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1.
Environmental factors that influence stomatal conductance (g
s) interact through a complex network of signal transduction and have therefore highly interdependent effect.
In the present study we examined how plant water status affects stomatal sensitivity to the change of CO2 concentration ([CO2]). We investigated the short-term dynamic of stomatal response to a sudden [CO2] increase (from 400 to 700 μmol(CO2) mol−1) in maize supplied with different amounts of water (resulting ψw = −0.35, −0.52 and −0.75 MPa). Gas exchange measurements were performed in short logging intervals and the response was monitored
under two different levels of water vapour pressure deficit (VPD) of 1 and 2 kPa in order to observe the impact of air humidity.
Generalized logistic curves were fitted to standardized stomatal response data, which enabled us to objectively estimate the
level (relative decrease of g
s) and the dynamics of the response. 相似文献
2.
I. E. Papadakis A. Giannakoula C. P. Antonopoulou M. Moustakas E. Avramaki I. N. Therios 《Photosynthetica》2007,45(2):208-213
Citrus volkameriana (L.) plants were grown for 43 d in nutrient solutions containing 0, 2, 14, 98, or 686 μM Mn (Mn0, Mn2, Mn14, Mn98, and Mn686, respectively). To adequately investigate the combined effects of Mn nutrition and irradiance on photosystem 2 (PS2) activity,
irradiance response curves for electron transport rate (ETR), nonphotochemical quenching (qN), photochemical quenching (qP), and real photochemical efficiency of PS2 (ΦPS2) were recorded under 10 different irradiances (66, 96, 136, 226, 336, 536, 811, 1 211, 1 911, and 3 111 μmol m−2 s−1, I66 to I3111, respectively) generated with the PAM-2000 fluorometer. Leaf chlorophyll content was significantly lower under Mn excess (Mn686) compared to Mn0; its highest values were recorded in the treatments Mn2-Mn98. However, ETR and ΦPS2 values were significantly lower under Mn0 compared to the other Mn treatments, when plants were exposed to irradiances ≥96 μmol m−2 s−1. Furthermore, Mn0 plants had significantly higher values of qN and lower values of qP at irradiances ≤226 and ≥336 μmol m−2 s−1, respectively, than those grown under Mn2-Mn686. Irrespective of Mn treatment, the values of ΦPS2 and qN decreased, while those of qP increased progressively by increasing irradiance from I136 to I3111. Finally, Mn2-Mn98 plants were less sensitive to photoinhibition of photosynthesis (≥811 μmol m−2 s−1) than the Mn686 (≥536 μmol m−2 s−1) and Mn0 (≥336 μmol m−2 s−1) ones. 相似文献
3.
Simultaneous measurements of chlorophyll (Chl) fluorescence and CO2 assimilation (A) in Vicia faba leaves were taken during the first weeks of growth to evaluate the protective effect of 24-epibrassinolide (EBR) against
damage caused by the application of the herbicide terbutryn (Terb) at pre-emergence. V. faba seeds were incubated for 24 h in EBR solutions (2 × 10−6 or 2 × 10−5 mM) and immediately sown. Terb was applied at recommended doses (1.47 or 1.96 kg ha−1) at pre-emergence. The highest dose of Terb strongly decreased CO2 assimilation, the maximum quantum yield of PSII photochemistry in the dark-adapted state (F
V/F
M), the nonphotochemical quenching (NPQ), and the effective quantum yield (ΔF/F′M) during the first 3–4 weeks after plant emergence. Moreover, Terb increased the basal quantum yield of nonphotochemical processes
(F
0/F
M), the degree of reaction center closure (1 − q
p), and the fraction of light absorbed in PSII antennae that was dissipated via thermal energy dissipation in the antennae
(1 − F′V/F′M). The herbicide also significantly reduced plant growth at the end of the experiment as well as plant length, dry weight,
and number of leaves. The application of EBR to V. faba seeds before sowing strongly diminished the effect of Terb on fluorescence parameters and CO2 assimilation, which recovered 13 days after plant emergence and showed values similar to those of control plants. The protective
effect of EBR on CO2 assimilation was detected at a photosynthetic photon flux density (PFD) of 650 μmol m−2 s−1 and the effect on ΔF/F′M and photosynthetic electron transport (J) was detected under actinic lightings up to 1750 μmol m−2 s−1. The highest dose of EBR also counteracted the decrease in plant growth caused by Terb, and plants registered the same growth
values as controls. 相似文献
4.
