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1.
When photon flux density incident on attached leaves of Zea mays L. was varied from the equivalent of 0.12 of full sunlight to full sunlight, leaf conductance to CO 2 transfer, g, changed in proportion to the change in rate of CO 2, assimilation, A, with the result that intercellular partial pressure of CO 2 remained almost constant. The proportionality was the same as that previously found in g and A measured at one photon flux density in plants of Zea mays L. grown at different levels of mineral nutrition, light intensities, and ambient partial pressures of CO 2. In shade-grown Phaseolus vulgaris L. plants, A as photon flux density was increased from about 0.12 up to about 0.5 full sunlight, the proportionality being almost the same in plants grown at low and at high light intensity. When photon flux density incident on the adaxial and abaxial surfaces of the isolateral leaves of Eucalyptus pauciflora Sieb. ex Spreng was varied, g and A also varied proportionally. The leaf conductance in a particular surface was affected by the photon flux density at the opposite surface to a greater extent than was expected on the basis of transmittance. The results indicated that stomata may, in some way, be sensitive to the photon flux absorbed within the leaf as a whole. 相似文献
2.
Rates of CO 2 assimilation and leaf conductances to CO 2 transfer were measured in plants of Zea mays during a period of 14 days in which the plants were not rewatered, and leaf water potential decreased from −0.5 to −8.0 bar. At any given ambient partial pressure of CO 2, water stress reduced rate of assimilation and leaf conductance similarly, so that intercellular partial pressure of CO 2 remained almost constant. At normal ambient partial pressure of CO 2, the intercellular partial pressure of CO 2 was estimated to be 95 microbars. This is the same as had been estimated in plants of Zea mays grown with various levels of nitrogen supply, phosphate supply and irradiance, and in plants of Zea mays examined at different irradiances. After leaves of Phaseolus vulgaris L. and Eucalyptus pauciflora Sieb. ex Spreng had been exposed to high irradiance in an atmosphere of CO2-free N2 with 10 millibars O2, rates of assimilation and leaf conductances measured in standard conditions had decreased in similar proportions, so that intercellular partial pressure of CO2 remained almost unchanged. As the conductance of each epidermis that had not been directly irradiated had declined as much as that in the opposite, irradiated surface it was hypothesized that conductance may have been influenced by photoinhibition within the mesophyll tissue. 相似文献
3.
The effect of long-term (weeks to months) CO 2 enhancement on (a) the gas-exchange characteristics, (b) the content and activation state of ribulose-1,5-bisphosphate carboxylase (rubisco), and (c) leaf nitrogen, chlorophyll, and dry weight per area were studied in five C 3 species ( Chenopodium album, Phaseolus vulgaris, Solanum tuberosum, Solanum melongena, and Brassica oleracea) grown at CO 2 partial pressures of 300 or 900 to 1000 microbars. Long-term exposure to elevated CO 2 affected the CO 2 response of photosynthesis in one of three ways: (a) the initial slope of the CO 2 response was unaffected, but the photosynthetic rate at high CO 2 increased ( S. tuberosum); (b) the initial slope decreased but the CO 2-saturated rate of photosynthesis was little affected ( C. album, P. vulgaris); (c) both the initial slope and the CO 2-saturated rate of photosynthesis decreased ( B. oleracea, S. melongena). In all five species, growth at high CO 2 increased the extent to which photosynthesis was stimulated following a decrease in the partial pressure of O 2 or an increase in measurement CO 2 above 600 microbars. This stimulation indicates that a limitation on photosynthesis by the capacity to regenerate orthophosphate was reduced or absent after acclimation to high CO 2. Leaf nitrogen per area either increased ( S. tuberosum, S. melongena) or was little changed by CO 2 enhancement. The content of rubisco was lower in only two of the five species, yet its activation state was 19% to 48% lower in all five species following long-term exposure to high CO 2. These results indicate that during growth in CO 2-enriched air, leaf rubisco content remains in excess of that required to support the observed photosynthetic rates. 相似文献
4.
