高温对仁用杏光合特性及PSⅡ光化学活性的影响

为探讨高温胁迫下仁用杏叶片的光合适应机制,以科尔沁沙地生长的4年生'超仁'仁用杏为试材,设置环境温度为25℃、30℃、40℃和50℃处理,利用气体交换技术和快速叶绿素荧光诱导动力学曲线分析技术(JIP-test),研究了仁用杏叶片光合特性和PSⅡ光化学活性.结果表明:在一定温度范围内,随着温度升高,仁用杏通过提高光合色素含量和比例来维持光能的吸收、传递和转换能力,从而保证光合机构正常运转;当高温超过叶片自身生理调节限度后,叶绿素发生分解、净光合速率(Pn)明显下降、胞间CO2浓度(Ci)上升,说明光合作用的下降是由叶肉因素造成的.温度40℃导致单位面积有活性反应中心数量(RC/CSo)显著下降;而50℃高温下荧光诱导曲线中K点(Wk)和J点(Vj)明显增加,高温对仁用杏叶片放氧复合体(OEC)、受体侧和PsⅡ反应中心造成了伤害.此外,50℃高温还导致初始荧光(Fo)显著升高,为对照的2.26倍,PSⅡ最大光化学效率(Fv/Fm)和光化学性能指数(PI/ABS)分别下降为对照的37.9%和10.3%.高温损害了PSⅡ供体侧和受体侧的功能,造成光合效率下降,这是高温胁迫对仁用杏叶片光合机构伤害的主要机制之一.     

The overaccumulation of glycinebetaine alleviated damages to PSII of wheat flag leaves under drought and high temperature stress combination

To analyze the physiological mechanisms underlying the increased tolerance to drought and high temperature stress combination by overproduction of glycinebetaine (GB) in wheat, a transgenic wheat line T6 and its wild-type (WT) Shi4185 were used. The transgenic line was generated by introducing a gene encoding betaine aldehyde dehydrogenase (BADH) into a wheat line Shi4185. The gene was cloned from Garden Orache (Atriplex hortensis L.). Wheat plants were exposed to drought (withholding irrigation), high temperature stress (40 °C), and their combination at the flowering stage. Analyses of oxygen-evolving activity and photosystem II (PSII) photochemistry, modulated chlorophyll fluorescence, rapid fluorescence induction kinetics, and the polyphasic fluorescence transients (OJIP) were used to evaluate PSII photochemistry in wheat plants. The results suggest that the PSII in transgenic plants showed higher resistance than that in wild-type plants under the stresses studied here, this increased tolerance was associated with an improvement in stability of the oxygen-evolving complex and the reaction center of PSII; streptomycin treatment can impair the protective effect of overaccumulated GB on PSII. The overaccumulated GB may protect the PSII complex from damage through accelerating D1 protein turnover to alleviate photodamage. The results also suggest that the PSII under combined high temperature and drought stress shows higher tolerance than under high temperature stress alone in both transgenic and wild-type plants.     

Effects of water stress on photosystem II photochemistry and its thermostability in wheat plants

Modulated chlorophyll fluorescence, rapid fluorescence induction kinetics and the polyphasic fluorescence transients (OJIP) were used to evaluate PSII photochemistry in wheat plants exposed to water stress and/or heat stress (25-45C). Water stress showed no effects on the maximal quantum yield of PSII photochemistry (Fv/Fm), the rapid fluorescence induction kinetics, and the polyphasic fluorescence transients in dark-adapted leaves, indicating that water stress had no effects on the primary photochemistry of PSII. However, in light-adapted leaves, water stress reduced the efficiency of excitation energycapture by open PSII reaction centres (F'v/F'm) and the quantum yield of PSII electron transport (PSII), increased the non-photochemical quenching (qN) and showed no effects on the photochemical quenching (qP). This suggests that water stress modified the PSII photochemistry in the light-adapted leaves and such modifications may be a mechanism to down-regulate the photosynthetic electron transport to match a decreased CO2 assimilation. In addition, water stress also modified the responses of PSII to heat stress. When temperature was above 35C, thermostability of PSII was strongly enhanced in water-stressed leaves, which was reflected in a less decrease in Fv/Fm, qP, F'v/F'm, and PSII in water-stressed leaves than in well-watered leaves. There were no significant variations in the above fluorescence parameters between moderately and severely water-stressed plants, indicating that the moderate water-stressed plants, indicating that the moderate water stress treatment caused the same effects on thermostability of PSII as the severe treatment. It was found that increased thermostability of PSII may be associated with an improvement of resistance of the O2-evolving complex and the reaction centres in water-stressed plants to high temperature.Key words: Chlorophyll fluorescence, heat stress, photosystem II photochemistry, water stress, wheat (Tritium aestivum L.).      

