Photoinhibition of Photosynthetic Oxygen Production and its Recovery in the Subtidal Red Alga Polyneura hilliae

In the marine red alga Polyneura hilliae photoinhibition of photosynthesis was investigated by measuring the photosynthetic oxygen production. The extent of photoinhibition in this alga depends on the fluence rate as well as on the time of exposure. Strongly photoinhibited algae recover slowly. Full recovery is reached only in weak light after 3 days. Two phases of recovery can be distinguished: a first relatively fast phase of recovery that is independent of light, and a second slow phase which begins after about 6 hours and requires weak light. Consequently, even in complete darkness partial recovery is observed. An action spectrum of photoinhibition and its comparison with the in vivo absorption spectrum of Polyneura demonstrates that photoinhibition is mainly caused by light which is absorbed by phycobiliproteins, chlorophyll a and carotenoids. This fact and the ineffectiveness of light above 686 nm clearly indicate that the main photoinhibition site in this alga is PS II. No photosynthetic oxygen production is detectable after 3 h irradiation at 402 nm, 150 μmol quanta m^?2s^?1. As photosynthetic activity recovers slowly and to a limited extent, the suppression of oxygen production is apparently only in part the result of photoinhibition sensu strictu and in part due to permanent photodamage.     

Tidal Dependence of Photoinhibition of Photosynthesis in Marine Macrophytes of the South China Sea*

During an expedition in spring 1992 to Hainandao, an island in the tropical zone of the South China Sea, the daily courses of photoinhibition of different brown algal species and of the seagrass Thalassia hemprichii were investigated. Experiments were carried out with the new portable chlorophyll fluorometer PAM 2000 (Walz, Germany). As a measure of photoinhibition Fv/Fm was used and as a measure of the photosynthetic yield ΔF/Fm'. Photoinhibition occurred in all algae floating near the water surface and reached its maximum between noon and the early afternoon. In the evening photosynthesis was always fully recovered. The extent of photoinhibition depended on both the depth of the algae and the course of the irradiance during the day. Algae of the sublittoral zone showed only a low degree of photoinhibition at high fluence rates when they were covered by a water column of more than 1 m, even if the water was clear. The seagrass Thalassia hemprichii grew in the middle and upper intertidal zone and showed a significant photoinhibition at low tide only when it was not water-covered. Apparently, it is able to cope with extreme high light conditions without downregulation of photosynthesis caused by photoinhibition.     

The Effect of Photoinhibition on Photosynthetic Oxygen Production in the Brown Alga Dictyota dichotoma

Photoinhibition of photosynthesis in the brown alga, Dictyota dichotoma, was studied with a PAM fluorometer (Walz, Effeltrich, Germany) and a homemade oxygen measuring device. As a measure of fluorescence, Fv/Fm, and for the photosynthetic yield, ΔF/Fm', were used. Oxygen measurements show clearly that the observed degree, as well as the time course, of photoinhibition depends on the fluence rate of the light used to measure changes of the production rate. After photoinhibition of photosynthesis the depression of oxygen production caused by non-saturating fluence rates was generally much more pronounced than that caused by saturating or nearly saturating fluence rates. At minimal photoinhibition the initial slope and the convexity of the fluence rate-response curve of oxygen evolution decrease, whereas the level of light saturation decreases only after strong photoinhibition. Nevertheless, at different degrees of photoinhibition, changes in the degree of the upper bending of the fluence rate-response curve of oxygen production are also linearly correlated to changes in the fluorescence ratios (Fv/Fm and ΔF/Fm'). The action spectrum of photoinhibition, calculated on the basis of changes of Fv/Fm, indicates that the reaction center of PS I is not involved in photoinhibition. The lower effectiveness of blue light in comparison to effects of green and red light may be due to chloroplast displacement, as in the so-called strong light position, the light absorbed by the thalli in vivo is decreased.     

