scholarly journals Evaluation of Light-Dependent Photosynthetic Reactions in Reynoutria japonica Houtt. Leaves Grown at Different Light Conditions

2021 ◽  
Vol 12 ◽  
Author(s):  
Selma Mlinarić ◽  
Lidija Begović ◽  
Neven Tripić ◽  
Antonija Piškor ◽  
Vera Cesar
Keyword(s):  
Electron Transport ◽  
Excitation Energy ◽  
Invasive Plants ◽  
Electron Flow ◽  
Cyclic Electron Flow ◽  
Light Conditions ◽  
Japanese Knotweed ◽  
Reynoutria Japonica ◽  
Short Term Exposure ◽  
Photosynthetic Reactions

The Japanese knotweed (Reynoutria japonica Houtt.) is considered as one of the most aggressive and highly successful invasive plants with a negative impact on invaded habitats. Its uncontrolled expansion became a significant threat to the native species throughout Europe. Due to its extensive rhizome system, rapid growth, and allelopathic activity, it usually forms monocultures that negatively affect the nearby vegetation. The efficient regulation of partitioning and utilization of energy in photosynthesis enables invasive plants to adapt rapidly a variety of environmental conditions. Therefore, we aimed to determine the influence of light conditions on photosynthetic reactions in the Japanese knotweed. Plants were grown under two different light regimes, namely, constant low light (CLL, 40 μmol/m2/s) and fluctuating light (FL, 0–1,250 μmol/m2/s). To evaluate the photosynthetic performance, the direct and modulated chlorophyll a fluorescence was measured. Plants grown at a CLL served as control. The photosynthetic measurements revealed better photosystem II (PSII) stability and functional oxygen-evolving center of plants grown in FL. They also exhibited more efficient conversion of excitation energy to electron transport and an efficient electron transport beyond the primary electron acceptor QA, all the way to PSI. The enhanced photochemical activity of PSI suggested the formation of a successful adaptive mechanism by regulating the distribution of excitation energy between PSII and PSI to minimize photooxidative damage. A faster oxidation at the PSI side most probably resulted in the generation of the cyclic electron flow around PSI. Besides, the short-term exposure of FL-grown knotweeds to high light intensity increased the yield induced by downregulatory processes, suggesting that the generation of the cyclic electron flow protected PSI from photoinhibition.

DCMU-Induced Fluorescence Changes and Photodestruction of Pigments Associated with an Inhibition of Photosystem I Cyclic Electron Flow

1984 ◽  
Vol 39 (5) ◽  
pp. 351-353 ◽  
Author(s):  
Stuart M. Ridley ◽  
Peter Horton
Keyword(s):  
Electron Transport ◽  
Photosystem Ii ◽  
Photosystem I ◽  
Dose Response ◽  
Electron Flow ◽  
Cyclic Electron Flow ◽  
Cyclic Flow ◽  
Working Hypothesis ◽  
Dose Responses

Diuron (DCMU) induces the photodestruction of pigments, which is the initial herbicidal symptom. As a working hypothesis, it is proposed that this symptom can only be produced when the herbicide dose is sufficiently high to inhibit not only photosystem II electron transport almost completely, but also inhibit (through over oxidation) the natural cyclic electron flow associated with photosystem I as well. Using freshly prepared chloroplasts, studies of DCMU-induced fluorescence changes, and dose responses for inhibition of electron transport, have been compared with a dose response for the photodestruction of pigments in chloroplasts during 24 h illumination. Photodestruction of pigments coincides with the inhibition of cyclic flow.

scholarly journals Regulation of cyclic electron flow by chloroplast NADPH-dependent thioredoxin system

2018 ◽  
Author(s):  
Lauri Nikkanen ◽  
Jouni Toivola ◽  
Andrea Trotta ◽  
Manuel Guinea Diaz ◽  
Mikko Tikkanen ◽  
...  
Keyword(s):  
Carbon Fixation ◽  
Electron Flow ◽  
Proton Pumping ◽  
Cyclic Electron Flow ◽  
Light Conditions ◽  
Oxidoreductase Activity ◽  
Atp Production ◽  
Fluctuating Light ◽  
Thioredoxin System

