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1.
Differential absorbance measurements and fluorometry were applied to examine the impact of dicyclohexylcarbodiimide (DCCD,
an inhibitor of H+ conductance in thylakoid membranes) and nigericin (a K+/H+ antiporter) on photoinduced redox state transients of chlorophyll P700 and the induction curves of chlorophyll fluorescence
in pea (Pisum sativum L., cv. Premium) leaves. The treatment of leaves with DCCD strongly modified the kinetics of P700+ absorbance changes (ΔA
810) by promoting rapid photooxidation of P700. These characteristic changes in ΔA
810 induction kinetics and P700+ accumulation did not appear when the leaves were treated with DCCD in the presence of nigericin. In addition to opposite
modifications of ΔA
810 kinetics evoked by permeability-modifying agents, the fluorescence induction curves differed conspicuously depending on leaf
incubation in DCCD solutions with or without nigericin. The observed modifications of fluorescence induction curves and ΔA
810 indicate that DCCD suppresses electron transport from photosystem II (PSII) to P700, whereas this inhibition is removed by
nigericin. The results suggest that slowing down of the electron transport rate in the presence of DCCD was caused by elevation
of ΔpH in thylakoids. The prevention of pH gradient formation in the presence of protonophore lowered also the steady-state
P700+ level in far-red irradiated leaves and accelerated the subsequent dark reduction of P700. These findings indicate that PSI-driven
cyclic electron flow is accelerated after the removal of the pH gradient. 相似文献
2.
Absorbance changes ΔA
810 were measured in pea (Pisum sativum L., cv. Premium) leaves to track redox transients of chlorophyll P700 during and after irradiation with far red (FR) light
under various preillumination conditions in the absence and presence of inhibitors and protonophorous uncoupler of photosynthetic
electron transport. It was shown that cyclic electron transport (CET) in chloroplasts of pea leaves operates at its highest
rate after preillumination of leaves with white light and is strongly suppressed after preillumination with FR light. The
FR light-induced suppression was partly released during prolonged dark adaptation. Upon FR illumination of dark-adapted leaves,
the induction of CET was observed, during which CET activity increased to the peak from the low level and then decreased gradually.
The kinetics of P700 oxidation induced by FR light of various intensities in leaves preilluminated with white light were fit
to empirical sigmoid curves containing two variables. In leaves treated with a protonophore FCCP, the amplitude of FR light-induced
changes ΔA
810 was strongly suppressed, indicating that the rate of CET is controlled by the pH gradient across the thylakoid membrane. 相似文献
3.
In vivo temperature dependence of cyclic and pseudocyclic electron transport in barley 总被引:4,自引:3,他引:1
The effect of temperature on the rate of electron transfer through photosystems I and II (PSI and PSII) was investigated
in leaves of barley (Hordeum vulgare L.). Measurements of PSI and PSII photochemistry were made in 21% O2 and in 2% O2, to limit electron transport to O2 in the Mehler reaction. Measurements were made in the presence of saturating CO2 concentrations to suppress photorespiration. It was observed that the O2 dependency of PSII electron transport is highly temperature dependent. At 10 °C, the quantum yield of PSII (ΦPSII) was insensitive
to O2 concentration, indicating that there was no Mehler reaction operating. At high temperatures (>25 °C) a substantial reduction
in ΦPSII was observed when the O2 concentration was reduced. However, under the same conditions, there was no effect of O2 concentration on the ΔpH-dependent process of non-photochemical quenching. The rate of electron transport through PSI was
also found to be independent of O2 concentration across the temperature range. We conclude that the Mehler reaction is not important in maintaining a thylakoid
proton gradient that is capable of controlling PSII activity, and present evidence that cyclic electron transport around PSI
acts to maintain membrane energisation at low temperature.
Received: 6 July 2000 / Accepted: 3 August 2000 相似文献
4.
