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1.
Plants of Zea mays were grown with different concentrations of nitrate (0.6, 4, 12, and 24 millimolar) and phosphate (0.04, 0.13, 0.53, and 1.33 millimolar) supplied to the roots, photon flux densities (0.12, 0.5, and 2 millimoles per square meter per second), and ambient partial pressures of CO 2 (305 and 610 microbars). Differences in mineral nutrition and irradiance led to a large variation in rate of CO 2 assimilation per unit leaf area ( A, 11 to 58 micromoles per square meter per second) when measured under standard conditions. The variation was shown, with the plants that had received different amounts of nitrate, to be related to variations in the nitrogen and chlorophyll contents, and phosphoenolpyruvate and ribulose-1,5-bisphosphate carboxylase activities per unit leaf area. Irrespective of growth treatment, A and leaf conductance to CO 2 transfer ( g), measured under standard conditions were in almost constant proportion, implying that intercellular partial pressure of CO 2 ( pi), was almost constant at 95 microbars. The same proportionality was maintained as A and g increased in an initially nitrogen-deficient plant that had been supplied with abundant nitrate. It was shown that pi measured at a given ambient partial pressure was not affected by the ambient partial pressure at which the plants had been grown, although it was different when measured at different ambient partial pressures. This suggests that the close coupling between A and g in these experiments is not associated with sensitivity of stomata to change in pi. Similar, though less comprehensive, experiments were done with Gossypium hirsutum, and yielded similar conclusions, except that the proportionality between A and g at normal ambient partial pressure of CO2 implied Pi ≈ 200 microbars. 相似文献
2.
The appearance of transverse sections of maize leaves indicates the existence of two airspace systems serving the mesophyll, one connected to the stomata of the upper epidermis and the other to the stomata of the lower surface, with few or no connections between the two. This study tests the hypothesis that the air-space systems of the upper and lower mesophyll are separated by a defined barrier of measurable conductance. A mathematical procedure, based on this hypothesis, is developed for the quantitative separation of the contributions made by the upper and lower halves of the mesophyll to carbon assimilation using gasexchange data. Serial paradermal sections and three-dimensional scanning-electron-microscope images confirmed the hypothesis that there were few connections between the two air-systems. Simultaneous measurements of nitrous-oxide diffusion across the leaf and of transpiration from the two surfaces showed that the internal conductance was about 15% of the maximum observed stomatal conductance. This demonstrates that the poor air-space connections, indicated by microscopy, represent a substantial barrier to gas diffusion. By measuring the CO 2 and water-vapour fluxes from each surface independently, the intercellular CO 2 concentration ( c
i) of each internal air-space system was determined and the flux between them calculated. This allowed correction of the apparent CO 2 uptake at each surface to derive the true CO 2 uptake by the mesophyll cells of the upper and lower halves of the leaf. This approach was used to analyse the contribution of the upper and lower mesophyll to CO 2 uptake by the leaf as a whole in response to varying light levels incident on the upper leaf surface. This showed that the upper mesophyll was light-saturated by a photon flux of approx. 1000 mol·m -2·s -1 (i.e. about one-half of full sunlight). The lower mesophyll was not fully saturated by photon fluxes of nearly double full sunlight. At low photon fluxes the c
i of the upper mesophyll was significantly less than that of the lower mesophyll, generating a significant upward flux of CO 2. At light levels equivalent to full sunlight, and above, c
i did not differ significantly between the two air space systems. The physiological importance of the separation of the air-space systems of the upper and lower mesophyll to gas exchange is discussed.Abbreviations and symbols
A
net leaf CO 2 uptake rate
-
A
upper
app.
and A
lower
app.
net rates of CO 2 uptake across the upper and lower surfaces
-
A
upper and A
lower
derived net rates of CO 2 uptake by the upper and lower mesophyll
-
A
upward
net flux of CO 2 from the lower to upper mesophyll
-
c
a, c
a, upper and c
a, lower
the CO 2 concentrations in the air around the leaf above the upper surface and below the lower surface
-
c
N2O
the concentration of N 2O in the air around the leaf
-
c
i, c
i, upper and c
i, lower
the mesophyll intercellular CO 2 concentration of the whole leaf, the upper mesophyll and the lower mesophyll
-
g
i
leaf internal conductance to CO 2
-
g
s, g
s, lower and g
s, upper
the stomatal conductance of the whole leaf, the lower surface and the upper surface
-
g
the total conductance across the leaf
-
Q
the photosynthetically active photon flux density 相似文献
3.
