Control Of Photosynthetic Electron Transport Research Articles

Sensitivity of rice to photooxidation associated with antioxidant enzyme activity and carbon assimilation

In this study, rice cultivar 8272 (yellowing leaves) was compared with cultivar 9311 (normal leaf color) to clarify the mechanism underlying the chlorosis. The 8272 leaf color was sensitive to intense sunlight accompanied by high temperatures, which induced the yellowing of leaves, whereas the 9311 leaf color was normal under the same growing conditions. A shading experiment in the field and an artificial climate chamber test revealed that the chlorosis of 8272 leaves was due to high-intensity light, rather than high temperatures. Analyses of chlorophyll fluorescence parameters indicated that the photosystem II (PSII) reaction center activity of 8272N (grown under natural high light conditions) was significantly lower than that of 8272S (under shade), with the electron transfer significantly inhibited. The H2O2, O2.−, and malondialdehyde (MDA) contents increased sharply in 8272N, and the antioxidant enzymes were also activated. A comparison of the enriched KEGG pathways among the differentially expressed genes (DEGs) between 8272 and 9311 indicated genes related to abiotic stress tolerance were highly expressed in 8272N. In contrast, the expression levels of the key genes in the carbon assimilation metabolic pathway were significantly lower in 8272N than in 9311N. A qRT-PCR analysis confirmed the results of the RNA-seq and antioxidant enzyme activity analyses. Thus, the chlorosis of 8272 leaves in response to intense light may be associated with the mechanisms contributing to the photosynthetic control of electron transport via carbon assimilation in leaves.

Energetic and regulatory role of proton potential in chloroplasts

The review focuses on the energetic and regulatory role of proton potential in the activity of chloroplasts, the light energy-converting organelles of plant cells. Mechanisms of generation of the transmembrane difference of electrochemical potentials of hydrogen ions (Δµ(~)(H+)) in the chloroplast thylakoid membranes are considered. Methods for measuring the intrathylakoid pH in chloroplasts are described. It is shown that under conditions of phosphorylation in chloroplasts, the pH of the intrathylakoid space decreases moderately (pH(in) ≥ 6.0-6.2, at the stroma pH(out) ≈ 7.8-8.0), with a corresponding concentration component of Δµ(~)(H+) equal to ΔpH ≤ 1.6-2.0. On analyzing the energy and structural features of ATP synthase of chloroplasts, we conclude that the energy stored as the concentration component of the proton potential ΔpH is sufficient to sustain ATP synthesis. The mechanisms of pH-dependent regulation of electron transport in chloroplasts (photosynthetic control of electron transport, enhancement of non-photochemical quenching of chlorophyll excitation in the light-harvesting antenna, light-induced activation of the Calvin-Benson cycle reactions, activation of ATP synthase) are considered briefly.

Photosynthetic control of electron transport and the regulation of gene expression

The term 'photosynthetic control' describes the short- and long-term mechanisms that regulate reactions in the photosynthetic electron transport (PET) chain so that the rate of production of ATP and NADPH is coordinated with the rate of their utilization in metabolism. At low irradiances these mechanisms serve to optimize light use efficiency, while at high irradiances they operate to dissipate excess excitation energy as heat. Similarly, the production of ATP and NADPH in ratios tailored to meet demand is finely tuned by a sophisticated series of controls that prevents the accumulation of high NAD(P)H/NAD(P) ratios and ATP/ADP ratios that would lead to potentially harmful over-reduction and inactivation of PET chain components. In recent years, photosynthetic control has also been extrapolated to the regulation of gene expression because mechanisms that are identical or similar to those that serve to regulate electron flow through the PET chain also coordinate the regulated expression of genes encoding photosynthetic proteins. This requires coordinated gene expression in the chloroplasts, mitochondria, and nuclei, involving complex networks of forward and retrograde signalling pathways. Photosynthetic control operates to control photosynthetic gene expression in response to environmental and metabolic changes. Mining literature data on transcriptome profiles of C(3) and C(4) leaves from plants grown under high atmospheric carbon dioxide (CO(2)) levels compared with those grown with ambient CO(2) reveals that the transition to higher photorespiratory conditions in C(3) plants enhances the expression of genes associated with cyclic electron flow pathways in Arabidopsis thaliana, consistent with the higher ATP requirement (relative to NADPH) of photorespiration.

