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1.
When dark 14CO 2 fixation in maize leaves was carried out under anaerobic conditions after preillumination in the absence of O 2, the 14C incorporation in aspartic acid was transient; its maximum level was very low compared with that of malic acid. The addition of 5% O 2 during the dark fixation period increased the total uptake of 14CO 2 and the 14C incorporation into aspartic acid. 相似文献
2.
The quantum requirement (QR) for photosynthesis in Sedum praealtum, a Crassulacean acid metabolism plant, was compared with that of wheat, a C 3 plant, and maize, a C 4 plant, at 30 C. During the deacidification phase in S. praealtum, approximately 16 moles quanta were absorbed per mole malate consumed. This is equivalent to 16 moles quanta per mole CO 2 fixed, assuming 1 mole CO 2 is assimilated per mole malate decarboxylated. This QR for Crassulacean acid metabolism is similar to that of the C 3 or C 4 plant under atmospheric conditions, even though there are considerable differences in the biochemistry of photosynthesis. During late-afternoon C 3-like fixation of atmospheric CO 2 in S. praealtum, the QR was relatively high with values of 41 under 21% O 2 and 19 under 2% O 2. During the deacidification phase in S. praealtum, the relatively low QR can be accounted for by the repression of photorespiration and saturation of photosynthesis from the elevated CO 2 concentration in the leaves during malate decarboxylation. 相似文献
3.
Abstract CO 2 gas exchange, transpiration and water uptake of the succulent Senecio medley-woodii were monitored simultaneously during a 10 day period of increasing drought. The measurements were performed with a combination of a CO 2 gas exchange chamber and a potometer system. Further, leaf water relations and CO 2 gas exchange of a branched potted plant were measured during 15 days of water shortage. The enhancement of CO 2 dark fixation at the beginning of drought modifies the leaf water relations according to the increased malate accumulation during the dark period. The enhancement of water uptake from dusk to dawn corresponds to the increase of Ψ leaf during the same period. Therefore at the beginning of drought a short time improvement of plant water status through the increased CO 2 dark fixation and malate accumulation can be maintained. 相似文献
4.
Experiments were designed to determine the significance of dark CO 2 fixation in excised maize roots, carrot slices and excised tomato roots grown in tissue culture. Bicarbonate- 14C was used to determine the pathway and amounts of CO 2 fixation, while leucine- 14C was used to estimate protein synthesis in tissues aerated with various levels of CO 2. Organic acids were labeled from bicarbonate-14C, with malate being the major labeled acid. Only glutamate and aspartate were labeled in the amino acid fraction and these 2 amino acids comprised over 90% of the 14C label in the ethanol-water insoluble residue. Studies with leucine-14C as an indicator of protein synthesis in carrot slices and tomato roots showed that those tissues aerated with air incorporated 33% more leucine-14C into protein than those aerated with CO2-free air. Growth of excised tomato roots aerated with air was 50% more than growth of tissue aerated with CO2-free air. These studies are consistent with the suggestion that dark fixation of CO2 is involved in the growth of plant tissues. 相似文献
5.
The net carbon incorporation in maize ( Zea mays) and tomato ( Lycopersicum esculentum) leaves was mainly the result of the carboxylation of ribulose 1,5-diphosphate. In both of these organisms synthesis of glycerate 3-phosphate was studied during short chase experiments (2 or 3 seconds in 14CO 2 then 8 to 27 seconds in unlabeled CO 2). Changes in the radioactivity in the individual carbon atoms of glycerate 3-phosphate, malate, and aspartate are consistent with the formation, in both leaves, of 2 molecules of glycerate 3-phosphate for each CO 2 molecule incorporated. The CO 2, before reacting with ribulose 1,5-diphosphate, is first incorporated in an intracellular CO 2 pool which has a different composition according to the species. This pool is constituted in tomato by volatile compounds (50 nanomoles per gram of fresh weight) more or less in equilibrium with atmospheric CO 2. In maize the pool consists of carbon atoms 4 of malate and aspartate (for at least 80% of the pool) and volatile compounds which correspond, in all, to 540 nanomoles per gram of fresh weight where atmospheric CO 2 enters through an irreversible reaction. 相似文献
6.