Effects of high temperature on photosynthesis, chlorophyll fluorescence, chloroplast ultrastructure, and antioxidant activities in fingered citron

Effects of heat stress on the photosynthesis system and antioxidant activities in Fingered citron (Citrus medica var. sarcodactylis Swingle) were investigated. Two-year-old Fingered citron plants were exposed to different temperature (28, 35, 40, and 45°C) for 6 h; then the photosynthetic capacity, chlorophyll fluorescence, chloroplast ultrastructure, and antioxidant activities in the leaves were evaluated. Exposure to 40 and 45°C for 6 h resulted in a significant decrease in the photosynthetic rate (P _n), carboxylation efficiency (CE), the maximal photochemical efficiency of photosystem II, and the light-saturated photosynthetic rate, which were related to the reduction of CO₂ assimilation, inactivation of photosystem II and photosynthetic electron transport. Moreover, transmission electron microscopy showed chloroplast ultrastructural alterations, including their swelling, matrix zone expanding, and lamella structure loosening. Furthermore, heat stress, especially at 45°C, caused oxidative damage resulted from ROS accumulation in Fingered citron leaves accompanied by increases in activities of superoxide dismutase, peroxidase, and catalase. However, exposure to 35°C for 6 h or 40°C for 4 h had no significant influence on the photosynthetic capacity at all. The results suggest that Fingered citron plants show no heat injury when temperature is below 40°C.     

Salinity treatment shows no effects on photosystem II photochemistry,but increases the resistance of photosystem II to heat stress in halophyte Suaeda salsa

Photosynthetic gas exchange, modulated chlorophyll fluorescence, rapid fluorescence induction kinetics, and the polyphasic fluorescence transients were used to evaluate PSII photochemistry in the halophyte Suaeda salsa exposed to a combination of high salinity (100-400 mM NaCl) and heat stress (35-47.5 degrees C, air temperature). CO(2) assimilation rate increased slightly with increasing salt concentration up to 300 mM NaCl and showed no decrease even at 400 mM NaCl. Salinity treatment showed neither effects on the maximal efficiency of PSII photochemistry (F(v)/F(m)), the rapid fluorescence induction kinetics, and the polyphasic fluorescence transients in dark-adapted leaves, nor effects on the efficiency of excitation energy capture by open PSII reaction centres (F(v)'/F(m)') and the actual PSII effciency (Phi(PSII)), photochemical quenching (q(P)), and non-photochemical quenching (q(N)) in light-adapted leaves. The results indicate that high salinity had no effects on PSII photochemistry either in a dark-adapted state or in a light-adapted state. With increasing temperature, CO(2) assimilation rate decreased significantly and no net CO(2) assimilation was observed at 47.5 degrees C. Salinity treatment had no effect on the response of CO(2) assimilation to high temperature when temperature was below 40 degrees C. At 45 degrees C, CO(2) assimilation rate in control plants decreased to zero, but the salt-adapted plants still maintained some CO(2) assimilation capacity. On the other hand, the responses of PSII photochemistry to heat stress was modified by salinity treatment. When temperature was above 35 degrees C, the declines in F(v)/F(m), Phi(PSII), F(v)'/F(m)', and q(P) were smaller in salt-adapted leaves compared to control leaves. This increased thermostability was independent of the degree of salinity, since no significant changes in the above-described fluorescence parameters were observed among the plants treated with different concentrations of NaCl. During heat stress, a very clear K step as a specific indicator of damage to the O(2)-evolving complex in the polyphasic fluorescence transients appeared in control plants, but did not get pronounced in salt-adapted plants. In addition, a greater increase in the ratio (F(i)-F(o))/(F(p)-F(o)) which is an expression of the proportion of the Q(B)-non-reducing PSII centres was observed in control plants rather than in salt-adapted plants. The results suggest that the increased thermostability of PSII seems to be associated with the increased resistance of the O(2)-evolving complex and the reaction centres of PSII to high temperature.     