Transcriptional Control of Photosynthesis Genes: The Evolutionarily Conserved Regulatory Mechanism in Plastid Genome Function

Chloroplast sensor kinase (CSK) is a bacterial-type sensor histidine kinase found in chloroplasts—photosynthetic plastids—in eukaryotic plants and algae. Using a yeast two-hybrid screen, we demonstrate recognition and interactions between: CSK, plastid transcription kinase (PTK), and a bacterial-type RNA polymerase sigma factor-1 (SIG-1). CSK interacts with itself, with SIG-1, and with PTK. PTK also interacts directly with SIG-1. PTK has previously been shown to catalyze phosphorylation of plastid-encoded RNA polymerase (PEP), suppressing plastid transcription nonspecifically. Phospho-PTK is inactive as a PEP kinase. Here, we propose that phospho-CSK acts as a PTK kinase, releasing PTK repression of chloroplast transcription, while CSK also acts as a SIG-1 kinase, blocking transcription specifically at the gene promoter of chloroplast photosystem I. Oxidation of the photosynthetic electron carrier plastoquinone triggers phosphorylation of CSK, inducing chloroplast photosystem II while suppressing photosystem I. CSK places photosystem gene transcription under the control of photosynthetic electron transport. This redox signaling pathway has its origin in cyanobacteria, photosynthetic prokaryotes from which chloroplasts evolved. The persistence of this mechanism in cytoplasmic organelles of photosynthetic eukaryotes is in precise agreement with the CoRR hypothesis for the function of organellar genomes: the plastid genome and its primary gene products are Co-located for Redox Regulation. Genes are retained in plastids primarily in order for their expression to be subject to this rapid and robust redox regulatory transcriptional control mechanism, whereas plastid genes also encode genetic system components, such as some ribosomal proteins and RNAs, that exist in order to support this primary, redox regulatory control of photosynthesis genes. Plastid genome function permits adaptation of the photosynthetic apparatus to changing environmental conditions of light quantity and quality.

Control of cytochrome b6f at low and high light intensity and cyclic electron transport in leaves

The light-dependent control of photosynthetic electron transport from plastoquinol (PQH 2) through the cytochrome b 6 f complex (Cyt b 6 f) to plastocyanin (PC) and P700 (the donor pigment of Photosystem I, PSI) was investigated in laboratory-grown Helianthus annuus L., Nicotiana tabaccum L., and naturally-grown Solidago virgaurea L., Betula pendula Roth, and Tilia cordata P. Mill. leaves. Steady-state illumination was interrupted (light–dark transient) or a high-intensity 10 ms light pulse was applied to reduce PQ and oxidise PC and P700 (pulse-dark transient) and the following re-reduction of P700 + and PC + was recorded as leaf transmission measured differentially at 810–950 nm. The signal was deconvoluted into PC + and P700 + components by oxidative (far-red) titration (V. Oja et al., Photosynth. Res. 78 (2003) 1–15) and the PSI density was determined by reductive titration using single-turnover flashes (V. Oja et al., Biochim. Biophys. Acta 1658 (2004) 225–234). These innovations allowed the definition of the full light response curves of electron transport rate through Cyt b 6 f to the PSI donors. A significant down-regulation of Cyt b 6 f maximum turnover rate was discovered at low light intensities, which relaxed at medium light intensities, and strengthened again at saturating irradiances. We explain the low-light regulation of Cyt b 6 f in terms of inactivation of carbon reduction cycle enzymes which increases flux resistance. Cyclic electron transport around PSI was measured as the difference between PSI electron transport (determined from the light–dark transient) and PSII electron transport determined from chlorophyll fluorescence. Cyclic e − transport was not detected at limiting light intensities. At saturating light the cyclic electron transport was present in some, but not all, leaves. We explain variations in the magnitude of cyclic electron flow around PSI as resulting from the variable rate of non-photosynthetic ATP-consuming processes in the chloroplast, not as a principle process that corrects imbalances in ATP/NADPH stoichiometry during photosynthesis.

Relationship between Photosynthetic Electron Transport and Stromal Enzyme Activity in Pea Leaves

The responses of the quantum efficiencies of photosystem (PS) II and PSI measured in vivo simultaneously with estimations of the activities and activation states of NADP-malate dehydrogenase, chloroplast fructose-1,6-bisphosphatase, and ribulose-1,5-bisphosphate carboxylase were used to study the relationship between electron transport and carbon metabolism. The effects of varying irradiance and CO(2) partial pressure on the relationship between the quantum efficiencies of PSI and II, and the activity of these enzymes shows that the interrelationships vary according to the limitations placed on the system. The relationship between the quantum efficiencies of PSII and PSI was linear in most situations. In response to increasing irradiance, the activity of all three enzymes increased. In the case of NADP-malate dehydrogenase this increase was well correlated with the estimated flux of electrons through PSI and PSII. The other two enzymes showed a more complex relationship with the estimated flux of electrons through both photosystems. These relationships are consistent with the known interactions between these stromal enzymes and the thylakoids. The response to varying CO(2) partial pressure is more complex. The efficiencies of PSI and II declined with decreasing CO(2) partial pressure and the activity of each enzyme varied uniquely. However, there are clear correlations between the activities of the enzymes and the flux of electrons through the photosystems. In contrast to the data obtained under conditions of varying irradiance, there is clear evidence of photosynthetic control of electron transport when the CO(2) concentration is varied.

