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1.
1. Chloroform in low concentration (0.25 per cent) causes an increase in the rate of production of CO 2 in Ulva; this is followed by a decrease. In higher concentration (0.5 per cent) only a decrease is observed. 2. Assuming that the normal oxidation depends on the action of peroxide and peroxidase, experiments were made by placing Ulva in 1.0 per cent H 2O 2 and in Fe 2(SO 4) 3 (which acts like a peroxidase). The former diminishes the rate, the latter increases and subsequently decreases it. 3. When Ulva is killed in such a manner as to destroy the oxidizing enzymes, no CO 2 is produced unless H 2O 2 and Fe 2(SO 4) 3 are present. If to this mixture chloroform is added, the effect depends on the concentration of the iron. If the concentration is low there is an increase in the production of CO 2 followed by a decrease. If the concentration is high the rate appears to decrease from the start. 相似文献
2.
The metabolic products of heterotrophic (dark) CO 2 fixation by Euglena gracilis Klebs strain Z Pringsheim were separated and identified. They consisted of amino acids, phosphorylated compounds, tricarboxylic acid cycle intermediates, and nucleotides. Exposure of the cells to NH 4+ after a period of NH 4+ deprivation stimulated heterotrophic CO 2 fixation almost 4-fold, modifying the spectrum of the fixation products. In particular, the NH 4+ treatment stimulated fixation of CO 2 into glutamine, glycine, alanine, and serine. 相似文献
3.
The net rate of CO 2 uptake for leaves of Gossypium hirsutum L. was reduced when the plants were grown at low concentrations of NO 3-, PO 42-, or K +. The water vapor conductance was relatively constant for all nutrient levels, indicating little effect on stomatal response. Although leaves under nutrient stress tended to be lower in chlorophyll and thinner, the ratio of mesophyll surface area to leaf area did not change appreciably. Thus, the reduction in CO 2 uptake rate at low nutrient levels was due to a decrease in the CO 2 conductance expressed per unit mesophyll cell wall area (g cellCO2). The use of g cellCO2 and nutrient levels expressed per unit of mesophyll cell wall provides a new means of assessing nutrient effects on CO 2 uptake of leaves. 相似文献
4.
1. The nerve cord of the lobster ( Homarus americanus Milne-Edwards) is very delicate and can be used as a living preparation for only a few hours after its removal from the animal. 2. During the first hour or so after removal it discharges CO 2 at a steadily decreasing rate beginning at about 0.20 mg. CO 2 per gram of cord per minute and ending at about 0.07 mg. 3. This discharge exhibits a steady decrease in rate and is not divisible into a period of gush and a period of uniform outflow as with the lateral-line nerve of the dogfish. It terminates in a very few hours with the complete death of the cord. 4. Both handling and cutting the cord temporarily increase the rate of CO 2 output. 5. The stimulated cord discharges CO 2 at a rate about 26 per cent higher than that of the quiescent cord, an increase of about 1.6 times that of the increase observed in the lateral-line nerve of the dogfish under similar circumstances. 相似文献
5.
Increased concentrations of CO 2 in air (1–50%) cause young plants of Marsilea vestita to exhibit many characteristics of the water form when they are grown on a solid substrate under sterile conditions. Thus these plants have longer internodes, shorter petioles, more rectangular-shaped epidermal cells and fewer stomata on the lower leaf epidermis than controls grown in 0.03% CO 2. Over a 2-week period, dry weight increase is considerably greater in 12.5% and 25% CO 2 than in 0.03% CO 2. Fifty percent CO 2 is inhibitory to growth. CO 2-enriched air has the same morphogenetic effect when supplied in the light or the dark. Possible explanations for this effect are discussed. 相似文献
6.
The effect of high-frequency x-ray irradiation in prolongation of the larval stage of Drosophila melanogaster has been studied further, and evidence presented of the attainment of a maximum effect followed by a decrease to an almost level plateau in the course curve of average (median) prepupal period (φ) as a function of the period of irradiation ( t) under otherwise fixed conditions. The variation of effects of the experimental treatment with age of the larvae at the time of irradiation has been demonstrated in both control and irradiated lots, and a strikingly decreased effect observed when ventilation was not supplied as usual. Means of employment of a living system of this type as an indicator of effectiveness of radiation as in phantom depth or other distributional experiments have been presented and their use illustrated. 相似文献
7.