高等植物光合作用的光抑制研究进展

光抑制是目前高等植物光合作用研究中的热点,近此年来无论是对其本质的认识,还是机理研究都已取得很进展。本文首先简要回顾了光抑制研究发展的历程,阐明现代光抑制理论包括耗散过剩光能的光保持机制运转和过剩光能对光合机构的破坏两个方面。然后,应叶黄素循环、Ｍｅｈｌｅｒ反应、光呼吸、ＬＨＣⅡ磷酸化、ＰＳⅡ光化学活性下降以及由类胡罗卜素、Ｃｙｔｂ－５５９参与的一些主要光保护机制作了综述,着重论述了其作用机理及研     

Optimization of Maintenance Conditions for Some Microforms of Red Algae in Collections

The effects of light and temperature conditions on the maintenance of some red microalgae (order Porphyridiales) in collections were studied. Periodical subculturing on solid and liquid media was used for maintenance. Halophilic species P. aeruginosa, P. cruentum, and P. sordidum were lost in 2.5 months if kept in darkness. The viability of algae in the dim light slightly declined in 4–5 months and was species-dependent. The results were compared with earlier obtained data on mesophilic Chlorococcales. For the green algae, darkness proved to be the optimal condition, while their viability markedly decreased at light. It was suggested that this discrepancy was caused by the presence of phycobiliproteins in the cells of red algae. Dim light conditions are optimal for the synthesis of phycobiliproteins, which are rapidly destroyed in darkness, thus leading to cell death.     

Photoinhibition of photosynthesis in intact kiwifruit (Actinidia deliciosa) leaves: effect of growth temperature on photoinhibition and recovery

Intact leaves of kiwifruit (Actinidia deliciosa (A. Chev.) C.F. Liang et A.R. Ferguson) from plants grown in a range of controlled temperatures from 15/10 to 30/25°C were exposed to a photon flux density (PFD) of 1500 μmol·m⁻²·s⁻¹ at leaf temperatures between 10 and 25°C. Photoinhibition and recovery were followed at the same temperatures and at a PFD of 20 μmol·m⁻²·s⁻¹, by measuring chlorophyll fluorescence at 77 K and 692 nm, by measuring the photon yield of photosynthetic O₂ evolution and light-saturated net photosynthetic CO₂ uptake. The growth of plants at low temperatures resulted in chronic photoinhibition as evident from reduced fluorescence and photon yields. However, low-temperature-grown plants apparently had a higher capacity to dissipate excess excitation energy than leaves from plants grown at high temperatures. Induced photoinhibition, from exposure to a PFD above that during growth, was less severe in low-temperature-grown plants, particularly at high exposure temperatures. Net changes in the instantaneous fluorescence,F ₀, indicated that little or no photoinhibition occurred when low-temperature-grown plants were exposed to high-light at high temperatures. In contrast, high-temperature-grown plants were highly susceptible to photoinhibitory damage at all exposure temperatures. These data indicate acclimation in photosynthesis and changes in the capacity to dissipate excess excitation energy occurred in kiwifruit leaves with changes in growth temperature. Both processes contributed to changes in susceptibility to photoinhibition at the different growth temperatures. However, growth temperature also affected the capacity for recovery, with leaves from plants grown at low temperatures having moderate rates of recovery at low temperatures compared with leaves from plants grown at high temperatures which had negligible recovery. This also contributed to the reduced susceptibility to photoinhibition in low-temperature-grown plants. However, extreme photoinhibition resulted in severe reductions in the efficiency and capacity for photosynthesis.     

Screening of Red Algae Filaments As a Potential Alternative Source of Eicosapentaenoic Acid

Lipids were extracted by a supercritical fluid extraction method from 10 species of filamentous red algae obtained from culture collections and their fatty acid compositions were determined. The fatty acid profiles of the 10 species were similar. The major fatty acids were 16:0, 20:4ω6 and 20:5ω3 (eicosapentaenoic acid, EPA), which amounted to over 70% of the total fatty acids. The highest EPA content (29.8 mg/L), as a percentage of total fatty acids, was produced by Liagora boergesenii filaments, which has good potential for EPA mass production in pilot plants.     