Characteristics of Slow Induction Curve of Chlorophyll Fluorescence and CO2 Exchange for the Assessment of Plant Heat Tolerance at Various Levels of Light Intensity

The heat tolerance of wheat (Triticum aestivum L.) and radish (Raphanus sativus L. var. minor) cenoses exposed to elevated and damaging air temperatures (35°C for 20 h, 45°C for 7 h) under photoculture conditions at various levels of photosynthetically active radiation (PAR) was assessed by measuring characteristics of the slow induction curve of chlorophyll fluorescence at 682 and 734 nm and the CO₂ exchange rate. Irrespective of the illumination level, the exposure of the cenoses to 35°C did not induce irreversible changes in the plant photosynthetic apparatus. The lowest extent of damage to wheat and radish cenoses exposed to 45°C was observed at 150 W/m² of PAR, whereas the highest damage of the plants was observed at an illumination level that was close to the compensation point of the cenose photosynthesis (50–70 W/m² of PAR at air temperature of 24°C). Viability index proved to be the most sensitive characteristic, compared to other characteristics, which were determined by measuring the slow phase of fluorescence induction at 682 and 734 nm. In the cenoses studied, the pattern of changes in the viability index in response to a stress factor was close to the changes in the photosynthetic rate.     

光叶眼子菜响应夏季高温的模拟研究

为探讨南四湖优势物种光叶眼子菜在夏季浅水区的衰亡原因, 用25℃、30℃、35℃和40℃的恒温水浴模拟夏季高温处理光叶眼子菜(Co. Potamogeton lucens L.)3h。生化结果显示, 在35℃及以上高温下, 光叶眼子菜的蛋白质含量、可溶性糖含量和叶绿素含量显著下降, 丙二醛含量显著上升, 说明35℃以上高温对光叶眼子菜产生了显著伤害。光叶眼子菜的光合系统对高温更为敏感, 在高温胁迫下标准化的叶绿素荧光动力学曲线上J相和K相显著隆起, 但并未发现明显的L-band。进一步解析叶片的叶绿素荧光动力学参数, 结果显示: 随着处理温度的升高, 反应中心的初始关闭速率(dVG/dt_o, dV/dt_o)变慢, 但到达P相的所需时间(T_fm)变短; 光系统Ⅱ (Photosystem Ⅱ, PSⅡ)的光化学效率(F_v/F_m)减小, 非光化学效率(K_n)、J相相对可变荧光强度(V_j)和热耗散(DI_o/RC、DI_o/CS_o、F_o/F_m)增大; 尽管高温下质体醌周转次数(N)、还原速率(S_m/T_fm)和I相相对可变荧光强度(V_i)变化不显著, 但质体醌库(S_m)明显减小; 单个反应中心光能的吸收(ABS/RC)和捕获效率(TR_o/RC)增加, 电子传递效率(ET_o/RC)却呈下降趋势; 单位激发态面积的光能捕获(TR_o/CS_o)和电子传递效率(ET_o/CS_o)均降低, 反应中心数目(RC/CS_o)显著减少。上述高温胁迫效应导致整个叶片的结构功能指数(SFI_abs)、性能指数(PI_abs)以及光合驱动力(DF)显著降低。高温对光叶眼子菜的伤害主要是导致其光系统II放氧复合体失活、反应中心数目减少和反应中心的光化学效率下降, 进而诱导活性氧的产生, 对细胞造成伤害。因此, 光叶眼子菜属于对高温敏感的水生植物。     

Photosynthetic Decline from High Temperature Stress during Maturation of Wheat : II. Interaction with Source and Sink Processes

