|
Plant Physiol. (1998) 117: 1205-1216
A Novel Gene, pmgA, Specifically Regulates
Photosystem Stoichiometry in the Cyanobacterium
Synechocystis Species PCC 6803 in Response to High
Light1
Yukako Hihara,
Kintake Sonoike, and
Masahiko Ikeuchi*
Department of Life Sciences, Graduate School of Arts and Sciences,
University of Tokyo, Komaba 3-8-1, Meguro-ku, Tokyo 153-8902, Japan
(Y.H., M.I.); and Department of Biological Sciences, Graduate School of
Science, University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo
113-0033, Japan (K.S.)
 |
ABSTRACT |
Previously, we identified a novel
gene, pmgA, as an essential factor to support
photomixotrophic growth of Synechocystis species PCC
6803 and reported that a strain in which pmgA was
deleted grew better than the wild type under photoautotrophic
conditions. To gain insight into the role of pmgA, we
investigated the mutant phenotype of pmgA in detail.
When low-light-grown (20 µE m 2 s1) cells
were transferred to high light (HL [200µE m2
s1]), pmgA mutants failed to respond in
the manner typically associated with Synechocystis.
Specifically, mutants lost their ability to suppress accumulation of
chlorophyll and photosystem I and, consequently, could not modulate
photosystem stoichiometry. These phenotypes seem to result in enhanced
rates of photosynthesis and growth during short-term exposure to HL.
Moreover, mixed-culture experiments clearly demonstrated that loss of
pmgA function was selected against during longer-term
exposure to HL, suggesting that pmgA is involved in
acquisition of resistance to HL stress. Finally, early induction of
pmgA expression detected by reverse transcriptase-PCR
upon the shift to HL led us to conclude that pmgA is the
first gene identified, to our knowledge, as a specific regulatory
factor for HL acclimation.
| |
INTRODUCTION |
Acclimation to light regimes is one of the most important and
complex responses of photosynthetic organisms to varying environmental conditions. Under different growth light cyanobacteria and plants regulate antenna pigment complexes, photochemical reaction centers, and
enzymes for CO2 fixation to optimize utilization
of light energy (for review, see Anderson, 1986 ; Melis, 1991; Anderson et al., 1995). Under light-limiting conditions, antenna pigments are
selectively accumulated to collect light energy efficiently. It is well
known that cyanobacteria increase their antenna size by elongation of
the phycobilisome rods and by an increase in the number of
phycobilisomes per unit area of thylakoid membrane upon the shift to LL
(Knanna et al., 1983; Lönneborg et al., 1985). Higher plants and
green algae having chlorophyll b as an antennae pigment show
a marked decline in chlorophyll a to b ratio upon
the shift to LL, reflecting accumulation of the light-harvesting chlorophyll a/b complex (Leong and Anderson,
1984). However, under light-saturating conditions these organisms
reduce their antenna size. Moreover, Rubisco, the rate-limiting enzyme
for CO2 fixation, is accumulated to balance with
high photochemical activities (Björkman, 1981). Expression of
enzymes such as catalase and superoxide dismutase is also enhanced to
scavenge reactive oxygen species, which are generated by excess light
energy (Foyer et al., 1994). The amount of PSII relative to that of
PSI, the photosystem stoichiometry, is another target for the
regulation in response to light intensity, since photosynthetic
electron transport to generate NADPH and ATP is driven by coordination
of the two photosystems with distinct antenna size (Melis et al., 1985;
Fujita et al., 1987, 1994). In general, the antenna size of PSII is
variable, whereas that of PSI is unchanged under various light
conditions. Under LL the photosystem stoichiometry is optimized based
on their antenna sizes, whereas it must be kept near unity irrespective
of the antenna size under HL. Thus, organisms must balance the electron flow between the two photosystems by modulating both antenna complexes and photosystem stoichiometry at different light intensities.
Although a number of reports have provided
information on the physiological and biochemical characterization of
various light acclimation, very little is known about molecular
mechanisms for sensing light conditions or for modulating expression
and/or assembly of the photosynthetic apparatus (Allen, 1995; Anderson
et al., 1995). One exception is the complementary chromatic adaptation, which has been studied extensively in a cyanobacterium having inducible
genes for phycocyanin and phycoerythrin. Several genes, including a
possible photoreceptor and signal transduction components, have been
identified based on the characterization of mutant phenotypes (Chiang
et al., 1992; Grossman et al., 1994; Kehoe and Grossman, 1996).
Since many light-acclimation responses are supposed to be common to
both cyanobacteria and plants, cyanobacteria seem to be better models
for molecular studies of light acclimation in photosynthetic
organisms.
Here we report that modulation of photosystem stoichiometry, one of the
responses typically observed upon the shift to HL, is specifically
supported by a novel gene, pmgA, in the cyanobacterium Synechocystis sp. PCC 6803. The gene was initially
identified as an essential factor required to support photomixotrophic
growth with both light and Glc. However, its mutants could grow better than the wild type under photoautotrophic conditions (Hihara and Ikeuchi, 1997). Surprisingly, the mutant, which appeared spontaneously in a wild-type culture under photoautotrophic conditions, completely took over the culture for a year or so in our laboratory. Further characterization of pmgA mutants in this communication
revealed its specific role in light acclimation. We also provide
evidence for the physiological role of modulation of photosystem
stoichiometry as a HL response.
| |
MATERIALS AND METHODS |
Strains and Culture Conditions
A Glc-tolerant wild-type strain of Synechocystis sp.
PCC 6803 (WS) and mutants (WL strain with 1 base replacement in
pmgA and a disruptant with spectinomycin-resistance
cassette: WL and pmgA::SpR) (Hihara and Ikeuchi,
1997) were grown at 32°C in BG-11 medium with 20 mM
Hepes-NaOH (pH 7.0) under continuous illumination provided by
fluorescent lamps. Liquid cultures were bubbled with air containing 1.0% (v/v) CO2. The pmgA-disrupted
mutant was usually maintained with 20 µg/mL spectinomycin. PPFD was
measured by a quantum sensor (model LI-250, Li-Cor, Lincoln, NE). Cell
density was estimated as A730 with a
spectrophotometer (model UV-160A, Shimadzu, Kyoto, Japan).
In all of the experiments, fresh media were inoculated at a cell
density of A730 = 0.05 with precultures
grown to late log phase (A730 = 0.8-0.9)
under LL and then transferred to HL or LL. Unless otherwise stated,
cells were grown in volumes of 50 mL with test tubes (3 cm in
diameter). A larger volume of culture was provided in 500- or 1000-mL
flat vessels illuminated with the same HL. The fixed culture conditions
were important for HL, since the self-shading started to cancel HL at
the later stage of the batch culture.
