Modulation of the Cytochrome b6/f Complex and Photosystem I Under Growth-Limiting Light in Amaranthus hypochondriacus, an NAD-ME C4 Plant

1996 ◽  
Vol 23 (3) ◽  
pp. 305 ◽  
Author(s):  
MV Sailaja ◽  
VSR Das
Keyword(s):  
Electron Transport ◽  
Photosystem Ii ◽  
Photosystem I ◽  
Thylakoid Membranes ◽  
Bundle Sheath ◽  
C4 Plant ◽  
Cytochrome B6 ◽  
Amaranthus Hypochondriacus ◽  
Energy Consuming ◽  
Electron Transport Rates

Highly characteristic responses of thylakoid membranes were observed in function and composition when fully developed plants of Amaranthus hypochondriacus L. grown under light sufficient (2000 μmol m-2 s-1) conditions were transferred to light limited conditions (650 μmol m-2 s-1 and 200 μmol m-2 s-1). The whole-chain, photosystem I and photosystem II electron transport rates were depressed in both bundle sheath and mesophyll thylakoids with remarkable differences between them in variation of rates under limiting light. The reduction in PSI electron transport in the mesophyll could be attributed to reduced PSI centres, while in the bundle sheath, a modulation of cytochrome b6/f complex regulated the rates of PSI electron transport. The requirement for an unaltered number of PSI centres under limiting light in the bundle sheath is ascribed to operation of an energy-consuming C4 pump.

Photosystem II Inhibition by Pyran-enamine Derivatives

1993 ◽  
Vol 48 (3-4) ◽  
pp. 163-167
Author(s):  
Koichi Yoneyama ◽  
Yoshihiro Nakajima ◽  
Masaru Ogasawara ◽  
Hitoshi Kuramochi ◽  
Makoto Konnai ◽  
...  
Keyword(s):  
Electron Transport ◽  
Photosystem Ii ◽  
Thylakoid Membranes ◽  
Major Determinant ◽  
Ps Ii ◽  
Structure Activity Relationships ◽  
Structure Activity

Abstract Through the studies on structure-activity relationships of 5-acyl-3-(1-aminoalkylidene)-4-hydroxy-2 H-pyran-2,6(3 H)-dione derivatives in photosystem II (PS II) inhibition, overall lipophilicity of the molecule was found to be a major determinant for the activity. In the substituted N -benzyl derivatives, not only the lipophilicity but also the electronic and steric characters of the substituents greatly affected the activity. Their mode of PS II inhibition seemed to be similar to that of DCMU , whereas pyran-enamine derivatives needed to be highly lipophilic to block the electron transport in thylakoid membranes, which in turn diminished the permeability through biomembranes.

Photoinhibition of Electron Transport Activity of Photosystem II in Isolated Thylakoids Studied by Thermoluminescence and Delayed Luminescence

1988 ◽  
Vol 43 (11-12) ◽  
pp. 871-876 ◽  
Author(s):  
Imre Vass ◽  
Narendranath Mohanty ◽  
Sándor Demeter
Keyword(s):  
Electron Transport ◽  
Photosystem Ii ◽  
Photosystem I ◽  
Half Life ◽  
Delayed Luminescence ◽  
Transport Activity ◽  
Primary Target ◽  
Electron Transport Activity ◽  
The Stability ◽  
Spinach Thylakoids

Abstract The effect of photoinhibition on the primary (QA) and secondary (QB) quinone acceptors of photosystem I I was investigated in isolated spinach thylakoids by the methods of thermoluminescence and delayed luminescence. The amplitudes of the Q (at about 2 °C) and B (at about 30 °C) thermoluminescence bands which are associated with the recombination of the S2QA- and S2QB charge pairs, respectively, exhibited parallel decay courses during photoinhibitory treatment. Similarly, the amplitudes of the flash-induced delayed luminescence components ascribed to the recombination of S20A and S2OB charge pairs and having half life-times of about 3 s and 30 s, respectively, declined in parallel with the amplitudes of the corresponding Q and B thermoluminescence bands. The course of inhibition of thermoluminescence and delayed luminescence intensity was parallel with that of the rate of oxygen evolution. The peak positions of the B and Q thermoluminescence bands as well as the half life-times of the corresponding delayed luminescence components were not affected by photoinhibition. These results indicate that in isolated thylakoids neither the amount nor the stability of the reduced OB acceptor is preferentially decreased by photoinhibition. We conclude that either the primary target of photodamage is located before the O b binding site in the reaction center of photosystem II or QA and OB undergo simultaneous damage.

