The kinetic difference between points I and P (30 ms to nearly 300 ms) reflects changes in the flow of electrons from plastoquinone
(PQ) to the final electron acceptor of PSI (Yusuf et al., 2010).
In intact leaves, the maximum fluorescence level ([F.sub.M]) is independent of the redox state of the plastoquinone
pool: A DCMU-inhibition study.
V Egorov et al., "Mitochondria-targeted plastoquinone
derivatives as tools to interrupt execution of the aging program.
The plastid ndh genes encode components of the thylakoid Ndh complex, which is analogous to the NADH dehydrogenase or complex I of the mitochondrial respiratory chain and catalyzes the transfer of electrons from NADH to plastoquinone
The reduction of electron acceptors such as [NADP.sup.+], and energy requirements as ATP, depending on enzyme-sensitive [Na.sup.+] and [Cl.sup.-] are undermining the activity cycle of carbon fixation (ABDEL-LATIF, 2008) can also be a reason for the rate of reoxidation of the plastoquinone
(Qa) being less than the rate of reduction, thus leading to a reduction of [F.sub.m] with increasing salinity.
Abbreviations: Car, carotenoid; Chl, chlorophyll; DCMU, 3(3,4-dichlorophenyl)-1,1-dimethylurea; [F.sub.0], Fm, Fv, minimum, maximum and variable fluorescence levels; [J.sub.F], photosynthetic electron transport rate; LHCII, light-harvesting complex of photosystem II; [P.sub.680], photochemically active Chl of PSII; PFD, photon flux density; Pheo, pheophytin a; PQ, plastoquinone
; PSI, PSII, photosystems I and II, respectively; [Q.sub.A], primary quinone acceptor of PSII; [Q.sub.B], secondary quinone acceptor of PSII; qE, energy-dependent component of qN; qN, non-photochemical quenching of variable Chl fluorescence; qP, photochemical quenching of variable Chl fluorescence; RCII, reaction center of photosystem II: [Y.sub.Z], secondary electron donor of PSII.
(Amino acids are the building blocks of proteins.) From the PS II reaction center, electrons flow to plastoquinone
molecules, which are floating freely in the thylakoid membrane, and from there to another membrane-protein complex, the cytochrome [b.sub.6] f complex.
derivatives covalently conjugated with lipophilic cations (SkQ) are one of the most intensively studied groups of mitochondria-targeted antioxidants .
PS II transfers electrons from water to plastoquinone
, and PSI move electrons from plastocyanin to NADP+ (Allakhverdiev et al., 1999).
Atrazine (ATZ) is an herbicide which binds irreversibly to the plastoquinone
binding sites of photosystem complex II on thylakoid membranes in chloroplasts, thereby inhibiting electron transport.
It is known that most PSII reaction centers are localized in the appressed region of the thylakoid membrane, within the grana stacks [6,7] and that diffusion of plastoquinone
(PQ) is restricted to small membrane domains, including a few PSII centers [8,] Consequently, PQH2 generated by PSII can only be reoxidized by that fraction of cyt bf also localized in the appressed region ([approximately equal to] 47%) (6).
A non-invasive assay of the plastoquinone
pool redox state based on the OJIP- transient.