Detelin Stefanov Elisaveta Stoimenova Galina Marinova Bistra Ivanova Aglika Edreva 《Acta Physiologiae Plantarum》2012,34(1):181-190
Altered photosynthetic reactions in cucumber mosaic virus (CMV) inoculated leaves of virus resistant lines L113 and L57 and
susceptible pepper (Capsicum annuum L.) plants cv. Albena grown in controlled environment and in the field were investigated. The CMV inoculated leaves of virus
resistant lines developed different symptoms—necrotic local lesions on L113 and chlorotic spots on L57 while the same leaves
of susceptible cv. Albena were symptomless. The changes in Photosystem II (PSII) and PSI electron transport were evaluated
by chlorophyll fluorescence, and far-red (FR) light induced leaf absorbance A
810–860. CMV infection caused a decrease in maximal PSII quantum yield, F
v/F
m, in susceptible leaves. Increased non-photochemical fluorescence quenching in CMV-inoculated leaves of both resistant lines
were observed. In CMV-inoculated leaves of all tested plants FR light induced P700 oxidation was decreased. In the present
study, the viral-infected pepper plants grown in controlled environment to avoid the effects of abiotic factors were used
as model system that allow us to investigate the differences in leaf senescence in CMV-inoculated leaves of susceptible and
resistant pepper lines expressing different symptoms. Earlier leaf falls of inoculated leaves as a result of accelerated leaf
senescence is important for building successful secondary virus resistance strategy following fast responses such as hypersensitive
reaction. 相似文献
5.
By simultaneously analyzing the chlorophyll a fluorescence transient and light absorbance at 820 nm as well as chlorophyll fluorescence quenching, we investigated the
effects of different photon flux densities (0, 15, 200 μmol m−2 s−1) with or without 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) on the repair process of cucumber (Cucumis sativus L.) leaves after treatment with low temperature (6°C) combined with moderate photon flux density (200 μmol m−2 s−1) for 6 h. Both the maximal photochemical efficiency of Photosystem II (PSII) (F
v/F
m) and the content of active P700 (ΔI/I
o) significantly decreased after chilling treatment under 200 μmol m−2 s−1 light. After the leaves were transferred to 25°C, F
v/F
m recovered quickly under both 200 and 15 μmol m−2 s−1 light. ΔI/I
o recovered quickly under 15 μmol m−2 s−1 light, but the recovery rate of ΔI/I
o was slower than that of F
v/F
m. The cyclic electron transport was inhibited by chilling-light treatment obviously. The recovery of ΔI/I
o was severely suppressed by 200 μmol m−2 s−1 light, whereas a pretreatment with DCMU effectively relieved this suppression. The cyclic electron transport around PSI recovered
in a similar way as the active P700 content did, and the recovery of them was both accelerated by pretreatment with DCMU.
The results indicate that limiting electron transport from PSII to PSI protected PSI from further photoinhibition, accelerating
the recovery of PSI. Under a given photon flux density, faster recovery of PSII compared to PSI was detrimental to the recovery
of PSI or even to the whole photosystem. 相似文献
6.
Photosynthetic Responses of Leaves to Water Stress, Expressed by Photoacoustics and Related Methods : II. The Effect of Rapid Drought on the Electron Transport and the Relative Activities of the Two Photosystems
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The effect of rapid dehydration of detached tobacco leaves (Nicotiana tabacum L.) on the photochemical apparatus of photosynthesis was studied in vivo by a combination of methods: photoacoustics, chlorophyll a fluorescence, and cytochrome f difference spectroscopy. It was shown that the inhibition of gross O2 evolution was mainly caused by inactivation of PSII: (a) The saturation curve of cytochrome-f photooxidation by farred (>710 nanometers) light was resistant to the stress, leading to the conclusion that photosystem I (PSI) was largely unaffected by the stress. (b) The extent of the chlorophyll a variable fluorescence arising from photosystem II (PSII) decreased with the progression of the stress, but was largely unaffected when the leaf was preincubated with electron donors to PSII, such as hydroxylamine. It is concluded that the drought damage to PSII occurred on the photooxidative side. Despite the extensive inhibition of PSII and the relative preservation of PSI, the apparent PSII/PSI activity balance was somewhat larger in stressed leaves than in the control, as indicated by photoacoustic measurements of Emerson enhancement. These measurements were performed continuously under conditions which favor transitions to either state 1 or 2, showing that the transition to state 2 was considerably inhibited. Simultaneous measurements of chlorophyll fluorescence induction at 680 and 730 mm at room temperature were also used to probe changes in energy distribution between PSII and PSI and indicated that the transition from a dark adapted state to state 2 was also affected in water-stressed leaves. The saturation curve of the far-red light effect in Emerson enhancement was not changed by the stress, giving another independent evidence for the drought resistance of PSI activity. This apparent preservation of the imbalance in photochemical activities in favor of PSII, despite the fact that PSII is strongly inhibited, and PSI is not, supports a previous suggestion that the electron transfer between the two photosystems is not random but that a large extent of PSII and PSI units are specifically linked. 相似文献
7.