Mature, field-grown Vitis vinifera L. grapevines grown in open-top chambers were exposed to either charcoal-filtered air or ambient ozone partial pressures throughout the growing season. Individual leaves also were exposed to ozone partial pressures of 0.2, 0.4, or 0.6 micropascals per pascal for 5 hours. No visual ozone damage was found on leaves exposed to any of the treatments. Chronic exposure to ambient O 3 partial pressures reduced net CO 2 assimilation rate (A) between 5 and 13% at various times throughout the season when compared to the filtered treatment. Exposure of leaves to 0.2 micropascals per pascal O 3 for 5 hours had no significant effect on A; however, A was reduced 84% for leaves exposed to 0.6 micropascals per pascal O 3 when compared to the controls after 5 hours. Intercellular CO 2 partial pressure ( ci) was lower for leaves exposed to 0.2 micropascals per pascal O 3 when compared to the controls, while ci of the leaves treated with 0.6 micropascals per pascal of 0 3 increased during the fumigation. The long-term effects of ambient O 3 and short-term exposure to acute levels of O 3 reduced grape leaf photosynthesis due to a reduction in both stomatal and mesophyll conductances. 相似文献
5.
Observations of nonuniform photosynthesis across leaves cast doubt on internal CO 2 partial pressures (p i) calculated on the assumption of uniformity and can lead to incorrect conclusions about the stomatal control of photosynthesis. The problem can be avoided by measuring p i directly because the assumptions of uniformity are not necessary. We therefore developed a method that allowed p i to be measured continuously in situ for days at a time under growth conditions and used it to investigate intact leaves of sunflower ( Helianthus annuus L.), soybean ( Glycine max L. Merr.), and bush bean ( Phaseolus vulgaris L.) subjected to high or low leaf water potentials (ψ w) or high concentrations of abscisic acid (ABA). The leaves maintained a relatively constant differential (Δp) between ambient CO 2 and measured p i throughout the light period when water was supplied. When water was withheld, ψ w decreased and the stomata began to close, but measured p i increased until the leaf reached a ψ w of −1.76 (bush bean), −2.12 (sunflower) or −3.10 (soybean) megapascals, at which point Δp = 0. The increasing p i indicated that stomata did not inhibit CO 2 uptake and a Δp of zero indicated that CO 2 uptake became zero despite the high availability of CO 2 inside the leaf. In contrast, when sunflower leaves at high ψ w were treated with ABA, p i did not increase and instead decreased rapidly and steadily for up to 8 hours even as ψ w increased, as expected if ABA treatment primarily affected stomatal conductance. The accumulating CO 2 at low ψ w and contrasting response to ABA indicates that photosynthetic biochemistry limited photosynthesis at low ψ w but not at high ABA. 相似文献
6.
Curly dock ( Rumex crispus L.) was grown from seed in a glasshouse at an ambient CO 2 partial pressure of about 35 pascals. Apparent respiration rate (CO 2 efflux in the dark) of expanded leaves was then measured at ambient CO 2 partial pressure of 5 to 95 pascals. Calculated intercellular CO 2 partial pressure was proportional to ambient CO 2 partial pressure in these short-term experiments. The CO 2 level strongly affected apparent respiration rate: a doubling of the partial pressure of CO 2 typically inhibited respiration by 25 to 30%, whereas a decrease in CO 2 elicited a corresponding increase in respiration. These responses were readily reversible. A flexible, sensitive regulatory interaction between CO 2 (a byproduct of respiration) and some component(s) of heterotrophic metabolism is indicated. 相似文献
7.
Diffusion of inorganic carbon into isolated bundle sheath cells from a variety of C 4 species was characterized by coupling inward diffusion of CO 2 to photosynthetic carbon assimilation. The average permeability coefficient for CO 2 ( PCO2) for five representatives from the three decarboxylation types was approximately 20 micromoles per minute per milligram chlorophyll per millimolar, on a leaf chlorophyll basis. The average value for the NAD-ME species Panicum miliaceum (10 determinations) was 26 with a standard deviation of 6 micromoles per minute per milligram chlorophyll per millimolar, on a leaf chlorophyll basis. A PCO2 of at least 500 micromoles per minute per milligram chlorophyll per millimolar was determined for cells isolated from the C 3 plant Xanthium strumarium. It is concluded that bundle sheath cells are one to two orders of magnitude less permeable to CO 2 than C 3 photosynthetic cells. These data also suggest that CO 2 diffusion in bundle sheath cells may be made up of two components, one involving an apoplastic path and the other a symplastic (plasmodesmatal) path, each contributing approximately equally. 相似文献
8.
