Acclimation of Tomato Leaves to Changes in Light Intensity; Effects on the Function of the Thylakoid Membrane (original) (raw)
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The photoinactivation of photosystem II in leaves: A personal perspective
2001
a, a parameter that describes how effectively photoinactivated PS II units protect their functional neighbours; Car, carotenoids; pH, transthylakoid pH difference; D1 protein, psbA gene product in the PS II reaction centre; f, functional fraction of PS II; F v /F m , the ratio of variable to maximum chlorophyll a fluorescence; k d , rate coefficient for degradation of D1 protein; k i and k r , rate coefficient for photoinactivation and repair of PS II, respectively; NADP + , oxidized nicotinamide adenine dinucleotide phosphate; P680, the primary electron donor in the PS II reaction centre; Ph, pheophytin; PS, photosystem; Q A , first quinone acceptor of an electron in PS II; R s , the gross rate of D1 protein synthesis.
Electron Fluxes through Photosystem I in Cucumber Leaf Discs Probed by far-red Light
Photosynthesis Research, 2000
Cucumber leaf discs were illuminated at room-temperature with far-red light to photo-oxidise P700, the chlorophyll dimer in Photosystem (PS) I. The post-illumination kinetics of P700 + re-reduction were studied in the presence of inhibitors or cofactors of photosynthetic electron transport. The re-reduction kinetics of P700 + were well fitted as the sum of three exponentials, each with its amplitude and rate coefficient, and an initial flux (at the instant of turning off far-red light) given as the product of the two. Each initial flux is assumed equal to a steady state flux during far-red illumination. The fast phase of re-reduction, with rate coefficient k 1 ∼ 10 s −1 , was completely abolished by a saturating concentration of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU); it is attributed to electron flow to P700 + from PS II, which was stimulated to some extent by far-red light. The intermediate phase, with rate coefficient k 1 ∼ 1 s −1 , was only partly diminished by methyl viologen (MV) which diverts electron flow to oxygen. The intermediate phase is attributed to electron donation from reduced ferredoxin to the intersystem pool; reduced ferredoxin could be formed: (1) directly by electron donation on the acceptor of PS I; and/or (2) indirectly by stromal reductants, in line with only a partial inhibition of the intermediate phase by MV. Duroquinol enhanced the intermediate phase in the presence of DCMU, presumably through its interaction with thylakoid membrane components leading to the partial reduction of plastoquinone. The slow phase of P700 + re-reduction, with rate coefficient k 1 ∼ 0.1 s −1 , was unaffected by DCMU and only slightly affected by MV; it could be associated with electron donation to either: (1) the intersystem chain by stromal reductants catalysed by NAD(P)H dehydrogenase slowly; or (2) plastocyanin/P700 + by ascorbate diffusing across the thylakoid membrane to the lumen. It is concluded that a post-illumination analysis of the fluxes to P700 + can be used to probe the pathways of electron flow to PS I in steady state illumination.
Photophosphorylation Associated with Photosystem II
Plant Physiology, 1977
Incubation of KCN-Hg-NH20H-inhibited spinach (Spinacia oleracea L.) chioroplasts with p-phenylenediamine for 10 minutes in the dark prior to Mumination produced rates of photosystem II cyclic photophosphorylation up to 2-fold greater than the rates obtained without incubation. Partial oxidation of p-phenylenedismine with ferricyanide produced a similar stimulation of ATP synthesis; addition of dithiothreitol suppressed the stimulation observed with incubation. Addition of ferricyanide in amounts sufficient to oxidize completely p-phenylenediamine failed to inhibit completely photosystem II cyclic activity. This is due at least in part to the fact that the ferrocyanide produced by oxidation of p-phenylenediamine is itself a catalyst of pbotosystem n cyclic photophosphorylation. N,N,N'N'-Tetramethyl-p-phenylenediamine catalyzes photosystem II cyclic photopbosphorylation at rates approaching those observed with p-phenylenedismine. The activities of both proton/electron and electron donor catalysts of the photosystem H cycle are inhibited by dibromothymoquinone and antimycin A. These findings are interpreted to indicate that photosystem II cyclic photophosphorylation requires the operation of endogenous membrane-bound electron carriers for optimal coupling of ATP synthesis to electron transport. not (6, 13), and by the finding that a sulfonated derivative of PMS, which has impaired membrane permeability, is an ineffective catalyst of PSI cyclic ATP synthesis (5).
INTRODUCTION The Photoinactivation of Photosystem II in Leaves: A Personal Perspective
2001
A paradox of photosynthesis is that light is both required for the process and detrimental to the photosynthetic apparatus. In C 3 photosynthesis under light-limiting conditions, about 9 to 10 photons are sufficient for the evolution of one O 2 molecule Photosystem II components plastoquinone pool cytochrome b/f complex plastocyanin photosystem I components NADP + Photosystem (PS) II is the pigment-protein complex responsible for the photooxidation of water molecules. It has to generate oxidants that are sufficiently strong to oxidise water. Because of its role in forming such strong oxidants, PS II is highly susceptible to damage by the strong oxidants themselves, particularly in strong light. For example, a leaf exposed to full sun of 2000 µmol photons m -2 s -1 absorbs about 1700 µmol photons m -2 s -1 . If the light-saturated rate of photosynthesis corresponds to the evolution of 40 µmol O 2 m -2 s -1 , and the evolution of each O 2 molecule requires 10 photons, then 400 µmol ph...
