Plastoquinone Research Articles

Redox-sensing is the basis of photophobic responses in cyanobacteria

Cyanobacteria lack specialized photoreceptors for photophobic responses (PPR), the action spectrum for photosynthesis coinciding with that for PPR. In the presence of 3-(3′,4′-dichlorophenyl)-1,1-dimethyl urea) (DCMU), which blocks electron transfer prior to plastoquinone (PQ), turning on the light increased the membrane potential, but simultaneously evoked an unusual phobic response, presumably due to oxidation of PQ · H2 via photosystem I (PS I). White light and the PQ reductant, (DQ · H2), acted as attractants and produced methylation of a 40 kDa membrane peptide. Repellents, an uncoupler, carbonyl cyanide m-chlorophenylhydrazone (CCCP), and an oxidant, tetramethyl-p-hydroquinone(duroquinon) (DQ), caused demethylation. The results are interpreted in the framework of Häder's ‘electron pool hypothesis’, according to which PQ · H2 level governs PPR. It is further concluded that the same system is the mechanism of pmf-sensing:

Modification of photosystem II activity by protein phosphorylation

Phosphorylation of proteins within pea thylakoid membranes decreases photosystem II (PSII) mediated electron transfer at saturating light intensities which, according to changes in room temperature chlorophyll fluorescence transients, is due to a modification in the electron transfer from Q A to Q B. However, a previously reported increase in the ability of DCMU to inhibit PS2 electron flow to DCPIP, as a consequence of protein phosphorylation, was not observed, although changes in DCMU efficacy were found to depend upon the redox state of the plastoquinone (PQ) pool.

The significance of the kinetic analysis of fluorescence induction in DCMU-inhibited chloroplasts in terms of photosystem 2 connectivity and heterogeneity

A study has been made on the slow component (β max) of chlorophyll fluorescence induction curves exhibited by DCMU-inhibited pea thylakoids. In the absence of high levels of screening cations, β max is high and the fluorescence yield low, while the addition of K +, Mg 2+ or Tris(ethylenediamine) cobaltic(III) cation (TEC 3+) decreases β max and increases fluorescence yield. These changes are inhibited when the thylakoids are fixed with glutaraldehyde. By comparing cation- and light-harvesting chlorophyll a/b-protein (LHCP) phosphorylation-induced changes it can be seen that β max correlates with changes in the overall kinetics of photosystem (PS) 2 photoreduction, as indicated from the normalised area over the induction curve (Anorm). When the plastoquinone (PQ) pool is chemically reduced by dithionite, prior to the initiation of the curve, both F o and F m are increased and the slow component removed. These observations are used to question the concept of two structurally distinct PS2 centres [Arch. Biochem. Biophys. (1978) 190, 523–530] and to discuss the use of β max in monitoring PS2 organisation.

BIOCHEMICAL COMPOSITION OF PLASTIDIC AND AMITROLE-INDUCED APLASTIDIC LEAF CELLS OF CANNA EDULIS KER.

ABSTRACT Sublethal concentrations of 3-amino-1,2,4-triazole (amitrole) cause leaf cells of Canna edulis Ker., to become aplastidic. The syntheses of both chlorophyll and carotenoid are inhibited. Among the various cellular constituents analysed in aplastidic (bleached) and plastidic (green) cells, the total lipid content was the one to be maximally reduced. Chlorophyll, β-carotene and plastoquinone are totally absent in the aplastidic cells. The aplastidic cells which are incapable of photosynthetic carbon reduction contained more starch than the plastidic cells. The levels of iron and magnesium were reduced marginally. The activities of hydrolytic enzymes increased in aplastidic leaves. Results are discussed in relation to the amitrole-induction of aplastidic cells.

Electron-dependent competition between plastoquinone and inhibitors for binding to photosystem II

Electron-dependent competition between plastoquinone and inhibitors for binding to photosystem II

Photosynthetic Electron Transport During Senescence of the Primary Leaves ofPhaseolus vulgarisL.

