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1.
The interaction of low water potential effects on photosynthesis, and leaf K + levels in wheat ( Triticum aestivum L.) plants was studied. Plants were grown at three K + fertilization levels; 0.2, 2, and 6 millimolar. With well watered plants, 2 millimolar K + supported maximal photosynthetic rates; 0.2 millimolar K + was inhibitory, and 6 millimolar K + was superoptimal ( i.e. rates were no greater than at 2 millimolar K +). Photosynthesis was monitored at high (930 parts per million) and low (330 parts per million) external CO 2 throughout a series of water stress cycles. Plants subjected to one stress cycle were considered nonacclimated; plants subjected to two successive cycles were considered acclimated during the second cycle. Sensitivity of photosynthesis to declining leaf water potential was affected by K + status; 6 millimolar K + plants were less sensitive, and 0.2 millimolar K + plants were more sensitive than 2 millimolar K + plants to declining water potential. This occurred with nonacclimated and acclimated plants at both high and low assay CO 2. It was concluded that the K + effect on photosynthesis under stress was not mediated by treatment effects on stomatal resistance. Differences between the K + treatments were much less pronounced, however, when photosynthesis of nonacclimated and acclimated plants was plotted at a function of declining relative water content during the stress cycles. These results suggest that K + effects on the relationship between relative water content and water potential in stressed plants was primarily responsible for the bulk of the K +-protective effect on photosynthesis in stressed plants. In vitro experiments with chloroplasts and protoplasts isolated from 2 millimolar K + and 6 millimolar K + plants indicated that upon dehydration, K + efflux from the chloroplast stroma into the cytoplasm is less pronounced in 6 millimolar K + protoplasts. 相似文献
2.
Relationships between induced high leaf intercellular CO 2 concentrations, leaf K + and NO 3 ? ion movement and early fruit formation under macronutrient limitation are not well understood. We examined the effects and interactions of reduced K/N input treatments on leaf intercellular CO 2, photosynthesis rate, carboxylation and water use efficiency, berry formation as well as leaf/fruit K +, NO 3 ? and photosynthate retention of strawberry ( Fragaria × ananassa Duch.) to enhance low-input agriculture. The field study was conducted in Nova Scotia, eastern Canada during 2009–2010. The experimental treatments consisted of five K 2O rates (0, 6, 12, 18, and 24 kg ha ?1) and five N rates (0, 5, 10, 15, and 20 kg ha ?1), representing respectively, 0, 25, 50, 75, and 100 % of regular macronutrient recommendations based on the soil testing. The treatments were arranged in a split-plot design with three blocks in the field. The cultivar was ‘Mira’, a June-bearing crop. The results showed that strawberry plants treated with 25 %-reduced inputs could induce significantly higher leaf intercellular CO 2 concentrations to improve plant photosynthesis, carboxylation and water use efficiency and translocation of leaf/fruit K + and dissolved solids, which could advance berry formation by 6 days and produce significantly higher marketable yields ( P < 0.05). Higher leaf intercellular CO 2 inhibited leaf/fruit NO 3 ? ion retention, but this inhibition did not occur in leaf/fruit K + retention. Linear interactions of the K/N treatments were significant on fruit marketable yields, intercellular CO 2, net photosynthesis, leaf transpiration rates, and leaf temperatures ( P < 0.05). It was concluded that higher leaf CO 2 could enhance plant photosynthesis, promote plant carboxylation and water use efficiency, and advance berry formation, but it could inhibit leaf NO 3 ? retention. This inhibition did not find in leaf K + ion and dissolved solid retention. Overlay co-limitation of leaf intercellular CO 2 and translocation of leaf/fruit K +/NO 3 ? and total dissolved solids could constrain more fruit formation attributes under full macronutrient supply than reduced inputs. It was suggested that low input would be an optimal and sustainable option for improving small fruit crop physiological development and dealing with macronutrient deficiency challenge. 相似文献
3.
