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1.
The carbon-dioxide response of photosynthesis of leaves of Quercus suber, a sclerophyllous species of the European Mediterranean region, was studied as a function of time of day at the end of the summer dry season in the natural habitat. To examine the response experimentally, a standard time course for temperature and humidity, which resembled natural conditions, was imposed on the leaves, and the CO2 pressure external to the leaves on subsequent days was varied. The particular temperature and humidity conditions chosen were those which elicited a strong stomatal closure at midday and the simultaneous depression of net CO2 uptake. Midday depression of CO2 uptake is the result of i) a decrease in CO2-saturated photosynthetic capacity after light saturation is reached in the early morning, ii) a decrease in the initial slope of the CO2 response curve (carboxylation efficiency), and iii) a substantial increase in the CO2 compensation point caused by an increase in leaf temperature and a decrease in humidity. As a consequence of the changes in photosynthesis, the internal leaf CO2 pressure remained essentially constant despite stomatal closure. The effects on capacity, slope, and compensation point were reversed by lowering the temperature and increasing the humidity in the afternoon. Constant internal CO2 may aid in minimizing photoinhibition during stomatal closure at midday. The results are discussed in terms of possible temperature, humidity, and hormonal effects on photosynthesis.Abbreviations and symbols CE
carboxylation efficiency
- NP
net photosynthesis rate
- PAR
photosynthetically active radiation
- Pi
leaf internal CO2 partial pressure
- W
water vapor mole fraction difference between leaf and air
-
T
CO2 compensation pressure
Dedicated to Professor Dr. Hubert Ziegler on the occasion of his 60th birthday 相似文献
2.
Midday depression of net photosynthesis and transpiration in the Mediterranean sclerophylls Arbutus unedo L. and Quercus suber L. occurs with a depression of mesophyll photosynthetic activity as indicated by calculated carboxylation efficiency (CE) and constant diurnal calculated leaf intercellular partial pressure of CO2 (Ci). This work examines the hypothesis that this midday depression can be explained by the distribution of patches of either wide-open or closed stomata on the leaf surface, independent of a coupling mechanism between stomata and mesophyll that results in a midday depression of photosynthetic activity of the mesophyll. Pressure infiltration of four liquids differing in their surface tension was used as a method to show the occurrence of stomatal patchiness and to determine the status of stomatal aperture within the patches. Liquids were selected such that the threshold leaf conductance necessary for infiltration through the stomatal pores covered the expected diurnal range of calculated leaf conductance (g) for these species. Infiltration experiments were carried out with leaves of potted plants under simulated Mediterranean summer conditions in a growth chamber. For all four liquids, leaves of both species were found to be fully infiltratable in the morning and in the late afternoon while during the periods leading up to and away from midday the leaves showed a pronounced patchy distribution of infiltratable and non-infiltratable areas. Similar linear relationships between the amount of liquid infiltrated and g (measured by porometry prior to detachment and infiltration) for all liquids clearly revealed the existence of pneumatically isolated patches containing only wide-open or closed stomata. The good correspondence between the midday depression of CE, calculated under the assumption of no stomatal patchiness, and the diurnal changes in non-infiltratable leaf area strongly indicates that the apparent reduction in mesophyll activity results from assuming no stomatal patchiness. It is suggested that simultaneous responses of stomata and mesophyll activity reported for other species may also be attributed to the occurrence of stomatal patchiness. In Quercus coccifera L., where the lack of constant diurnal calculated Ci and major depression of measured CE at noontime indicates different stomatal behavior, non-linear and dissimilar relationships between g and the infiltratable quantities of the four liquids were found. This indicates a wide distribution of stomatal aperture on the leaf surface rather than only wide-open or closed stomata.Dedicated to Professor Otto L. Lange on the occasion of his 65th birthday 相似文献
3.