The kinetics of changes in photosystem I (PSI), photosystemII (PSII), and whole chain (PSII and PSI) electron transport,chlorophyll fluorescence parameters, the capacity to bind atrazineand the polypeptide profiles of thylakoids isolated from wheatleaves on exposure to a photon flux density of 2000 µmolm2 s1 were determined. Severe and similar levelsof photo-inhibitory damage to both PSII and whole chain electrontransport occurred and were correlated with decreases in theratio of variable to maximal fluorescence, the proportionalcontribution of the rapid a phase of the fluorescence kineticsand the capacity to bind atrazine. Severe photo-inhibition ofelectron transport was not associated with a major loss of chlorophyllor total thylakoid protein. However, a small decrease in a 70kDa polypeptide together with increases in a number of low molecularmass polypeptides (824 kDa) occurred. Phosphorylation of thylakoid polypeptides alleviated photo-inhibitionof PSII electron transport but stimulated photoinhibitory damageto whole chain electron transport. The consequences of suchphosphorylation-induced effects on photoinhibition in vivo areconsidered. Key words: Chlorophyll fluorescence, electron transport, photo-inhibition, protein phosphorylation, thylakoid membranes, wheat (Triticum aestivum) 相似文献
8.
Garstka M Venema JH Rumak I Gieczewska K Rosiak M Koziol-Lipinska J Kierdaszuk B Vredenberg WJ Mostowska A 《Planta》2007,226(5):1165-1181
The effect of dark-chilling and subsequent photoactivation on chloroplast structure and arrangements of chlorophyll–protein
complexes in thylakoid membranes was studied in chilling-tolerant (CT) pea and in chilling-sensitive (CS) tomato. Dark-chilling
did not influence chlorophyll content and Chl a/b ratio in thylakoids of both species. A decline of Chl a fluorescence intensity and an increase of the ratio of fluorescence intensities of PSI and PSII at 120 K was observed after
dark-chilling in thylakoids isolated from tomato, but not from pea leaves. Chilling of pea leaves induced an increase of the
relative contribution of LHCII and PSII fluorescence. A substantial decrease of the LHCII/PSII fluorescence accompanied by
an increase of that from LHCI/PSI was observed in thylakoids from chilled tomato leaves; both were attenuated by photoactivation.
Chlorophyll fluorescence of bright grana discs in chloroplasts from dark-chilled leaves, detected by confocal laser scanning
microscopy, was more condensed in pea but significantly dispersed in tomato, compared with control samples. The chloroplast
images from transmission-electron microscopy revealed that dark-chilling induced an increase of the degree of grana stacking
only in pea chloroplasts. Analyses of O-J-D-I-P fluorescence induction curves in leaves of CS tomato before and after recovery
from chilling indicate changes in electron transport rates at acceptor- and donor side of PS II and an increase in antenna
size. In CT pea leaves these effects were absent, except for a small but irreversible effect on PSII activity and antenna
size. Thus, the differences in chloroplast structure between CS and CT plants, induced by dark-chilling are a consequence
of different thylakoid supercomplexes rearrangements.
Dedicated to Prof. Zbigniew Kaniuga on the 25th anniversary of his initiation of studies on chilling-induced stress in plants. 相似文献
9.