After two weeks of moderate N restriction, growth of 3-week-old Zea mays L. plants was less than half that of the control and aspartate and malate levels in the leaves were severely suppressed (45 and 65% decrease, respectively). Since in NADP malic enzyme type C 4 plants, such as maize, malate and aspartate are intermediates in the C 4 photosynthetic pathway, the operation of the latter was investigated. Moderate nitrogen deficiency had only a small effect on the rate of photosynthesis (20% decrease) measured under 1000 umol m ?2 s ?1 irradiance. 14CO 2 pulse- 12CO 2 chase experiments combined with measurements of in vitro photosynthetic enzyme activities demonstrated the operation of a typical C 4 photosynthetic pathway in N-restricted plants. The turnover rates of malate and aspartate molecules involved in the C 4 cycle were determined by the loss of label in the carbon 4 moiety of these molecules during the chase period. It is shown that N restriction did not alter the turnover of malate but greatly accelerated that of aspartate. The amounts of malate and aspartate moving through photosynthetically active pools were estimated using a kinetic model. For malate, the size of this pool appeared to be only slightly diminished whereas for aspartate the size of the corresponding pool decreased by a factor of 3. It is proposed that under moderate NO 3? deficiency, despite deviations in malate metabolism leading to a pronounced decrease in the size of its cellular pool, a large amount of malate remained in the operation of the C 4 pathway. By contrast, the participation of aspartate in the operation of the C 4 pathway was greatly reduced. 相似文献
7.
The products of short time photosynthesis and of enhanced dark 14CO 2 fixation (illumination in helium prior to addition of 14CO 2 in dark) by Chlorella pyrenoidosa and Anacystis nidulans were compared. Glycerate 3-phosphate, phosphoenolpyruvate, alanine, and aspartate accounted for the bulk of the 14C assimilated during enhanced dark fixation while hexose and pentose phosphates accounted for the largest fraction of isotope assimilated during photosynthesis. During the enhanced dark fixation period, glycerate 3-phosphate is carboxyl labeled and glucose 6-phosphate is predominantly labeled in carbon atom 4 with lesser amounts in the upper half of the C 6 chain and traces in carbon atoms 5 and 6. Tracer spread throughout all the carbon atoms of photosynthetically synthesized glycerate 3-phosphate and glucose 6-phosphate. During the enhanced dark fixation period, there was a slow formation of sugar phosphates which subsequently continued at 5 times the initial rate long after the cessation of 14CO 2 uptake. To explain the kinetics of changes in the labelling patterns and in the limited formation of the sugar phosphates during enhanced dark CO 2 fixation, the suggestion is made that most of the reductant mediating these effects did not have its origin in the preillumination phase. It is concluded that a complete photosynthetic carbon reduction cycle operates to a limited extent, if at all, in the dark period subsequent to preillumination. 相似文献
8.
- The capacity of light-enhanced dark fixation of 14CO2 from theambient atmosphere decayed following time-course characteristicsof a first-order reaction (half-life, 12 min). The levelof phosphoenolpyruvate in maize leaves under CO2-free air didnot decrease in the dark subsequent to preillumination. Theseresults indicate that phosphoenolpyruvate carboxylase is activatedin light and quickly inactivated in the following darkness.
- Removal of oxygen from the atmosphere did not exert any effecton the products of light-enhanced dark fixation of 14CO2 providedfrom the atmosphere, the major labeled compounds being malateand aspartate. This confirms that the transfer of carboxyl carbonof C4-acids to form 3-phosphoglycerate is light-dependent.
