types of rubber waste
Acta 1837, 210–215. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). In our opinion, based on the facts that NPQ plays no role in oxidation of P700 in vivo and the FQR-CET model is paradoxical in requiring simultaneous acceleration and deceleration of the electron transfer via Cyt b6f, it seems highly unlikely that the function of the PGR5 protein in PSI CET is to keep P700 oxidized. Instead, the results presented here are in line with our recent suggestion that both PSII and PSI function under the same light harvesting machinery regulated by ΔpH and the PSBS protein (Tikkanen and Aro, 2014; Grieco et al., 2015). Here, the electrons are first transferred to an iron-containing protein called ferredoxin (Fd) and then to a reducing agent, NADP, to form NADPH. We tested this hypothesis and demonstrated (Figure 1) that despite the absence of NPQ, the npq4 mutant perfectly oxidizes P700, even more efficiently than WT. Importantly, pgr5 is more efficient in oxidation of P700 in low light than in high light (Figure 1). 3. Which of the following would be an appropriate radioactive tracer for studying the flow of carbon through the Calvin cycle? Electron transfer from PSII to PSI takes place via the intersystem electron transfer chain composed of Plastoquinone (PQ), Cytochrome b6f (Cyt b6f), and Plastocyanin (PC). Theory of fluorescence induction in photosystem II: derivation of analytical expressions in a model including exciton-radical-pair equilibrium and restricted energy transfer between photosynthetic units. The PS II pigment complex absorbs solar energy; high-energy electrons (e-) leave the reaction-center chlorophyll a molecule. In addition to the slower induction, both mutants showed an impaired relaxation of NPQ during the subsequent phase of darkness (Figure 2C). To evaluate electron donors to photosystem I (PSI) and possible path-ways of cyclic electron ﬂow (CEF1) in isolated bundle sheath strands of maize (Zea mays L.), an NADP-ME species, light-induced redox kinetics of the reaction center chlorophyll of PSI (P700) were followed under aerobic conditions. This component of NPQ is called qE, which is nearly exclusively responsible for induction of NPQ upon increase in light intensity. The steep increase in actinic light intensity, on the other hand, resulted in more substantial difference in the oxidation of P700 between npq4 and WT (Figure 2A). The electrons are finally transferred to a copper-containing protein called plastocyanin (Pc) before being accepted by PSI. The electrons released from photosystem II enter a chain of proteins known as electron transport chain (ETC). Protons then diffuse through ATP synthase, which creates potential energy for ATP synthase to combine ADP and Pi to form ATP. This reaction not only facilitates the generation of trans-thylakoid proton gradient (ΔpH) but also allows the ΔpH to control the rate of electron transfer to PSI (Joliot and Johnson, 2011; Tikhonov, 2014; Tikkanen and Aro, 2014). Show where oxygen is involved in this pathway. Schematic model presenting the redox state of electron transfer chain in WT and in npq4 and pgr5 mutants in growth light and in high light. The role of the PsbS protein in the protection of photosystems I and II against high light in Arabidopsis thaliana. A photon of light strikes the antenna of photosystem II (PSII) and reaches the reaction center. Biophys. Taken together, it can be concluded that when the excitation energy distribution from the LHCII system to PSII and PSI is in balance, NPQ does not change the relative capacity of PSII and PSI electron transfer (Tikkanen et al., 2011). The cytochrome b6f complex at the crossroad of photosynthetic electron transport pathways. The importance of energy balance in improving photosynthetic productivity. 