The effects of temperature (25–45 °C) and pH (7.5–5.5) on photosystem (PS) 2 was studied in spinach (Spinacia oleracea L.) thylakoid membranes using chlorophyll a fluorescence induction kinetics. In high temperature and low pH treated thylakoid membranes a decline in the variable to
maximum fluorescence ratio (Fv/Fm) and PS 2 electron transport rate were observed. More stacking in thylakoid membranes, studied by digitonin fractionation
method, was observed at low pH, while the degree of unstacking increased under high temperature conditions. We conclude that
the change in pH does not significantly affect the donor/acceptor side of PS 2 while high temperature does. Fluorescence emission
spectra at 77 K indicated that low pH is associated with energy redistribution between the two photosystems while high temperature
induced changes do not involve energy re-distribution. We suggest that both, high temperature and low pH, show an inhibitory
effect on PS 2 but their mechanisms of action are different. 相似文献
10.
V. G. Ladygin 《Biology Bulletin》2007,34(3):248-258
Xantha-702 mutant of cotton (Gossypium hirsutum L.) proved to have blocked synthesis of 5-aminolevulinic acid in the light. Accordingly, mutant leaves accumulated 2–5% chlorophyll of baseline. Mutant plants demonstrated disturbed production of pigment-protein complexes of photosystems I (PSI) and II (PSII) and generation of the chloroplast membrane system blocked at the early stages, largely, at the stages of vesicles and single short thylakoid. The functional activity of the PSI and PSII reaction centers was close to zero. Only the chlorophyll a/b light-harvesting complexes of PSI and PSII with the chlorophyll fluorescence peaks at 728 and 681 nm, respectively, were produced in the xantha-702 mutant. We propose that the genetic block of 5-aminolevunilic acid biosynthesis in the light in the xantha-702 mutant disturbs the formation and activity of the complexes of the reaction centers of PS-I and PS-II and inhibits the development of the whole membrane system of chloroplasts. 相似文献
11.
The polyphasic patterns of fluorescence induction rise in pea leaves in vivo and after the treatment with ionophores have
been studied using a Plant Efficiency Analyzer. To analyze in detail photosystem II (PS II) electron transfer processes, an
extended PS II model was applied, which included the sums of exponential functions to specify explicitly the light-driven
formation of the transmembrane electric potential (ΔΨ(t)) as well as pH in the lumen (pHL(t)) and stroma (pHS(t)). PS II model parameters and numerical coefficients in ΔΨ(t), pHL(t), and pHS(t) were evaluated to fit fluorescence induction data for different experimental conditions: leaf in vivo or after ionophore
treatment at low or high light intensity. The model imitated changes in the pattern of fluorescence induction rise due to
the elimination of transmembrane potential in the presence of ionophores, when ΔΨ = 0 and pHL(t), pHS(t) changed to small extent relative to control values in vivo, with maximum ΔΨ(t) ∼ 90 mV and ΔΨ(t) ∼ 40 mV for the stationary state at ΔpH ≅ 1.8. As the light intensity was increased from 300 to 1200 μmol m−2 s−1, the heat dissipation rate constants increased threefold for nonradiative recombination of P680+Phe− and by ∼30% for P680+QA−. The parameters ΔΨ, pHS and pHL were analyzed as factors of PS II redox state populations and fluorescence yield. The kinetic mechanism of fluorescence quenching
is discussed, which is related with light-induced lumen acidification, when +QA− and P680+ recombination probability increases to regulate the QA reduction. 相似文献
12.
Igor N. Stadnichuk Evgeny P. Lukashev Irina V. Elanskaya 《Photosynthesis research》2009,99(3):227-241
The features of the two types of short-term light-adaptations of photosynthetic apparatus, State 1/State 2 transitions, and
non-photochemical fluorescence quenching of phycobilisomes (PBS) by orange carotene-protein (OCP) were compared in the cyanobacterium
Synechocystis sp. PCC 6803 wild type, CK pigment mutant lacking phycocyanin, and PAL mutant totally devoid of phycobiliproteins. The permanent
presence of PBS-specific peaks in the in situ action spectra of photosystem I (PSI) and photosystem II (PSII), as well as
in the 77 K fluorescence excitation spectra for chlorophyll emission at 690 nm (PSII) and 725 nm (PSI) showed that PBS are
constitutive antenna complexes of both photosystems. The mutant strains compensated the lack of phycobiliproteins by higher
PSII content and by intensification of photosynthetic linear electron transfer. The detectable changes of energy migration
from PBS to the PSI and PSII in the Synechocystis wild type and the CK mutant in State 1 and State 2 according to the fluorescence excitation spectra measurements were not
registered. The constant level of fluorescence emission of PSI during State 1/State 2 transitions and simultaneous increase
of chlorophyll fluorescence emission of PSII in State 1 in Synechocystis PAL mutant allowed to propose that spillover is an unlikely mechanism of state transitions. Blue–green light absorbed by
OCP diminished the rout of energy from PBS to PSI while energy migration from PBS to PSII was less influenced. Therefore,
the main role of OCP-induced quenching of PBS is the limitation of PSI activity and cyclic electron transport under relatively
high light conditions. 相似文献
13.