The relationship between leaf K + concentration, in vitro dehydration, and nonstomatal-controlled photosynthesis was investigated using leaf slices that were vacuum infiltrated with media containing varying sorbitol concentrations. The leaf slices were from plants either supplied with complete or K +-deficient medium throughout a 35-day growth period. During this time, leaf K + concentration, water potential, osmotic potential, and turgor pressure were monitored. Leaf K + concentration averaged 239 micomoles per gram (fresh weight) in control plants, and dropped to 74.3 micromoles per gram (fresh weight) in K +-deficient plants. Less negative osmotic potentials and resultant turgor loss in K +-deficient plants indicated that the osmotically active pool of cellular K + was lower in those plants. The decrease in leaf K+ concentration enhanced the dehydration inhibition of photosynthesis. For example, increasing sorbitol from 0.33 to 0.5 molar during incubation inhibited photosynthesis in the controls by 14% or less. This same protocol resulted in an inhibition of photosynthesis by as much as 41% in K+-deficient tissue. In contrast to the data obtained with leaf slices, dehydration inhibition of isolated chloroplast photosynthesis was not affected by K+ status of parent plant material. These data are consistent with the hypothesis that one effect of leaf K+ deficiencies on photosynthetic response to dehydration may be mediated by extra-choloroplastic factors. Ammonium ions, which facilitate stromal alkalinization, reversed the increased sensitivity of K+-deficient leaf slice photosynthesis to cell dehydration. However, NH4+ had no effect on photosynthesis of K+-deficient leaf slices under nonhypertonic conditions. These data suggest that endogenous extra-chloroplastic K+ may modulate dehydration inhibition of photosynthesis, possibly by facilitating stromal alkalinization. 相似文献
4.
Photosynthetic CO 2 assimilation, transpiration, ribulose-1,5-bisphosphate carboxylase (RuBPCase), and soluble protein were reduced in leaves of water-deficit (stress) `Valencia' orange ( Citrus sinensis [L.] Osbeck). Maximum photosynthetic CO 2 assimilation and transpiration, which occurred before midday for both control and stressed plants, was 58 and 40%, respectively, for the stress (−2.0 megapascals leaf water potential) as compared to the control (−0.6 megapascals leaf water potential). As water deficit became more severe in the afternoon, with water potential of −3.1 megapascals for the stressed leaves vs. −1.1 megapascals for control leaves, stressed-leaf transpiration declined and photosynthetic CO 2 assimilation rapidly dropped to zero. Water deficit decreased both activation and total activity of RuBPCase. Activation of the enzyme was about 62% (of fully activated enzyme in vitro) for the stress, compared to 80% for the control. Water deficit reduced RuBPCase initial activity by 40% and HCO 3−/Mg 2+-saturated activity by 22%. However, RuBPCase for both stressed and control leaves were similar in Kcat (25 moles CO 2 per mole enzyme per second) and Km for CO 2 (18.9 micromolar). Concentrations of RuBPCase and soluble protein of stressed leaves averaged 80 and 85%, respectively, of control leaves. Thus, reductions in activation and concentration of RuBPCase in Valencia orange leaves contributed to reductions in enzyme activities during water-deficit periods. Declines in leaf photosynthesis, soluble protein, and RuBPCase activation and concentration due to water deficit were, however, recoverable at 5 days after rewatering. 相似文献
5.
The commercial tomato, lycopersicon esculentum Mill. cv Walter, and its wild relative, Lycopersicon cheesmanii ssp. minor (Hook.) C.H. Mull., were grown for 30 days under controlled conditions and in solution culture varying in its content of Na + and K +. Subsequently, 86Rb-labeled K + uptake and distribution were studied. From all solutions, `Walter' consistently absorbed 86Rb-labeled K + at a higher rate in micromoles per gram fresh weight per 30 minutes than L. cheesmanii. L. cheesmanii distributed a greater proportion of the absorbed K + from its root to its shoot. When 0.6 millimolar NaNO 3 replaced 0.6 millimolar KNO 3 in the pretreatment solution, intact plants of both genotypes followed a similar pattern as when they were pretreated with K + only, but a greater percentage of the absorbed K + remained in the roots. Leaf slices of L. cheesmanii plants deprived of K + for 6 days showed a greater rate of K + uptake than did slices from `Walter' plants pretreated the same way. Stem slices of L. cheesmanii, however, had a lower uptake rate than did those of `Walter'. Both leaf and stem slices of `Walter' plants, pretreated 6 days with 0.6 millimolar NaNO 3 substituting for 0.6 millimolar KNO 3 in their growth medium, had greater rates of 86Rb-labeled K + uptake from 0.5 and 20 millimolar KCl solutions than did slices of L. cheesmanii. These marked differences in patterns of ion uptake and translocation indicate that these genotypes of tomato have evolved different mechanisms to deal with K + and Na + in their environments. 相似文献
6.