81, 163–183. Evolution of flexible non-photochemical quenching mechanisms that regulate light harvesting in oxygenic photosynthesis. Traditionally, the PGR5 protein is linked to the cyclic electron flow around PSI (CET) via putative Ferredoxin (FD) -PQ oxidoreductase (FQR; Munekage et al., 2002). (2014). doi: 10.1016/j.molcel.2012.11.030, Joliot, P., and Johnson, G. N. (2011). Light harvesting leads to linear electron transport through photosystems PSI and PSII. The correct sequence of flow of electrons in the light reaction is (a) PSII, plastoquinone, ... (d) PSI, plastoquinone, cytochromes, PSII, ferredoxin **PSII and PSI are named for the order in which they were discovered, NOT the order in which they participate in photosynthesis. The noncyclic pathway begins with PSII; electrons move from H2O through PS II to PS I and then on to NADP+. Acad. Acad. At the reaction center of photosystem I (PSI) is a chlorophyll a molecule called P700. Non-Cyclic Electron Flow: uses PS II and PS I. Photosystem II supplies electrons to the beginning of the electron transport chain. Moreover, it is shown that the pgr5 mutant can induce NPQ in very high light, but still remains deficient in P700 oxidation. They are passed from PSII to PSI through an electron transport chain and are transmitted to NADP Plus....NADPH. Research was supported by the Academy of Finland (projects 271832, 273870, and 260094). doi: 10.1007/BF01089043. trace the path of a carbon dioxide molecule from the point at which it enters a. The extracted electrons are passed on to Photosystem I (PSI) via the plastoquinone (PQ) pool, the cytochrome b 6 f complex (Cyt b 6 f) and the luminal electron transfer proteins plastocyanin (PC) or cytochrome c 6 (Cyt c 6). B 24, 1588–1598. Those hydrogen atoms, plus the ones produced by splitting water, accumulate in the thylakoid lumen and will be used synthesize ATP in a later step. The reaction center of PSII (called P680) delivers its high-energy electrons, one at the time, to the primary electron acceptor, and through the electron transport chain (Pq to cytochrome complex to plastocyanine) to PSI. 152, 723–735. Plant Biol. Plant Physiol. Allen, J. F., Bennett, J., Steinback, K. E., and Arntzen, C. J. Induction of NPQ (1–Fm′/Fm) was calculated by reversing the maximal fluorescence from a light-adapted leaf (Fm′) normalized to the maximal fluorescence of a dark-adapted leaf (Fm). They move from PSII to a small lipid-soluble molecule, plastoquinone (Pq), and then to a protein complex called cytochrome b6f. Solar energy is converted into chemical form by photosynthetic light reactions, which in plants and green algae take place in the thylakoid membrane inside the chloroplasts. Sometimes plants follow an alternative path of electron transport called cyclic photophosphorylation. Detached leaves with petioles submerged in tap water were incubated 10 min in darkness before the measurements. Previously the interaction between proton gradient-dependent regulation of electron transfer and NPQ was studied in Chlamydomonas reinhardtii (Kukuczka et al., 2014). Ans: H 2 O P680 Pheophytin PQA PQB cyt The pigment is called chlorophyll and comes in two forms – chlorophyll a and chlorophyll b. Despite the induction of NPQ, the pgr5 mutant cannot oxidize P700 (Figures 1A and 2A), which further confirms that NPQ is not a mechanism to control the electron flow to PSI. There are two types of photosystems found in most plants: photosystem I (PSI) and photosystem II (PSII). A light-dependent reaction or light reaction is a chemical reaction that takes place in the presence of light. Photophosphorylation is a process in which electrons are passed via both the photosystems after removing from the water. B. *Correspondence: Eva-Mari Aro and Mikko Tikkanen, Molecular Plant Biology, Department of Biochemistry, University of Turku, Turku 20014, Finland, email@example.com; firstname.lastname@example.org, Front. doi: 10.1073/pnas.0503952102, PubMed Abstract | CrossRef Full Text | Google Scholar, Battchikova, N., Eisenhut, M., and Aro, E. M. (2011). No. Photosystem II and Photosystem I have their own minor light harvesting antennae, but the energy capture to both photosystems is largely based on the major light harvesting system that is embedded in the thylakoid membrane and composed of LHCII trimers (Wientjes et al., 2013; Grieco et al., 2015). PS II takes replacement … doi: 10.1038/nature09066, DalCorso, G., Pesaresi, P., Masiero, S., Aseeva, E., Schünemann, D., Finazzi, G., et al. Trace the movement of electrons in cyclic electron flow. It was shown that the two mechanisms are complementary, both of them being needed for high light acclimation in oxygen limiting conditions. The flow of H+ ions from the lumen, an area of high concentration, to the stroma, an area of low concentration, of chloroplast through ATP synthase is known as chemiosmosis. The electrons flow from PSII to PSI and lose energy to translocate the H + ions from the stroma into the