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  • 1
    Electronic Resource
    Electronic Resource
    Photoinactivation of photosystem II in leaves of Capsicum annuum (1999)
    Copenhagen : Munksgaard International Publishers
    Physiologia plantarum 105 (1999), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Leaf discs of Capsicum annuum L. were illuminated in air enriched with 1% CO2 in the absence or presence of lincomycin, an inhibitor of chloroplast-encoded protein synthesis. The loss of functional photosystem (PS) II complexes with increase in cumulative light dose (photon exposure), assessed by the O2 yield per single-turnover flash, was greater in leaves of plants grown in low light than those in high light; it was also exacerbated in the presence of lincomycin. A single exponential decay can describe the relationship between the loss of functional PSII and increase in cumulative photon exposure. From this relationship we obtained both the maximum quantum yield of photoinactivation of PSII at limiting photon exposures and the coefficient k, interpreted as the probability of photoinactivation of PSII per unit photon exposure. Parallel measurements of chlorophyll fluorescence after light treatment showed that 1/Fo−1/Fm was linearly correlated with the functionality of PSII, where Fo and Fm are the chlorophyll fluorescence yields corresponding to open and closed PSII reaction centers, respectively. Using 1/Fo−1/Fm as a convenient indicator of PSII functionality, it was found that PSII is present in excess; only after the loss of about 40% functional PSII complexes did PSII begin to limit photosynthetic capacity in capsicum leaves.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1034/j.1399-3054.1999.105224.x
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  • 2
    Electronic Resource
    Electronic Resource
    The rate coefficient of repair of photosystem II after photoinactivation (2003)
    Oxford, UK : Munksgaard International Publishers
    Physiologia plantarum 118 (2003), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: During photosynthesis, photoinactivation and repair of photosystem II (PSII) occur simultaneously, resulting in a net loss of functional PSII under a given irradiance. This study determines the rate coefficients for the partial processes, allowing the calculation of the partial rates at any concentration of functional/non-functional PSII. The rate coefficient of photoinactivation was obtained from the onset of photoinactivation of PSII in leaf segments of Capsicum annuum L. in the absence of repair, and was in turn used to obtain the rate coefficient (kr) of repair of PSII when repair was occurring. The value of kr was found to be near maximum at an irradiance as low as 29 µmol photons m−2 s−1 and peaked at or somewhat above the growth irradiance; however, it declined on further increasing the irradiance, possibly due to oxidative stress. The value of kr was considerably decreased by elevating the CO2 to about 1%, particularly at low irradiance, probably due to acidification of the stroma to a pH outside the range that is optimal for protein synthesis. The method of determining kr is convenient to apply, not relying on radiolabelling and pulse-chase experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1034/j.1399-3054.2003.00107.x
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  • 3
    Electronic Resource
    Electronic Resource
    Processes contributing to photoprotection of grapevine leaves illuminated at low temperature (2004)
    Oxford, UK; Malden, USA : Munksgaard International Publishers
    Physiologia plantarum 121 (2004), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Photoinactivation of photosystem II (PSII) and energy dissipation at low leaf temperatures were investigated in leaves of glasshouse-grown grapevine (Vitis vinifera L. cv. Riesling). At low temperatures (〈 15°C), photosynthetic rates of CO2 assimilation were reduced. However, despite a significant increase in the amount of light excessive to that required by photosynthesis, grapevine leaves maintained high intrinsic quantum efficiencies of PSII (Fv/Fm) and were highly resistant to photoinactivation compared to other species. Non-photochemical energy dissipation involving xanthophylls and fast D1 repair were the main protective processes reducing the ‘gross’ rate of photoinactivation and the ‘net’ rate of photoinactivation, respectively. We developed an improved method of energy dissipation analysis that revealed up to 75% of absorbed light is dissipated thermally via pH- and xanthophyll-mediated non-photochemical quenching at low temperatures (5–15°C) and moderate (800 µmol quanta m−2 s−1) light. Up to 20% of the energy flux contributing to electron transport was dissipated via photorespiration when taking into account temperature-dependent mesophyll conductance; however, this flux used in photorespiration was only a relatively small amount of the total absorbed light energy. Photoreduction of O2 at photosystem I (PSI) and subsequent superoxide detoxification (water-water cycle) was more sensitive to inhibition by low temperature than photorespiration. Therefore the water-water cycle represents a negligibly small energy sink below 15°C, irrespective of mesophyll conductance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.0031-9317.2004.0324.x
