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1.
A method is described for rapid enzymatic isolation of protoplasts from the Crassulacean acid metabolism (CAM) plant Kalanchoe blossfeldiana cv. Tom Thumb. Young leaves were sampled at low, middle or full CAM levels induced by increasing number of short-days (14, 31 and 49 SD). Maximum O 2 exchange in light or dark and maximum CO 2 fixation in light occur with protoplasts obtained at 1730 (end of the day) for all CAM levels. Dark CO 2 fixation, typical of CAM, is performed by protoplasts isolated in the middle of the night from plants having received at least 31 SD. Rates of dark CO 2 fixation by these protoplasts are of the same order as those of intact leaves. The capacity for O 2 exchange and CO 2 fixation increases with the level of CAM. These protoplasts retain characteristics typical of CAM, such as diurnal oscillations in phospho enolpyruvate carboxylase (EC 4.1.1.31; PEPC) capacity and malate content. 相似文献
2.
Intact chloroplasts were obtained from mesophyll protoplasts isolated from Mesembryanthemum crystallinum in the C 3 or Crassulacean acid metabolism (CAM) photosynthetic mode, and examined for the influence of inorganic phosphate (Pi) on aspects of bicarbonate-dependent O 2 evolution and CO 2 fixation. While the chloroplasts from both modes responded similarly to varying Pi, some features appear typical of chloroplasts from species capable of CAM, including a relatively high capacity for photosynthesis in the absence of Pi, a short induction period, and resistance to inhibition of photosynthesis by high levels of Pi. In the absence of Pi the chloroplasts retained 75–85% of the 14CO 2 fixed and the total export of dihydroxyacetone phosphate was low compared with the rate of photosynthesis. In CAM plants the ability to conduct photosynthesis and retain most of the fixed carbon in the chloroplasts at low external Pi concentrations may enable storage of carbohydrates which are essential for providing a carbon source for the nocturnal synthesis of malic acid. At high external Pi concentrations (e.g. 10 25 mM), the amount of total dihydroxyacetone phosphate exported to the assay medium relative to the rate of photosynthesis was high while the products of 14CO 2 fixation were largely retained in the chloroplasts which indicates starch degradation is occurring at high Pi levels. Starch degradation normally occurs in CAM plants in the dark; high levels of Pi may induce starch degradation in the light which has the effect of limiting export of the immediate products of photosynthesis and thus the degree of Pi inhibition of photosynthesis with the isolated chloroplast. 相似文献
3.
Crassulacean acid metabolism (CAM) is a physiological adaptation of plants that live in stress environment conditions. A good model of CAM modulation is the epiphytic bromeliad, Guzmania monostachia, which switches between two photosynthetic pathways (C 3–CAM) in response to different environmental conditions, such as light stress and water availability. Along the leaf length a gradient of acidity can be observed when G. monostachia plants are kept under water deficiency. Previous studies showed that the apical portions of the leaves present higher expression of CAM, while the basal regions exhibit lower expression of this photosynthetic pathway. The present study has demonstrated that it is possible to induce the CAM pathway in detached leaves of G. monostachia kept under water deficit for 7 d. Also, it was evaluated whether CAM expression can be modulated in detached leaves of Guzmania and whether some spatial separation between NO 3− reduction and CO 2 fixation occurs in basal and apical portions of the leaf. In addition, we analyzed the involvement of endogenous cytokinins (free and ribosylated forms) as possible signal modulating both NO 3− reduction and CO 2 fixation along the leaf blade of this bromeliad. Besides demonstrating a clear spatial and functional separation of carbon and nitrogen metabolism along G. monostachia leaves, the results obtained also indicated a probable negative correlation between endogenous free cytokinins – zeatin (Z) and isopentenyladenine (iP) – concentration and PEPC activity in the apical portions of G. monostachia leaves kept under water deficit. On the other hand, a possible positive correlation between endogenous Z and iP levels and NR activity in basal portions of drought-exposed and control leaves was verified. Together with the observations presented above, results obtained with exogenous cytokinins treatments, strongly suggest that free cytokinins might act as a stimulatory signal involved in NR activity regulation and as a negative regulator of PEPC activity in CAM-induced leaves of G. monostachia during a diel cycle. 相似文献
4.