Gas exchange and contents of photosynthetic intermediates of leaves of Arbutus unedo L. were determined with the aim of recognizing the mechanisms of inhibition that were responsible for the midday depression of photosynthesis following exposure to dry air, and the decline in photosynthetic capacity following application of abscisic acid (ABA). Rapidly killed (<0.1 s) leaf samples were taken when gas analysis showed reduced CO2 assimilation. Determination of the contents of 3-phosphoglyceric acid (PGA), ribulose 1,5-bisphosphate (RuBP), triose phosphates, fructose 1,6-bisphosphate and hexose phosphates in the samples showed that significant variation occurred only in the level of PGA. As a result, the ratio PGA/RuBP decreased with increasing inhibition of photosynthesis, particularly when application of ABA had been the cause. A comparison of metabolite patterns did not bring out qualitative differences that would have indicated that effects of ABA and of dry air had been caused by separate mechanisms. Depression of photosynthesis occurred in the presence of sufficient RuBP which indicated that the carboxylation reaction of the carbon-reduction-cycle was inhibited after application of ABA or exposure to dry air.Abbreviations and symbols ABA
abscisic acid
-
C
a
partial pressure of CO2 in the ambient air
-
C
i
partial pressure of CO2 in the intercellular spaces
- I
quantum flux
- PGA
3-phosphoglyceric acid
- RuBP
ribulose 1,5-bisphosphate
-
I
L
leaf temperature
- w
water-vapor pressure difference between leaf and air 相似文献
4.
Summary Seasonal changes in the photosynthetic characteristics of intact involucral leaves of Anemone raddeana were investigated under laboratory conditions. Net photosynthesis and constant water vapor pressure deficit showed almost the same seasonal trend. They increased rapidly from mid-April immediately after unfolding of the leaves and reached the maximum in late-April, before the maximum expansion of the leaves. They retained the maximum values until early-May and then decreased toward late-May with a progress of leaf senescence. The calculated values of intercellular CO2 concentration and relative stomatal limitation of photosynthesis showed no significant change throughout the season. The carboxylation efficiency as assessed by the initial slope of Ci-photosynthesis curve and the net photosynthesis under a high Ci regime varied seasonally in parallel with the change of the light-saturated photosynthesis. The results indicate that the seasonal changes in light-saturated net photosynthesis are not due to a change of stomatal conductance, but to a change in the photosynthetic capacity of mesophyll. Nevertheless, leaf conductance changed concomitantly with photosynthetic capacity, indicating that the seasonal change in stomatal conductance is modulated by the mesophyll photosynthetic capacity such that the intercellular CO2 concentrations is maintained constant. The shape of light-photosynthesis curve was similar to that of sun-leaf type. The quantum yield also changed simultaneously with the photosynthetic capacity throughout the season.Contribution No. 2965 from the Institute of Low Temperature Science 相似文献
5.
Photosynthesis was studied in relation to the carbohydrate status in intact leaves of the C4 plant Amaranthus edulis. The rate of leaf net CO2 assimilation, stomatal conductance and intercellular partial pressure of CO2 remained constant or showed little decline towards the end of an 8-h period of illumination in ambient air (340 bar CO2, 21% O2). When sucrose export from the leaf was inhibited by applying a 4-h cold-block treatment (1°C) to the petiole, the rate of photosynthesis rapidly decreased with time. After the removal of the cold block from the petiole, further reduction in photosynthetic rate occurred, and there was no recovery in the subsequent light period. Although stomatal conductance declined with time, intercellular CO2 partial pressure remained relatively constant, indicating that the inhibition of photosynthesis was not primarily caused by changes in stomatal aperture. Analysis of the leaf carbohydrate status showed a five- to sixfold increase in the soluble sugar fraction (mainly sucrose) in comparison with the untreated controls, whereas the starch content was the same. Leaf osmotic potential increased significantly with the accumulation of soluble sugars upon petiole chilling, and leaf water potential became slightly more negative. After 14 h recovery in the dark, photosynthesis returned to its initial maximum value within 1 h of illumination, and this was associated with a decline in leaf carbohydrate levels overnight. These data show that, in Amaranthus edulis, depression in photosynthesis when translocation is impaired is closely related to the accumulation of soluble sugars (sucrose) in source leaves, indicating feedback control of C4 photosynthesis. Possible mechanisms by which sucrose accumulation in the leaf may affect the rate of photosynthesis are discussed with regard to the leaf anatomy of C4 plants.Abbreviations and symbols A
net CO2 assimilation rate
- Ci
intercellular CO2 partial pressure
- PEP
phosphoenolpyruvate
- RuBP
ribulose-1,5-bisphosphate
-
water potential
-
osmotic pressure 相似文献
6.