短期高温伤害蓝藻Anabaena7120的固氮活性恢复与生理条件的关系

蓝藻经短期高温处理后,其固氮活性显著下降,但在合宜条件下,这种受伤害的固氮活性可以有一定程度的恢复。光下不仅比暗中恢复快,而且活性也高得多。光合抑制剂和外源碳水化合物分别减缓和促进受高温伤害的蓝藻固氮活性恢复。在光、暗和供给外源碳水化合物的条件下,厌氧(氩和氮中)对受高温伤害的蓝藻固氮活性恢复不利。与正常蓝藻有异的是,H_2,CO_2及H_2与O_2,CO_2与N_2的加合都阻碍受高温伤害的蓝藻固氮活性的恢复。     

Photoinhibition by flash and continuous light of oxygen uptake by intact photosynthetic bacteria

The inhibition of respiration by continuous or flashing light has been studied in intact cells of different species of photosynthetic bacteria. For Rhodopseudomonas palustris, Rhodopseudomonas sphaeroides and Rhodopseudomonas capsulata, the inhibition by short actinic flashes shows a remarkable periodicity of two: each flash induces an inhibition of respiration, but a stimulation is observed after an even number of flashes. On the other hand, no oscillation is observed for Rhodospirillum rubrum and Rhodopseudomonas viridis cells. These different behaviours are explained by a difference in the redox state of the secondary electron acceptor as shown by the effect of ortho-phenanthroline on the amperometric signal. Addition of uncouplers (carbonyl cyanide m-chlorophenylhydrazone) or of an ATPase inhibitor (tri-N-butyl tin), has little effect on the oscillatory pattern induced by flash excitation. However, inhibition of respiration by continuous light is suppressed in the presence of carbonyl cyanide m-chlorophenylhydrazone. In the presence of tri-N-butyl tin the steady-state level is reached more rapidly than in the control experiment for a given light intensity. These results are interpreted as evidence of two modes of light inhibition of respiration in photosynthetic bacteria. A first type of inhibition, clearly shown under flash excitation, is due to interaction between respiratory and photosynthetic chains at the level of electron carriers. After each flash, an electron is diverted from the respiratory chain to the photooxidized reaction center. Because of the gating mechanism at the level of the secondary acceptor, the respiration is stimulated after an even number of flashes. The second mode of inhibition prevails under continuous illumination. Under these conditions, the rate of respiration is controlled essentially by the photoinduced proton electrochemical gradient.     

Gene Loci in Maize Influencing Susceptibility to Chilling Dependent Photoinhibition of Photosynthesis

Variation in tolerance in chilling-dependent photoinhibition has been associated with a wide range of traits in comparative physiological studies. A sweet corn (Zea mays L.) population of 214 F_2:3 families previously mapped to near-saturation with 93 RFLP DNA markers were subjected to low temperature and high-light events prior to measurement of the maximum dark-adapted quantum efficiency of PS II (F_v/F_m), to identify loci associated with variation in chilling-dependent photoinhibition. In the first assay with ten families varying in seedling growth and germination, significant differences were observed among families in their response to and recovery from exposure to high light at low temperature. All the 214 F_2:3 families from this population were then evaluated for tolerance of chilling-dependent photoinhibition in a controlled environment and then in three replicated trials in the field, each following naturally occurring chilling events during spring. The measured effects on F_v/F_m were analyzed with software that mapped segregating loci that regulate trait expression and linked to genetic markers (PLABQTL). QTL 3.096 (i.e. 96 cM on chromosome three) was consistently identified in both controlled environment and in the mean of the three field trails. Another QTL at 8.025, described the greatest percentage of total phenotypic variance (ca. 10%) for the mean reduction in F_v/F_m of all three periods of measurement in the field. A third QTL (4.136) showed a highly significant association in the third field trial. These three QTLs were closely associated with genes that have been mechanistically related to photoinhibition tolerance and repair. The results suggest that the ratio of F_v/F_m is an approach that may be used in establishing marker-assisted breeding for improved tolerance to chilling of maize in the light and in turn better early-season growth in cool temperate climates.     