Francesco Ripullone Maria Rosa Guerrieri Angelo Nole’ Federico Magnani Marco Borghetti 《Trees - Structure and Function》2007,21(3):371-378
In this study, tree hydraulic conductance (K
tree) was experimentally manipulated to study effects on short-term regulation of stomatal conductance (g
s), net photosynthesis (A) and bulk leaf water potential (Ψleaf) in well watered 5–6 years old and 1.2 m tall maritime pine seedlings (Pinus pinaster Ait.). K
tree was decreased by notching the stem and increased by progressively excising the root system and stem. Gas exchange was measured
in a chamber at constant irradiance, vapour pressure deficit, leaf temperature and ambient CO2 concentration. As expected, we found a strong and positive relationship between g
s and K
tree (r = 0.92, P = 0.0001) and between A and K
tree (r = 0.9, P = 0.0001). In contrast, however, we found that the response of Ψleaf to K
tree depended on the direction of change in K
tree: increases in K
tree caused Ψleaf to decrease from around −1.0 to −0.6 MPa, but reductions in K
tree were accompanied by homeostasis in Ψleaf (at −1 MPa). Both of these observations could be explained by an adaptative feedback loop between g
s and Ψleaf, with Ψleaf prevented from declining below the cavitation threshold by stomatal closure. Our results are consistent with the hypothesis
that the observed stomatal responses were mediated by leaf water status, but they also suggest that the stomatal sensitivity
to water status increased dramatically as Ψleaf approached −1 MPa. 相似文献
5.
A controlled growth chamber experiment was conducted to investigate the short-term water use and photosynthetic responses
of 30-d-old carrot seedlings to the combined effects of CO2 concentration (50–1 050 μmol mol−1) and moisture deficits (−5, −30, −55, and −70 kPa). The photosynthetic response data was fitted to a non-rectangular hyperbola
model. The estimated parameters were compared for effects of moisture deficit and elevated CO2 concentration (EC). The carboxylation efficiency (α) increased in response to mild moisture stress (−30 kPa) under EC when
compared to the unstressed control. However, moderate (−55 kPa) and extreme (−70 kPa) moisture deficits reduced α under EC.
Maximum net photosynthetic rate (P
Nmax) did not differ between mild water deficit and unstressed controls under EC. Moderate and extreme moisture deficits reduced
P
Nmax by nearly 85 % compared to controls. Dark respiration rate (R
D) showed no consistent response to moisture deficit. The CO2 compensation concentration (Γ) was 324 μmol mol−1 for −75 kPa and ranged 63–93 μmol mol−1 for other moisture regimes. Interaction between moisture deficit and EC was noticed for P
N, ratio of intercellular and ambient CO2 concentration (C
i/C
a), stomatal conductance (g
s
), and transpiration rate (E). P
N was maximum and C
i/C
a was minimum at −30 kPa moisture deficit and at C
a of 350 μmol mol−1. The g
s and E showed an inverse relationship at all moisture deficit regimes and EC. Water use efficiency (WUE) increased with moisture
deficit up to −55 kPa and declined thereafter. EC showed a positive influence towards sustaining P
N and increasing WUE only under mild moisture stress, and no beneficial effects of EC were noticed at moderate or extreme moisture
deficits. 相似文献
6.
M. Bertamini L. Zulini R. Zorer K. Muthuchelian N. Nedunchezhian 《Photosynthetica》2007,45(3):426-432
Photoinhibition under irradiance of 2 000 μmol m−2 s−1 (HI) was studied in detached control (C) and water deficit (WD) leaves of grapevine (Vitis vinifera L.) plants. The degree of photoinhibition was determined by means of the ratio of variable to maximum chlorophyll (Chl) fluorescence
(Fv/Fm) and electron transport measurements. The potential efficiency of photosystem (PS) 2, Fv/Fm, marginally declined under HI in WD-leaves without significant increase of F0. In contrast, Fv/Fm ratio declined markedly with significant increase of F0 in C-leaves. In isolated thylakoids, the rate of whole chain and PS2 activity under HI were more decreased in C-than WD-leaves.