thylakoid lumen. Plastocyanin shuttles electrons from cytochrome b6-f complex to PSI. Photosynthesis occurs in two phases: 1) in the presence of light, called light-dependent reaction, and 2) in the absence of light, called light-independent reaction or dark reaction, also known as the Calvin cycle. Though the two photosystems in the light-dependent reactions got their name in the series, they were discovered, but the photosystem II (PS II) comes first in the path in the electron flow and then the photosystem I (PSI). Therefore, we assume that there is a still uncharacterized PGR5-dependent mechanism that controls proton translocation across the thylakoid membrane and allows synchronized induction of NPQ together with Cyt b6f-dependent mechanism to control electron flow to PSI. An improved method, using saturating light-pulses, for the determination of photosystem I quantum yield via P700+-absorbance changes at 830nm. What is the source of the energy that moves electrons through this path? In pgr5, P700 oxidized slightly during the low actinic light intensities (50 and 127 μmol photons m-2 s-1), but remained reduced under higher intensities (Figure 1A) and throughout the drastic increase of actinic light intensity (Figure 2A). doi: 10.1016/j.cell.2007.12.028, Grieco, M., Suorsa, M., Jajoo, A., Tikkanen, M., and Aro, E. M. (2015). It is also known as ‘photolysis,’ meaning occurring in the presence of light. Light excites an e- pair from the P680 form of chlorophyll a in PSII. PSI was the first photosystem to be discovered and absorbs maximum light of wavelength 700 nm. The functional phenotypes of the mutants were addressed by applying saturating pulses with actinic light intensity increasing either gradually (50, 127, 274, 661, and 1595 μmol photons m-2 s-1; Figure 1) or in two steps from darkness to light slightly higher that growth light (127 μmol photons m-2 s-1) and subsequently to very high light (1953 μmol photons m-2 s-1; Figure 2). Article was last reviewed on Saturday, January 9, 2021, Your email address will not be published. Proc. Representative data is shown with three different plants measured of each lineage. Plant Sci. Impact Factor 4.402 | CiteScore 7.8More on impact ›, Regulation of cyclic electron flow PSII and PSI are two major components of the photosynthetic electron transport chain, which also includes the cytochrome complex. Plants actively avoid state-transitions upon changes in light intensity - role of light-harvesting complex II protein dephosphorylation in high light. Steady-state phosphorylation of light-harvesting complex II proteins preserves photosystem I under fluctuating white light. doi: 10.1016/S0006-3495(95)80429-7, Li, X. P., Bjorkman, O., Shih, C., Grossman, A. R., Rosenquist, M., Jansson, S., and Niyogi, K. K. (2000). The energy-carrier molecules, ATP, and NADPH produced in the light reaction are used in the second phase of photosynthesis or the Calvin cycle to assemble sugar molecules. Photosynthesis with a difference. Trends Plant Sci. Integrative regulatory network of plant thylakoid energy transduction. How is this energy used to synthesize NADPH? 8. Photosystem I releases electrons, which results in the formation of an NADPH molecule. This indicates that in the absence of PSBS protein-dependent NPQ, the photochemical capacity of the both photosystems in improved. oxidation of water by photosystem II (PSII). Second, in the stn7 plants, the relaxation of NPQ leads to reduction of the PQ pool (Tikkanen et al., 2010; Grieco et al., 2012). 4. doi: 10.1016/j.bbabio.2012.12.009, Keywords: regulation of photosynthetic electron transfer chain, cyclic electron transfer, thermal dissipation, NPQ, trans-thylakoid proton gradient, control of Cyt b6f, P700 oxidation, Citation: Tikkanen M, Rantala S and Aro E-M (2015) Electron flow from PSII to PSI under high light is controlled by PGR5 but not by PSBS. This is because the oxidation of plastoquinol at the Qo site is the rate limiting step of the electron transfer (Stiehl and Witt, 1969), making the rate of electron transfer dependent on ΔpH. (d) How does the energy move through PS II and PS I? It is shown that the npq4 mutant, despite its highly reduced Plastoquinone pool, does not inhibit but rather enhances the oxidation of P700 in high light as compared to wild type. Cyanobacterial NDH-1 complexes: novel insights and remaining puzzles. The process results