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1.
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
2.
Photosynthetic CO 2 and O 2 exchange was studied in two moss species, Hypnum cupressiforme Hedw. and Dicranum scoparium Hedw. Most experiments were made during steady state of photosynthesis, using 18O 2 to trace O 2 uptake. In standard experimental conditions (photoperiod 12 h, 135 micromoles photons per square meter per second, 18°C, 330 microliters per liter CO 2, 21% O 2) the net photosynthetic rate was around 40 micromoles CO 2 per gram dry weight per hour in H. cupressiforme and 50 micromoles CO 2 per gram dry weight per hour in D. scoparium. The CO 2 compensation point lay between 45 and 55 microliters per liter CO 2 and the enhancement of net photosynthesis by 3% O 2versus 21% O 2 was 40 to 45%. The ratio of O 2 uptake to net photosynthesis was 0.8 to 0.9 irrespective of the light intensity. The response of net photosynthesis to CO 2 showed a high apparent Km (CO 2) even in nonsaturating light. On the other hand, O 2 uptake in standard conditions was not far from saturation. It could be enhanced by only 25% by increasing the O 2 concentration (saturating level as low as 30% O 2), and by 65% by decreasing the CO 2 concentration to the compensation point. Although O 2 is a competitive inhibitor of CO 2 uptake it could not replace CO 2 completely as an electron acceptor, and electron flow, expressed as gross O 2 production, was inhibited by both high O 2 and low CO 2 levels. At high CO 2, O 2 uptake was 70% lower than the maximum at the CO 2 compensation point. The remaining activity (30%) can be attributed to dark respiration and the Mehler reaction. 相似文献
3.
The mass transfer rate of 14C-sucrose translocation from sugar beet ( Beta vulgaris, L.) leaves was measured over a range of net photosynthesis rates from 0 to 60 milligrams of CO 2 decimeters −2 hour −1 under varying conditions of light intensity, CO 2 concentration, and O 2 concentration. The resulting rate of translocation of labeled photosynthate into total sink tissue was a linear function (slope = 0.18) of the net photosynthesis rate of the source leaf regardless of light intensity (2000, 3700, or 7200 foot-candles), O 2 concentration (21% or 1% O 2), or CO 2 concentration (900 microliters/liter of CO 2 to compensation concentration). These data support the theory that the mass transfer rate of translocation under conditions of sufficient sink demand is limited by the net photosynthesis rate or more specifically by sucrose synthesis and this limitation is independent of light intensity per se. The rate of translocation was not saturated even at net photosynthesis rates four times greater than the rate occurring at 300 microliters/liter of CO 2, 21% O 2, and saturating light intensity. 相似文献
4.
The 18O-enrichment of CO 2 produced in the light or during the post-illumination burst was measured by mass spectrometry when a photoautotrophic cell suspension of Euphorbia characias L. was placed in photorespiratory conditions in the presence of molecular 18O 2. The only 18O-labeled species produced was C 18O 16O; no C 18O 18O could be detected. Production of C 18O 16O ceased after addition of two inhibitors of the photosynthetic carbon-oxidation cycle, aminooxyacetate or aminoacetonitrile, and was inhibited by high levels of CO 2. The average enrichment during the post-illumination burst was estimated to be 46 ± 15% of the enrichment of the O 2 present during the preceding light period. Addition of exogenous carbonic anhydrase, by catalyzing the exchange between CO 2 and H 2O, drastically diminished the 18O-enrichment of the produced CO 2. The very low carbonio-anhydrase level of the photoautotrophic cell suspension probably explains why the 18O labeling of photorespiratory CO 2 could be observed for the first time. These data allow the establishment of a direct link between O 2 consumption and CO 2 production in the light, and the conclusion that CO 2 produced in the light results, at least partially, from the mitochondrial decarboxylation of the glycine pool synthesized through the photosynthetic carbon-oxidation cycle. Analysis of the C 18O 16O and CO 2 kinetics provides a direct and reliable way to assess in vivo the real contribution of photorespiratory metabolism to CO 2 production in the light. 相似文献
5.
1. The effect of H 2 tension, CO 2 tension, pH, time, light intensity, density of suspension, salt content of the medium, and certain spectral regions on the rate of photoassimilation of H 2 and CO 2 by Streptococcus varians has been studied. 2. The method of making light absorption measurements with thin suspensions of bacteria is described. 3. A light source, optical system, and filter for isolating 852 mµ with 894 mµ in sufficient intensity for photochemical work and an improved design of thermostat are given. 4. The photoassimilation of 2H 2 with 1CO 2 apparently involves little over all energy change but nevertheless requires 4 quanta. 相似文献
6.