Summary Seasonal changes in photosynthetic capacity, and photosynthetic responses to intercellular CO2 concentration and irradiance were investigated under laboratory conditions on intact leaves of Pachysandra terminalis. Photosynthetic capacity and stomatal conductance under saturating light intensity and constant water vapor pressure deficit showed almost the same seasonal trend. They increased from early June just after the expansion of leaves, reached the maximum in late-Septemer, and then decreased to winter. In over-wintering leaves they recovered and increased immediately after snow-melting, reached a first maximum in late April, and then decreased to early July in response to the reduction of light intensity on the forest floor. There-after, they increased from mid August, reached a second maximum in late September, and then decreased to winter. The parallel changes of photosynthesis and stomatal conductane indicate a more or less constant intercellular CO2 concentration throughout the year. The calculated values of relative stomatal limitation of photosynthesis were nearly constant throughout the year, irrespective of leaf age. The results indicate that the seasonal changes in light-saturated photosynthetic capacity are not due to a change of stomatal conductance, but to a change in the photosynthetic capacity of mesophyll. Indeed, carboxylation efficiency assessed by the inital slope of the Ci-photosynthesis curve changed in proportion to seasonal changes of the photosynthetic capacity in both current-year and over-wintered leaves. High photosynthetic capacity in current-year leaves as compared with one-year-old leaves was also due to the high photosynthetic capacity of mesophyll. Nevertheless, stomatal conductance changed in proportion to photosynthetic capacity, indicating that stomatal conductance is regulated by the mesophyll photosynthetic capacity such that the intercellular CO2 concentrations are maintained constant. The quantum yield also changed seasonally parallel with that in the photosynthetic capacity.Contribution No. 2893 from the Institute of Low Temperature Science 相似文献
7.
Transpiration-induced changes in the photosynthetic capacity of leaves 总被引:18,自引:0,他引:18
Thomas D. Sharkey 《Planta》1984,160(2):143-150
High transpiration rates were found to affect the photosynthetic capacity of Xanthium strumarium L. leaves in a manner analagous to that of low soil water potential. The effect was also looked for and found in Gossypium hirsutum L., Agathis robusta (C. Moore ex Muell.) Bailey, Eucalyptus microcarpa Maiden, Larrea divaricata Cav., the wilty flacca tomato mutant (Lycopersicon esculentum (L.) Mill.) and Scrophularia desertorum (Munz) Shaw. Two methods were used to distinguish between effects on stomatal conductance, which can lower assimilation by reducing CO2 availability, and effects on the photosynthetic capacity of the mesophyll. First, the response of assimilation to intercellular CO2 pressure (C
i) was compared under conditions of high and low transpiration. Second, in addition to estimating C
i using the usual Ohm's law analogy, C
i was measured directly using the closed-loop technique of T.D. Sharkey, K. Imai, G.D. Farquhar and I.R. Cowan (1982, Plant Physiol, 60, 657–659). Transpiration stress responses of Xanthium strumarium were compared with soil drought effects. Both stresses reduced photosynthesis at high C
i but not at low C
i; transpiration stress increased the quantum requirement of photosynthesis. Transpiration stress could be induced in small sections of leaves. Total transpiration from the plant did not influence the photosynthetic capacity of a leaf kept under constant conditions, indicating that water deficits develop over small areas within the leaf. The effect of high transpiration on photosynthesis was reversed approximately half-way by returning the plants to low-transpiration conditions. This reversal occurred as fast as measurements could be made (5 min), but little further recovery was observed in subsequent hours.Abbreviations and symbols
A
photosynthetic CO2 assimilation rate
-
C
a
ambient CO2 partial pressure
-
C
i
partial pressure of CO2 inside the leaf
- VPD
leaf-to-air water-vapor pressure difference
This research was begun while the author was a Postdoctoral Research Fellow at the Australian National University, Canberra 相似文献
8.