1. The effects of O 2, CO 2, and pressure were studied in two very different species of protozoa, a flagellate, Chilomonas paramecium, grown in acetate-ammonium solution and a ciliate, Tetrahymena geleii, grown in 2 per cent proteose-peptone solution. 2. Chilomonas and Tetrahymena live and reproduce in solutions exposed to a wide range of O 2 concentrations, but Chilomonas is killed at high O 2 tensions in which Tetrahymena grows best. The optimum O 2 concentration for Chilomonas is about 75 mm. pressure but it lives and reproduces in O 2 tensions as low as 0.5 mm. while Tetrahymena fails to grow in concentrations below 10 mm. O 2 pressure. 3. With a constant O 2 tension of 50 mm. pressure, it was found that there is no significant variation in growth in Chilomonas between 50 mm. and 740 mm. total pressure. In Tetrahymena, however, under the same conditions, an optimum total pressure was found at about 500 mm. and growth is comparatively poor at 50 mm. total pressure. 4. Tetrahymena does not live very long in CO 2 tensions over 122 mm., although Chilomonas grows as well at 400 mm. CO 2 as in air at atmospheric pressure (0.2 mm. CO 2). Tetrahymena grows best in an environment minus CO 2, but the optimum for Chilomonas is 100 mm. CO 2 at which pressure an average of 668,600 ± 30,000 organisms per ml. was produced (temperature, 25 ± 1° C.). 5. Chilomonads grown in high CO 2 concentrations ( e.g., 122 mm.) produce larger starch granules and more starch than those grown in ordinary air at atmospheric pressure. 6. In solutions exposed to 75 mm. O 2 tension (optimum) and 122 mm. CO 2 plus 540 mm. N 2 pressure, chilomonads contain very little, if any, fat. This phenomenon seems to be due to the action of CO 2 on the mechanisms concerned with fat production. 7. In Tetrahymena exposed to pure O 2, there is very little fat compared to those grown in atmospheric air. This may be due to the greater oxidation of fat in the higher O 2 concentrations. 8. Further evidence is presented in support of the contention that Chilomonas utilizes CO 2 in the production of starch. 相似文献
8.
Net CO 2 and water vapor exchange were studied in the Crassulacean acid metabolism plant Kalanchoë pinnáta during a normal 12-hour light/12-hour dark cycle and during a prolonged light period. Leaf temperature and leaf-air vapor pressure difference were kept constant at 20 C and 9 to 10 millibar. There was a 25% increase in the rate of CO 2 fixation during the first 6 hours prolonged light without change in stomatal conductance. This was associated with a decrease in the intracellular partial pressure of CO 2, a decrease in the stimulation of net CO 2 uptake by 2% O 2, and a decrease in the CO 2 compensation point from 45 to 0 microbar. In the normal light period after deacidification, leaves showed a normal light dependence of CO 2 uptake but, in prolonged light, CO 2 uptake was scarcely light-dependent. The increase in titratable acidity in prolonged light was similar to that in the dark. 相似文献
9.
Biomass production by the green algae Scenedesmus obliquus and Chlorella vulgaris in intensive laboratory continuous cultures was considerably affected by the pH at which the cultures were maintained. Carbon photoassimilation experiments revealed that pH values in the range of 8 to 9 were important for determining the free CO 2 concentrations in the medium. With higher pH values, additional pH effects were observed involving a decrease in the relative high affinity of low CO 2-adapted algae to free CO 2. The carbon uptake rate by high CO 2-adapted algae after transfer to low free CO 2 medium was characterized by a lag period of about 30 min, after which the affinity of the algae to CO 2 increased considerably. Both continuous growth and carbon uptake experiments indicated that artificially maintained high free CO 2 concentrations are recommended for maximal production in intensive outdoor algal cultures. 相似文献
10.
Seedlings of Schima superba were exposed to both ambient (375 ppm) and 720 ppm levels of CO 2 in combination with two incubation temperatures (25/20, 30/25°C, day/night) for a six-month period. Net height growth of seedlings was enhanced in the early period of exposure to high levels of CO 2. However, when seedlings were exposed for a longer period of time to this high concentration, net height growth was inhibited. Decreased photosynthetic rate with elevated CO 2 was observed when measured in the ambient CO 2 over a long-term exposure of 6 months. In contrast, a significant increase in photosynthesis was noted for seedlings exposed to higher incubation temperature in either ambient or 720 ppm CO 2 concentrations. The response of CO 2 assimilation to internal Ci was indicated by the lower sensitivity in seedlings grown in elevated CO 2 concentration. Though this response could also be found in a higher sensitivity in seedlings grown at higher temperature, the seedlings grown in normal conditions (ambient CO 2 and temperature) were still more sensitive to CO 2 assimilation response to internal Ci. This experiment suggests that: (1) exposure of seedlings to higher CO 2 levels for longer periods may lead to a decrease in seedling height growth and photosynthetic rate, as well as decreasing sensitivity to changing internal CO 2 concentrations; (2) the optimum temperature for photosynthesis of seedlings grown in an elevated CO 2 concentration was higher than that for seedlings grown in ambient concentration. 相似文献
11.
