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1.
The assembly, organization and function of the photosynthetic apparatus was investigated in the wild type and a chlorophyll
(Chl) b-less mutant of the unicellular green alga Chlamydomonas reinhardtii, generated via DNA insertional mutagenesis. Comparative analyses were undertaken with cells grown photoheterotrophically
(acetate), photomixotrophically (acetate and HCO −
3) or photoautotrophically (HCO −
3). It is shown that lack of Chl b diminished the photosystem-II (PSII) functional Chl antenna size from 320 Chl ( a and b) to about 95 Chl a molecules. However, the functional Chl antenna size of PSI remained fairly constant at about 290 Chl molecules, independent
of the presence of Chl b. Western blot and kinetic analyses suggested the presence of inner subunits of the Chl a-b light-harvesting complex of PSII (LHCII) and the entire complement of the Chl a-b light-harvesting complex of PSI (LHCI) in the mutant. It is concluded that Chl a can replace Chl b in the inner subunits of the LHCII and in the entire complement of the LHCI. Growth of cells on acetate as the sole carbon
source imposes limitations in the photon-use efficiency and capacity of photosynthesis. These are manifested as a lower quantum
yield and lower light-saturated rate of photosynthesis, and as lower variable to maximal (F v/F max) chlorophyll fluorescence yield ratios. This adverse effect probably originates because acetate shifts the oxidation-reduction
state of the plastoquinone pool, and also because it causes a decrease in the amount and/or activity of Rubisco in the chloroplast.
Such limitations are fully alleviated upon inclusion of an inorganic carbon source (e.g. bicarbonate) in the cell growth medium.
Further, the work provides evidence to show that transformation of green algae can be used as a tool by which to generate
mutants exhibiting a permanently truncated Chl antenna size and a higher (per Chl) photosynthetic productivity of the cells.
Received: 10 November 1999 / Accepted: 22 December 1999 相似文献
2.
Using iron stress to reduce the total amount of light-harvesting and electron transport components per unit leaf area, the influence of light-harvesting and electron transport capacity on photosynthesis in sugar beet ( Beta vulgaris L. cv F58-554H1) leaves was explored by monitoring net CO 2 exchange rate ( P) in relation to changes in the content of Chl. In most light/CO2 environments, and especially those with high light (≥1000 microeinsteins photosynthetically active radiation per square meter per second) and high CO2 (≥300 microliters CO2 per liter air), P per area was positively correlated with changes in Chl (a + b) content (used here as an index of the total amount of light-harvesting and electron transport components). This positive correlation of P per area with Chl per area was obtained not only with Fe-deficient plants, but also over the normal range of variation in Chl contents found in healthy, Fe-sufficient plants. For example, light-saturated P per area at an ambient CO2 concentration close to normal atmospheric levels (300 microliters CO2 per liter air) increased by 36% with increase in Chl over the normal range, i.e. from 40 to 65 micrograms Chl per square centimeter. Iron deficiency-mediated changes in Chl content did not affect dark respiration rate or the CO2 compensation point. The results suggest that P per area of sugar beet may be colimited by light-harvesting and electron transport capacity (per leaf area) even when CO2 is limiting photosynthesis as occurs under field conditions. 相似文献
3.
The photon use efficiencies and maximal rates of photosynthesis in Dunaliella salina (Chlorophyta) cultures acclimated to
different light intensities were investigated. Batch cultures were grown to the mid-exponential phase under continuous low-light
(LL: 100 μmol photon m -2 s -1) or high-light (HL: 2000 μmol photon m -2 s -1) conditions. Under LL, cells were normally pigmented (deep green) containing ∼500 chlorophyll (Chl) molecules per photosystem
II (PSII) unit and ∼250 Chl molecules per photosystem I (PSI). HL-grown cells were yellow-green, contained only 60 Chl per
PSII and 100 Chl per PSI and showed signs of chronic photoinhibition, i.e., accumulation of photodamaged PSII reaction centers
in the chloroplast thylakoids. In LL-grown cells, photosynthesis saturated at ∼200 μmol photon m -2 s -1 with a rate (P max) of ∼100 mmol O 2 (mol Chl) -1 s -1. In HL-grown cells, photosynthesis saturated at much higher light intensities, i.e. ∼2500 μmol photon m -2 s -1, and exhibited a three-fold higher P max (∼300 mmol O 2 (mol Chl) -1 s -1) than the normally pigmented LL-grown cells. Recovery of the HL-grown cells from photoinhibition, occurring prior to a light-harvesting
Chl antenna size increase, enhanced P max to ∼675 mmol O 2 (mol Chl) -1 s -1. Extrapolation of these results to outdoor mass culture conditions suggested that algal strains with small Chl antenna size
could exhibit 2–3 times higher productivities than currently achieved with normally pigmented cells.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
4.
