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1.
To investigate the diurnal variation of stomatal sensitivity to CO2 , stomatal response to a 30 min pulse of low CO2 was measured four times during a 24 h time-course in two Crassulacean acid metabolism (CAM) species Kalanchoe daigremontiana and Kalanchoe pinnata , which vary in the degree of succulence, and hence, expression and commitment to CAM. In both species, stomata opened in response to a reduction in p CO2 in the dark and in the latter half of the light period, and thus in CAM species, chloroplast photosynthesis is not required for the stomatal response to low p CO2 . Stomata did not respond to a decreased p CO2 in K. daigremontiana in the light when stomata were closed, even when the supply of internal CO2 was experimentally reduced. We conclude that stomatal closure during phase III is not solely mediated by high internal p CO2 , and suggest that in CAM species the diurnal variability in the responsiveness of stomata to p CO2 could be explained by hypothesizing the existence of a single CO2 sensor which interacts with other signalling pathways. When not perturbed by low p CO2 , CO2 assimilation rate and stomatal conductance were correlated both in the light and in the dark in both species. 相似文献
2.
The effect of long-term water stress on photosynthetic carbon metabolism in Casuarina equisetifolia Forst. & Forst. was analysed by measuring CO2 assimilation, stomatal conductance, the quantum yield of photosystem II ( Φ PSII ), enzyme activities, and the levels of photosynthetic intermediates and carbohydrates. CO2 assimilation decreased under water stress while the intercellular CO2 concentration ( C i ) as estimated by gas exchange measurements remained high. However, the estimates of C i from measurements of Φ PSII suggest that the decrease in photosynthesis can be explained in terms of stomatal closure. Water stress decreased total stromal fructose-1,6-bisphosphatase activity and did not alter the activities and activation states of ribulose bisphosphate carboxylase oxygenase and NADP-dependent malate dehydrogenase (NADP-MDH). The concentration of photosynthetic metabolites, glucose, fructose and sucrose decreased, whereas starch concentrations increased under drought conditions. 相似文献
3.
This study reports evidence that the timing of leaf growth responds to developmental and environmental constraints in Clusia spp. We monitored diel patterns of leaf growth in the facultative C3 -crassulacean acid metabolism (CAM) species Clusia minor and in the supposedly obligate CAM species Clusia alata using imaging methods and followed diel patterns of CO2 exchange and acidification. Developing leaves of well-watered C. minor showed a C3 -like diel pattern of gas exchange and growth, with maximum relative growth rate (RGR) in the early night period. Growth slowed when water was withheld, accompanied by nocturnal CO2 exchange and the diel acid change characteristic of CAM. Maximum leaf RGR shifted from early night to early in the day when water was withheld. In well-watered C. alata , similar changes in the diel pattern of leaf growth occurred with the development of CAM during leaf ontogeny. We hypothesize that the shift in leaf growth cycle that accompanies the switch from C3 photosynthesis to CAM is mainly caused by the primary demand of CAM for substrates for nocturnal CO2 fixation and acid synthesis, thus reducing the availability of carbohydrates for leaf growth at night. Although the shift to leaf growth early in the light is presumably associated with the availability of carbohydrates, source–sink relationships and sustained diurnal acid levels in young leaves of Clusia spp. need further evaluation in relation to growth processes. 相似文献
4.
Analyses of chlorophyll fluorescence were undertaken to investigate the alterations in photosystem II (PSII) function during senescence of wheat ( Triticum aestivum L. cv. Shannong 229) leaves. Senescence resulted in a decrease in the apparent quantum yield of photosynthesis and the maximal CO2 assimilation capacity. Analyses of fluorescence quenching under steady‐state photosynthesis showed that senescence also resulted in a significant decrease in the efficiency of excitation energy capture by open PSII reaction centers (F'v /F'm ) but only a slight decrease in the maximum efficiency of PSII photochemistry (F'v /F'm ). At the same time, a significant increase in non‐photochemical quenching (qN ) and a considerable decrease in photochemical quenching (qP ) were observed in senescing leaves. Rapid fluorescence induction kinetics indicated a decrease in the rate of QA reduction and an increase in the proportion of QB ‐non‐reducing PSII reaction during senescence. The decrease in both F'v /F'm and qP explained the decrease in the actual quantum yield of PSII electron transport ((φPSII ). We suggest that the modifications in PSII function, which led to the down‐regulation of photosynthetic electron transport, would be in concert with the lower demand for ATP and NADPH in the Calvin cycle which is often inhibited in senescing leaves. 相似文献
5.