Analysis of Stomatal and Nonstomatal Components in the Environmental Control of CO(2) Exchange in Leaves of Welwitschia mirabilis 总被引:5,自引:3,他引:2
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In well-watered plants of Welwitschia mirabilis, grown in the glass-house under high irradiance conditions, net CO2 assimilation was almost exclusively observed during the daytime. The plants exhibited a very low potential for Crassulacean acid metabolism, which usually resulted in reduced rates of net CO2 loss for several hours during the night. In leaves exposed to the diurnal changes in temperature and humidity typical of the natural habitats, CO2 assimilation rates in the light were markedly depressed under conditions resembling those occurring during midday, when leaf temperatures and the leaf-air vapor pressure differences were high (36°C and 50 millibars bar−1, respectively). Studies on the relationship between CO2 assimilation rate and intercellular CO2 partial pressure at various temperatures and humidities showed that this decrease in CO2 assimilation was largely due to stomatal closure. The increase in the limitation of photosynthesis by CO2 diffusion, which is associated with the strong decline in stomatal conductance in Welwitschia exposed to midday conditions, may significantly contribute to the higher 13C content of Welwitschia compared to the majority of C3 species. 相似文献
9.
Gas exchange and abscisic acid content of Digitalis lanata EHRH. have been examined at different levels of plant water stress. Net photosynthesis, transpiration and conductance of attached leaves declined rapidly at first, then more slowly following the withholding of irrigation. The intercellular partial pressure of CO2 decreased slightly. The concentration of 2-cis(S)ABA increased about eight-fold in the leaves of non-irrigated plants as compared with well-watered controls. A close linear correlation was found between the ABA content of the leaves and their conductance on a leaf area basis. In contrast, the plot of net assimilation versus ABA concentration was curvilinear, leading to an increased efficiency of water use during stress. After rewatering, photosynthesis reached control values earlier than transpiration, leaf conductance and ABA content. From these data it is concluded that transpiration through the stomata is directly controlled by the ABA content, whereas net photosynthesis is influenced additionally by other factors.Possible reasons for the responses of photosynthesis and water use efficiency to different stress and ABA levels are discussed.Abbreviations A
net CO2 assimilation
- ABA
abscisic acid
- Ci
intercellular CO2 concentration
- g
stomatal conductance
- T
transpiration
- WUE
water use efficiency 相似文献
10.
Barbara Demmig-Adams William W. Adams III Klaus Winter Angelika Meyer Ulrich Schreiber João S. Pereira Almuth Krüger Franz-Christian Czygan Otto L. Lange 《Planta》1989,177(3):377-387
During the midday depression of net CO2 exchange in the mediterranean sclerophyllous shrub Arbutus unedo, examined in the field in Portugal during August of 1987, several parameters indicative of photosynthetic competence were strongly and reversibly affected. These were the photochemical efficiency of photosystem (PS) II, measured as the ratio of variable to maximum chlorophyll fluorescence, as well as the photon yield and the capacity of photosynthetic O2 evolution at 10% CO2, of which the apparent photon yield of O2 evolution was most depressed. Furthermore, there was a strong and reversible increase in the content of the carotenoid zeaxanthin in the leaves that occurred at the expense of both violaxanthin and -carotene. Diurnal changes in fluorescence characteristics were interpreted to indicate three concurrent effects on the photochemical system. First, an increase in the rate of radiationless energy dissipation in the antenna chlorophyll, reflected by changes in 77K fluorescence of PSII and PSI as well as in chlorophyll a fluorescence at ambient temperature. Second, a state shift characterized by an increase in the proportion of energy distributed to PSI as reflected by changes in PSI fluorescence. Third, an effect lowering the photon yield of O2 evolution and PSII fluorescence at ambient temperature without affecting PSII fluorescence at 77K which would be expected from a decrease in the activity of the water splitting enzyme system, i.e. a donor side limitation.Abbreviations and symbols ci
concentration of CO2 within the leaf
- Fo
instantaneous fluorescence emission
- FM
maximum fluorescence emission
- Fv
variable fluorescence emission
- PFD
photon flux density (400–700 nm)
- PSI, II
photosystem I, II
- TL
leaf temperature 相似文献
11.