High temperature stress reduces grain growth in wheat (Triticum aestivum L.) by altering source activity and sink capacity. The impact of stress on source and sink interactions in two wheat cultivars of differing source thermotolerance was monitored by analysis of chlorophyll fluorescence transients, Fv (variable fluorescence) and PSM (peak, stationary, maximum), of attached flag leaves on intact and decapitated tillers grown at optimum (20°C) and stress (35°C) temperatures after anthesis. The thermotolerant cultivar Waverly had reduced Fv and PS quenching and a large increase of SM during heat stress. The less thermotolerant cultivar, Len, exhibited increased Fv and PS quenching and a small increase of SM. Fluorescence induction was similar in intact and decapitated tillers of Len, indicating diminished sinksource interaction during heat stress. The present results and previous observations of photosynthetic activities indicate that cyclic electron transport and photophosphorylation in flag leaves of the thermotolerant cultivar were stimulated by sink demand (increased SM in intact plants). Reduced grain development in the thermolabile cultivar resulted from limited capacity to support cyclic electron transport and photophosphorylation (slight increase in SM of intact plants and large reduction of Cytochrome f/b₆-mediated electron transport capacity). It was concluded that heat stress injures the photosynthetic apparatus during reproductive growth of wheat and that diminished source activity and sink capacity may be equally important in reducing productivity.     

Temperature stress can alter the photosynthetic efficiency and secondary metabolite concentrations in St. John's wort.

Temperature stress is known to cause many physiological, biochemical and molecular changes in plant metabolism and possibly alter the secondary metabolite production in plants. The hypothesis of the current study was that temperature stress can increase the secondary metabolite concentrations in St. John's wort. Plants were grown under controlled environments with artificial light using cool white fluorescent lamps and CO2 enrichment and 70-day-old plants were subjected for 15 days to different temperature treatments of 15, 20, 25, 30 and 35 degrees C before harvested. Major aim of the study was to increase the major secondary metabolites in St. John's wort by applying temperature stress and to evaluate the physiological status of the plant especially the photosynthetic efficiency and peroxidase activity of the leaf tissues exposed to different temperatures under precisely controlled environmental factors. Results revealed that relatively high (35 degrees C) or low (15 degrees C) temperatures reduced the photosynthetic efficiency of the leaves of St. John's wort plants and resulted in low CO2 assimilation. Net photosynthetic rates and the maximal quantum efficiency of PSII photochemistry of the dark adopted leaves (phi(p)max) decreased significantly in the leaves of plants grown under 35 or 15 degrees C temperature treatments. High temperature (35 degrees C) treatment increased the leaf total peroxidase activity and also increased the hypericin, pseudohypericin and hyperforin concentrations in the shoot tissues. These results provide the first indication that temperature is an important environmental factor to optimize the secondary metabolite production in St. John's wort and controlled environment technology can allow the precise application of such specific stresses.     

番茄叶片光合作用对快速水分胁迫的响应

采用聚乙二醇(PEG 6000)溶液控制番茄根际水势和叶片离体的方式设置了水分胁迫处理,测算了光合诱导过程中净光合速率、暗呼吸速率和CO₂补偿点等光合参数的变化.结果表明： 在1000 μmol·m^-2·s^-1光诱导下,水分胁迫处理的番茄叶片净光合速率(P_n)达到最大值所需时间缩短为对照的1/3,气孔导度(g_s)快速增大为对照的1.5倍.水分胁迫处理的番茄叶片光饱和点(LSP)比对照降低了65%～85%,而光补偿点(LCP)比对照增加了75%～100%,缩小了番茄叶片利用光能的有效范围.水分胁迫处理的番茄叶片最大光合能力(A_max)低于对照40%以上,暗呼吸速率(R_d)增大了约45%.可见,快速水分胁迫处理使番茄叶片气孔迅速开放,光合诱导初始阶段消失.水分胁迫导致植物利用光能的效率和潜力降低是植物生产力下降的重要原因,而气孔调节是番茄适应快速水分胁迫的重要生理机制.     