The artificial exogenous electron donors diphenyl carbazide, NH2OH, and Mn2+ failed to restore the HI-induced loss of PS2 activity in both C-and WD-leaves. Thus HI operates at the acceptor side of PS2
in both leaf types. Quantification of the PS2 reaction centre protein D1 following HI exposure of leaves showed pronounced
differences between C-and WD-leaves. The marked loss of PS2 activity under HI of C-leaves was due to the marked loss of D1
protein of the PS2 reaction centre. 相似文献
7.
Q. Chen L. F. Wang N. Su H. D. Qin H. B. Niu J. L. Wang H. Q. Zhai J. M. Wan 《Photosynthetica》2008,46(1):35-39
A yellow leaf colouration mutant (named ycm) generated from rice T-DNA insertion lines was identified with less grana lamellae and low thylakoid membrane protein contents.
At weak irradiance [50 μmol(photon) m−2 s−1], chlorophyll (Chl) contents of ycm were ≈20 % of those of WT and Chl a/b ratios were 3-fold that of wild type (WT). The leaf of ycm showed lower values in the actual photosystem 2 (PS2) efficiency (ΦPS2), photochemical quenching (qP), and the efficiency of excitation capture by open PS2 centres 1 (Fv′/Fm′) than those of WT, except no difference in the maximal efficiency of PS2 photochemistry (Fv/Fm). With progress in irradiance [100 and 200 μmol(photon) m−2 s−1], there was a change in the photosynthetic pigment stoichiometry. In ycm, the increase of total Chl contents and the decrease in Chl a/b ratio were observed. ΦPS2, qP, and Fv′/Fm′ of ycm increased gradually along with the increase of irradiance but still much less than in WT. The increase of xanthophyll ratio
[(Z+A)/(V+A+Z)] associated with non-photochemical quenching (qN) was found in ycm which suggested that ycm dissipated excess energy through the turnover of xanthophylls. No significant differences in pigment composition were observed
in WT under various irradiances, except Chl a/b ratio that gradually decreased. Hence the ycm mutant developed much more tardily than WT, which was caused by low photon energy utilization independent of irradiance. 相似文献
8.
Water status of Pinus taeda L. callus supported on Murashige and Skoog (MS) liquid medium was characterized over an 8 week period using thermocouple
psychrometry. Medium with 30 gl−1 sucrose was used to produce a high water potential (Ψw) of −0.4 MPa (H), and the same medium was used to create a moderate Ψw of −0.7 MPa (M) by the addition of 10% polyethylene glycol (PEG, w/v, MW=8000). Calli were produced from cotyledon explants
on H medium for 2 weeks and then transferred to either M or H medium. Callus absorption of PEG accounted for 40% of the callus
dry weight and less than 7% of the callus fresh weight. Callus dry weight (without the PEG fraction) on M medium was 40% of
that observed on H medium. Fresh weight on M medium was only 15% of that observed on H medium. The Ψw of both H and M media remained constant throughout the culture period. On H medium, callus Ψw and osmotic potential (Ψs) both increased 0.05 MPa/week with the callus Ψw approaching that of the external medium. On M medium, callus Ψw and Ψs both decreased more than 0.1 MPa/week with the callus Ψw decreasing greatly below that of the external medium. The latter was attributed to a rapidly produced osmotic shock induced
upon callus transfer and/or PEG which caused less callus hydration and resulted in reduced growth. Callus turgor potential
(Ψp) was estimated to be +0.02 to +0.09 MPa and turgor was maintained as callus Ψw increased or decreased. After 8 weeks, cell volumes from callus on M medium were 50 to 60% less than on H medium, suggesting
that reduced cell volumes were related to turgor maintenance. 相似文献
9.
Inhibition of photosynthetic processes in foliose lichens induced by temperature and osmotic stress 总被引:2,自引:0,他引:2
Negative effects of osmotically-induced dehydration of two foliose lichen species, Lasallia pustulata and Umbilicaria hirsuta, was studied at physiological (22 °C), low (5 °C) and freezing temperature (−10 °C), using chlorophyll (Chl) fluorescence.