The diurnal variations in volume and in specific weight were determined for green stems and leaves of Crassulacen acid metabolism (CAM) plants. Volume changes were measured by a water displacement method. Diurnal variations occurred in the volume of green CAM tissues. Their volume increased early in the light period reaching a maximum about mid-day, then the volume decreased to a minimum near midnight. The maximum volume increase each day was about 2.7% of the total volume. Control leaves of C 3 and C 4 plants exhibited reverse diurnal volume changes of 0.2 to 0.4%. The hypothesis is presented and supported that green CAM tissues should exhibit a diurnal increase in volume due to the increase of internal gas pressure from CO 2 and O 2 when their stomata are closed. Conversely, the volume should decrease when the gas pressure is decreased. The second hypothesis presented and supported was that the specific weight (milligrams of dry weight per square centimeter of green surface area) of green CAM tissues should increase at night due to the net fixation of CO2. Green CAM tissues increased their specific weight at night in contrast to control C3 and C4 leaves which decreased their specific weight at night. With Kalanchoë daigremontiana leaves, the calculated increase in specific leaf weight at night based on estimates of carbohydrate available for net CO2 fixation was near 6% and the measured increase in specific leaf weight was 6%. Diurnal measurements of CAM tissue water content were neither coincident nor reciprocal with their diurnal patterns of either volume or specific weight changes. 相似文献
5.
Chlorophyll a fluorescence of Synechococcus UTEX 625 was quenched during the transport of inorganic carbon, even when CO 2 fixation was inhibited by iodoacetamide. Measurements with a pulse modulation fluorometer showed that at least 75% of the quenching was due to oxidation of Q a, the primary acceptor of photosystem II. Mass spectrometry revealed that transport of inorganic carbon increased the rate of O 2 photoreduction. Hence, O 2 could serve as an electron acceptor to allow oxidation of Q a even in the absence of CO 2 fixation. 相似文献
6.
Mesembryanthemum crystallinum, a halophilic, inducible Crassulacean acid metabolism (CAM) species, was grown at NaCl concentrations of 20 and 400 millimolar in the rooting medium. Plants from the low salinity treatment showed exclusively C 3-photosynthetic net CO 2 fixation, whereas plants exposed to the high salinity level exhibited net CO 2 dark fixation involving CAM. Mesophyll protoplasts, isolated from both tissues, were gently ruptured, and the intracellular localization of enzymes was studied following differential centrifugation and Percoll density gradient centrifugation of protoplast extracts. Both centrifugation techniques resulted in the separation of intact chloroplasts, with up to 90% yield, from other organelles and the nonparticulate fraction of cells. Enzymes were identified by determination of activity and by sodium dodecyl sulfate gel electrophoresis of enzyme protein. 相似文献
7.
Simultaneous measurements have been made of inorganic carbon accumulation (by mass spectrometry) and chlorophyll a fluorescence yield of the cyanobacterium Synechococcus UTEX 625. The accumulation of inorganic carbon by the cells was accompanied by a substantial quenching of chlorophyll a fluorescence. The quenching occurred even when CO 2 fixation was inhibited by iodoacetamide and whether the accumulation of inorganic carbon resulted from either active CO 2 or HCO 3− transport. Measurement of chlorophyll a fluorescence yield of cyanobacteria may prove to be a rapid and convenient means of screening for mutants of inorganic carbon accumulation. 相似文献
8.
Summary Carbon fixation by CAM at high night temperatures was examined in the stem succulent, Opuntia basilaris. Nighttime accumulation of titratable acids was uniformly high among plants growing naturally along an altitudinal temperature gradient in Death Valley, California during the hot summer period. Plants grown at high temperature regimes (40°/30°C) had rates of CAM and C 3 fixation similar to rates observed in plants maintained at a cool temperature (20°/10°C). C 3 fixation comprised 30% of the total carbon fixed by the potted, well watered plants. However, when pads were excised, C 3 fixation was suppressed while CAM continued unabated. 相似文献
9.