Simultaneous measurements of net CO 2 exchange, water vapor exchange, and leaf water relations were performed in Mesembryanthemum crystallinum during the development of crassulacean acid metabolism (CAM) in response to high NaCl salinity in the rooting medium. Determinations of chlorophyll a fluorescence were used to estimate relative changes in electron transport rate. Alterations in leaf mass per unit area, which—on a short-term basis—largely reflect changes in water content, were recorded continuously with a beta-gauge. Turgor pressure of mesophyll cells was determined with a pressure probe. As reported previously (K Winter, DJ von Willert [1972] Z Pflanzenphysiol 67: 166-170), recently expanded leaves of plants grown under nonsaline conditions showed gas-exchange characteristics of a C 3 plant. Although these plants were not exposed to any particular stress treatment, water content and turgor pressure regularly decreased toward the end of the 12 hour light periods and recovered during the following 12 hours of darkness. When the NaCl concentration of the rooting medium was raised to 400 millimolar, in increments of 100 millimolar given at the onset of the photoperiods for 4 consecutive days, leaf water content and turgor pressure decreased by as much as 30 and 60%, respectively, during the course of the photoperiods. These transient decreases probably triggered the induction of the biochemical machinery which is required for CAM to operate. After several days at 400 millimolar NaCl, when leaves showed features typical of CAM, overall turgor pressure and leaf mass per unit area had increased above the levels before onset of the salt treatment, and diurnal alterations in leaf water content were reduced. Net carbon gain during photoperiods and average intercellular CO 2 partial pressures at which net CO 2 uptake occurred, progressively decreased upon salinization. Reversible diurnal depressions in leaf conductance and net CO 2 uptake, with minima recorded in the middle of the photoperiods, preceded the occurrence of nocturnal net CO 2 uptake. During these reductions, intercellular CO 2 partial pressure and rates of photosynthetic electron transport decreased. With advancing age, leaves of plants grown under nonsaline conditions exhibited progressively greater diurnal reductions in turgor pressure and developed a low degree of CAM activity. 相似文献
9.
The gas exchange of spinach plants, salt-stressed by adding NaCl to the nutrient solution in increments of 25 millimolar per day to a final concentration of 200 millimolar, was studied 3 weeks after starting NaCl treatment. Photosynthesis became light saturated at 1100 to 1400 micromoles per square meter per second in salt-treated plants and at approximately 2000 micromoles per square meter per second in control plants. Photosynthetic capacity of the mesophyll measured as a function of intercellular partial pressure of CO 2 at the light intensity prevailing during growth and at light saturation were both decreased in the salttreated plants. The CO 2 compensation points and relative enhancements of photosynthesis at low O 2 were not affected by salinity. The lower photosynthetic rates in salt-treated leaves at 450 micromoles per square meter per second were associated with a 70% reduction in stomatal conductance and low intercellular CO 2 (219 microbars; cf. 285 microbars for controls). Increasing photon flux density to light saturation extended the linear portions of the CO 2 response curves, increased stomatal conductances, increased intercellular CO 2 in the salt-treated plants, but lowered it in controls, and accentuated differences in photosynthetic rate (area basis) between the treatments. Leaves from salt-treated plants were thicker but contained about 73% of the chlorophyll per unit area of control plants. When photosynthetic rates were expressed on a chlorophyll basis there was no difference in initial slope of assimilation versus intercellular CO2 between treatments. Photosynthetic rates (chlorophyll basis) at light saturation differed only by 20% which was also observed earlier with isolated, intact chloroplasts (Robinson et al. 1983 Plant Physiol 73: 238-242). Measurement of carbon isotope ratio revealed less discrimination against 13C with salt treatment and confirmed the persistence of low intercellular partial pressures of CO2 during plant growth. The development of a thicker leaf with less chlorophyll per unit area during salt treatment permitted stomatal conductance and intercellular partial pressure of CO2 to decline without restricting photosynthesis and had the benefit of greatly increasing water use efficiency. 相似文献
10.