Absorption and 77 K Fluorescence Emission Spectra
In vivo absorption spectra of whole cells of the wild type and
mutants suspended in BG-11 medium were measured at room temperature using a spectrophotometer (model U3500, Hitachi, Tokyo, Japan) with an
end-on photomultiplier. Chlorophyll and phycocyanin were calculated
using the equations of Arnon et al. (1974). Low-temperature fluorescence emission spectra at 77 K were recorded using a
custom-made apparatus (Sonoike and Terashima, 1994). Cells containing
100 µg chlorophyll/mL in BG-11 medium were placed in a sample holder. Pigments were excited with light 400 to 600 nm in wavelength produced by passing white light from a 100-W halogen lamp through a filter (CS4-96, Corning Inc., Corning, NY). Before measurement, cells were
dark adapted (>10 min) at room temperature to eliminate
possible effects of the state transition.
Measurement of Rates of Electron-Transfer Reactions
Oxygen evolution and consumption of cells were measured in BG-11
medium with a Clark-type electrode at a chlorophyll concentration of
2.5 µg/mL. The medium was continuously stirred at 25°C and illuminated with saturating actinic light (4000 µE
m2 s1). Whole-cell
photosynthetic activity or PSII-mediated electron transfer activity was
measured as oxygen evolution supported by 2 mM
NaHCO3 or 2 mM 2,6-DCBQ,
respectively. PSI-mediated electron transfer activity was measured as
oxygen consumption in the presence of 1 mM ascorbic acid, 5 mM DAD, 2 mM MV, 20 µM DCMU, and
1 mM KCN.
Determination of Photosystems
Thylakoid membranes used for measurements of PSII and PSI were
isolated from cells grown in 1000 mL of culture volume. Cells suspended
in HN buffer (5 mM Hepes-NaOH and 10 mM NaCl,
pH 7.5) were broken with a Mini-Bead Beater (Biospec, Bartlesville, OK) with zircon beads (100 µm in diameter, Biospec) for three pulses of
50 s each with 2-min cooling intervals at 0°C. After brief centrifugation to remove the beads, cell debris and thylakoid membranes
were collected at 45,000g for 20 min with a rotor (RP80AT, Hitachi). Pellets were resuspended in HN buffer and sonicated for three
pulses of 10 s each with 10-s cooling intervals at 0°C to
liberate thylakoid membranes from cell debris. After centrifugation at
2,500g for 5 min with a RT15A8 rotor (Hitachi),
thylakoid-containing supernatants were used to determine P700 and Cyt
b559.
PSII content was estimated as one-half molar of Cyt
b559, as described in Fujita and Murakami
(1987). Cyt b559 was determined from the
difference spectrum (520-600 nm) between ascorbate- and hydroquinone-reduced conditions using a U3500 spectrophotometer. The
chlorophyll concentration of thylakoid membranes was 80 µg/mL, and a
difference absorption coefficient of 21 mM1 cm1
(Garewall and Wasserman, 1974) was used.
PSI content was estimated as photoactive P700 content upon illumination
by continuous light. Absorbance changes at 703 nm were measured with a
spectrophotometer (model 356, Hitachi) (Terashima et al., 1994). The
reaction mixture contained thylakoid membranes at a chlorophyll
concentration of 3 µg/mL in 50 mM Tris-HCl (pH 7.5), 10 mM sodium ascorbate, 30 µM TMPD, 10 µM MV, and 0.05% dodecylmaltoside. The
reduced-minus-oxidized differential absorption coefficient of P700 is
known to vary with species (Hiyama and Ke, 1972; Sonoike and Katoh,
1990) and with the preparation used (Sonoike and Katoh, 1988, 1989).
Thus, we determined the absorption coefficient of P700 in the thylakoid
membranes from Synechocystis sp. PCC 6803 by measuring
oxidation of TMPD coupled with the reduction of flash-oxidized P700,
basically as described by Hiyama and Ke (1972). Flash-induced
absorbance changes on a millisecond time scale were measured with a
single-beam spectrophotometer (model RA-401, Otsuka Electronics, Osaka,
Japan) under aerobic conditions.
Absorption changes were measured at 703 nm for P700 and 575 nm for
TMPD, and the absorption coefficient of oxidized TMPD at this
wavelength was assumed to be 10.7 mM1 cm1
(Hiyama and Ke, 1972). Saturating xenon flashes (half-duration time of
5 µs) that passed through two band-pass filters (CS 4-96 and CS
7-59, Corning) and a dichroic filter (DF-B, Japan Vacuum Optics,
Gotenba, Japan) were fired at 0.1 Hz, and signals were recorded with a
photomultiplier (R374, Hamamatsu Photonics, Shizuoka, Japan) blocked
with two cutoff filters (R-69, Toshiba, Tokyo, Japan) for P700 or with
an orange cutoff filter (O-57, Toshiba) and a dichroic filter (DF-C,
Japan Vacuum Optics) for TMPD. The reaction mixture contained thylakoid
membranes equivalent to 3 µg/mL chlorophyll, 0.8 mM TMPD,
10 µM DCMU, 1 mM KCN, 0.05%
dodecylmaltoside, and 50 mM Tris/HCl (pH 7.5). The
absorption coefficient of P700 in thylakoid membranes from
Synechocystis sp. PCC 6803 in the presence of
dodecylmaltoside was determined as 71 ± 3 mM1 cm1.
This value was significantly greater than that determined for Synechococcus elongatus in similar conditions (Sonoike and
Katoh, 1988), but close to the value for the PSI preparation from
Triton-solubilized thylakoid membranes from Anabaena
variabilis (Hiyama and Ke, 1972).
Immunoblot Analysis
Whole-cell extracts before removal of cell debris, as described
above, were treated with LDS and subjected to SDS-PAGE. For detection
of D2, PsbO, and Rubisco proteins, the extracts were solubilized with
1% LDS, 60 mM DTT, and 60 mM Tris-HCl (pH 8.0) for 10 min at room temperature, whereas for PsaA/B proteins, they were
solubilized with 5% LDS, 60 mM DTT, and 60 mM
Tris-HCl (pH 8.0) for 2 h at room temperature to achieve complete
denaturation. SDS gel electrophoresis was done by the procedure of
Laemmli (1970) with a gel containing 12.5% acrylamide and 6 M urea for D2, PsbO, and Rubisco or a gradient gel of 16%
to 22% acrylamide with 7.5 M urea for PsaA/B. Samples
corresponding to 0.32 × 107, 0.48 × 107, 1.92 × 107, and
1.15 × 107 cells were loaded for the
detection of D2, PsbO, and Rubisco and PsaA/B, respectively. Proteins
were electroblotted onto PVDF membranes (Immobilon-P; Millipore). The
antiserum against PsaA/B from S. elongatus was kindly
provided by Dr. I. Enami (Science University of Tokyo). The antiserum
against Rubisco from spinach was a generous gift from Dr. K. Okada
(Tokyo University of Pharmacy and Lifescience). The antisera against D2
and PsbO were from spinach (Ikeuchi and Inoue, 1987). Reaction with
antisera and immunodetection by alkaline phosphatase or peroxidase were
performed according to the manufacturer's instructions (Bio-Rad).
Direct Sequencing Analysis
Direct sequencing analysis of pmgA was performed as
described previously (Hihara and Ikeuchi, 1997).