A computer model comprising light reactions, electron–proton transport, enzymatic reactions, and regulatory functions of C 3 photosynthesis has been developed as a system of differential budget equations for intermediate compounds. The emphasis is
on electron transport through PSII and PSI and on the modeling of Chl fluorescence and 810 nm absorptance signals. Non-photochemical
quenching of PSII excitation is controlled by lumenal pH. Alternative electron transport is modeled as the Mehler type O 2 reduction plus the malate-oxaloacetate shuttle based on the chloroplast malate dehydrogenase. Carbon reduction enzymes are
redox-controlled by the ferredoxin–thioredoxin system, sucrose synthesis is controlled by the fructose 2,6-bisphosphate inhibition
of cytosolic FBPase, and starch synthesis is controlled by ADP-glucose pyrophosphorylase. Photorespiratory glycolate pathway
is included in an integrated way, sufficient to reproduce steady-state rates of photorespiration. Rate-equations are designed
on principles of multisubstrate-multiproduct enzyme kinetics. The parameters of the model were adopted from literature or
were estimated from fitting the photosynthetic rate and pool sizes to experimental data. The model provided good simulations
for steady-state photosynthesis, Chl fluorescence, and 810 nm transmittance signals under varying light, CO 2 and O 2 concentrations, as well as for the transients of post-illumination CO 2 uptake, Chl fluorescence induction and the 810 nm signal. The modeling shows that the present understanding of photosynthesis
incorporated in the model is basically correct, but still insufficient to reproduce the dark-light induction of photosynthesis,
the time kinetics of non-photochemical quenching, ‘photosynthetic control’ of plastoquinone oxidation, cyclic electron flow
around PSI, oscillations in photosynthesis. The model may find application for predicting the results of gene transformations,
the analysis of kinetic experimental data, the training of students. 相似文献
5.
Spectrophotometric and kinetic measurements were applied to yield photosystem (PS) stoichiometries and the functional antenna size of PSI, PSII α, and PSII β in Zea mays chloroplasts in situ. Concentrations of PSII and PSI reaction centers were determined from the amplitude of the light-induced absorbance change at 320 and 700 nm, which reflect the photoreduction of the primary electron acceptor Q of PSII and the photooxidation of the reaction center P700 of PSI, respectively. Determination of the functional chlorophyll antenna size ( N) for each photosystem was obtained from the measurement of the rate of light absorption by the respective reaction center. Under the experimental conditions employed, the rate of light absorption by each reaction center was directly proportional to the number of light-harvesting chlorophyll molecules associated with the respective photosystem. We determined NP700 = 195, Nα = 230, Nβ = 50 for the number of chlorophyll molecules in the light-harvesting antenna of PSI, PSII α, and PSII β, respectively. The above values were used to estimate the PSII/PSI electron-transport capacity ratio (C) in maize chloroplasts. In mesophyll chloroplasts C > 1.4, indicating that, under green actinic excitation when Chl a and Chl b molecules absorb nearly equal amounts of excitation, PSII has a capacity to turn over electrons faster than PSI. In bundle sheath chloroplasts C < 1, suggesting that such chloroplasts are not optimally poised for linear electron transport and reductant generation. 相似文献
6.