Rates of CO 2 assimilation and steady state chlorophyll a fluorescence were measured simultaneously at different intercellular partial pressures of CO 2 in attached cotton ( Gossypium hirsutum L. cv Deltapine 16) leaves at 25°C. Electron transport activity for CO 2 assimilation plus photorespiration was calculated for these experiments. Under light saturating (1750 microeinsteins per square meter per second) and light limiting (700 microeinsteins per square meter per second) conditions there was a good correlation between fluorescence and the calculated electron transport activity at 19 and 200 millibars O 2, and between fluorescence and rates of CO 2 assimilation at 19 millibars but not 200 millibars O 2. The values of fluorescence measured at about 220 microbars intercellular CO 2 were not greatly affected by increasing O 2 from 19 to 800 millibars. Fluorescence increased with light intensity at any one intercellular CO 2 partial pressure. But the values obtained for fluorescence, expressed as a ratio of the maximum fluorescence obtained in DCMU-treated tissue, over the same range of CO 2 partial pressure at 500 microeinsteins per square meter per second were similar to those obtained at 1000 and 2000 microeinsteins per square meter per second. There were two phases in the observed correlation between fluorescence and calculated electron transport activity: an initial inverse relationship at low CO 2 partial pressures which reversed to a positive correlation at higher values of CO 2 partial pressures. Similar results were observed in the C 3 species Helianthus annuus L., Phaseolus vulgaris L., and Brassica chinensis. In all C 4 species ( Zea mays L., Sorghum bicolor L., Panicum maximum Jacq., Amaranthus edulis Speg., and Echinochloa frumentacea [Roxb.] Link) examined changes in fluorescence were directly correlated with changes in CO 2 assimilation rates. The nature and the extent to which Q (primary quencher) and high-energy state ( qE) quenching function in determining the steady state fluorescence obtained during photosynthesis in leaves is discussed. 相似文献
11.
A complementary DNA for the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) was cloned from tobacco ( Nicotiana tabacum) and fused in the antisense orientation to the cauliflower mosaic virus 35S promoter. This antisense gene was introduced into the tobacco genome, and the resulting transgenic plants were analyzed to assess the effect of the antisense RNA on Rubisco activity and photosynthesis. The mean content of extractable Rubisco activity from the leaves of 10 antisense plants was 18% of the mean level of activity of control plants. The soluble protein content of the leaves of anti-small subunit plants was reduced by the amount equivalent to the reduction in Rubisco. There was little change in phosphoribulokinase activity, electron transport, and chlorophyll content, indicating that the loss of Rubisco did not affect these other components of photosynthesis. However, there was a significant reduction in carbonic anhydrase activity. The rate of CO 2 assimilation measured at 1000 micromoles quanta per square meter per second, 350 microbars CO 2, and 25°C was reduced by 63% (mean value) in the antisense plants and was limited by Rubisco activity over a wide range of intercellular CO 2 partial pressures (p i). In control leaves, Rubisco activity only limited the rate of CO 2 assimilation below a p i of 400 microbars. Despite the decrease in photosynthesis, there was no reduction in stomatal conductance in the antisense plants, and the stomata still responded to changes in p i. The unchanged conductance and lower CO 2 assimilation resulted in a higher p i, which was reflected in greater carbon isotope discrimination in the leaves of the antisense plants. These results suggest that stomatal function is independent of total leaf Rubisco activity. 相似文献
12.
