Mechanism for photoinactivation of PSII by methyl viologen at two temperatures in the leaves of rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.)

We studied the photooxidative effects of methyl viologen (MV) on PSII in rice (Oryza sativa L). Leaves were held at either room temperature (RT) or 4°C. In the presence of MV, the photochemical efficiency of PSII, or F_v/F_m, was more depressed at RT than at the low temperature (LT), but the loss of D1 protein that was detected at RT was not observed at LT. However, the decline in the content of functional PSII, 1/F_o - 1/F_m, was similar for MV-treated leaves at either temperature. These results suggest that, at LT, PSII is not protected from MV-induced photooxidation, although degradation of the D1 protein is delayed. The 1/F_o - 1/F_m decreased by MV treatment at RT was significantly recovered during dark incubation for 2 h. Recovery of a small portion of 1/F_o - 1/F_m was also possible, even for tissues treated with MV at LT. Therefore, we believe that MV-induced reversible photoinactivation may exist This possibility is further discussed in terms of changes in the de-epoxidation state and the rate of PSII-driven electron transport.     

在光氧化条件下不同类型高产稻的叶绿素荧光特性和膜脂过氧化特点

用不同类型高产稻 (OryzasativaL .)粳稻 95 16、具有粳型成分的两系法亚种间杂交稻培矮 6 4/E32、两优培九(培矮 6 4/ 9311)和籼型杂交稻X0 7S/紫恢 10 0、冈优 881、汕优 6 3为材料 ,研究了孕穗期叶片在光氧化条件下的叶绿素荧光特性和膜脂过氧化表现。光氧化处理后 ,与籼型杂交稻比较 ,粳稻和具有粳型组分的亚种间杂交稻的PSⅡ原初光化学效率 (Fv/Fm)、PSⅡ的线性电子传递的量子效率 (ΦPSⅡ)和光化学猝灭系数 (qP)下降的较少 ;超氧化物歧化酶 (SOD)、过氧化氢酶 (CAT)、过氧化物酶 (POD)诱导的活性较高 ,活性氧 (O-·2 、H2 O2 )和丙二醛 (MDA)的产生积累较少 ,叶绿素和蛋白质含量下降较少 ,表现出耐光氧化特性 ,这与在自然条件下生育后期叶绿素含量变化相一致。相关分析表明它们的耐光氧化特性与结实率密切相关 ,说明耐光氧化品种抗早衰 ,有利籽粒充实。这些结果启示我们 :从超高产育种出发 ,兼顾杂种优势利用和抗早衰两方面考虑 ,在母本不育系中引入粳型成分是一个值得重视的育种策略。     

转C4光合酶基因水稻株系的抗光氧化特性

用经转入磷酸烯醇式丙酮酸羧化酶(PEPC)、丙酮酸磷酸二激酶(PPDK)、NADP-苹果酸酶(NADP-ME)、PEPC+PPDK等酶的基因的水稻株系及原种为材料,研究了光氧化条件下的叶绿素荧光特性和膜脂过氧化.光氧化处理后,与原种相比,转C4光合酶基因特别是转PEPC和转PEPC+PPDK基因水稻株系的PSⅡ原初光化学效率(Fv/Fm)、PSⅡ在照光下的实际光化学效率(ФPSⅡ)和光化学猝灭(qp)下降的比原种少,而非光化学猝灭(qN)增加的比原种多,说明在光氧化条件下,转C4光合酶基因水稻株系吸收的光能中有较多的光能转化为化学能,过剩的光能通过热耗散而减轻光破坏;同时转C4光合酶基因水稻株系诱导产生的的内源活性氧清除酶系超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、过氧化物酶(POD)的活性比原种高,从而有效清除水稻叶片内的活性氧(O-2、H2O2),使活性氧积累比原种少,因而膜脂过氧化产物丙二醛(MDA)产生较少.表明转C4光合酶基因特别是转PEPC和转PEPC+PPDK基因水稻株系耐光氧化能力较强.在光氧化条件下,它们的叶绿素和蛋白质含量下降较少,表现出耐光氧化特性.这些结果为应用生物技术创造耐光氧化种质提供了实验依据.     