In both species, exposure to increasing sucrose concentrations led to a pronounced decrease in potential (FV/FM), and actual (Φ2) quantum yields of photochemical processes in photosystem 2. L. pustulata was more sensitive to osmotic stress, because comparable osmotic dehydration inhibited FV/FM and Φ2 more than in U. hirsuta. Critical concentration of sucrose that fully inhibited photochemical processes of photosynthesis was 2.5 M, which represented
water potential (Ψw) of −18.8 MPa. Decrease in background Chl fluorescence (F0) and increase in non-photochemical quenching (qN) revealed two phases of osmotic stress in lichens: phase I with no change
(Ψw 0 to −6.6 MPa) and phase II (Ψw −11.3 to −18.8 MPa) typical by substantial change in Chl fluorescence parameters. Effects of thallus anatomy on species-specific
response to osmotic dehydration is discussed and attributed to the results obtained by optical microscopy and Chl fluorescence
imaging technique. 相似文献
10.
B. R. Maricle R. W. Lee C. E. Hellquist O. Kiirats G. E. Edwards 《Photosynthetica》2007,45(3):433-440
The effects of salinity (sea water at 0 ‰ versus 30 ‰) on gross rates of O2 evolution (J
O2) and net rates of CO2 uptake (P
N) were measured in the halotolerant estuarine C4 grasses Spartina patens, S. alterniflora, S. densiflora, and Distichlis spicata in controlled growth environments. Under high irradiance, salinity had no significant effect on the intercellular to ambient
CO2 concentration ratio (C
i/C
a). However, during photosynthesis under limiting irradiance, the maximum quantum efficiency of CO2 fixation decreased under salinity across species, suggesting there is increased leakage of the CO2 delivered to the bundle sheath cells by the C4 pump. Growth under salinity did not affect the maximum intrinsic efficiency of photosystem 2, PS2 (FV/FM) in these species, suggesting salinity had no effect on photosynthesis by inactivation of PS2 reaction centers. Under saline
conditions and high irradiance, P
N was reduced by 75 % in Spartina patens and S. alterniflora, whereas salinity had no effect on P
N in S. densiflora or D. spicata. This inhibition of P
N in S. patens and S. alterniflora was not due to an effect on stomatal conductance since the ratio of C
i/C
a did not decrease under saline conditions. In growth with and without salt, P
N was saturated at ∼500 μmol(quantum) m−2 s−1 while J
O2 continued to increase up to full sunlight, indicating that carbon assimilation was not tightly coupled to photochemistry
in these halophytic species. This increase in alternative electron flow under high irradiance might be an inherent function
in these halophytes for dissipating excess energy. 相似文献
11.
Subsurface CO<Subscript>2</Subscript> Dynamics in Temperate Beech and Spruce Forest Stands 总被引:1,自引:0,他引:1
Rates of soil respiration (CO2 effluxes), subsurface pore gas CO2/O2 concentrations, soil temperature and soil water content were measured for 15 months in two temperate and contrasting Danish
forest ecosystems: beech (Fagus sylvatica L.) and Norway spruce (Picea abies [L.] Karst.). Soil CO2 effluxes showed a distinct seasonal trend in the range of 0.48–3.3 μmol CO2 m−2 s−1 for beech and 0.50–2.92 μmol CO2 m−2 s−1 for spruce and were well-correlated with near-surface soil temperatures. The soil organic C-stock (upper 1 m including the
O-horizon) was higher in the spruce stand (184±23 Mg C ha−1) compared to the beech stand (93±19 Mg C ha−1) and resulted in a faster turnover time as calculated by mass/flux in soil beneath the beech stand (28 years) compared to
spruce stand (60 years). Observed soil CO2 concentrations and effluxes were simulated using a Fickian diffusion-reaction model based on vertical CO2 production rates and soil diffusivity. Temporal trends were simulated on the basis of observed trends in the distribution
of soil water, temperature, and live roots as well as temperature and water content sensitivity functions. These functions
were established based on controlled laboratory incubation experiments. The model was successfully validated against observed
soil CO2 effluxes and concentrations and revealed that temporal trends generally could be linked to variations in subsurface CO2 production rates and diffusion over time and with depths. However, periods with exceptionally high CO2 effluxes (> 20 μmol CO2 m−2 s−1) were noted in March 2000 in relation to drying after heavy rain and after the removal of snow from collars. Both cases were
considered non-steady state and could not be simulated. 相似文献
12.