盐胁迫对不同抗盐性小麦叶片荧光诱导动力学的影响

以不同抗盐性小麦为材料,研究了NaCl胁迫对叶片叶绿素。荧光诱导动力学的影响。指出150 mmol/L NaCl使小麦幼苗生长降低,叶绿素含量下降,同时使光系统Ⅱ的潜在光化学活性和原初光能转化率降低,使光反应受到抑制。     

外源Ca2+对高温强光胁迫下小麦叶绿体D1蛋白磷酸化及光系统Ⅱ功能的影响

用10 mmol·L^-1 CaCl₂溶液预处理灌浆期小麦叶片,以水预处理为对照,然后将预处理植株进行高温强光（35 ℃,1600 μmol·m^-2·s^-1）胁迫,测定胁迫处理过程中小麦旗叶光合电子传递速率、净光合速率、叶绿素荧光参数及D₁蛋白的变化,以研究外源Ca²⁺对高温强光胁迫下小麦叶片类囊体膜D₁蛋白磷酸化和PSⅡ功能的影响.结果表明：CaCl₂溶液预处理使小麦叶片在高温强光逆境下PSⅡ反应中心发生可逆失活,有效抑制了高温强光下D₁蛋白的净降解,保持了较高的D₁蛋白磷酸化水平,暗恢复后PSⅡ反应中心活性迅速恢复,全链电子传递速率和PSⅡ电子传递速率恢复至对照水平,维持了较高的PSⅡ原初光化学效率（F_v/F_m）、实际光化学效率(Ф_PSⅡ)、光化学猝灭系数（q_P）和净光合速率（P_n）.表明外源Ca²⁺通过调节小麦叶绿体D₁蛋白的周转,促进了PSⅡ的正常运转,减轻了高温强光胁迫对叶片光合机构的损伤.     

Mycorrhizal impact on drought stress tolerance of rose plants probed by chlorophyll a fluorescence, proline content and visual scoring

Micropropagated rose plants (Rosa hybrida L., cv. New Dawn) were inoculated with the arbuscular mycorrhizal (AM) fungus Glomus intraradices (Schenk and Smith) and subjected to different drought regimens. The dual objectives of these experiments were to investigate the mechanism and the extent to which AM can prevent drought damages and whether physiological analyses reveal enhanced drought tolerance of an economically important plant such as the rose. In a long-term drought experiment with four different water regimens, visual scoring of wilt symptoms affirmed that AM in a selected host–symbiont combination increased plant performance. This effect was mostly expressed if moderate drought stress was constantly applied over a long period. In a short-term experiment in which severe drought stress was implemented and plants were allowed to recover after 4 or 9 days, no visual differences between mycorrhizal and non-mycorrhizal roses were observed. Therefore, the early physiological steps conferring drought tolerance were prone to investigation. Proline content in leaves proved to be an unsuitable marker for AM-induced drought tolerance, whereas analysis of chlorophyll a fluorescence using the JIP test (collecting stress-induced changes of the polyphasic O-J-I-P fluorescence kinetics in a non-destructive tissue screening) was more explanatory. Parameters derived from this test could describe the extent of foliar stress response and help to differentiate physiological mechanisms of stress tolerance. AM led to a more intense electron flow and a higher productive photosynthetic activity at several sites of the photosynthetic electron transport chain. A K step, known as a stress indicator of general character, appeared in the fluorescence transient only in drought-stressed non-mycorrhizal plants; conversely, the data elucidate a stabilising effect of AM on the oxygen-evolving complex at the donor site of photosystem (PS) II and at the electron-transport chain between PS II and PS I. If drought stress intensity was reduced by a prolonged and milder drying phase, these significant tolerance features were less pronounced or missing, indicating a possible threshold level for mycorrhizal tolerance induction.     