Angeles Calatayud Vicente I. Deltoro Eva Barreno Secundino del Valle-Tascon 《Physiologia plantarum》1997,101(1):93-102
The function of photosystem II (PSII) during desiccation was investigated via analysis of Chl a fluorescence emission in thalli from Parmelia quercina (Willd.) Vainio, Parmelia acetabulum (Necker) Duby, Ramalina farinacea (L.) Ach., Pseudevernia furfuracea (L.) Zopf., and Evernia prunastri (L.) Ach. Water loss followed the same exponential pattern in all these species, the half time being dependent on species. Desiccation affected the fluorescence parameters. Dark-adapted maximum fluorescence (Fm ), instantaneous fluorescence (Fo ) and the ratio of variable (Fm –Fo ) to Fm were dependent on water content and decreased in two distinct phases: a slow and apparently linear phase, followed by a more steep decline at low water content. Actual PSII photochemical yield (φPSII ), non-photochemical quenching (NPQ), efficiency of photon capture (φexc ), and photochemical quenching (qp ) remained nearly constant until 30% relative water content (RWC), decreasing rapidly thereafter. In contrast, increased NPQ appeared to occur only at water content values lower than 20%. Treatment of thalli with dithiothreitol (DTT) effectively reduced NPQ during desiccation and increased susceptibility to photoinhibition caused by exposure to high light as measured by dark recovery of the Fv Fm ratio. HPLC analysis showed that the level of the de-epoxidized xanthophyll cycle pigments antheraxanthin (Anth) and zeaxanthin (Zea) increased during lichen desiccation. The results point towards the existence of a photoprotective mechanism with the involvement of Zea and Anth in non-radiative dissipation of the desiccation-induced excess of energy. 相似文献
6.
Persistence of photosynthetic components and photochemical efficiency in ears of water-stressed wheat (Triticum aestivum) 总被引:3,自引:0,他引:3
Dana E. Martinez Virginia M. Luquez Carlos G. Bartoli Juan J. Guiamét 《Physiologia plantarum》2003,119(4):519-525
Ear photosynthesis may be an important source of C for grain growth in water-stressed plants of cereals. The main objectives of this work were to determine the stability of the photosynthetic apparatus and the photochemical efficiency of ears in plants subjected to post-anthesis drought. Plants of wheat ( Triticum aestivum L. cv. Granero INTA) were grown in pots under a rain shelter and subjected to water stress (soil water potential around −0.6 to −0.8 MPa) starting 4 days after anthesis. Post-anthesis drought substantially accelerated the loss of chlorophyll, Rubisco and the light-harvesting complex of photosystem II (LHCII) in the flag leaf, but the degradation of these photosynthetic components was much less affected by water deficit in awns and ear bracts. Quantum yield of PSII (ΦPSII ) decreased in leaves of water-stressed plants. In contrast, ear bracts had a higher ΦPSII than leaves, and ΦPSII of ear bracts did not decrease at all in response to drought. Removing the grains immediately before fluorescence measurements (less than 30 min) slightly reduced ΦPSII , indicating that CO2 supplied by grain respiration may contribute to the high photochemical efficiency of ears in droughted plants. However, other factors may be involved in maintaining high ΦPSII , since even in the absence of grains ΦPSII remained much higher in ear bracts than in the flag leaf. The relative stability of ear photosynthetic components and their relatively high photochemical efficiency may help to maintain ear photosynthesis during the grain filling period in droughted plants. 相似文献
7.
Stomatal responses to light in the facultative Crassulacean acid metabolism species, Portulacaria afra 总被引:2,自引:0,他引:2
Guard cell responses to light are mediated by guard cell chlorophyll and by a specific blue light photoreceptor. Gas exchange and epidermal peel techniques were employed to investigate these responses in the facultative Crassulacean acid metabolism (CAM) species, Portulacaria afra (L.) Jacq. In P. afra individuals performing C3 metabolism, red light stimulated an increase in leaf conductance in intact leaves and stomatal opening in isolated epidermal peels, indicating the presence in guard cells of the chlorophyll-mediated response to light. Under a background of continuous red illumination, conductance exhibited transient increases following pulses of blue but not red light, indicating that the specific stomatal response to blue light was also operative. In contrast, in CAM individuals, conductance in gas exchange experiments and stomatal opening in epidermal peel experiments were not stimulated by red light. In CAM plants, conductance did not increase following blue light pulses administered over a range of temperatures, vapor pressure differences (VPD), ambient CO2 concentrations and background red light intensities. These results indicate that P. afra does possess typical guard cell responses to light when performing C3 metabolism. The metabolic pathways mediating these responses are either lost or inhibited when CAM is induced. 相似文献
8.