The effects of temperature and photosynthetically active radiation levels on photorespiration were investigated in Panicum milioides Nees ex Trin. and Panicum schenckii Hack., species known to have low photorespiration rates and other characteristics intermediate between C 3 and C 4 species. Comparisons were made with the C 3 grass species tall fescue ( Festuca arundinacea Schreb.). An increase in temperature from 20 to 35 C raised photorespiration from 7.3 to 10.2 milligrams per square decimeter per hour in tall fescue, but the increase in P. schenckii was less than 1 milligram per square decimeter per hour. Increases in temperature caused much less change in CO 2 compensation concentration in P. milioides and P. schenckii than in tall fescue, values of 160 microliters per liter being obtained in tall fescue at 40 C compared to about 40 microliters per liter for P. milioides and P. schenckii. Photorespiration in P. schenckii increased by only about 1 milligram CO 2 per square decimeter per hour as the photosynthetically active radiation level was raised from 100 to 2,000 microEinsteins per square meter per second. Loss of CO 2 into CO 2-free air actually decreased from 2.2 to 1.0 milligrams per square decimeter per hour as the radiation level was raised from 100 to 1,100 microEinsteins per square meter per second but tended to rise again at 2,000 microEinsteins per square meter per second. In contrast, photorespiration in tall fescue tripled with radiation level over the same range, reaching a maximum value of 7.2 milligrams per square decimeter per hour as determined by extrapolation of the CO 2 response curves to zero CO 2. The CO 2 compensation concentration in tall fescue was nearly insensitive to photosynthetically active radiation above 140 microEinsteins per square meter per second but, in P. milioides and P. schenckii, it decreased from values of 69 and 62 microliters per liter, respectively, to values of 21 and 16 as the radiation level was increased from 50 to 1075 microEinsteins per square meter per second. Interpolation of CO 2-response curves showed that an increase in photosynthetically active radiation level from 100 to 2,000 microEinsteins per square meter per second reduced the CO 2 compensation value of P. schenckii from 38 to 19 microliters per liter. Data from these experiments indicate reduced photorespiration or a CO 2-recycling mechanism in P. milioides and P. schenckii which causes apparent photorespiration to be nearly insensitive to temperature in the 20 to 35 C range and to decrease at high radiation intensities. 相似文献
12.
The effects of irradiation (300, 500 and 1500 rads) on mitosis and DNA synthesis in the estrogen primed vaginal epithelium have been studied. Dose-effect relations and the time sequence of effects on the two processes were investigated. The technique of tritiated thymidine labeling of DNA with autoradiography was used, in conjunction with the mitotic count, to study alterations in the generative cycle. Prior to irradiation, ovariectomized female rats were treated daily with diethylstilbestrol for a period of 2 weeks to create a steady state in the vaginal cell population. It was observed that: - 1 Within 1 hr following ionizing radiation, mitotic figures disappear from the population and reappear at a time that is dose dependent. Those cells that have begun mitosis at the time of irradiation were able to complete that phase but no cells which were in G2 were able to begin mitosis. Therefore, a G2 block occurs within 1 hr post-irradiation.
- 2 Radiation reduces the rate of DNA synthesis thus prolonging the S phase. There is no evidence of a radiation-induced G1 to S block in this system.
Based on these observations, it was further hypothesized that: - 1 Cells in G1 at the time of irradiation are relatively insensitive and continue to progress through the generative cycle at a rate primarily determined by the level of estrogen stimulation.
- 2 Radiation may interfere with the estrogen priming mechanism in this hormonedependent system thereby reducing the effective level of estrogen stimulation. This is seen in the behavior of cells which were in G1 at the time of irradiation. The extent of the blockage of estrogen increases with radiation dose and after 1500 rads, estrogen stimulation is essentially at castrate level.
相似文献
13.