The mechanisms contributing to photosynthetic control of electron transport by carbon assimilation in leaves

'Photosynthetic control' describes the processes that serve to modify chloroplast membrane reactions in order to co-ordinate the synthesis of ATP and NADPH with the rate at which these metabolites can be used in carbon metabolism. At low irradiance, optimisation of the use of excitation energy is required, while at high irradiance photosynthetic control serves to dissipate excess excitation energy when the potential rate of ATP and NADPH synthesis exceed demand. The balance between ΔpH, ATP synthesis and redox state adjusts supply to demand such that the [ATP]/[ADP] and [NADPH]/[NADP(+)] ratios are remarkably constant in steady-state conditions and modulation of electron transport occurs without extreme fluctuations in these pools.

Photosynthetic control, ?energy-dependent? quenching of chlorophyll fluorescence and photophosphorylation under influence of tertiary amines

The effects of the tertiary amines tetracaine, brucine and dibucaine on photophosphorylation and control of photosynthetic electron transport in isolated chloroplasts of Spinacia oleracea were investigated. Tertiary amines inhibited photophosphorylation while the related electron transport decreased to the rates, observed under non-phosphorylating conditions. Light induced quenching of 9-aminoacridine fluorescence and uptake of (14)C-labelled methylamine in the thylakoid lumen declined in parallel with photophosphorylation, indicating a decline of the transthylakoid proton gradient. In the presence of ionophoric uncouplers such as nigericin, no effect of tertiary amines on electron transport was seen in a range of concentration where photophosphorylation was inhibited. Under the influence of the tertiary amines tested, pH-dependent feed-back control of photosystem II, as indicated by energy-dependent quenching of chlorophyll fluorescence, was unaffected or even increased in a range of concentration where 9-aminoacridine fluorescence quenching and photophosphorylation were inhibited. The data are discussed with respect to a possible involvement of localized proton flow pathways in energy coupling and feed-back control of electron transport.

Respiratory control over photosynthetic electron transport in chloroplasts of higher-plant cells: evidence for chlororespiration

Flash-induced primary charge separation, detected as electrochromic absorbance change, the operation of the cytochrome b/f complex and the redox state of the plastoquinone pool were measured in leaves, protoplasts and open-cell preparations of tobacco (Nicotiana tabacum L.), and in isolated intact chloroplasts of peas (Pisum sativum L.). Addition of 0.5-5 mM KCN to these samples resulted in a large increase in the slow electrochromic rise originating from the electrogenic activity of the cytochrome b/f complex. The enhancement was also demonstrated by monitoring the absorbance transients of cytochrome f and b 6 between 540 and 572 nm. In isolated, intact chloroplasts with an inhibited photosystem (PS) II, low concentrations of dithionite or ascorbate rendered turnover of only 60% of the PSI reaction centers, KCN being required to reactivate the remainder. "Silent" PSI reaction centers which could be reactivated by KCN were shown to occur in protoplasts both in the absence and presence of a PSII inhibitor. Contrasting spectroscopic data obtained for chloroplasts before and after isolation indicated the existence of a continuous supply of reducing equivalents from the cytosol.Our data indicate that: (i) A respiratory electron-transport pathway involving a cyanide-sensitive component is located in chloroplasts and competes with photosynthetic electron transport for reducing equivalents from the plastoquinone pool. This chlororespiratory pathway appears to be similar to that found in photosynthetic prokaryotes and green algae. (ii) There is an influx of reducing equivalents from the cytosol to the plastoquinone pool. These may be indicative of a complex respiratory control of photosynthetic electron transport in higher-plant cells.

The kinetics of P‐700+ reduction in leaves: a novel in situ probe of thylakoid functioning

Abstract. The half time (t1/2) of the reduction of P‐700+ in the millisecond time frame is known to be limited by the reaction between plastoquinol and the cytochrome cytb6f complex. This is considered to be the rate limiting reaction of thylakoid electron transport and measurements of it provide a means of analysing how thylakoid election transport is regulated in vivo. The half time for the reduction of photochemically oxidized P‐700 has been measured in vivo using absorbance changes around 820 nm. The results showed that t1/2 is independent of irradiance and decreases as photosynthetic induction progresses. Even with a constant t1/2 the quantum efficiency of PSI declined as irradiance increased. The significance of the concept of photosynthetic control of electron transport is discussed in the light of these observations.