Photoinhibition and Recovery of Photosynthesis in psbA Gene-Inactivated Strains of Cyanobacterium Anacystis nidulans

The susceptibility of photosynthesis to photoinhibition and the rate of its recovery were studied in cyanobacterium Anacystis nidulans strain R2 and its two psbA gene-inactivated mutants R2S2C3 and R2K1. Changes in the fluorescence kinetics at 77K as well as the rate of O₂ evolution were measured when cells were exposed to high photosynthetic photon flux densities in the range of 0 to 2,000 micromoles per square meter per second. The R2S2C3 mutant has an active psbAI gene highly expressed under low and normal light intensities, whereas R2K1 possesses psbAII and psbAIII genes highly expressed under very high light intensities. The level of overall susceptibility of photosynthesis to photoinhibition was more pronounced in the wild type and the mutant R2S2C3 than in the mutant R2K1, especially at higher light intensities. In constrast, all three strains showed an increased but similar sensitivity to photoinhibition after addition of the translational inhibitor streptomycin; mutant R2K1 being slightly less sensitive at lower light intensities. The result is interpreted as demonstrating similar intrinsic susceptibility to photoinhibition of the two different forms of the D1 protein, form I and form II, encoded by the psbAI and psbAII/psbAIII genes, respectively. The increased resistance to photoinhibition of the R2K1 mutant was ascribed to an approximately 3 times higher rate of recovery than the wild type and the mutant R2S2C3. On the basis of our experiments we conclude that the susceptibilities to photoinhibition of the Anacystis nidulans psbA genes mutants studied are regulated mainly by modifying the rate of repair, i.e. the rate of turnover of the D1 protein.     

Photoinhibition and repair in Dunaliella salina acclimated to different growth irradiances

The light-dependent rate of photosystem-II (PSII) damage and repair was measured in photoautotrophic cultures of Dunaliella salina Teod. grown at different irradiances in the range 50–3000 mol photons · m^–2· s^–1. Rates of cell growth increased in the range of 50–800 mol photons·m^–2·s^–1, remained constant at a maximum in the range of 800–1,500 mol photons·m^–2 ·s^–1, and declined due to photoinhibition in the range of 1500–3000 mol photons·m^–2·s^–1. Western blot analyses, upon addition of lincomycin to the cultures, revealed first-order kinetics for the loss of the PSII reaction-center protein (D1) from the 32-kDa position, occurring as a result of photodamage. The rate constant of this 32-kDa protein loss was a linear function of cell growth irradiance. In the presence of lincomycin, loss of the other PSII reaction-center protein (D2) from the 34-kDa position was also observed, occurring with kinetics similar to those of the 32-kDa form of D1. Increasing rates of photodamage as a function of irradiance were accompanied by an increase in the steady-state level of a higher-molecular-weight protein complex ( 160-kDa) that cross-reacted with D1 antibodies. The steady-state level of the 160-kDa complex in thylakoids was also a linear function of cell growth irradiance. These observations suggest that photodamage to D1 converts stoichiometric amounts of D1 and D2 (i.e., the D1/D2 heterodimer) into a 160-kDa complex. This complex may help to stabilize the reaction-center proteins until degradation and replacement of D1 can occur. The results indicated an intrinsic half-time of about 60 min for the repair of individual PSII units, supporting the idea that degradation of D1 after photodamage is the rate-limiting step in the PSII repair process.Abbreviations Chl chlorophyll - PSI photosystem I - PSII photosystem II - D1 the 32-kDa reaction-center protein of PSII, encoded by the chloroplast psbA gene - D2 the 34-kDa reactioncenter protein of PSII, encoded by the chloroplast psbD gene - Q_A primary electron-accepting plastoquinone of PSII The work was supported by grant 94-37100-7529 from the US Department of Agriculture, National Research Initiative Competitive Grants Program.     