In response to water stress, Portulacaria afra (L.) Jacq. (Portulacaceae) shifts its photosynthetic carbon metabolism from the Calvin-Benson cycle for CO 2 fixation (C 3) photosynthesis or Crassulacean acid metabolism (CAM)-cycling, during which organic acids fluctuate with a C 3-type of gas exchange, to CAM. During the CAM induction, various attributes of CAM appear, such as stomatal closure during the day, increase in diurnal fluctuation of organic acids, and an increase in phosphoenolpyruvate carboxylase activity. It was hypothesized that stomatal closure due to water stress may induce changes in internal CO 2 concentration and that these changes in CO 2 could be a factor in CAM induction. Experiments were conducted to test this hypothesis. Well-watered plants and plants from which water was withheld starting at the beginning of the experiment were subjected to low (40 ppm), normal ( ca. 330 ppm), and high (950 ppm) CO 2 during the day with normal concentrations of CO 2 during the night for 16 days. In water-stressed and in well-watered plants, CAM induction as ascertained by fluctuation of total titratable acidity, fluctuation of malic acid, stomatal conductance, CO 2 uptake, and phosphoenolpyruvate carboxylase activity, remained unaffected by low, normal, or high CO 2 treatments. In well-watered plants, however, both low and high ambient concentrations of CO 2 tended to reduce organic acid concentrations, low concentrations of CO 2 reducing the organic acids more than high CO 2. It was concluded that exposing the plants to the CO 2 concentrations mentioned had no effect on inducing or reducing the induction of CAM and that the effect of water stress on CAM induction is probably mediated by its effects on biochemical components of leaf metabolism. 相似文献
11.
BackgroundIn obligate Crassulacean acid metabolism (CAM), up to 99 % of CO 2 assimilation occurs during the night, therefore supporting the hypothesis that CAM is adaptive because it allows CO 2 fixation during the part of the day with lower evaporative demand, making life in water-limited environments possible. By comparison, in facultative CAM (inducible CAM, C 3-CAM) and CAM-cycling plants drought-induced dark CO 2 fixation may only be, with few exceptions, a small proportion of C 3 CO 2 assimilation in watered plants and occur during a few days. From the viewpoint of survival the adaptive advantages, i.e. increased fitness, of facultative CAM and CAM-cycling are not obvious. Therefore, it is hypothesized that, if it is to increase fitness, CAM must aid in reproduction. ScopeAn examination of published reports of 23 facultative CAM and CAM-cycling species finds that, in 19 species, drought-induced dark CO 2 fixation represents on average 11 % of C 3 CO 2 assimilation of watered plants. Evidence is discussed on the impact of the operation of CAM in facultative and CAM-cycling plants on their survival – carbon balance, water conservation, water absorption, photo-protection of the photosynthetic apparatus – and reproductive effort. It is concluded that in some species, but not all, facultative and cycling CAM contribute, rather than to increase carbon balance, to increase water-use efficiency, water absorption, prevention of photoinhibition and reproductive output.Key words: Facultative CAM, CAM-cycling, water, crassulacean acid metabolism, deficit 相似文献
12.
Contrary to earlier reports, CO 2 fixation by extracts of Chlamydomonas is inhibited by glutamate and aspartate. These amino acids and some organic acids are shown to be inhibitors of phosphoenolpyruvate carboxylase. Inorganic phosphate is shown to activate CO 2 fixation, but there is a time lag before inorganic phosphate exerts its full activating effect. 相似文献
13.
Malate concentration and stem osmotic pressure concomitantly increase during nighttime CO 2 fixation and then decrease during the daytime in the obligate Crassulacean acid metabolism (CAM) plant, Cereus validus (Cactaceae). Changes in malate osmotic pressure calculated using the Van't Hoff relation match the changes in stem osmotic pressure, indicating that changes in malate level affected the water relations of the succulent stems. In contrast to stem osmotic pressure, stem water potential showed little day-night changes, suggesting that changes in cellular hydrostatic pressure occurred. This was corroborated by direct measurements of hydrostatic pressure using the Jülich pressure probe where a small oil-filled micropipette is inserted directly into chlorenchyma cells, which indicated a 4-fold increase in hydrostatic pressure from dusk to dawn. A transient increase of hydrostatic pressure at the beginning of the dark period was correlated with a short period of stomatal closing between afternoon and nighttime CO 2 fixation, suggesting that the rather complex hydrostatic pressure patterns could be explained by an interplay between the effects of transpiration and malate levels. A second CAM plant, Agave deserti, showed similar day-night changes in hydrostatic pressure in its succulent leaves. It is concluded that, in addition to the inverted stomatal rhythm, the oscillations of malate markedly affect osmotic pressures and hence water relations of CAM plants. 相似文献
14.