YONG‐JIANG ZHANG FREDERICK C. MEINZER JIN‐HUA QI GUILLERMO GOLDSTEIN KUN‐FANG CAO 《Plant, cell & environment》2013,36(1):149-158
Midday depressions in stomatal conductance (gs) and photosynthesis are common in plants. The aim of this study was to understand the hydraulic determinants of midday gs, the coordination between leaf and stem hydraulics and whether regulation of midday gs differed between deciduous and evergreen broadleaf tree species in a subtropical cloud forest of Southwest (SW) China. We investigated leaf and stem hydraulics, midday leaf and stem water potentials, as well as midday gs of co‐occurring deciduous and evergreen tree species. Midday gs was correlated positively with midday stem water potential across both groups of species, but not with midday leaf water potential. Species with higher stem hydraulic conductivity and greater daily reliance on stem hydraulic capacitance were able to maintain higher stem water potential and higher gs at midday. Deciduous species exhibited significantly higher stem hydraulic conductivity, greater reliance on stem capacitance, higher stem water potential and gs at midday than evergreen species. Our results suggest that midday gs is more associated with midday stem than with leaf water status, and that the functional significance of stomatal regulation in these broadleaf tree species is probably for preventing stem xylem dysfunction. 相似文献
12.
(±)-Abscisic acid (ABA) at 10-5 M was added to the transpiration stream of leaves of 16 species (C3 and C4, monocotyledons and dicotyledons). Stomatal responses followed one of three patterns: i) stomata that were wide and insensitive to CO2 initially, closed partially and became sensitive to CO2; ii) for stomata that were sensitive to CO2 before the application of ABA, the range of highest sensitivity to CO2 shifted from high to low intercellular partial pressures of CO2, for instance in leaves of Zea mays from 170–350 to 70–140 bar; iii) when stomata responded strongly to ABA, their conductance was reduced to a small fraction of the initial conductance, and sensitivity to CO2 was lost. The photosynthetic apparatus was affected by applications of ABA to various degrees, from no response at all (in agreement with several previous reports on the absence of effects of ABA on photosynthesis) through a temporary decrease of its activity to a lasting reduction. Saturation curves of photosynthesis with respect to the partial pressure of CO2 in the intercellular spaces indicated that application of ABA could produce three phenomena: i) a reduction of the initial slope of the saturation curve (which indicates a diminished carboxylation efficiency); ii) a reduction of the level of the CO2-saturated rate of assimilation (which indicates a reduction of the ribulose-1,5-bisphosphate regeneration capacity); and iii) an increase of the CO2 compensation point. Photosynthesis of isolated mesophyll cells was not affected by ABA treatments. Responses of the stomatal and photosynthetic apparatus were usually synchronous and often proportional to each other, with the result that the partial pressure of CO2 in the intercellular spaces frequently remained constant in spite of large changes in conductance and assimilation rate. Guard cells and the photosynthetic apparatus were able to recover from effects of ABA applications while the ABA supply continued. Recovery was usually partial, in the case of the photosynthetic apparatus occasionally complete. Abscisic acid did not cause stomatal closure or decreases in the rate of photosynthesis when it was applied during a phase of stomatal opening and induction of photosynthesis that followed a transition from darkness to light.Abbreviations and symbols
A
rate of CO2 assimilation
- ABA
(±)-abscisic acid
-
c
a
partial pressure of CO2 in the ambient air or in the gas supplied to the leaf chambers
-
c
i
partial pressure of CO2 in the intercellular spaces of a leaf
-
e
a
partial pressure of H2O in the air
-
g
conductance for water vapor
-
J
quantum flux
-
T
1
leaf temperature 相似文献
13.
