scholarly journals Over Expression of the Cyanobacterial Pgr5-Homologue Leads to Pseudoreversion in a Gene Coding for a Putative Esterase in Synechocystis 6803

Life ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 174
Author(s):  
Ketty Margulis ◽  
Hagit Zer ◽  
Hagar Lis ◽  
Hanan Schoffman ◽  
Omer Murik ◽  
...  
Keyword(s):  
Redox Regulation ◽  
Electron Flow ◽  
Photosynthetic Apparatus ◽  
Redox Balance ◽  
Synechocystis 6803 ◽  
Experimental Conditions ◽  
Direct Role ◽  
Transfer Rates ◽  
Gene Coding ◽  
Eukaryotic Phytoplankton

Pgr5 proteins play a major direct role in cyclic electron flow paths in plants and eukaryotic phytoplankton. The genomes of many cyanobacterial species code for Pgr5-like proteins but their function is still uncertain. Here, we present evidence that supports a link between the Synechocystis sp. PCC6803 Pgr5-like protein and the regulation of intracellular redox balance. The knockout strain, pgr5KO, did not display substantial phenotypic response under our experimental conditions, confirming results obtained in earlier studies. However, the overexpression strain, pgr5OE, accumulated 2.5-fold more chlorophyll than the wild type and displayed increased content of photosystems matching the chlorophyll increase. As a result, electron transfer rates through the photosynthetic apparatus of pgr5OE increased, as did the amount of energy stored as glycogen. While, under photoautotrophic conditions, this metabolic difference had only minor effects, under mixotrophic conditions, pgr5OE cultures collapsed. Interestingly, this specific phenotype of pgr5OE mutants displayed a tendency for reverting, and cultures which previously collapsed in the presence of glucose were now able to survive. DNA sequencing of a pgr5OE strain revealed a second site suppression mutation in slr1916, a putative esterase associated with redox regulation. The phenotype of the slr1916 knockout is very similar to that of the strain reported here and to that of the pmgA regulator knockout. These data demonstrate that, in Synechocystis 6803, there is strong selection against overexpression of the Pgr5-like protein. The pseudoreversion event in a gene involved in redox regulation suggests a connection of the Pgr5-like protein to this network.

scholarly journals Bi-directional electron transfer between H2 and NADPH mitigates light fluctuation responses in green algae

2021 ◽  
Author(s):  
Yuval Milrad ◽  
Shira Schweitzer ◽  
Yael Feldman ◽  
Iftach Yacoby
Keyword(s):  
Green Algae ◽  
Fossil Fuels ◽  
Electron Flow ◽  
Scale Up ◽  
Photosynthetic Apparatus ◽  
Nicotinamide Adenine Dinucleotide Phosphate ◽  
Redox Balance ◽  
Promising Alternative ◽  
Photosynthetic Organisms ◽  
Nadph Metabolism

Abstract The metabolism of green algae has been the focus of much research over the last century. These photosynthetic organisms can thrive under various conditions and adapt quickly to changing environments by concomitant usage of several metabolic apparatuses. The main electron coordinator in their chloroplasts, nicotinamide adenine dinucleotide phosphate (NADPH), participates in many enzymatic activities and is also responsible for inter-organellar communication. Under anaerobic conditions, green algae also accumulate molecular hydrogen (H2), a promising alternative for fossil fuels. However, to scale-up its accumulation, a firm understanding of its integration in the photosynthetic apparatus is still required. While it is generally accepted that NADPH metabolism correlates to H2 accumulation, the mechanism of this collaboration is still vague and relies on indirect measurements. Here, we investigated this connection in Chlamydomonas reinhardtii using simultaneous measurements of both dissolved gases concentration, NADPH fluorescence and electrochromic shifts at 520-546 nm. Our results indicate that energy transfer between H2 and NADPH is bi-directional and crucial for the maintenance of redox balance under light fluctuations. At light onset, NADPH consumption initially eventuates in H2 evolution, which initiates the photosynthetic electron flow. Later on, as illumination continues the majority of NADPH is diverted to the Calvin-Benson-Bassham cycle. Dark onset triggers re-assimilation of H2, which produces NADPH and so, enables initiation of dark fermentative metabolism.