The kinetics of 685 nm chlorophyll fluorescence emission were measured at 20 °C following illumination of primary leaves of P. vulgaris. During foliar senescence, a large reduction was observed in the maximal level of fluorescence emission (P) of the induction curve, normalized with respect to the minimal level (O), and in the time taken to reach P. This suggests that fewer plastoquinone (PQ) molecules were able to accept electrons from each photosystem two (PS II) reaction centre in older leaves. Measurements of fluorescence emission at 77 °K indicated that the primary photochemical quantum yield of the PS II reaction centres remained constant during senescence. The redox state of the PQ pool was estimated throughout the induction curve at 20 °C. In both mature and senescent leaves PQ was highly reduced at P. There followed a reoxidation of PQ in the mature leaves, but in the old leaves the PQ pool remained reduced. This indicates that the rate of electron flow from PQ to photosystem one (PS I) decreased considerably during senescence. Fluorescence was quenched from P to a steady state level (T) in leaves of all ages, and this was associated with a redistribution of excitation in favour of PS I. Since, in senescent leaves, changes in the redox state of PQ were absent, it is suggested that quenching resulted from the generation of proton and ion gradients across the thylakoid membranes, and the synthesis of ATP.

Effects of CO 2-depletion on proton uptake and release in thylakoid membranes

The ability of COz to stimulate the Hill reaction in thylakoid membrane is well established [ 11. When NaHCOs is added to COz-depleted thylakoids, a large (4-6-fold) increase in oxygen evolution is observed. Recent experiments [2-61 have demonstrated that a major site of inhibition of Hill reaction by CO2 depletion is between electron acceptor Q of photosystem II (PS II) and the plastoquinone (PQ) pool, and more specifically between the two electron acceptor R (or B) and PQ [4,5]. Although a major site of bicarbonate action has been clearly established, and recent experiments suggest that CO1 is the species that diffuses and may initially bind to the membrane [7], the mechanism of its action is not known. During illumination of thylakoids there is an uptake of protons from the external phase and a release of protons into the interior space [g-lo]. There are two proton uptake sites on the outer side of the membrane [ 1 I] and two sites of proton release on the inner side [ 121. One of the sites on the outer surface is attributable to the reduction of the electron acceptor used. The second site of proton uptake is associated with the reduction of plastoquinone (PQ + 2 H’ + 2 e--, PQH2) which acts as a shuttle such that its oxidation releases protons at the inner side of the membrane. The other site of proton release into the inner phase is attributed to the oxidation of water (1/2H,0~1/402+I-l++e-).Thesitesofprotonbinding from the outer phase and proton release into the inner aqueous volume have been studied with pH

Inhibition of O 2 evolution by NADP in isolated potato tuber chloroplast and its identity with 3-(3,4-Dichlorophenyl)-1,1-dimethyl urea inhibition site

Chloroplast from greening potato tuber showed good photosynthetic capacity. The evolution of O 2 was dependent upon the intensity of light. A light intensity of 30 lux gave maximum O 2 evolution. At higher intensities inhibition was observed. The presence of bicarbonate in the reaction mixture was essential for O 2 evolution. NADP was found to be a potent inhibitor of O 2 evolution in this system. NADP and 3-(3,4-dichlorophenyl)-1,1-dimethyl urea (DCMU) inhibited the O 2 evolution completely at a 3 μ m concentration level, which was reversed by oxidized 2,6-dichlorophenol-indophenol (DCIP). Cyanide (CN)-treated chloroplasts showed full O 2 evolution capacity, when a lipophilic electron acceptor like N-tetramethyl- p-phenylenediamine (TMPD) or DCIP was used along with ferricyanide. Ferricyanide alone showed only 20% reduction. NADP or DCMU could inhibit O 2 evolution only when TMPD was the acceptor but not with DCIP. Photosystem II (PS II) isolated from these chloroplasts also showed inhibition by NADP or DCMU and its reversal by DCIP. Here also the evolution of O 2 with only TMPD as acceptor was sensitive to NADP or DCMU. In the presence of added silicotungstate in PS II NADP or DCMU did not affect ferricyanide reduction or oxygen evolution. The chloroplasts were able to bind exogenously added NADP to the extent of 120 nmol/mg chlorophyll. It is concluded that the site of inhibition of NADP is the same as in DCMU, and it is between the DCIP and TMPD acceptor site in the electron transport from the quencher (Q) to plastoquinone (PQ).

