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1.
Contrasting metabolic regimes operate in Opuntia basilaris Engelm. and Bigelov, before and after precipitation. During periods of drought, atmospheric CO 2 exchange and transpiration are greatly reduced throughout the day/night cycle by stomatal closure and a highly impervious cuticle. The hypothesis is that endogenously produced CO 2 is retained and recycled through dark CO 2 fixation, organic acid transformations, photosynthesis, and respiration. Immediately following precipitation, nighttime stomatal opening is initiated, permitting increased atmospheric CO 2 assimilation and organic acid synthesis. 相似文献
2.
High levels of variability in gas exchange characteristics and degree of CAM-cycling were found in the same and different individuals of Talinum calycinum Engelm. collected from rock outcrops in Missouri. Differences in CO 2 assimilation were mostly correlated with differences in shoot conductance to CO 2 not shoot internal CO 2 concentration. As found previously, CAM acid fluctuations were evident in well-watered plants exhibiting C 3 gas exchange patterns (CAM-cycling) and also in drought-stressed plants with stomata closed, or nearly so, day and night (CAM-idling). Drought stress also resulted in rapid stomatal closure, conserving water during droughts. Maximal CO 2 uptake rates occurred below 35°C; higher temperatures induced decreases in CO 2 assimilation and conductance while shoot internal CO 2 concentrations remained similar. Plant water-use-efficiency was severely curtailed at temperatures above 30°C. Tissue acid fluctuations were the result of changes in malic acid concentrations. Calculations of the amount of water potentially conserved by CAM-cycling yielded values of approximately 5 to 44% of daytime water loss. Thus, CAM-cycling may be an important adaptation minimizing water loss by perennial succulents growing in shallow soil on rock outcrops. 相似文献
3.
Non-food-based biofuel feedstocks are in high demand worldwide. Among the various feedstocks, microalgae are the most promising feedstock for mitigating atmospheric CO 2 and producing biodiesel. In this study, various concentrations of CO 2, from 0.03 to 12%, were used to investigate their effect on the cell growth, biomass and lipid production and fatty acid composition of Dunaliella sp. in a closed photobioreactor. The results showed that the highest biomass and total lipids, 521 mg/L/d and 40 mg/L/d, respectively, were produced with 5% CO 2 aeration during the logarithmic growth phase. The oleic acid (18:1n9c) and elaidic acid (18:1n9t) contents were increased approximately two fold. The physiological responses of Dunaliella sp. at 10% CO 2 were similar to those at 5% CO 2. Therefore, the present results suggest that 5–10% is a suitable CO 2 concentration range for Dunaliella sp. growth to mitigate atmospheric CO 2 and increase biofuel production. 相似文献
4.
A year round study of photosynthesis and carbon isotope fractionation was conducted with plants of Opuntia phaeacantha Engelm. and Yucca baccata Torr. occurring in natural stands at elevations of 525, 970, 1450 and 1900 m. Plant water potentials and the daytime pattern of 14CO 2 photosynthesis were similar for all cacti along the elevational gradient, despite significant differences in temperature regime and soil water status. Carbon isotope ratios of total tissue and soluble extract fractions were relatively constant throughtout the entire year. Additionally, the σ 13C values were similar in all plants of the same species along the elevational gradient, i.e. −12.5 ± 0.86 ‰ for O. phaeacantha and −15.7 ± 0.95 ‰ for Y. baccata. The results of this study indicate Crassulacean acid metabolism predominates as the major carbon pathway of these plants, which do not facultatively utilize the reductive pentose phosphate cycle of photosynthesis as the primary carboxylation reaction. 相似文献
5.
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
6.