- WhenNaH14CO3 solution was vacuum-infiltrated through vasculartissuesof maize leaves, the main initial photosynthetic 14CO2fixationproducts were phosphate esters. This indicates thatby thistechnique, 14CO2 could be directly provided to the bundlesheathcells, and was fixed via the reductive pentose phosphatecycle.On the other hand, the main initial 14CO2-fixation productswere malate and aspartate even when 14CO2 was provided throughvascular tissues in the dark immediately following preillumination.The possible regulatory mechanisms underlying the above findingsare discussed.
1 This work was reported at the 4th International Congress onPhotosynthesis, Reading, September 1977. Request for reprintsshould be addressed to S. Miyachi, Institute of Applied Microbiology,University of Tokyo, Bunkyo-ku, Tokyo 113, Japan
2 Present address: Okinawa Branch of Tropical Agriculture ResearchCenter, Ishigaki-shi, Okinawa 907, Japan. (Received October 28, 1977; ) 相似文献
9.
The rates of dark CO 2 fixation and the label distribution in malate following dark 14CO 2 fixation in a C-4 plant (maize), a C-3 plant (sunflower), and two Crassulacean acid metabolism plants ( Bryophyllum calycinum and Kalanchoë diagremontianum leaves and plantlets) are compared. Within the first 30 minutes of dark 14CO 2 fixation, leaves of maize, B. calycinum, and sunflower, and K. diagremontianum plantlets fix CO 2 at rates of 1.4, 3.4, 0.23, and 1.0 μmoles of CO 2/mg of chlorophyll· hour, respectively. Net CO 2 fixation stops within 3 hours in maize and sunflower, but Crassulaceans continue fixing CO 2 for the duration of the 23-hour experiment. A bacterial procedure using Lactobacillus plantarum ATCC No. 8014 and one using malic enzyme to remove the β-carboxyl (C4) from malate are compared. It is reported that highly purified malic enzyme and the bacterial method provide equivalent results. Less purified malic enzyme may overestimate the label in C4 as much as 15 to 20%. The contribution of carbon atom 1 of malate is between 18 and 21% of the total carboxyl label after 1 minute of dark CO2 fixation. Isotopic labeling in the two carboxyls approached unity with time. The rate of increase is greatest in sunflower leaves and Kalanchoë plantlets. In addition, Kalanchoë leaves fix 14CO2 more rapidly than Kalanchoë plantlets and the equilibration of the malate carboxyls occurs more slowly. The rates of fixation and the randomization are tissue-specific. The rate of fixation does not correlate with the rate of randomization of isotope in the malate carboxyls. 相似文献
10.
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
11.
Summary The distribution of radioactivity between the products of 14CO 2 light fixation in phyllodia of Bryophyllum tubiflorum could be influenced experimentally by manipulating the malic acid content of the cells. Accelerating the deacidification of the tissue during the light period by application of higher light intensities accelerated the increase of malate labelling and the decrease of the sucrose labelling after 14CO 2 light fixation under our standard conditions (10 min preillumination, 15 min 14CO 2 light fixation, 8000 lux).In other experiments different malate contents of the tissues were induced by treating the phyllodia with different temperatures during the night period. In the morning, phyllodia with low malate content transferred most of the label into malate, and phyllodia with high malate content incorporated most of the 14C radioactivity into sugars. However, this was true only after preillumination of 1 hour. When the phyllodia fixed 14CO 2 without preillumination, no differences in the labelling patterns between acidified and non-acidified phyllodia could be observed.In experiments using leaf tissue slices of Bryophyllum daigremontianum we could again observe that malate was labelled more heavily in the deacidified tissue than in the acidified controls, with less radioactivity being transferred into phosphate esters and sugars. The rates of 14CO 2 light fixation were identical in tissue slices with high and low malate content. However, the rates of CO 2 dark fixation in the acidified samples were clearly lower than those in the deacidified ones. The low rate of CO 2 dark fixation in acidified samples could not be inhibited by an inhibitor of PEP-carboxylase as the high CO 2 dark fixation rate of the deacidified tissue could be inhibited.The results are discussed in relation to the feed back inhibition of PEP-carboxylase in vivo by malate. Compartmentation also seemed to be involved in controlling the flow of carbon during CO 2 light fixation in succulent tissue. 相似文献
12.