Enhancement of Energy Conservation by Hill Reaction Inhibitors in Isolated Spinach(Spinacia oleracea)Chloroplast Fragments

The effect of diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea], desmedipham [ethylm-hydroxycarbanilate carbanilate(ester)], propanil (3′,4′-dichloropropionanilide), and dibromothymoquinone (DBMIB) (2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone) on proton translocation and photophosphorylation in isolated spinach(Spinacia oleraceaL.) chloroplast fragments was investigated. In the absence of added cofactors, O2, or artificial electron acceptors, cyclic electron transport occurred, which was coupled to energy conservation. Under aerobic conditions O2acted as the terminal acceptor in non-cyclic electron transport. Proton translocation and photophosphorylation in the cyclic process were enhanced by diuron, desmedipham, and propanil, while in the non-cyclic process they were inhibited by all three herbicides. DBMIB inhibited proton translocation and photophosphorylation in both processes. Proton translocation and its enhancement increased with increasing light intensities. The finding that the plastoquinone (PQ) antagonist DBMIB disrupted cyclic as well as noncyclic electron flow, while diuron enhanced the cyclic and inhibited the noncyclic process, indicated that the acceptor site for endogenously-cycling electrons must lie between the active site of diuron inhibition and PQ, The close similarity in the behavior of diuron, desmedipham, and propanil suggests that their site of action is the same.

A QUALITATIVE AND QUANTITATIVE STUDY OF PLASTOQUINONE A IN TWO THERMOPHILIC BLUE‐GREEN ALGAE1

SUMMARYThe thermophilic blue‐green alga Synechococcus lividus strain Y52 was shown to have plastoquinone (PQ) types A, B, and C. The values PQA per cell and chlorophyll a per cell are presented with the changes in the ratio of PQA to chlorophyll a for cells grown at different light intensities.

Über die Chinone mit isoprenoider Seitenkette in Poteriochromonas stipitata

The fraction of quinones of P. stipitata contains ubiquinone-50, plastoquinone A, α-tocopherylquinone, and α-tocopherol. Traces of phylloquinone were found in this fraction too. Therefore the non-photosynthesizing organism does not differ from photosynthesizing algae relating to its chloroplastic quinones.

THE TOCOPHEROL, VITAMIN K, AND RELATED ISOPRENOID QUINONE COMPOSITION OF A UNICELLULAR RED ALGA (PORPHYRIDIUM CRUENTUM)1

SUMMARYThe total lipids of axenically cultivated cells of Porphyridium cruentum were extracted with aqueous methanol‐chloroform mixture and fractionated into neutral and polar lipids by silicic acid column chromatography. Thin‐layer and reversed‐phase paper chromatographic analyses of the neutral lipid fractions revealed the occurrence of plastoquinones (PQ) A and C, vitamin K1 (K), ubiquinone‐10 (Q10), α‐tocopherol (α‐T), and α‐tocopherolquinone (α‐TQ) in the photoautotrophically cultured alga, and the same quinones but no tocopherol in the alga grown photoheterotrophically on glycerol. The plastoquinone A and vitamin K1 were isolated, identified, and estimated by spectroscopic methods. The results indicated the following decreasing order of concentrations: autotrophic culture, PQ A > K > Q10 > PQ C, α‐TQ, α‐T; heterotrophic culture, PQ A > Q10 > K > PQ C, α‐TQ. Except for the absence of plastoquinone B, the overall quinonoid composition was in general agreement with those previously reported for multicellular members of Rhodophyta, but the concentration level in total lipid was markedly lower.

