The observed changes in [F.sub.o] (initial fluorescence) and [F.sub.m] (peak fluorescence) are relative to the situation where the acceptor QA is reduced, since the rate of the competitor reoxidation of QA by the pool of plastoquinone
is lower than the rate of reduction of the (Zanandrea et al., 2006).
Salt stress limits these processes in photosynthesis, such as the limitation in thylakoid electron transport by enhancing membrane viscosity and restricting the plastoquinone
diffusion (Li et al.
Seregin and Ivanov  stated that the decline in net photosynthetic rate in Cd exposed plants results from the distorted chloroplast ultrastructure, restrained synthesis of chlorophylls, plastoquinone
, and carotenoids, disturbed electron transport, and inhibited activities of Calvin cycle enzymes and carbon dioxide deficiency in the cells.
The analysis of the O-I phase helped clarify the sequence of events involved in exciton capture by PSII up to the reduction of plastoquinone
(PQ) (Yusuf et al., 2010).
Quantitation of the rapid electron donors to P700, the functional plastoquinone
pool, and the ratio of the photosystems in spinach chloroplasts.
This normalization serves to distinguish the sequence of events from exciton trapping by PSII up to plastoquinone
(PQ) reduction (O-I phase; [W.sub.OI] from 0 to 1) (YUSUF et al., 2010).
Biosynthesis of isoprenoids (carotenoids, sterols, prenyl side-chains of chlorophylls and plastoquinone
) via a novel pyruvate/glyceraldehydes 3-phosphate non-mevalonate pathway in the green alga Scenedesmus obliquus.
[7.] Chistyakov VA, Prazdnova EV, Gutnikova LV, Sazykina MA, Sazykin IS (2012) Superoxide scavenging activity of plastoquinone
derivative 10-(6'-plastoquinonyl) decyltriphenylphosphonium (SkQ1).
Although the mode of action of some herbicidal benzoxazoles and benzothiazoles consists in inhibition of fatty acid synthesis, over 50% of commercially available herbicides act by reversible binding to photosystem II (PS II), a membrane-protein complex in the thylakoid membranes, which catalyses the oxidation of water and the reduction of plastoquinone
, and thereby inhibit photosynthesis [33-35].
Anisimov et al., "Mitochondrial-targeted plastoquinone
derivatives: effect on senescence and acute age-related pathologies," Current Drug Targets, vol.
Photosystem II (PSII) of the photosynthetic apparatus is a multi subunit pigment-protein complex in the thylakoid membrane, which performs light-induced oxidation of water and reduction of plastoquinone
. Most of the cofactors needed for this process are associated with the D1 core protein of PSII.
(1998), the relationship between [F.sub.m] (all reduced plastoquinone
) and [F.sub.0] (all oxidized plastoquinone
) is approximately 5 to 6 in healthy leaves and adapted to shade.