Photorespiration of photosynthetically active organs of C 3 plants (leaf, ear, stem, and leaf sheath) and C 4 plants (leaf, tassel, stem, leaf sheath, ear husk) grown under greenhouse and field conditions was studied. Photorespiration was measured using a PTM-48A high-technology monitor of photosynthesis (Bioinstruments S.R.L., Moldova). It is shown that photorespiration (CO 2 ejection after light turning off — apparent photorespiration) in C 3 plants is characteristic only for their leaves. In other photosynthesizing organs, photorespiration was absent, like in the photosynthesizing organs of C 4 plants. The absence of such after-light CO 2 outburst was observed for 31 genotypes: 18 cereal species belonging to four species ( Triticum aestivum L., T. durum Desf., Secale cereale L., and Triticale); 6 grain legumes belonging to 2 species ( Pisum sativum L. and Glycine max L.); 7 species of wild and rarely cultivated genotypes ( T. boeoticum Boiss., T. dicoccoides Koern., T. dicoccum Schuebl., T. spelta L., T. compactum Host., T. monococcum L., and T. sphaerococcum Persiv.), and 2 genotypes of C 4 plants ( Zea mays L. and Sorgum vulgaris L.). In all tested photosynthetically active genotypes, except of the C 3 plant leaves, apparent photorespiration was absent, but rather active glycolate cycle operated. The activity of this cycle was determined from the activity of the key enzyme of this cycle — glycolate oxidase. It was supposed that C 3 plants have two mechanisms of CO 2 assimilation: the first one — the mechanism of C 3 type localized in the leaves and the second one localized in other photosynthesizing organs, similar or with some elements of C 4 mechanism of CO 2 assimilation, limiting after-light CO 2 ejection during the metabolism of glycolate. 相似文献
7.
Temperature effects on nocturnal carbon gain and nocturnal acid accumulation were studied in three species of plants exhibiting Crassulacean acid metabolism: Mamillaria woodsii, Opuntia vulgaris, and Kalanchoë daigremontiana. Under conditions of high soil moisture, nocturnal CO 2 gain and acid accumulation had temperature optima at 15 to 20°C. Between 5 and 15°C, uptake of atmospheric CO 2 largely accounted for acid accumulation. At higher tissue temperatures, acid accumulation exceeded net carbon gain indicating that acid synthesis was partly due to recycling of respiratory CO 2. When plants were kept in CO 2-free air, acid accumulation based on respiratory CO 2 was highest at 25 to 35°C. Net acid synthesis occurred up to 45°C, although the nocturnal carbon balance became largely negative above 25 to 35°C. Under conditions of water stress, net CO 2 exchange and nocturnal acid accumulation were reduced. Acid accumulation was proportionally more decreased at low than at high temperatures. Acid accumulation was either similar over the whole temperature range (5-45°C) or showed an optimum at high temperatures, although net carbon balance became very negative with increasing tissue temperatures. Conservation of carbon by recycling respiratory CO 2 was temperature dependent. At 30°C, about 80% of the dark respiratory CO 2 was conserved by dark CO 2 fixation, in both well irrigated and water stressed plants. 相似文献
8.
Acid metabolism and gas exchange studies were conducted in situ on the cactus Opuntia basilaris Engelm. and Bigel. A pattern of significant seasonal variation was evident. The pattern was controlled by rainfall, which significantly influenced plant water potentials, total gas transfer resistances, and nocturnal organic acid synthesis. In winter and early spring, when plant water stress was mild, stomatal and mesophyll resistances remained low, permitting enhanced nocturnal assimilation of 14CO 2. The day/night accumulation of acidity was large during these seasons. In summer and fall, plant water stress was moderate, although soil water stress was severe. The nocturnal assimilation of 14CO 2 was very low during these seasons, even in stems with open stomata, indicating large mesophyll resistances restricting exogenous gas incorporation. The day/night accumulation of acidity was reduced, and a low level of acid metabolism persisted throughout this period. The rapid response to a midsummer rainfall emphasizes the importance of plant water potential as a parameter controlling over-all metabolic activity. The seasonal variations of acid metabolism and gas exchange significantly influenced the efficiency of water use and carbon dioxide assimilation. Periods of maximal efficiency followed rainfall throughout the course of the year. 相似文献
9.
Soybean ( Glycine max L. Merrill cv `Bragg') plants were grown in pots at six elevated atmospheric CO 2 concentrations and two watering regimes in open top field chambers to characterize leaf xylem potential, stomatal resistance and conductance, transpiration, and carbohydrate contents of the leaves in response to CO 2 enrichment and water stress conditions. Groups of plants at each CO 2 concentration were subjected to water stress by withholding irrigation for 4 days during the pod-filling stage. Under well watered conditions, the stomatal conductance of the plants decreased with increasing CO2 concentration. Therefore, although leaf area per plant was greater in the high CO2 treatments, the rate of water loss per plant decreased with CO2 enrichment. After 4 days without irrigation, plants in lower CO2 treatments showed greater leaf tissue damage, lower leaf water potential, and higher stomatal resistance than high CO2 plants. Stomatal closure occurred at lower leaf water potentials for the low CO2 grown plants than the high CO2 grown plants. Significantly greater starch concentrations were found in leaves of high CO2 plants, and the reductions in leaf starch and increases in soluble sugars due to water stress were greater for low CO2 plants. The results showed that even though greater growth was observed at high atmospheric CO2 concentrations, lower rates of water use delayed and, thereby, prevented the onset of severe water stress under conditions of low moisture availability. 相似文献
10.