Kinetic changes with temperature of phosphoenolpyruvate carboxylase from a CAM plant 总被引:4,自引:1,他引:3
Abstract. Purified and crude phosphoenolpyruvate carboxylase from the CAM plant Kalanchoë daigremontiana Hamet et Perrier ( Bryophyllum diagremontianum ) was assayed at temperatures between 10 and 45° C. The optimum temperature of the enzyme activity changed with substrate availability and effector concentration in the assay. l -malate inhibited the enzyme activity and lowered the optimum temperature. Glucose-6-phosphate raised the optimum temperature to 43°C. K m values for phosphoenolpyruvate increased with assay temperature from 0.12 mol m-3 at 15° C to 0.36 molm−3 at 35° C. Inhibition by malate increased with temperature and acidity of the assay. In the crude enzyme 50% of control activity was inhibited by 1.65 mol m-3 malate at 15° C and by 0.5 mol m-3 at 35° C (at pH 7.0). With purification malate sensitivity was lost ( K i values for malate at least 10 times higher). The shift in optimum temperatures for PEP-carboxylase activity thus results from changes in the kinetic parameters with temperature and allosteric effectors. The often low optimum temperatures for CO2 fixation observed in nature may thus be the result of substrate and effector concentrations in the cytoplasm and the antagonistic effect of temperature on substrate affinity and effector efficiency on phosphoenolpyruvate carboxylase. 相似文献
9.
Graham J. C. Underwood Claes Nilsson Kristina Sundbäck Angela Wulff 《Journal of phycology》1999,35(4):656-666
The effects on UVB radiation on a subtidal, cohesive-sediment biofilm dominated by the diatom Gyrosigma balticum (Ehrenberg) Rabenhorst were investigated. Chlorophyll fluorescence parameters ( F v / F m , φPSII ), pigment concentrations, cell densities, and carbohydrate fractions were measured in four treatments (no UVBR, ambient UVBR, +7%, and +15% enhancement with UVBR). Enhanced UVBR was provided by a computer-controlled system directly linked to natural diel UVBR levels. Increases in φPSII values in the UVBR-enhanced treatments and a decrease in the steady-state fluorescence yield ( F s ) from the surface of the biofilms during the middle and latter part of daily exposure periods suggested that G. balticum responded to enhanced UVBR by migrating down into the sediment. Diatoms in the +15% UVBR treatment also had significantly higher concentrations of β-carotene after 5 days of treatment. Although G. balticum responded to enhanced UVBR by migration and increased β-carotene concentrations, significant reduction in maximum quantum yield of PSII ( F v / F m ) and in minimal fluorescence ( F o ) and decreases in cell densities occurred after 5 days. Concentrations of different carbohydrate fractions (colloidal carbohydrate, glucan, exopolymers [EPS]) associated with diatom biomass and motility also decreased in the UVBR-enhanced treatments. Short-term responses (migration) to avoid UVBR appear insufficient to prevent longer-term decreases in photosynthetic potential and biofilm carbohydrate concentration and biomass. 相似文献
10.
Kojiro Nishida 《Physiologia plantarum》1982,54(4):451-454
The CO2 concentration within the leaf of Kalanchoë pinnatum (Persoon) was measured during deacidification in the light. When the acidified leaf was treated with DCMU, the CO2 concentration within the leaf was increased about 3-fold as compared to that of the non-treated leaf, concomitant with a decline in deacidification. Low light intensity during deacidification also increased CO2 concentration within the leaf. From these experiments, it was concluded that in order for deacidification to proceed, CO2 released from malate must be fixed continuously by photosynthesis. Otherwise, an equilibrium for malate decomposition is soon established and results in suppression of deacidification. Thus, the CO2 concentration within the leaf seems to be one of the regulatory factors of deacidification. 相似文献
11.