scholarly journals Bi-directional electron transfer between H2 and NADPH mitigates the response to light fluctuations in green algae

2020 ◽  
Author(s):  
Yuval Milrad ◽  
Shira Schweitzer ◽  
Yael Feldman ◽  
Iftach Yacoby
Keyword(s):  
Energy Transfer ◽  
Green Algae ◽  
Fossil Fuels ◽  
Electron Flow ◽  
Scale Up ◽  
Photosynthetic Apparatus ◽  
Nicotinamide Adenine Dinucleotide Phosphate ◽  
Redox Balance ◽  
Promising Alternative ◽  
Light Fluctuations

AbstractThe metabolism of green algae has been the focus of much research over the last century. These photosynthetic organisms can thrive under various conditions and adapt quickly to changing environments by concomitant usage of several metabolic apparatuses. The main electron coordinator in their chloroplasts, nicotinamide adenine dinucleotide phosphate (NADPH), participates in many enzymatic activities and is also responsible for interorganelle communication. Under anaerobic conditions, green algae also accumulate molecular hydrogen (H2), a promising alternative for fossil fuels. However, in order to scale-up its accumulation, a firm understanding of its integration in the photosynthetic apparatus is still lacking. While it is generally accepted that NADPH metabolism correlates to H2 accumulation, the mechanism of this collaboration is still vague and rely on indirect measurements. Here, we investigated this connection using simultaneous measurements of both dissolved gases concentration, NADPH fluorescence and electrochromic shifts at 520-546 nm. Our results indicate that energy transfer between H2 and NADPH is bi-directional and crucial for the maintenance of redox balance under light fluctuations. At light onset, NADPH consumption is initially eventuated in H2 evolution, which initiate the photosynthetic electron flow. Later on, as illumination continues the majority of NADPH is recycled by Nda2 rather than consumed by terminal sinks such as CBB cycle and H2 production. Dark onset triggers re-assimilation of H2, which produces NADPH and so, enables initiation of dark fermentative metabolism.One sentence summaryEnergy transfer between H2 and NADPH is bi-directional and crucial for the maintenance of redox balance under light fluctuations.

scholarly journals NTRC-dependent redox balance of 2-Cys peroxiredoxins is needed for optimal function of the photosynthetic apparatus

2017 ◽  
Vol 114 (45) ◽  
pp. 12069-12074 ◽  
Author(s):  
Juan Manuel Pérez-Ruiz ◽  
Belén Naranjo ◽  
Valle Ojeda ◽  
Manuel Guinea ◽  
Francisco Javier Cejudo
Keyword(s):  
Redox Regulation ◽  
Photosynthetic Apparatus ◽  
Reducing Power ◽  
Redox Balance ◽  
Light Energy ◽  
Energy Utilization ◽  
Antioxidant Systems ◽  
Redox Systems ◽  
Triple Mutant ◽  
Low Efficiency

