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1.
The effects of phosphate deficiency on the composition and photosyntheticCO 2 assimilation rates of fully expanded leaves of sunflower,maize and wheat plants are described. The regulation of photosynthesisby stomatal and mesophyll characteristics of leaves of differentphosphate status is analysed and related to structure. Phosphatedeficient leaves had small concentrations of inorganic phosphate,Pi, in the tissue water. Rate of photosynthesis in leaves andstomatal conductance were smaller in plants grown with inadequatephosphate when measured under any given light intensity or CO 2partial pressure. Despite the decrease in stomatal conductance(and without evidence of patchy stomatal closure), the relativestomatal limitation of photosynthesis was similar in the plantsgrown with deficient or abundant phosphate. However, the mesophyllcapacity for photosynthesis was greatly limited by phosphatedeficiency. Leaves deficient in phosphate had larger numbersof small size cells per unit leaf area than leaves with adequatephosphate. The total soluble protein content of leaves decreasedwith phosphate deficiency in all three species; however, theleaf chlorophyll content was decreased only in sunflower andmaize and not in wheat. These results suggest that stomatalconductance did not restrict the CO 2 diffusion rate, ratherthe metabolism of the mesophyll was the limiting factor. Thisis shown by poor carboxylation efficiency and decreased apparentquantum yield for CO 2 assimilation, both of which contributedto the increase in relative mesophyll limitation of photosynthesisin phosphate deficient plants. Key words: Apparent quantum yield, carboxylation efficiency, phosphate nutrition, photosynthesis, stomatal and mesophyll limitation 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.
The resistance to diffusion of CO 2 from the intercellular airspaces within the leaf through the mesophyll to the sites of carboxylation during photosynthesis was measured using three different techniques. The three techniques include a method based on discrimination against the heavy stable isotope of carbon, 13C, and two modeling methods. The methods rely upon different assumptions, but the estimates of mesophyll conductance were similar with all three methods. The mesophyll conductance of leaves from a number of species was about 1.4 times the stomatal conductance for CO 2 diffusion determined in unstressed plants at high light. The relatively low CO 2 partial pressure inside chloroplasts of plants with a low mesophyll conductance did not lead to enhanced O 2 sensitivity of photosynthesis because the low conductance caused a significant drop in the chloroplast CO 2 partial pressure upon switching to low O 2. We found no correlation between mesophyll conductance and the ratio of internal leaf area to leaf surface area and only a weak correlation between mesophyll conductance and the proportion of leaf volume occupied by air. Mesophyll conductance was independent of CO 2 and O 2 partial pressure during the measurement, indicating that a true physical parameter, independent of biochemical effects, was being measured. No evidence for CO 2-accumulating mechanisms was found. Some plants, notably Citrus aurantium and Simmondsia chinensis, had very low conductances that limit the rate of photosynthesis these plants can attain at atmospheric CO 2 level. 相似文献
4.
Images of chlorophyll fluorescence were used to demonstrate patchy stomatal closure at low humidities in leaves of well-watered Xanthium strumarium plants. The pattern and extent of patchy stomatal closure were shown to be different for the two surfaces of amphistomatous leaves by taking images of leaves with CO 2 available to only one leaf was exposed to low humidity, patchiness was more extensive on that surface. Gas-exchange experiments were also conducted to determine the apparent photosynthetic capacity of the mesophyll (photosynthesis rate at constant ci when it was supplied with CO 2 through both surfaces or through each surface alone. These experiments showed declines in the apparent photosynthetic capacity of the mesophyll at low humidities that were consistent with patchy stomatal closure on one or both surfaces. The results suggest that patchy stomatal closure can be a factor in the steady-state reponses of stomata to humidity. In amphistomatous leaves this is further complicated by the fact that patches on one epidermis may not coincide with those of the other surface. 相似文献
5.
Measurements of gas exchange characteristics were made on intact, attached leaves of hydroponically grown seedlings of Avicennia marina (Forstk.) Vierh. var australasica (Walp.) Moldenke as the NaCl concentration of the culture solution was varied by step changes of 50 millimolar NaCl every 2nd day from 50 to 500 to 50 millimolar NaCl. The CO 2 assimilation rate, stomatal conductance, intercellular CO 2 concentration, and evaporation rate decreased at salinities above 250 millimolar NaCl and recovered substantially upon return to the original salinity. The assimilation rate was measured as a function of the intercellular CO2 concentration [A(ci) curve]. The lower linear portion of this curve was insensitive to variation in salinity, whereas the upper nonlinear portion declined with increasing salinity, indicating a reduction in the capacity for CO2 assimilation which recovered upon return to the original salinity. Stomatal conductance changed such that the intercellular CO2 concentration measured under normal atmospheric conditions occurred in the transition between the lower, linear and upper nonlinear portions of the A(ci) curve. Thus, stomatal conductance and photosynthetic capacity together co-limited the assimilation rate. The changes in gas exchange characteristics were such that water loss was minimal relative to carbon gain. 相似文献
6.