Geum montanum L. is an alpine plant usually found at altitudes between 1700 and 2600 m. Its wintergreen leaves can be subjected to very
low temperatures and at the same time receive high photon flux densities at the beginning of the growth season when the snow
melts. We report results of a study, performed with classical methods of biophysics, showing that leaves of G. montanum were remarkably tolerant to sunlight even at low temperatures. This tolerance results from the interplay of photorespiration
and CO 2 photosassimilation. When temperatures approach 0°C, responses include stomatal opening and CO 2 uptake even under desiccation stress. This permits linear electron transport that is sufficient to avoid the excessive reduction
of the electron transport chain which is known to lead to photodamage. In addition, excitation energy was shifted from photosystem
(PS)II to PSI which is a very efficient energy quencher. Sensitivity of P700 in PSI to oxidation by far-red light was decreased
and rates of dark reduction of photooxidized P700 were increased by actinic illumination, suggesting activation of cyclic
electron transport. Consistent with this, far-red light was able to decrease the quantum yield of PSII (measured by the F
v/ F
m ratio of chlorophyll fluorescence). We suggest that cyclic electron transport decreases the lumenal pH under strong light.
In the presence of zeaxanthin, this increases energy dissipation at the PSII level. At low temperatures, P700 remained strongly
oxidized under high irradiation while the primary electron acceptor of PSII, Q A, was largely reduced. This shows efficient control of electron transport presumably at the level of the cytochrome b/f complex
and suggests formation of a protective transthylakoid proton gradient even when linear electron transport is much reduced
in the cold. Thus, several mechanisms cooperate to effectively protect the photosynthetic apparatus of G. montanum from photodamage. We see no indication of destructive “photostress” in this species during the growth season under alpine
low-temperature and drought conditions.
Received: 2 March 1998 / Accepted: 7 January 1999 相似文献
7.
Anacystis nidulans cells grown under high (3%) CO 2 partial pressure have greater phycocyanin to chlorophyll ratio (Phc/Chl) relative to cells grown under low (0.2%) CO 2 tension (Eley (1971) Plant Cell Physiol 12: 311-316). Absorbance difference spectrophotometry of A. nidulans thylakoid membranes in the ultraviolet (Δ A320) and red (Δ A700) regions of the spectrum reveal photosystem II/photosystem I (PSII/PSI) reaction center ratio (RCII/RCI) changes that parallel those of Phc/Chl. For cells growing under 3% CO 2, the Phc/Chl ratio was 0.48 and RCII/RCI = 0.40. At 0.2% CO 2, Phc/Chl = 0.38 and RCII/RCI = 0.24. Excitation of intact cells at 620 nm sensitized RCII at a rate approximately 20 times faster than that of RCI, suggesting that Phc excitation is delivered to RCII only. In the presence of DCMU, excitation at 620 nm induced single exponential RCII photoconversion kinetics, suggesting a one-to-one structural-functional correspondance between phycobilisome and PSII complex in the thylakoid membrane. Therefore, phycobilisomes may serve as microscopic markers for the presence of PSII in the photosynthetic membrane of A. nidulans. Neither the size of individual phycobilisomes nor the Chl light-harvesting antenna of PSI changed under the two different CO 2 tensions during cell growth. Our results are compatible with the hypothesis that, at low CO 2 concentrations, the greater relative amounts of PSI present may facilitate greater rates of ATP synthesis via cyclic electron flow. The additional ATP may be required for the active uptake of CO 2 under such conditions. 相似文献
8.
The photosynthetic linear electron transport rate in excess of that used for CO 2 reduction was evaluated in Sorghum bicolor Moench. [NADP-malic enzyme (ME)-type C 4 plant], Amaranthus cruentus L. (NAD-ME-type C 4 plant) and Helianthus annuus L. (C 3 plant) leaves at different CO 2 and O 2 concentrations. The electron transport rate ( J
F) was calculated from fluorescence using the light partitioning factor (relative PSII cross-section) determined under conditions
where excess electron transport was assumed to be negligible: low light intensities, 500 μmol CO 2 · mol −1 and 2% O 2. Under high light intensities there was a large excess of J
F/4 at 10–100% O 2 in the C 3 plant due to photorespiration, but very little in sorghum and somewhat more in amaranth, showing that photorespiration is
suppressed, more in the NADP-ME- and less in the NAD-ME-type species. It is concluded that when C 4 photosynthesis is limited by supply of atmospheric CO 2 to the C 4 cycle, the C 3 cycle becomes limited by regeneration of ribulose 1,5-bisphosphate (RuBP) which in turn limits RuBP oxygenase activity and
photorespiration. The rate of excess electron transport over that consumed for CO 2 fixation in C 4 plants was very sensitive to the presence of O 2 in the gas phase, rapidly increasing between 0.01 and 0.1% O 2, and at 2% O 2 it was about two-thirds of that at 21% O 2. This shows the importance of the Mehler O 2 reduction as an electron sink, compared with photorespiration in C 4 plants. However, the rate of the Mehler reaction is still too low to fully account for the extra ATP which is needed in C 4 photosynthesis.