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
4.
The study presents a theoretical basis of a stomatal behavior-based coupled model for estimating photosynthesis, A, and transpiration, E. Outputs of the model were tested against data observed in a maize ( Zea mays L.) field. The model was developed by introducing the internal conductance, g
ic, to CO 2 assimilation, and the general equation of stomatal conductance, g
sw, to H 2O diffusion, into models of CO 2 and H 2O diffusion through the stomata of plant leaves. The coupled model is easier for practical use since the model only includes environmental variables, such as ambient CO 2 concentration, leaf temperature, humidity and photosynthetic photon flux received at the leaves within the canopy. Moreover, concept of g
ic, and factors controlling A and E were discussed, and applicability of the model was examined with the data collected in the maize field. 相似文献
5.
Abstract. Fully expanded leaves of 25°C grown Phaseolus vulgaris and six other species were exposed for 3 h to chilling temperatures at photon flux densities equivalent to full sunlight. In four of the species this treatment resulted in substantial inhibition of the subsequent quantum yield of CO 2 uptake, indicating reduction of the photochemical efficiency of photosynthesis. The extent of inhibition was dependent on the photon flux density during chilling and no inhibition occurred when chilling occurred at a low photon flux density. No inhibition occurred at temperatures above 11.5°C, even in the presence of the equivalent of full sunlight. This interaction between chilling and light to cause inhibition of photosynthesis was promoted by the presence of oxygen at normal air partial pressures and was unaffected by the CO 2 partial pressure present when chilling occurred in air. When chilling occurred at low O 2 partial pressures, CO 2 was effective in reducing the degree of inhibition. Apparently, when leaves of chilling-sensitive plants are exposed to chilling temperatures in air of normal composition then light is instrumental in inducing rapid damage to the photochemical efficiency of photosynthesis. 相似文献
6.
Detached leaf is in the state of increasing water deficit; it is a good experimental model for looking into the hardening effect of adaptation of eight-day-old maize ( Zea mays L.) seedlings to short-term drought (five days without watering). The light stage of photosynthesis and photosynthetic CO 2/H 2O exchange in detached leaves were studied. Specific surface density of leaf tissue (SSDL), the content of chlorophylls a and b, proline, MDA as well as photosynthetic parameters: quantum yield of photosystem II fluorescence, assimilation of CO 2, and transpiration at room temperature and light saturation (density of PAR quantum flux of 2000 μmol/(m 2 s)) at normal and half atmospheric CO 2 concentration were determined. The leaves of seedlings exposed to short-term drought differed from control material by a greater SSDL and higher content of proline. The hardening effect of the stress agent on the dark stage of photosynthesis was detected; it was expressed in the maintenance of the higher photosynthetic CO 2 assimilation against control material due to the elevation of stomatal conductance for CO 2 diffusing into the leaf. Judging from the lack of differences in the MDA content, short-term drought did not injure photosynthetic membranes. In detached leaves of experimental maize seedlings, photosynthesis was maintained on a higher level than in control material. 相似文献
7.
Summary Seedlings of the Caesalpinoids Hymenaea courbaril, H. parvifolia and Copaifera venezuelana, emergent trees of Amazonian rainforest canopies, and of the Araucarian conifers Agathis microstachya and A. robusta, important elements in tropical Australian rainforests, were grown at 6% (shade) and 100% full sunlight (sun) in glasshouses. All species produced more leaves in full sunlight than in shade and leaves of sun plants contained more nitrogen and less chlorophyll per unit leaf area, and had a higher specific leaf weight than leaves of shade plants. The photosynthetic response curves as a function of photon flux density for leaves of shade-grown seedlings showed lower compensation points, higher quantum yields and lower respiration rates per unit leaf area than those of sun-grown seedlings. However, except for A. robusta, photosynthetic acclimation between sun and shade was not observed; the light saturated rates of assimilation were not significantly different. Intercellular CO 2 partial pressure was similar in leaves of sun and shade-grown plants, and assimilation was limited more by intrinsic mesophyll factors than by stomata. Comparison of assimilation as a function of intercellular CO 2 partial pressure in sun- and shade-grown Agathis spp. showed a higher initial slope in leaves of sun plants, which was correlated with higher leaf nitrogen content. Assimilation was reduced at high transpiration rates and substantial photoinhibition was observed when seedlings were transferred from shade to sun. However, after transfer, newly formed leaves in A. robusta showed the same light responses as leaves of sun-grown seedlings. These observations on the limited potential for acclimation to high light in leaves of seedlings of rainforest trees are discussed in relation to regeneration following formation of gaps in the canopy. 相似文献
8.