Summary Well watered plants of Vigna unguiculata (L.) Walp cv. California Blackeye No. 5 had maximum photosynthetic rates of 16 mol m -2 s -1 (at ambient CO 2 concentration and environmental parameters optimal for high CO 2 uptake). Leaf conductance declined with increasing water vapour concentration difference between leaf and air ( w), but it increased with increasing leaf temperature at a constant small w. When light was varied, CO 2 assimilation and leaf conductance were correlated linearly. We tested the hypothesis that g was controlled by photosynthesis via intercellular CO 2 concentration ( c
i). No unique relationship between (1) c
i, (2) the difference between ambient CO 2 concentration ( c
a) and c
i, namely c
a- c
i, or (3) the c
i/ c
a ratio and g was found. g and A appeared to respond to environmental factors fairly independently of each other. The effects of different rates of soil drying on leaf gas exchange were studied. At unchanged air humidity, different rates of soil drying were produced by using (a) different soils, (b) different irrigation schemes and (c) different soil volumes per plant. Although the soil dried to wilting point the relative leaf water content was little affected. Different soil drying rates always resulted in the same response of photosynthetic capacity ( A
max) and corresponding leaf conductance ( g( Amax)) when plotted against percent relative plant-extractable soil water content ( W
e
%) but the relationship with relative soil water content ( W
e
) was less clear. Above a range of W
e
of 15%–25%, A
max and g( Amax) were both high and responded little to decreasing W
e
. As soon as W
e
fell below this range, A
max and g( Amax) declined. The data suggest root-to-leaf communication not mediated via relative leaf water content. However, g( Amax) was initially more affected than A
max.List of abbreviations
A CO 2
assimilation
-
A
max
photosynthetic capacity at favourable ambient conditions
-
c
a CO 2
concentration of the air in the leaf chamber
-
c
i
intercellular
- CO 2
concentration
-
E
transpiration
-
g
leaf conductance
-
g( Amax)
leaf conductance corresponding to photosynthetic capacity
-
I
photon flux rate
-
T
l
leaf temperature
-
W
e
relative plant-extractable soil water content
-
W
e
absolute plant-extractable soil water content
-
W
l
relative leaf water content
-
W
s
relative soil water content
- w
difference in water vapour mole fraction between leaf and air
-
leaf water potential 相似文献
13.
The light and CO 2 response of (a) photosynthesis, (b) the activation state and total catalytic efficiency ( kcat) of ribulose-1,5-bisphosphate carboxylase (rubisco), and (c) the pool sizes of ribulose 1,5-bisphosphate, (RuBP), ATP, and ADP were studied in the C 3 annuals Chenopodium album and Phaseolus vulgaris at 25°C. The initial slope of the photosynthetic CO 2 response curve was dependent on light intensity at reduced light levels only (less than 450 micromoles per square meter per second in C. album and below 200 micromoles per square meter per second in P. vulgaris). Modeled simulations indicated that the initial slope of the CO 2 response of photosynthesis exhibited light dependency when the rate of RuBP regeneration limited photosynthesis, but not when rubisco capacity limited photosynthesis. Measured observations closely matched modeled simulations. The activation state of rubisco was measured at three light intensities in C. album (1750, 550, and 150 micromoles per square meter per second) and at intercellular CO 2 partial pressures ( C1) between the CO 2 compensation point and 500 microbars. Above a C1 of 120 microbars, the activation state of rubisco was light dependent. At light intensities of 550 and 1750 micromoles per square meter per second, it was also dependent on C1, decreasing as the C1 was elevated above 120 microbars at 550 micromoles per square meter per second and above 300 microbars at 1750 micromoles per square meter per second. The pool size of RuBP was independent of C1 only under conditions when the activation state of rubisco was dependent on C1. Otherwise, RuBP pool sizes increased as C1 was reduced. ATP pools in C. album tended to increase as C1 was reduced. In P. vulgaris, decreasing C1 at a subsaturating light intensity of 190 micromoles per square meter per second increased the activation state of rubisco but had little effect on the kcat. These results support modelled simulations of the rubisco response to light and CO 2, where rubisco is assumed to be down-regulated when photosynthesis is limited by the rate of RuBP regeneration. 相似文献
14.