Spinach leaf chloroplasts isolated in isotonic media (330 millimolar sorbitol, −1.0 megapascals osmotic potential) had optimum rates of photosynthesis when assayed at −1.0 megapascals. When chloroplasts were isolated in hypertonic media (720 millimolar sorbitol, −2.0 megapascals osmotic potential) the optimum osmotic potential for photosynthesis was shifted to −1.8 megapascals and the chloroplasts had higher rates of CO 2-dependent O 2 evolution than chloroplasts isolated in 330 millimolar sorbitol when both were assayed at high solute concentrations. Transfer of chloroplasts isolated in 330 millimolar sorbitol to 720 millimolar sorbitol resulted in decreased chloroplast volume but this shrinkage was only transient and the chloroplasts subsequently swelled so that within 2 to 3 minutes at 20°C the chloroplast volume had returned to near the original value. Thus, actual steady state chloroplast volume was not decreased in hypertonic media. In isotonic media, there was a slow but significant uptake of sorbitol by chloroplasts (10 to 20 micromoles per milligram chlorophyll per hour at 20°C). Transfer of chloroplasts from 330 millimolar sorbitol to 720 millimolar sorbitol resulted in rapid uptake of sorbitol (up to 280 micromoles per milligram chlorophyll per hour at 20°C) and after 5 minutes the concentration of sorbitol inside the chloroplasts exceeded 500 millimolar. This uptake of sorbitol resulted in a significant underestimation of chloroplast volume unless [14C]sorbitol was added just prior to centrifuging the chloroplasts through silicone oil. Sudden exposure to osmotic stress apparently induced a transient change in the permeability of the chloroplast envelope since addition of [14C]sorbitol 3 minutes after transfer to hypertonic media (when chloroplast volume had returned to normal) did not result in rapid uptake of labeled sorbitol. It is concluded that chloroplasts can osmotically adjust in vitro by uptake of solutes which do not normally penetrate the chloroplast envelope, resulting in a restoration of normal chloroplast volume and partially preventing the inhibition of photosynthesis by high solute concentrations. The results indicate the importance of matching the osmotic potential of isolation media to that of the tissue, particularly in studies of stress physiology. 相似文献
7.
The effect of foliar application of K + on processes associated with phloem loading was investigated in source leaves of sugar beet ( Beta vulgaris L.). KCI was supplied exogenously at concentrations of up to 100 millimolar in the solution bathing the abraded upper epidermis of source leaves. K + added at concentrations below 30 millimolar generally promoted the rate of export of material derived from 14CO 2 but not from exogenously applied [ 14C]sucrose. Paralleling promotion of export, the level of material derived from photosynthesis, which was released into the bathing solution, also increased in response to addition of K + to the free space. Net photosynthetic rate was not affected. K + at 5 and 15 millimolar concentrations did not stimulate uptake of [ 14C]sucrose into source leaf discs. 相似文献
8.
Spinach ( Spinacia oleracea) plants were subjected to salt stress by adding NaCl to the nutrient solution in increments of 25 millimolar per day to a final concentration of 200 millimolar. Plants were harvested 3 weeks after starting NaCl treatment. Fresh and dry weight of both shoots and roots was decreased more than 50% compared to control plants but the salt-stressed plants appeared healthy and were still actively growing. The salt-stressed plants had much thicker leaves. The salt-treated plants osmotically adjusted to maintain leaf turgor. Leaf K + was decreased but Na + and Cl − were greatly increased. The potential photosynthetic capacity of the leaves was measured at saturating CO2 to overcome any stomatal limitation. Photosynthesis of salt-stressed plants varied only by about 10% from the controls when expressed on a leaf area or chlorophyll basis. The yield of variable chlorophyll a fluorescence from leaves was not affected by salt stress. Stomatal conductance decreased 70% in response to salt treatment. Uncoupled rates of electron transport by isolated intact chloroplasts and by thylakoids were only 10 to 20% below those for control plants. CO2-dependent O2 evolution was decreased by 20% in chloroplasts isolated from salt-stressed plants. The concentration of K+ in the chloroplast decreased by 50% in the salt-stressed plants, Na+ increased by 70%, and Cl− increased by less than 20% despite large increases in leaf Na+ and Cl−. It is concluded that, for spinach, salt stress does not result in any major decrease in the photosynthetic potential of the leaf. Actual photosynthesis by the plant may be reduced by other factors such as decreased stomatal conductance and decreased leaf area. Effective compartmentation of ions within the cell may prevent the accumulation of inhibitory levels of Na+ and Cl− in the chloroplast. 相似文献
9.
