Iron Deficiency Promotes the Lack of Photosynthetic Cytochrome and Affects the Binding of the Luminal Extrinsic Subunits to Photosystem II in the Diatom .

In the diatom , iron limitation promotes a decrease in the content of photosystem II, as determined by measurements of oxygen-evolving activity, thermoluminescence, chlorophyll fluorescence analyses and protein quantification methods. Thermoluminescence experiments also indicate that iron limitation induces subtle changes in the energetics of the recombination reaction between reduced Q and the S/S states of the water-splitting machinery. However, electron transfer from Q to Q, involving non-heme iron, seems not to be significantly inhibited.

The heterologous expression of a plastocyanin in the diatom Phaeodactylum tricornutum improves cell growth under iron-deficient conditions.

We have investigated if the heterologous expression of a functional green alga plastocyanin in the diatom Phaeodactylum tricornutum can improve photosynthetic activity and cell growth. Previous in vitro assays showed that a single-mutant of the plastocyanin from the green algae Chlamydomonas reinhardtii is effective in reducing P. tricornutum photosystem I.

The afterglow photosynthetic luminescence.

The afterglow (AG) photosynthetic luminescence is a long-lived chlorophyll fluorescence emitted from PSII after the illumination of photosynthetic materials by FR or white light and placed in darkness. The AG emission corresponds to the fraction of PSII centers in the S Q non-radiative state immediately after pre-illumination, in which the arrival of an electron transferred from stroma along cyclic/chlororespiratory pathway(s) produces the S Q radiative state that emits luminescence. This emission can be optimally recorded by a linear temperature gradient as sharp thermoluminescence (TL) band peaking at about 45°C.

The afterglow thermoluminescence band as an indicator of changes in the photorespiratory metabolism of the model legume Lotus japonicus.

The afterglow (AG) luminescence is a delayed chlorophyll fluorescence emitted by the photosystem II that seems to reflect the level of assimilatory potential (NADPH+ATP) in chloroplast. In this work, the thermoluminescence (TL) emissions corresponding to the AG band were investigated in plants of the WT and the Ljgln2-2 photorespiratory mutant from Lotus japonicus grown under either photorespiratory (air) or non-photorespiratory (high concentration of CO ) conditions. TL glow curves obtained after two flashes induced the strongest overall TL emissions, which could be decomposed in two components: B band (t  = 27-29°C) and AG band (t  = 44-45°C).

The singular properties of photosynthetic cytochrome c from the diatom Phaeodactylum tricornutum suggest new alternative functions.

Cytochrome c is an extrinsic component in the luminal side of photosystem II (PSII) in cyanobacteria, as well as in eukaryotic algae from the red photosynthetic lineage including, among others, diatoms. We have established that cytochrome c from the diatom Phaeodactylum tricornutum can be obtained as a complete protein from the membrane fraction of the alga, although a C-terminal truncated form is purified from the soluble fractions of this diatom as well as from other eukaryotic algae. Eukaryotic cytochromes c show distinctive electrostatic features as compared with cyanobacterial cytochrome c .

The photosynthetic cytochrome c from the diatom Phaeodactylum tricornutum.

The photosynthetic cytochrome c from the marine diatom Phaeodactylum tricornutum has been purified and characterized. Cytochrome c is mostly obtained from the soluble cell extract in relatively large amounts. In addition, the protein appeared to be truncated in the last hydrophobic residues of the C-terminus, both in the soluble cytochrome c and in the protein extracted from the membrane fraction, as deduced by mass spectrometry analysis and the comparison with the gene sequence.

Iron Deficiency Induces a Partial Inhibition of the Photosynthetic Electron Transport and a High Sensitivity to Light in the Diatom Phaeodactylum tricornutum.

Iron limitation is the major factor controlling phytoplankton growth in vast regions of the contemporary oceans. In this study, a combination of thermoluminescence (TL), chlorophyll fluorescence, and P700 absorbance measurements have been used to elucidate the effects of iron deficiency in the photosynthetic electron transport of the marine diatom P. tricornutum.

Mutations of Cytochrome b559 and PsbJ on and near the QC Site in Photosystem II Influence the Regulation of Short-Term Light Response and Photosynthetic Growth of the Cyanobacterium Synechocystis sp. PCC 6803.

The characteristic features of two types of short-term light adaptations of the photosynthetic apparatus of the cyanobacterium Synechocystis sp. PCC 6803, state transition and blue-green light-induced fluorescence quenching, were compared in wild-type and cytochrome b559 and PsbJ mutant cells with mutations on and near the QC site in photosystem II (PSII). All mutant cells grew photoautotrophically and assembled stable PSII.