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  • 4
    Electronic Resource
    Electronic Resource
    Photosystem I acceptor side limitation is a prerequisite for the reversible decrease in the maximum extent of P700 oxidation after short-term chilling in the light in four plant species with different chilling sensitivities (2005)
    Oxford, UK; Malden, USA : Munksgaard International Publishers
    Physiologia plantarum 123 (2005), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Changes in the extent of P700 oxidation (P700+) were investigated after chilling of barley, rice, pumpkin, and cucumber leaf segments at 4°C for 1 h under light with various photon flux densities. At 50 µmol photons m−2 s−1, the decrease in P700+ was observed only in cucumber, but at 150 µmol photons m−2 s−1, it was found in all plants except barley, revealing their expected chilling sensitivities. However, the decrease in P700+ by this short-term chilling was reversible in the presence of 3-(3′,4′-dichlorophenyl)-1,1-dimethylurea or methyl viologen, and it did not show any causal relationship with the decrease in the electron transfer rate nor with the down-regulation of photosystem II through the accumulation of zeaxanthin and the development of non-photochemical quenching. These results led to the suggestion that photosystem I (PSI) acceptor side limitation is a prerequisite for the decrease of P700+. Furthermore, PSI acceptor side limitation could be mainly due to limitation of electron-sink pathways such as CO2 assimilation and ascorbate–glutathione cycle, because treatment with glycolaldehyde which inhibits the former pathway, and with KCN which inhibits both pathways, decreased P700+ by 20–30% in barley leaves after chilling in the light.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.2005.00443.x
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  • 5
    Electronic Resource
    Electronic Resource
    Light inactivation of functional photosystem II in leaves of peas grown in moderate light depends on photon exposure (1995)
    Springer
    Planta 196 (1995), S. 401-411 
    Details
    ISSN: 1432-2048
    Keywords: Chlorophyll fluorescence ; D1 protein ; Photoinhibition ; Photoprotection ; Photosystem II heterogeneity ; Pisum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract To determine the dependence of in vivo photosystem (PS) II function on photon exposure and to assign the relative importance of some photoprotective strategies of PSII against excess light, the maximal photochemical efficiency of PSII (Fv/Fm) and the content of functional PSII complexes (measured by repetitive flash yield of oxygen evolution) were determined in leaves of pea (Pisum satlvum L.) grown in moderate light. The modulation of PSII functionality in vivo was induced by varying either the duration (from 0 to 3 h) of light treatment (fixed at 1200 or 1800 μmol photons · m-2 · s-1) or irradiance (from 0 to 3000 μmol photons · m-2 · s-1) at a fixed duration (1 h) after infiltration of leaves with water (control), lincomycin (an inhibitor of chloroplast-encoded protein synthesis), nigericin (an uncoupler), or dithiothreitol (an inhibitor of the xanthophyll cycle) through the cut petioles of leaves of 22 to 24-day-old plants. We observed a reciprocity of irradiance and duration of illumination for PSII function, demonstrating that inactivation of functional PSII depends on the total number of photons absorbed, not on the rate of photon absorption. The Fv/Fm ratios from photoinhibitory light-treated leaves, with or without inhibitors, declined pseudo-linearly with photon exposure. The number of functional PSII complexes declined multiphasically with increasing photon exposure, in the following decreasing order of inhibitor effect: lincomycin 〉 nigericin 〉 DTT, indicating the central role of D1 protein turnover. While functional PSII and Fv/Fm ratio showed a linear relationship under high photon exposure conditions, in inhibitor-treated leaves the Fv/Fm ratio failed to reveal the loss of up to 25% of the total functional PSII under low photon exposure. The loss of this 25% of less-stable functional PSII was accompanied by a decrease of excitation-energy trapping capacity at the reaction centre of PSII (revealed by the fluorescence parameter, 1/Fo-1/Fm, where Fo and Fm stand for chlorophyll fluorescence when PSII reaction centres are open and closed, respectively), but not by a loss of excitation energy at the antenna (revealed by the fluorescence parameter, 1/Fm). We conclude that (i) PSII is an intrinsic photon counter under photoinhibitory conditions, (ii) PSII functionality is mainly regulated by D1 protein turnover, and to a lesser extent, by events mediated via the transthylakoid pH gradient, and (iii) peas exhibit PSII heterogeneity in terms of functional stability during photon exposure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00203636
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  • 6
    Electronic Resource
    Electronic Resource