Plant Physiology, 2008
Photosystem II (PSII) of oxygen-evolving cyanobacteria, algae, and land plants mediates electron transfer from the Mn 4 Ca cluster to the plastoquinone pool. It is a dimeric supramolecular complex comprising more than 30 subunits per monomer, of which 16 are bitopic or peripheral, low-molecular-weight components. Directed inactivation of the plastid gene encoding the low-molecular-weight peptide PsbTc in tobacco (Nicotiana tabacum) does not prevent photoautotrophic growth. Mutant plants appear normal green, and levels of PSII proteins are not affected. Yet, PSII-dependent electron transport, stability of PSII dimers, and assembly of PSII light-harvesting complexes (LHCII) are significantly impaired. PSII light sensitivity is moderately increased and recovery from photoinhibition is delayed, leading to faster D1 degradation in DpsbTc under high light. Thermoluminescence emission measurements revealed alterations of midpoint potentials of primary/secondary electronaccepting plastoquinone of PSII interaction. Only traces of CP43 and no D1/D2 proteins are phosphorylated, presumably due to structural changes of PSII in DpsbTc. In striking contrast to the wild type, LHCII in the mutant is phosphorylated in darkness, consistent with its association with PSI, indicating an increased pool of reduced plastoquinone in the dark. Finally, our data suggest that the secondary electron-accepting plastoquinone of PSII site, the properties of which are altered in DpsbTc, is required for oxidation of reduced plastoquinone in darkness in an oxygen-dependent manner. These data present novel aspects of plastoquinone redox regulation, chlororespiration, and redox control of LHCII phosphorylation.
Structure, function and regulation of plant photosystem I
Biochimica et Biophysica Acta (BBA) - Bioenergetics, 2007
Photosystem I (PSI) is a multisubunit protein complex located in the thylakoid membranes of green plants and algae, where it initiates one of the first steps of solar energy conversion by light-driven electron transport. In this review, we discuss recent progress on several topics related to the functioning of the PSI complex, like the protein composition of the complex in the plant Arabidopsis thaliana, the function of these subunits and the mechanism by which nuclear-encoded subunits can be inserted into or transported through the thylakoid membrane. Furthermore, the structure of the native PSI complex in several oxygenic photosynthetic organisms and the role of the chlorophylls and carotenoids in the antenna complexes in light harvesting and photoprotection are reviewed. The special role of the 'red' chlorophylls (chlorophyll molecules that absorb at longer wavelength than the primary electron donor P700) is assessed. The physiology and mechanism of the association of the major lightharvesting complex of photosystem II (LHCII) with PSI during short term adaptation to changes in light quality and quantity is discussed in functional and structural terms. The mechanism of excitation energy transfer between the chlorophylls and the mechanism of primary charge separation is outlined and discussed. Finally, a number of regulatory processes like acclimatory responses and retrograde signalling is reviewed with respect to function of the thylakoid membrane. We finish this review by shortly discussing the perspectives for future research on PSI.
Photoinactivation of Photosystem II in leaves
Photosynthesis Research, 2005
Photoinactivation of Photosystem II (PS II), the light-induced loss of ability to evolve oxygen, inevitably occurs under any light environment in nature, counteracted by repair. Under certain conditions, the extent of photoinactivation of PS II depends on the photon exposure (light dosage, x), rather than the irradiance or duration of illumination per se, thus obeying the law of reciprocity of irradiance and duration of illumination, namely, that equal photon exposure produces an equal effect. If the probability of photoinactivation (p) of PS II is directly proportional to an increment in photon exposure (p=kDx, where k is the probability per unit photon exposure), it can be deduced that the number of active PS II complexes decreases exponentially as a function of photon exposure: N=N o exp()kx). Further, since a photon exposure is usually achieved by varying the illumination time (t) at constant irradiance (I), N=N o exp()kI t), i.e., N decreases exponentially with time, with a rate coefficient of photoinactivation kI, where the product kI is obviously directly proportional to I. Given that N=N o exp()kx), the quantum yield of photoinactivation of PS II can be defined as )dN/dx=kN, which varies with the number of active PS II complexes remaining. Typically, the quantum yield of photoinactivation of PS II is ca. 0.1 lmol PS II per mol photons at low photon exposure when repair is inhibited. That is, when about 10 7 photons have been received by leaf tissue, one PS II complex is inactivated. Some species such as grapevine have a much lower quantum yield of photoinactivation of PS II, even at a chilling temperature. Examination of the longer-term time course of photoinactivation of PS II in capsicum leaves reveals that the decrease in N deviates from a single-exponential decay when the majority of the PS II complexes are inactivated in the absence of repair. This can be attributed to the formation of strong quenchers in severely photoinactivated PS II complexes which are able to dissipate excitation energy efficiently and to protect the remaining active neighbours against damage by light.
Electron transport to oxygen mitigates against the photoinactivation of Photosystem II in vivo
Photosynthesis Research, 1996
The role of electron transport to 02 in mitigating against photoinactivation of Photosystem (PS) II was investigated in leaves of pea (Pisum sativum L.) grown in moderate light (250 #mol m -2 s -1). During short-term illumination, the electron flux at PS II and non-radiative dissipation of absorbed quanta, calculated from chlorophyll fluorescence quenching, increased with increasing 02 concentration at each light regime tested. The photoinactivation of PS II in pea leaves was monitored by the oxygen yield per repetitive flash as a function of photon exposure (mol photons m-2). The number of functional PS II complexes decreased nonlinearly with increasing photon exposure, with greater photoinactivation of PS II at a lower 02 concentration. The results suggest that electron transport to 02, via the twin processes of oxygenase photorespiration and the Mehler reaction, mitigates against the photoinactivation of PS II in vivo, through both utilization of photons in electron transport and increased nonradiative dissipation of excitation. Photoprotection via electron transport to 02 in vivo is a useful addition to the large extent of photoprotection mediated by carbon-assimilatory electron transport in 1.1% CO2 alone.