In vivo reconstitution of a homodimeric cytochrome b559 like structure: The role of the N-terminus α-subunit from Synechocystis sp. PCC 6803.

The cytochrome b559 is a heme-bridged heterodimeric protein with two subunits, α and β. Both subunits from Synechocystis sp. PCC 6803 have previously been cloned and overexpressed in Escherichia coli and in vivo reconstitution experiments have been carried out.

Thermoluminescence as a complementary technique for the toxicological evaluation of chemicals in photosynthetic organisms.

Thermoluminescence is a simple technique very useful for studying electron transfer reactions on photosystem II (standard thermoluminescence) or the level of lipid peroxidation in membranes (high temperature thermoluminescence) in photosynthetic organisms. Both techniques were used to investigate the effects produced on Chlorella vulgaris cells by six compounds: the chemical intermediates bromobenzene and diethanolamine, the antioxidant propyl gallate, the semiconductor indium nitrate, the pesticide sodium monofluoroacetate and the antimalarial drug chloroquine. Electron transfer activity of the photosystem II significantly decreased after the exposure of Chlorella cells to all the six chemicals used.

The role of the high potential form of the cytochrome b559: Study of Thermosynechococcus elongatus mutants.

Cytochrome b559 is an essential component of the photosystem II reaction center in photosynthetic oxygen-evolving organisms, but its function still remains unclear. The use of photosystem II preparations from Thermosynechococcus elongatus of high integrity and activity allowed us to measure for the first time the influence of cytochrome b559 mutations on its midpoint redox potential and on the reduction of the cytochrome b559 by the plastoquinone pool (or QB). In this work, five mutants having a mutation in the α-subunit (I14A, I14S, R18S, I27A and I27T) and one in the β-subunit (F32Y) of cytochrome b559 have been investigated.

Spectroscopic and functional characterization of cyanobacterium Synechocystis PCC 6803 mutants on the cytoplasmic-side of cytochrome b559 in photosystem II.

We performed spectroscopic and functional characterization on cyanobacterium Synechocystis PCC6803 with mutations of charged residues of the cytoplasmic side of cytochrome (Cyt) b559 in photosystem II (PSII). All of the mutant cells grew photoautotrophically and assembled stable PSII. However, R7Eα, R17Eα and R17Lβ mutant cells grew significantly slower and were more susceptible to photoinhibition than wild-type cells.

Reconstitution, spectroscopy, and redox properties of the photosynthetic recombinant cytochrome b(559) from higher plants.

A study of the in vitro reconstitution of sugar beet cytochrome b(559) of the photosystem II is described. Both α and β cytochrome subunits were first cloned and expressed in Escherichia coli. In vitro reconstitution of this cytochrome was carried out with partially purified recombinant subunits from inclusion bodies.

Photosynthetic cytochrome c550.

Cytochrome c550 (cyt c550) is a membrane component of the PSII complex in cyanobacteria and some eukaryotic algae, such as red and brown algae. Cyt c550 presents a bis-histidine heme coordination which is very unusual for monoheme c-type cytochromes. In PSII, the cyt c550 with the other extrinsic proteins stabilizes the binding of Cl(-) and Ca(2+) ions to the oxygen evolving complex and protects the Mn(4)Ca cluster from attack by bulk reductants.

Peculiar properties of chlorophyll thermoluminescence emission of autotrophically or mixotrophically grown Chlamydomonas reinhardtii.

The microalgae Chlamydomonas reinhardtii and Chlorella sp. CCAP 211/84 were grown autotrophically and mixotrophically and their thermoluminescence emissions were recorded above 0 °C after excitation by 1, 2 or 3 xenon flashes or by continuous far-red light. An oscillation of the B band intensity according to the number of flashes was always observed, with a maximum after 2 flashes, accompanied by a downshift of the B band temperature maximum in mixotrophic compared to autotrophic grown cells, indicative of a dark stable pH gradient.

A high redox potential form of cytochrome c550 in photosystem II from Thermosynechococcus elongatus.

Cytochrome c(550) (cyt c(550)) is a component of photosystem II (PSII) from cyanobacteria, red algae, and some other eukaryotic algae. Its physiological role remains unclear. In the present work, measurements of the midpoint redox potential (E(m)) were performed using intact PSII core complexes preparations from a histidine-tagged PSII mutant strain of the thermophilic cyanobacterium Thermosynechococcus (T.

Changes in photosynthetic metabolism induced by tobamovirus infection in Nicotiana benthamiana studied in vivo by thermoluminescence.

* In thylakoids from Nicotiana benthamiana infected with the pepper mild mottle virus (PMMoV), a decreased amount of the PsbP and PsbQ proteins of photosystem II and different proteins of the Calvin cycle have been previously observed. We used thermoluminescence to study the consequences in vivo. * Measurements on unfrozen discs from symptomatic and asymptomatic leaves of plants infected by two tobamovirus PMMoV-S and PMMoV-I strains were compared with homologous samples in control plants.

