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1.
An immediate, marked response to small amounts of rainfall occurs in Opuntia basilaris, despite previous drought conditions. The effect of rainfall is upon plant water potential, which is the single most important parameter influencing stomatal opening, CO 2 assimilation, and organic acid synthesis. Nocturnal stomatal opening is initiated following rainfall, and stomata remain open during the daytime. Decreasing stomatal and mesophyll resistances correlate with increasing rates of nocturnal assimilation of 14CO 2. Photosynthetic rates of 14CO 2 assimilation are low, despite high plant water potentials and low stomatal diffusion resistances. The decreased mesophyll resistances and increased rates of nocturnal 14CO 2 assimilation correlate with the increases of nocturnal efficiency of water use and CO 2 assimilation. The diurnal efficiency of water use and CO 2 assimilation is lower than the nocturnal gas exchange efficiency values. 相似文献
2.
Portulacaria afra, a succulent plant, shifts from a predominantly C 3 mode of gas exchange to a typical Crassulacean acid metabolism type CO 2 uptake in response to water or NaCl stress. Control plants in the absence of water stress assimilated CO 2 during the light (about 7-8 mg CO 2 dm −2 hr −1), transpiration (about 1.5 g dm −2 hr −1) was predominantly during the day, stomates were open during the day, and there was little diurnal organic acid fluctuation. Stressed plants showed only dark CO 2 uptake and dark water loss, nocturnal stomatal opening, and an increased diurnal fluctuation of titratable acidity. Within 2 weeks after rewatering, stressed plants returned to the control acid fluctuation levels indicating that the response to stress was reversible. 相似文献
3.
Experiments were performed to test the hypothesis that succulents “shift” their method of photosynthetic metabolism in response to environmental change. Our data showed that there were at least three different responses of succulents to plant water status. When plant water status of Portulacaria afra (L.) Jacq. was lowered either by withholding water or by irrigating with 2% NaCl, a change from C 3-photosynthesis to Crassulacean acid metabolism (CAM) occurred. Fluctuation of titratable acidity and nocturnal CO 2 uptake was induced in the stressed plants. Stressed Peperomia obtusifolia A. Dietr. plants showed a change from C 3-photosynthesis to internal cycling of CO 2. Acid fluctuation commenced in response to stress but exogenous CO 2 uptake did not occur. Zygocactus truncatus Haworth plants showed a pattern of acid fluctuation and nocturnal CO 2 uptake typical of CAM even when well irrigated. The cacti converted from CAM to an internal CO 2 cycle similar to Peperomia when plants were water-stressed. Reverse phase gas exchange in succulents results in low water loss to carbon gain. Water is conserved and low levels of metabolic activity are maintained during drought periods by complete stomatal closure and continual fluctuation of organic acids. 相似文献
4.
Summary Evidence for the operation of CAM in the deciduous climber, Cissus trifoliata L., was obtained in field and laboratory studies. Under natural conditions, diurnal oscillations of titratable acidity and colorimetric measurements of night CO 2 fixation, determined for a period of two and a half years, suggested that acid accumulation was related to plant water status, assessed through the daily courses of stomatal resistance and xylem water potential during dry and rainy seasons. These findings were confirmed by gas exchange studies under controlled conditions which showed that the plant fixed all its CO 2 during the day when it was well irrigated; as water stress increased, dark CO 2 uptake gradually replaced fixation during the day until the plant only performed dark fixation. In severe water stress, even the rate of the latter process decreased until leaves fell.Abbreviations CAM
Crassulacean acid metabolism
- FW
leaf fresh weight
- SWC
relative soil water content
- PAR
photosynthetically active radiation
- TR
total radiation; r, leaf diffusive resistance
- WSD
water saturation deficit (leaf-air vapour concentration difference)
- RWC
relative water content of leaves 相似文献
5.
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
6.
A new theory and experimental method was developed to measure the diffusion resistance to CO 2 in the gas phase of mesophyll leaf tissue. Excised leaves were placed in a chamber and their net evaporation and CO 2 assimilation rates measured at two different ambient pressures. These data were used to calculate CO 2 gas phase diffusion resistances. A variety of field grown leaves were tested and the effects of various experimental errors considered. Increasing the gas phase diffusion resistance decreased transpiration more than it decreased CO 2 assimilation. It was concluded that gas phase diffusion resistance associated with CO 2 assimilation may sometimes be 100 or 200 s·m -1 greater than the resistance implied by transpiration rates. This may be due to longer path lengths for the CO 2 diffusion, constricted in places by the shape and arrangement of mesophyll cells. 相似文献
7.