Photoinduced changes in the redox state of photosystem I (PSI) primary donor, chlorophyll P700 were studied by measuring differential absorbance changes of pea leaves at 810 nm minus 870 nm (ΔA 810). The kinetics of ΔA 810 induced by 5-s pulses of white light were strongly affected by preillumination. In dark-adapted leaves, the light pulse caused a transient oxidation of P700 and its subsequent reduction. An identical pulse, applied after 30-s preillumination with white light, induced sequential appearance of two peaks of P700 oxidation. These kinetic differences of ΔA 810 reflect regulatory changes of electron flow on the donor and acceptor sides of PSI induced by illumination of leaf for 20–40 s. The amplitude of ΔA 810 second peak depended nonmonotonically on the dark interval preceding illumination: it increased with the length of dark period in the range 3–10 s and decreased upon longer dark intervals. The second wave of ΔA 810 disappeared after the treatment with combination of ionophores preventing ΔpH and electric potential formation at the thylakoid membrane. In leaves treated with monensin eliminating ΔpH only, the ΔA 810 signals become incompletely reversible and were characterized by slow relaxation in darkness. The results indicate an important role of electrochemical proton gradient in generation of the second wave of light-induced P700 oxidation. 相似文献
14.
Non-photochemical quenching of chlorophyll fluorescence (NPQ) and quantum yield of photosystem II (PSII) were studied with
intact mesophyll chloroplasts of maize (Zea mays L.) during the initial minutes of illumination using the pulse-modulated chlorophyll fluorescence technique. Non-photochemical
quenching was rapidly reversible in the dark at any point during illumination, which is indicative of energy-dependent dissipation
of energy (mediated via thylakoid ΔpH changes and ascorbate-dependent synthesis of zeaxanthin). In chloroplasts suspensions
including 15 mM ascorbate in the medium, with addition of oxaloacetate and pyruvate, the PSII yield, rate of reduction of
oxaloacetate and phosphorylation of pyruvate reached a maximum after approximately 2 min of illumination. Under these conditions,
which promote phosphorylation and a decreased ΔpH across the thylakoid membrane, NPQ rose to a maximum after 2–3 min of illumination,
dropped to a minimum after about 6 min, and then increased to a steady-state level. A rather similar pattern was observed
when leaves were illuminated following a 30-min dark period. Providing chloroplasts with higher levels of ascorbate (60 mM),
prevented the transient drop in NPQ. Anaerobic conditions or addition of potassium cyanide caused a decrease in PSII yield,
providing evidence for operation of the ascorbate-dependent Mehler-peroxidase reaction. These conditions also strongly suppressed
the transient drop in NPQ. Dithiothreitol, an inhibitor of violaxanthin de-epoxidase, caused a large drop in NPQ even in the
presence of high levels of ascorbate. The results suggest that the decline of NPQ occurs in response to an increase in lumen
pH after initiation of phosphorylation, that this decline can be suppressed by conditions where ascorbate is not limiting
for violaxanthin de-epoxidase, and that the increase of NPQ after such a decline is the result of development of energy dissipation
in PSII reaction centers.
Received: 13 August 1999 / Accepted: 17 September 1999 相似文献
15.