The effects of nuclear genome duplication on the chlorophyll-protein content and photochemical activity of chloroplasts, and photosynthetic rates in leaf tissue, have been evaluated in haploid, diploid, and tetraploid individuals of the castor bean, Ricinus communis L. Analysis of this euploid series revealed that both photosystem II (2,6-dichlorophenolindophenol reduction) and photosystem I oxygen uptake ( N,N,N′,N′-tetramethyl- p-phenylenediamine to methyl viologen) decrease in plastids isolated from cells with increasingly larger nuclear complement sizes. Photosynthetic O 2-evolution and 14CO 2-fixation rates in leaf tissue from haploid, diploid, and tetraploid individuals were also found to decrease with the increase in size of the nuclear genome. Six chlorophyll-protein complexes, in addition to a zone of detergent complexed free pigment, were resolved from sodium dodecyl sulfate-solubilized thylakoid membranes from cells of all three ploidy levels. In addition to the P700-chlorophyll a-protein complex and the light-harvesting chlorophyll a/b-protein complex, four minor complexes were revealed, two containing only chlorophyll a and two containing both chlorophyll a and b. The relative distribution of chlorophyll among the resolved chlorophyll-protein complexes and free pigment was found to be similar for all three ploidy levels. 相似文献
14.
The objectives of this study were to determine the effects of elevated CO 2 on relationships between leaf area (A) and linear leaf dimensions (length [L] and width [W]) and leaf dry weight (M) in soybeans ( Glycine max (L.) Merr. cv. Bragg). Based on dimensional measurements made on trifoliolates 1–6 for plants grown under three CO 2 levels (348, 502 and 645 μl l −-1), the best predictor for both trifoliolate leaf area and for fully expanded central leaflets of the trifoliolates was an equation of the form A = b o + b 1L·W; these relationships were unaffected by CO 2, although there was a small effect of leaf position. For expanding central leaflets of the fifth trifoliolate, no CO 2, leaf size (age) or CO 2 × leaf size effect was found. Specific leaf weight (i.e., M/A) was significantly affected by CO 2, increasing with increasing CO 2. Hence, trifoliolate dry weight can be nondestructively estimated from trifoliolate area using the equation M = 0.097 + (6.71 × 10 −-3 + 1.04 × 10 −-6[CO 2])A, where [CO 2] is mean daytime CO 2 concentration of the growth environment. 相似文献
15.
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
16.
The effects of light upon the potential difference across the protoplasm of impaled Halicystis cells are described. These effects are very slight upon the normal P.D., increasing it 3 or 4 per cent, or at most 10 per cent, with a characteristic cusped time course, and a corresponding decrease on darkening. Light effects become much greater when the P.D. has been decreased by low O 2 content of the sea water; light restores the P.D. in much the same time course as aeration, and doubtless acts by the photosynthetic production of O 2. There are in both cases anomalous cusps which decrease the P.D. before it rises. Short light exposures may give only this anomaly. Over part of the potential range the light effects are dependent upon intensity. Increased CO 2 content of the sea water likewise depresses the P.D. in the dark, and light overcomes this depression if it is not carried too far. Recovery is probably due to photosynthetic consumption of CO 2, unless there is too much present. Again there are anomalous cusps during the first moments of illumination, and these may be the only effect if the P.D. is too low. The presence of ammonium salts in the sea water markedly sensitizes the cells to light. Subthreshold NH 4 concentrations in the dark become effective in the light, and the P.D. reverses to a negative sign on illumination, recovering again in the dark. This is due to increase of pH outside the cell as CO 2 is photosynthetically reduced, with increase of undissociated NH 3 which penetrates the cell. Anomalous cusps which first carry the P.D. in the opposite direction to the later drift are very marked in the presence of ammonia, and may represent an increased acidity which precedes the alkaline drift of photosynthesis. This acid gush seems to be primarily within the protoplasm, persisting when the sea water is buffered. Glass electrode measurements also indicate anomalies in the pH drift. There are contrary cusps on darkening which suggest temporarily increased alkalinity. Even more complex time courses are given by combining low O 2 and NH 4 exposures with light; these may have three or more cusps, with reversal, recovery, and new reversal. The ultimate cause of the light effects is to be found in an alteration of the surface properties by the treatments, which is overcome (low O 2, high CO 2), or aided (NH 4) by light. This alteration causes the surface to lose much of its ionic discrimination, and increases its electrical resistance. Tests with various anion substitutions indicate this, with recovery of normal response in the light. A theory of the P.D. in Halicystis is proposed, based on low mobility of the organic anions of the protoplasm, with differences in the two surfaces with respect to these, and the more mobile Na and K. ions. 相似文献
17.
