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1.
Excised green leaves of mung bean ( Phaseolus aureus L. var. Mungo) were used to determine the effect of light on the rate of endogenous respiration via the tricarboxylic acid cycle. Illumination with white light at an intensity of 0.043 gram calories cm −2min −1 (approximately 8600 lux) of visible radiation (400-700 nm) gave a rate of apparent photosynthesis, measured as net CO 2 uptake, of 21 mg CO 2 dm −2hr −1 which was about 11-fold greater than the rate of dark respiration. The feeding of 14CO 2 or 14C-labeled acids of the tricarboxylic acid cycle in the dark for 2 hours was established as a suitable method for labeling mitochondrial pools of cycle intermediates. 相似文献
2.
A normal appearing plant with a low rate of photorespiration (ratio of 14CO 2 released light/dark = 1.6) was found in an unselected tobacco ( Nicotiana tabacum) cultivar. The plant was self-pollinated, and further selections were made on several successive generations. Excised leaves from the progeny of the selections were examined for photorespiration and net CO 2 assimilation in normal air during photosynthesis. Similar measurements were made of plants derived from selfed parents with high rates of photorespiration (ratio of 14CO 2 released light/dark = 3.0 or greater). Efficient photosynthetic plants (greater than 22.0 mg of CO 2 dm −2 hr −1) with low rates of photorespiration produced a larger proportion of efficient progeny (about 25%) than did selfing inefficient plants (about 6%), but this proportion did not increase in successive generations. 相似文献
3.
We grew velvetleaf ( Abutilon theophrasti Medic.) and cotton ( Gossypium hirsutum L. var. Stoneville 213) at three irradiances and determined the photosynthetic responses of single leaves to a range of six irradiances from 90 to 2000 μeinsteins m −2sec −1. In air containing 21% O 2, velvetleaf and cotton grown at 750 μeinsteins m −2sec −1 had maximum photosynthetic rates of 18.4 and 21.9 mg of CO 2 dm −2hr −1, respectively. Maximum rates for leaves grown at 320 and 90 μeinsteins m −2sec −1 were 15.3 and 10.3 mg of CO 2 dm −2hr −1 in velvetleaf and 12 and 6.7 mg of CO 2 dm −2hr −1 in cotton, respectively. In 1 O 2, maximum photosynthetic rates were 1.5 to 2.3 times the rates in air containing 21% O 2, and plants grown at medium and high irradiance did not differ in rate. In both species, stomatal conductance was not significantly affected by growth irradiance. The differences in maximum photosynthetic rates were associated with differences in mesophyll conductance. Mesophyll conductance increased with growth irradiance and correlated positively with mesophyll thickness or volume per unit leaf area, chlorophyll content per unit area, and photosynthetic unit density per unit area. Thus, quantitative changes in the photosynthetic apparatus help account for photosynthetic adaptation to irradiance in both species. Net assimilation rates calculated for whole plants by mathematical growth analysis were closely correlated with single-leaf photosynthetic rates. 相似文献
4.
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
5.
Xerosicyos danguyi H. Humb. (Cucurbitaceae) is an unusual leaf succulent endemic to Madagascar. Under well-watered conditions the plant exhibited Crassulacean acid metabolism (CAM), as characterized by large diurnal changes in titratable acidity, predominantly nighttime stomatal opening and CO 2 uptake, and high δ 13C values. When plants were exposed to water stress for a minimum of a month, they shifted to a mode of carbon metabolism previously labeled CAM-idling. Under this mode of metabolism, the plants exhibited reduced stomatal opening, reduced CO 2 uptake, dampened diurnal fluctuations in titratable acidity, and no apparent changes in the δ 13C values. Additionally, investigations showed that the stress hormones 1-aminocyclopropane-1-carboxylic acid (an ethylene precursor) and abscisic acid increased as much as 6-fold in the water-stressed plants. The results are discussed in relation to physiological significance and evolution of the CAM-idling mode of metabolism. 相似文献
6.
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
7.
Plants of Sedum rubrotinctum R. T. Clausen were studied in a green-house over a 2-year period without watering. Only the apical leaves survived and were turgid at the end of the experiment. The midday leaf water potential of these apical leaves was −1.20 megapascals, while the leaf water potential of comparable leaves on well-watered control plants was −0.20 megapascals. The unwatered plants appear to have maintained turgor by means of an osmotic adjustment. After 2 years without water the plants no longer exhibited a nocturnal accumulation of titratable acidity. However, the daytime levels of titratable acidity of the unwatered plants were more than 2-fold greater than the levels in well-watered control plants. Well-watered plants of S. rubrotinctum exhibited seasonal shifts in biomass stble carbon isotope ratios, indicating a greater proportion of day versus night CO 2 uptake in the winter than in the summer. The imposition of water stress prevented the expression of this seasonal rhythm and restricted the plants to dark CO 2 uptake. 相似文献
8.
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
9.