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
13.
The potential for C 4 photosynthesis was investigated in five C 3-C 4 intermediate species, one C 3 species, and one C 4 species in the genus Flaveria, using 14CO 2 pulse- 12CO 2 chase techniques and quantum-yield measurements. All five intermediate species were capable of incorporating 14CO 2 into the C 4 acids malate and aspartate, following an 8-s pulse. The proportion of 14C label in these C 4 products ranged from 50–55% to 20–26% in the C 3-C 4 intermediates F. floridana Johnston and F. linearis Lag. respectively. All of the intermediate species incorporated as much, or more, 14CO 2 into aspartate as into malate. Generally, about 5–15% of the initial label in these species appeared as other organic acids. There was variation in the capacity for C 4 photosynthesis among the intermediate species based on the apparent rate of conversion of 14C label from the C 4 cycle to the C 3 cycle. In intermediate species such as F. pubescens Rydb., F. ramosissima Klatt., and F. floridana we observed a substantial decrease in label of C 4-cycle products and an increase in percentage label in C 3-cycle products during chase periods with 12CO 2, although the rate of change was slower than in the C 4 species, F. palmeri. In these C 3-C 4 intermediates both sucrose and fumarate were predominant products after a 20-min chase period. In the C 3-C 4 intermediates, F. anomala Robinson and f. linearis we observed no significant decrease in the label of C 4-cycle products during a 3-min chase period and a slow turnover during a 20-min chase, indicating a lower level of functional integration between the C 4 and C 3 cycles in these species, relative to the other intermediates. Although F. cronquistii Powell was previously identified as a C 3 species, 7–18% of the initial label was in malate+aspartate. However, only 40–50% of this label was in the C-4 position, indicating C 4-acid formation as secondary products of photosynthesis in F. cronquistii. In 21% O 2, the absorbed quantum yields for CO 2 uptake (in mol CO 2·[mol quanta] -1) averaged 0.053 in F. cronquistii (C 3), 0.051 in F. trinervia (Spreng.) Mohr (C 4), 0.052 in F. ramosissima (C 3-C 4), 0.051 in F. anomala (C 3-C 4), 0.050 in F. linearis (C 3-C 4), 0.046 in F. floridana (C 3-C 4), and 0.044 in F. pubescens (C 3-C 4). In 2% O 2 an enhancement of the quantum yield was observed in all of the C 3-C 4 intermediate species, ranging from 21% in F. ramosissima to 43% in F. pubescens. In all intermediates the quantum yields in 2% O 2 were intermediate in value to the C 3 and C 4 species, indicating a co-function of the C 3 and C 4 cycles in CO 2 assimilation. The low quantum-yield values for F. pubescens and F. floridana in 21% O 2 presumably reflect an ineffcient transfer of carbon from the C 4 to the C 3 cycle. The response of the quantum yield to four increasing O 2 concentrations (2–35%) showed lower levels of O 2 inhibition in the C 3-C 4 intermediate F. ramosissima, relative to the C 3 species. This indicates that the co-function of the C 3 and C 4 cycles in this intermediate species leads to an increased CO 2 concentration at the site of ribulose-1,5-bisphosphate carboxylase/oxygenase and a concomitant decrease in the competitive inhibition by O 2.Abbreviations PEP
phosphoenolpyruvate
- PGA
3-phosphoglycerate
- RuBP
ribulose-1,5-bisphosphate 相似文献
14.