Soybean [ Glycine max (L.) Merr. cv. Williams 82 and A3127] plants were grown in the field under long-term soil moisture deficit and irrigation to determine the effects of severe drought stress on the photosynthetic capacity of soybean leaves. Afternoon leaf water potentials, stomatal conductances, intercellular CO 2 concentrations and CO 2-assimilation rates for the two soil moisture treatments were compared during the pod elongation and seed enlargement stages of crop development. Leaf CO 2-assimilation rates were measured with either ambient (340 l CO 2 l –1) or CO 2-enriched (1800 l CO 2 l –1) air. Although seed yield and leaf area per plant were decreased an average of 48 and 31%, respectively, as a result of drought stress, leaf water potentials were reduced only an average of 0.27 MPa during the sampling period. Afternoon leaf CO 2-assimilation rates measured with ambient air were decreased an average of 56 and 49% by soil moisture deficit for Williams 82 and A3127, respectively. The reductions in leaf photosynthesis of both cultivars were associated with similar decreases in leaf stomatal conductance and with small increases in leaf intercellular CO 2 concentration. When the CO 2-enriched air was used, similar afternoon leaf CO 2-assimilation rates were found between the soil moisture treatments at each stage of crop development. These results suggest that photosynthetic capacity of soybean leaves is not reduced by severe soil moisture deficit when a stress develops gradually under field conditions.Abbreviations C i
intercellular CO 2 concentrations
- A a
rates of CO 2 assimilation measured with ambient air
- A e
rates of CO 2 assimilation measured with CO 2-enriched air
- g s
stomatal conductances
- RuBPCase
ribulose-1,5-bisphosphate carboxylase 相似文献
15.
Water hyacinth ( Eichhornia crassipes [Mart.] Solms) plants were grown in environmental chambers at ambient and enriched CO 2 levels (330 and 600 microliters CO 2 per liter). Daughter plants (ramets) produced in the enriched CO 2 gained 39% greater dry weight than those at ambient CO 2, but the original mother plants did not. The CO 2 enrichment increased the number of leaves per ramet and leaf area index, but did not significantly increase leaf size or the number of ramets formed. Flower production was increased 147%. The elevated CO 2 increased the net photosynthetic rate of the mother plants by 40%, but this was not maintained as the plants acclimated to the higher CO 2 level. After 14 days at the elevated CO 2, leaf resistance increased and transpiration decreased, especially from the adaxial leaf surface. After 4 weeks in elevated as compared to ambient CO 2, ribulose bisphosphate carboxylase activity was 40% less, soluble protein content 49% less, and chlorophyll content 26% less; whereas starch content was 40% greater. Although at a given CO 2 level the enriched CO 2 plants had only half the net photosynthetic rate of their counterparts grown at ambient CO 2, they showed similar internal CO 2 concentrations. This suggested that the decreased supply of CO 2 to the mesophyll, as a result of the increased stomatal resistance, was counterbalanced by a decreased utilization of CO 2. Photorespiration and dark respiration were lower, such that the CO 2 compensation point was not altered. The photosynthetic light and CO 2 saturation points were not greatly changed, nor was the O 2 inhibition of photosynthesis (measured at 330 microliters CO 2 per liter). It appears that with CO 2 enrichment the temporary increase in net photosynthesis produced larger ramets. After acclimation, the greater total ramet leaf area more than compensated for the lower net photosynthetic rate on a unit leaf area basis, and resulted in a sustained improvement in dry weight gain. 相似文献
16.
Imaging of photochemical yield of photosystem II (PSII) computed from leaf chlorophyll fluorescence images and gas-exchange measurements were performed on Rosa rubiginosa leaflets during abscisic acid (ABA) addition. In air ABA induced a decrease of both the net CO 2 assimilation ( An) and the stomatal water vapor conductance ( gs). After ABA treatment, imaging in transient nonphotorespiratory conditions (0.1% O 2) revealed a heterogeneous decrease of PSII photochemical yield. This decline was fully reversed by a transient high CO 2 concentration (7400 μmol mol −1) in the leaf atmosphere. It was concluded that ABA primarily affected An by decreasing the CO 2 supply at ribulose-1,5-bisphosphate carboxylase/oxygenase. Therefore, the An versus intercellular mole fraction ( Ci) relationship was assumed not to be affected by ABA, and images of Ci and gs were constructed from images of PSII photochemical yield under nonphotorespiratory conditions. The distribution of gs remained unimodal following ABA treatment. A comparison of calculations of Ci from images and gas exchange in ABA-treated leaves showed that the overestimation of Ci estimated from gas exchange was only partly due to heterogeneity. This overestimation was also attributed to the cuticular transpiration, which largely affects the calculation of the leaf conductance to CO 2, when leaf conductance to water is low. 相似文献
17.