When seven crop species were grown under identical environmental conditions, decreased sink:source ratio led to a decreased photosynthetic rate within 1 to 3 days in Cucumis sativus L., Gossypium hirsutum L., and Raphanus sativus L., but not in Capsicum annuum L., Solanum melongena L., Phaseolus vulgaris L., or Ricinus communis L. The decrease was not associated with stomatal closure. In cotton and cucumber, sink removal led to an increase in starch and sugar content, in glucose 6-phosphate and fructose 6-phosphate pools, and in the proportion of 14C detected in sugar phosphates and UDPglucose following 14CO 2 supply. When mannose was supplied to leaf discs to sequester cytoplasmic inorganic phosphate, promotion of starch synthesis, and inhibition of CO 2 fixation, were observed in control discs, but not in discs from treated plants. Phosphate buffer reduced starch synthesis in the latter, but not the former discs. The findings suggest that sink removal led to a decreased ratio inorganic phosphate:phosphorylated compounds. In beans 14C in sugar phosphates increased following sink removal, but without sucrose accumulation, suggesting tighter feedback control of sugar level. Starch accumulated to higher levels than in the other plants, but CO 2 fixation rate was constant for several days. 相似文献
11.
Lycopersicon esculentum Mill. cv Vedettos and Lycopersicon chmielewskii Rick, LA 1028, were exposed to two CO 2 concentrations (330 or 900 microliters per liter) for 10 weeks. Tomato plants grown at 900 microliters per liter contained more starch and more sugars than the control. However, we found no significant accumulation of starch and sugars in the young leaves of L. esculentum exposed to high CO 2. Carbon exchange rates were significantly higher in CO 2-enriched plants for the first few weeks of treatment but thereafter decreased as tomato plants acclimated to high atmospheric CO 2. This indicates that the long-term decline of photosynthetic efficiency of leaf 5 cannot be attributed to an accumulation of sugar and/or starch. The average concentration of starch in leaves 5 and 9 was always higher in L. esculentum than in L. chmielewskii (151.7% higher). A higher proportion of photosynthates was directed into starch for L. esculentum than for L. chmielewskii. However, these characteristics did not improve the long-term photosynthetic efficiency of L. chmielewskii grown at high CO 2 when compared with L. esculentum. The chloroplasts of tomato plants exposed to the higher CO 2 concentration exhibited a marked accumulation of starch. The results reported here suggest that starch and/or sugar accumulation under high CO 2 cannot entirely explain the loss of photosynthetic efficiency of high CO 2-grown plants. 相似文献
12.
Conductance for water vapor, assimilation of CO 2, and intercellular CO 2 concentration of leaves of five species were determined at various irradiances and ambient CO 2 concentrations. Conductance and assimilation were then plotted as functions of irradiance and intercellular CO 2 concentration. The slopes of these curves allowed us to estimate infinitesimal changes in conductance (and assimilation) that occurred when irradiance changed and intercellular CO 2 concentration was constant, and when CO 2 concentration changed and irradiance was constant. On leaves of Xanthium strumarium L., Gossypium hirsutum L., Phaseolus vulgaris L., and Perilla frutescens (L.), Britt., the stomatal response to light was determined to be mainly a direct response to light and to a small extent only a response to changes in intercellular CO 2 concentration. This was also true for stomata of Zea mays L., except at irradiances < 150 watts per square meter, when stomata responded primarily to the depletion of the intercellular spaces of CO 2 which in turn was caused by changes in the assimilation of CO 2. 相似文献
13.