    Photoinactivation of functional photosystem II and D1-protein synthesis in vivo are independent of the modulation of the photosynthetic apparatus by growth irradiance (1996)
    Springer
    Planta 198 (1996), S. 300-309 
    Details
    ISSN: 1432-2048
    Keywords: D1-protein ; Photoinhibition ; Photon exposure ; Photosystem II heterogeneity ; Light acclimation ; Pisum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract To investigate whether the in-vivo photoinhibition of photosystem II (PSII) function by excess light is an intrinsic property of PSII, the maximal photochemical efficiency of PSII (Fv/Fm) and the content of functional PSII (measured by repetitive flash yield of oxygen evolution) were determined in leaves of pea (Pisum sativum L.), grown in 50 (low light), 250 (medium light), and 650 (high light) μmol photons·m−2·s−1. The modulation of PSII functionality in vivo was induced in 1.1% CO2 by varying either (i) the duration (0–2 h) of light treatment (fixed at 1800 μmol photons· m−2·s−1) or (ii) irradiance (0–3200 μmol photons·m−2·s−1) at a fixed duration (1 h), after infiltration of leaves with water (control), lincomycin (an inhibitor of chloroplast-encoded protein synthesis), or a combination of lincomycin with nigericin (an uncoupler), through the cut petioles of leaves of 22-to 24-d-old plants. The reciprocity law of irradiance and duration of illumination for PSII function in vivo (Park et al. 1995, Planta 196: 401–411) holds in all differently light-grown peas, demonstrating that inactivation of functional PSII depends on photon exposure (mol photons·m−2), not on the rate of photon absorption. In vivo, PSII acts as an intrinsic “photon counter” and at higher photon exposures is inactivated following absorption of about 3 × 107 photons. There is a functional heterogeneity of PSII in vivo with 25% less-stable PSIIs that are inactivated at low photon exposure, compared to 75% more-stable PSIIs regardless of modulation of the photosynthetic apparatus. We suggest that the less-stable PSIIs represent monomers located in the nonappressed granal margins, while the more-stable PSIIs are dimers located in the appressed grana membrane cores. The capacity for D1-protein synthesis was the same in all the light-acclimated peas and saturated at low light, indicating that D1-protein repair is also an intrinsic property of PSII. This accounts for the low intensity required for recovery of photoinhibition in sun and shade plants which is independent of light-harvesting antennae size or PSII/PSI stoichiometries.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00206257
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  • 7
    Electronic Resource
    Electronic Resource
    UV-B damage and protection at the molecular level in plants (1994)
    Springer
    Photosynthesis research 39 (1994), S. 475-489 
    Details
    ISSN: 1573-5079
    Keywords: DNA repair ; flavonoids ; gene expression ; oxidative stress ; photosynthesis ; promoter
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Influx of solar UV-B radiation (280–320 nm) will probably increase in the future due to depletion of stratospheric ozone. In plants, there are several targets for the deleterious UV-B radiation, especially the chloroplast. This review summarizes the early effects and responses of low doses of UV-B at the molecular level. The DNA molecules of the plant cells are damaged by UV due to the formation of different photoproducts, such as pyrimidine dimers, which in turn can be combatted by specialized photoreactivating enzyme systems. In the chloroplast, the integrity of the thylakoid membrane seems to be much more sensitive than the activities of the photosynthetic components bound within. However, the decrease of mRNA transcripts for the photosynthetic complexes and other chloroplast proteins are among very early events of UV-B damage, as well as protein synthesis. Other genes, encoding defence-related enzymes, e.g., of the flavonoid biosynthetic pathway, are rapidly up-regulated after commencement of UV-B exposure. Some of the cis-acting nucleotide elements and trans-acting protein factors needed to regulate the UV-induced expression of the parsley chalcone synthase gene are known.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00014600
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  • 8
    Electronic Resource
    Electronic Resource
    Unifying model for the photoinactivation of Photosystem II in vivo under steady-state photosynthesis (1998)
    Springer
    Photosynthesis research 56 (1998), S. 1-13 
    Details
    ISSN: 1573-5079
    Keywords: photoinhibition ; Photosystem II ; primary radical pair ; singlet oxygen ; triplet P680