Preparation of Total RNA
Cells were collected by brief centrifugation at 4°C and stored
in liquid N2. The frozen cells were thawed with
20 mM EDTA and 50 mM Tris-HCl (pH 8.0) and
immediately treated with phenol at 75°C for 10 min. Cells were
further treated with 0.8% (w/v) SDS at 75°C for 10 min with shaking,
and then extracted once with phenol/chloroform and twice with
chloroform. After precipitation with ethanol, RNA was solubilized in 8 M guanidine-HCl, 0.1 M sodium acetate, pH 5.2, 5 mM DTT, and 0.5% sodium lauryl sarcosinate and
precipitated with ethanol. Residual DNA in the RNA preparation was
removed by digestion with DNase I at 25°C for 2 h. After ethanol precipitation, the amount of RNA was determined by UV absorption at 260 nm.
RT-PCR
First-strand cDNA was synthesized using 1 µg of total RNA with a
RT-PCR High Kit (Toyobo, Osaka, Japan) in a final volume of 20 µL,
according to the manufacturer's instructions. The amount of cDNA used
as a template was experimentally determined for each set of primers to
achieve proportional production of the PCR product (the cDNA equivalent
to RNA of 0.1 µg and 5 pg was used for amplification of
pmgA and rnpB, respectively). The oligonucleotide
primers 5 -TGTAAAACGACGGCCA-GTCAGCACATTCAGGCCTCC-3 and
5-CAGGAAAC-AGCTATGACCGCTTAATTTTCTTGCTGA-3 were used for amplification of a 565-bp fragment of pmgA and
5-AGTTAGGGAGGGAGTTGC-3 and 5-TAAGCCGGGTTCTGTTCC-3 were used for
amplification of a 417-bp fragment of the constitutive RNase P gene,
rnpB, as a positive control (Frías et al., 1994).
After a first denaturation step of 3 min at 93°C, 30 PCR cycles were
performed (93°C for 30 s, 57°C for 2 min, and 72°C for 2 min) followed by a final extension step of 10 min at 72°C. As a
negative control for RT-PCR, 1 µg of RNA without the RT reaction was
subjected to PCR amplification of rnpB.
| |
RESULTS |
Absorption Spectra and Content of Photosynthetic Pigment
We isolated a mutant clone with a larger colony size (WL strain)
compared with smaller colonies of the wild type (WS strain) under HL
and identified a point mutation in a novel gene, pmgA, responsible for the change of colony size (Hihara and Ikeuchi, 1997).
Here we observed that the WL strain and pmgA-disruptant (pmgA::SpR) cells in the
liquid culture showed enhanced pigmentation and slightly higher
cell density relative to wild-type cells under HL, as shown in Figure
1. In HL, doubling time of the WL strain (5.39 ± 0.25 h) and the pmgA-disruptant strain
(5.41 ± 0.28 h) was significantly shorter than that of the
wild type (5.82 ± 0.14 h). Figure
2 shows absorption spectra of cells grown
in liquid culture under HL or LL. Absorption spectra were significantly different between the wild type and pmgA mutants under HL:
the peak of chlorophyll absorption at 678 nm was higher than the peak of phycocyanin absorption at 628 nm in the mutants, whereas it was
lower in the wild type (Fig. 2B). However, there was no difference in
the relative peak heights between the wild type and mutants when grown
under LL (Fig. 2A). Compared with cells grown under HL, the content of
both pigments increased relative to cell density and to carotenoid
absorption (approximately 495 nm) in both cell types under LL. The
difference in pigmentation was barely discernible for colonies on agar
plates under similar HL conditions (Hihara and Ikeuchi, 1997) or for
liquid cultures under LL conditions (data not shown).
View larger version (79K):
[in this window]
[in a new window]
| Figure 1.
Liquid culture of wild type (WS) and
pmgA mutants (WL and the disruptant
pmgA::SpR) at log phase (20 h
after inoculation) under HL. A730 of WS, WL,
and pmgA-disruptant was 0.56, 0.73, and 0.66, respectively.
|
|
View larger version (22K):
[in this window]
[in a new window]
| Figure 2.
Absorption spectra of cells grown under different
light intensities. A, Absorption spectra of LL-grown cells. B,
Absorption spectra of cells 18 h after shift to HL. The spectra of
wild type (a), WL (b), and pmgA-disruptant cells (c) are
normalized at A730. rel., Relative.
|
|
Figure 3 shows time-course changes in
cell density and pigment abundance in the small batch culture defined
in ``Materials and Methods''. Data at time 0, representing LL-grown
cells, showed no significant differences between the wild type and
pmgA mutants. Upon transfer to HL, the content of both
chlorophyll (Fig. 3B) and phycocyanin (Fig. 3C) on a per-cell basis
showed changes with three different phases: (a) drastically reduced to
about two-thirds within 3 h, (b) further decreased but at a lesser
rate until 12 h, and (c) gradually recovered, although cells
continued to grow logarithmically (Fig. 3A). Notably, the chlorophyll
content was significantly greater in pmgA mutants than in
the wild type after 9 h, whereas the phycocyanin content was not
much different between the strains throughout the batch culture. The
cellular content of both pigments almost recovered to the initial level
after 30 h due to the self-shading effect at high cell density.
Taking into account that cells were dividing logarithmically,
accumulation of pigments, expressed per milliliter of culture
volume, is shown on a log scale (Fig. 3, D and E). Accumulation of both
pigments stopped during the initial 3 h (phase 1). The pigment
accumulation restarted at a low rate from 3 to 12 h (phase 2) and
accelerated after 12 h (phase 3). Clearly, the pmgA
mutants differed from the wild type in their chlorophyll accumulation
during phase 2 (Fig. 3D), leading to a higher cellular chlorophyll
content in phase 3 (Fig. 3B). However, accumulation of phycocyanin did
not differ between the wild type and the mutants (Fig. 3E), although
its time course was similar to that of chlorophyll. In short, loss of
pmgA function seems to abolish the specific retardation of
chlorophyll synthesis at phase 2 (3-12 h) in response to HL. However,
the initial suppression of chlorophyll synthesis, the recovery of
chlorophyll synthesis during phase 3, and phycocyanin synthesis do not
seem to be affected by the pmgA mutation.
View larger version (22K):
[in this window]
[in a new window]
| Figure 3.