水稻对稻瘿蚊为害补偿力与经济阈值研究

１９９４－１９９８年针对水地稻瘿蚊为害补偿力及经济阈值进行了研究,结果表明：⑴水稻对稻瘿蚊为害具有较强的补偿能力,但基本属于不足补偿,不同标葱梯度其补偿力不同,每造成１％的标葱引起的产量损失远小于１％,其补偿率一般在５５％－８０％之间,产量损失及其损失率与标葱数呈极显正相关,有效穗和产量补偿率与标葱数则呈显负相关;⑵在相同受害程度下,密植损失大,补偿力小,而稀植损失小,补偿能力大,秧苗期补偿效     

水稻叶片对模拟酸雨伤害的生理反应

水稻暴露于ｐＨ２．５～４．２的模拟酸雨中２个月后测定表明：叶片叶绿素含量下降,细胞液离子外渗率增加,气孔阻抗增高,蒸腾速率降低。不同叶位的水稻叶片对模拟酸雨的敏感性不同,杂交稻（汕优６３）对模拟酸雨的敏感性较粳稻（中粳８６４）高     

光氧化胁迫下几种植物叶片的超氧自由基产生速率和光合特性

以甲基紫精 (MV) 0～ 1mmol/L在 15 0 0 μmolm-2s-1光下处理C3 植物花生、水稻和C4 植物玉米、甘蔗的叶圆片 30min ,O- ·2 产生速率随MV浓度提高而加快。MV浓度超过 10 μmol/L ,光合放氧出现负值并持续增大。光氧化作用降低叶绿素荧光参数Fv/Fm ,ΦPSⅡ和qP,而qN 则或提高 (C3 植物 ,MV 10 μmol/L )或几乎不变甚至有所降低 (C4 植物或C3 植物在高浓度MV下 )。热耗散系数KD 的变化与qN 相似。与C4 植物相比 ,C3 植物的O- ·2 产生速率和光下吸氧的速率较高 ,SOD活性较低 ,Fv/Fm ,ΦPSⅡ和qP 的降低幅度比C4植物大。对田间玉米叶片的MV涂抹试验看到 ,MV降低光合CO2 同化速率的同时 ,也降低气孔导度、PEP羧化酶和SOD活性 ,Ci增大。结果表明MV光氧化作用刺激PSⅠ的O2 光还原作用 ,引起PSⅡ部份失活 ,气孔部份关闭和关键酶类氧化失活 ,从而抑制了光合作用     

Breeding and application of Jiafuzhan, a new elite early indica rice cultivar in China

After 20 years of dedicated research,Jiafuzhan has been successfully developed under the new technologies in breeding high-quality early indica rice cultivars.Its rice quality has almost reached the A-level Editable Rice of Agriculture Department of China,and its average production reaches 400-500 kg/(666.7 m2).This new cultivar also has other characteristics such as enhanced resistance of blast and fallen,steady productivity,and strong adaptability.Jiafuzhan has been put into production of over 11.4×104 hm2 in Fujian Province and has been introduced and extended in other Provinces like Jiangxi,Guangdong,and Guangxi,China.The successes of breeding Jiafuzhan is a solution to the existing perennial problems in the rice industry,such as poor grain quality of big-grain rice and early indica rice,low productivity,and poor blast resistance of elite rice.     

The effect of copper on chlorophyll organization during greening of barley leaves

The effect of copper on chlorophyll organization and function during greening of barley was examined, using chlorophyll fluorescence and photoacoustic techniques. Copper was found to inhibit pigment accumulation and to retard chlorophyll integration into the photosystems, as evident from low temperature (77 K) fluorescence spectra. Resolution of the minimal fluorescence (F₀) into active and inactive parts, indicated a higher inactive fraction with copper treatment. This was attributed to chlorophyll molecules which failed to integrate normally, a conclusion supported by the longer fluorescence lifetime observed in copper treated plants. A lower ratio of chlorophyll a to b and fluorescence induction transients, showing accelerated Photosystem II closure, both indicate that copper treatment resulted in a larger light-harvesting antenna. Another effect of copper treatment was the suppression of oxygen evolution, indicating a decrease in photosynthetic capacity. We suggest that the non-integrated chlorophyll fraction sensitizes photodamage in the membrane, contributing to disruption of electron flow and pigment accumulation.     