In response to water stress, Portulacaria afra (L.) Jacq. (Portulacaceae) shifts its photosynthetic carbon metabolism from the Calvin-Benson cycle for CO 2 fixation (C 3) photosynthesis or Crassulacean acid metabolism (CAM)-cycling, during which organic acids fluctuate with a C 3-type of gas exchange, to CAM. During the CAM induction, various attributes of CAM appear, such as stomatal closure during the day, increase in diurnal fluctuation of organic acids, and an increase in phosphoenolpyruvate carboxylase activity. It was hypothesized that stomatal closure due to water stress may induce changes in internal CO 2 concentration and that these changes in CO 2 could be a factor in CAM induction. Experiments were conducted to test this hypothesis. Well-watered plants and plants from which water was withheld starting at the beginning of the experiment were subjected to low (40 ppm), normal ( ca. 330 ppm), and high (950 ppm) CO 2 during the day with normal concentrations of CO 2 during the night for 16 days. In water-stressed and in well-watered plants, CAM induction as ascertained by fluctuation of total titratable acidity, fluctuation of malic acid, stomatal conductance, CO 2 uptake, and phosphoenolpyruvate carboxylase activity, remained unaffected by low, normal, or high CO 2 treatments. In well-watered plants, however, both low and high ambient concentrations of CO 2 tended to reduce organic acid concentrations, low concentrations of CO 2 reducing the organic acids more than high CO 2. It was concluded that exposing the plants to the CO 2 concentrations mentioned had no effect on inducing or reducing the induction of CAM and that the effect of water stress on CAM induction is probably mediated by its effects on biochemical components of leaf metabolism. 相似文献
10.
Crassulacean acid metabolism (CAM) was examined under natural environmental conditions in the succulent C 4 dicot Portulaca oleracea L. Two groups of plants were monitored; one was watered daily (well watered), while the other received water once every 3 to 4 weeks to produce a ψ of −8 bars (drought stressed). Gas exchange, transpiration rate, and titratable acidity were measured for 24-hour periods during the growing season. CAM activity was greatest in drought-stressed plants during late August which had 13 hour days and day/night temperatures of 35/15°C. Under these conditions net CO 2 uptake occurred slowly throughout the night. Diurnal fluctuations of titratable acidity took place in both leaves and stems with amplitudes of 17 and 47 microequivalents per gram fresh weight, respectively. Transpiration data indicated greater opening of stomata during the night than the day. CAM was less pronounced in drought-stressed P. oleracea plants in July and September; neither dark CO 2 uptake nor positive carbon balance occurred during the July measurements. In contrast, well-watered plants appeared to rely on C 4 photosynthesis throughout the season, although some acid fluctuations occurred in stems of these plants during September. 相似文献
11.
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
12.
Cotton ( Gossypium hirsutum L. cv Acala SJ2) plants were exposed to three levels of osmotic or matric potentials. The first was obtained by salt and the latter by withholding irrigation water. Plants were acclimated to the two stress types by reducing the rate of stress development by a factor of 4 to 7. CO 2 assimilation was then determined on acclimated and nonacclimated plants. The decrease of CO 2 assimilation in salinity-exposed plants was significantly less in acclimated as compared with nonacclimated plants. Such a difference was not found under water stress at ambient CO 2 partial pressure. The slopes of net CO 2 assimilation versus intercellular CO 2 partial pressure, for the initial linear portion of this relationship, were increased in plants acclimated to salinity of −0.3 and −0.6 megapascal but not in nonacclimated plants. In plants acclimated to water stress, this change in slopes was not significant. Leaf osmotic potential was reduced much more in acclimated than in nonacclimated plants, resulting in turgor maintenance even at −0.9 megapascal. In nonacclimated plants, turgor pressure reached zero at approximately −0.5 megapascal. The accumulation of Cl − and Na + in the salinity-acclimated plants fully accounted for the decrease in leaf osmotic potential. The rise in concentration of organic solutes comprised only 5% of the total increase in solutes in salinity-acclimated and 10 to 20% in water-stress-acclimated plants. This acclimation was interpreted in light of the higher protein content per unit leaf area and the enhanced ribulose bisphosphate carboxylase activity. At saturating CO 2 partial pressure, the declined inhibition in CO 2 assimilation of stress-acclimated plants was found for both salinity and water stress. 相似文献
13.
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
14.
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
15.
Abstract The paper reports the results of the comprehensive study of crassulacean acid metabolism in two epiphytic tropical ferns, Drymoglossum piloselloides and Pyrrosia longifolia. The plants were investigated under different light, temperature and water status. It was found that both species are obligate CAM plants. The diurnal acidity rhythm is due to the fluctuation in malic acid concentration, which accounts for the change in titratable acidity. Besides malic acid, shikimate and oxalate are found to be present, but not contributing to the CAM acid rhythm. The diurnal rhythm of malic acid content results in a corresponding rhythm in leaf water relations. Both Φ Φ and Φ total, were lowest at the end of the night, i.e. when the level of malic acid was highest. The effects of temperature on CO 2 exchange were inverse to those observed in other CAM plants. In both ferns studied, dark CO 2 fixation increased when the night temperature was increased. Increase in day temperature reduced CO 2 uptake during phase IV and during the following night. The observed responses of the ferns to temperature changes suggest that the in situ environmental conditions are optimal for their CAM performance. In weak light, the plants showed net CO 2 output during the midday deacidification period. Increases in light intensity reduced such CO 2 output. Under drought conditions, the CO 2 exchange in the ferns was reduced to zero within 5–6 d, indicating that the ferns studied are more susceptible to water deficiency than other CAM plants. This could be due to a higher cuticular conductance for water. The results are discussed, in particular, in relation to CAM performance of epiphytes growing in the wet tropics. 相似文献
16.