The dissolved inorganic carbon concentrating mechanism(s) of Chlamydomonas moewusii CC 55 was compared with C. reinhardtii strain 137. C. moewusii is similar to C. reinhardtii with respect to maximal rates of photosynthetic oxygen evolution, CO 2 fixation, respiration, and the ability to efficiently concentrate inorganic carbon. C. moewusii has a low, but measurable amount of external carbonic anhydrase (CA) that was not inhibited by acetazolamide (AZ), an inhibitor of periplasmic carbonic anhydrase (pCA) in C. reinhardtii. The K 0.5(CO 2) for air-grown C. moewusii is about 1 μM and the algal cells accumulated dissolved inorganic carbon (DIC) to a level of about 1 mM in 60 s. AZ did not inhibit CO 2 fixation and the DIC accumulation by air-grown cells of C. moewusii. The K 0.5(CO 2) for both species remains constant from pH 6.5 to 9.5 while K 0.5(HCO 3-) increased logarithmically, which indicates that CO 2 is the apparent inorganic carbon species that enters the cells in both algae. Antiserum prepared against the 37 kDa peptide of pCA from C. reinhardtii was immunoreactive with polypeptides of 26, 28, and 32 kDa in C. moewusii. The periplasmic carbonic anhydrase (pCA) activity is a part of the dissolved inorganic carbon concentrating mechanism in C. reinhardtii, but C moewusii accomplished inorganic carbon accumulation without an AZ-sensitive pCA. 相似文献
15.
Photosynthetically highly active chloroplasts were routinely obtained by rupture of leaf protoplasts from the halophyte Mesembryanthemum crystallinum which exhibited the photosynthetic characteristics of either a C 3 plant when grown with 20 mmol l -1 NaCl in the rooting medium, or a Crassulacean-acid-metabolism (CAM) plant when grown with 400 mmol l -1 NaCl. Photosynthesis rates of C 3 and CAM chloroplasts were 150–250 and 90–150 μmol mg -1 chlorophyll h -1, respectively. Because of osmotic adjustment, CAM chloroplasts required higher sorbitol concentrations (0.7–0.8 mol l -1) in the assay medium than C 3 chloroplasts (0.3–0.4 mol l -1) for optimum activity. Substitution of sorbitol by NaCl as the osmoticum strongly reduced photosynthesis of CAM chloroplasts. Rates of electron transport (ferricyanide reduction, uncoupled) remained unaffected over a range of sorbitol concentrations (0 to 1 mol l -1). Sensitivity of electron transport to increasing levels of NaCl was less pronounced than the NaCl-sensitivity of CO 2 fixation by intact chloroplasts. The CAM chloroplasts showed a broad pH optimum of photosynthesis between pH 7.0 and 8.2; photosynthesis of C 3 chloroplasts dropped markedly below pH 7.6. The CAM chloroplasts maintained a higher transenvelope proton gradient than C 3 chloroplasts both in the light and dark. External pyruvate (5 mmol l -1) inhibited photosynthesis of CAM chloroplasts, but not of C 3 chloroplasts. Inhibition was reduced by increased external concentrations of orthophosphate. 相似文献
16.
The CAM has been tested in six species of the Aeonium genus by studying the diurnal fluctuation of organic acids, pH and night fixation of CO 2. The existence of a mesophyll structure able to support this metabolism has been shown as well as a congruent periodicity in the pool of cell starch. We have calculated the S, ES and Sm indices in the six species. A series of regression equations of different grades and types were calculated and shown to have correlation coefficients statistically significant. This allows us to confirm the suitability of the Sm index as a rapid test to establish the CAM as postulated by former authors. 相似文献
17.
Abstract Ecological aspects of C3, C4 and CAM photosynthetic pathways. - Three different photosynthetic CO 2 fixation pathways are known to occur in higher plants. However all three pathways ultimately depend on the Calvin-Benson cycle for carbon reduction. The oxygenase activity of RuBP carboxilase is responsible for photorespiratory CO 2 release. Both C 4 and CAM pathways behave as a CO 2 concentrating mechanism which prevent photorespiration. The CO 2-concentrating mechanism in C 4 plants is based on intracellular symplastic transport of C 4 dicarboxylic acids from mesophyll-cells to the adjacent bundle-sheath cells. On the contrary in CAM plants the CO 2-concentrating mechanism is based on the intracellular transport of malic acid into and out of the vacuole. The C 4 photosynthetic pathway as compared to the C 3 pathway permits higher rates of CO 2 fixation in high light and high temperature environments at low costs in terms of water loss, given the stability of the photosynthetic apparatus under such conditions. CAM is interpreted as an adaptation to arid environments because it enables carbon assimilation to take place at very low water costs during the night when the evaporative demand is low. Nevertheless many aquatic species of Isoetes and some relatives are CAM, suggesting the adaptive role of CAM to environments which become depleted in CO 2. The photosynthetic carbon fixation pathway certainly contributes to the ecological success of plants in different environments. However the distribution of plants may also reflect their biological history. On the other hand plants with different photosynthetic pathways coexist in many communities and tend to share resources in time. In any case some generalizations are possible: C 4 plants enjoy an ecological advantage in hot, moist, high light regions while the majority of species in desert environments are C 3; CAM plants are more frequent in semiarid regions with seasonal rainfall, coastal fog deserts, and in epiphytic habitats in tropical rain forests. 相似文献
18.