The primary stable products of photosynthetic electron flow are NADPH and ATP. Stoichiometry of their production depends
on the ratio of protons pumped across the thylakoid membrane to electrons passed through the electron transport pathway (H+/e− ratio). Flexible requirements of the ATP/NADPH ratio by various assimilatory reactions in chloroplasts must be fulfilled
by the H+/e− ratio during the electron flow. In addition to the well-known role of ΔpH during ATP synthesis, ΔpH also functions as a trigger
of the down-regulation of photosystem II (PSII) photochemistry. Excessive light energy is safely dissipated as heat by this
regulatory process to suppress the generation of toxic reactive oxygen species. Thus, regulation of the H+/e− ratio may function in the photoprotection, as well as in the regulation of the ATP/NADPH production ratio. It has long been
the consensus that the H+/e− ratio can be controlled by regulating the proton-transporting Q-cycle in the cytochrome b
6
f complex and by the cyclic electron flow around photosystem I (PSI). Despite the possible physiological importance and the
long history of interest, the molecular identity of Q-cycle regulation and the cyclic electron flow around PSI have been remained
unclear. The recent improvements in research tools, including the genetic approach using chlorophyll fluorescence imaging
and establishment of the chloroplast transformation technique, are providing new insights into classical topics. In this review,
we focus on regulation of the H+/e− ratio especially from the view of photosynthetic regulation.
Received: August 2, 2001 / Accepted: October 1, 2001 相似文献
16.
Eight chlorophyll b deficient nuclear mutants of pea (Pisum sativum L.) have been characterized by low temperature fluorescence emission spectra of their leaves and by the ultrastructure, photochemical activities and polypeptide compositions of the thylakoid membranes. The room temperature fluorescence induction kinetics of leaves and isolated thylakoids have also been recorded. In addition, the effects of Mg2+ on the fluorescence kinetics of the membranes have been investigated. The mutants are all deficient in the major polypeptide of the light-harvesting chlorophyll a/b protein of photosystem II. The low temperature fluorescence emission spectra of aurea-5106, xantha-5371 and –5820 show little or no fluorescence around 730 nm (photosystem I fluorescence), but possess maxima at 685 and 695 nm (photosystem II fluorescence). These three mutants have low photosystem II activities, but significant photosystem I activities. The long-wavelength fluorescence maximum is reduced for three other mutants. The Mg2+ effect on the variable component of the room temperature fluorescence (685 nm) induction kinetics is reduced in all mutants, and completely absent in aurea-5106 and xantha-5820. The thylakoid membranes of these 2 mutants are appressed pairwise in 2-disc grana of large diameter. Chlorotica-1-206A and–130A have significant long-wavelength maxima in the fluorescence spectra and show the largest Mg2+ enhancement of the variable part of the fluorescence kinetics. These two mutants have rather normally structured chloroplast membranes, though the stroma regions are reduced. The four remaining mutants are in several respects of an intermediate type.Abbreviations Chl
chlorophyll
- CPI
Chi-protein complex I, Fo, Fv
- Fm
parameters of room temperature chlorophyll fluorescence induction kinetics
- F685, F695 and F-1
components of low temperature chlorophyll emission with maximum at 685, 695 and ca 735 nm, respectively
- PSI
photosystem I
- PSII
photosystem II
- LHCI and LHCII
light-harvesting chlorophyll a/b complexes associated with PSI and PSII, respectively
- SDS
sodium dodecyl sulfate 相似文献
17.
Fluorimetric, photoacoustic, polarographic and absorbance techniques were used to measure in situ various functional aspects of the photochemical apparatus of photosynthesis in intact pea leaves (Pisum sativum L.) after short exposures to a high temperature of 40 ° C. The results indicated (i) that the in-vivo responses of the two photosystems to high-temperature pretreatments were markedly different and in some respects opposite, with photosystem (PS) II activity being inhibited (or down-regulated) and PSI function being stimulated; and (ii) that light strongly interacts with the response of the photosystems, acting as an efficient protector of the photochemical activity against its inactivation by heat. When imposed in the dark, heat provoked a drastic inhibition of photosynthetic oxygen evolution and photochemical energy storage, correlated with a marked loss of variable PSII-chlorophyll fluorescence emission. None of the above changes were observed in leaves which were illuminated during heating. This photoprotection was saturated at rather low light fluence rates (around 10 W · m–2). Heat stress in darkness appeared to increase the capacity for cyclic electron flow around PSI, as indicated by the enhanced photochemical energy storage in far-red light and the faster decay of P
700
+
(oxidized reaction center of PSI) monitored upon sudded interruption of the far-red light. The presence of light during heat stress reduced somewhat this PSI-driven cyclic electron transport. It was also observed that heat stress in darkness resulted in the progressive closure of the PSI reaction centers in leaves under steady illumination whereas PSII traps remained largely open, possibly reflecting the adjustment of the photochemical efficiency of undamaged PSI to the reduced rate of photochemistry in PSII.Abbreviations B1 and B2
fraction of closed PSI and PSII reaction centers, respectively
- ES
photoacoustically measured energy storage
- Fo, Fm and Fs
initial, maximal and steady-state levels of chlorophyll fluorescence
- P700
reaction center of PSI
- PS (I, II)
photosystem (I, II)
- V = (Fs – Fo)/(Fm – Fo)
relative variable chlorophyll fluorescence
We wish to thank Professor R. Lannoye (ULB, Brussels) for the use of this photoacoustic spectrometer and Mrs. M. Eyletters for her help. 相似文献
18.
