Role Of Plastoquinone Research Articles

Plastid retrograde regulation of miRNA expression in response to light stress

BackgroundMicroRNAs (miRNAs) are a class of endogenous noncoding RNAs that play a pivotal role in the regulation of plant development and responses to the surrounding environment. Despite the efforts made to elucidate their function in the adaptation of plants to many abiotic and biotic stresses, their role in high light (HL) stress is still vague. HL stress often arises upon plant exposure to full sunlight. Subsequent changes in nuclear gene expression are triggered by chloroplast-derived retrograde signals.ResultsIn this study, we show that HL is involved in miRNA-dependent regulation in Arabidopsis thaliana rosettes. Microtranscriptomic screening revealed a limited number of miRNAs reacting to HL. To explain the miRNA regulation mechanisms at the different biogenesis stages, chemical and genetic approaches were applied. First, we tested the possible role of plastoquinone (PQ) redox changes using photosynthetic electron transport chain inhibitors. The results suggest that increased primary transcript abundance (pri-miRNAs) of HL-regulated miRNAs is dependent on signals upstream of PQ. This indicates that such signals may originate from photosystem II, which is the main singlet oxygen (1O2) source. Nevertheless, no changes in pri-miRNA expression upon a dark–light shift in the conditional fluorescent (flu) mutant producing 1O2 were observed when compared to wild-type plants. Thus, we explored the 1O2 signaling pathway, which is initiated independently in HL and is related to β-carotene oxidation and production of volatile derivatives, such as β-cyclocitral (β-CC). Pri-miRNA induction by β-CC, which is a component of this 1O2 pathway, as well as an altered response in the methylene blue sensitivity 1 (mbs1) mutant support the role of 1O2 signaling in miRNA regulation.ConclusionsWe show that light stress triggers changes in miRNA expression. This stress response may be regulated by reactive oxygen species (ROS)-related signaling. In conclusion, our results link ROS action to miRNA biogenesis, suggesting its contribution to inconsistent pri- and mature miRNA dynamics.

Role of polyisoprenoids in tobacco resistance against biotic stresses

Infection with avirulent pathogens, tobacco mosaic virus (TMV) or Pseudomonas syringae pv. tabaci induced accumulation of polyisoprenoid alcohols, solanesol and a family of polyprenols [from polyprenol composed of 14 isoprene units (Pren-14) to -18, with Pren-16 dominating] in the leaves of resistant tobacco plants Nicotiana tabacum cv. Samsun NN. Upon TMV infection, solanesol content was increased seven- and eight-fold in the inoculated and upper leaves, respectively, while polyprenol content was increased 2.5- and 2-fold in the inoculated and upper leaves, respectively, on the seventh day post-infection. Accumulation of polyisoprenoid alcohols was also stimulated by exogenously applied hydrogen peroxide but not by exogenous salicylic acid (SA). On the contrary, neither inoculation of the leaves of susceptible tobacco plants nor wounding of tobacco leaves caused an increase in polyisoprenoid content. Taken together, these results indicate that polyisoprenoid alcohols might be involved in plant resistance against pathogens. A putative role of accumulated polyisoprenoids in plant response to pathogen attack is discussed. Similarly, the content of plastoquinone (PQ) was increased two-fold in TMV-inoculated and upper leaves of resistant plants. Accumulation of PQ was also stimulated by hydrogen peroxide, bacteria (P. syringae) and SA. The role of PQ in antioxidant defense in cellular membranous compartments is discussed in the context of the enzymatic antioxidant machinery activated in tobacco leaves subjected to viral infection. Elevated activity of several antioxidant enzymes (ascorbate peroxidase, guaiacol peroxidase, glutathione reductase and superoxide dismutase, especially the CuZn superoxide dismutase isoform) and high, but transient elevation of catalase was found in inoculated leaves of resistant tobacco plants but not in susceptible plants.

Herbicides in Photosynthesis Research

AbstractPhotosynthesis and herbicide research have a long common history. Soon after the introduction of a new group of highly effective herbicides in 1956, the substituted aryl ureas, their mode of action was recognized to be the inhibition of light‐driven electron flow and photosynthetic oxygen evolution. Many subsequent highly successful commercial herbicides, including those from other chemical classes, act by this mechanism. The study of their interaction with the photosynthetic system at the molecular level is a prime example of how rapidly advances in unraveling the mechanism of photosynthesis can be translated into practical uses. At the same time the herbicides continued to be valuable and efficient tools in photosynthesis research. In the past herbicides were instrumental in establishing many principal features of the biochemistry and biophysics of photosynthesis, in particular the role of plastoquinone, which is displaced from its binding pocket in one of the protein subunits of the photosystem II. Their further use in elucidating the molecular biology of photosynthesis is illustrated by the recent importance of herbicide‐tolerant mutants for determining structural aspects of photosystem II. We will review the past and present state of the interaction of herbicide and photosynthesis research and will provide a model for the orientation of herbicides within the three dimensional structure of their target, the D1 protein of photosystem II.