A mass spectrometric method combining 16O/ 18O and 12C/ 13C isotopes was used to quantify the unidirectional fluxes of O 2 and CO 2 during a dark to light transition for guard cell protoplasts and mesophyll cell protoplasts of Commelina communis L. In darkness, O 2 uptake and CO 2 evolution were similar on a protein basis. Under light, guard cell protoplasts evolved O 2 (61 micromoles of O 2 per milligram of chlorophyll per hour) almost at the same rate as mesophyll cell protoplasts (73 micromoles of O 2 per milligram of chlorophyll per hour). However, carbon assimilation was totally different. In contrast with mesophyll cell protoplasts, guard cell protoplasts were able to fix CO 2 in darkness at a rate of 27 micromoles of CO 2 per milligram of chlorophyll per hour, which was increased by 50% in light. At the onset of light, a delay observed for guard cell protoplasts between O 2 evolution and CO 2 fixation and a time lag before the rate of saturation suggested a carbon metabolism based on phospho enolpyruvate carboxylase activity. Under light, CO 2 evolution by guard cell protoplasts was sharply decreased (37%), while O 2 uptake was slowly inhibited (14%). A control of mitochondrial activity by guard cell chloroplasts under light via redox equivalents and ATP transfer in the cytosol is discussed. From this study on protoplasts, we conclude that the energy produced at the chloroplast level under light is not totally used for CO 2 assimilation and may be dissipated for other purposes such as ion uptake. 相似文献
7.
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
8.
The gas exchange of spinach plants, salt-stressed by adding NaCl to the nutrient solution in increments of 25 millimolar per day to a final concentration of 200 millimolar, was studied 3 weeks after starting NaCl treatment. Photosynthesis became light saturated at 1100 to 1400 micromoles per square meter per second in salt-treated plants and at approximately 2000 micromoles per square meter per second in control plants. Photosynthetic capacity of the mesophyll measured as a function of intercellular partial pressure of CO 2 at the light intensity prevailing during growth and at light saturation were both decreased in the salttreated plants. The CO 2 compensation points and relative enhancements of photosynthesis at low O 2 were not affected by salinity. The lower photosynthetic rates in salt-treated leaves at 450 micromoles per square meter per second were associated with a 70% reduction in stomatal conductance and low intercellular CO 2 (219 microbars; cf. 285 microbars for controls). Increasing photon flux density to light saturation extended the linear portions of the CO 2 response curves, increased stomatal conductances, increased intercellular CO 2 in the salt-treated plants, but lowered it in controls, and accentuated differences in photosynthetic rate (area basis) between the treatments. Leaves from salt-treated plants were thicker but contained about 73% of the chlorophyll per unit area of control plants. When photosynthetic rates were expressed on a chlorophyll basis there was no difference in initial slope of assimilation versus intercellular CO2 between treatments. Photosynthetic rates (chlorophyll basis) at light saturation differed only by 20% which was also observed earlier with isolated, intact chloroplasts (Robinson et al. 1983 Plant Physiol 73: 238-242). Measurement of carbon isotope ratio revealed less discrimination against 13C with salt treatment and confirmed the persistence of low intercellular partial pressures of CO2 during plant growth. The development of a thicker leaf with less chlorophyll per unit area during salt treatment permitted stomatal conductance and intercellular partial pressure of CO2 to decline without restricting photosynthesis and had the benefit of greatly increasing water use efficiency. 相似文献
9.
The nature of the process responsible for the stationary O 2 uptake occurring in the light under saturating CO 2 concentration in Chlamydomonas reinhardii has been investigated. For this purpose, a mass spectrometer with a membrane inlet system was used to measure O 2 uptake and evolution in the algal suspension. First, we observed that the O 2 uptake rate was constant (about 0.5 micromoles of O 2 per milligram chlorophyll per minute) during a light to dark transition and was not affected by 3-(3,4-dichlorophenyl)-1,1-dimethylurea. Salicylhydroxamic acid had no effect on O 2 uptake in the dark or in the light, but was found to have the same inhibitory effect either in the dark or in the light when added to cyanide-treated algae. The stimulation of the O 2 uptake rate due to the uncoupling effect of carbonyl cyanide m-chlorophenylhydrazone was about the same in the dark or in the light. From these results, we conclude that mitochondrial respiration is maintained during illumination and therefore is not inhibited by high ATP levels. Another conclusion is that in conditions where photorespiration is absent, no other light-dependent O 2 uptake process occurs. If Mehler reactions are involved, in Chlamydomonas, under conditions where both photosynthetic carbon oxidation and reduction cycles cannot operate (as in cyanide-treated algae), their occurrence in photosynthesizing algae either under saturating CO 2 concentration or at the CO 2 compensation point appears very unlikely. The comparison with the situation previously reported in Scenedesmus (R. J. Radmer and B. Kok 1976 Plant Physiol 58: 336-340) suggests that different O 2 uptake processes might be present in these two algal species. 相似文献
10.