The Na + requirement for photosynthesis and its relationship to dissolved inorganic carbon (DIC) concentration and Li + concentration was examined in air-grown cells of the cyanobacterium Synechococcus leopoliensis UTEX 625 at pH 8. Analysis of the rate of photosynthesis (O 2 evolution) as a function of Na + concentration, at fixed DIC concentration, revealed two distinct regions to the response curve, for which half-saturation values for Na + ( K½[Na +]) were calculated. The value of both the low and the high K½(Na +) was dependent upon extracellular DIC concentration. The low K½(Na +) decreased from 1000 micromolar at 5 micromolar DIC to 200 micromolar at 140 micromolar DIC whereas over the same DIC concentration range the high K½(Na +) decreased from 10 millimolar to 1 millimolar. The most significant increases in photosynthesis occurred in the 1 to 20 millimolar range. A fraction of total photosynthesis, however, was independent of added Na + and this fraction increased with increased DIC concentration. A number of factors were identified as contributing to the complexity of interaction between Na + and DIC concentration in the photosynthesis of Synechococcus. First, as revealed by transport studies and mass spectrometry, both CO 2 and HCO 3− transport contributed to the intracellular supply of DIC and hence to photosynthesis. Second, both the CO 2 and HCO 3− transport systems required Na +, directly or indirectly, for full activity. However, micromolar levels of Na + were required for CO 2 transport while millimolar levels were required for HCO 3− transport. These levels corresponded to those found for the low and high K½(Na +) for photosynthesis. Third, the contribution of each transport system to intracellular DIC was dependent on extracellular DIC concentration, where the contribution from CO 2 transport increased with increased DIC concentration relative to HCO 3− transport. This change was reflected in a decrease in the Na + concentration required for maximum photosynthesis, in accord with the lower Na +-requirement for CO 2 transport. Lithium competitively inhibited Na +-stimulated photosynthesis by blocking the cells' ability to form an intracellular DIC pool through Na +-dependent HCO 3− transport. Lithium had little effect on CO 2 transport and only a small effect on the size of the pool it generated. Thus, CO 2 transport did not require a functional HCO 3− transport system for full activity. Based on these observations and the differential requirement for Na + in the CO 2 and HCO 3− transport system, it was proposed that CO 2 and HCO 3− were transported across the membrane by different transport systems. 相似文献
10.
The effects of elevated CO 2 concentrations on the photochemistry, biochemistry and physiology of C 4 photosynthesis were studied in maize ( Zea mays L.). Plants were grown at ambient (350 μL L −1) or ca. 3 times ambient (1100 μL L −1) CO 2 levels under high light conditions in a greenhouse for 30 d. Relative to plants grown at ambient CO 2 levels, plants grown under elevated CO 2 accumulated ca. 20% more biomass and 23% more leaf area. When measured at the CO 2 concentration of growth, mature leaves of high-CO 2-grown plants had higher light-saturated rates of photosynthesis (ca. 15%), lower stomatal conductance (71%), higher water-use
efficiency (225%) and higher dark respiration rates (100%). High-CO 2-grown plants had lower carboxylation efficiencies (23%), measured under limiting CO 2, and lower leaf protein contents (22%). Activities of a number of C 3 and C 4 cycle enzymes decreased on a leaf-area basis in the high-CO 2-grown plants by 5–30%, with NADP-malate dehydrogenase exhibiting the greatest decrease. In contrast, activities of fructose
1,6-bisphosphatase and ADP-glucose pyrophosphorylase increased significantly under elevated CO 2 condition (8% and 36%, respectively). These data show that the C 4 plant maize may benefit from elevated CO 2 through acclimation in the capacities of certain photosynthetic enzymes. The increased capacity to synthesize sucrose and
starch, and to utilize these end-products of photosynthesis to produce extra energy by respiration, may contribute to the
enhanced growth of maize under elevated CO 2.