A coupled model of photosynthesis-transpiration based on the stomatal behavior for maize (Zea mays L.) grown in the field 总被引:1,自引:0,他引:1
Yu Gui-Rui Kobayashi Tatsuaki Zhuang Jie Wang Qiu-Feng Qu Le-Qing 《Plant and Soil》2003,249(2):401-415
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 CO2 assimilation, and the general equation of stomatal conductance, g
sw, to H2O diffusion, into models of CO2 and H2O 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 CO2 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
14.
The effect of D-(+)-mannose, inorganic phosphate (Pi) and mannose-6-phosphate on net mesophyll CO2 assimilation rate (A) and stomatal conductance (gs) of wheat (Triticum aestivum L.) leaves was studied. The compounds were supplied through the transpiration stream of detached leaves from plants grown in sand in growth cabinets or glasshouses, with different concentrations of Pi (0.25, 1.0 and 4.0 mM) supplied during growth. In all cases, 10 mM D-(+)mannose caused 40–60% reduction of A within 30 min, though the time courses differed for flag leaves and the sixth leaf on the mainstem of glasshouse- and cabinet-grown plants. D-(+)Mannose had a similar effect on A in leaves having a fourfold range in total phosphate content. Effects of D-(+)mannose in reducing gs were always slower than on A. When the CO2 concentration in the leaf chamber was adjusted to maintain intercellular CO2 concentration (Ci) constant as A declined after mannose supply, gs still declined indicating that stomatal closure was not caused by changing Ci. Supplying mannose-6-phosphate at 10 and 1 mM and Pi at 5 and 10 mM concentrations caused rapid reductions in gs and also direct reductions in A. The observed effects of mannose and Pi on assimilation are consistent with the proposed regulatory role of cytoplasmic Pi in determining mesophyll carbon assimilation that has been derived previously using leaf discs, protoplasts and chloroplasts.Abbreviations and symbols A
net mesophyll CO2-assimilation rate
- Ca, Ci
external (assimilation-chamber) and intercellular CO2 concentration, respectively
- gs
stomatal conductance
- Man6P
mannose-6-phosphate
- Pi
orthophosphate 相似文献
15.
Hiroyuki Muraoka Yanhong Tang Ichiro Terashima Hiroshi Koizumi & Izumi Washitani 《Plant, cell & environment》2000,23(3):235-250
Diurnal changes in photosynthetic gas exchange and chlorophyll fluorescence were measured under full sunlight to reveal diffusional and non‐diffusional limitations to diurnal assimilation in leaves of Arisaema heterophyllum Blume plants grown either in a riparian forest understorey (shade leaves) or in an adjacent deforested open site (sun leaves). Midday depressions of assimilation rate (A) and leaf conductance of water vapour were remarkably deeper in shade leaves than in sun leaves. To evaluate the diffusional (i.e. stomatal and leaf internal) limitation to assimilation, we used an index [1–A/A350], in which A350 is A at a chloroplast CO2 concentration of 350 μ mol mol ? 1. A350 was estimated from the electron transport rate (JT), determined fluorometrically, and the specificity factor of Rubisco (S), determined by gas exchange techniques. In sun leaves under saturating light, the index obtained after the ‘peak’ of diurnal assimilation was 70% greater than that obtained before the ‘peak’, but in shade leaves, it was only 20% greater. The photochemical efficiency of photosystem II ( Δ F/Fm ′ ) and thus JT was considerably lower in shade leaves than in sun leaves, especially after the ‘peak’. In shade leaves but not in sun leaves, A at a photosynthetically active photon flux density (PPFD) > 500 μ mol m ? 2 s ? 1 depended positively on JT throughout the day. Electron flows used by the carboxylation and oxygenation (JO) of RuBP were estimated from A and JT. In sun leaves, the JO/JT ratio was significantly higher after the ‘peak’, but little difference was found in shade leaves. Photorespiratory CO2 efflux in the absence of atmospheric CO2 was about three times higher in sun leaves than in shade leaves. We attribute the midday depression of assimilation in sun leaves to the increased rate of photorespiration caused by stomatal closure, and that in shade leaves to severe photoinhibition. Thus, for sun leaves, increased capacities for photorespiration and non‐photochemical quenching are essential to avoid photoinhibitory damage and to tolerate high leaf temperatures and water stress under excess light. The increased Rubisco content in sun leaves, which has been recognized as raising photosynthetic assimilation capacity, also contributes to increase in the capacity for photorespiration. 相似文献
16.