Evaluation of a technique for the measurement of chlorophyll fluorescence from leaves exposed to continuous white light

Abstract An instrument for the generation and measurement of modulated chlorophyll fluorescence signals from leaves exposed to continuous, highintensity white light is described. Modulated fluorescence is generated in the leaf by pulsed diodes emitting low-intensity yellow radiation and is detected with a photodiode whose output is fed to an amplifier locked in to the frequency of the lightemitting diodes. Comparisons are made between the modulated fluorescence signals measured with this instrument and the continuous fluorescence signals emitted from dark-adapted leaf tissue and isolated thylakoids when photosynthetic activity is induced by exposure to a range of intensities of continuous broad-band, blue-green light. The modulated fluorescence signals were similar to the continuous fluorescence signals, but they were not always identical. The small differences between the two signals are mainly attributable to differences in the populations of chloroplasts being monitored in the two measurements as a result of differential penetration of the modulated and actinic light sources into the sample.     

Feedback inhibition of photosynthesis in rice measured by O2 dependent transients

The kinetic properties of photosynthesis (both transient and steady-state) were monitored using three non-invasive techniques to evaluate limitations on triose-phosphate (triose-P) conversion to carbohydrate in rice. These included analyzing the O₂ sensitivity of CO₂ fixation and the assimilatory charge (AC) using gas exchange (estimate of the ribulose 1,5- bisphosphate pool) and measuring Photosystem II activity by chlorophyll fluorescence analysis under varying light, temperature and CO₂ partial pressures. Photosynthesis was inhibited transiently upon switching from 20 to 2 kPa O₂ (reversed O₂ sensitivity), the degree of which was correlated with a terminal, steady-state suppression of low O₂ enhancement of photosynthesis. Under current ambient levels of CO₂ and moderate to high light, the transient pattern was more obvious at 18 °C than at 26 °C while at 34 °C no tra nsient response was observed. The transient inhibition at 18 °C ranged from 15% to 31% depending on the pre-measurement temperature. This pattern, symptomatic of feedback, was observed with increasing light and CO₂ partial pressures with the degree of feedback decreasing from moderate (18 °C) up to high temperature (34 °C). Under feedback conditions, the rate of assimilation is shifted from being photorespiration limited to being triose-P utilization limited. Transitory changes in CO₂ assimilation rates (A) under low O₂ indicative of feedback coincided with a transitory drop in assimilatory charge (AC) and inhibition of electron transport. In contrast to previous studies with many C₃ species, our studies indicate that rice shows susceptibility to feedback inhibition under moderate temperatures and current atmospheric levels of CO₂.     

Photosystem I-dependent cyclic electron transport is important in controlling Photosystem II activity in leaves under conditions of water stress