Two rice chlorophyll (Chl) b-less mutants (VG28-1, VG30-5) and the respective wild type (WT) plant (cv. Zhonghua No. 11) were analyzed for the changes
in Chl fluorescence parameters, xanthophyll cycle pool, and its de-epoxidation state under exposure to strong irradiance,
SI (1 700 μmol m−2 s−1). We also examined alterations in the chloroplast ultrastructure of the mutants induced by methyl viologen (MV) photooxidation.
During HI (0–3.5 h), the photoinactivation of photosystem 2 (PS2) appeared earlier and more severely in Chl b-less mutants than in the WT. The decreases in maximal photochemical efficiency of PS2 in the dark (Fv/Fm), quantum efficiency of PS2 electron transport (ΦPS2), photochemical quenching (qP), as well as rate of photochemistry (Prate), and the increases in de-epoxidation state (DES) and rate of thermal dissipation of excitation energy (Drate) were significantly greater in Chl b-mutants compared with the WT plant. A relatively larger xanthophyll pool and 78–83 % conversion of violaxanthin into antheraxanthin
and zeaxanthin in the mutants after 3.5 h of HI was accompanied with a high ratio of inactive/total PS2 (0.55–0.73) and high
1–qP (0.57–0.68) which showed that the activities of the xanthophyll cycle were probably insufficient to protect the photosynthetic
apparatus against photoinhibition. No apparent difference of chloroplast ultrastructure was found between Chl b-less mutants and WT plants grown under low, LI (180 μmol m−2 s−1) and high, HI (700 μmol m−2 s−1) irradiance. However, swollen chloroplasts and slight dilation of thylakoids occurred in both mutants and the WT grown under
LI followed by MV treatment. These typical symptoms of photooxidative damage were aggravated as plants were exposed to HI.
Distorted and loose scattered thylakoids were observed in particular in the Chl b-less mutants. A greater extent of photoinhibition and photooxidation in these mutants indicated that the susceptibility to
HI and oxidative stresses was enhanced in the photosynthetic apparatus without Chl b most likely as a consequence of a smaller antenna size. 相似文献
13.
Aguedo M Gomes N Garcia EE Waché Y Mota M Teixeira JA Belo I 《Biotechnology letters》2005,27(20):1617-1621
Yarrowia lipolytica converts methyl ricinoleate to γ-decalactone, a high-value fruity aroma compound. The highest amount of 3-hydroxy-γ-decalactone
produced by the yeast (263 mg l-1) occurred by increasing the kLa up to 120 h−1 at atmospheric pressure; above it, its concentration decreased, suggesting a predominance of the activity of 3-hydroxyacyl-CoA
dehydrogenase. Cultures were grown under high-pressure, i.e., under increased O2 solubility, but, although growth was accelerated, γ-decalactone production decreased. However, by applying 0.5 MPa during
growth and biotransformation gave increased concentrations of dec−2-en-4-olide and dec-3-en-4-olide (70 mg l−1). 相似文献
14.
To investigate how excess excitation energy is dissipated in a ribulose-1,5-bisphospate carboxylase/oxygenase activase antisense
transgenic rice with net photosynthetic rate (P
N) half of that of wild type parent, we measured the response curve of P
N to intercellular CO2 concentration (C
i), electron transport rate (ETR), quantum yield of open photosystem 2 (PS2) reaction centres under irradiation (Fv′/Fm′), efficiency of total PS2 centres (ΦPS2), photochemical (qP) and non-photochemical quenching (NPQ), post-irradiation transient increase in chlorophyll (Chl) fluorescence (PITICF), and
P700+ re-reduction. Carboxylation efficiency dependence on C
i, ETR at saturation irradiance, and Fv′/Fm′, ΦPS2, and qP under the irradiation were significantly lower in the mutant. However, NPQ, energy-dependent quenching (qE), PITICF, and P700+ re-reduction were significantly higher in the mutant. Hence the mutant down-regulates linear ETR and stimulates cyclic electron
flow around PS1, which may generate the ΔpH to support NPQ and qE for dissipation of excess excitation energy. 相似文献
15.