Growth curve and changes in the pigment content in
the course of a batch culture under HL. A, Cell density. B, Chlorophyll
content expressed on a per-cell basis. C, Phycocyanin content expressed
on a per-cell basis. D, Chlorophyll accumulation expressed per
milliliter of culture volume. E, Phycocyanin accumulation expressed per
milliliter of culture volume. At time 0, the batch culture was
inoculated with LL-grown cells.  , WS;  , WL;  ,
pmgA::SpR.
|
|
Chlorophyll-Fluorescence Spectra and Content of Photosystems
Differences in chlorophyll content are assumed to reflect changes
in photosystems of cyanobacteria, since they have no apparent chlorophyll-binding antenna proteins. It is widely accepted that chlorophylls of PSII emit fluorescence around 685 and 695 nm, whereas
chlorophylls of PSI emit at 720 to 730 nm at 77 K (Murata et al.,
1966). Thus, as shown in Figure 4, we
investigated the chlorophyll-fluorescence emission spectra of cells at
77 K to determine whether photosystem stoichiometry is different
between the wild type and pmgA mutants. When the spectra
were normalized at the peaks of PSI fluorescence, it was notable that
the peak at 695 nm originating from PSII was about 1.5-fold higher in
wild-type cells grown under HL than under LL (Fig. 4A). However, the
695-nm peak was virtually unchanged in pmgA mutants (Fig. 4,
B and C). This strongly indicates that the ratio of PSII to PSI
increased in the wild type in response to HL, whereas it remained
unchanged in the mutants. Since the fluorescence ratio (F695/F725) is a good index of the ratio of PSII to PSI, the ratio was plotted in the
course of the same experimental conditions as in Figure 3. Clearly, the
ratio gradually increased in the wild type 12 h after the shift to
HL, reaching the maximum (about 1.5-fold of the initial) at around 18 to 24 h, whereas the ratio changed little in pmgA
mutants (Fig. 4D). These differences in the time-course change of the
F695/F725 ratio between the wild type and pmgA mutants appear to reflect the difference in chlorophyll accumulation (Fig. 3D).
A decline of the ratio after 20 h in the wild type is possibly due
to the self-shading effect in the large vessel.
View larger version (32K):
[in this window]
[in a new window]
| Figure 4.
Low-temperature (77 K) fluorescence emission
spectra of cells. A, Fluorescence emission spectra of WS (wild type) at
77 K. B, Fluorescence emission spectra of WL at 77 K. C, Fluorescence
emission spectra of pmgA-disruptant at 77 K. Spectra of LL-grown cells (solid line) and cells 20 h after a
shift to HL (dashed line) were normalized at the 725-nm peak of PSI. D,
Time course of the change in the ratio of F695/F725 under HL.
Conditions for the culture were the same as in Figure 3. Data are the
means ± SE for at least three separate experiments.
rel., Relative.
|
|
To confirm the results of fluorescence measurement, we determined the
photosystem content of thylakoid membranes isolated from LL-and
HL-grown cells by measuring Cyt b559 and
P700. Cyt b559 has been known to be tightly
associated with the PSII reaction center in thylakoid membranes at a
molar ratio of 2:1 (Whitmarsh and Ort, 1984), whereas P700, a
photoactive pigment of PSI reaction center, was used to determine PSI
content (Hiyama and Ke, 1972). Table I
shows that the PSII content on a per-cell basis decreased to about 74%
in the wild type during the first 13 h after the shift to HL
conditions, whereas the PSI content markedly decreased to about 40% of
the initial value. As a result, the ratio of PSII to PSI increased from
0.48 for LL-grown cells to 0.81 for HL-grown cells. Since cells grew
logarithmically during this period, the accumulation of PSI and PSII
may have been transiently suppressed and recovered as chlorophyll
synthesis, as shown in Figure 3D. In pmgA mutants, content
of both photosystems similarly decreased under HL but the marked
suppression of PSI accumulation did not take place. As a result, the
photosystem stoichiometry remained unchanged in the mutants under HL.
Wild-type cells showed a slight recovery of their photosystem content
and stoichiometry after 22 h. Consistently, the low-temperature
fluorescence ratio (F695/F725) of the wild-type thylakoids was at the
maximum level at 13 h and slightly lower at 22 h, whereas the
ratio of the mutant thylakoids was not much changed (data not shown).
These fluorescence changes seemed to occur slightly earlier than those
observed in Figure 4D. This may be due to higher self-shading in the
larger culture volume required for the measurement of Cyt
b559.
From the data in Table I and the phycocyanin content of the samples, we
also calculated the ratio of phycocyanin to PSII, which represents the
antenna size of PSII. It dropped to about 80% not only in the wild
type but also in pmgA mutants during the first 13 h
after the shift to HL conditions (data not shown). Thus, we conclude
that pmgA is essential for the modulation of the PSII-to-PSI
ratio as acclimation to HL but not for the adjustment of antenna size
of PSII.
Electron-Transfer Activities under Different Light Intensities
We pursued the relationship between the two phenotypic features of
pmgA mutants, the lack of modulation of the photosystem stoichiometry and the enhanced growth under photoautotrophic
conditions, by measuring photosynthetic activities (Table
II). Under LL, there were no significant
differences in activities of whole-cell photosynthesis (from water to
CO2), PSII (from water to 2,6-DCBQ), and PSI
(from reduced DAD to MV) between the wild type and pmgA
mutants. This is consistent with our previous observation that the
growth rate of pmgA mutants was comparable to that of the
wild type under LL (Hihara and Ikeuchi, 1997). When cells were grown
under HL for 18 h, the whole photosynthetic activity of the
mutants was much greater than that of the wild type. This seems to
account partly for the fact that pmgA mutants grew slightly
better than the wild type under HL (Fig. 3A). The PSI activity was
higher in pmgA mutants than in the wild type. This is
because the wild type markedly decreased PSI activity as well as PSI
content in response to HL, whereas pmgA mutants did not. The
slight discrepancy was observed between P700 content and PSI activity.
Since DAD indirectly as well as directly donates electrons to P700, the PSI activity may also be affected by other unknown conditions (Izawa,
1980). The PSII activity was also higher in pmgA mutants than in the wild type under HL. This was due to a significant decrease
in the ratio of PSII activity to PSII content only in wild-type cells
transferred to HL. A possible reason for the HL effect will be
addressed in ``''.
View this table:
[in this window]
[in a new window]
|
Table II.
Photosynthetic activities of cells
All values represent the means ± SE for at least
three separate experiments.
|
|
It is also of interest that the ratio of the whole photosynthetic
activity to PSII or PSI activity was much higher in HL-grown than in
LL-grown cells, regardless of functionality of pmgA. This suggests that the enzyme(s) for carbon assimilation were up-regulated under HL, in contrast to the down-regulation of chlorophyll content. Both regulations are typical responses of photosynthetic organisms to
HL (Björkman, 1981; Raps et al., 1983).
Western Analysis
To confirm the measurements of photosystem content and activities,
photosystem proteins and Rubisco were probed with specific antibodies
as shown in Figure 5. Clearly, the
cellular content of the D2 protein of PSII reaction centers, the PsbO
protein of PSII oxygen-evolving complexes, and the PsaA/B proteins of
PSI reaction centers were down-regulated under HL, whereas the content of the Rubisco large subunit was up-regulated. These differences in
accumulation of photosystems and Rubisco proteins seem to coincide with
the data on photosynthetic activity. It is interesting that only PsaA/B
proteins under HL seemed to be down-regulated in the wild type and not
in pmgA mutants. Although the difference in PsaA/B content
was not clear, possibly due to inaccuracy of the method, the results
seem to support the idea that pmgA is involved in the
modulation of photosystem stoichiometry by regulating the accumulation
of PSI under HL.