Received: 8 November 1997 / Accepted: 26 December 1997 相似文献
9.
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% O 2 and in 2% O 2, to limit electron transport to O 2 in the Mehler reaction. Measurements were made in the presence of saturating CO 2 concentrations to suppress photorespiration. It was observed that the O 2 dependency of PSII electron transport is highly temperature dependent. At 10 °C, the quantum yield of PSII (ΦPSII) was insensitive
to O 2 concentration, indicating that there was no Mehler reaction operating. At high temperatures (>25 °C) a substantial reduction
in ΦPSII was observed when the O 2 concentration was reduced. However, under the same conditions, there was no effect of O 2 concentration on the ΔpH-dependent process of non-photochemical quenching. The rate of electron transport through PSI was
also found to be independent of O 2 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
10.
The contribution of changes in stomatal conductance and metabolism in determining heterogeneous photosynthesis inhibition
during dehydration and abscisic acid (ABA) feeding was investigated using detached leaves of Rosa rubiginosa L. The steady-state and maximal rates of electron transport under a transient high CO 2 concentration were monitored using chlorophyll fluorescence imaging. The decrease in electron transport rate induced by dehydration
and ABA treatment almost reverted to the control rate under transient high CO 2 availability. Therefore, inhibition of photosynthesis was mainly mediated through stomatal closure. However, since reversion
was not complete, a metabolic inhibition was also identified as a decrease in the maximal electron transport rate driven by
carboxylation. Under dehydration or ABA feeding, as under low ambient CO 2 treatment, in 21% or 0.4% O 2, the lower the steady-state electron transport was, the lower was the maximal electron transport rate during transient high
CO 2 availability. We conclude that low CO 2 availability reduced the capacity of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco) to drive electron transport.
The potential contribution of Rubisco deactivation mediated by stomatal closure is discussed.
Received: 1 February 1999 / Accepted: 15 June 1999 相似文献
11.
Plants often regulate the amount and size of light-harvesting antenna (LHCII) to maximize photosynthesis at low light and avoid photodamage at high light. Gas exchange, 77 K chlorophyll fluorescence, photosystem II (PSII) electron transport as well as LHCII protein were measured in leaves irradiated at different light intensities. After irradiance transition from saturating to limiting one leaf photosynthetic rate in some species such as soybean and rice declined first to a low level, then increased slowly to a stable value (V pattern), while in other species such as wheat and pumpkin it dropped immediately to a stable value (L pattern). Saturating pre-irradiation led to significant declines of both 77 K fluorescence parameter F685/F735 and light-limited PSII electron transport rate in soybean but not in wheat leaves, indicating that some LHCIIs dissociate from PSII in soybean but not in wheat leaves. The L pattern of LHCII-decreased rice mutant and the V pattern of its wild type demonstrate that the V pattern is linked to dissociation/reassociation of some LHCIIs from/to PSII. 相似文献
12.
Barley ( Hordeum vulgare L.) plants were grown at different photon flux densities ranging from 100 to 1800 μmol m −2 s −1 in air and/or in atmospheres with reduced levels of O 2 and CO 2. Low O 2 and CO 2 partial pressures allowed plants to grow under high photosystem II (PSII) excitation pressure, estimated in vivo by chlorophyll fluorescence measurements, at moderate photon flux densities. The xanthophyll-cycle pigments, the early light-inducible proteins, and their mRNA accumulated with increasing PSII excitation pressure irrespective of the way high excitation pressure was obtained (high-light irradiance or decreased CO 2 and O 2 availability). These findings indicate that the reduction state of electron transport chain components could be involved in light sensing for the regulation of nuclear-encoded chloroplast gene expression. In contrast, no correlation was found between the reduction state of PSII and various indicators of the PSII light-harvesting system, such as the chlorophyll a-to- b ratio, the abundance of the major pigment-protein complex of PSII (LHCII), the mRNA level of LHCII, the light-saturation curve of O 2 evolution, and the induced chlorophyll-fluorescence rise. We conclude that the chlorophyll antenna size of PSII is not governed by the redox state of PSII in higher plants and, consequently, regulation of early light-inducible protein synthesis is different from that of LHCII. 相似文献
13.
