320 to 1,000 microliters CO 2 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 CO 2-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 CO 2 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 N 2 fixation in soybean plants grown under controlled environmental conditions functioned at maximum capacity and was not limited by shoot CER. Whether N 2-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
14.
The effect of light and CO 2 on both the endogenous and 1-aminocyclopropane-1-carboxylic acid (ACC)-dependent ethylene evolution from metabolically active detached leaves and leaf discs of Gomphrena globosa L. is reported. Treatment with varying concentrations of ACC did not appear to inhibit photosynthesis, respiration, or stomatal behavior. In all treatments, more ethylene was released into a closed flask from ACC-treated tissue, but the pattern of ethylene release with respect to light/dark/CO 2 treatments was the same. Leaf tissue in the light with a source of CO2 sufficient to maintain photosynthesis always generates 3 to 4 times more ethylene than tissue in the dark. Conversely, the lowest rate of ethylene release occurs when leaf tissue is illuminated and photosynthetic activity depletes the CO2 to the compensation point. Ethylene release in the dark is also stimulated by CO2 either added to the flask as bicarbonate or generated by dark respiration. Ethylene release increases dramatically and in parallel with photosynthesis at increasing light intensities in this C4 plant. Ethylene release appears dependent on CO2 both in the light and in the dark. Therefore, it is suggested that the important factor regulating the evolution of ethylene gas from leaves of Gomphrena may be CO2 metabolism rather than light per se. 相似文献
15.
Apples ( Malus sylvestris Mill, cv Golden Delicious) were treated before harvest with aminoethoxyvinylglycine (AVG). AVG is presumed to reversibly inhibit 1-aminocyclopropane-1-carboxylic acid (ACC) activity, but not the formation of ACC synthase. AVG treatment effectively blocked initiation of autocatalytic ethylene production and ripening of harvested apples. Exogenous ethylene induced extractable ACC synthase activity and ripening in AVG-treated apples. Removal of exogenous ethylene caused a rapid decline in ACC synthase activity and in CO 2 production. The results with ripened, AVG-treated apples indicate (a) a dose-response relationship between ethylene and enhancement of ACC synthase activity with a half-maximal response at approximately 0.8 μl/l ethylene; (b) reversal of ethylene-enhanced ACC synthase activity by CO 2; (c) enhancement of ACC synthase activity by the ethylene-activity analog propylene. Induction of ACC synthase activity, autocatalytic ethylene production, and ripening of preclimacteric apples not treated with AVG were delayed by 6 and 10% CO2, but not by 1.25% CO2. However, each of these CO2 concentrations reduced the rate of increase of ACC synthase activity. 相似文献
16.
The saturating photon flux density (400 to 700 nanometers) for induction of flowering of the long day plant Anagallis arvensis L. was 1,900 micromoles per square meter per second (6,000 foot-candles) when an 8-hour daylength was extended to 24 hours by a single period of supplementary irradiation. The saturating photon flux density for photosynthetic CO 2 uptake during the same single supplementary light period was lower, at about 1,000 to 650 micromoles per square meter per second (3,000 to 2,000 foot-candles). The per cent flowering and mean number of floral buds per plant were significantly reduced when the light extension treatment was given in CO2-free air, and glucose (10 kilograms per cubic meter in water) relieved this effect. Glucose solution also significantly increased flowering of plants given supplementary light treatment in atmospheric air under a photon flux density of 80 micromoles per square meter per second. Increasing the CO2 concentration to 1.27 grams per cubic meter of CO2 in air during the supplementary light period did not increase flowering. It is concluded that high photon flux densities promote flowering of Anagallis through both increased photosynthesis and the photomorphogenic action of high irradiance. 相似文献
17.