Net CO 2 uptake over 24-hour periods was examined for the leaves and for the stems of 11 species of cacti representing all three subfamilies. For Pereskia aculeata, Pereskia grandifolia, and Maihuenia poeppigii (subfamily Pereskioideae), all the net shoot CO 2 uptake was by the leaves and during the daytime. In contrast, for the leafless species Carnegiea gigantea, Ferocactus acanthodes, Coryphantha vivipara, and Mammillaria dioica (subfamily Cactoideae), all the shoot net CO 2 uptake was by the stems and at night. Similarly, for leafless Opuntia ficus-indica (subfamily Opuntioideae), all net CO 2 uptake occurred at night. For leafy members of the Opuntioideae ( Pereskiopsis porteri, Quiabentia chacoensis, Austrocylindropuntia subulata), at least 88% of the shoot CO 2 uptake over 24 hours was by the leaves and some CO 2 uptake occurred at night. Leaves responded to the instantaneous level of photosynthetically active radiation (PAR) during the daytime, as occurs for C 3 plants, whereas nocturnal CO 2 uptake by stems of O. ficus-indica and F. acanthodes responded to the total daily PAR, as occurs for Crassulacean acid metabolism (CAM) plants. Thus, under the well-watered conditions employed, the Pereskioideae behaved as C 3 plants, the Cactoideae behaved as CAM plants, and the Opuntioideae exhibited characteristics of both pathways. 相似文献
14.
Crassulacean acid metabolism (CAM) was investigated in leaves and stems of the succulent C 4 dicot Portulaca oleracea L. Diurnal acid fluctuations, CO 2 gas exchange, and leaf resistance were monitored under various photoperiod and watering regimes. No CAM activity was seen in well watered plants grown under 16-hour days. Under 8-hour days, however, well watered plants showed a CAM-like pattern of acid fluctuation with amplitudes of 102 and 90 microequivalents per gram fresh weight for leaves and stems, respectively. Similar patterns were also observed in detached leaves and defoliated stems. Leaf resistance values indicated that stomata were open during part of the dark period, but night acidification most likely resulted from refixation of respiratory CO 2. In water-stressed plants maximum acid accumulations were reduced under both long and short photoperiods. At night, these plants showed short periods of net CO 2 uptake and stomatal opening which continued all night long during preliminary studies under natural environmental conditions. Greatest acid fluctuations, in P. oleracea, with amplitudes of 128 microequivalents per gram fresh weight, were observed in water-stressed plants which had been rewatered, especially when grown under short days. No net CO 2 uptake took place, but stomata remained open throughout the night under these conditions. These results indicate that under certain conditions, such as water stress or short photoperiods, P. oleracea is capable of developing an acid metabolism with many similarities to CAM. 相似文献
15.
In vivo CO 2 fixation activity and in vitro phosphoenolpyruvate carboxylase activity were demonstrated in effective and ineffective nodules of alfalfa ( Medicago sativa L.) and in the nodules of four other legume species. Phosphoenolpyruvate carboxylase activity was greatly reduced in nodules from both host and bacterially conditioned ineffective alfalfa nodules as compared to effective alfalfa nodules. Forage harvest and nitrate application reduced both in vivo and in vitro CO2 fixation activity. By day 11, forage harvest resulted in a 42% decline in in vitro nodule phosphoenolpyruvate carboxylase activity while treatment with either 40 or 80 kilograms nitrogen per hectare reduced activity by 65%. In vitro specific activity of phosphoenolpyruvate carboxylase and glutamate synthase were positively correlated with each other and both were positively correlated with acetylene reduction activity. The distribution of radioactivity in the nodules of control plants (unharvested, 0 kilograms nitrogen per hectare) averaged 73% into the organic acid and 27% into the amino acid fraction. In nodules from harvested plants treated with nitrate, near equal distribution of radioactivity was observed in the organic acid (52%) and amino acid (48%) fractions by day 8. Recovery to control distribution occurred only in those nodules whose in vitro phosphoenolpyruvate carboxylase activity recovered. The results demonstrate that CO2 fixation is correlated with nitrogen fixation in alfalfa nodules. The maximum rate of CO2 fixation for attached and detached alfalfa nodules at low CO2 concentrations (0.13-0.38% CO2) were 18.3 and 4.9 nanomoles per hour per milligram dry weight, respectively. Nodule CO2 fixation was estimated to provide 25% of the carbon required for assimilation of symbiotically fixed nitrogen in alfalfa. 相似文献
16.