Portulacaria afra (L.) Jacq., a perennial facultative Crassulacean acid metabolism (CAM) species, was studied under natural photoperiods and temperatures in San Diego, California. The plants were irrigated every fourth day throughout the study period. Measurements of 14CO 2 uptake, stomatal resistance, and titratable acidity were made periodically from July 1981 through May 1982. P. afra maintained C 3 photosynthesis during the winter and the spring. Diurnal acid fluctuations were low and maximal 14CO 2 uptake occurred during the day. The day/night ratio of carbon uptake varied from 5 to 10 and indicated little nocturnal CO 2 uptake. CAM photosynthesis occurred during the summer and a mixture of both C 3 and CAM during the fall. Large acid fluctuations of 100 to 200 microequivalents per gram fresh weight were observed and maximal 14CO 2 uptake shifted to the late night and early morning hours. Daytime stomatal closure was evident. A reduction in the day/night ratio of carbon uptake to 2 indicated a significant contribution of nocturnal CO 2 uptake to the overall carbon gain of the plant. The seasonal shift from C 3 to CAM was facilitated by increasing daytime temperature and accompanied by reduced daytime CO 2 uptake despite irrigation. 相似文献
8.
Leaves of Peperomia camptotricha contain three distinct upper tissue layers and a one-cell thick lower epidermis. Light and dark CO 2 fixation rates and the activity of ribulose bisphosphate carboxylase/oxygenase and several C 4 enzymes were determined in the three distinct tissue layers. The majority of the C 4 enzyme activity and dark CO 2 fixation was associated with the spongy mesophyll, including the lower epidermis; and the least activity was found in the median palisade mesophyll. In contrast, the majority of the C 3 activity, that is ribulose bisphosphate carboxylase/oxygenase and light CO 2 fixation, was located in the palisade mesophyll. In addition, the diurnal flux in titratable acidity was greatest in the spongy mesophyll and lowest in the palisade mesophyll. The spatial separation of the C 3 and C 4 phases of carbon fixation in P. camptotricha suggests that this Crassulacean acid metabolism plant may have low photorespiratory rates when it exhibits daytime gas exchange (that is, when it is well watered). The results also indicate that this plant may be on an evolutionary path between a true Crassulacean acid metabolism plant and a true C 4 plant. 相似文献
9.
Nocturnal CO 2 uptake by a Crassulacean acid metabolism succulent, Agave deserti Engelm. (Agavaceae), was measured so that the resistance properties of the mesophyll chlorenchyma cells and their CO 2 concentrations could be determined. Two equivalents of acidity were produced at night per mole of CO 2 taken up. The nocturnal CO 2 uptake became light-saturated at 3.5 mEinsteins cm −2 of photosynthetically active radiation (400-700 nm) incident during the preceding day; at least 46 Einsteins were required per mole of CO 2 fixed. Variations in the daytime leaf temperature between 20 and 37 C had little effect on nocturnal CO 2 uptake. After the first few hours in the dark, the leaf liquid phase CO 2 resistance (r liqCO2) and the CO 2 concentration in the chlorenchyma cells (c iCO2) both increased, the latter usually reaching the ambient external CO 2 level at the end of the dark period. Increasing the leaf surface temperature above 15 C at night markedly increased the stomatal resistance, r liqCO2, and c iCO2. The minimum rliqCO2 at night was about 1.6 seconds cm−1. Based on the ratio of chlorenchyma surface area to total leaf surface area of 82, this rliqCO2 corresponded to a minimum cellular resistance of approximately 130 seconds cm−1, comparable to values for mesophyll cells of C3 plants. The contribution of the carboxylation reaction and/or other biochemical steps to rliqCO2 may increase appreciably as the nighttime temperature shifts a few degrees from the optimum or after a few hours in the dark, both of which caused large increases in rliqCO2. This necessitates a large internal leaf area for CO2 diffusion into the chlorenchyma to support moderate nocturnal CO2 uptake rates by these succulent leaves. 相似文献
10.