View larger version (57K):
[in this window]
[in a new window]
| Figure 5.
Immunoblotting of polypeptides of the wild type
(WS) and pmgA mutants (WL and the disruptant
pmgA::SpR). Total cell extracts of
LL-grown cells or cells 18 h after a shift to HL were separated by
SDS-PAGE, electrotransferred, and challenged with anti-D2, anti-PsbO,
anti-PsaA/B, or anti-Rubisco (RuBisCO). Proteins extracted from the
same number of cells were probed with each antibody (see ``Materials and Methods'').
|
|
Mixed-Culture Experiments at Various Light Intensities
We have shown that the higher chlorophyll content and the lower
PSII-to-PSI ratio in the pmgA mutants were apparently linked to the higher photosynthetic activities per cell and the higher growth
rates than the wild type under HL. Next, we explored the physiological
significance of the pmgA-mediated regulation mechanism, which had been acquired in wild-type Synechocystis in
evolution. We attempted to answer this question by examining growth
rates of a point mutant of pmgA (WL) and the wild type in
mixed-culture experiments as shown in Figure
6. Relative growth was estimated by
direct sequencing of the pmgA gene in genomic DNA extracted from the mixed cultures, which consisted of several consecutive batch
cultures. Direct sequencing provided information about the population
of the two strains at the time of sampling irrespective of the
extent of photodamage. Examination by direct sequencing seemed to be
more reliable than subsequent growth tests, especially for damaged
cells. Consistent with our previous observation on agar plates (Hihara
and Ikeuchi, 1997), the mutant and the wild type grew similarly under
LL or medium light (50 µE m2
s1). Under higher-light conditions (100 µE
m2 s1), the mutant
became dominant in the second and third culture. We also confirmed that
the mutant became dominant in the second culture at 200 and 400 µE
m2 s1, when the culture
was transferred every 2 d (data not shown), as shown in our
previous report (Hihara and Ikeuchi, 1997). However, the WL mutant
suddenly disappeared from the mixed culture under similar conditions
when transferred every 24 h (Fig. 6, 200-300 µE
m2 s1). The latter
culture regime kept cells at a relatively low density so that they
would receive more HL stress due to reduced self-shading. Therefore,
disappearance of the pmgA mutant indicates that the pmgA mutation responsible for higher photosynthetic
activities (Table II) is fatal under prolonged conditions of HL stress,
suggesting that alteration in the PSII-to-PSI ratio has been selected
during evolution as an adaptation to HL in
Synechocystis.
View larger version (15K):
[in this window]
[in a new window]
| Figure 6.
Effects of light intensities for mixed-liquid
culture on the ratio of the WL to WS genotype as determined by direct
sequencing. The ratio is expressed as a pie chart, whereas cell density
is shown as A730 under each pie chart. A
horizontal line indicates each batch culture, and a dotted line
indicates the inoculation of the following batch culture.
|
|
RT-PCR of pmgA mRNA
Although we have shown that pmgA is essential for
modulation of photosystem stoichiometry, which molecular processes are
mediated by pmgA is still unknown. To learn more about the
role of pmgA, we investigated the expression of
pmgA in the wild type by RT-PCR as shown in Figure
7. In contrast to relatively constant
amplification of the constitutive RNase P gene (rnpB)
(Frías et al., 1994), production of a pmgA fragment
was largely dependent on the light conditions. When cells were grown
under LL, cDNA for pmgA was barely detectable, as can be
seen at time 0. After 4 h of HL, cDNA for pmgA
increased severalfold and was then maintained at the high level for up
to 16 h. A decrease in the cDNA level was observed at 20 h,
possibly due to the self-shading effect. It was also interesting that
the amount of cDNA sufficient for PCR amplification was more than
10,000 times higher for pmgA than for rnpB,
suggesting that expression of pmgA is very low even under
inducible conditions. We confirmed almost no DNA in the RNA preparation
before the RT reactions, as shown in the negative control experiments.
These suggest that the pmgA gene becomes active upon
exposure to HL to acclimate to conditions of HL stress.
View larger version (59K):
[in this window]
[in a new window]
| Figure 7.
Expression of pmgA in the wild type
revealed by RT-PCR. The top and middle panels show PCR with primers
specific to pmgA and rnpB, respectively.
(+) indicates use of reverse-transcribed RNA from wild-type cells at HL
as a template of PCR. The bottom panel shows PCR with primers specific
to rnpB. ( ) indicates use of RNA before
reverse-transcription as a template. The culture for RNA isolation was
inoculated with LL-grown cells and transferred to HL at time 0.
|
|
| |
DISCUSSION |
We have demonstrated that functional pmgA is
specifically involved in acclimation to HL by modulating photosystem
stoichiometry and, partly, chlorophyll synthesis. In our experimental
conditions with Synechocystis sp. PCC 6803, we observed many
changes due to HL acclimation: (a) decrease of cellular pigment
content; (b) decrease of photochemical activities (on a per-cell
basis); (c) decrease of antenna size of PSII; (d) increase of the PSII
to PSI ratios; (e) increase of Rubisco; and (f) increase of maximum photosynthetic rate. These responses, possibly resulting from HL-induced modulation of accumulation of pigments and proteins for the
photosynthetic apparatus, have been widely recognized in cyanobacteria,
algae, and higher plants (Kawamura et al., 1979; Vierling and Alberte,
1980; Björkman, 1981; Raps et al., 1983; Zevenboom and Mur, 1984;
Anderson et al., 1988). Our mutant analysis revealed that
pmgA is specifically responsible for the slow recovery of
chlorophyll accumulation during phase 2 after the shift from LL to HL
(Fig. 3D) and for an increase in the PSII-to-PSI ratio (Fig. 4; Table
I). Importantly, pmgA is not directly involved in other
responses. To our knowledge, this is the first gene to be identified as
a regulatory factor for HL acclimation. Since modulation of photosystem
stoichiometry under different growth irradiances has been well
documented in various cyanobacteria, algae, and higher plants
(Kawamura et al., 1979; Falkowski et al., 1981; Leong and Anderson,
1984; Neale and Melis, 1986; Wild et al., 1986; Anderson et al., 1988;
Smith and Melis, 1988; Murakami and Fujita, 1991; Yokoyama et al.,
1991), it would be interesting to survey other cyanobacteria and/or
plants for a pmgA homolog.