The effect of leaf temperature on stomatal conductance and net CO2 uptake was studied on French bean (Phaseolus vulgaris L.) using either dehydrated attached leaves (25–40% water deficit) or cut leaves supplied with 10–4 M abscisic acid (ABA) solution to the transpiration stream. Decreasing leaf temperature caused stomatal opening and increased net CO2 uptake (which was close to zero at around 25° C) to a level identical to that of control leaves (without water deficit) at around 15° C. (i) The ABA effect on stomatal closure was modulated by temperature and, presumably, ABA is at least partly responsible for stomatal closure of french bean submitted to a drought stress. (ii) For leaf temperatures lower than 15° C, net CO2 uptake was no longer limited by water deficit even on very dehydrated leaves. This shows that dehydrated leaves retain a substantial part of their photosynthetic capacity which can be revealed at normal CO2 concentrations when stomata open at low temperature. In contrast to leaves fed with ABA, decreasing the O2 concentration from 21% to 1% O2 did not increase either the rate of net CO2 uptake or the thermal optimum for photosynthesis of dehydrated leaves. The quantum yield of PSII electron flow (measured by F/Fm) was lower in 1% O2 than in 21% O2 for each leaf pretreatment given (non-dehydrated leaves, dehydrated leaves, and leaves fed with ABA) even within a temperature range in which leaf photosynthesis at normal CO2 concentration was the same in these two O2 concentrations. It is concluded that this probably indicates an heterogeneity of photosynthesis, since this difference in quantum yield disappears when using high CO2 concentrations during measurements.Abbreviations and Symbols ABA
abscisic acid
- Fm
maximum chlorophyll fluorescence
- F
difference between steady-state chlorophyll fluorescence and Fm
- PPFD
photosynthetic photon flux density
We would like to thank Dr. J.-M. Briantais (Laboratoire d'écologie végétale, Orsay, France) for help during fluorescence measurements and Ms. J. Liebert for technical assistance. 相似文献
17.
Activity regulation and physiological impacts of maize C4-specific phosphoenolpyruvate carboxylase overproduced in transgenic rice plants 总被引:6,自引:0,他引:6
Fukayama H Hatch MD Tamai T Tsuchida H Sudoh S Furbank RT Miyao M 《Photosynthesis research》2003,77(2-3):227-239
Phosphoenolpyruvate carboxylase (PEPC) was overproduced in the leaves of rice plants by introducing the intact maize C4-specific PEPC gene. Maize PEPC in transgenic rice leaves underwent activity regulation through protein phosphorylation in
a manner similar to endogenous rice PEPC but contrary to that occurring in maize leaves, being downregulated in the light
and upregulated in the dark. Compared with untransformed rice, the level of the substrate for PEPC (phosphoenolpyruvate) was slightly lower and the product (oxaloacetate) was slightly higher in transgenic rice, suggesting that maize
PEPC was functioning even though it remained dephosphorylated and less active in the light. 14CO2 labeling experiments indicated that maize PEPC did not contribute significantly to the photosynthetic CO2 fixation of transgenic rice plants. Rather, it slightly lowered the CO2 assimilation rate. This effect was ascribable to the stimulation of respiration in the light, which was more marked at lower
O2 concentrations. It was concluded that overproduction of PEPC does not directly affect photosynthesis significantly but it
suppresses photosynthesis indirectly by stimulating respiration in the light. We also found that while the steady-state stomatal
aperture remained unaffected over a wide range of humidity, the stomatal opening under non-steady-state conditions was destabilized
in transgenic rice.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
18.