Moderate heat stress induces state transitions in Arabidopsis thaliana

The effect of temperature on the photosynthetic machinery is crucial for the fundamental understanding of plant physiology and the bioengineering of heat-tolerant varieties. In our study, Arabidopsis thaliana was exposed to mild (40°C), short-term heat stress in the dark to evaluate the heat-triggered phosphorylation and migration of light harvesting complex (LHC) II in both wild-type (wt) and mutant lacking STN7 kinase. The 77K emission spectra revealed an increase in PSI relative to PSII emission similar to increases observed in light-induced state I to state II transitions in wt but not in stn7 mutant. Immunoblotting results indicated that the major LHCII was phosphorylated at threonine sites under heat stress in wt plants but not in the mutant. These results support the proposition that mild heat stress triggers state transitions in the dark similar to light-induced state transitions, which involve phosphorylation of LHCII by STN7 kinase. Pre-treatment of Arabidopsis leaves with inhibitor DBMIB, altered the extent of LHCII phosphorylation and PSI fluorescence emission suggests that activation of STN7 kinase may be dependent on Cyt b(6)/f under elevated temperatures in dark. Furthermore, fast Chl a transient of temperature-exposed leaves of wt showed a decrease in the F(v)/F(m) ratio due to both an increase in F(o) and a decrease in F(m). In summary, our findings indicate that a mild heat treatment (40°C) induces state transitions in the dark resulting in the migration of phosphorylated LHCII from the grana to the stroma region.     

基于叶绿素荧光参数的小麦叶片叶绿素相对含量估算方法

叶绿素含量是植物学和农业相关研究领域常用的生理指标.叶绿素含量和叶片光合功能密切相关,但是现有的叶绿素含量的测定方法无法实现叶绿素含量和光合功能的同步测定和关联分析.为解决该问题,本研究通过测定35个小麦品种旗叶的SPAD值和叶绿素荧光诱导动力学曲线,分别使用不同时间的快速叶绿素荧光动力学曲线的荧光值,以及33个常用荧...     

Effects of arbuscular mycorrhizal fungus on photosynthesis and water status of maize under high temperature stress

The purpose of this study was to investigate the effects of arbuscular mycorrhizal (AM) symbiosis on gas exchange, chlorophyll fluorescence, pigment concentration and water status of maize plants in pot culture under high temperature stress. Zea mays L. genotype Zhengdan 958 were cultivated in soil at 26/22°C for 6 weeks, and later subjected to 25, 35 and 40°C for 1 week. The plants inoculated with the AM fungus Glomus etunicatum were compared with the non-inoculated plants. The results showed that high temperature stress decreased the biomass of the maize plants. AM symbiosis markedly enhanced the net photosynthetic rate, stomatal conductance and transpiration rate in the maize leaves. Compared with the non-mycorrhizal plants, mycorrhizal plants had lower intercellular CO₂ concentration under 40°C stress. The maximal fluorescence, maximum quantum efficiency of PSII photochemistry and potential photochemical efficiency of mycorrhizal plants were significantly higher than corresponding non-mycorrhizal plants under high temperature stress. AM-inoculated plants had higher concentrations of chlorophyll a, chlorophyll b and carotenoid than non-inoculated plants. Furthermore, AM colonization increased water use efficiency, water holding capacity and relative water content. In conclusion, maize roots inoculated with AM fungus may protect the plants against high temperature stress by improving photosynthesis and water status.     

Characterization of PSII photochemistry and thermostability in salt-treated Rumex leaves

A study was conducted, using chlorophyll fluorescence, rapid fluorescence induction kinetics, and polyphasic fluorescence transients, to determine the effect of salt treatment and heat stress on PSII photochemistry in Rumex leaves. Salt treatment was accomplished by adding NaCl solutions of different concentrations ranging from 50 to 200 mmol/L. Heat stress was induced by exposing the plant leaves to temperatures ranging from 29 to 47 degrees C. The control plants were grown without NaCl treatment. The data acquired in this study showed that NaCl treatment alone had no effect on the maximal photochemistry of PSH or the polyphasic rise of chlorophyll fluorescence. However, the NaCl treatment modified heat stress on PSII photochemistry in Rumex leaves, which was manifested by a lesser heat-induced decrease in photochemical quenching (qP), efficiency of excitation energy capture by open PSII reaction centers (Fv'/Fm'), and quantum yield of PSII electron transport (phiPSII). The data also showed that NaCl treatment compromised the impact of heat stress on the capacity of transferring electrons from Q(A)- to Q(B). Furthermore, the NaCl treatment promoted heat resistance of O2-evolving complex (OEC). In summary, NaCl treatment enhanced the thermostability of PSII.     