The phenotype causing photoautotrophic growth of pmgA
mutants on agar plates to be much better than the wild type under
almost all light intensities (Hihara and Ikeuchi, 1997) was totally
unexpected. In this report we showed that the mutants grew
significantly faster than the wild type in liquid medium when grown
separately (Fig. 3A) or in mixed culture (Fig. 6). The higher growth
rate of the mutants seems to be accounted for by their higher
whole-cell photosynthetic activity (Table II). The higher
photosynthetic activity of the mutants as compared with the wild type
seems to reflect their higher activity of PSI, which is consistent with
the results of P700 measurements (Table I) and immunoblotting of PSI
reaction center PsaA/B proteins (Fig. 5). However,the PSII activity of the mutants was also higher than the wild type (Table II), although the
cellular content of Cyt b559 and reaction
center D2 protein were not much different between the mutant and
wild-type cells (Table I; Fig. 5). This could be explained by the
difference in sensitivity to PSII photoinhibition under HL. Since
photoinhibition of PSII is caused by accumulation of reduced quinone at
the primary acceptor QA site (Aro et al., 1993),
the higher activity of PSI in the mutants is supposed to extract more
electrons from PSII, possibly resulting in less photoinhibition of
PSII, namely higher PSII activity. Thus, it can be concluded that the
higher photosynthetic activity of the mutants resulting from enhanced
accumulation of PSI due to loss of pmgA function is
responsible for the mutant's ability to grow faster than the wild type
under HL conditions.
However, our results with mixed-culture experiments under extended HL
stress (Fig. 6) demonstrated that the pmgA mutant, with its
higher PSI content, was more sensitive to prolonged stress than the
wild type. One explanation for this apparent discrepancy is increased
accumulation of reactive oxygen species in the cells of the
pmgA mutant under HL conditions. The increase of PSI content mitigates photoinhibition of PSII, and results in the higher activity of whole-electron transport. The increase of PSI content also results
in the accumulation of electrons on the reducing side of PSI rather
than on the QA site of PSII. Both the increase in the electron-transfer rate and the accumulation of electrons on the
reducing side of PSI are conditions that stimulate the production of
reactive oxygen species. Thus, the increased PSI content in the mutants
may result in much more production of reactive species of oxygen, which
might account for the loss of viability of the mutants under the
prolonged stress of HL. It is widely accepted that electrons generated
from PSI react with oxygen to produce the superoxide anions, which are
mainly scavenged by superoxide dismutase and ascorbate peroxidase
(Asada, 1992; Herbert et al., 1992). It was recently demonstrated that
irreversible photoinhibition of PSI occurs at its acceptor side in
chilling-sensitive plants under chilling stress, possibly due to a loss
of protection against the reactive species of oxygen (Sonoike and
Terashima, 1994; Sonoike, 1996). The protection against reactive oxygen
species is particularly important under HL stress (Foyer et al., 1994).
The physiological significance of the HL response that adjusts
photosystem stoichiometry has not been fully established, although the
adjustment is widespread in photosynthetic organisms. For example, it
was simply stated in a review (Anderson et al., 1995) that adaptation
of the photosystem stoichiometry serves to regulate the distribution of
excitation energy between the photosystems and correct any imbalances.
This is in contrast to many other responses of HL acclimation, such as
the reduction in pigments and antenna size and the increase in
CO2 fixation activity, which can be easily
recognized as avoiding photoinhibition (Björkman, 1981; Anderson
et al., 1988). Here we proposed another explanation for the adjustment
of photosystem stoichiometry under HL: the decrease of PSI content
makes cells resistant to HL stress by reducing the production of
reactive oxygen species, which is otherwise lethal under prolonged HL
stress. In conclusion, relative decrease of PSI content under HL
conditions mediated by pmgA in Synechocystis can
be a physiological response to the HL stress. pmgA mutants lack this response, resulting in the production of reactive oxygen species. It would be interesting to attempt to detect generation of the
reactive oxygen species under HL in pmgA mutants.
pmgA mutants have another interesting phenotypic character:
They are unable to grow on agar plates under photomixotrophic conditions with 5 mM Glc even under medium light (50 µE
m2 s1) (Hihara and
Ikeuchi, 1997). On the other hand, they can grow in liquid under the
same photomixotrophic conditions, although their growth is
significantly slower than the wild type, as demonstrated by mixed
culture (Hihara and Ikeuchi, 1997). Here we observed that wild-type
cells grown in liquid under photomixotrophic conditions showed a much
reduced chlorophyll content on a per-cell basis and a higher ratio of
PSII to PSI than those under photoautotrophic conditions. However,
pmgA mutants did not show any change in the photosystem
stoichiometry under the same photomixotrophic conditions (data not
shown). Since these changes were almost the same as those of HL-grown
cells, the addition of Glc is supposed to intensify the light stress.
This interpretation may be reasonable, since Glc provided cells with
NADPH via the oxidative pentose phosphate cycle (Pelroy et al., 1972),
which presumably makes the acceptor side of PSI more reductive (like
the HL treatment). Thus, the phenotype of pmgA mutants
unable to grow under the photomixotrophic conditions could be also
explained by the inability to reduce the PSI content.
How does pmgA work on the accumulation of chlorophyll and
photosystem stoichiometry? Our data on photosystem content suggest that
photosystem stoichiometry was mainly modulated by accumulation of PSI.
Studies on light acclimation in cyanobacteria demonstrated that
cellular PSI content is more variable than PSII during the adjustment
of photosystem stoichiometry (Kawamura et al., 1979; Murakami and
Fujita, 1991). However, it remains to be determined whether chlorophyll
accumulation or PSI accumulation is the primary target of the
pmgA-mediated acclimation to HL. The retardation of
chlorophyll accumulation (Fig. 3D) seemed to precede the increase of
the F695/F725 ratio (Fig. 4D). However, it would be rather difficult to
imagine a mechanism whereby chlorophyll biosynthesis preferentially
regulates assembly of the PSI complex. It should be noted that mRNA
levels of pmgA were elevated severalfold for the initial
4 h after HL was begun (Fig. 7). This observation, coupled with
the fact that the level of pmgA is very low even after HL
induction, suggests that the pmgA product is involved in an
early signaling process of the HL acclimation.
So far, two genes have been documented to be specifically involved in
accumulation of PSI complexes but not PSII (Wilde et al., 1995;
Bartsevich and Pakrasi, 1997; Boudreau et al., 1997). Disruption of a
chloroplast open reading frame, ycf4, and a
Synechocystis homolog, orf184, induced a
significant decline in PSI content per unit of chlorophyll. As a
result, the PSII-to-PSI ratio was elevated about 3-fold in the mutant
compared with wild-type Synechocystis (Wilde et al., 1995),
whereas there was almost no accumulation of the PSI complex in the
C. reinhardtii mutant (Boudreau et al., 1997). A second
gene, btpA, seems to regulate a posttranscriptional process
that affects biogenesis of the PSI complex in Synechocystis (Bartsevich and Pakrasi, 1997). A disruption mutant of btpA
had only 10% to 15% of PSI reaction center proteins compared with the
wild type, whereas the PSII content remained unaffected. These different genes may regulate accumulation of PSI at a step of translation, assembly, or turnover of the PSI complex, although no
relevant data were presented that indicated their involvement in
physiological adjustment of photosystem stoichiometry under varying
environment conditions. To our knowledge, pmgA is the first
gene shown to be involved in the regulation of the PSII-to-PSI ratio
under physiological conditions.
| |
FOOTNOTES |
1
This work was supported by a Research Fellowship
for Young Scientists from the Japan Society of the Promotion of Science
(to Y.H.); by grants-in-aid for encouragement of young scientists (no.