The objective of this study was to determine the response of nitrogen metabolism to drought and recovery upon rewatering in barley ( Hordeum vulgare L.) plants under ambient (350 μmol mol −1) and elevated (700 μmol mol −1) CO 2 conditions. Barley plants of the cv. Iranis were subjected to drought stress for 9, 13, or 16 days. The effects of drought under each CO 2 condition were analysed at the end of each drought period, and recovery was analysed 3 days after rewatering 13-day droughted plants. Soil and plant water status, protein content, maximum (NR max) and actual (NR act) nitrate reductase, glutamine synthetase (GS), and aminant (NADH-GDH) and deaminant (NAD-GDH) glutamate dehydrogenase activities were analysed. Elevated CO 2 concentration led to reduced water consumption, delayed onset of drought stress, and improved plant water status. Moreover, in irrigated plants, elevated CO 2 produced marked changes in plant nitrogen metabolism. Nitrate reduction and ammonia assimilation were higher at elevated than at ambient CO 2, which in turn yielded higher protein content. Droughted plants showed changes in water status and in foliar nitrogen metabolism. Leaf water potential ( Ψw) and nitrogen assimilation rates decreased after the onset of water deprivation. NR act and NR max activity declined rapidly in response to drought. Similarly, drought decreased GS whereas NAD-GDH rose. Moreover, protein content fell dramatically in parallel with decreased leaf Ψw. In contrast, elevated CO 2 reduced the water stress effect on both nitrate reduction and ammonia assimilation coincident with a less-steep decrease in Ψw. On the other hand, Ψw practically reached control levels after 3 days of rewatering. In parallel with the recovery of plant water status, nitrogen metabolism was also restored. Thus, both NR act and NR max activities were restored to about 75-90% of control levels when water supply was restored; the GS activity reached 80-90% of control values; and GDH activities and protein content were similar to those of control plants. The recovery was always faster and slightly higher in plants grown under elevated CO 2 conditions compared to those grown in ambient CO 2, but midday Ψw dropped to similar values under both CO 2 conditions. The results suggest that elevated CO 2 improves nitrogen metabolism in droughted plants by maintaining better water status and enhanced photosynthesis performance, allowing superior nitrate reduction and ammonia assimilation. Ultimately, elevated CO 2 mitigates many of the effects of drought on nitrogen metabolism and allows more rapid recovery following water stress. 相似文献
11.
The potential for Crassulacean acid metabolism (CAM) was investigated in the sandstone outcrop succulent Talinum calycinum in central Kansas. Field studies revealed CAM-like diurnal acid fluctuations in these plants. These fluctuations persisted under all moisture and temperature regimes in the laboratory. Despite this CAM-like acid metabolism, simultaneous gravimetric determinations of day- and nighttime transpiration rates indicated the presence of a C 3 gas exchange pattern. Subsequent analyses of diurnal CO 2 and H 2O exchange patterns under well-watered conditions and after 3, 5, and 7 days of drought confirmed these findings, though low rates of nocturnal CO 2 uptake were observed on the fifth night after continuous drought. Finally, the δ 13C/ 12C value of this succulent, −27.8‰, emphasizes the insignificance of any nocturnal CO 2 uptake in the lifelong accumulation of carbon in this species. Thus, it is proposed that T. calycinum is a C 3 plant with some CAM characteristics, including the ability to re-fix respiratory CO 2 at night under all moisture regimes, potentially resulting in a conservation of carbon, and occasionally to fix atmospheric CO 2 at night. These findings may prove to be common among rock outcrop succulents. 相似文献
12.
Kalanchoë blossfeldiana Poelln. cv Hikan plants were grown hydroponically with nutrient solution containing 5 millimolar NO 3− (or NH 4+) for 1 to 2 months and then transferred to nutrient solution containing no nitrogen. CO 2 uptake at night, nocturnal increase in titratable acidity, and activity of phosphoenolpyruvate carboxylase increased after the transfer. Thus, transfer to nitrogen-deficient conditions stimulates Crassulacean acid metabolism (CAM photosynthesis) in K. blossfeldiana. The importance of the plant nitrogen status (nitrogen-withdrawal status) for induction and stimulation of CAM photosynthesis is discussed. 相似文献
13.
The water relations and photosynthesis of Agave deserti Engelm., a plant exhibiting Crassulacean acid metabolism, were measured in the Colorado desert. Although no natural stomatal opening of A. deserti occurred in the summer of 1975, it could be induced by watering. The resistance for water vapor diffusion from a leaf (R WV) became less than 20 sec cm −1 when the soil water potential at 10 cm became greater than −3 bars, as would occur after a 7-mm rainfall. As a consequence of its shallow root system (mean depth of 8 cm), A. deserti responded rapidly to the infrequent rains, and the succulent nature of its leaves allowed stomatal opening to continue for up to 8 days after the soil became drier than the plant. When the leaf temperature at night was increased from 5 to 20 C, R WV increased 5-fold, emphasizing the importance of cool nighttime temperatures for gas exchange by this plant. Although most CO 2 uptake occurred at night, a secondary light-dependent rise in CO 2 influx generally occurred after dawn. The transpiration ratio (mass of water transpired/mass of CO 2 fixed) had extremely low values of 18 for a winter day, and approximately 25 for an entire year. 相似文献
14.