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
11.
In leaves, the light reactions of photosynthesis support fatty acid synthesis but disagreement exists as to whether this occurs in green oilseeds. To address this question, simultaneous measurements of the rates of CO 2 and O 2 exchange (CER and OER, respectively) were made in soybean ( Glycine max L.) fruits. The imbalance between CER and OER was used to estimate the diverted reductant utilization rate (DRUR) in the equation: DRUR = 4 × (OER + CER). This yielded a quantitative measure of the rate of synthesis of biomass that is more reduced per unit carbon than glucose (in photosynthesizing tissues) or than the substrates of metabolism (in respiring tissues). The DRUR increased by about 2.2-fold when fruits were illuminated due to a greater increase in OER than decrease in CER. This characteristic was shown to be a property of the seed (not the pod wall), to be present in fruits at all developmental stages, and to reach a maximal response at relatively low light. When seeds were provided with 13CO 2, light reduced 12CO 2 production but had little effect on 13CO 2 fixation. When they were provided with 18O 2, light stimulated 16O 2 production but had no effect on 18O 2 uptake. Together, these findings indicate that light stimulates fatty acid synthesis in photosynthetic oilseeds, probably by providing both ATP and carbon skeletons. 相似文献
12.
A closed system consisting of an assimilation chamber furnished with a membrane inlet from the liquid phase connected to a mass spectrometer was used to measure O 2 evolution and uptake by Chlamydomonas reinhardtii cells grown in ambient (0.034% CO 2) or CO 2-enriched (5% CO 2) air. At pH = 6.9, 28°C and concentrations of dissolved inorganic carbon (DIC) saturating for photosynthesis, O 2 uptake in the light (U o) equaled O 2 production (E o) at the light compensation point (15 micromoles photons per square meter per second). E o and U o increased with increasing photon fluence rate (PFR) but were not rate saturated at 600 micromoles photons per square meter per second, while net O 2 exchange reached a saturation level near 500 micromoles photons per square meter per second which was nearly the same for both, CO 2-grown and air-grown cells. Comparison of the U o/E o ratios between air-grown and CO 2-grown C. reinhardtii showed higher values for air-grown cells at light intensities higher than light compensation. For both, air-grown and CO 2-grown algae the rates of mitochondrial O 2 uptake in the dark measured immediately before and 5 minutes after illumination were much lower than U o at PFR saturating for net photosynthesis. We conclude that noncyclic electron flow from water to NADP + and pseudocyclic electron flow via photosystem I to O 2 both significantly contribute to O 2 exchange in the light. In contrast, mitochondrial respiration and photosynthetic carbon oxidation cycle are regarded as minor O 2 consuming reactions in the light in both, air-grown and CO 2-grown cells. It is suggested that the “extra” O 2 uptake by air-grown algae provides ATP required for the energy dependent CO 2/HCO 3− concentrating mechanism known to be present in these cells. 相似文献
13.
Highly chlorophyllous photomixotrophic callus was visually selected from callus originating from soybean ( Glycine max (L.) Merr. var. Corsoy) cotyledon. Suspension cultures initiated from this callus became photoautotrophic under continuous light with an atmosphere of 5% CO 2 (balance air). Dry weight increases of 1000 to 1400% in the 2-week subculture period have been observed. The cellular Chl content ranged from 4.4 to 5.9 micrograms per milligram dry weight which is about 75 to 90% of the Chl content in soybean leaves under equivalent illumination (300 micro-Einsteins per square meter per second). No growth can be observed in the dark in sucrose-lacking medium or in the presence of 0.5 micromolar 3-(3,4-dichlorophenyl)-1,1-dimethylurea, a concentration which does not inhibit heterotrophic growth (on sucrose). Photoautotrophic growth has an absolute requirement for elevated CO2 concentrations (>1%). During the 14-day subculture period, growth (fresh weight and dry weight) is logarithmic. Photosynthesis quickly increases after day 4, reaching a peak of 83 micromoles CO2 incorporated per milligram Chl per hour while dark respiration decreases 90% from day 2 to day 6. The pH of the growth medium quickly drops from 7.0 to 4.5 before slowly increasing to 5.0 by day 14. At this pH range and light intensity (200-300 microEinsteins per square meter per second), no O2 evolution could be detected although at high pH and light intensity O2 evolution was recorded. 相似文献
14.