Leaves of the C₃ plant Brassica oleracea were illuminated with red and/or far-red light of different photon flux densities, with or without additional short pulses of high intensity red light, in air or in an atmosphere containing reduced levels of CO₂ and/or oxygen. In the absence of CO₂, far-red light increased light scattering, an indicator of the transthylakoid proton gradient, more than red light, although the red and far-red beams were balanced so as to excite Photosystem II to a comparable extent. On red background light, far-red supported a transthylakoid electrical field as indicated by the electrochromic P₅₁₅ signal. Reducing the oxygen content of the gas phase increased far-red induced light scattering and caused a secondary decrease in the small light scattering signal induced by red light. CO₂ inhibited the light-induced scattering responses irrespective of the mode of excitation. Short pulses of high intensity red light given to a background to red and/or far-red light induced appreciable additional light scattering after the flashes only, when CO₂ levels were decreased to or below the CO₂ compensation point, and when far-red background light was present. While pulse-induced light scattering increased, non-photochemical fluorescence quenching increased and F₀ fluorescence decreased indicating increased radiationless dissipation of excitation energy even when the quinone acceptor Q_A in the reaction center of Photosystem II was largely oxidized. The observations indicate that in the presence of proper redox poising of the chloroplast electron transport chain cyclic electron transport supports a transthylakoid proton gradient which is capable of controlling Photosystem II activity. The data are discussed in relation to protection of the photosynthetic apparatus against photoinactivation.Abbreviations F, F_M, F'_M, F"_M, F₀, F'₀ chlorophyll fluorescence levels - _exc quantum efficiency of excitation energy capture by open Photosystem II - _{PS II} quantum efficiency of electron flow through Photosystem II - P₅₁₅ field indicating rapid absorbance change peaking at 522 nm - P₇₀₀ primary donor of Photosystem I - Q_A primary quinone acceptor in Photosystem II - Q_N non-photochemical fluorescence quenching - Q_q photochemical quenching of chlorophyll fluorescence     

The inhibited xanthophyll cycle is responsible for the increase in sensitivity to low temperature photoinhibition in rice leaves fed with glutathione

Exposure of intact rice leaves to an irradiance of 1000 μmol m⁻² s⁻¹ at 6 °C for 2 h caused severe photoinhibition of Photosystem II. The rate and extent of photoinhbition were greatly exacerbated in leaves fed with 10 mM reduced glutathione (GSH) or 10 mM cysteine. Analyses of antioxidant enzyme activities as well as the application of protein synthesis inhibitors revealed that the increased sensitivity to photoinhibition following GSH feeding was not related to its effect on cellular antioxidant systems. On the other hand, feeding with GSH markedly suppressed the formation of zeaxanthin and antheraxanthin via the xanthophyll cycle and its associated nonradiative energy dissipation in leaves chilled in high light, suggesting that the stimulating effect of exogenous GSH on photoinhibition may be attributable to its action on the xanthophyll cycle. In vitro experiments using isolated thylakoids indicated that GSH is a weak inhibitor of violaxanthin deepoxidation. The possible implications of these results are discussed. This revised version was published online in June 2006 with corrections to the Cover Date.     

Measurement of chlorophyll fluorescence within leaves using a modified PAM Fluorometer with a fiber-optic microprobe

By using a fiber-optic microprobe in combination with a modified PAM Fluorometer, chlorophyll fluorescence yield was measured within leaves with spatial resolution of approximately 20 m. The new system employs a miniature photomultiplier for detection of the pulse-modulated fluorescence signal received by the 20 m fiber tip. The obtained signal/noise ratio qualifies for recordings of fluorescence induction kinetics (Kautsky effect), fluorescence quenching by the saturation pulse method and determination of quantum yield of energy conversion at Photosystem II at different sites within a leaf. Examples of the system performance and of practical applications are given. It is demonstrated that the fluorescence rise kinetics are distinctly faster when chloroplasts within the spongy mesophyll are illuminated as compared to palisade chloroplasts. Photoinhibition is shown to affect primarily the quantum yield of the palisade chloroplasts when excessive illumination is applied from the adaxial leaf side. The new system is envisaged to be used in combination with light measurements within leaves for an assessment of the specific contributions of different leaf regions to overall photosynthetic activity and for an integrative modelling of leaf photosynthesis.This paper is dedicated to Ulrich Heber on the occasion of his 65th birthday, with great respect for his outstanding achievements in photosynthesis research.     