Apex and Bristol cultivars of oilseed rape ( Brassica napus) were irradiated with 0.63 W m ?2 of UV-B over 5 d. Analyses of the response of net leaf carbon assimilation to intercellular CO 2 concentration were used to examine the potential limitations imposed by stomata, carboxylation velocity and capacity for regeneration of ribulose 1,5-bis-phosphate on leaf photosynthesis. Simultaneous measurements of chlorophyll fluorescence were used to estimate the maximum quantum efficiency of photosystem II (PSII) photochemistry, the quantum efficiency of linear electron transport at steady-state photosynthesis, and the light and CO 2-saturated rate of linear electron transport. Ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) content and activities were assayed in vitro. In both cultivars the UV-B treatment resulted in decreases in the light-saturated rate of CO 2 assimilation, which were accompanied by decreases in carboxylation velocity and Rubisco content and activity. No major effects of UV-B were observed on end-product inhibition and stomatal limitation of photosynthesis or the rate of photorespiration relative to CO 2 assimilation. In the Bristol cultivar, photoinhibition of PSII and loss of linear electron transport activity were observed when CO 2 assimilation was severely inhibited. However, the Apex cultivar exhibited no major inhibition of PSII photochemistry or linear electron transport as the rate of CO 2 assimilation decreased. It is concluded that loss of Rubisco is a primary factor in UV-B inhibition of CO 2 assimilation. 相似文献
14.
The regulation of photosystem II (PSII) by light-, CO 2-, and O 2-dependent changes in the capacity for carbon metabolism was studied. Estimates of the rate of electron transport through PSII were made from gas-exchange data and from measurements of chlorophyll fluorescence. At subsaturating photon-flux density (PFD), the rate of electron transport was independent of O 2 and CO 2. Feedback on electron transport was observed under two conditions. At saturating PFD and low partial pressure of CO 2, p(CO 2), the rate of electron transport increased with p(CO 2). However, at high p(CO 2), switching from normal to low p(O 2) did not affect the net rate of photosynthetic CO 2 assimilation but the rate of electron-transport decreased by an amount related to the change in the rate of photorespiration. We interpret these effects as 1) regulation of ribulose-1,5-bisphosphatecarboxylase (RuBPCase, EC 4.1.1.39) activity to match the rate of electron transport at limiting PFD, 2) regulation of electron-transport rate to match the rate of RuBPCase at low p(CO 2), and 3) regulation of the electron-transport rate to match the capacity for starch and sucrose synthesis at high p(CO 2) and PFD. These studies provide evidence that PSII is regulated so that the capacity for electron transport is matched to the capacity for other processes required by photosynthesis, such as ribulose-bisphosphate carboxylation and starch and sucrose synthesis. We show that at least two mechanisms contribute to the regulation of PSII activity and that the relative engagement of these mechanisms varies with time following a step change in the capacity for ribulose-bisphosphate carboxylation and starch and sucrose synthesis. Finally, we take advantage of the relatively slow activation of deactivated RuBPCase in vivo to show that the activation level of this enzyme can limit the rate of electron transport as evidenced by increased feedback on PSII following a step change in p(CO 2). As RuBPCase as activated, the feedback on PSII declined.Abbreviations and symbols J C
electron-transport rate calculated from CO 2-assimilation measurements
- J F
electron-transport rate calculated from fluorescence parameters
- PFD
photon-flux density
- q E
energy-dependent quenching
- PSII
photosystem II
- q Q
Q-dependent quenching
- QY
quantum yield
- RuBPCase
ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39)
C.I.W. publication No. 1015 相似文献
15.