Thiol-dependent redox regulation allows the rapid adaptation of chloroplast function to unpredictable changes in light intensity. Traditionally, it has been considered that chloroplast redox regulation relies on photosynthetically reduced ferredoxin (Fd), thioredoxins (Trxs), and an Fd-dependent Trx reductase (FTR), the Fd-FTR-Trxs system, which links redox regulation to light. More recently, a plastid-localized NADPH-dependent Trx reductase (NTR) with a joint Trx domain, termed NTRC, was identified. NTRC efficiently reduces 2-Cys peroxiredoxins (Prxs), thus having antioxidant function, but also participates in redox regulation of metabolic pathways previously established to be regulated by Trxs. Thus, the NTRC, 2-Cys Prxs, and Fd-FTR-Trxs redox systems may act concertedly, but the nature of the relationship between them is unknown. Here we show that decreased levels of 2-Cys Prxs suppress the phenotype of the Arabidopsis thaliana ntrc KO mutant. The excess of oxidized 2-Cys Prxs in NTRC-deficient plants drains reducing power from chloroplast Trxs, which results in low efficiency of light energy utilization and impaired redox regulation of Calvin–Benson cycle enzymes. Moreover, the dramatic phenotype of the ntrc-trxf1f2 triple mutant, lacking NTRC and f-type Trxs, was also suppressed by decreased 2-Cys Prxs contents, as the ntrc-trxf1f2-Δ2cp mutant partially recovered the efficiency of light energy utilization and exhibited WT rate of CO2 fixation and growth phenotype. The suppressor phenotype was not caused by compensatory effects of additional chloroplast antioxidant systems. It is proposed that the Fd-FTR-Trx and NTRC redox systems are linked by the redox balance of 2-Cys Prxs, which is crucial for chloroplast function.

Prediction of Growth Parameters of Frost Deposits in Forced Convection

1981 ◽  
Vol 103 (1) ◽  
pp. 3-6 ◽  
Author(s):  
J. E. White ◽  
C. J. Cremers
Keyword(s):  
Mass Transfer ◽  
Forced Convection ◽  
Growth Parameters ◽  
Experimental Investigations ◽  
Experimental Conditions ◽  
Transfer Rates ◽  
Air Stream ◽  
Transient Period ◽  
Approximate Expressions ◽  
Frost Layer

Experimental investigations of frost deposition under forced convection conditions have shown that in most cases heat and mass transfer rates become constant after an initial transient period. It is shown that, in such cases, approximately half of the mass transfer from a humid air stream to a frost layer diffuses inward, condenses and increases the density of the frost. The other half is deposited at the surface and increases the thickness of the layer. Approximate expressions for density and thickness of the frost layer are derived and compared with data from the literature and also with experimental work reported in this paper. The correlations are shown to work well for a broad range of experimental conditions.

scholarly journals A commonly used photosynthetic inhibitor fails to block electron flow to photosystem I in intact systems

2019 ◽  
Author(s):  
Duncan Fitzpatrick ◽  
Eva-Mari Aro ◽  
Arjun Tiwari
Keyword(s):  
Electron Flow ◽  
Photosynthetic Apparatus ◽  
Intact Cells ◽  
Membrane Inlet Mass Spectrometry ◽  
Redox Kinetics ◽  
Species Formation ◽  
Intact Leaves ◽  
Transfer Chain ◽  
Photosynthetic Electron Transfer

AbstractIn plant science, 2,4-dinitrophenylether of iodonitrothymol (DNP-INT) is frequently used as an alternative to 2,5-dibromo-6-isopropyl-3-methyl-1,4-benzoquinone (DBMIB) to examine the capacity of plastoquinol and semiquinone to reduce O2. DNP-INT is considered an effective inhibitor of the photosynthetic electron transfer chain (PETC) through its binding at the Q0 site of Cyt-b6f. The binding and action of DNP-INT has been previously characterized spectroscopically in purified Cyt-b6f complex reconstituted with Plastocyanin, PSII membranes and plastoquinone, as well as in isolated thylakoids based on its property to block MV-mediated O2 consumption. Contrary to the conclusions made from these experiments, we observed clear reduction of P700+ in samples incubated with DNP-INT during our recent investigation into the sites of oxygen consumption in isolated thylakoids. Therefore, we carried out an extensive investigation of DNP-INT’s chemical efficacy in isolated thylakoids and intact leaves. This included examination of its capacity to block the PETC before PSI, and therefore its inhibition of CO2 fixation. P700 redox kinetics were measured using Dual-PAM whilst Membrane Inlet Mass Spectrometry (MIMS) was used for simultaneous determination of the rates of O2 evolution and O2 consumption in isolated thylakoids and CO2 fixation in intact leaves, using two stable isotopes of oxygen (16O2,18O2) and CO2 (12C,13C), respectively. Based on these investigations we confirmed that DNP-INT is unable to completely block the PETC and CO2 fixation, therefore its use may produce artefacts if applied to isolated thylakoids or intact cells, especially when determining the locations of reactive oxygen species formation in the photosynthetic apparatus.