Down-regulation of linear and activation of cyclic electron transport during drought 总被引:11,自引:0,他引:11
The effects of short-term drought on the regulation of electron transport through photosystems I and II (PSI and PSII) have been studied in Hordeum vulgare L. cv. Chariot. Fluorescence measurements demonstrated that electron flow through PSII decreased in response to both drought and CO2 limitation. This was due to regulation, as opposed to photoinhibition. We demonstrate that this regulation occurs between the two photosystems—in contrast to PSII, PSI became more oxidised and the rate constant for P700 re-reduction decreased under these conditions. Thus, when carbon fixation is inhibited, electron transport is down-regulated to match the reduced requirement for electrons and minimise reactive oxygen production. At the same time non-photochemical quenching (NPQ) increases, alleviating the excitation pressure placed on PSII. We observe an increase in the proportion of PSI centres that are active (i.e. can be oxidised with a saturating flash and then rapidly re-reduced) under the conditions when NPQ is increased. We suggest that these additional centres are primarily involved in cyclic electron transport, which generates the pH to support NPQ and protect PSII.Abbreviations
A
assimilation rate
- Ci
internal CO2 concentration
- ETC
electron transport chain
-
g
stomatal conductance
- FR
far red
-
k
pseudo first-order rate constant for the reduction of oxidised P700
- NPQ
non-photochemical quenching
- P700
primary electron donor of photosystem I
- PSI, PSII
photosystem I, II
- qP
proportion of open PSII centres
- ROS
reactive oxygen species
- pH
pH gradient across the thylakoid membrane
- PSII
quantum yield of photosystem II
An erratum to this article can be found at 相似文献
19.
Fast and slow chlorophyll fluorescence induction curves at high and low actinic visible light, post-illumination changes in fluorescence yield and reflectance changes at 820 nm induced by far-red light were used to characterize the state of PSII and PSI and their electron transport capabilities in chlorophyllous twig cortices of Eleagnus angustifolius L., while corresponding leaves served as controls. Twigs displayed low dark-adapted PSII photochemical efficiencies and particularly low linear electron transport rates when illuminated. In addition, their PSII population was characterized by a high proportion of inactive, non-QB-reducing centers and an incomplete quenching of fluorescence during the slow induction phase. It is suggested that PSII in twigs is an inefficient electron donor to PSI and/or the reductive pentose phosphate cycle. Yet, in spite of this apparent PSII deficiency, pools of intermediate electron carriers and potential PSI activity were more than sufficient to support the observed linear electron transport rates. Moreover, the rate of PSI reduction upon far-red/dark transitions and the magnitude of fluorescence yield increase upon white light/dark transitions were compatible with an efficient electron flow to PSI from stromal donors in the absence of PSII activity. We conclude that corticular chlorenchyma may be actively engaged in cyclic at the expense of a linear electron flow and discuss the possible physiological significance of this finding in conjunction with the particular microenvironmental conditions encountered within twigs. 相似文献
20.
The role of chloroplast NAD(P)H dehydrogenase in protection of tobacco plant against heat stress 总被引:2,自引:0,他引:2
The environmental temperature is one of the mainfactors affecting plant growth and development. Insummer, plants are frequently influenced by hightemperature. In recent years, global temperature wasremarkably elevated accompanied with the climaticchanges,… 相似文献