Intact vacuoles were isolated from leaves of the CAM plant, Kalanchoë daigremontiana Hamet et Perr. Both ATPase and acid phosphatase activities were found in the vacuoles. Purified tonoplast vesicles showed only ATPase activity with a pH optimum of 8.0. This activity was Mg2+ -dependent and KCI or NaCI caused a further stimulation. N,N'-dicyclohexylcarbodiimide, diethylstilbestrol and quercetin inhibited the ATPase almost completely at concentrations well below 1 m M. NaVo3 , 1-ethyl-3(3-dimethylaminopropyl)carbodiimide, oligomycin and NaN3 had little or no effect. Carbonyl cyanide m -chlorophenylhydrazone stimulated the ATPase about 40% at 5 × 10−4 M. The Km for ATP was found to be 0.55 m M. These results indicate that the ATPase found in the tonoplast membrane of Kalanchoë daigremontiana is qualitatively similar to that of other plant species. 相似文献
12.
Nocturnal citrate accumulation and its response to environmental stress in the CAM plant Kalanchoe pinnata (Lam.) Pers. 总被引:2,自引:2,他引:0
U. LÜTTGE 《Plant, cell & environment》1990,13(9):977-982
Abstract. Kalanchoe pinnata (Lam.) Pers., a plant having crassulacean acid metabolism (CAM), was grown in high light (16–23 mol photons m−2 d−1 ) and in the shade (0.8–2.1 mol photons m−2 d−1 ), respectively. Plants were stressed in three ways, i.e. by transfer from high light to shade or vice versa just before measurements, and by withholding nitrogen and/or water. During the day-night cycle of CAM, K. pinnata showed day-night changes of citrate levels (Δ citrate) in addition to malate changes (Δ malate). Changes of leaf-cell sap osmotic pressure. Δπ, were linearly correlated with these changes of organic-acid anion levels with a relation of Δπ/(Δ citrate +Δ malate) = 1/1. The environmental stressor, i.e. limited N-nutrition, drought and higher or lower irradiance than experienced during growth, affected the absolute and relative contributions made by Δ citrate and Δ malate to total nocturnal organic-acid accumulation. In the high-light-grown plants transferred to the shade, changes of citrate levels were much less affected than changes of malate levels by the generally decreased metabolic activity and inhibition of CO2 uptake. In the shade-grown plants, Δ citrate increased in response to stress imposed by interactive effects of the three stressors. 相似文献
13.
Vulnerability of stem xylem to cavitation was measured in 10 species of conifers using high pressure air to induce xylem embolism. Mean values of air pressure required to induce a 50% loss in hydraulic conductivity (φ50 ) varied enormously between species, ranging from a maximum of 14.2±0.6 MPa (corresponding to a xylem water potential of −14.2 MPa) in the semi-arid species Actinostrobus acuminatus to a minimum of 2.3±0.2 MPa in the rainforest species Dacrycarpus dacrydioides . Mean φ50 was significantly correlated with the mean rainfall of the driest quarter within the distribution of each species. The value of φ50 was also compared with leaf drought tolerance data for these species in order to determine whether xylem dysfunction during drought dictated drought response at the leaf level. Previous data describing the maximum depletion of internal CO2 concentration (ci ) in the leaves of these species during artificial drought was strongly correlated with φ50 suggesting a primary role of xylem in effecting leaf drought response. The possibility of a trade-off between xylem conductivity and xylem vulnerability was tested in a sub-sample of four species, but no evidence of an inverse relationship between φ50 and either stem-area specific (Ka ) or leaf-area specific conductivity (K1 ) was found. 相似文献
14.
The developmental profile of the activities of some enzymes involved in malate metabolism, namely phosphoenolpyruvate carboxylase (PEPC; EC 4. 1. 1. 31), NAD+ -linked (EC 1. 1. 1. 37) and NADP+ -linked (EC 1. 1. 1. 82) malate dehydrosenase (MDH), NAD+ linked (EC 1. 1. 1. 39) and NADP+ -linked (EC 1. 1. 1. 40) malic enzyme (ME), has been determined in leaves of peach [ Prunus persica (L.) Batsch cv. Maycrest], a woody C3 species. In order to study the role of these enzymes, their activities were related to developmental changes of photosynthesis, respiration, and capacity for N assimilation. Activities of PEPC, NAD(P)+ -MDH and NADP+ -ME were high in young expanding leaves and decreased 2- to 3-fold in mature ones, suggesting that such enzymes play some role during the early stages of leaf expansion. In leaves of peach, such a role did not seem to be linked to C3 photosynthesis or nitrate assimilation, in that photosynthetic O2 evolution and activities of nitrate reductase (EC 1. 6. 6. 1) and glutamine synthetase (EC 6. 3. 1. 2) increased during leaf development. In contrast, leaf respiration strongly decreased with increasing leaf age. We suggest that in expanding leaves of this woody species the enzymes associated with malate metabolism have anaplerotic functions, and that PEPC may also contribute to the recapture of respiratory CO2 . 相似文献
15.