Acquired tolerance of the photosynthetic apparatus to photoinhibition as a result of growing Solanum lycopersicum at moderately higher temperature and light intensity

2019 ◽  
Vol 46 (6) ◽  
pp. 555 ◽  
Author(s):  
Milena T. Gerganova ◽  
Aygyun K. Faik ◽  
Maya Y. Velitchkova
Keyword(s):  
High Temperature ◽  
Quantum Yield ◽  
Light Intensity ◽  
Electron Flow ◽  
Photosynthetic Apparatus ◽  
High Light ◽  
Cyclic Electron Flow ◽  
Photochemical Quenching ◽  
Kinetics Of ◽  
Moderately High Temperature

The kinetics of photoinhibition in detached leaves from tomato plants (Solanium lycopersicum L. cv. M82) grown for 6 days under different combinations of optimal and moderately high temperature and optimal and high light intensity were studied. The inhibition of PSII was evaluated by changes in maximal quantum yield, the coefficient of photochemical quenching and the quantum yield of PSII. The changes of PSI activity was estimated by the redox state of P700. The involvement of different possible protective processes was checked by determination of nonphotochemical quenching and cyclic electron flow around PSI. To evaluate to what extent the photosynthetic apparatus and its response to high light treatment was affected by growth conditions, the kinetics of photoinhibition in isolated thylakoid membranes were also studied. The photochemical activities of both photosystems and changes in the energy distribution and interactions between them were evaluated by means of a Clark electrode and 77 K fluorescence analysis. The data showed an increased tolerance to photoinhibition in plants grown under a combination of moderately high temperature and light intensity, which was related to the stimulation of cyclic electron flow, PSI activity and rearrangements of pigment–protein complexes, leading to a decrease in the excitation energy delivered to PSII.

Distribution and Effects of Bentazon in Crop Plants and Weeds

1982 ◽  
Vol 37 (10) ◽  
pp. 889-897 ◽  
Author(s):  
H. K. Lichtenthaler ◽  
D. Meier ◽  
G. Retzlaff ◽  
R. Hamm
Keyword(s):  
Electron Flow ◽  
Photosynthetic Apparatus ◽  
Crop Plants ◽  
Light Conditions ◽  
Low Light ◽  
Tolerant Plants ◽  
Variable Chlorophyll Fluorescence ◽  
Pigment Ratios ◽  
Kautsky Effect ◽  
Uptake And Transport

Abstract The inhibition of photosynthetic CO2-assimilation and of the variable chlorophyll fluorescence as well as uptake and transport of 14C-labelled bentazon and the possibilities for a herbicideinduced shade-type modification of the photosynthetic apparatus were investigated in bentazonsensitive weeds (Galium, Sinapis, Raphanus) and in the tolerant crop plants wheat and maize.1. In weeds the depression of photosynthetic CO2-assimilation is irreversible, whereas tolerant plants recover due to the metabolization of the active herbicide.2. A lower rate of uptake and transport of bentazon associated with its fast metabolization is the reason for the tolerance of crop plants towards bentazon.3. The transport of [14C]bentazon proceeds in the tracheary elements of the xylem. Uptake and transport of bentazon in the weeds are light dependent.4. The loss of variable fluorescence (Kautsky effect) in the leaves after root application o f bentazon proceeds much faster at high-light than at low light conditions and confirms the light-dependency of the bentazon transport.5. In the sensitive dicot weeds bentazon not only inhibits photosynthetic electron flow and depresses CO2-fixation but also induces the formation of shade-type chloroplasts which are less efficient in photosynthetic quantum conversion. This bentazon-induced modification of the photosynthetic apparatus (e.g. changes in ultrastructure, pigment ratios, and levels of chloro-phyll-proteins) contributes to the effectiveness of bentazon as a herbicide.