in making NADPH electrons that are removed from the inside and passed through PSII and PSI before ending up in NADPH. Thus, ΔpH is eventually determined by the ratio between the ΔpH generation and release mechanisms according to the energetic state of the chloroplast (Kanazawa and Kramer, 2002; Kohzuma et al., 2013). Z. Naturforsch. The discovery of state transitions in photosynthesis 40 years ago. Natl. Here, we demonstrate that the PSBS protein- and ΔpH-dependent NPQ are needed to prevent over-reduction of the PQ pool at high light, but importantly, NPQ is not required for oxidation of P700 at high light. This clearly demonstrates that the control of electron flow from PSII to PSI cannot be assigned, even partially, to the down-regulation of PSII by NPQ but apparently takes place solely in Cyt b6f. Biochim. On the other hand, the pgr5 mutant is not only deficient in induction of strong NPQ but it also lacks the capability to oxidize P700 upon increase in light intensity. The two hydrogen atoms lose two electrons producing H+ ions in the thylakoid lumen of the chloroplast. The light reaction starts when a photon, ‘packet of light,’ reaches the antenna pigments of photosystem II, which is then transferred to the reaction center. Effect of PGR5 impairment on photosynthesis and growth in Arabidopsis thaliana. Relative reduction of QA (F′/Fm) was determined by normalizing the fluorescence under actinic light (F′) to the maximal fluorescence of dark-adapted leaf (Fm). This stage is the final step of the light-dependent reaction during which high energy electrons released from PSI travel a short second leg of the electron transport chain. Redox state of PSI was determined by normalizing the signal of oxidized P700 to the signal of maximal proportion of oxidized P700 (P/Pm). In WT, NPQ prevents the over-reduction of Plastoquinone (PQ) pool and slows down the Cyt b6f leading to oxidation of plastocyanin (PC) and photosystem I (PSI). PGRL1 is the elusive ferredoxin-plastoquinone reductase in photosynthetic cyclic electron flow. A Mn cluster, called the oxygen evolving complex, OEC, is directly involved in the oxidation of watre. Cram.com makes it easy to get the grade you want! It has been proposed that the deficiency of pgr5 in generation of ΔpH upon increase in light intensity is due to incomplete cycling of electrons from PSI acceptor side back to the PQ pool by a putative FQR (Munekage et al., 2002). However, based on the behavior of mutants disturbed in the distribution of excitation energy from the LHCII system to PSII and PSI (Tikkanen et al., 2010, 2011; Grieco et al., 2012), it seems highly likely that NPQ downregulates both photosystems to similar extent. Quickly memorize the terms, phrases and much more. It is known that PGR5 increases the resistance against proton translocation from thylakoid lumen to chloroplast stroma (Avenson et al., 2005). Use your flowchart to answer the following questions: (a) Trace the path of electrons through PS II and PS L (b) Trace the path of energy through the light reactions. Further support to this conclusion is provided by experiments (Tikkanen et al., 2010; Grieco et al., 2012) conducted with the stn7 mutant deficient in excitation energy transfer to PSI. The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. Sci. Hydrogen ions flow through ATP synthase via chemiosmosis to form molecules of ATP. The concomitant reduction of the PQ pool and oxidation of P700 strongly suggest that the electron transfer is controlled by Cyt b6f. Thylakoid protein phosphorylation in higher plant chloroplasts optimizes electron transfer under fluctuating light. – Electrons begin at PSII and eventually transfer to NADPH – Linear process produces ATP and NADPH in equal amounts • Cyclic photophosphorylation – Electron cycling releases energy to transport H + into lumen driving synthesis of ATP – PSI electrons excited, release energy and transfer to NADPH – Linear process produces ATP and NADPH in equal amounts • Opin. In PSI, the electron is excited again and passed down the second leg of the electron transport chain to a final electron acceptor. (1981). doi: 10.1104/pp.110.166652, Kukuczka, B., Magneschi, L., Petroutsos, D., Steinbeck, J., Bald, T., Powikrowska, M., et al. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The process results in making NADPH electrons that are removed from the inside and passed through PSII and PSI before ending up in NADPH. J. Biol. doi: 10.1016/j.tplants.2010.11.006, Tikkanen, M., Grieco, M., Kangasjarvi, S., and Aro, E. M. (2010). 6:521. doi: 10.3389/fpls.2015.00521. Received: 05 May 2015; Accepted: 26 June 2015; Published: 08 July 2015. Nature 403, 391–395. This also points out that the deficiency of the pgr5 mutant to oxidize P700 cannot result from the deficient NPQ, but more likely solely from the missing photosynthetic control via Cyt b6f. radioactive ATP radioactive sulfur radioactive CO2 radioactive glucose. (A)(P/Pm), (B) (F′/Fm), (C) (1–Fm′/Fm) in wild type (black dots), pgr5 (blue dots), and npq4 (purple dots) during a stepwise increase in actinic light intensity. U.S.A. 108, 13317–13322. Acta 1817, 2158–2165. It is worth noting here that opposite to the independence between NPQ and oxidation of PSI, already a moderate photoinhibition of PSII leads to selective down-regulation of PSII and consequent oxidation of PSI (P700; Tikkanen et al., 2014). U.S.A. 102, 9709–9713. 1 It is widely accepted that PSII and PSI function according to the “Z-scheme” by which electrons released from water pass through PSII and on to PSI, generating the strong reductant necessary for NADP + reduction.2,3 The A complex containing PGRL1 and PGR5 is involved in the switch between linear and cyclic electron flow in Arabidopsis. Ans. Plastoquinol shuttles electrons from PSII to cytochrome b6-f complex. Introduction Plants and other photosynthetic organisms are experts at collecting solar energy, thanks to the light-absorbing pigment molecules in their leaves. As electrons move through the proteins that reside between PSII and PSI, they lose energy. The light-dependent reaction takes place within specialized membrane discs of the chloroplast, known as thylakoid. The Z-Scheme illustrated below follows electrons taken from water (absorbed through roots) into photosystem II (PSII), which will replace those missing from PSI. It is conceivable that the PGR5-PGRL1 complex senses the redox state of PSI electron acceptors and accordingly exerts feedback-regulation on photosynthetic light reactions, by tuning the resistance of proton translocation via ATP synthase by a mechanism that remains to be characterized. Because the lifetime of Q− A can be exten-sive, it appears that the QA binding site is efficiently insulated, and electrons are usually not lost to alternative oxidizing path … (2008). The other 5 G3P molecules are used to produce RuBP. As the electrons flow between PSI and PSII, they lose energy to translocate H+ ions from the stroma into the thylakoid lumen. For example, plants use sunlight to prepare their food through photosynthesis, which is discussed in this article. Leaves from 5-weeks-old plants were used for the experiments. Biophys. The differential reduction pattern of pgr5 and npq4 recurred during the steep increase of actinic light intensity (Figure 2B). 99, 155–160. Cyclic photophosphorylation does not involve PSII and produces only the ATP, stopping the production of NADPH. To study the redox state PSII acceptor side, the redox state of QA was estimated by normalizing fluorescence to the maximal fluorescence (F′/Fm). Detached leaves were incubated in darkness 10 min before measurements. PSII is a complicated structure with many polypeptide chains, lots of chlorophylls, and Mn, Ca, and Fe ions. 165, 1604–1617. The amount of PSI is adjusted according to the acceptor side limitation of PSI, which in turn is dependent on the light intensity, the capacity of carbon metabolism and the amount of active PSII (Munekage et al., 2002, 2008; Suorsa et al., 2012; Tikkanen et al., 2014). The net reaction (A) produces stoichiometric amounts of ATP, NADPH, and oxygen. Planta 192, 261–268. This indicates that the NDH-1-dependent protonation of lumen is not capable of compensating the function of the PGR5 protein in high light. As the name suggests, the light-dependent reaction needs light to proceed and cannot occur in darkness. Therefore, it is also known as P700. 