09740590 to K.S.), for scientific research on priority areas (no.
07251204 to M.I.), and for scientific research C (no. 08836002 to M.I.) from the Ministry of Education, Science, and Culture, Japan;
and by a grant for Scientific Research from the Human Frontier Science
program (to M.I.).
*
Corresponding author; e-mail mikeuchi{at}ims.u-tokyo.ac.jp; fax
81-3-5454-4337.
Received February 26, 1998;
accepted May 14, 1998.
| |
ABBREVIATIONS |
Abbreviations:
2,6-DCBQ, 2,6-dichlorobenzoquinone.
DAD, diaminodurene.
HL, high light (in this study, 200 µE m2
s1).
LDS, lithium dodecyl sulfate.
LL, low light (in this
study, 20 µE m2 s1).
MV, methyl viologen.
RT-PCR, reverse transcriptase-PCR.
TMPD, N,N,N,N-tetramethyl-p-phenylenediamine.
| |
ACKNOWLEDGMENTS |
We thank Dr. Gerry Plumley for critical reading of the
manuscript, Dr. Akio Murakami for advice on the measurement of Cyt b559, Dr. Arthur Grossman for advice on
preparation of total RNA, and Ms. Ayako Kamei for her help with the
experiments. We are also grateful to Drs. Isao Enami and Katsuhiko
Okada for providing antibodies.
| |
LITERATURE CITED |
Allen JF
(1995)
Thylakoid protein phosphorylation, state 1-state 2 transitions, and photosystem stoichiometry adjustment: redox control at multiple levels of gene expression.
Physiol Plant
93:
196-205
[CrossRef]
Anderson JM
(1986)
Photoregulation of the composition, function, and structure of thylakoid membranes.
Annu Rev Plant Physiol
37:
93-136
[CrossRef][ISI]
Anderson JM,
Chow WS,
Goodchild DJ
(1988)
Thylakoid membrane organization in sun/shade acclimation.
Aust J Plant Physiol
15:
11-26
[ISI]
Anderson JM,
Chow WS,
Park Y-I
(1995)
The grand design of photosynthesis: acclimation of the photosynthetic apparatus to environmental cues.
Photosynth Res
46:
129-139
[CrossRef]
Arnon DI,
McSwain BD,
Tsujimoto HY,
Wada K
(1974)
Photochemical activity and components of membrane preparations from blue-green algae. I. Coexistence of two photosystems in relation to chlorophyll a and removal of phycocyanin.
Biochim Biophys Acta
357:
231-245
[Medline]
Aro E-M,
Virgin I,
Andersson B
(1993)
Photoinhibition of photosystem II. Inactivation, protein damage and turnover.
Biochim Biophys Acta
1143:
113-134
[Medline]
Asada K
(1992)
Ascorbate peroxidase: a hydrogen peroxide-scavenging enzyme in plants.
Physiol Plant
85:
235-241
[CrossRef]
Bartsevich VV,
Pakrasi HB
(1997)
Molecular identification of a novel protein that regulates biogenesis of photosystem I, a membrane protein complex.
J Biol Chem
272:
6382-6387
[Abstract/Free Full Text]
Björkman O
(1981)
Responses to different quantum flux densities.
In
OLL Lange,
PS Nobel,
CB Osmond,
H Ziegler,
eds, Physiological Plant Ecology I. Responses to the Physical Environment. Encyclopedia of Plant Physiology, New Series 12A.
Springer-Verlag, Berlin, pp 57-107
Boudreau E,
Takahashi Y,
Lemieux C,
Turmel M,
Rochaix J-D
(1997)
The chloroplast ycf3 and ycf4 open reading frames of Chlamydomonas reinhardtii are required for the accumulation of the photosystem I complex.
EMBO J
16:
6095-6104
[CrossRef][ISI][Medline]
Chiang GG,
Schaefer MR,
Grossman AR
(1992)
Complementation of a red-light-indifferent cyanobacterial mutant.
Proc Natl Acad Sci USA
89:
9415-9419
[Abstract/Free Full Text]
Falkowski PG,
Owens TG,
Ley AC,
Mauzerall DC
(1981)
Effect of growth irradiance levels on the ratio of reaction centers in two species of marine phytoplankton.
Plant Physiol
68:
969-973
[Abstract/Free Full Text]
Foyer CH,
Lelandais M,
Kunert KJ
(1994)
Photooxidative stress in plants.
Physiol Plant
92:
696-717
[CrossRef]
Frías JE,
Flores E,
Herrero A
(1994)
Requirement of the regulatory protein NtcA for the expression of nitrogen assimilation and heterocyst development genes in the cyanobacterium Anabaena sp. PCC 7120.
Mol Microbiol
14:
823-832
[ISI][Medline]
Fujita Y,
Murakami A
(1987)
Regulation of electron transport composition in cyanobacterial photosynthetic system: stoichiometry among photosystem I and II complexes and their light-harvesting antennae and cytochrome b6/f complex.
Plant Cell Physiol
28:
1547-1553
[Abstract/Free Full Text]
Fujita Y,
Murakami A,
Aizawa K,
Ohki K
(1994)
Short-term and long-term adaptation of the photosynthetic apparatus: homeostatic properties of thylakoids.
In
DA Bryant,
eds, The Molecular Biology of Cyanobacteria.
Kluwer Academic Publishers, Dordrecht, The Netherlands, pp 677-692
Fujita Y,
Murakami A,
Ohki K
(1987)
Regulation of photosystem composition in the cyanobacterial photosynthetic system: the regulation occurs in response to the redox state of the electron pool located between the two photosystems.
Plant Cell Physiol
28:
283-292
[Abstract/Free Full Text]
Garewal HS,
Wasserman AR
(1974)
Triton X-100-4 M urea an as extraction medium for membrane proteins. I. Purification of chloroplast cytochrome b559.
Biochemistry
13:
4063-4071
[CrossRef][Medline]
Grossman AR,
Schaefer MR,
Chiang GG,
Collier JL
(1994)
The responses of cyanobacteria to environmental conditions: light and nutrients.
In
DA Bryant,
eds, The Molecular Biology of Cyanobacteria.
Kluwer Academic Publishers, Dordrecht, The Netherlands, pp 641-675
Herbert SK,
Samson G,
Fork DC,
Laudenbach DE
(1992)
Characterization of damage to photosystem I and II in a cyanobacterium lacking detectable iron superoxide dismutase activity.
Proc Natl Acad Sci USA
89:
8716-8720
[Abstract/Free Full Text]
Hihara Y,
Ikeuchi M
(1997)
Mutation in a novel gene required for photomixotrophic growth leads to enhanced photoautotrophic growth of Synechocystis sp. PCC 6803.
Photosynth Res
53:
243-252
[CrossRef]
Hiyama T,
Ke B
(1972)
Difference spectra and extinction coefficients of P700.