Peng-Min Li Rui-Guo Cai Hui-Yuan Gao Tao Peng Zhen-Lin Wang 《Physiologia plantarum》2007,129(4):822-829
Influences of different nitrogen applications on photosynthesis and utilization of excitation energy were explored by comparing two field-grown wheat ( Triticum aestivum L.) cultivars with high or low grain protein content [High protein cultivar '8901' (HC) and low protein cultivar '1391' (LC)]. High nitrogen application significantly decreased both CO2 assimilation and photorespiration in both cultivars during the early stages after anthesis. However, the actual photosystem II (PSII) efficiency ( Ф PSII ) was not significantly different between high, moderate and low nitrogen applications in the HC. As a result, the ratio of Ф PSII to the quantum yield of carbon metabolism ( Φ CO2 ) measured under non-photorespiratory conditions in the HC was higher under high nitrogen application than under low or medium nitrogen application. The grain protein content of the HC was also increased by high nitrogen application. In contrast, high nitrogen application decreased the actual PSII efficiency in the flag leaves of the LC in the early stages after anthesis and different nitrogen applications did not significantly alter the Ф PSII / Φ CO2 ratio or grain protein content in the LC. No significant difference was detected in the activity of superoxide dismutase or ascrobate peroxidase between different nitrogen treatments in either cultivar throughout the entire experimental period. These results indicate that more excitation energy is partitioned to nitrogen metabolism in the flag leaves of the HC under high nitrogen application whereas the partitioning of excitation energy in the LC was not affected by nitrogen application. 相似文献
16.
By analysis of gas exchange and chlorophyll fluorescence, the effects of NaCl treatment and supplemental CaCl2 on photosynthesis, photosystem II (PSII) photochemistry and photoinhibition were investigated in Rumex leaves. Photosynthesis in Rumex leaves was strongly inhibited by 200 m M NaCl treatment. Such inhibition of photosynthesis was ameliorated by CaCl2 supplement. Neither NaCl treatment nor CaCl2 supplement had any significant effects on the PSII primary photochemical reaction in dark-adapted leaves. In light-adapted leaves, however, 200 m M NaCl treatment significantly decreased photochemical quenching (qp ), efficiency of excitation energy capture by open PSII reaction centers (FV '/FM ') and quantum yield of PSII electron transport (ΦPSII ). These decreases in qp, FV '/FM ' and ΦPSII were mitigated by CaCl2 supplement with the maximum of its effect appearing at a concentration of 8 m M CaCl2 . A similar mitigating effect was shown in 200 m M NaCl-treated Rumex leaves when susceptibility of PSII to photoinhibition was determined under high irradiance. It is suggested that the mitigation of photoinhibition in NaCl-treated leaves is because of the amelioration of inhibition of photosynthesis. 相似文献
17.
Abstract. A portable apparatus has been constructed to measure simultaneously the quantum yield of CO2 assimilation, light absorption, chlorophyll fluorescence emission and water vapour exchange of attached intact leaves in the field. The core of the instrument is a light-integrating spherical leaf chamber which includes ports for a light source, photosynthetically active radiation sensor, fluorescence probes and gas inlet and outlet manifolds. Measurement of the quantum flux inside the empty chamber and with a leaf present allows determination of leaf absorptance. An open gas exchange system is employed using an infra-red analyser to measure leaf CO2 exchange. Using a DC white light source the quantum yield of CO2 assimilation based on absorbed light (φabs ) may be determined rapidly in either ambient air or artificial gas mixtures. Inclusion of capacitance humidity probes into the gas inlet and outlet ports allows simultaneous determination of water vapour exchange and subsequent estimation of stomatal conductance to CO2 and intercellular CO2 concentration. Measurement of fluorescence emission by the sample leaf exposed to white light is achieved by a modulated fluorescence detection system. In addition to determination of the minimal, maximal and variable fluorescence levels, a further analysis allows the photochemical and non-photochemical components of fluorescence quenching, to be estimated. The theory and design of this apparatus is described in detail. The use of the apparatus in the field is demonstrated through a study of the photosynthetic performance of a maize and bean crop during the growing season and by analysis of the photosynthetic performance of crops subjected to nitrogen-stress and a herbicide treatment. 相似文献
18.