ABSTRACTLinear electron transport in the thylakoid membrane drives both photosynthetic NADPH and ATP production, while cyclic electron flow (CEF) around photosystem I only promotes the translocation of protons from stroma to thylakoid lumen. The chloroplast NADH-dehydrogenase-like complex (NDH) participates in one CEF route transferring electrons from ferredoxin back to the plastoquinone pool with concomitant proton pumping to the lumen. CEF has been proposed to balance the ratio of ATP/NADPH production and to control the redox poise particularly in fluctuating light conditions, but the mechanisms regulating the NDH complex remain unknown. We have investigated potential regulation of the CEF pathways by the chloroplast NADPH-thioredoxin reductase (NTRC) in vivo by using an Arabidopsis knockout line of NTRC as well as lines overexpressing NTRC. Here we present biochemical and biophysical evidence showing that NTRC activates the NDH-dependent CEF and regulates the generation of proton motive force, thylakoid conductivity to protons and redox balance between the thylakoid electron transfer chain and the stroma during changes in light conditions. Further, protein–protein interaction assays suggest a putative thioredoxin-target site in close proximity to the ferredoxin binding domain of NDH, thus providing a plausible mechanism for regulation of the NDH ferredoxin:plastoquinone oxidoreductase activity by NTRC.One sentence summaryChloroplast thioredoxins regulate photosynthetic cyclic electron flow that balances the activities of light and carbon fixation reactions and improves plant fitness under fluctuating light conditions.

Inhibition of Photosynthetic Electron Transport by Halogenated 4-Hydroxy-pyridines

1985 ◽  
Vol 40 (5-6) ◽  
pp. 391-399 ◽  
Author(s):  
A. Trebst ◽  
B. Depka ◽  
S. M. Ridley ◽  
A. F. Hawkins
Keyword(s):  
Electron Transport ◽  
Photosystem Ii ◽  
Photosystem I ◽  
Electron Flow ◽  
Essential Element ◽  
Photosynthetic Electron Transport ◽  
Cyclic Electron Flow ◽  
Acceptor Side

Abstract Herbicidal halogen substituted 4-hydroxypyridines are inhibitors of photosynthetic electron flow in isolated thylakoid membranes by interfering with the acceptor side of photosystem II. Tetrabromo-4-hydroxypyridine, the most active compound found, has a pI50-value of 7.6 in the inhibition of oxygen evolution in both the reduction of an acceptor of photosystem I and an acceptor of photosystem II. The new inhibitors displace both metribuzin and ioxynil from the membrane. The 4-hydroxypyridines, like ioxynil, have unimpaired inhibitor potency in Tristreated chloroplasts, whereas the DCMU-type family of herbicides does not. It is suggested that 4-hydroxypyridines are complementary to phenol-type inhibitors, and a common essential element is proposed. The 4-hydroxypyridines do not inhibit photosystem I or non-cyclic electron flow through the cytochrome b/f complex. But they do have a second inhibition site in photosynthetic electron transport since they inhibit ferredoxin-catalyzed cyclic electron flow, indicating an antimycin-like property. A comparison of the in vitro potency of the compounds with the in vivo potency shows no correlation. A major herbicidal mode of action of the group is related to the inhibition of carotenoid synthesis, and access to the chloroplast lamellae in vivo for inhibition of electron transport may be restricted.

scholarly journals Cyclic electron flow in Chlamydomonas reinhardtii

2017 ◽  
Author(s):  
W. J. Nawrocki ◽  
B. Bailleul ◽  
P. Cardol ◽  
F. Rappaport ◽  
F.-A. Wollman ◽  
...  
Keyword(s):  
Electron Transport ◽  
Chlamydomonas Reinhardtii ◽  
Electron Flow ◽  
Cyclic Electron Flow ◽  
Maximal Rate ◽  
Linear Electron ◽  
Transport Pathways ◽  
Acceptor Side ◽  
Kinetic Information

AbstractCyclic electron flow (CEF), one of the major alternative electron transport pathways to the primary linear electron flow (LEF) in chloroplasts has been discovered in the middle of the last century. It is defined as a return of the reductants from the acceptor side of the Photosystem I (PSI) to the pool of its donors via the cytochrome b6f, and has proven essential for photosynthesis. However, despite many efforts aimed at its characterisation, the pathway and regulation of CEF remain equivocal, and its physiological significance remains to be properly defined. Here we use novel spectroscopic approaches to measure CEF in transitory conditions in the green alga Chlamydomonas reinhardtii. We show that CEF operates at the same maximal rate regardless of the oxygen concentration, and that the latter influences LEF, rather than CEF in vivo, which questions the recent hypotheses about the CEF supercomplex formation. We further reveal that the pathways proposed for CEF in the literature are inconsistent with the kinetic information provided by our measurements. We finally provide cues on the regulation of CEF by light.

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