A Study of Plastoquinones in Photochemical Reactions in the Chloroplasts of Euglena gracilis Strain Z

Plastoquinone-9 (PQ-9) was isolated from the chloroplasts of Euglena gracilis Strain Z and spinach. The functional involvement and the structural specificity of PQ-9 in photochemical reactions was investigated in the isolated chloroplasts of Euglena gracilis. It was found that PQ-9 was required for both photoreduction of ferricyanide and photosynthetic phosphorylation in Euglena chloroplasts. The structural integrity of PQ-9 was not required to the same degree in the 2 photochemical reactions. Photosynthetic phosphorylation seemed to require the entire molecular structure of PQ-9 for the activity, whereas shortening in isoprenoid chain and modification of quinoid nucleus of PQ-9 do not seem to alter the photoreduction activity significantly. Addition of PQ-9 to the lyophilized Euglena chloroplasts inhibited the photoreduction of ferricyanide significantly, while it stimulated photosynthetic phosphorylation activity.

The structure of the plastoquinones B and C

The structure of the plastoquinones B and C

Presence of a Series of Plastoquinones in Plants

Presence of a Series of Plastoquinones in Plants

Incorporation of [G- 14C]shikimate and [U- 14C]para-hydroxybenzoate into phytoquinones and chromanols

Para-hydroxybenzoic acid (PHBA) and p -hydroxybenzaldehyde, compounds which in microorganisms and higher plants can be formed by the shikimic acid (SKA) pathway of aromatic biosynthesis, are effective precursors o of the ubiquinone (Q) ring in a variety of organisms (see Miller 1965). An intermediate in the conversion of PHBA to Q has been isolated from Rhodospirillum rubrum and characterised as 2-decaprenylphenol ( Parson and Rudney, 1965; Olsen et al ., 1965 ). Cox and Gibson (1964) showed that in Escherichia coli the Q and menaquinone rings are derived from shikimic acid, PHBA and protocatechuic acid, respectively, appearing to be obligate intermediates. In this communication we present evidence which indicates that in maize shoots the nuclei of phylloquinone (K), plastoquinone (PQ), ubiquinone (Q), α-tocopherolquinone (α-TQ), α-tocopherol (α-T) and γ-tocopherol (γ-T) are all formed from SKA. In this and all other plant tissues examined PHBA was incorporated only into Q and an uncharacterised prenyl-containing phenol which may be a Q-precursor.

Influence of Ioxynil on the Photo-reduction of Endogenous Plastoquinone by Isolated Chloroplasts of Vicia faba L.

ALTHOUGH plastoquinone (a 2,3-dimethyl p-benzoquinone, with a C45 side chain at C5) was first isolated in 1946 by Kofler from alfalfa grass, it did not excite much interest until Crane1 extracted the compound from the chloroplasts of green leaves. Plastoquinone (PQ) was first implicated as a participant in photosynthetic electron transport systems by Bishop2. Recently, Redfearn et al.3 have shown plastoquinone to be an intermediary electron carrier in the photosynthetic system, being a part of the light-dependent water-splitting mechanism as outlined by Duysens et al.4. We have recently reported5 that ioxynil (4-hydroxy-3,5-diiodo-benzonitrile)6 inhibits photophosphorylation and the accompanying reduction of pyridine nucleotide by chloroplasts. The results reported have been improved in recent months to give 50 per cent inhibition of both processes at a concentration of ioxynil of 5 × 10−5 M. In an attempt to elucidate the action of ioxynil on the photosynthetic electron transport system, the ability of chloroplasts to photo-reduce endogenous plastoquinone was investigated.

Isolation of two analogues of plastoquinone from senescent leaves of tobacco.

Isolation of two analogues of plastoquinone from senescent leaves of tobacco.