Photoinhibition of Photosynthesis Without Net Loss of D1 Protein in Wheat Leaves Under Field Conditions

To determine whether the net loss of D1 protein is the main cause of photoinhibition of photosynthesis in wheat leaves under field conditions in the absence of any environmental stress other than strong sunlight, the D1 protein content, photosynthetic evolution of oxygen and chlorophyll a fluorescence parameters were measured in field grown wheat leaves. After exposure to midday strong light for about 3 h, apparent photosynthetic quantum efficiency (Φ), Fv/Fm and Fo in wheat leaves declined, and these parameters recovered almost completely 1 h after transfer to the weak light of 30~40 ttmol photons · m-2 · s-1. No evident change in the D1 protein content was observed in the leaves after exposure to midday strong light for 3 h. After 3 hours exposure to strong light, the slow-relaxed fluorescence quenching in the leaves treated with streptomycin (SM) increased much more than that in the control leaves, but there was no effect SM on the recovery of Fv/Fm and F0; dithiothretol (DTT) treatment enhanced photoinhibition of photosynthesis and reduced the D1 protein content in the leaves after exposure to midday strong light. These results indicated that under field conditions with no environmental stress other than strong sunlight, photoinhibition of photosynthesis in wheat leaves was not due to the net loss of D1 protein, and it could be attributed mainly by the increased nonradiative energy dissipation.     

Chlorophyll thermoluminescence of leaf discs: simple instruments and progress in signal interpretation open the way to new ecophysiological indicators

Luminescence from photosynthetic material observed in darkness following illumination is a delayed fluorescence produced by a recombination of charge pairs stored in photosystem II, i.e. the back-reaction of photosynthetic charge separation. Thermoluminescence (TL) is a technique consisting of a rapid cooling followed by the progressive warming of a preilluminated sample to reveal the different types of charge pairs as successive emission bands, which are resolved better than the corresponding decay phases recorded at constant temperatures. Progress in thermoelectric Peltier elements and in compact light detectors made the development of simple, affordable and transportable instruments possible. These instruments take advantage of multifurcated light guides for combined TL, fluorescence and absorbance/reflectance measurements. Meanwhile, experiments on unfrozen leaf discs, with excitation by single turn-over flashes or far red light and infiltration by specific inhibitors/uncouplers, have led to a better understanding of in vivo TL signals. Much like chlorophyll fluorescence and in a complementary way, TL in the 0-60 degrees C temperature range not only informs on the state of photosystem II in leaf tissues and its possible alterations, but also gives a broader insight into the energetic state inside the chloroplast by probing (1) the light-induced or dark-stable thylakoid proton gradient through the protonation of the Mn oxygen-evolving complex, (2) the induction of cyclic/chlororespiratory electron flow towards the plastoquinone pool, (3) the [NADPH+ATP] assimilatory potential. By a different mechanism, warming above 60 degrees C without preillumination reveals chemiluminescence high temperature thermoluminescence (HTL) bands due to the radiative thermolysis of peroxides, which are indicators of oxidative stress in leaves.     

Biophysical Methods of Ecological Monitoring. Photosynthetic characteristics of tree plants growing in Moscow city

In this work, we studied the influence of ecological factors (distance from thoroughfares) on photosynthetic characteristics of leaves of four tree species growing in Moscow city. Photosynthetic activity of leaves was assayed by instrumental methods of probing the functional state of the photosynthetic apparatus, using electron paramagnetic resonance for measuring the kinetics of photooxidation of P₇₀₀ centers, thermoluminescence, and slow induction of chlorophyll fluorescence. It has been shown that the kinetic parameters of the induction curves, as determined from the kinetics of P₇₀₀ photooxidation and slow fluorescence induction in dark-adapted leaves, are sensitive to variations of plant growth conditions. These parameters can be used as informative characteristics in ecological monitoring.