The Pereskia are morphologically primitive, leafed members of the Cactaceae. Gas exchange characteristics using a dual isotope porometer to monitor 14CO 2 and tritiated water uptake, diurnal malic acid fluctuations, phosphoenolpyruvate carboxylase, and malate dehydrogenase activities were examined in two species of the genus Pereskia, Pereskia grandifolia and Pereskia aculeata. Investigations were done on well watered (control) and water-stressed plants. Nonstressed plants showed a CO 2 uptake pattern indicating C 3 carbon metabolism. However, diurnal fluctuations in titratable acidity were observed similar to Crassulacean acid metabolism. Plants exposed to 10 days of water stress exhibited stomatal opening only during an early morning period. Titratable acidity, phosphoenolpyruvate carboxylase activity, and malate dehydrogenase activity fluctuations were magnified in the stressed plants, but showed the same diurnal pattern as controls. Water stress causes these cacti to shift to an internal CO 2 recycling (“idling”) that has all attributes of Crassulacean acid metabolism except nocturnal stomata opening and CO 2 uptake. The consequences of this shift, which has been observed in other succulents, are unknown, and some possibilities are suggested. 相似文献
15.
The possibility that Crassulacean acid metabolism (CAM) is subject to long day photoperiodic control in Portulacaria afra (L.) Jacq., a facultative CAM plant, was studied. Periodic measurements of 14CO 2 uptake, stomatal resistance, and titratable acidity were made on plants exposed to long and short day photoperiods. Results indicates that waterstressed P. afra had primarily nocturnal CO 2 uptake, daytime stomatal closure, and a large diurnal acid fluctuation in either photoperiod. Mature leaf tissue from nonstressed plants under long days exhibited a moderate diurnal acid fluctuation and midday stomatal closure. Under short days, there was a reduced diurnal acid fluctuation in mature leaf tissue. Young leaf tissue taken from nonstressed plants did not utilize the CAM pathway under either photoperiod as indicated by daytime CO 2 uptake, lack of diurnal acid fluctuation, and incomplete daytime stomatal closure. The induction of CAM in P. afra appears to be related to the water status of the plant and the age of the leaf tissue. The photosynthetic metabolism of mature leaves may be partly under the control of water stress and of photoperiod, where CAM is favored under long days. 相似文献
16.
The CO 2 and H 2O vapour exchange of single attached orange, Citrus sinensis (L.), leaves was measured under laboratory conditions using infrared gas analysis. Gaseous diffusive resistances were derived from measurements at a saturating irradiance and at a leaf temperature optimum for photosynthesis. Variation in leaf resistance (within the range 1.6 to 60 s cm -1) induced by moisture status, or by cyclic oscillations in stomatal aperture, was associated with changes in both photosynthesis and transpiration. At low leaf resistance (ri less than 10 s cm -1) the ratio of transpiration to photosynthesis declined with reduced stomatal aperture, indicating a tighter stomatal control over H 2O vapour loss than over CO 2 assimilation. At higher leaf resistance (ri greater than 10 s cm -1) changes in transpiration and photosynthesis were linearly related, but leaf resistance and mesophyll resistance were also positively correlated, so that strictly stomatal control of photosynthesis became more apparent than real. This evidence, combined with direct measurements of CO 2 diffusive resistances (in a -O 2 gas stream) emphasised the presence of a significant mesophyll resistance; i.e., an additional and rate limiting resistance to CO 2 assimilation over and above that encountered by H 2O vapour escaping from the leaf. 相似文献
17.