The effect of oxygen concentration on the rate of CO 2-uptake in continuous and intermittent light was studied as well as the CO 2-fixation during a short dark period after light was turned off. In addition the dark respiration and the CO 2-compensation point of attached and detached corn leaves were determined. Leaves of 4 to 22-day old plants were used as experimental material. A closed circuit system of an infrared carbon dioxide analyzer was employed to measure the rate of CO 2-exchange. It was found that in an atmosphere consisting of 100 % oxygen, there was about 50 per cent inhibition of the rate of CO 2-uptake in continuous and intermittent light compared to that in an atmosphere consisting of 21% oxygen. The same was true of the rate of CO 2-fixation in darkness during a short period after the light was turned off. Since the response to oxygen concentration of the CO 2-uptake in light and of the CO 2-fixation in darkness after the light was turned off were similar, it is concluded that the fixation of CO 2 in the short dark period represents an over- shoot of photosynthesis. The rate of dark respiration was little affected by the oxygen concentration in the ranges used in the experiments. The carbon dioxide compensation point which has been observed in leaves of 4 to 14-day old plants was not influenced by either oxygen concentration or light intensity. Since the changes in the rate of CO 2-uptake due to changes in the concentration of oxygen and light intensity had no effect on the CO 2-compensation point, it is concluded that a reabsorption of respiratory CO 2 by photosynthesis could not account for the low value of this point. These results are interpreted as a further corroboration of the statement that the leaves of corn lack the process of photorespiration and that dark respiration is inhibited in light. It was observed that the rate of the CO 2-uptake gradually increased in plants which were from 4 to 22-days old. The inhibitory effect of high concentration of oxygen on the rate of CO 2-uptake was relatively higher in old plants than in young ones. 相似文献
18.
Some previous studies of photorespiration and glycolate oxidation were re-examined and correlated by infra-red CO 2 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 CO 2 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 CO 2 to photosynthesis. 相似文献
19.
Control coefficients were used to describe the degree to which ribulose bisphosphate carboxylase/oxygenase (Rubisco) limits the steady-state rate of CO 2 assimilation in sunflower leaves from plants grown at high (800 μmol mol −1) and low (350 μmol mol −1) CO 2. The magnitude of a control coefficient is approximately the percentage change in the flux that would result from a 1% rise in enzyme active site concentration. In plants grown at low CO 2, leaves of different ages varied considerably in their photosynthetic capacities. In a saturating light flux and an ambient CO 2 concentration of 350 μmol mol −1, the Rubisco control coefficient was about 0.7 in all leaves, indicating that Rubisco activity largely limited the assimilation flux. The Rubisco control coefficient for leaves grown at 350 μmol mol −1 CO 2 dropped to about zero when the ambient CO 2 concentration was raised to 800 μmol mol −1. In relatively young, fully expanded leaves of plants grown at high CO 2, the Rubisco control coefficient was also about 0.7 at a saturating light flux and at the CO 2 concentration at which the plants were grown (800 μmol mol −1). This apparently resulted from a decrease in the concentration of Rubisco active sites. In older leaves, however, the control coefficient was about 0.2. Because, on the whole, Rubisco activity still largely limits the assimilation flux in plants grown at high CO 2, the kinetics of this enzyme can still be used to model photosynthesis under these conditions. The relatively high Rubisco control coefficient under enhanced CO 2 indicates that the young sunflower leaves have the capacity to acclimate their photosynthetic biochemistry in a way consistent with an optimal use of protein resources. 相似文献
20.
Photosynthetic O 2 production and photorespiratory O 2 uptake were measured using isotopic techniques, in the C 3 species Hirschfeldia incana Lowe., Helianthus annuus L., and Phaseolus vulgaris L. At high CO 2 and normal O 2, O 2 production increased linearly with light intensity. At low O 2 or low CO 2, O 2 production was suppressed, indicating that increased concentrations of both O 2 and CO 2 can stimulate O 2 production. At the CO 2 compensation point, O 2 uptake equaled O 2 production over a wide range of O 2 concentrations. O 2 uptake increased with light intensity and O 2 concentration. At low light intensities, O 2 uptake was suppressed by increased CO 2 concentrations so that O 2 uptake at 1,000 microliters per liter CO 2 was 28 to 35% of the uptake at the CO 2 compensation point. At high light intensities, O 2 uptake was stimulated by low concentrations of CO 2 and suppressed by higher concentrations of CO 2. O 2 uptake at high light intensity and 1000 microliters per liter CO 2 was 75% or more of the rate of O 2 uptake at the compensation point. The response of O 2 uptake to light intensity extrapolated to zero in darkness, suggesting that O 2 uptake via dark respiration may be suppressed in the light. The response of O 2 uptake to O 2 concentration saturated at about 30% O 2 in high light and at a lower O 2 concentration in low light. O 2 uptake was also observed with the C 4 plant Amaranthus edulis; the rate of uptake at the CO 2 compensation point was 20% of that observed at the same light intensity with the C 3 species, and this rate was not influenced by the CO 2 concentration. The results are discussed and interpreted in terms of the ribulose-1,5-bisphosphate oxygenase reaction, the associated metabolism of the photorespiratory pathway, and direct photosynthetic reduction of O 2. 相似文献
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