Plants of Solidago virgaurea L. from exposed and shaded habitats differ with respect to the response of the photosynthetic apparatus to the level of irradiance during growth. An analysis was carried out on leaf characteristies which might be responsible for the differences established in the rates of Hght-saturated CO 2 uptake. The clones were grown in controlled environment chambers at high and low levels of irradiance. Light-saturated rates of photosynthesis and transpiration were measured at natural and lower ambient CO 2 concentrations. A low temperature dependence of light-saturated CO 2 uptake at natural CO 2 concentrations, and a strong response to changes in stomatal width, suggested that the rate of CO 2 transfer from ambient air towards reaetion sites in chloroplasts was mainly limiting the pholosynthetic rate. Resistances to transfer of CO 2 for different parts of the pathway were calculated. There was a weak but significant correlation between stomatal conductance and the product stomatal frequency ± pore length. Mesopbyll conductance and dry weight per unit area were highly correlated in leaves not damaged by high irradiance. This suggests that mesophyll conductance increases with increasing cross sectional area (per unit leaf area) of the pathways of CO 2 transfer in the mesophyll from cell surfaces to reaction sites. The higher light-saturated photosynthesis in clones from exposed habitats when grown at high irradiance than when grown at low irradiance was attributable mainly to a lower mesophyll resistance. In shade clones the effect upon CO 2 uptake of the increase in leaf thickness when grown at high irradiance was counteracted by the associated inactivation of the photosynthetic apparatus. The difference in CO 2 uptake present between clones from exposed and shaded habitats when preconditioned to high irradiance resulted from differences in both mesophyll and stomatal resistances. A few hybrid clones of an F 1-population from a cross between a clone from an exposed habitat and a clone from a shaded habitat reacted, on the whole, in the same way as the exposed habitat parent. When grown at high irradiance, the hybrid clones showed higher photosynthetic rates than either parent; this was largely attributable to the unusually low stomatal resistance of the hybrid leaves. 相似文献
7.
- Stomata modulate the exchange of water and CO2 between plant and atmosphere. Although stomatal density is known to affect CO2 diffusion into the leaf and thus photosynthetic rate, the effect of stomatal density and patterning on CO2 assimilation is not fully understood.
- We used wild types Col‐0 and C24 and stomatal mutants sdd1‐1 and tmm1 of Arabidopsis thaliana, differing in stomatal density and pattern, to study the effects of these variations on both stomatal and mesophyll conductance and CO2 assimilation rate. Anatomical parameters of stomata, leaf temperature and carbon isotope discrimination were also assessed.
- Our results indicate that increased stomatal density enhanced stomatal conductance in sdd1‐1 plants, with no effect on photosynthesis, due to both unchanged photosynthetic capacity and decreased mesophyll conductance. Clustering (abnormal patterning formed by clusters of two or more stomata) and a highly unequal distribution of stomata between the adaxial and abaxial leaf sides in tmm1 mutants also had no effect on photosynthesis.
- Except at very high stomatal densities, stomatal conductance and water loss were proportional to stomatal density. Stomatal formation in clusters reduced stomatal dynamics and their operational range as well as the efficiency of CO2 transport.
相似文献
8.
The purpose of this study was to investigate effects of N nutrition and water stress on stomatal behavior and CO 2 exchange rate in wheat ( Triticum aestivum L. cv Olaf). Wheat plants were grown hydroponically with high (100 milligrams per liter) and low (10 milligrams per liter) N. When plants were 38 days old, a 24-day water stress cycle was begun. A gradual increase in nutrient solution osmotic pressure from 0.03 to 1.95 mega Pascals was achieved by incremental additions of PEG-6,000. Plants in both N treatments adjusted osmotically, although leaf water potential was consistently lower and relative water content greater for low N plants in the first half of the stress cycle. Leaf conductance of high N plants appeared greater than that of low N plants at high water potentials, but showed greater sensitivity to reductions in water potential as indicated by earlier stomatal closure during the stress cycle. The apparent greater stomatal sensitivity of high N plants was associated with a curvilinear relationship between leaf conductance and leaf water potential; low N plants exhibited more of a threshold response. Trends in [CO 2] INT throughout the stress cycle indicated nonstomatal effects of water stress on CO 2 exchange rate were greater in high N plants. Although estimates of [CO 2] INT were generally lower in high N plants, they were relatively insensitive to leaf water potential-induced changes in leaf conductance. In contrast, [CO 2] INT of low N plants dropped concomitantly with leaf conductance at low leaf water potentials. Oxygen response of CO 2 exchange rate for both treatments was affected less by reductions in water potential than was CO 2 exchange rate at 2.5% O 2, suggesting that CO 2 assimilation capacity of the leaves was affected more by reductions in leaf water potential than were processes related to photorespiration. 相似文献
9.