Received: 30 April 1999 / Accepted: 17 June 1999 相似文献
11.
Photosynthetic rates and photosynthate partitioning were studied in three-week-old soybean [ Glycine max (L.) Merr. cv. Williams] plants exposed to either ambient (35 Pa) or elevated (70 Pa) CO 2 in controlled environment chambers. Ambient CO 2-grown plants also were given a single 24 h treatment with 70 Pa CO 2 1 d prior to sampling. Photosynthetic rates of ambient CO 2-grown plants initially increased 36% when the measurement CO 2 was doubled from 35 to 70 Pa. Photosynthetic rates of the third trifoliolate leaf, both after 1 and 21 d of elevated CO 2 treatment, were 30 to 45% below those of ambient CO 2-grown plants when measured at 35 Pa CO 2. These reduced photosynthetic rates were not due to increased stomatal resistance and were observed for 2 to 8 h after plants given 1 d of CO 2 enrichment were returned to ambient CO 2. Initial and total ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) activities, percent activation, Rubisco protein, soluble protein and leaf chlorophyll content were similar in all CO 2 treatments. Quantum yields of photosynthesis, determined at limiting irradiances and at 35 Pa CO 2, were 0.049±0.003 and 0.038±0.005 mol CO 2 fixed per mol quanta for ambient and elevated CO 2-grown plants, respectively (p<0.05). Leaf starch and sucrose levels were greater in plants grown at 70 than at 35 Pa CO 2. Starch accumulation rates during the day were greater in ambient CO 2-grown plants than in plants exposed to elevated CO 2 for either 1 or 21 d. However, the percentage of C partitioned to starch relative to total C fixed was unaffected by 1 d of CO 2 enrichment. The above results showed that both photosynthetic and starch accumulation rates of soybean leaflets measured at 35 Pa CO 2 were temporarily reduced after 1 and 21 d of CO 2 enrichment. The biochemical mechanism affecting these responses was not identified.Abbreviations SLW-
specific leaf weight (g m –2)
- Rubisco-
ribulose 1,5-bisphosphate carboxylase/oxygenase
- Rul-
5bisP, ribulose 1,5 bisphosphate
- DAP-
days after planting
- SAR-
starch accumulation rate
- C i-
intercellular CO 2 concentration 相似文献
12.
The extent and occurrence of water stress-induced “patchy” CO 2 uptake across the surface of leaves was evaluated in a number of plant species. Leaves, while still attached to a plant, were illuminated and exposed to air containing [ 14C]CO 2 before autoradiographs were developed. Plant water deficits that caused leaf water potential depression to −1.1 megapascals during a 4-day period did result in heterogenous CO 2 assimilation patterns in bean ( Phaseolus vulgaris). However, when the same level of stress was imposed more gradually (during 17 days), no patchy stomatal closure was evident. The patchy CO 2 assimilation pattern that occurs when bean plants are subjected to a rapidly imposed stress could induce artifacts in gas exchange studies such that an effect of stress on chloroplast metabolism is incorrectly deduced. This problem was characterized by examining the relationship between photosynthesis and internal [CO 2] in stressed bean leaves. When extent of heterogenous CO 2 uptake was estimated and accounted for, there appeared to be little difference in this relationship between control and stressed leaves. Subjecting spinach ( Spinacea oleracea) plants to stress (leaf water potential depression to −1.5 megapascals) did not appear to cause patchy stomatal closure. Wheat ( Triticum aestivum) plants also showed homogenous CO 2 assimilation patterns when stressed to a leaf water potential of −2.6 megapascals. It was concluded that water stress-induced patchy stomatal closure can occur to an extent that could influence the analysis of gas exchange studies. However, this phenomenon was not found to be a general response. Not all stress regimens will induce patchiness; nor will all plant species demonstrate this response to water deficits. 相似文献
13.