When plants of Zea mays L. cv. LG11 that have been grown at optimal temperatures are transferred to chilling temperatures (0–12°C) photoinhibition of photosynthetic CO 2 assimilation can occur. This study examines how growth at sub-optimal temperatures alters both photosynthetic capacity and resistance to chilling-dependent photoinhibition. Plants of Z. mays cv. LG11 were grown in controlled environments at 14, 17, 20 and 25°C. As a measure of the capacity for photosynthesis under light limiting conditions, the maximum quantum yields of CO 2 assimilation (φ a.c) and O 2 evolution (φ a.o) were determined for the laminae of the second leaves at photon fluxes of 50–150 μmol m -2s -1. To determine photosynthetic capacity at photon fluxes approaching light saturation, rates of CO 2 uptake (A 1500) and O 2 evolution (A 1500) were determined in a photon flux of 1500 μmol m -2s -1. In leaves developed at 14°C, φ and φ were 26 and 43%, respectively, of the values for leaves grown at 25°C. Leaves grown at 17°C showed intermediate reductions in φ and φ, whilst leaves developed at 20°C showed no significant differences from those grown at 25°C. Similar patterns of decrease were observed for A 1500 and A 1500.0 with decreasing growth temperature. Leaves developed at 25°C showed higher rates of CO 2 assimilation at all light levels and measurement temperatures in comparison to leaves developed at 17 and 14°C. A greater reduction in A 1500 relative to A 1500.0 with decreasing growth temperature was attributed to increased stomatal limitation. Exposure of leaves to 800–1000 μmol m -2 s -1 when plant temperature was depressed to ca 6.5°C produced a photoinhibition of photosynthetic CO 2 assimilation in all leaves. However, in leaves developed at 17°C the decrease in A 1500 following this chilling treatment was only 25% compared to 90% in leaves developed at 25°C. Recovery following chilling was completed earlier in leaves developed at 17°C. The results suggest that growth at sub-optimal temperatures induces increased tolerance to exposure to high light at chilling temperatures. This is offset by the large loss in photosynthetic capacity imposed by leaf development at sub-optimal temperatures. 相似文献
9.
Cotton plants ( Gossypium hirsutum L. var Deltapine 90) and radish plants ( Raphanus sativus L var Round Red) were grown under full sunlight using a factorial combination of atmospheric CO 2 concentrations (350 µmol mol -1 and 700 µmol mol -1) and humidities (35% and 90% RH at 32 °C during the day). Cotton plants showed large responses to increased humidity and to doubled CO 2. In cotton plants, the enhanced dry matter yield due to doubled CO 2 concentration was 1.6-fold greater at low humidity than at high humidity. Apart from the direct effect of elevated CO 2 level on photosynthesis, the greater effect of doubled CO 2 concentration on dry matter yield at low humidity was probably due to: (1) increased leaf water potential caused by reduction of transpiration resulting from the negative CO 2 response of stomata to increased CO 2 concentration the consequence being greater leaf area expansion; (2) reduction of CO 2 assimilation rate at low humidity and normal CO 2 concentration as a result of humidity response of stomata causing reduction of intercellular CO 2 concentration. In contrast, apart from the very early stage of development, radish plants do not respond to increased humidity but had a relatively large response to doubled CO 2 concentration. Furthermore, due to the determinate growth pattern as well as having a prominent storage root, the extra photoassimilate derived at doubled CO 2 level is allocated to the storage root.Abbreviatios DAE
day after emergence
- LAD
leaf areal density (leaf dry weight/leaf area)
- LAR
leaf area ratio (leaf area/plant dry weight)
- NAR
net assimilation rate
- c i
internal CO 2 concentration
- PPFD
photosynthetic photon flux density
- RGR
relative growth rate
- RLAGR
relative leaf area growth rate
- VPD
vapour pressure deficit 相似文献
10.
The response of the photosynthetic apparatus to low temperature periods differed among three hybrids of maize ( Zea mays L.) grown in a phytotron. Light-saturated photosynthetic rates, leaf chlorophyll content, and mesophyll cell photosynthetic unit density all declined with increasing duration of low temperature. No single metabolic or physiological parameter appeared to control the response of the three hybrids to low temperature stress. Among all temperature treatments, net photosynthetic rate on a leaf area basis was more closely correlated with leaf chlorophyll content than with any other measured parameter. Final shoot dry weight was most highly correlated with stomatal conductance to CO 2. 相似文献
11.