The regulation of electron transport between photosystems II and I was investigated in the plant Silene dioica L. by means of measurement of the kinetics of reduction of P 700 following a light-to-dark transition. It was found that, in this species, the rate constant for P 700 reduction is sensitive to light intensity and to the availability of CO 2. The results indicated that at 25 °C the rate of electron transport is down-regulated by approximately 40–50% relative to
the maximum rate achievable in saturating CO 2 and that this down-regulation can be explained by regulation of the electron transport chain itself. Measurements of the
temperature sensitivity of this rate constant indicated that there is a switch in the rate-limiting step that controls electron
transport at around 20 °C: at higher temperatures, CO 2 availability is limiting; at lower temperatures some other process regulates electron transport, possibly a diffusion step
within the electron transport chain itself. Regulation of electron transport also occurred in response to drought stress and
sucrose feeding. Measurements of non-photochemical quenching of chlorophyll fluorescence did not support the idea that electron
transport is regulated by the pH gradient across the thylakoid membrane, and the possibility is discussed that the redox potential
of a stromal component may regulate electron transport.
Received: 4 March 1999 / Accepted: 25 May 1999 相似文献
16.
To investigate the photoinhibition of photosynthesis in ‘Honeycrisp’ apple ( Malus domestica Borkh. cv. Gala) leaves with zonal chlorosis, we compared pigments, CO 2 assimilation and chlorophyll (Chl) a fluorescence (OJIP) transient between chlorotic leaves and normal ones. Chl and carotenoids (Car) contents, Chl a/ b ratio, and absorptance were lower in chlorotic leaves than in normal ones, whereas Car/Chl ratio was higher in the former.
Although CO 2 assimilation and stomatal conductance were lower in chlorotic leaves, intercellular CO 2 concentration did not differ significantly between the two leaf types. Compared with normal leaves, chlorotic ones had increased
deactivation of oxygen-evolving complexes (OEC), minimum fluorescence ( F
o), dissipated energy, relative variable fluorescence at L-, W-, J- and I-steps, and decreased maximum fluorescence ( F
m), maximum quantum yield for primary photochemistry ( F
v
/ F
m or TR o/ABS), quantum yield for electron transport (ET o/ABS), quantum yield for the reduction of end acceptors of photosystem I (PSI) (φ Ro and RE o/ABS), maximum amplitude of IP phase, amount of active photosystem II (PSII) reaction centers (RCs) per cross section (CS)
and total performance index (PI tot,abs). In conclusion, photoinhibition occurs at both the donor (i.e., the OEC) and the acceptor sides of PSII in chlorotic leaves.
The acceptor side is damaged more severely than the donor side, which possibly is the consequence of over-reduction of PSII
due to the slowdown of Calvin cycle. In addition to decreasing light absorptance by lowering Chl level, energy dissipation
is enhanced to protect chlorotic leaves from photo-oxidative damage. 相似文献
17.
Cells of the green alga Chlorella
vulgaris were grown under conditions where total Chl/cell varied by a factor of almost 80; from 0.02 fmol/cell to nearly 1.6 fmol/cell. The change in Chl/cell was accomplished by an approximately 11-fold increase in RCII/cell along with a 7-fold increase in Chl/RCII. The effective absorption cross section per RCII at 596 nm varied by a factor of 6, increasing with Chl/cell from a minimum of 20 A 2 to a maximum of 116 A 2. In contrast, over the same range of Chl/cell, the quantum requirement for O 2 production remained relatively constant at 10.4±1.8 quanta absorbed/O 2 evolved. The results are well described by a simple model in which changes in Chl/cell are produced by coordinated changes in reaction center and light-harvesting complexes. The model predicts that between 20 and 40% of the light-harvesting chlorophyll-protein complexes commonly assigned to PSII, do not function as antenna for PSII.This paper is dedicated to the memory of Warren L. Butler, a pioneer in the field of photobiology. His creativity and innovativeness as a scientist were matched only by his patience as a mentor. 相似文献
18.