Photoinhibition in Euglena gracilis: Involvement of reactive oxygen species

Photoinhibition of isolated Euglena gracilis thylakoids was characterised by a drastic decline in PSII photochemistry, chlorophyll-a fluorescence and an enhanced degradation of the 32-kDa protein. The process of protein degradation, as shown by studies of [¹⁴C] atrazine binding, was clearly slower than the other events. The activity of PSI was not affected. Decrease of electron-transport activity and loss of herbicide binding were prevented in the presence of various antioxidants and enzymes which protect against free radicals; however, the protection was not total. The strongest effect was observed by addition of dimethylsulfoxide, a potent hydroxyl-radical (OH^*) quencher. Furthermore, combinations of various protective substances were even more effective in reducing photoinhibition. Different reactive oxygen species, including H₂O₂, superoxide radicals and OH^* radicals were obviously involved in photoinhibition. These results were confirmed by the addition of potential OH^*-radical-generating substances. Simultaneous enhancement of OH^*-radical formation and photoinhibitory damage were observed in these cases. The involvement of this highly toxic species could be shown directly by a colorimetric test, thus enabling its light-mediated formation during photoinhibition to be quantified for the first time. In all, the data indicate that a site in PSII is the origin of radical formation involved in photoinhibition and that H₂O₂ is an important precursor in the formation of hydroxyl-radicals.Abbreviations Chl chlorophyll - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - DCPIP 2,6-dichlorphenolindophenol - DMSO dimethyl sulfoxide - F_M maximum fluorescence - F_V variable fluorescence - Fecy ferricyanide - MSA methane sulfinic acid - MV 1,1 dimethyl-4,4 bipyridylium dichloride - OH^* hydroxyl radical - PBQ p-phenylbenzoquinone - PDA p-phenylenediamine - PPFD photosynthetic photon flux density - SOD superoxide dismutase This reasearch was supported by a grant from the Volkswagen-Stiftung.     

Photoinhibition of photosynthesis in intact bean leaves: role of light and temperature,and requirement for chloroplast-protein synthesis during recovery

Photoinhibition of photosynthesis was induced in intact leaves of Phaseolus vulgaris L. grown at a photon flux density (PFD; photon fluence rate) of 300 mol·m^-2·s^-1, by exposure to a PFD of 1400 mol·m^-2·s^-1. Subsequent recovery from photoinhibition was followed at temperatures ranging from 5 to 35°C and at a PFD of either 20 or 140 mol·m^-2·s^-1 or in complete darkness. Photoinhibition and recovery were monitored mainly by chlorophyll fluorescence emission at 77K but also by photosynthetic O₂ evolution. The effects of the protein-synthesis inhibitors, cycloheximide and chloramphenicol, on photoinhibition and recovery were also determined. The results demonstrate that recovery was temperature-dependent with rates slow below 15°C and optimal at 30°C. Light was required for maximum recovery but the process was light-saturated at a PFD of 20 mol·m^-2·s^-1. Chloramphenicol, but not cycloheximide, inactivated the repair process, indicating that recovery involved the synthesis of one or more chloroplast-encoded proteins. With chloramphenicol, it was shown that photoinhibition and recovery occurred concomitantly. The temperature-dependency of the photoinhibition process was, therefore, in part determined by the effect of temperature on the recovery process. Consequently, photoinhibition is the net difference between the rate of damage and the rate of repair. The susceptibility of chilling-sensitive plant species to photoinhibition at low temperatures is proposed to result from the low rates of recovery in this temperature range.Abbreviations and symbols Da Dalton - Fo, Fm, Fv instantaneous, maximum, variable fluorescence emission - PFD photon flux density - PSII photosystem II - photon yield C.I.W.-D.P.B. Publication No. 871     

光合作用对光响应新模型及其应用

讨论了光合作用对光响应新模型的一些特性．用新模型拟合超级杂交水稻新组合-II优明86和丹参的光响应数据,并与用非直角双曲线模型、直角双曲线模型和二项式回归方法拟合结果进行了比较．结果比较表明：该模型不仅能处理植物在光抑制条件下的光响应问题,而且还能处理植物在低光强条件下的光响应问题．在光补偿点附近这两种植物的光合速率对光强的响应是非线性的．     