Changes in photosynthetic electron transfer and state transitions in an herbicide-resistant D1 mutant from soybean cell cultures.

Anomalies in photosynthetic activity of the soybean cell line STR7, carrying a single mutation (S268P) in the chloroplastic gene psbA that codes for the D1 protein of the photosystem II, have been examined using different spectroscopic techniques. Thermoluminescence emission experiments have shown important differences between STR7 mutant and wild type cells. The afterglow band induced by both white light flashes and far-red continuous illumination was downshifted by about 4 degrees C and the Q band was upshifted by 5 degrees C.

Afterglow thermoluminescence band as a possible early indicator of changes in the photosynthetic electron transport in leaves.

The afterglow (AG) band of thermoluminescence (TL) has been investigated in leaves of Arabidopsis thaliana. Excitation of dark-adapted leaves with two saturating single turn-over flashes induced the appearance of a complex TL glow curve that could be well simulated by three components: the two components, B1 and B2, of the usually called B-band, peaking at 18 and 26 degrees C, respectively, and a band with tmax at 41 degrees C, which we attributed to an AG emission. Illumination of dark-adapted leaves with 720 nm monochromatic and FR lights generated the emission of a sharp single band peaking also around at 41 degrees C, that it is usually assigned to an AG emission band.

A thermoluminescence study of photosystem II back electron transfer reactions in rice leaves - effects of salt stress.

The recombination reactions of Photosystem II have been investigated in vivo in rice leaves by using the thermoluminescence (TL) emission technique. Excitation of dark-adapted leaf segments at 0 degrees C with different number of single turn-over flashes induced the appearance of complex TL glow curves. The mathematical analysis of these curves showed the existence of four TL components: B1-band (temperature maximum, t(max), at 24 degrees C, originating from S3QB - recombination), B2-band (tmax at 35 degrees C, from S2QB -), AG-band (tmax at 46 degrees C) and C-band (tmax at 55 degrees C, from TyrD +QA -).

Cytochrome c550 in the cyanobacterium Thermosynechococcus elongatus: study of redox mutants.

Cytochrome c(550) is one of the extrinsic Photosystem II subunits in cyanobacteria and red algae. To study the possible role of the heme of the cytochrome c(550) we constructed two mutants of Thermosynechococcus elongatus in which the residue His-92, the sixth ligand of the heme, was replaced by a Met or a Cys in order to modify the redox properties of the heme. The H92M and H92C mutations changed the midpoint redox potential of the heme in the isolated cytochrome by +125 mV and -30 mV, respectively, compared with the wild type.

Copper effect on cytochrome b of photosystem II under photoinhibitory conditions.

Toxic Cu (II) effect on cytochrome b(559) under aerobic photoinhibitory conditions was examined in two different photosystem II (PSII) membrane preparations active in oxygen evolution. The preparations differ in the content of cytochrome b(559) redox potential forms. Difference absorption spectra showed that the presence of Cu (II) induced the oxidation of the high-potential form of cytochrome b(559) in the dark.

Redox properties of the photosystem II cytochromes b559 and c550 in the cyanobacterium Thermosynechococcus elongatus.

Redox properties of cytochrome b559 (Cyt b559) and cytochrome c550 (Cyt c550) have been studied by using highly stable photosystem II (PSII) core complex preparations from a mutant strain of the thermophilic cyanobacterium Thermosynechococcus elongatus with a histidine tag on the CP43 protein of PSII. Two different redox potential forms for Cyt b559 are found in these preparations, with a midpoint redox potential ( E'(m)) of +390 mV in about half of the centers and +275 mV in the other half. The high-potential form, whose E'(m)is pH independent, can be converted into the lower potential form by Tris washing, mild heating or alkaline pH incubation.

Characterization of a photosynthetic Euglena strain isolated from an acidic hot mud pool of a volcanic area of Costa Rica.

Abstract Conspicuous green patches on the surface of an acidic hot mud pool located near the Rincón de la Vieja volcano (northwestern Costa Rica) consisted of apparently unialgal populations of a chloroplast-bearing euglenoid. Morphological and physiological studies showed that it is a non-flagellated photosynthetic Euglena strain able to grow in defined mineral media at temperatures up to 40 degrees C and exhibiting higher thermotolerance than Euglena gracilis SAG 5/15 in photosynthetic activity analyses. Molecular phylogeny studies using 18S rDNA and GapC genes indicated that this strain is closely related to Euglena mutabilis, another acid-tolerant photosynthetic euglenoid, forming a clade deeply rooted in the Euglenales lineage.