The effects of Mg deficiency on the photosynthesis and respiration of sugar beets ( Beta vulgaris L. cv. F58-554H1) were studied by withholding Mg from the culture solution and by following changes in CO 2 and water vapor exchange of attached leaves. Leaf blade Mg concentration decreased from about 1200 to less than 200 meq kg −1 dry matter without change in the rate of photosynthetic CO 2 uptake per unit leaf area, while from 200 to 50 meq kg −1 the rate decreased to one-third. Rates of photorespiratory evolution of CO 2 into CO 2-free air responded to Mg like those of photosynthetic CO 2 uptake, the rates decreasing to one-half, below 200 meq kg −1. Respiratory CO 2 evolution in the dark increased almost 2-fold in low Mg leaves. Magnesium deficiency had less effect on leaf (mainly stomatal) diffusion resistance (r 1) than on mesophyll resistance (r m); in Mg-deficient plants r m increased from 2.9 to 7.1 sec cm −1, whereas r 1 became significantly greater than the control value only in the most severe instances of Mg deficiency. 相似文献
17.
Experiments were conducted to examine the development of photosynthetic carbon metabolism in Peperomia scandens, a tropical epiphyte. Leaves were sampled during a 10-day period when they were between 30 to 165 days old. P. scandens exhibits a C 3 to CAM-cycling to CAM shift during maturation with the magnitude of CAM increasing with age. Initially, during both day and night, no significant CO 2 uptake or diurnal acid flux was evident. C 3 gas exchange was detected at 41 days of age with a gradual shift towards CAM gas exchange maximized thereafter. An acidity flux of 130 to 150 microequivalents per gram fresh weight was evident by 41 days. Between 40 and 90 days, the leaves shifted their CO 2 uptake pattern from a daytime to a nighttime peak. After 90 days, the leaves remained in CAM. The δ 13C values became progressively less negative as the leaves matured. In the 30-day-old leaves, the δ 13C value was −21.1% while in the 165-day-old leaves the δ 13C value was −18.3%. The time-dependent shift from C 3 to CAM-cycling to CAM in P. scandens does not appear to result from changes in water, light, or temperature regimes since these variables were constant for all leaves sampled. 相似文献
18.
Phosphorus deficiency was induced in sugar beet plants ( Beta vulgaris L. var. F5855441), cultured hydroponically under standardized environmental conditions, by removal of phosphorus from the nutrient supply at the ten leaf stage 28 days after germination. CO 2 and water vapor exchange rates of individual attached leaves were determined at intervals after P cutoff. Leaves grown with an adequate nutrient supply attained net rates of photosynthetic CO 2 fixation of 125 ng CO 2 cm −2 sec −1 at saturating irradiance, 25 C, and an ambient CO 2 concentration of about 250 μl l −1. After P cutoff, leaf phosphorus concentrations decreased as did net rates of photosynthetic CO 2 uptake, photorespiratory evolution of CO 2 into CO 2-free air, and dark respiration, so that 30 days after cutoff these rates were about one-third of the control rates. The decrease in photosynthetic rates during the first 15 days after cutoff was associated with increased mesophyll resistance ( rm) which increased from 2.4 to 4.9 sec cm −1, while from 15 to 30 days there was an increase in leaf (mainly stomatal) diffusion resistance ( rl′) from 0.3 to 0.9 sec cm −1, as well as further increases in rm to 8.5 sec cm −1. Leaf diffusion resistance ( rl′) was increased greatly by low P at low but not at high irradiance, rl′ for plants at low P reaching values as high as 9 sec cm −1. 相似文献
19.
After 23 days without water in a greenhouse, rates of nocturnal CO 2 uptake in Tillandsia schiedeana decreased substantially and maximum rates occurred later in the dark period eventually coinciding with the onset of illumination. Nocturnal CO 2 uptake accounted for less than half the total nighttime increase in acidity measured in well-watered plants. With increased tissue desiccation, only 11–12% of measured acid accumulation was attributable to atmospheric CO 2 uptake. Plants desiccated for 30 days regained initial levels of nocturnal acid accumulation and CO 2 uptake after rehydration for 10h. These results stress the importance of CO 2 recycling via CAM in this epiphytic bromeliad, especially during droughts.Partially supported by Biomedical Sciences Support Grant RR07037. 相似文献
20.
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
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