The size of the Emerson photosynthetic unit was measured in Chlorella pyrenoidosa strain no. 252 grown at light intensities between 50 and 1000 foot candles. The Emerson photosynthetic unit changed from a minimum size of 1970 molecules chlorophyll a + b/O 2 per flash in cells grown at 1000 foot candles to a maximum size of 3150 molecules chlorophyll a + b/O 2 per flash for cells grown at 50 foot candles. The size changes were interpreted as a partial adaptation where the trapping center antenna responded to changes in incident light intensity. Light-induced changes in chlorophyll content and size of the Emerson photosynthetic unit were directly related. 相似文献
15.
Rates of CO 2 assimilation and steady state chlorophyll a fluorescence were measured simultaneously at different intercellular partial pressures of CO 2 in attached cotton ( Gossypium hirsutum L. cv Deltapine 16) leaves at 25°C. Electron transport activity for CO 2 assimilation plus photorespiration was calculated for these experiments. Under light saturating (1750 microeinsteins per square meter per second) and light limiting (700 microeinsteins per square meter per second) conditions there was a good correlation between fluorescence and the calculated electron transport activity at 19 and 200 millibars O 2, and between fluorescence and rates of CO 2 assimilation at 19 millibars but not 200 millibars O 2. The values of fluorescence measured at about 220 microbars intercellular CO 2 were not greatly affected by increasing O 2 from 19 to 800 millibars. Fluorescence increased with light intensity at any one intercellular CO 2 partial pressure. But the values obtained for fluorescence, expressed as a ratio of the maximum fluorescence obtained in DCMU-treated tissue, over the same range of CO 2 partial pressure at 500 microeinsteins per square meter per second were similar to those obtained at 1000 and 2000 microeinsteins per square meter per second. There were two phases in the observed correlation between fluorescence and calculated electron transport activity: an initial inverse relationship at low CO 2 partial pressures which reversed to a positive correlation at higher values of CO 2 partial pressures. Similar results were observed in the C 3 species Helianthus annuus L., Phaseolus vulgaris L., and Brassica chinensis. In all C 4 species ( Zea mays L., Sorghum bicolor L., Panicum maximum Jacq., Amaranthus edulis Speg., and Echinochloa frumentacea [Roxb.] Link) examined changes in fluorescence were directly correlated with changes in CO 2 assimilation rates. The nature and the extent to which Q (primary quencher) and high-energy state ( qE) quenching function in determining the steady state fluorescence obtained during photosynthesis in leaves is discussed. 相似文献
16.
Data from a small cylindrical culture unit with variable annular culture chambers indicate that (i) the rate of oxygen evolution by an algal culture in the linear phase of growth is a logarithmic function of light intensity, and (ii) the rate of oxygen evolution per unit volume of suspension is linearly related to the reciprocal of culture thickness. These two relationships have been combined in an empirical equation which gives the expected variation of the oxygen production rate with light intensity, culture thickness, and suspension volume. The applicability of this equation has been tested on a larger, multilight culture unit in this laboratory. The agreement between the experimental and calculated oxygen production rates was very satisfactory, suggesting that the equation is not limited to a particular culture unit but may have wide applicability. The efficiency of the culture unit from the standpoint of oxygen output (chemical energy) relative to electrical energy to supply the light source has been calculated, and the maximum value of 0.51% was obtained. The energy to run auxiliary equipment was not a factor in these calculations. The maximum efficiency in converting light energy to chemical energy was approximately 12%. An extrapolation of the experimental results suggests that approximately 2 ft 3 and 30 kw would be required to provide the oxygen needs of one man. 相似文献
17.