Effects of irradiance on photosynthetic characteristics were examined in senescent leaves of rice ( Oryza sativa L.). Two irradiance treatments (100 and 20% natural sunlight) were imposed after the full expansion of the 13th leaf through senescence. The photosynthetic rate was measured as a function of intercellular CO 2 pressure with a gas-exchange system. The amounts of cytochrome f, coupling factor 1, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), and chlorophyll were determined. The coupling factor 1 and cytochrome f contents decreased rapidly during senescence, and their rates of decrease were much faster from the 20% sunlight treatment than from the full sunlight treatment. These changes were well correlated with those in the photosynthetic rate at CO 2 pressure = 600 microbars, but not with those under the ambient air condition (350 microbars CO 2) and 200 microbars CO 2. This suggested that the amounts of coupling factor 1 and cytochrome f from the full sunlight treatment cannot be limiting factors for the photosynthetic rate at ambient air conditions. The Rubisco content also decreased during senescence, but its decrease from the 20% sunlight treatment was appreciably retarded. However, this difference was not reflected in the photosynthetic rates at the ambient and 200 microbars CO 2. This implied that in vivo Rubisco activity may be regulated in the senescent leaves from the 20% sunlight treatment. The chlorophyll content decreased most slowly. In the 20% sunlight treatment, it remained apparently constant with a decline in chlorophyll a/b ratio. These photosynthetic characteristics of the senescent rice leaves under low irradiance were discussed in relation to acclimation of shade plants. 相似文献
18.
The correlation between CO 2 assimilation and nitrate reduction in detached spinach ( Spinacia oleracea L.) leaves was examined by measuring light-dependent changes in leaf nitrate levels in response to mild water stress and to artificially imposed CO 2 deficiency. The level of extractable nitrate reductase (NR) activity was also measured. The results are: (a) In the light, detached turgid spinach leaves reduced nitrate stored in the vacuoles of mesophyll cells at rates between 3 and 10 micromoles per milligram of chlorophyll per hour. Nitrate fed through the petiole was reduced at similar rates as storage nitrate. Nitrate reduction was accompanied by malate accumulation. (b) Under mild water stress which caused stomatal closure, nitrate reduction was prevented. The inhibition of nitrate reduction observed in water stressed leaves was reversed by external CO 2 concentrations (10-15%) high enough to overcome stomatal resistance. (c) Nitrate reduction was also inhibited when turgid leaves were kept in CO 2-free air or at the CO 2-compensation point or in nitrogen. (d) When leaves were illuminated in CO 2-free air, activity of NR decreased rapidly. It increased again, when CO 2 was added back to the system. The half-time for a 50% change in activity was about 30 min. It thus appears that there is a rapid inactivation/activation mechanism of NR in leaves which couples nitrate reductase to net photosynthesis. 相似文献
19.
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
20.
Most current photosynthesis models, and interpretations of many wholeleaf CO 2 gas exchange measurements, are based on the often unstated assumption that the partial pressure of CO 2 is nearly uniform throughout the airspaces of the leaf mesophyll. Here we present measurements of CO 2 gradients across amphistomatous leaves allowed to assimilate CO 2 through only one surface, thus simulating hypostomatous leaves. We studied five species: Eucalyptus pauciflora Sieb. ex Spreng., Brassica chinensis L., Gossypium hirsutum L., Phaseolus vulgaris L., and Spinacia oleracea L. For Eucalyptus, maximum CO 2 pressure differences across the leaf mesophyll were 73 and 160 microbar when the pressures outside the lower leaf surface were 310 and 590 microbar, respectively. Using an approximate theoretical calculation, we infer that if the CO 2 had been supplied equally at both surfaces then the respective mean intercellular CO 2 pressures would have been roughly 12 and 27 microbar less than the pressures in the substomatal cavities in these cases. For ambient CO 2 pressures near 320 microbar, the average and minimum pressure differences across the mesophyll were 45 and 13 microbar. The corresponding mean intercellular CO 2 pressures would then be roughly 8 and 2 microbar less than those in the substomatal cavities. Pressure differences were generally smaller for the four agricultural species than for Eucalyptus, but they were nevertheless larger than previously reported values. 相似文献
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