Saturation of membrane lipids by hydrogenation induces thermal stability in chloroplast inhibiting the heat-dependent stimulation of Photosystem I-mediated electron transport

Mild hydrogenation (up to 20%) of cis double bonds of acyl lipids within thylakoid membranes results in a marked increase in the threshold temperature at which heat stress-induced stimulation of DCPIPH 2-supported PS I-mediated electron transport is initiated. Lipid saturation above 35% totally prevents the appearance of any increase in electron flow to PS I upon heat pretreatment. Experiments conducted on uncoupled chloroplast show that photosynthetic control of electron transport is not involved in the protective effect associated with lipid saturation. Homogeneous catalytic hydrogenation of unsaturated fatty acids within chloroplast membranes proved to be a powerful technique in verifying that heat stability of chloroplasts is coupled to the level of fatty acid unsaturation.

Differential sensitivity to dibucaine of photosynthetic control of electron transport and photophosphorylation in chloroplasts

The effect of dibucaine on the photosynthetic control of electron transport, as related to acidification of the thylakoid lumen, and photophosphorylation in isolated chloroplasts of Spinacia oleracea was studied and compared to that of a typical uncoupler (nigericin) and energy transfer inhibitor (3′- O-napthyl-ADP). In some respects, dibucaine resembled an uncoupler: it inhibited photophosphorylation and decreased quenching of 9-aminoacridine fluorescence as well as uptake of [ 14C]methylamine and inhibited the intrathylakoid accumulation of H +, as measured by a glass electrode. The preactivated thylakoid ATPase was stimulated by dibucaine, although this stimulatory effect was to some extent superimposed by an inhibition of the enzyme. However, as opposed to what is expected for an uncoupler, dibucaine did not release the pH-dependent control of electron transport. In addition, pH-dependent high-energy quenching of chlorophyll fluorescence, normally inhibited by uncouplers, was not affected by dibucaine. It is concluded that dibucaine selectively reduces the driving force of photophosphorylation, while pH-dependent control of electron transport remains largely unaffected. The data are discussed regarding current models on coupling of photophosphorylation and on regulation of electron transport.

On the mechanism of control of photosynthetic electron transport by phosphorylation

FEBS LettersVolume 69, Issue 1-2 p. 81-85 Full-length articleFree Access On the mechanism of control of photosynthetic electron transport by phosphorylation Donald Ort, Donald Ort Department of Biological Sciences, Purdue University, West Lafayette, In. 47909, USASearch for more papers by this author Donald Ort, Donald Ort Department of Biological Sciences, Purdue University, West Lafayette, In. 47909, USASearch for more papers by this author First published: October 15, 1976 https://doi.org/10.1016/0014-5793(76)80658-8Citations: 11AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat References 1 B. Rumberg, U. Siggel, Naturwissenschaften, 55, (1968), 77– 79. 2 E. Bamberger, H. Rottenberg, H. Avron, Eur. J. Biochem., 34, (1973), 557– 563. 3 A. Trebst, W. Briggs Ann. Review of Plant Physiol. 25, (1974), Annual Review Inc Palo Alto, Calif 423– 458. 4 D. Ort, R. Dilley, Biochim. Biophys. Acta, (1976), in press 5 D. Ort, R. Dilley, N. Good, Biochim. Biophys. Acta, (1976), in press 6 S. Izawa, G. Hind, Biochim. Biophys. Acta, 143, (1967), 377– 390. 7 W. Schliephake, W. Junge, H. Witt, Z. Naturforsch., 23b, (1968), 1571– 1578. 8 S. Izawa, J. Gould, D. Ort, P. Felker, N. Good, Biochim. Biophys. Acta, 305, (1973), 119– 128. 9 A. Trebst, S. Reimer, Biochim. Biophys. Acta, 305, (1973), 129– 139. 10 J. Gould, D.R. Ort, Biochim. Biophys. Acta, 325, (1973), 157– 166. 11 A. Trebst, E. Harth, W. Draber, Z. Naturforsch, 25b, (1970), 1157– 1159. 12 B. Kok, P. Joliot, M. McGloin, H. Metzner Progress in Photosynthesis Research II, (1969), Internat. Union Biol. Sci. Tubingen 1042– 1056. 13 R. Gaensslen, R. McCarty, Anal. Biochem., 48, (1972), 504– 514. 14 M. Black, R. Brandt, Anal. Biochem., 58, (1974), 246– 254. 15 M. Avron, B. Chance, Brookhaven Symposia in Biol., 19, (1966), 149– 160. Citing Literature Volume69, Issue1-2October 15, 1976Pages 81-85 ReferencesRelatedInformation