Different kinetics of photoinactivation of photosystem I-mediated electron transport and P700 in isolated thylakoid membranes

2003 ◽  
Vol 69 (1) ◽  
pp. 41-48 ◽  
Author(s):  
Maya Velitchkova ◽  
Inmaculada Yruela ◽  
Miguel Alfonso ◽  
Pablo J. Alonso ◽  
Rafael Picorel
Keyword(s):  
Electron Transport ◽  
Photosystem I ◽  
Thylakoid Membranes ◽  
Kinetics Of

Further Studies of Proton Translocations in Chloroplasts After Single-Turnover Flashes. IV. Effects of Cytochrome b/f Complex Inhibitors on Proton Uptake and Cytochrome b6 Turnover

1987 ◽  
Vol 14 (1) ◽  
pp. 47 ◽  
Author(s):  
AB Hope ◽  
S Birch ◽  
DB Matthews
Keyword(s):  
Electron Transport ◽  
Photosystem Ii ◽  
Reduction Rate ◽  
Maximum Effect ◽  
Phenol Red ◽  
Cytochrome B6 ◽  
Oxidation Rates ◽  
Single Turnover ◽  
Proton Uptake ◽  
Reduction And Oxidation

The effects of the substances 2-n-heptyl- and 2-n-nonyl-4-hydroxyquinoline N-oxide (HQNO, NQNO), and antimycin A (AMA) on proton uptake stimulated by a 10-20 Hz train of single-turnover flashes given to pea thylakoids were investigated. Electron transport was from H2O to ferricyanide ('oxidising conditions') and the pH indicator of proton uptake was phenol red. All three of HQNO, NQNO and AMA inhibited proton uptake in control conditions, with concentrations (c½) for half-maximum effect of 1.7, 0.1 and 5 �M, respectively. The valinomycin-stimulated proton uptake, which has been attributed to Q-cycle activity in thylakoids, was more sensitive to HQNO and NQNO, with c½ of 0.6 and < 0.05 �M respectively. AMA had the same or less relative effect on proton uptake in the presence of valinomycin as in its absence. In oxidising conditions the maximum extent of flash-induced cytochrome (cyt) b6 reduction was 7-9% of the total present (which was 2 molecules/620 chlorophylls), as an average during 10 flashes, valinomycin being always added to reduce interference from the electrochromic effect. The average half- time for this reduction was 3.4 ms, while that for oxidation was 420 ms. The amount of cyt b6 reduced was increased by NQNO to a maximum of 14-19%, the c½ being 0.05 �M. Reduction and oxidation rates were both diminished by NQNO. In reducing conditions [electrons from duroquinol to methyl viologen, 3-(3,4-dichlorophenyl)-l,l- dimethylurea added to inhibit photosystem II], the cytochrome b6 was 12-16% reduced during flashes at 0.5-1 Hz, with half-times of 3.1 and 21 ms for reduction and oxidation, respectively. NQNO increased the percentage reduced to a maximum of 34-45, with a c½ of 0.05 �M. The diminution of the oxidation rate of cyt b6 was similarly related to [NQNO] but that of the reduction rate had a c½ of -1 �M. The findings on proton uptake are seen as consistent with HQNO and NQNO inhibiting at the Qc sites on cyt b/f complexes, at QB sites near photosystem II with less specificity and possibly at Q2 sites during the first few turnovers. Data for AMA indicated that it does not inhibit at Qc. Electron transport from H2O to methyl purple was more sensitive to NQNO for the first few turnovers (c½ 0.1 �M) than in the steady state (c½ - 1 �M).

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.

Stimulation of electron transport from Photosystem II to Photosystem I in spinach chloroplasts

1980 ◽  
Vol 12 (3-4) ◽  
pp. 197-203 ◽  
Author(s):  
Rita Barr ◽  
Randa Melhem ◽  
Anne L. Lezotte ◽  
Frederick L. Crane
Keyword(s):  
Electron Transport ◽  
Photosystem Ii ◽  
Photosystem I ◽  
Spinach Chloroplasts ◽  
Stimulation Of
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