Two different genotypes of Lycopersicon esculentum Mill. (cv. Cuor di Bue, O3-sensitive and line 93.1033/1, O3-resistant) were treated with a single dose of ozone (150 mm3 m−3 for 3 h). The PS 2 activity was examined by measurements of chlorophyll a fluorescence on symptomatic and asymptomatic leaves. Symptoms were evident on the 4th leaves from the bottom, in both genotypes, while the 2nd leaves of the line 93.1033/1 were asymptomatic. In these leaves, the net photosynthetic rate (PN) did not change even if the Fv/Fm ratio significantly decreased. A strong reduction in PN, mostly due to the stomatal closure, was observed in Cuor di Bue. The non photochemical quenching coefficient (qNP) and the degree of PS 2 reaction centres closure (1-qP) were higher, while the quantum efficiency of PS 2 photochemistry (ΦPS2) and quantum efficiency of excitation energy capture (Φexc.) were lower in O3 treated leaves of both genotypes. The limitation of photosynthesis was shown also by a decrease in the parameter %P, which
diminished compared to controls in both genotypes. The response of the two genotypes for the energy fraction dissipated as
thermal energy in the PS 2 antennae (%D) was similar. The fraction of %P remained lower during the recovery in symptomatic
leaves of the resistant line as compared to the controls, whereas %X, which represents the amount of light energy that is
not utilized in photochemistry or dissipated in the PS 2 antennae, significantly rose in the asymptomatic leaves of this line
and in both the leaves of Cuor di Bue. From data obtained we concluded that ozone affected the plants independently on the
appearance of visible symptoms of injury because the leaves without visible symptoms of both the genotypes were negatively
influenced. 相似文献
16.
We analysed plant growth, ion accumulation, leaf water relations, and gas exchange of Avicennia germinans (L.) L. subjected to a long-term, controlled salinity gradient from 0 to 55 ‰. Growth and leaf area were affected by salinity
higher than 10 ‰. As salinity increased, the predawn leaf water potential (Ψw) and leaf osmotic potential (Ψs) decreased. Leaf Ψw was at least −0.32 MPa lower than the Ψw of solution. Na+ and K+ ions explained about 78 % of decrease in Ψs. K+ tissue water concentration decreased by more than 60 % in all salinity treatments as compared with those grown at 0 ‰. Inversely,
Na+ concentration in tissue water increased with nutrient solution salinity. The maximum net photosynthetic rate (P
N) and stomatal conductance (g
s) decreased by 68 and 82 %, respectively, as salinity increased from 0 to 55 ‰; the intercellular CO2 concentration (C
i) followed the same trend. The P
N as a function of C
i showed that both the initial linear slope and upper plateau of the P
N
vs. C
i curve were markedly affected by high salinity (40 and 55 ‰). 相似文献
17.
Rehmannia glutinosa seedlings were pretreated with choline chloride (CC) in concentrations of 0, 0.7, 2.1 and 3.5 mM, and then subjected to drought
and rewatering treatment to study the effects of CC on the generation of reactive oxygen species (O2−, H2O2), lipid peroxidation, proline accumulation, water status and photosynthesis. The results showed that pretreatment with CC
alleviated the inhibition of SOD and APX activity caused by drought stress, and therefore, the rate of O2− production and H2O2 concentration were reduced and lipid peroxidation decreased in pretreated plants. CC pretreatment also accelerated accumulation
of proline, maintained higher Ψw and RWC, deferred leaf water loss during drought stress and retarded the drop in proline
concentration after rewatering. Consequently, drought-induced decreases in Fm/F0, Fv/Fm, ΦPS2, qP, and A and increase in qNP were inhibited and the recovery of photosynthesis after rewatering was quicker in pretreated plants. Although differences
in Fv/Fm, ΦPS2 and qP between treatments were not significant, there was a general trend that the effects of CC increased with the rise of its
concentrations. The data suggested that 2.1 mM of CC be suitable for alleviating lipid peroxidation, promoting proline accumulation,
retarding leaf water loss and improving photosynthesis of R. glutinosa seedlings under drought stress. 相似文献
18.