C 4 grasses of the NAD‐ME type ( Astrebla lappacea, Eleusine coracana, Eragrostis superba, Leptochloa dubia, Panicum coloratum, Panicum decompositum) and the NADP‐ME type ( Bothriochloa bladhii, Cenchrus ciliaris, Dichanthium sericeum, Panicum antidotale, Paspalum notatum, Pennisetum alopecuroides, Sorghum bicolor) were used to investigate the role of O 2 as an electron acceptor during C 4 photosynthesis. Mass spectrometric measurements of gross O 2 evolution and uptake were made concurrently with measurements of net CO 2 uptake and chlorophyll fluorescence at different irradiances and leaf temperatures of 30 and 40 °C. In all C 4 grasses gross O 2 uptake increased with increasing irradiance at very high CO 2 partial pressures ( pCO 2) and was on average 18% of gross O 2 evolution. Gross O 2 uptake at high irradiance and high pCO 2 was on average 3.8 times greater than gross O 2 uptake in the dark. Furthermore, gross O 2 uptake in the light increased with O 2 concentration at both high CO 2 and the compensation point, whereas gross O 2 uptake in the dark was insensitive to O 2 concentration. This suggests that a significant amount of O 2 uptake may be associated with the Mehler reaction, and that the Mehler reaction varies with irradiance and O 2 concentration. O 2 exchange characteristics at high pCO 2 were similar for NAD‐ME and NADP‐ME species. NAD‐ME species had significantly greater O 2 uptake and evolution at the compensation point particularly at low irradiance compared to NADP‐ME species, which could be related to different rates of photorespiratory O 2 uptake. There was a good correlation between electron transport rates estimated from chlorophyll fluorescence and gross O 2 evolution at high light and high pCO 2. 相似文献
15.
The net CO 2 assimilation by leaves of maize ( Zea mays L. cv. Adonis) plants subjected to slow or rapid dehydration decreased without changes in the total extractable activities of phospho enolpyruvate carboxylase (PEPC), malate dehydrogenase (MDH) and malic enzyme (ME). The phosphorylation state of PEPC extracted from leaves after 2–3 h of exposure to light was not affected by water deficit, either. Moreover, when plants which had been slowly dehydrated to a leaf relative water content of about 60% were rehydrated, the net CO 2 assimilation by leaves increased very rapidly without any changes in the activities of MDH, ME and PEPC or phosphorylation state of PEPC. The net CO 2-dependent O 2 evolution of a non-wilted leaf measured with an oxygen electrode decreased as CO 2 concentration increased and was totally inhibited when the CO 2 concentration was about 10%. Nevertheless, high CO 2 concentrations (5–10%) counteracted most of the inhibitory effect of water deficit that developed during a slow dehydration but only counteracted a little of the inhibitory effect that developed during a rapid dehydration. In contrast to what could be observed during a rapidly developing water deficit, inhibition of leaf photosynthesis by cis-abscisic acid could be alleviated by high CO 2 concentrations. These results indicate that the inhibition of leaf net CO 2 uptake brought about by water deficit is mainly due to stomatal closure when a maize plant is dehydrated slowly while it is mainly due to inhibition of non-stomatal processes when a plant is rapidly dehydrated. The photosynthetic apparatus of maize leaves appears to be as resistant to drought as that of C 3 plants. The non-stomatal inhibition observed in rapidly dehydrated leaves might be the result of either a down-regulation of the photosynthetic enzymes by changes in metabolite pool sizes or restricted plasmodesmatal transport between mesophyll and bundle-sheath cells. 相似文献
16.
The metabolism of [ 13C]malate was studied in the Crassulacean plant Kalanchoë tubiflora following exposure to 13CO 2 for 2 hour intervals during a 16 hour dark cycle. Nuclear magnetic resonance spectroscopy of [ 13C]malate extracted from labeled tissue revealed that the transient flux of malate to the mitochondria, estimated by the randomization of [4- 13C]malate to [1- 13C]malate by fumarase, varied substantially during the dark period. At both 15 and 25°C, the extent of malate label randomization in the mitochondria was greatest during the early and late parts of the dark period and was least during the middle of the night, when the rate of 13CO 2 uptake was highest. Randomization of labeled malate continued for many hours after malate synthesis had initially occurred. Internally respired 12CO 2 also served as a source of carbon for malate formation. At 15°C, 15% of the total malate was formed from respired 12CO 2, while at 25°C, 49% of the accumulated malate was derived from respired 12CO 2. Some of the malate synthesized from external 13CO 2 was also respired during the night. The proportion of the total [ 13C]malate respired during the dark period was similar at 15 and 25°C, and respiration of newly formed [ 13C]malate increased as the night period progressed. These data are discussed with regard to the relative fluxes of malate to the mitochondria and the vacuole during dark CO 2 fixation. 相似文献
17.