Segments of oat ( Avena sativa L.) roots which had been exposed to 1 millimolar CdSO 4 in quarter-strength Hoagland No. 1 solution exhibited decreased respiratory rates, ATP levels, membrane-bound ATPase activity, and reduced K + fluxes. Respiration and ATP levels were decreased after a 2-hour treatment with 1 millimolar CdSO 4 to 65 and 75%, respectively, of control rates. A membrane-bound, Mg 2+-dependent, K +-stimulated acid ATPase was rapidly inhibited to 12% of control activity in the presence of 1 millimolar CdSO 4. Potassium uptake into root segments was inhibited to 80% of control values after 30 minutes in the presence of CdSO 4. A 2-hour pretreatment of root segments with CdSO 4 inhibited K + uptake to 15% of control values. Cytoplasmic K + efflux was inhibited with 1 millimolar CdSO 4. The rates and the degree of Cd2+ inhibition of the parameters listed above suggest that one of the first sites of Cd2+ action is the plasmalemma K+ carrier (ATPase) in oat roots. 相似文献
14.
Protoplasts, protoplast extracts (intact chloroplasts plus extrachloroplastic material), and chloroplasts isolated from protoplasts of wheat ( Triticum aestivum) have rates of photosynthesis as measured by light-dependent O 2 evolution of about 100 to 150 micromoles of O 2 per milligram of chlorophyll per hour at 20 C and saturating bicarbonate. The assay conditions sufficient for this activity were 0.4 molar sorbitol, 50 millimolar N-2-hydroxyethylpiperazine-N′-2-ethanesulfonic acid KOH (pH 7.6), and 10 millimolar NaHCO 3 with protoplast, plus a requirement of 1 to 10 millimolar ethylenediaminetetraacetate (EDTA) and 0.2 to 0.5 millimolar inorganic orthophosphate (Pi) with protoplast extracts and chloroplasts. Protoplast extracts evolved approximately 6 micromoles of O 2 per milligram of chlorophyll before photosynthesis became largely dependent on exogenous Pi while photosynthesis by chloroplasts had a much stronger dependence on exogenous Pi from the outset. Photosynthesis by chloroplasts from 6-day-old wheat plants under optimum levels of Pi was similar to that with the addition of 5 millimolar inorganic pyrophosphate (PPi) plus 0.2 millimolar adenosine-5′-diphosphate (ADP). Either PPi or ADP added separately inhibited photosynthesis. When chloroplasts were incubated in the dark for 2 to 6 minutes, photosynthesis was strongly inhibited by 5 millimolar PPi and this inhibiting was relieved by including adenosine-5′-triphosphate (ATP) or ADP (0.2 to 0.6 millimolar). Chloroplasts from 9-day-old wheat leaves were slightly less sensitive to inhibition by PPi and showed little or no inhibition by ADP. Chloroplasts isolated from protoplasts and assayed with 0.3 millimolar Pi added before illumination have an induction time from less than 1 minute up to 16 minutes depending on the time of the assay after isolation and the components of the medium. In order to obtain maximum rates of photosynthesis and minimum induction time, NaHCO3 and chelating agents, EDTA or PPi (+ATP), are required in the chloroplast isolation, resuspension and assay medium. With these inclusions in the isolation and resuspension medium the induction time decreased rapidly during the first 20 to 30 minutes storage of chloroplasts on ice. Requirements for isolating intact and photosynthetically functional chloroplasts from wheat protoplasts are discussed. 相似文献
15.