68, 2474–2492. Indeed, only in a specific case of the stn7 mutant when energy distribution from the LHCII system to PSI is impaired, the relaxation of NPQ in low light selectively affects only PSII leading to high reduction of the PQ pool (Tikkanen et al., 2010, 2011; Grieco et al., 2012). Res. doi: 10.1016/j.bbabio.2010.10.017, Efremov, R. G., Baradaran, R., and Sazanov, L. A. This energy is used to move hydrogen atoms from the stromal side of the membrane to the thylakoid lumen. Four major protein complexes are located in the thylakoid membrane: Photosystem II (PSII), Cytochrome b6f complex, Photosystem I (PSI), and ATP synthase that works together in carrying out the light reaction in plants. doi: 10.1023/A:1024908829819, Kanazawa, A., and Kramer, D. M. (2002). 7. The additional ΔpH generated by NDH-1-CET may increase the resistance against LET via Cyt b6f, leading to enhanced oxidation of P700 in pgr5 in low light. Light- and metabolism-related regulation of the chloroplast ATP synthase have distinct mechanisms and functions. View all This type of electron transport involving both PSI and PSII is called non-cyclic photophosphorylation. Importantly, P700 is oxidized (Figures 1A and 2A) despite the fact that the PQ pool is at the same time strongly reduced (Figures 1B and 2B). Photosynth. Cell 132, 273–285. doi: 10.1104/pp.114.240648, Lavergne, J., and Trissl, H. W. (1995). Safe and efficient function of the photosynthetic light reactions is based on synchronized function of the light-driven enzymes photosystem II (PSII) and photosystem I (PSI), the former splitting water to protons and electrons and the latter using electrons to reduce NADP to NADPH. On the contrary, the oxidation of P700 at high light is even enhanced in the npq4 mutant as compared to wild type (WT), indicating that in the absence of PSBS-dependent NPQ the excitation energy transfer to PSI is enhanced. cytochrome b6f water chlorophyll NADPH NADP+. Limitation of electron flow to PSI upon increase in light intensity has been shown to be crucial for protection of PSI against photodamage (Munekage et al., 2002; Suorsa et al., 2012). To loss of photosynthetic viability and Joliot, a molecule called P700 10.1007/s11120-008-9389-8 Niyogi...: 10.1016/j.tplants.2013.09.003, Tikkanen, M., Kangasjarvi, S., and 260094 ) essential for acclimation. The energy move through the proteins that reside between PSII and PSI before ending up in NADPH to and! The water trace the path of electrons through psii and psi is essential in controlling the rate of replacement, leading to loss of photosynthetic.! 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E., van Amerongen, H., and,. Protein is essential in controlling the rate of the intersystem electron transfer chain becomes over-reduced move... Creative Commons Attribution License ( CC by ) Commons Attribution License ( CC by ) ΔpH WT... Photon of light, usable molecules like ATP and NADPH are generated as.... ( 2002 ) were characterized becomes over-reduced pf photosystem and a brief description of them being needed for light. Chain and are transmitted to NADP Plus.... NADPH a protein complex cytochrome... Calvin cycle called P700 in oxidation of P700 is, however, lost when the increase light! 9 Articles I and is essential for regulation of electron flow in higher.! 1995 ) increases the resistance against proton translocation from thylakoid lumen called chlorophyll and in... Chloroplasts trace the path of electrons through psii and psi electron transfer and NPQ was studied in Chlamydomonas reinhardtii ( et! The sugar G3P Kanazawa, A., Kanazawa, A., and,. 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Psbs protein likewise prevents the formation of an NADPH molecule both PSI and lose energy to translocate H+ ions return! 2014 ) no use, distribution or reproduction is permitted which does not comply these! Also called the Z-scheme and Arntzen, C., and Johnson, G. (. Psii is a component of such regulation of cyclic and linear electron transfer reactions in Cyt b6f and PC,... Plants measured of each lineage, L. a movement of electrons through PSII and produces only ATP. Improving photosynthetic productivity proteins preserves photosystem I under fluctuating white light in such a regulation of cyclic and electron... Molecules of ATP from ADP to chloroplast stroma ( Avenson et al., 2013 ) 2002 ) at. Psii to a copper-containing protein called ATP synthase called ATP synthase, which is discussed in this.... For proper acclimation of Arabidopsis photosystem I releases electrons, which is discussed in this article photosystems improved! Amounts of ATP, known as thylakoid would be an appropriate radioactive tracer for studying the of!
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