The kinetics of chlorophyll fluorescence were measured in Portulacaria afra (L.) Jacq. when the plants were functioning in either Crassulacean acid metabolism (CAM) or C 3/CAM cycling (called cycling) modes, as determined by fluctuation in titratable acidity and gas exchange properties. Cycling plants showed primarily daytime CO 2 uptake typical of C 3 plants, but with a slight diurnal acid fluctuation, whereas CAM plants showed nocturnal CO 2 uptake, daytime stomatal closure, and a large diurnal acid fluctuation. Results from fluorescence measurements indicated no significant differences in photochemical quenching between cycling and CAM plants; however, sizable differences were detected in nonphoto-chemical quenching (q n), with the largest differences being observed during the middle of the day. Cycling plants had lower q n than CAM plants, indicating altered photosynthetic regulation processes. This q n difference was believed to be related to reduced internal CO 2 concentration in the CAM plants because of daytime stomatal closure and reduced deacidification rates in the late afternoon when most of the malic acid has been utilized. Experimentally, higher external CO 2 given to plants in the CAM mode resulted in a decline in q n in comparison to that measured in plants in the cycling mode. No changes were observed in photochemical quenching when CO 2 was added. 相似文献
17.
Respiration and gas exchange in the light were studied manometrically with tissue slices from stem material of Opuntia basilaris Engelm. and Bigel. Dark respiration rates were greater in young stems than in mature stems. The timing of the experiment in the day/night cycle influences the magnitude and pattern of respiration and gas exchange in the light. Net dark respiration has a temperature optimum between 35 and 40 C, and is maintained at 60% of the control rate in tissue equilibrated with experimental osmotic potentials of −25 bars. Net gas exchange in the light is regulated by the titratable acidity of the tissue and by the tissue temperature. Increased rates of net CO 2 evolution and net O 2 consumption occur in the light with high levels of titratable acidity and high temperatures. An efflux of CO 2 and influx of O 2 occur following light/dark transitions. These patterns are reversed following dark/light transitions. Similar results were demonstrated at 15, 25, and 35 C, and are interpreted as a mechanism of adaptation to desert environments. 相似文献
19.
Summary Measurements of acid metabolism and gas exchange were carried out four times during a year to assess the relative importance of temperature and the accompanying seasonal change to the carbon metabolism of Opuntia basilaris Engelm. & Bigel. plants growing in situ under irrigated and natural (control) conditions. Our experiments showed that this cactus did not change its pattern of carbon assimilation when continuously irrigated under field conditions. Non-irrigated cacti had maximum acid accumulation after periods of precipitation. Maximum acid accumulation in irrigated cacti occurred when there was a large difference between day/night temperatures (i.e., 16°C), and when nighttime temperatures were moderate (14C). Irrigated cacti had greater duration of stomatal opening and lower resistance to 14CO 2 uptake. When temperatures were low, daytime stomatal resistance to 14CO 2 uptake decreased (to 20–40 s cm -1), but never to the level of the nocturnal resistances (5–10 s cm -1). During periods of drought, nonirrigated cycti changed to a pattern in which organic acids fluctuated. Irrigated cacti continued to have 14CO 2 uptake when nighttime temperatures were as high as 33°C. 13C/ 12C isotope composition ratios, determined after two years of irrigation, were near -12 in irrigated and non-irrigated plants. Therefore, under conditions of continual irrigation, seasonal and temperature changes affected the degree of dark CO 2 fixation and acid metabolism, but these cacti did not change from CAM to CO 2 fixation in the light.Abbreviations C 3
reductive pentose phosphate cycle
- C 4
dicarboxylic acid cacle
- CAE
carbon assimilation efficiency
- CAM
Crassulacean acid metabolism
- THO
tritiated water
- T/P
transpiration ratio
- vpd
vapor pressure deficit
-
water potential
This study was supported in part by National Science Foundation grant OIP 74-15673. Under the auspice of this grant a cooperative research project was carried out between the Australian National University, Canberra, and the Philip L. Boyd Deep Canyon Desert Research Center, University of California, Riverside. The studies involved a comparison of the photosynthetic pathways employed by succulents during growth in their native environment (the Sonoran Desert of southeastern California) and in a favorable introduced environment (Queensland and New South Wales, Australia). Studies carried out in Australia are under the direction of Dr. C.B. Osmond 相似文献
20.
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
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