The submersed angiosperms Myriophyllum spicatum L. and Hydrilla verticillata (L.f.) Royal exhibited different photosynthetic pulse-chase labeling patterns. In Hydrilla, over 50% of the 14C was initially in malate and aspartate, but the fate of the malate depended upon the photorespiratory state of the plant. In low photorespiration Hydrilla, malate label decreased rapidly during an unlabeled chase, whereas labeling of sucrose and starch increased. In contrast, for high photorespiration Hydrilla, malate labeling continued to increase during a 2-hour chase. Thus, malate formation occurs in both photorespiratory states, but reduced photorespiration results when this malate is utilized in the light. Unlike Hydrilla, in low photorespiration Myriophyllum, 14C incorporation was via the Calvin cycle, and less than 10% was in C 4 acids. Ethoxyzolamide, a carbonic anhydrase inhibitor and a repressor of the low photorespiratory state, increased the label in glycolate, glycine, and serine of Myriophyllum. Isonicotinic acid hydrazide increased glycine labeling of low photorespiration Myriophyllum from 14 to 25%, and from 12 to 48% with high photorespiration plants. Similar trends were observed with Hydrilla. Increasing O2 increased the per cent [14C]glycine and the O2 inhibition of photosynthesis in Myriophyllum. In low photorespiration Myriophyllum, glycine labeling and O2 inhibition of photosynthesis were independent of the CO2 level, but in high photorespiration plants the O2 inhibition was competitively decreased by CO2. Thus, in low but not high photorespiration plants, glycine labeling and O2 inhibition appeared to be uncoupled from the external [O2]/[CO2] ratio. These data indicate that the low photorespiratory states of Hydrilla and Myriophyllum are mediated by different mechanisms, the former being C4-like, while the latter resembles that of low CO2-grown algae. Both may require carbonic anhydrase to enhance the use of inorganic carbon for reducing photorespiration. 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.
When Vicia faba guard cell protoplasts were treated with fusicoccin, dark 14CO 2 fixation rates increased by as much as 8-fold. Rate increase was saturated with less than 1 micromolar fusicoccin. Even after 6 minutes of dark 14CO 2 fixation, more than 95% of the incorporated radioactivity was in stable products derived from carboxylation of phosphoenolpyruvate (about 50% and 30% in malate and aspartate, respectively). The relative distribution of 14C among products and in the C-4 position of malate (initially more than 90% of [ 14C]malate) was independent of fusicoccin concentration. After incubation in the dark, malate content was higher in protoplasts treated with fusicoccin. A positive correlation was observed between the amounts of 14CO 2 fixed and malate content. It was concluded that (a) fusicoccin causes an increase in the rate of dark 14CO2 fixation without alteration of the relative fluxes through pathways by which it is metabolized, (b) fusicoccin causes an increase in malate synthesis, and (c) dark 14CO2 fixation and malate synthesis are mediated by phosphoenolpyruvate carboxylase. 相似文献
20.
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 12/12 h 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 1state 2 transition, pH) during the induction period proceeded faster in plants taken from the light phase than in plants taken from the dark phase.Abbreviations C 3 plant
plant with primary CO 2 fixation on ribulose-1,5-bis-phosphate (Calvin-Benson cycle)
- CAM
Crassulacean Acid Metabolism 相似文献
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