Intact air-grown (photosynthetic photon flux density, 400 microeinsteins per square meter per second) clover plants ( Trifolium subterraneum L.) were transfered to high CO 2 (4000 microliters CO 2 per liter; photosynthetic photon flux density, 400 microeinsteins per square meter per second) or to high light (340 microliters CO 2 per liter; photosynthetic photon flux density, 800 microeinsteins per square meter per second) to similarly stimulate photosynthetic net CO 2 uptake. The daily increment of net CO 2 uptake declined transiently in high CO 2, but not in high light, below the values in air/standard light. After about 3 days in high CO 2, the daily increment of net CO 2 uptake increased but did not reach the high light values. Nightly CO 2 release increased immediately in high light, whereas there was a 3-day lag phase in high CO 2. During this time, starch accumulated to a high level, and leaf deterioration was observed only in high CO 2. After 12 days, starch was two- to threefold higher in high CO 2 than in high light, whereas sucrose was similar. Leaf carbohydrates were determined during the first and fourth day in high CO 2. Starch increased rapidly throughout the day. Early in the day, sucrose was low and similar in high CO 2 and ambient air (same light). Later, sucrose increased considerably in high CO 2. The findings that (a) much more photosynthetic carbon was partitioned into the leaf starch pool in high CO 2 than in high light, although net CO 2 uptake was similar, and that (b) rapid starch formation occurred in high CO 2 even when leaf sucrose was only slightly elevated suggest that low sink capacity was not the main constraint in high CO 2. It is proposed that carbon partitioning between starch (chloroplast) and sucrose (cytosol) was perturbed by high CO 2 because of the lack of photorespiration. Total phosphate pools were determined in leaves. Concentrations based on fresh weight of orthophosphate, soluble esterified phosphate, and total phosphate markedly declined during 13 days of exposure of the plants to high CO 2 but changed little in high light/ambient air. During this time, the ratio of orthophosphate to soluble esterified phosphate decreased considerably in high CO 2 and increased slightly in high light/ambient air. It appears that phosphate uptake and growth were similarly stimulated by high light, whereas the coordination was weak in high CO 2. 相似文献
12.
We hypothesized that decreased stomatal conductance ( g s) at elevated CO 2 might decrease transpiration ( E), increase leaf water potential (Ψ W), and thereby protect net photosynthesis rate ( P N) from heat damage in maize ( Zea mays L) seedlings. To separate long-term effects of elevated CO 2, plants grew at either ambient CO 2 or elevated CO 2. During high-temperature treatment (HT) at 45°C for 15 min, leaves were exposed either to ambient CO 2 (380 μmol mol ?1) or to elevated CO 2 (560 μmol mol ?1). HT reduced P N by 25 to 38% across four CO 2 combinations. However, the g s and E did not differ among all CO 2 treatments during HT. After returning the leaf temperature to 35°C within 30 min, g s and E were the same or higher than the initial values. Leaf water potential (Ψ W) was slightly lower at ambient CO 2, but not at elevated CO 2. This study highlighted that elevated CO 2 failed in protecting P N from 45°C via decreasing g s and Ψ W. 相似文献
13.
Gas-exchange measurements were performed to analyze the leaf conductances and assimilation rates of potato ( Solanum tuberosum L. cv. Desireé) plants expressing an antisense construct against chloroplastic fructose-1,6-bisphosphatase (FBPase, EC 3.1.3.11)
in response to increasing photon flux densities, different relative air humidities and elevated CO 2 concentrations. Assimilation rates (A) and transpiration rates (E) were observed during a stepwise increase of photon flux
density. These experiments were carried out under atmospheric conditions and in air containing 500 μmol mol −1 CO 2. In both gas atmospheres, two levels of relative air humidity (60–70% and 70–80%) were applied in different sets of measurements.
Intercellular CO 2 concentration, leaf conductance, air-to-leaf vapour pressure deficit, and instantaneous water-use efficiency (A/E) were determined.