Physiological response of Pinus halepensis needles under ozone and water stress conditions 总被引:1,自引:0,他引:1
The aim of this study was to evaluate how physiological processes of potted Pinus halepensis plants, grown under controlled conditions, were affected by ozone (O3 ) and/or water stress, integrating the gas exchange and biochemical data with fluorescence OJIP polyphasic transient data. Plants submitted to only water stress (T1 ) and with ozone (T3 ) showed a strong decrease in stomatal conductance and gas exchange, coinciding with a reduction of maximum yield of photochemistry ( φ po ) and very negative values of leaf water potential. Simultaneously, a great increase of both PSII antenna size, indicated by absorption per reaction centre, and electron transport per reaction centre were found. The reduction of photosynthesis in the O3 -treated plants (T2 ) by a slowing down of the Calvin cycle was supported by the increase of related fluorescence parameters such as relative variable fluorescence, heat de-excitation constant, energy de-excitation by spillover, and the decrease of φ po . We suggest an antagonistic effect between the two stresses to explain the delayed ozone-induced decrease of stomatal conductance values for T3 with respect to T1 plants, by an alteration of the physiological mechanisms of stomatal opening, which involve the increase of intra-cellular free-calcium induced by ABA under co-occurring water shortage. We emphasise the importance of considering the intensity of the individual stress factor in studies concerning the interaction of stresses. 相似文献
19.
Z. Miszalski E. Niewiadomska I. Slesak U. Lüttge M. Kluge R. Ratajczak 《Plant biology (Stuttgart, Germany)》2001,3(1):17-23
Abstract: In Mesembryanthemum crystallinum plants, treated for 9 days with 0.4 M NaCl at low light intensities (80 - 90 or 95 - 100 μE m-2 s-1 ; λ = 400 - 700 nm), no day/night malate level differences (Δmalate) were detected. At high light (385 - 400 μE m-2 s-1 ) strong stimulation of PEPC activity, accompanied by a Δmalate of 11.3 mM, demonstrated the presence of CAM metabolism. This indicates that, to evolve day/night differences in malate concentration, high light is required. Salt treatment at low light induces and increases the activity of NAD- and NADP-malic enzymes by as much as 3.7- and 3.9-fold, while at high light these values reach 6.4- and 17.7-fold, respectively. The induction of activity of both malic enzymes and PEPC (phospo enol pyruvate carboxylase) take place before Δmalate is detectable. An increase in SOD (superoxide dismutase) was observed in plants cultivated at high light in both control and salt-treated plants. However, in salt-treated plants this effect was more pronounced. Carboxylating and decarboxylating enzymes seem to be induced by a combination of different signals, i.e., salt and light intensity. Plants performing CAM, after the decrease of activity of both the decarboxylating enzymes at the beginning of the light period, showed an increase in these enzymes in darkness when the malate pool reaches higher levels. In CAM plants the activity of fumarase (Krebs cycle) is much lower than that in C3 plants. The role of mitochondria in CAM plants is discussed. 相似文献
20.
Britta Herzog T. E. E. Grams Angela Haag-Kerwer Erika Ball A. C. Franco U. Lüttge 《Plant biology (Stuttgart, Germany)》1999,1(3):357-364
Abstract: The large majority of the Ca . 150 species of the neotropical shrub and tree genus Clusia have the potential to perform Crassulacean acid metabolism (CAM). They are either obligate CAM plants or C3 /CAM intermediate plants. Only a very small percentage of the plants studied so far are apparently obligate C3 species. Among these was C. criuva , until recent laboratory studies showed that it may also have a certain CAM capacity under artificial stress conditions. Measurements of stomatal conductance (porometry) and chlorophyll fluorescence variables of C. criuva occurring along a transect from deep shade inside a gallery forest across the semi-shaded ecotone towards a cerrado and into the exposed cerrado itself in central Brazil now show that it can adapt its photosynthetic apparatus to effective performance of C3 photosynthesis under highly different photosynthetic photon flux densities. In addition, however, it does have a certain potential for CAM and cannot be considered as a strictly obligate C3 plant. Should a basic capacity for performing CAM be a general property of the genus, the quest for CAM traits in other remaining putatively obligate C3 species of the genus ought to be pursued. 相似文献