Plastoquinone as a mobile redox carrier in the photosynthetic membrane

The role of plastoquinone as a mobile redox carrier linking photosystem II and the cytochrome b6−f complex is considered. It is proposed that plastoquinone is located primarily within the fluid bilayer-midplane region of the thylakoid membrane and thus can move laterally at very fast rates corresponding to a microscopic diffusion coefficient of 10−6 cm2·s−1. Because of the presence of integral proteins the diffusion path will be tortuous and extended, giving rise to a sub-macroscopic diffusion coefficient which is lower than the above value. Even so it is concluded that within the half-time for electron donation to the cytochrome b6−f complex there is adequate time for plastoquinone to diffuse over a distance equivalent to the radius of a granum membrane.

Photosynthesis mechanism proposed

A research team at the University of California, Berkeley, says that recent experiments cast doubt on the currently prevalent concept, called the Z scheme, of photooxidation of water by green plants and subsequent generation of reduced ferrodoxin. The team, led by professor of cell physiology and research biochemist Daniel I. Arnon and including research associates Harry Y. Tsujimoto and George M. S. Tang, has proposed an alternative hypothesis for the process, which, Arnon says, explains his group's results and fits well with other recent discoveries on the structure of chloroplasts [ Proc. Natl. Acad. Sci , 78 , 2942 (1981)]. Their work is funded in part by the National Science Foundation. Central to Arnon's experiments and theory is the role of plastoquinone in the photosynthetic electron transport process that reduces ferrodoxin. Ferrodoxin is a soluble protein with an iron-sulfur prosthetic group found in all photosynthetic cells. It acts as a source of reducing power. In the photosynthetic reduction ...

The effect on photosynthetic electron transport of temperature-dependent changes in the fluidity of the thylakoid membrane in a thermophilic blue-green alga

Various electron transport reactions in cell or isolated thylakoid membranes of the thermophilic blue-green alga, Synechococcus sp. were measured at a different temperatures between 72 and 3°C. They are classified into two groups with respect to their temperature dependency. The first group involves cytochrome 553 photooxidation, methyl viologen photoreduction with reduced 2,6-dichlorophenolindophenol as electron donor and 3-(3′,4′-dichlorophenyl)-1,1-dimethylurea-resistant ferricyanide photoreduction determined in the presence or absence of silicomolybdate. The Arrhenius plot of these reactions showed a single straight line with the activation energy of about 10 kcal/mol throughout wide temperature ranges studied. Methyl viologen photoreduction with water as electron donor, reduction of flash-oxidized cytochrome 553, ferricyanide photoreduction and photosynthetic O 2 evolution form the second group. Their Arrhenius plots are characterized by discontinuities or breaks at about 30 and 10°C, which respectively correspond to the upper and lower boundaries of the lateral phase separation of the membrane lipids. The first group reactions represent short spans of electron transport which are mediated either by Photosystem I or Photosystem II alone and not related to plastoquinone, whereas all the reactions of the second group involve plastoquinone. It is concluded therefore that the membrane fluidity affect electron transport specifically at the region of plastoquinone. It is proposed that the reaction center chlorophyll-protein complexes of both Photosystems I and II are closely associated with related electron carrier proteins to form functional supramolecular assemblies so that electron transfer within such a cluster of proteins proceeds independently of the phase changes in the membrane lipids. On the other hand, the role of plastoquinone as a mobile electron carrier mediating electron trnasfer from the protein assembly of Photosystem II to that of Photosystem I through the fluid hydrophobic matrix of the membranes is highly sensitive to the physical state of the membrane lipids. It is proposed that the reaction center chlorophyll-protein complexes of both Photosystems I and II are closely associated with related electron carrier proteins to form functional supramolecular assemblies so that electron transfer within such a cluster of proteins proceeds independently of the phase changes in the membrane lipids. On the other hand, the role of plastoquinone as a mobile electron carrier mediating electron transfer from the protein assembly of Photosystem II to that of Photosystem I through the fluid hydrophobic matrix of the membranes is highly sensitive to the physical state of the membrane lipids.

Plastoquinone as a common link between photosynthesis and respiration in a blue-green alga

The role of plastoquinone in a thermophilic blue-green alga, Shynechococcus sp., was studied by measuring reduction kinetics of cytochrome 553 which was oxidized with red flash preferentially exciting photosystem I. Sensitivity of the cytochrome reduction to DBMIB Abbreviations: DCMU = 3-(3,4-dichlorophenyl)-1,1-dimethylurea; DBMIB = 2,5-dib romo-3-methyl-6-isopropyl-p-benzoquinone; HOQNO = 2-n-heptyl-4-hydroxyquinoline-N-oxide indicates that cytochrome 553 accepts electrons from reduced plastoquinone. Plastoquinone is in turn reduced in cells without electrons from photosystem II, since DCMU Abbreviations: DCMU = 3-(3,4-dichlorophenyl)-1,1-dimethylurea; DBMIB = 2,5-dib romo-3-methyl-6-isopropyl-p-benzoquinone; HOQNO = 2-n-heptyl-4-hydroxyquinoline-N-oxide , which inhibited methyl viologen photoreduction more strongly than DBMIB, failed to affect the cytochrome reduction. Participation of cyclic electron transport around photosystem I in cytochrome reduction in the presence of DCMU was excluded, because methyl viologen and antimycin A had no effect on the cytochrome kinetics. On the other hand, electron donation from endogenous substrates to plastoquinone was suggested from decreases in rate of the cytochrome reduction by dark starvation of cells and also from restoration of fast reduction kinetics by the addition of exogenous substrates to or by reillumination of starved cells.KCN, which completely suppressed respiratory O2-uptake, induced a marked acceleration of the cytochrome reduction in starved cells. The poison was less or not effective in stimulating the cytochrome reduction in more extensively starved or reilluminated cells.Results indicate that plastoquinone is functioning not only in the photosynthetic but also in the respiratory electron transport chain, thereby forming a common link between the two energy conservation systems of the blue-green alga.