As expected, assimilation rates of the FBPase antisense plants were significantly reduced as compared to the wild type. Saturation
of assimilation rates in transgenic plants occurred at a photon flux density of 200 μmol m −2 s −1, whereas saturation in wild type plants was observed at 600 μmol m −2 s −1. Elevated ambient CO 2 levels did not effect assimilation rates of transgenic plants. At 70–80% relative humidity and atmospheric CO 2 concentration the FBPase antisense plants had significantly higher leaf conductances than wild-type plants while no difference
emerged at 60–70%. These differences in leaf conductance vanished at elevated levels of ambient CO 2. Stomatal response to different relative air humidities was not affected by mesophyll photosynthetic activity. It is suggested
that the regulation of stomatal opening upon changes in photon flux density is merely mediated by a signal transmitted from
mesophyll cells, whereas the intercellular CO 2 concentration plays a minor role in this kind of stomatal response. The results are discussed with respect to stomatal control
by environmental parameters and mesophyll photosynthesis.
Received: 24 September 1998 / Accepted: 9 February 1999 相似文献
14.
Live-oak plants ( Quercus virginiana Mill.) were subjected to various levels of CO 2, water stress or photosynthetic photon flux density to test the hypothesis that isoprene biosynthesis occurred only under conditions of restricted CO 2 availability. Isoprene emission increases as the ambient CO 2 concentration decreased, independent of the amount of time that plants had photosynthesized at ambient CO 2 levels. When plants were water-stressed over a 4-d period photosynthesis and leaf conductance decreased 98 and 94%, respectively, while isoprene emissions remained constant. Significant isoprene emissions occurred when plants were saturated with CO 2, i.e., below the light compensation level for net photosynthesis (100 mol m -2 s -1). Isoprene emission rates increased with photosynthetic photon flux density and at 25 and 50 mol m -2 s -1 were 7 and 18 times greater than emissions in the dark. These data indicate that isoprene is a normal plant metabolite and not — as has been suggested — formed exclusively in response to restricted CO 2 or various stresses.Abbreviation PPFD
photosynthetic photon flux density 相似文献
15.
Summary
Gossypium hirsutum L. var. Delta Pine 61 was cultivated in controlled-environment chambers at 1000–1100 mol photosynthetically active photons m -2 s -1 (medium photon flux density) and at 1800–2000 mol photons m -2 s -1 (high photon flux density), respectively. Air temperatures ranged from 20° to 34°C during 12-h light periods, whereas during dark periods temperature was 25° C in all experiments. As the leaf temperature decreased from about 33° to 27° C, marked reductions in dry matter production, leaf chlorophyll content and photosynthetic capacity occurred in plants growing under high light conditions, to values far below those in plants growing at 27° C and medium photon flux densities. The results show that slightly suboptimum temperatures, well above the so-called chilling range (0–12° C), greatly reduce dry matter production in cotton when combined with high photon flux densities equivalent to full sunlight.Abbreviations DW
dry weight
-
F
v
variable fluorescence yield
-
F
M
maximum fluorescence yield
- PFD
photon flux density (400–700 nm) 相似文献
16.
A synthetic model of photosynthesis-transpiration was established based on a comprehensive consideration of models of CO 2 and H 2O fluxes controlled by stomata of plant leaves.The synthetic model was developed by introducing the internal conductance to CO 2 assimilation, gic, and the general equation of stomatal conductance model to H 2O diffusion, gsw = g0+a 1Amf( Ds)/( Cs-Γ), into models of CO 2 and H 2O diffusion through the plant leaves stomata. In the above expression, g0 and a 1 are coefficients, Cs ambient CO 2 concentration at leaf surface, Γ CO 2 compensation point, and f( Ds) the general function describing the response of stomatal conductance to humidity. Using the data observed in maize ( Zea mays L.) and soybean ( Glycine max Merr.) plants grown in the field, the parameters in the model were identified, and the applicability of the model was examined. The verification indicated that the developed model could be used to estimate net assimilation rate, transpiration rate, and water use efficiency with a high enough level of precision. The examination also showed that when f( Ds) = hs or f( Ds) = (1+ Ds/ D0) −1 was employed, the estimation precision of the synthetic model was highest. In the study, the parameter gic was estimated by means of a linear function of QP because it was shown to be mostly correlated with photosynthetic photon flux, QP, among various environmental factors. 相似文献
17.
Leaves on a bush of Hyptis emoryi Torr. varied in length from less than 1 cm when development occurred in full sunlight ( e.g. 40 Mjoules m −2) to over 7 cm when the total daily solar irradiance was less than 3 Mjoules m −2. The 1-cm sun leaves were 3-fold higher than the 7-cm shade leaves in chlorophyll per unit area, mesophyll thickness, and the internal to external leaf area ratio (A mes/A). The higher A mes/A caused a 1.2-cm leaf to have a 3-fold lower CO 2 liquid phase resistance than did a 7.1-cm leaf. Large thin shade leaves captured photosynthetically active radiation effectively (less than 7% passed through), but were not adapted to full sunlight. Specifically, when a 6.9-cm leaf was placed at 910 w m −2 for 30 min, its temperature exceeded that of the air by nearly 8 C. For the common daytime air temperatures above 30 C for this desert shrub, large shade leaves would have temperatures far in excess of that optimum for photosynthesis for H. emoryi, 29 to 32 C. 相似文献
18.