Microcystis aeruginosa Kütz. 7820 was cultured at 350 and 700 μL·L ? 1 CO 2 to assess the impacts of doubled atmospheric CO 2 concentration on this bloom‐forming cyanobacterium. Doubling of CO 2 concentration in the airflow enhanced its growth by 52%–77%, with pH values decreased and dissolved inorganic carbon (DIC) increased in the medium. Photosynthetic efficiencies and dark respiratory rates expressed per unit chl a tended to increase with the doubling of CO 2. However, saturating irradiances for photosynthesis and light‐saturated photosynthetic rates normalized to cell number tended to decrease with the increase of DIC in the medium. Doubling of CO 2 concentration in the airflow had less effect on DIC‐saturated photosynthetic rates and apparent photosynthetic affinities for DIC. In the exponential phase, CO 2 and HCO 3 ? levels in the medium were higher than those required to saturate photosynthesis. Cultures with surface aeration were DIC limited in the stationary phase. The rate of CO 2 dissolution into the liquid increased proportionally when CO 2 in air was raised from 350 to 700 μL·L ? 1, thus increasing the availability of DIC in the medium and enhancing the rate of photosynthesis. Doubled CO 2 could enhance CO 2 dissolution, lower pH values, and influence the ionization fractions of various DIC species even when the photosynthesis was not DIC limited. Consequently, HCO 3 ? concentrations in cultures were significantly higher than in controls, and the photosynthetic energy cost for the operation of CO 2 concentrating mechanism might decrease. 相似文献
18.
Increased atmospheric CO 2 and gamma irradiation have a significant impact on the plant photosynthetic apparatus and organic compound production. In this study, we evaluated the effect of elevated CO 2 on the photosynthetic efficiency and production of defensive secondary metabolites (flavonoids) induced by gamma irradiation as a physical elicitor in Centella asiatica. Irradiated and non-irradiated 10-week-old plants of C. asiatica were exposed to 400 and 800 μmol mol ?1 of atmospheric CO 2 in growth chambers for 2 h every day until six weeks. A CO 2-enriched atmosphere initially improved the photosynthetic efficiency and ameliorated the detrimental impact of gamma irradiation on the photosynthetic apparatus, increasing carbon allocation into the flavonoid pathway. Elevated CO 2 combined with gamma irradiation resulted in the highest concentration of flavonoids in C. asiatica tissues compared with the other treatments. There was an enhancement in rutin (2.49 fold), naringin (2.15 fold), fisetin (4.07 fold), and morin (4.62 fold) with rising CO 2 concentrations from 400 to 800 μmol mol ?1 in the irradiated plants. With increasing CO 2 concentration, the compensation point and the respiration declined, whereas the apparent quantum yield and the maximum net photosynthesis ( A max) rate increased. The efficiency of photosystem II (PSII) was improved in the irradiated plants grown under high concentrations of CO 2. The total carbohydrate concentration reached the maximum value at the highest level of CO 2, followed by gamma irradiation combined with the highest level of CO 2. Irradiated plants of C. asiatica grown under elevated CO 2 could be superior to non-irradiated plants due to increased carbon availability both for the flavonoid biosynthesis and for the photosynthetic pathway. 相似文献
19.
With Chlorella ellipsoidea cells, the effect of oxygen was investigated on the products of enhanced dark 14CO 2 fixation immediately following preillumination in the absence of CO 2. When the reaction mixture was made aerobic by bubbling air (CO 2-free) throughout preillumination and the following dark 14CO 2 fixation periods, the initial fixation product was mainly 3-phosphoglyceric acid. When nitrogen gas had been used instead of air, only about one-half of the total radioactivity in the initial fixation products was in 3-phosphoglyceric acid and the rest in aspartic, phosphoenolpyruvic, and malic acids. The percentage distribution of radioactivity incorporated in these initial products rapidly decreased during the rest of the dark period. Concurrent with the decrease in the initial 14CO 2 fixation products, some increase was observed in the radioactivities of the sugar phosphates. The maximal radioactivity incorporated in sugar mono- and diphosphates accounted for only 10% of total 14C, under either the aerobic or anaerobic conditions. Under anaerobic conditions most of the 14C incorporated was eventually transferred to alanine, whereas the main end products under aerobic conditions were aspartate and glutamate. The pattern of 14CO 2 fixation products was unaffected by the atmospheric condition during the period of preillumination. The preferential flow of the fixed carbon atom to alanine or aspartate depended on the presence or absence of oxygen during the period of dark CO 2 fixation. 相似文献
20.
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
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