The induction kinetics of the 680 nm chlorophyll fluorescence were measured on attached leaves of Kalanchoë daigremontiana R. Hamet et Perr. (CAM plant), Sedum telephium L. and Sedum spectabile Bor. (C 3 plant in spring, CAM plant in summer) and Raphanus sativus L. (C 3 plant) at three different times during a 12/12h day/night cycle. During the fluorescence transient the fluorescence intensity at the O, P and T-level (f O, f max, f st,) was different for the plant species tested; this may be due to their different leaf structure, pigment composition and organization of their photosystems. The kinetics of the fluorescence induction depended on the time of preillumination or dark adaptation during the light/dark cycle but not on the type of primary CO 2 fixation mechanism (C 3 and CAM). For dark adapted leaves measured either at the end of the dark phase or after dark adaptation of plants taken from the light phase a higher P-level fluorescence, a higher variable fluorescence (P-O) and a larger complementary area were found than for leaves of plants taken directly from the light phase. This indicates the presence of largely oxidized photosystem 2 acceptor pools during darkness. During the light phase the fluorescence decline after the P-level was faster than during the dark phase; from this we conclude that the light adaptation of the photosynthetic apparatus (state 1→ state 2 transition, Δ pH) during the induction period proceeded faster in plants taken from the light phase than in plants taken from the dark phase. 相似文献
19.
In the autotrophic bacterium, Thiobacillus thiooxidans, the oxidation of sulfur is coupled to transfers of phosphate from the medium to the cells. CO 2 fixation is coupled to transfers of inorganic phosphate from the cells to the medium and is dependent, in the absence of concomitant sulfur oxidation, upon the amount of phosphate previously taken up during sulfur oxidation. The energy reservoir, which is formed by sulfur oxidation in the absence of CO 2 and which can be released for the fixation of CO 2 under conditions which do not permit sulfur oxidation, is a phosphorylated compound and the data suggest that the energy is stored in the cell as phosphate bond energy. It is possible to oxidize sulfur at a constant rate for hours in the absence of CO 2. The phosphate energy formed during this process is probably released by cell phosphotases. It is possible to inhibit these phosphotases by means of inorganic phosphate and thus to inhibit sulfur oxidation in the absence of CO 2. In the presence of CO 2, where alternative uses for the phosphate energy are available, the inhibition is relieved. Sulfur oxidation (energy input) is coupled, not to CO 2 fixation, but to phosphate esterification. CO 2 fixation (energy utilization) is coupled with phosphate release. 相似文献
20.
Two succulents with similar growth forms but different types of photosynthesis, Cotyledon orbiculata (crassulacean acid metabolism, CAM) and Othonna opima (C 3 pathway), were investigated with respect to the modulation of water use efficiency (WUE) during the transition from the rainy season to subsequent drought. Environmental conditions were simulated in a controlled-environment experiment on the basis of data collected in the habitat of the two species in the southern Namib desert. Experiments included one or more periods of hot bergwind, which frequently occurs in this region. When water was readily available, daily net CO 2 fixation was similar in the two species. This result confirms that the daily CO 2 fixation of CAM plants is as high as that of morphologically similar C 3 plants adapted to the same habitat. As expected, both species reduced CO 2 fixation and water loss through transpiration during simulated hot bergwind periods and their WUE values increased. However, after the second hot bergwind period, nearly identical WUEs were recorded: 41.0 and 40.0 mmol mol ?1 for C. orbiculata and O. opima, respectively. Therefore the statement that a CAM plant is a better ‘water saver’ than a C 3 plant does not necessarily hold for CAM and C 3 plants with similar growth forms growing under the same environmental conditions. 相似文献
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