At low levels of dissolved inorganic carbon (DIC) and alkaline pH the rate of photosynthesis by air-grown cells of Synechococcus leopoliensis (UTEX 625) was enhanced 7- to 10-fold by 20 millimolar Na +. The rate of photosynthesis greatly exceeded the CO 2 supply rate and indicated that HCO 3− was taken up by a Na +-dependent mechanism. In contrast, photosynthesis by Synechococcus grown in standing culture proceeded rapidly in the absence of Na + and exceeded the CO 2 supply rate by 8 to 45 times. The apparent photosynthetic affinity ( K½) for DIC was high (6-40 micromolar) and was not markedly affected by Na + concentration, whereas with air-grown cells K½ (DIC) decreased by more than an order of magnitude in the presence of Na +. Lithium, which inhibited Na +-dependent HCO 3− uptake in air-grown cells, had little effect on Na +-independent HCO 3− uptake by standing culture cells. A component of total HCO 3− uptake in standing culture cells was also Na +-dependent with a K½ (Na +) of 4.8 millimolar and was inhibited by lithium. Analysis of 14C-fixation during isotopic disequilibrium indicated that standing culture cells also possessed a Na +-independent CO 2 transport system. The conversion from Na +-independent to Na +-dependent HCO 3− uptake was readily accomplished by transferring cells grown in standing to growth in cultures bubbled with air. These results demonstrated that the conditions experienced during growth influenced the mode by which Ssynechococcus acquired HCO 3− for subsequent photosynthetic fixation. 相似文献
16.
One-year-old plants of the CAM leaf succulent Agave vilmoriniana Berger were grown outdoors at Riverside, California. Potted plants were acclimated to CO 2-enrichment (about 750 microliters per liter) by growth for 2 weeks in an open-top polyethylene chamber. Control plants were grown nearby where the ambient CO 2 concentration was about 370 microliters per liter. When the plants were well watered, CO 2-induced differences in stomatal conductances and CO 2 assimilation rates over the entire 24-hour period were not large. There was a large nocturnal acidification in both CO 2 treatments and insignificant differences in leaf chlorophyll content. Well watered plants maintained water potentials of −0.3 to −0.4 megapascals. When other plants were allowed to dry to water potentials of −1.2 to −1.7 megapascals, stomatal conductances and CO 2 uptake rates were reduced in magnitude, with the biggest difference in Phase IV photosynthesis. The minor nocturnal response to CO 2 by this species is interpreted to indicate saturated, or nearly saturated, phosphoenolpyruvate carboxylase activity at current atmospheric CO 2 concentrations. CO 2-enhanced diurnal activity of ribulose bisphosphate carboxylase activity remains a possibility. 相似文献
17.
Three species, wheat, maize and cotton, were grown in pots and subjected to high (85–100% field capacity, F), medium (65–85% F) and low (45–65% F) soil moisture treatments and high (700 l l –1) and low (350 l l –1) CO 2 concentrations. Biomass production, photosynthesis, evapotranspiration and crop water use efficiency were investigated. Results showed that the daily photosynthesis rate was increased more in wheat and cotton at high [CO 2] than in maize. In addition, differences were more substantial at low soil water treatment than at high soil water treatment. The daily leaf transpiration was reduced significantly in the three crops at the high CO 2 concentration. The decrease at low soil water was smaller than at high soil water. Crop biomass production responses showed a pattern similar to photosynthesis, but the CO 2-induced increase was more pronounced in root production than shoot production under all soil water treatments. Low soil water treatment led to more root biomass under high [CO 2] than high soil water treatment. CO 2 enrichment caused a higher leaf water use efficiency (WUE) of three crops and the increase was more significant in low than in high soil water treatment. Crop community WUE was also increased by CO 2 enrichment, but the increase in wheat and cotton was much greater than in maize. We conclude that at least in the short-term, C 3 plants such as wheat and cotton may benefit from CO 2 enrichment especially under water shortage condition. 相似文献
18.
Abstract: Growth in elevated CO 2 led to an increase in biomass production per plant as a result of enhanced carbon uptake and lower rates of respiration, compared to ambient CO 2-grown plants. No down-regulation of photosynthesis was found after six months of growth under elevated CO 2. Photosynthetic rates at 15°C or 35 °C were also higher in elevated than in ambient CO 2-grown plants, when measured at their respective CO 2 growth condition. Stomata of elevated CO 2-grown plants were less responsive to temperature as compared to ambient CO 2 plants. The after effect of a heat-shock treatment (4 h at 45 °C in a chamber with 80% of relative humidity and 800–1000 tmol m -2 s -1 photon flux density) on A max was less in elevated than in ambient CO 2-grown plants. At the photochemical level, the negative effect of the heat-shock treatment was slightly more pronounced in ambient than in elevated CO 2-grown plants. A greater tolerance to oxidative stress caused by high temperatures in elevated CO 2-grown plants, in comparison to ambient CO 2 plants, is suggested by the increase in superoxide dismutase activity, after 1 h at 45 °C, as well as its relatively high activity after 2 and 4 h of the heat shock in the elevated CO 2-grown plants in contrast with the decrease to residual levels of superoxide dismutase activity in ambient CO 2-grown plants immediately after 1 h at 45 °C. The observed increase in catalase after 1 h at 45 °C in both ambient and elevated CO 2-grown plants, can be ascribed to the higher rates of photorespiration and respiration under this high temperature. 相似文献
19.