Measurements of carbon dioxide exchange and transpiration were made, at various air temperatures, on wheat and barley using a field enclosure system. From these were derived the stomatal and mesophyll resistances to carbon dioxide transfer. Optimum temperatures for net CO 2 uptake were about 24°C for wheat and barley. Above these optima, as temperature increased so net CO 2 uptake rates decreased, because of increasing stomatal and mesophyll resistances; transpiration rates decreased in wheat but were constant in barley. In laboratory growth cabinets, wheat plants were subjected to different regimes of temperature and humidity. Optimum temperature for net CO 2 uptake of individual leaves was 25°C. At constant humidity, a decline in net uptake rates above 25°C was associated with large increases in mesophyll resistance. At a constant 25°C, as the vapour pressure deficit (v.p.d. was increased above 1 k Pa (10 mb) v.p.d. the net uptake declined, with an increase in mesophyll resistance and a small increase in stomatal resistance. When the v.p.d. exceeded 1 k Pa at a temperature of 30°C, conditions that are experienced by field plants, then there were large increases in both mesophyll and stomatal resistances and the net uptake rates declined. Photo-respiration, as measured by CO 2 uptake in oxygen-free air, was independent of temperature, but both dark respiration and CO 2 compensation concentration increased with temperature. 相似文献
10.
A dual-surface leaf chamber was used to investigate the responsesof net photosynthesis and leaf conductance to independent changesin the humidity environments of the upper and lower surfacesof leaves of sunflower and soybean. In sunflower decreasingthe humidity around the upper leaf surface while maintainingthat of the lower surface constant and high reduced both thephotosynthetic rate and the conductance of the lower surface.These reductions could not be attributed to changes in bulkleaf water potential since the transpiration rate of the wholeleaf remained constant. Similarly, the reductions were not relatedto localized water deficits in the lower epidermis or lowermesophyll since the transpiration rate of the lower surfacewas reduced. Possible mechanisms whereby the gas exchange characteristicsof the lower leaf surface of sunflower respond to the humidityenvironment of the upper surface are discussed. In contrastto sunflower, the photosynthetic rate of the lower surface ofsoybean was insensitive to the humidity environment of the uppersurface. In leaves of sunflower grown under a moderate temperature anda medium light level, simultaneous decreases of humidity atboth leaf surfaces reduced the photosynthetic rate of the wholeleaf without affecting the substomatal partial pressure of CO 2.In contrast, with leaves developed under a cool temperatureand a high light level, both the photosynthetic rate and thesubstomatal partial pressure of CO 2 were reduced. Evidently,the occurrence in sunflower of the response pattern suggestinga non-stomatal inhibition of photosynthesis by low humiditydepends upon the environment during growth. The possibilitythat this non-stomatal inhibition may be an artifact due toan error in the assumption of water vapour saturation withinthe leaf airspace is considered. Key words: Vapour pressure deficit, photosynthesis, conductance, non-stomatal inhibition, Helianthus annuus, Glycine max 相似文献
11.
The net rate of CO 2 uptake for leaves of Gossypium hirsutum L. was reduced when the plants were grown at low concentrations of NO 3-, PO 42-, or K +. The water vapor conductance was relatively constant for all nutrient levels, indicating little effect on stomatal response. Although leaves under nutrient stress tended to be lower in chlorophyll and thinner, the ratio of mesophyll surface area to leaf area did not change appreciably. Thus, the reduction in CO 2 uptake rate at low nutrient levels was due to a decrease in the CO 2 conductance expressed per unit mesophyll cell wall area (g cellCO2). The use of g cellCO2 and nutrient levels expressed per unit of mesophyll cell wall provides a new means of assessing nutrient effects on CO 2 uptake of leaves. 相似文献
12.