We examined the elongation rate, water status and solute accumulation in the seminal roots of wheat seedlings (Triticum aestivum L.) that were growing in vermiculite with a water potential (Ψw) ranging from −0 03 to −1 10 MPa. The elongation rate of the primary seminal root was similar to that of the first pair of
seminal roots but that of the second pair of seminal roots was lower at all values of Ψw tested. The elongation rate was highest in vermiculite with a Ψw of −0.03 MPa but did not decrease significantly until the Ψw was reduced to −0.15 MPa. Further reductions in Ψw reduced the elongation rate markedly. The Ψw of mature tissues was always similar to that of vermiculite. The osmotic potential (Ψo) decreased to the same extent as the decrease in Ψw. Thus, the turgor pressure (Ψp) remained unchanged even in vermiculite with a low Ψw. In elongating tissues, Ψw and Ψo were far lower than they were in mature tissues and, thus, reductions in turgor were not significant. Even when the Ψw of vermiculite changed, there were no consistent changes in terms of a difference in Ψw between elongating plus mature tissues and vermiculite. There were also no consistent changes in levels of osmotica, calculated
using the van’t Hoff’s law, in the elongating tissues but the levels in mature tissues increased in vermiculite with a low
Ψw. Our results suggest that (1) reductions in root elongation in vermiculite with a low Ψw were caused by reductions in the extensibility and/or increases in the yield threshold of cell walls and by reductions in
the hydraulic conductivity of the tissues; and (2) a seminal root regulates its growth to keep turgor pressure unchanged. 相似文献
19.
Involvement of betacyanin in chilling-induced photoinhibition in leaves of <Emphasis Type="Italic">Suaeda salsa</Emphasis> 总被引:1,自引:0,他引:1
Seeds of Suaeda salsa were cultured in dark for 3 d and betacyanin accumulation in seedlings was promoted significantly. Then the seedlings with
accumulated betacyanin (C+B) were transferred to 14/10 h light/dark and used for chilling treatment 15 d later. Photosystem
2 (PS2) photochemistry, D1 protein content, and xanthophyll cycle during the chilling-induced photoinhibition (exposed to
5 °C at a moderate photon flux density of 500 μmol m−2 s−1 for 3 h) and the subsequent restoration were compared between the C+B seedlings and the control (C) ones. The maximal efficiency
of PS2 photochemistry (Fv/Fm), the efficiency of excitation energy capture by open PS2 centres (Fv′/Fm′), and the yield of PS2 electron transport (ΦPS2) of the C+B and C leaves both decreased during photoinhibition. However, smaller decreases in Fv/Fm, Fv′/Fm′, and ΦPS2 were observed in the C+B leaves than in C ones. At the same time, the deepoxidation state of xanthophyll cycle, indicated
by (A+Z)/(V+A+Z) ratio, increased rapidly but the D1 protein content decreased considerably during the photoinhibition. The
increase in rate of (A+Z)/(V+A+Z) was higher but the D1 protein turnover was slower in C+B than C leaves. After photoinhibition
treatment, the plants were transferred to a dim irradiation (10 μmol m−2 s−1) at 25 °C for restoration. During restoration, the chlorophyll (Chl) fluorescence parameters, D1 protein content, and xanthophyll
cycle components relaxed gradually, but the rate and level of restoration in the C+B leaves was greater than those in the
C leaves. The addition of betacyanins to the thylakoid solution in vitro resulted in similar changes of Fv/Fm, D1 protein content, and (A+Z)/(V+A+Z) ratio during the chilling process. Therefore, betacyanin accumulation in S. salsa seedlings may result in higher resistance to photoinhibition, larger slowing down of D1 protein turnover, and enhancement
of non-radiative energy dissipation associated with xanthophyll cycle, as well as in greater restoration after photoinhibition
than in the control when subjected to chilling at moderate irradiance. 相似文献
20.
de Magalhães Erismann N Caruso Machado E Sant' Anna Tucci ML 《Photosynthesis research》2008,96(2):163-172
Photosynthetic limitations under moderate water deficit were evaluated in ‘Valência’ orange trees grafted on three different
rootstocks, in pots. Net CO2 assimilation rate (A
N), stomatal conductance (g
s), and photosystem II (PS II) operating efficiency (
) in response to changing intercellular CO2 partial pressure (C
i) were analyzed under controlled conditions. Drought decreased A
N and g
s, whereas remained unchanged. This resulted in a higher ratio between electron transport rate (ETR) and gross CO2 assimilation rate (A
G). Since the comparison of A
N–C
i gas exchange curves can lead to incorrect conclusions, a normalization of C
i values () of stressed leaves was applied. Then, the relationship established for irrigated trees between the ETR/A
G ratio and C
i was used to estimate the from ETR/A
G ratios measured under water stress. The response of A
N to suggests that the CO2 diffusional restriction is the main factor that limits photosynthesis in orange leaves under moderate water deficit. 相似文献