The role of plastoquinone and β-carotene in the primary reaction of plant Photosystem II

Extraction of Triton Photosystem II chloroplast fragments with 0.2% methanol in hexane for 3 h results in the removal of 90 to 95% of the plastoquinone in the original preparation. The extracted fragments (chlorophyll : plastoquinone ratio, 900 : 1) showed no P-680 photooxidation at 15 K after a single laser flash. The extracted fragments also showed no light-induced C-550 absorbance change at 77 K. Reconstitution of the primary reaction of Photosystem II, as evidenced by restoration of low-temperature photooxidation of P-680, could be obtained by the addition of plastoquinone A but not by the addition of β-carotene. The addition of β-carotene plus plastoquinone A restored the C-550 absorbance change. These results indicate that plastoquinone functions as the primary electron acceptor of Photosystem II and that β-carotene does not play a direct role in the primary photochemistry but is required for the C-550 absorbance change.

The role of plastoquinone in the in vivo photosynthetic cyclic electron transport pathway in algae

The role of plastoquinone in the in vivo photosynthetic cyclic electron transport pathway in algae

On the Role of Plastoquinone in Photosynthesis

Dibromothymoquinone and its hydroquinone are inhibitors of non cyclic electron flow from water to NADP, anthraquinone or methylviologen. The inhibition is competetively reversed by plastoquinone. It appears that dibromothymoquinone is an antagonist of plastoquinone and that it prevents the enzymic (by the next endogenous carrier of the chloroplast electron transport chain) but not the chemical (by ferricyanide) reoxidation of reduced plastoquinone. This follows from the result that the photoreduction of ferricyanide and DCPIP * is not inhibited by dibromothymoquinone in sonicated chloroplasts and is inhibited in intact chloroplasts to only 60% or 80% respectively. It is concluded that dibromothymoquinone does not inhibit photoreductions by photosystem II. According to their response to dibromothymoquinone, cyclic photophosphorylations can be subdivided in those requiring plastoquinone and those which do not. Menadione catalyzed cyclic photophosphorylation is inhibited by dibromothymoquinone, whereas the PMS catalyzed system is not. The DAD cyclic system is only partly inhibited by dibromothymoquinone. The PMS catalyzed cyclic photophosphorylation in the presence of dibromothymoquinone is antimycin sensitive, which suggests that the PMS system can switch from a plastoquinone dependent system to a plastoquinone independent, but cytochrome b dependent system, which is now antimycin sensitive. Ferredoxin catalyzed cyclic photophosphorylation is inhibited by dibromothymoquinone as well as by antimycin. The data indicate that non cyclic electron flow through both photosystems is obligatory dependent on plastoquinone, whereas cyclic systems do not necessarily include plastoquinone. The relevance of the results to the possibility of different coupling sites in cyclic and non cyclic electron flow systems is discussed.

Plastoquinone C involved in electron transport in chloroplasts.

CHLOROPLASTS contain at least nine quinones. These are plastoquinones A, B, C and D, vitamin K1, α, β, γ tocopherolquinones and an unknown naphthoquinone1. Of these quinones plastoquinones A and C, vitamin K1 and α tocopherolquinone occur in sufficient quantity to be considered as candidates for a role in photosynthetic electron transport. Evidence for a role of plastoquinone A has been reviewed2,3. We can now show evidence for a specific role of plastoquinone C in addition to plastoquinone A as an electron carrier between the second and first light reactions of chloroplasts.

The role of plastoquinone in the photosynthetic reactions of Anabaena variabilis.

The role of plastoquinone in the photosynthetic reactions of cell-free preparations of the blue-green alga, Anabaena variabilis, has been studied. Plastoquinone is required for the reduction of several oxidants in the Hill reaction, but is not required for the photoreduction of TPN+ when either reduced indophenol dye or N,N.N′,N′-tetramethyl-p-phenylenediamine is used as the electron donor instead of water. Also, plastoquinone is not required for the photooxidation of reduced cytochrome c. The synthesis of ATP elicited by PMS is dependent on the presence of plastoquinone in the preparations from A. variabilis. The light-triggered hydrolysis of ATP is apparently independent of plastoquinone while the light-dependent hydrolysis of ATP requires plastoquinone.