scholarly journals Photosynthesis Regulation in Response to Fluctuating Light in the Secondary Endosymbiont Alga Nannochloropsis gaditana

2019 ◽  
Vol 61 (1) ◽  
pp. 41-52 ◽  
Author(s):  
Alessandra Bellan ◽  
Francesca Bucci ◽  
Giorgio Perin ◽  
Alessandro Alboresi ◽  
Tomas Morosinotto
Keyword(s):  
Electron Transport ◽  
Electron Flow ◽  
Incident Light ◽  
Photosynthetic Apparatus ◽  
Photosynthetic Electron Transport ◽  
Thermal Dissipation ◽  
Photochemical Quenching ◽  
Nannochloropsis Gaditana ◽  
Fluctuating Light ◽  
Light Fluctuations

Abstract In nature, photosynthetic organisms are exposed to highly dynamic environmental conditions where the excitation energy and electron flow in the photosynthetic apparatus need to be continuously modulated. Fluctuations in incident light are particularly challenging because they drive oversaturation of photosynthesis with consequent oxidative stress and photoinhibition. Plants and algae have evolved several mechanisms to modulate their photosynthetic machinery to cope with light dynamics, such as thermal dissipation of excited chlorophyll states (non-photochemical quenching, NPQ) and regulation of electron transport. The regulatory mechanisms involved in the response to light dynamics have adapted during evolution, and exploring biodiversity is a valuable strategy for expanding our understanding of their biological roles. In this work, we investigated the response to fluctuating light in Nannochloropsis gaditana, a eukaryotic microalga of the phylum Heterokonta originating from a secondary endosymbiotic event. Nannochloropsis gaditana is negatively affected by light fluctuations, leading to large reductions in growth and photosynthetic electron transport. Exposure to light fluctuations specifically damages photosystem I, likely because of the ineffective regulation of electron transport in this species. The role of NPQ, also assessed using a mutant strain specifically depleted of this response, was instead found to be minor, especially in responding to the fastest light fluctuations.

Involvement of the Xanthophyll Cycle in Regulation of Cyclic Electron Flow around Photosystem II

1996 ◽  
Vol 51 (1-2) ◽  
pp. 47-52 ◽  
Author(s):  
W. I. Gruszecki ◽  
K. Strzałk ◽  
K.P. Bader ◽  
A. Radunz ◽  
G.H. Schmid
Keyword(s):  
Electron Transport ◽  
Photosystem Ii ◽  
Oxygen Evolution ◽  
Xanthophyll Cycle ◽  
Electron Flow ◽  
Photosynthetic Apparatus ◽  
Photosynthetic Oxygen Evolution ◽  
Cyclic Electron Transport ◽  
Ps Ii ◽  
Low Levels

Abstract In our previous study (Gruszecki et al., 1995) we have postulated that the mechanism of cyclic electron transport around photosystem II, active under overexcitation of the photosynthetic apparatus by light is under control of the xanthophyll cycle. The combination of dif­ferent light quality and thylakoids having various levels of xanthophyll cycle pigments were applied to support this hypothesis. In the present work photosynthetic oxygen evolution from isolated tobacco chloroplasts was measured by means of mass spectrometry under conditions of high or low levels of violaxanthin, being transformed to zeaxanthin during dark incubation in an ascorbate containing buffer at pH 5.7. Analysis of oxygen evolution and of light-induced oxygen uptake indicate that the de-epoxidation of violaxanthin to zeaxanthin results in an increased cyclic electron transport around PS II, thus dimishing the vectorial electron flow from water. An effect similar to de-epoxidation was observed after incubation of thylakoid membranes with specific antibodies against violaxanthin.

Sign in / Sign up

Export Citation Format

Share Document