Action spectra for photosystem II (PSII)-driven oxygen evolution and of photosystem I (PSI)-mediated H 2 photoproduction and photoinhibition of respiration were used to determine the participation of chlorophyll (Chl) a/b-binding Pcb proteins in the functions of pigment apparatus of Prochlorothrix hollandica. Comparison of the in situ action spectra with absorption spectra of PSII and PSI complexes isolated from the cyanobacterium Synechocystis 6803 revealed a shoulder at 650 nm that indicated presence of Chl b in the both photosystems of P. hollandica. Fitting of two action spectra to absorption spectrum of the cells showed a chlorophyll ratio of 4:1 in favor of PSI. Effective antenna sizes estimated from photochemical cross-sections of the relevant photoreactions were found to be 192 ± 28 and 139 ± 15 chlorophyll molecules for the competent PSI and PSII reaction centers, respectively. The value for PSI is in a quite good agreement with previous electron microscopy data for isolated Pcb-PSI supercomplexes from P. hollandica that show a trimeric PSI core surrounded by a ring of 18 Pcb subunits. The antenna size of PSII implies that the PSII core dimers are associated with ∼ 14 Pcb light-harvesting proteins, and form the largest known Pcb-PSII supercomplexes. 相似文献
19.
Mature pea (Pisum sativum L., cv. Meteor) leaves were exposed to two levels of UV-B radiation, with and without supplementary UV-C radiation, during 15 h photoperiods. Simultaneous measurements of CO 2 assimilation and modulated chlorophyll fluorescence parameters demonstrated that irradiation with UV-B resulted in decreases in CO 2 assimilation that are not accompanied by decreases in the maximum quantum efficiency of photosystem II (PSII) primary photochemistry. Increased exposure to UV-B resulted in a further loss of CO 2 assimilation and decreases in the maximum quantum efficiency of PSII primary photochemistry, which were accompanied by a loss of the capacity of thylakoids isolated from the leaves to bind atrazine, thus demonstrating that photodamage to PSII reaction centres had occurred. Addition of UV-C to the UV-B treatments increased markedly the rate of inhibition of photosynthesis, but the relationships between CO 2 assimilation and PSII characteristics remained the same, indicating that UV-B and UV-C inhibit leaf photosynthesis by a similar mechanism. It is concluded that PSII is not the primary target site involved in the onset of the inhibition of photosynthesis in pea leaves induced by irradiation with UV-B. 相似文献
20.
Acclimation of the photosynthetic apparatus to changes in the light environment was studied in the unicellular red alga Porphyridium cruentum (American Type Culture Collection No. 50161). Absolute or relative amounts of four photosynthetic enzymes and electron carriers were measured, and the data were compared with earlier observations on light-harvesting components (F.X. Cunningham, Jr., R.J. Dennenberg, L. Mustárdy, P.A. Jursinic, E. Gantt [1989] Plant Physiol 91: 1179-1187; F.X. Cunningham, Jr., R.J. Dennenberg, P.A. Jursinic, E. Gantt [1990] Plant Physiol 93: 888-895) and with measurements of photosynthetic capacity. Pmax, the light-saturated rate of photosynthesis on a chlorophyll (Chl) basis, increased more than 4-fold with increase in growth irradiance from 6 to 280 μeinsteins·m −2·s −1. Amounts of ferredoxin-NADP + reductase, ribulose-1,5-bisphosphate carboxylase, and cytochrome f increased in parallel with Pmax, whereas numbers of the light-harvesting complexes (photosystem [PS] I, PSII, and phycobilisomes) changed little, and ATP synthase increased 7-fold relative to Chl. The calculated minimal turnover time for PSII under the highest irradiance, 5 ms, was thus about 4-fold faster than that calculated for cultures grown under the lowest irradiance (19 ms). A change in the spectral composition of the growth light (irradiance kept constant at 15 μeinsteins·m −2·s −1) from green (absorbed predominantly by the phycobilisome antenna of PSII) to red (absorbed primarily by the Chl antenna of PSI) had little effect on the amounts of ribulose-1,5-bisphosphate carboxylase, ATP synthase, and phycobilisomes on a Chl, protein, or thylakoid area basis. However, the number of PSI centers declined by 40%, cytochrome f increased by 40%, and both PSII and ferredoxin-NADP + reductase increased approximately 3-fold on a thylakoid area basis. The substantial increase in ferredoxin-NADP + reductase under PSI light is inconsistent with a PSI-mediated reduction of NADP as the sole function of this enzyme. Our results demonstrate a high degree of plasticity in content and composition of thylakoid membranes of P. cruentum. 相似文献
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