The saturating photon flux density (400 to 700 nanometers) for induction of flowering of the long day plant Anagallis arvensis L. was 1,900 micromoles per square meter per second (6,000 foot-candles) when an 8-hour daylength was extended to 24 hours by a single period of supplementary irradiation. The saturating photon flux density for photosynthetic CO 2 uptake during the same single supplementary light period was lower, at about 1,000 to 650 micromoles per square meter per second (3,000 to 2,000 foot-candles). The per cent flowering and mean number of floral buds per plant were significantly reduced when the light extension treatment was given in CO2-free air, and glucose (10 kilograms per cubic meter in water) relieved this effect. Glucose solution also significantly increased flowering of plants given supplementary light treatment in atmospheric air under a photon flux density of 80 micromoles per square meter per second. Increasing the CO2 concentration to 1.27 grams per cubic meter of CO2 in air during the supplementary light period did not increase flowering. It is concluded that high photon flux densities promote flowering of Anagallis through both increased photosynthesis and the photomorphogenic action of high irradiance. 相似文献
19.
We used a pale-green maize ( Zea mays L.) mutant that fails to accumulate ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) to test the working hypothesis that the regulatory phosphorylation of C 4 phospho enolpyruvate carboxylase (PEPC) by its Ca 2+-insensitive protein-serine/threonine kinase (PEPC kinase) in the C 4 mesophyll cytosol depends on cross-talk with a functional Calvin cycle in the bundle sheath. Wild-type (W22) and bundle sheath defective2-mutable1 ( bsd2-m1) seeds were grown in a controlled environment chamber at 100 to 130 μmol m −2 s −1 photosynthetic photon flux density, and leaf tissue was harvested 11 d after sowing, following exposure to various light intensities. Immunoblot analysis showed no major difference in the amount of polypeptide present for several mesophyll- and bundle-sheath-specific photosynthetic enzymes apart from Rubisco, which was either completely absent or very much reduced in the mutant. Similarly, leaf net CO 2-exchange analysis and in vitro radiometric Rubisco assays showed that no appreciable carbon fixation was occurring in the mutant. In contrast, the sensitivity of PEPC to malate inhibition in bsd2-m1 leaves decreased significantly with an increase in light intensity, and there was a concomitant increase in PEPC kinase activity, similar to that seen in wild-type leaf tissue. Thus, although bsd2-m1 mutant plants lack an operative Calvin cycle, light activation of PEPC kinase and its target enzyme are not grossly perturbed. 相似文献
20.
Gains of the feedback loops involving intercellular CO 2 concentration on one hand, and CO 2 assimilation and stomata on the other (= assimilation loop with gain [G A] and conductance loop with gain [G g]) were determined in detached leaves of Amaranthus powelli S. Wats., Avena sativa L., Gossypium hirsutum L., Xanthium strumarium L., and Zea mays in the absence and presence of 10 −5 m (±) abscisic acid (ABA) in the transpiration stream. Determinations were made for an ambient CO 2 concentration of 300 microliters per liter. In the absence of ABA, stomata were insensitive to CO 2 (G g between 0.00 and −0.02) in A. sativa, G. hirsutum, and X. strumarium, sensitive in A powelli (G g = −0.46), and very sensitive in Z. mays (G g = −3.6). Addition of ABA increased the absolute values of the gain of the conductance loop in A. powelli (G g = −2.0), G. hirsutum (G g = −0.31), and X. strumarium (G g = −1.14). Stomata closed completely in A. sativa. In Z. mays, G g decreased after application of ABA to a value of −0.86, but stomatal sensitivity to CO 2 increased for intercellular CO 2 concentrations < 100 microliters per liter. The gain of the assimilation loop increased after application of ABA in all cases, from values between 0.0 ( A. powelli) and −0.21 ( Z. mays) in the absence of ABA to values between −0.19 ( A. powelli) and −0.43 ( Z. mays) in the presence of ABA. In none of the species examined did ABA affect the photosynthetic capacity of the leaves. 相似文献
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