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We present a unifying mechanism for photoinhibition based on current obsevations from in vivo studies rather than from in vitro studies with isolated thylakoids or PS II membranes. In vitro studies have limited relevance for in vivo photoinhibition because very high light is used with photon exposures rarely encountered in nature, and most of the multiple, interacting, protective strategies of PS II regulation in living cells are not functional. It is now established that the photoinactivation of Photosystem II in vivo is a probability and light-dosage event which depends on the photons absorbed and not the irradiance per se. As the reciprocity law is obeyed and target theory analysis strongly suggests that only one photon is required, we propose that a single dominant molecular mechanism occurs in vivo with one photon inactivating PS II under limiting, saturating or sustained high light. Two mechanisms have been proposed for photoinhibition under high light, acceptor-side and donor-side photoinhibition [see Aro et al. (1994) Biochim Biophys Acta 1143: 113–134], and another mechanism for very low light, the low-light syndrome [Keren et al. (1995) J Biol Chem 270: 806–814]. Based on the exciton-radical pair equilibrium model of exciton dynamics, we propose a unifying mechanism for the photoinactivation of PS II in vivo under steady-state photosynthesis that depends on the generation and maintenance of increased concentrations of the primary radical pair, P680+Pheo−, and the different ways charge recombination is regulated under varying environmental conditions [Anderson et al. (1997) Physiol Plant 100: 214–223]. We suggest that the primary cause of damage to D1 protein is P680+, rather than singlet O2 formed from triplet P680, or other reactive oxygen species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005946808488
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  • 9
    Electronic Resource
    Electronic Resource
    The grand design of photosynthesis: Acclimation of the photosynthetic apparatus to environmental cues (1995)
    Springer
    Photosynthesis research 46 (1995), S. 129-139 
    Details
    ISSN: 1573-5079
    Keywords: light quantity ; light quality ; temperature ; photoreceptors ; photosystem stoichiometry ; redox sensing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Dynamic acclimation of the photosynthetic apparatus in response to environmental cues, particularly light quantity and quality, is a widely-observed and important phenomenon which contributes to the tolerance of plants against stress and helps to maintain, as far as possible, optimal photosynthetic efficiency and resource utilization. This mini-review represents a scrutiny of a number of possible photoreceptors (including the two photosystems acting as light sensors) and signal transducers that may be involved in producing acclimation responses. We suggest that regulation by signal transduction may be effected at each of several possible points, and that there are multiple regulatory mechanisms for photosynthetic acclimation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00020423
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  • 10
    Electronic Resource
    Electronic Resource
    Photoinactivation of photosystem II by cumulative exposure to short light pulses during the induction period of photosynthesis (1996)
    Springer
    Photosynthesis research 47 (1996), S. 51-59 
    Details
    ISSN: 1573-5079
    Keywords: chlorophyll fluorescence ; photoinhibition ; photon exposure ; photosynthetic induction ; susceptibility to light stress
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Photoinactivation of Photosystem (PS) II in vivo was investigated by cumulative exposure of pea, rice and spinach leaves to light pulses of variable duration from 2 to 100 s, separated by dark intervals of 30 min. During each light pulse, photosynthetic induction occurred to an extent depending on the time of illumination, but steady-state photosynthesis had not been achieved. During photosynthetic induction, it is clearly demonstrated that reciprocity of irradiance and duration of illumination did not hold: hence the same cumulative photon exposure (mol m−2) does not necessarily give the same extent of photoinactivation of PS II. This contrasts with the situation of steady-state photosynthesis where the photoinactivation of PS II exhibited reciprocity of irradiance and duration of illumination (Park et al. (1995) Planta 196: 401–411). We suggest that, for reciprocity to hold between irradiance and duration of illumination, there must be a balance between photochemical (qP) and non-photochemical (NPQ) quenching at all irradiances. The index of susceptibility to light stress, which represents an intrinsic ability of PS II to balance photochemical and non-photochemical quenching, is defined by the quotient (1-qP)/NPQ. Although constant in steady-state photosynthesis under a wide range of irradiance (Park et al. (1995). Plant Cell Physiol 36: 1163–1169), this index of susceptibility for spinach leaves declined extremely rapidly during photosynthetic induction at a given irradiance, and, at a given cumulative photon exposure, was dependent on irradiance. During photosynthetic induction, only limited photoprotective strategies are developed: while the transthylakoid pH gradient conferred some degree of photoprotection, neither D1 protein turnover nor the xanthophyll cycle was operative. Thus, PS II is more easily photoinactivated during photosynthetic induction, a phenomenon that may have relevance for understorey leaves experiencing infrequent, short sunflecks.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00017753
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