Assimilatory power was measured in ten C 3 species by means of a rapid-response gas exchange device as the total amount of CO 2 fixed in N 2-CO 2 atmosphere after switching the light off. Different steady-state levels of the assimilatory power were obtained by varying light intensity and O 2 and CO 2 concentrations during the preexposition periods in the leaf chamber. Within the limits of the linear part of the CO2 curve of photosynthesis in N2, the assimilatory power is constant, being sufficient for the assimilation of about 20 nanomoles CO2 per square centimeter leaf. The pool starts to decrease with the onset of the CO2 saturation of photosynthesis. Increase in O2 concentration from 0 to 100% at 350 microliters CO2 per liter produces a considerable decrease in the assimilatory power. The mesophyll conductance (M) was found to be proportional to the assimilatory power (A): M = mA. The most frequently occurring values of the proportionality constant (m) (called the specific efficiency of carboxylation) were concentrated between 0.03 and 0.04 centimeter per second per nanomole A per square centimeter but the measured extreme values were 0.01 and 0.06 centimeter per second per nanomole A per square centimeter. The specific rate of carboxylation (the rate per unit A) showed a hyperbolic dependence on CO2 conentration with the most frequent values of Km (CO2) ranging from 25 to 35 micromolar in the liquid phase of mesophyll cells (extremes 23 and 100 micromolar). It is concluded that the CO2− and light-saturated rate of photosynthesis is limited by the reactions of the formation of the assimilatory power and not by ribulose-1,5-bisphosphate carboxylase. O2 is a competitive consumer of the assimilatory power, and the inhibitory effect of O2 on photosynthesis is caused mainly by a decrease in the pool of the assimilatory power at high O2 concentrations. In intact leaves, the kinetic properties of ribulose-1,5-bisphosphate carboxylase seem to be variable. 相似文献
18.
1. Chlorella pyrenoidosa has been grown in a continuous-culture apparatus under various light intensities provided by incandescent lamps, other conditions of culture being maintained constant. Light intensity curves for cells immersed in the No. 11 Warburg buffer and in Knop''s solution + 4.4 per cent CO 2 at a saturating light intensity were determined as characteristics of the photosynthetic mechanism. These characteristics were referred to the centrifuged cell volume as an index of quantity of cellular material. 2. Cells grown at intensities in the range of about 35 f.-c. develop a capacity for a high rate of photosynthesis (c.mm. O 2/hour/c.mm. cells). At culture intensities above or below this range the cells produced have a lower capacity for photosynthesis. A similar effect is observed for rate of photosynthesis per unit dry weight or rate per unit cell nitrogen. 3. The rate of photosynthesis per cell or rate per unit chlorophyll shows no maximum at any light intensity of culture but increases continuously throughout the range of light intensities studied. 4. Maximum rate of growth is attained at a light intensity of about 100 f.-c. The hypothesis is advanced that at culture intensities above that needed to give maximum rate of growth (100 f.-c.) a mechanism is developed which opposes the photosynthetic process and removes the photosynthetic products. 5. The low capacity for photosynthesis shown by cells grown at culture intensities below 35 f.-c. finds no immediate explanation. 6. The shape of the light intensity curve is markedly affected by the light intensity at which the cells have been cultured. Cells grown at lower intensities give light intensity curves approaching the Blackman type with a short transitional region between light limitation and light saturation. 相似文献
19.
A procedure is described for isolating photosynthetically active rhodoplasts (“red algal chloroplasts”) from the marine alga Griffithsia monilis. The rhodoplasts exhibited rates of CO 2 fixation and CO 2-dependent O 2 evolution in the order of 200 micromoles per milligram chlorophyll a per hour when illuminated with red or green light and were approximately 80% intact. The response of the rate of photosynthesis to the inorganic phosphate and pyrophosphate concentrations in the medium was qualitatively similar to that previously reported for spinach chloroplasts. Osmotically shocked rhodoplasts evolved O 2 from ferricyanide in red, but not in green, light and were completely uncoupled. Rhodoplast envelope rupture appeared to be accompanied by phycobilisome loss from the thylakoids. 相似文献
20.
Unidirectional O 2 fluxes were measured with 18O 2 in a whole plant of wheat cultivated in a controlled environment. At 2 or 21% O 2, O 2 uptake was maximum at 60 microliters per liter CO 2. At lower CO 2 concentrations, it was strongly inhibited, as was photosynthetic O 2 evolution. At 2% O 2, there remained a substantial O 2 uptake, even at high CO 2 level; the O 2 evolution was inhibited at CO 2 concentrations under 330 microliters per liter. The O 2 uptake increased linearly with light intensity, starting from the level of dark respiration. No saturation was observed at high light intensities. No significant change in the gas-exchange patterns occurred during a long period of the plant life. An adaptation to low light intensities was observed after 3 hours illumination. These results are interpreted in relation to the functioning of the photosynthetic apparatus and point to a regulation by the electron acceptors and a specific action of CO 2. The behavior of the O 2 uptake and the study of the CO 2 compensation point seem to indicate the persistence of mitochondrial respiration during photosynthesis. 相似文献
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