Biochim Biophys Acta
267:
160-171
[Medline]
Ikeuchi M,
Inoue Y
(1987)
Specific 125I labeling of D1 (herbicide-binding protein): an indication that D1 functions on both the donor and acceptor sides of photosystem II.
FEBS Lett
210:
71-76
[CrossRef]
Izawa S
(1980)
Acceptors and donors for chloroplast electron transport.
Methods Enzymol
69:
413-433
Kawamura M,
Mimuro M,
Fujita Y
(1979)
Quantitative relationship between two reaction centers in the photosynthetic system of blue-green algae.
Plant Cell Physiol
20:
697-705
[Abstract/Free Full Text]
Kehoe DM,
Grossman AR
(1996)
Similarity of a chromatic adaptation sensor to phytochrome and ethylene receptors.
Science
273:
1409-1412
[Abstract]
Knanna R,
Graham JR,
Myers J,
Gantt E
(1983)
Phycobilisome composition and possible relationship to reaction centers.
Arch Biochem Biophys
224:
534-542
[Medline]
Laemmli UK
(1970)
Cleavage of structural proteins during the assembly of the head of bacteriophage T4.
Nature
227:
680-685
[CrossRef][Medline]
Leong T-Y,
Anderson JM
(1984)
Adaptation of the thylakoid membranes of pea chloroplasts to light intensities. I. Study on the distribution of chlorophyll-protein complexes.
Photosynth Res
5:
105-115
[CrossRef]
Lönneborg A,
Lind LK,
Kalla SR,
Gustafsson P,
Öquist G
(1985)
Acclimation processes in the light-harvesting system of the cyanobacterium Anacystis nidulans following a light shift from white to red light.
Plant Physiol
78:
110-114
[Abstract/Free Full Text]
Melis A
(1991)
Dynamics of photosynthetic membrane composition and function.
Biochim Biophys Acta
1058:
87-106
[CrossRef]
Melis A,
Mandori A,
Glick RE,
Ghirardi ML,
McCauley SW,
Neale PJ
(1985)
The mechanism of photosynthetic membrane adaptation to environmental stress conditions: a hypothesis on the role of electron-transport capacity and of ATP/NADPH pool in the regulation of thylakoid membrane organization and function.
Physiol Vég
23:
757-765
Murakami A,
Fujita Y
(1991)
Regulation of photosystem stoichiometry in the photosynthetic system of the cyanophyte Synechocystis PCC 6714 in response to light-intensity.
Plant Cell Physiol
32:
223-230
[Abstract/Free Full Text]
Murata N,
Nishimura M,
Takamiya A
(1966)
Fluorescence of chlorophyll in photosynthetic systems. III. Emission and action spectra of fluorescence-three emission bands of chlorophyll a and the energy transfer between two pigment systems.
Biochim Biophys Acta
126:
234-243
[Medline]
Neale PJ,
Melis A
(1986)
Algal photosynthetic membrane complexes and the photosynthesis-irradiance curve: a comparison of light-adaptation responses in Chlamydomonas reinhardtii (Chlorophyta).
J Phycol
22:
531-538
[ISI]
Pelroy RA,
Rippka R,
Stanier RY
(1972)
Metabolism of glucose by unicellular blue-green algae.
Arch Microbiol
87:
303-322
Raps S,
Wyman K,
Siegelman HW,
Falkowski PG
(1983)
Adaptation of the cyanobacterium Microcystis aeruginosa to light intensity.
Plant Physiol
72:
829-832
[Abstract/Free Full Text]
Smith BM,
Melis A
(1988)
Photochemical apparatus organization in the diatom Cylindrotheca fusiformis: photosystem stoichiometry and excitation distribution in cells grown under high and low irradiance.
Plant Cell Physiol
29:
761-769
[Abstract/Free Full Text]
Sonoike K
(1996)
Photoinhibition of photosystem I: Its physiological significance in the chilling sensitivity of plants.
Plant Cell Physiol
37:
239-247
[Abstract/Free Full Text]
Sonoike K,
Katoh S
(1988)
Effects of sodium dodecyl sulfate and methyl viologen on the differential extinction coefficient of P-700: a band shift of chlorophyll a associated with oxidation of P-700.
Biochim Biophys Acta
935:
61-71
Sonoike K,
Katoh S
(1989)
Simple estimation of the differential absorption coefficient of P-700 in detergent-treated preparations.
Biochim Biophys Acta
976:
210-213
Sonoike K,
Katoh S
(1990)
Variation and estimation of the differential absorption coefficient of P-700 in spinach photosystem I preparations.
Plant Cell Physiol
31:
1079-1082
[Abstract/Free Full Text]
Sonoike K,
Terashima I
(1994)
Mechanism of photosystem-I photoinhibition in leaves of Cucumis sativus L.
Planta
194:
287-293
[CrossRef]
Terashima I,
Funayama S,
Sonoike K
(1994)
The site of photoin-hibition in leaves of Cucumis sativus L. at low temperatures is photosystem I, not photosystem II.
Planta
193:
300-306
Vierling E,
Alberte RS
(1980)
Functional organization and plasticity of the photosynthetic unit of the cyanobacterium Anacystis nidulans.
Physiol Plant
50:
93-98
Whitmarsh J,
Ort DR
(1984)
Stoichiometries of electron transport complexes in spinach chloroplasts.
Arch Biochem Biophys
231:
378-389
[Medline]
Wild A,
Höpfner M,
Rühle W,
Richter M
(1986)
Changes in the stoichiometry of photosystem II components as an adaptive response to high-light and low-light conditions during growth.
Z Naturforsch
41c:
597-603
Wilde A,
Härtel H,
Hübschmann T,
Hoffmann P,
Shestakov SV,
Börner T
(1995)
Inactivation of a Synechocystis sp. strain PCC 6803 gene with homology to conserved chloroplast open reading frame 184 increases the photosystem II-to-photosystem I ratio.
Plant Cell
7:
649-658
[Abstract]
Yokoyama E,
Murakami A,
Sakurai H,
Fujita Y
(1991)
Effect of supra-high irradiation on the photosynthetic system of the cyanophyte Synechocystis PCC 6714.
Plant Cell Physiol
32:
827-834
[Abstract/Free Full Text]
Zevenboom W,
Mur LR
(1984)
Growth and photosynthetic response of the cyanobacterium Microcystis aeruginosa in relation to photoperiodicity and irradiance.
Arch Microbiol
139:
232-239
This article has been cited by other articles:
|
|
|
|
 
M. R. Islam, S. Aikawa, T. Midorikawa, Y. Kashino, K. Satoh, and H. Koike
slr1923 of Synechocystis sp. PCC6803 Is Essential for Conversion of 3,8-Divinyl(proto)chlorophyll(ide) to 3-Monovinyl(proto)chlorophyll(ide)
Plant Physiology,
October 1, 2008;
148(2):
1068 - 1081.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
Top
Abstract
Introduction