One and a half year-old Ginkgo saplings were grown for 2 years in 7 litre pots with medium fertile soil at ambient air CO2 concentration and at 700 μmol mol−1 CO2 in temperature and humidity-controlled cabinets standing in the field. In the middle of the 2nd season of CO2 enrichment, CO2 exchange and transpiration in response to CO2 concentration was measured with a mini-cuvette system. In addition, the same measurements were conducted in the crown of one 60-year-old tree in the field. Number of leaves/tree was enhanced by elevated CO2 and specific leaf area decreased significantly.CO2 compensation points were reached at 75–84 μmol mol−1 CO2. Gas exchange of Ginkgo saplings reacted more intensively upon CO2 than those of the adult Ginkgo. On an average, stomatal conductance decreased by 30% as CO2 concentration increased from 30 to 1000 μmol mol−1 CO2. Water use efficiency of net photosynthesis was positively correlated with CO2 concentration levels. Saturation of net photosynthesis and lowest level of stomatal conductance was reached by the leaves of Ginkgo saplings at >1000 μmol mol−1 CO2. Acclimation of leaf net CO2 assimilation to the elevated CO2 concentration at growth occurred after 2 years of exposure. Maximum of net CO2 assimilation was 56% higher at ambient air CO2 concentration than at 700 μmol mol−1 CO2. 相似文献
19.
Diurnal changes in gas exchange, chlorophyll fluorescence and leaf water potential (leaf) were measured to determine the environmental and physiological factors that limit carbon gain in the horizontal leaves of Fagus crenata Blume at the canopy top. Although midday depression of the net CO2 assimilation rate (An) and stomatal conductance (gH2O) were clearly evident on a fine day, the potential quantum yield of PS II (Fv/Fm) was fairly constant around 0.83 throughout the day. This result indicates that the leaves at the canopy top do not suffer from chronic photoinhibition, and the excess energy is dissipated safely. Large reversible increases in non-photochemical quenching (NPQ) were evident on fine days. Therefore, the non-radiative energy dissipation of excess light energy contributed to avoid chronic photoinhibition. The electron transfer rate (ETR) reached maximum during the midday depression, and thus there was no positive relation between ETR and An under high light conditions, indicating a high rate of photorespiration and the absence of non-stomatal effect during midday. The protective mechanisms such as non-radiative energy dissipation and photorespiration play an important role in preventing photoinhibitory damage, and stomatal limitation is the main factor of midday depression of An. To separate the effect of air to leaf vapor pressure deficit (ALVPD) and leaf temperature (Tleaf) on gas exchange, the dependencies of An and gH2O on ALVPD and Tleaf were measured using detached branches under controlled conditions. An and gH2O were insensitive to an increase in Tleaf. With the increase in ALVPD, An and gH2O exhibited more than a 50% decrease even though water supply was optimum, suggesting the dominant role of high ALVPD in the midday depression of gH2O. We conclude that midday depression of An results from the midday stomatal closure caused by high ALVPD. 相似文献
20.
The aim of this work was to examine the effect of abrupt changes in temperature in the range 5 to 30°C upon the rate of photosynthetic carbon assimilation in leaves of barley (Hordeum vulgare L.). Measurement of the CO2-assimilation rate in relation to the intercellular partial pressure of CO2 at different temperatures and O2 concentrations and at saturating irradiance showed that as the temperature was decreased photosynthesis was saturated at progressively lower CO2 partial pressures and that the transition between the CO2-limited and ribulose-1,5-bisphosphate-regeneration-limited rate became more abrupt. Feeding of orthophosphate to leaves resulted in an increased rate of CO2 assimilation at lower temperatures at around ambient or higher CO2 partial pressures both in 20% O2 and in 2% O2 and it removed the abruptness in the transition between the CO2-limited and ribulose-1,5-bisphosphate-regeneration-limited rates. Phosphate feeding tended to inhibit carbon assimilation at higher temperatures. The response of carbon assimilation to temperature was altered by feeding orthophosphate, by changing the concentrations of CO2 or of O2 or by leaving plants in the dark at 4°C for several hours. Similarly, the response of carbon assimilation to phosphate feeding or to changes in 2% O2 was altered by leaving the plants in the dark at 4°C. The mechanism of limitation of photosynthesis by an abrupt lowering of temperature is discussed in the light of the results.Abbreviations A
rate of CO2 assimilation
-
P
i
intercellular partial pressure of CO2
- RuBP
ribulose-1,5-bisphosphate 相似文献