We investigated the photosynthetic capacity and plant growth of tobacco plants overexpressing ice plant ( Mesembryanthemum crystallinum L.) aquaporin McMIPB under (1) a well-watered growth condition, (2) a well-watered and temporal higher vapor pressure deficit (VPD) condition, and (3) a soil water deficit growth condition to investigate the effect of McMIPB on photosynthetic responses under moderate soil and atmospheric humidity and water deficit conditions. Transgenic plants showed a significantly higher photosynthesis rate (by 48 %), higher mesophyll conductance (by 52 %), and enhanced growth under the well-watered growth condition than those of control plants. Decreases in the photosynthesis rate and stomatal conductance from ambient to higher VPD were slightly higher in transgenic plants than those in control plants. When plants were grown under the soil water deficit condition, decreases in the photosynthesis rate and stomatal conductance were less significant in transgenic plants than those in control plants. McMIPB is likely to work as a CO 2 transporter, as well as control the regulation of stomata to water deficits. 相似文献
13.
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
14.
Conductance to gaseous transfer is normally considered to be greater from the abaxial than from the adaxial side of a leaf. Measurements of the conductance to water vapor of peanut leaves ( Arachis hypogaea L.) under well watered and stress conditions in a controlled environment, however, indicated a 2-fold higher conductance from the adaxial side of the leaf than from the abaxial. Studies of conductance as light level was varied showed an increase in conductance from either surface with increasing light level, but conductance was always greater from the adaxial surface at any given light level. In contrast, measurements of soybean ( Glycine max [L.] Merr.) and snapbean ( Phaseolus vulgaris L.) leaf conductance showed an approximate 2-fold greater conductance from the abaxial surface than from the adaxial. Approximately the same number of stomata were present on both peanut leaf surfaces and stomatal size was similar. Electron microscopic examination of peanut leaves did not reveal any major structural differences between stomata on the two surfaces that would account for the differences in conductance. Light microscope studies of leaf sections revealed an extensive network of bundle sheaths with achloraplastic bundle sheath extensions; the lower epidermis was lined with a single layer of large achloraplastic parenchyma cells. Measurements of net photosynthesis made on upper and lower leaf surfaces collectively and individually indicated that two-thirds of the peanut leaf's total net photosynthesis can be attributed to diffusion of CO 2 through the adaxial leaf surface. Possibly the high photosynthetic efficiency of peanut cultivars as compared with certain other C 3 species is associated with the greater conductance of CO 2 through their upper leaf surfaces. 相似文献
15.
Transport of CO 2 in leaves was investigated by combining a 2-D, microscale CO 2 transport model with photosynthesis kinetics in wheat ( Triticum aestivum L.) leaves. The biophysical microscale model for gas exchange featured an accurate geometric representation of the actual 2-D leaf tissue microstructure and accounted for diffusive mass exchange of CO 2. The resulting gas transport equations were coupled to the biochemical Farquhar-von Caemmerer-Berry model for photosynthesis. The combined model was evaluated using gas exchange and chlorophyll fluorescence measurements on wheat leaves. In general a good agreement between model predictions and measurements was obtained, but a discrepancy was observed for the mesophyll conductance at high CO 2 levels and low irradiance levels. This may indicate that some physiological processes related to photosynthesis are not incorporated in the model. The model provided detailed insight into the mechanisms of gas exchange and the effects of changes in ambient CO 2 concentration or photon flux density on stomatal and mesophyll conductance. It represents an important step forward to study CO 2 diffusion coupled to photosynthesis at the leaf tissue level, taking into account the leaf''s actual microstructure. 相似文献
16.
Leaf gas exchange parameters and the content of ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco) in the leaves of two 2‐year‐old aspen ( Populus tremuloides Michx.) clones (no. 216, ozone tolerant and no. 259, ozone sensitive) were determined to estimate the relative stomatal and mesophyll limitations to photosynthesis and to determine how these limitations were altered by exposure to elevated CO 2 and/or O 3. The plants were exposed either to ambient air (control), elevated CO 2 (560 p.p.m.) elevated O 3 (55 p.p.b.) or a mixture of elevated CO 2 and O 3 in a free air CO 2 enrichment (FACE) facility located near Rhinelander, Wisconsin, USA. Light‐saturated photosynthesis and stomatal conductance were measured in all leaves of the current terminal and of two lateral branches (one from the upper and one from the lower canopy) to detect possible age‐related variation in relative stomatal limitation (leaf age is described as a function of leaf plastochron index). Photosynthesis was increased by elevated CO 2 and decreased by O 3 at both control and elevated CO 2. The relative stomatal limitation to photosynthesis ( ls) was in both clones about 10% under control and elevated O 3. Exposure to elevated CO 2 + O 3 in both clones and to elevated CO 2 in clone 259, decreased ls even further – to about 5%. The corresponding changes in Rubisco content and the stability of Ci/ Ca ratio suggest that the changes in photosynthesis in response to elevated CO 2 and O 3 were primarily triggered by altered mesophyll processes in the two aspen clones of contrasting O 3 tolerance. The changes in stomatal conductance seem to be a secondary response, maintaining stable Ci under the given treatment, that indicates close coupling between stomatal and mesophyll processes. 相似文献
17.