Elevated CO 2 interactions with other factors affects the plant performance. Regarding the differences between cultivars in response to CO 2 concentrations, identifying the cultivars that better respond to such conditions would maximize their potential benefits. Increasing the ability of plants to benefit more from elevated CO 2 levels alleviates the adverse effects of photoassimilate accumulation on photosynthesis and increases the productivity of plants. Despite its agronomic importance, there is no information about the interactive effects of elevated CO 2 concentration and plant growth regulators (PGRs) on potato ( Solanum tuberosum L.) plants. Hence, the physiological response and source-sink relationship of potato plants ( cvs. Agria and Fontane) to combined application of CO 2 levels (400 vs. 800 µmol mol −1) and plant growth regulators (PGR) [6-benzylaminopurine (BAP) + Abscisic acid (ABA)] were evaluated under a controlled environment. The results revealed a variation between the potato cultivars in response to a combination of PGRs and CO 2 levels. Cultivars were different in leaf chlorophyll content; Agria had higher chlorophyll a, b, and total chlorophyll content by 23, 43, and 23%, respectively, compared with Fontane. The net photosynthetic rate was doubled at the elevated compared with the ambient CO 2. In Agria, the ratio of leaf intercellular to ambient air CO 2 concentrations [C i:C a] was declined in elevated-CO 2-grown plants, which indicated the stomata would become more conservative at higher CO 2 levels. On the other hand, the increased C i:C a in Fontane showed a stomatal acclimation to higher CO 2 concentration. The higher leaf dark respiration of the elevated CO 2-grown and BAP + ABA-treated plants was associated with a higher leaf soluble carbohydrates and starch content. Elevated CO 2 and BAP + ABA shifted the dry matter partitioning to the belowground more than the above-media organs. The lower leaf soluble carbohydrate content and greater tuber yield in Fontane might indicate a more efficient photoassimilate translocation than Agria. The results highlighted positive synergic effects of the combined BAP + ABA and elevated CO 2 on tuber yield and productivity of the potato plants. 相似文献
20.
Stromal acidification has been reported to mediate reduced osmotic potential (ψ π) effects on photosynthesis in the isolated spinach chloroplast (Berkowitz, Gibbs 1983 Plant Physiol 72: 1100-1109). To determine if stromal acidification mediates osmotic dehydration inhibition of photosynthesis in vivo, the effects of a weak base (NH 4Cl), which raises stromal pH, on CO 2 fixation of vacuum-infiltrated spinach leaf slices, Chlamydomonas reinhardii cells and Aphanocapsa 6308 cells under isotonic and dehydrating conditions were investigated. Five millimolar NH 4Cl stimulated spinach leaf slice CO 2 fixation by 43% under stress (0.67 molar sorbitol) conditions, and had little effect on fixation under isotonic (0.33 molar sorbitol) conditions. Chlamydomonas cells were found to be more sensitive to reduced ψ π than spinach leaf slices. CO 2 fixation in the cells of the green alga Chlamydomonas reinhardii was 99 and 17 micromoles per milligram chlorophyll per hour, respectively, at 0.1 molar mannitol and 0.28 molar mannitol. Five millimolar NH 4Cl stimulated CO 2 fixation of Chlamydomonas cells by 147% under stress (0.28 molar mannitol) conditions. Aphanocapsa 6308 cells (blue-green alga) were also found to be sensitive to reduced ψ π, and inhibitions in photosynthesis were partially reversed by NH 4Cl. These data indicate that in vivo water stress inhibition of photosynthesis is facilitated by stromal acidification, and that this inhibition can be at least partially reversed in situ. 相似文献
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