Both Carpobrotus edulis and Senecio ?mandraliscae possess leaves with a peripheral chlorenchyma and colourless internal water-storage tissue. Water stress in C. edulis growing under semi-natural conditions resulted in the induction of weak Crassulacean acid metabolism (CAM) whereas well-watered plants of S. ?mandraliscae exhibited a similar degree of CAM. Titratable acidity in the separated water-storage tissue was substantially lower than in the chlorenchyma in both species but, nevertheless, increased during the night and decreased during the day either when sampled from the intact plant or from incubated tissue slices. Indeed, the increase in nocturnal titratable acidity produced by the water-storage tissue in situ accounted for approx. 30% of total acidification on a per-leaf basis. It appears that during the night the water-storage tissue in these species is able to fix CO 2 which is subsequently released during the day to enter the photosynthetic carbon-reduction cycle of the chlorenchyma. Diurnal rhythms of water potential (Ψ) and osmotic potential (Ψs) were measured in separated chlorenchyma and water-storage tissue by thermocouple psychrometry. Both parameters increased during the latter part of the daytime and initial nocturnal period and decreased during the rest of the night and into the post-dawn period. The chlorenchyma of water-stressed plants of C. edulis appeared to possess a marked negative turgor pressure (as determined from Ψ-Ψs) but this was caused by a severe underestimation in the measurement of the chlorenchyma Ψ. It is suggested that this artefact arose from release of colloidal polysaccharide mucilage, or possibly tannins, from broken tannin cells producing a lowering of water activity when measured using thermocouple psychrometry. 相似文献
18.
Rate of net CO 2 assimilation by soil-grown soybean plants were studied over a range of relative leaf water contents at each of four levels of irradiance. There was a large interaction between light level and leaf water deficit on the rate of CO 2 assimilation. The effect of leaf water deficit on assimilation became larger as irradiance increased. Both stomatal resistance to CO 2 transport and mesophyll resistance to CO 2 assimilation increased as leaf-water deficit increased. The increase in both resistance with changing leaf-water content was largest at high irradiance and became smaller as irradiance decreased. Relief of soil-moisture stress by watering induced large oscillations of CO 2 assimilation, stomatal resistance, and mesophyll resistance. The oscillation of the mesophyll resistance occurred in the absence of changes in relative water content and appeared to be related to oscillations in leaf temperature. The observed increase in mesophyll resistance with decreasing leaf-water content under nonoscillative conditions may be caused by changes in leaf temperature rather than leaf water content. 相似文献
19.
Summary The structural characteristics, water relations, and photosynthesis of Ferocactus acanthodes (Lemaire) Britton and Rose, a barrel cactus exhibiting Crassulacean acid metabolism (CAM), were examined in its native habitat in the western Colorado desert. Water storage in its succulent stem permitted nighttime stomatal opening ot continue for about 40 days after the soil water potential became less than that of the stem, a period whe the plant would be unable to extract water from the soil. After 7 months of drought and consequent unreplenished water loss from a plant, diurnal stomatal activity was not observed and the stem osmotic pressure was 6.4 bars, more than double the value measured during wet periods with nighttime stomatal opening. F. acanthodes had a shallow root system (mean depth of 8 cm) which responded within 24 h to rainfall.When the nocturnal stem surface temperature was raised from 8.0° C to 35.0° C, the stomatal resistance increased 4-fold, indicating that cool nighttime temperatures are advantageous for gas exchange by F. acanthodes. Moreover, the optimal temperature for CO 2 uptake in the dark was only 12.6° C. CO 2 uptake at night became maximal for 3.0 mEinsteins cm -2 of photosynthetically active radiation incident during the preceding day, and the minimum number of incident quanta absorbed per CO 2 fixed was 68. The transpiration ratio (mass of water transpired/mass of CO 2 fixed) had the relatively low value of 70 for an entire year, consistent with values obtained for other CAM plants. The total amount of water annually diverted to the floral structures was about 6% of the stem wet weight. The annual growth increment estimated from the net CO 2 assimilation corresponded to about 10% of the stem mass for barrel cacti 34 cm tall, in agreement with measured dimension changes, and indicated that such plants were about 26 years old. 相似文献
20.
In the epiphytic tillandsioids, Guzmania monostachia, Werauhia sanguinolenta, and Guzmania lingulata (Bromeliaceae), juvenile plants exhibit an atmospheric habit, whereas in adult plants the leaf bases overlap and form water-holding tanks. CO 2 gas-exchange measurements of the whole, intact plants and δ 13C values of mature leaves demonstrated that C 3 photosynthesis was the principal pathway of CO 2 assimilation in juveniles and adults of all three species. Nonetheless, irrespective of plant size, all three species were able to display features of facultative CAM when exposed to drought stress. The capacity for CAM was the greatest in G. monostachia, allowing drought-stressed juvenile and adult plants to exhibit net CO 2 uptake at night. CAM expression was markedly lower in W. sanguinolenta, and minimal in G. lingulata. In both species, low-level CAM merely sufficed to reduce nocturnal respiratory net loss of CO 2. δ 13C values were generally less negative in juveniles than in adult plants, probably indicating increased diffusional limitation of CO 2 uptake in juveniles. 相似文献
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