Photoinhibition and recovery in tropical plant species: response to disturbance

Disturbance or rainforest is often followed by mass mortality of understorey seedlings. Transitions of shade grown plants to full sunlight can cause reductions in the efficiency with which light is used in photosynthesis, called photoinhibition. In order to assess the influence of photoinhibition on mortality and growth after rainforest disturbance this study examined photoinhibition in both simulated and real forest disturbances in northern Papua New Guinea. In an experiment simulating rainforest disturbance, exposure of shade-grown plants to full sunlight resulted in abrupt decreases in the chlorophyll fluorescence parameter F _v/F _m that is characteristic of photoinhibition. However, in the well-watered plants used in these experiments there were no fatalities during 3 weeks after exposure to full sunlight. Thus, it is unlikely that photoinhibition, alone, is responsible for seedling fatalities after rainforest disturbances, but more likely that fatalities are due to photoinhibition in conjunction with other environmental stress. There were differences between the response of species to the simulated disturbance that concurred with their preferred habitats. For example, species form the genus Barringtonia, which is commonly found in shaded understorey environments, underwent greater reductions in F _v/F _m and were slower to recover than species that usually inhabit high solar radiation environments. The extent of photoinhibition and the rate of recovery appeared to be dependent on avoidance of direct solar radiation by altering leaf angles and on increasing maximum photosynthetic rates. A field survey of photoinhibition in man-made rainforest gaps corroborated the findings of the simulated disturbance experiment showing that plant species commonly found in shaded environments showed a greater degree of photoinhibition in forest gaps at midday than those species which are classified as species that benefit from gaps or specialist gap inhabitors.     

黄瓜幼苗子叶在低温下的光抑制及其恢复

用PAM脉冲调制荧光仪测定叶绿素荧光的变化研究了黄瓜幼苗子叶在PFD为50和100μmolm-2s-1,温度为4、7、10、15℃下的光抑制及其恢复。结果表明,黄瓜幼苗子叶Fv／Fm随着温度的下降和PFD的增加而下降,并且增加等量的PFD在4℃下比在10℃下引起更大的Fv／Fm下降。在黑暗条件下光抑制有轻微恢复,但完士恢复必需光照,且恢复起始时的光照十分重要。DTT可部分抑制叶绿素荧光Fo和Fm的猝灭,且15℃下比在4℃下抑制效果更大。CAP能强烈地加剧光抑制并几乎完全抑制恢复,且10℃下比在4℃下对光抑制的加剧作用更大。冷锻炼提高了黄瓜幼苗抵抗低温先抑制的能力,而CAP对冷锻炼苗比未锻炼苗的低温光抑制具有更大的加剧作用。     

光强在低温弱光胁迫后番茄叶片光合作用恢复中的作用

为了研究光强在低温弱光胁迫后番茄叶片光合作用恢复中的作用,以番茄品种浙粉202为材料,研究了低温弱光后恢复期全光照与遮荫对光合作用和叶绿素荧光参数的影响。结果表明：低温弱光（8℃/12℃,PFD 80 μmol·m^-2·s^-1）导致番茄叶片P_n、Φ_PSⅡ、qP和F_v′/F_m′的下降,但诱导了NPQ的上升,未引起F_v/F_m的变化;全光照（100%光照）下恢复1 使得植株叶片P_n、F_v/F_m、Φ_PSⅡ、qP、NPQ和F_v′/F_m′均大幅下降,随后光合和荧光参数可缓慢恢复至对照水平;遮荫（40%光照）恢复植株F_v/F_m、Φ_PSⅡ和F_v′/F_m′仅在第一天稍有下降,而P_n和qP还略有上升,NPQ虽有所降低但仍显著高于对照水平,随后光合和荧光参数均可迅速恢复到对照水平。说明低温弱光虽抑制了光合作用的进行,但并未引起光抑制的发生;全光照恢复加剧了叶片光抑制的发生,而遮荫恢复可通过叶片PSⅡ光化学活性的快速恢复和天线色素热耗散能力的增强以保护光合机构免受伤害,有利于光合作用的迅速恢复。