We analysed the impact of elevated CO 2 on water relations, water use efficiency and photosynthetic gas exchange in barley ( Hordeum vulgare L.) under wet and drying soil conditions. Soil moisture was less depleted under elevated compared to ambient [CO 2]. Elevated CO 2 had no significant effect on the water relations of irrigated plants, except on whole plant hydraulic conductance, which was markedly decreased at elevated compared to ambient CO 2 concentrations. The values of relative water content, water potential and osmotic potential were higher under elevated CO 2 during the entire drought period. The better water status of water-limited plants grown at elevated CO 2 was the result of stomatal control rather than of osmotic adjustment. Despite the low stomatal conductance produced by elevated CO 2, net photosynthesis was higher under elevated than ambient CO 2 concentrations. With water shortage, photosynthesis was maintained for longer at higher rates under elevated CO 2. The reduction of stomatal conductance and therefore transpiration, and the enhancement of carbon assimilation by elevated CO 2, increased instantaneous and whole plant water use efficiency in both irrigated and droughted plants. Thus, the metabolism of barley plants grown under elevated CO 2 and moderate or mild water deficit conditions is benefited by increased photosynthesis and lower transpiration. The reduction in plant water use results in a marked increase in soil water content which delays the onset and severity of water deficit. 相似文献
18.
The regulation of plant hydraulic conductance and gas conductance involves a number of different morphological, physiological and molecular mechanisms working in harmony. At the molecular level, aquaporins play a key role in the transport of water, as well as CO 2, through cell membranes. Yet, their tissue-related function, which controls whole-plant gas exchange and water relations, is less understood. In this study, we examined the tissue-specific effects of the stress-induced tobacco Aquaporin1 ( NtAQP1), which functions as both a water and CO 2 channel, on whole-plant behavior. In tobacco and tomato plants, constitutive overexpression of NtAQP1 increased net photosynthesis ( A N), mesophyll CO 2 conductance ( g m) and stomatal conductance ( g s) and, under stress, increased root hydraulic conductivity ( L pr) as well. Our results revealed that NtAQP1 that is specifically expressed in the mesophyll tissue plays an important role in increasing both A N and g m. Moreover, targeting NtAQP1 expression to the cells of the vascular envelope significantly improved the plants’ stress response. Surprisingly, NtAQP1 expression in the guard cells did not have a significant effect under any of the tested conditions. The tissue-specific involvement of NtAQP1 in hydraulic and gas conductance via the interaction between the vasculature and the stomata is discussed. 相似文献
19.
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
20.
Environmental factors that induce spatial heterogeneity of stomatal conductance, g
s, called stomatal patchiness, also reduce the photochemical capacity of CO 2 fixation, yet current methods cannot distinguish between the relative effect of stomatal patchiness and biochemical limitations
on photosynthetic capacity. We evaluate effects of stomatal patchiness and the biochemical capacity of CO 2 fixation on the sensitivity of net photosynthetic rate ( P
N) to stomatal conductance ( g
s), θ (θ = δ P
N/ g
s). A qualitative model shows that stomatal patchiness increases the sensitivity θ while reduced biochemical capacity of CO 2 fixation lowers θ. We used this feature to distinguish between stomatal patchiness and mesophyll impairments in the photochemistry
of CO 2 fixation. We compared gas exchange of sunflower ( Helianthus annuus L.) plants grown in a growth chamber and fed abscisic acid, ABA (10 −5 M), for 10 d with control plants (-ABA). P
N and g
s oscillated more frequently in ABA-treated than in control plants when the leaves were placed into the leaf chamber and exposed
to a dry atmosphere. When compared with the initial CO 2 response measured at the beginning of the treatment (day zero), both ABA and control leaves showed reduced P
N at particular sub-stomatal CO 2 concentration ( c
i) during the oscillations. A lower reduction of P
N at particular g
s indicated overestimation of c
i due to stomatal patchiness and/or omitted cuticular conductance, g
c. The initial period of damp oscillation was characterised by inhibition of chloroplast processes while stomatal patchiness
prevailed at the steady state of gas exchange. The sensitivity θ remained at the original pre-treatment values at high g
s in both ABA and control plants. At low g
s, θ decreased in ABA-treated plants indicating an ABA-induced impairment of chloroplast processes. In control plants, g
c neglected in the calculation of g
s was the likely reason for apparent depression of photosynthesis at low g
s.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
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