Potassium nutrition of rice (Oryza sativa L.) varieties under NaCl salinity

A salt-tolerant (Pokkali) and a salt-sensitive (IR28) variety of rice (Oryza sativa L.) were grown in a phytotron to investigate the effect of K (0, 25, 50 and 75 mg K kg^–1 soil) application on their salt tolerance. Potassium application significantly increased potential photosynthetic activity (Rfd value), percentage of filled spikelets, yield and K concentration in straw. At the same time, it also significantly reduced Na and Mg concentrations and consequently improved the K/Na, K/Mg and K/Ca ratios. IR28 responded better to K application than Pokkali. Split application of K failed to exert any beneficial effect over basal application.     

A system for imaging transverse distribution of scattered light and chlorophyll fluorescence in intact rice leaves

In order to examine the transverse distribution of scattered light and chlorophyll fluorescence in intact rice leaves, a micro-fluorescence imaging system was devised using a microscope, a CCD camera with an image intensifier, an Ar and a He-Ne laser light source, an image processor, and a microcomputer. A laser light was projected vertically on to the surface of a rice leaf segment at a cut-edge, and scattered light and induced fluorescence were observed at the cut-section from a 90° angle to the axis of the laser beam. The intensity of scattered light showed a maximum at several micrometres depth from the leaf surface and a steep gradient afterwards. Fluorescence reached a maximum crossing with the decline curve of the scattered light. The maximum of fluorescence measured at 741 nm was observed at a greater depth from the leaf surface than that at 687 nm, suggesting that part of the fluorescence of the longer wavelength was emitted due to absorption of fluorescence of the shorter wavelength. Profiles of the scattered light and the chlorophyll fluorescence depended on leaf anatomy.     

Measurement of chlorophyll fluorescence within leaves using a fibreoptic microprobe

Abstract. The distribution of chlorophyll fluorescence was measured within leaves of Medicago saliva with a fibre optic microprobe. Leaves were irradiated with broad band blue light (1000 μmol m⁻²s⁻¹) and chlorophyll fluorescence was measured at 688 nm. The amount of fluorescence measured within the leaf depended upon the direction in which the probe was inserted. When the probe was advanced directly through the leaf from the shaded towards the irradiated surface, the maximum amount of detected fluorescence occurred near the boundary between the palisade and spongy mesophyll. When the probe was advanced through the leaf from the opposite direction maximum detected fluorescence was at the boundary between the epidermis and palisade. These results appear to be a consequence of the blue light gradient, which declined exponentially within the palisade but was counterbalanced by increasing chlorophyll content within the leaf. Modelling indicates that the measured distribution of chlorophyll fluorescence can be explained by relatively uniform emission of fluorescence throughout the palisade layer, indicating that the chloroplasts may be photosynthetically specialized to their light environment within the leaf.     

Enhancement of susceptivity to photoinhibition and photooxidation in rice chlorophyll <Emphasis Type="Italic">b</Emphasis>-less mutants

Two rice chlorophyll (Chl) b-less mutants (VG28-1, VG30-5) and the respective wild type (WT) plant (cv. Zhonghua No. 11) were analyzed for the changes in Chl fluorescence parameters, xanthophyll cycle pool, and its de-epoxidation state under exposure to strong irradiance, SI (1 700 μmol m⁻² s⁻¹). We also examined alterations in the chloroplast ultrastructure of the mutants induced by methyl viologen (MV) photooxidation. During HI (0–3.5 h), the photoinactivation of photosystem 2 (PS2) appeared earlier and more severely in Chl b-less mutants than in the WT. The decreases in maximal photochemical efficiency of PS2 in the dark (F_v/F_m), quantum efficiency of PS2 electron transport (Φ_PS2), photochemical quenching (q_P), as well as rate of photochemistry (P_rate), and the increases in de-epoxidation state (DES) and rate of thermal dissipation of excitation energy (D_rate) were significantly greater in Chl b-mutants compared with the WT plant. A relatively larger xanthophyll pool and 78–83 % conversion of violaxanthin into antheraxanthin and zeaxanthin in the mutants after 3.5 h of HI was accompanied with a high ratio of inactive/total PS2 (0.55–0.73) and high 1–q_P (0.57–0.68) which showed that the activities of the xanthophyll cycle were probably insufficient to protect the photosynthetic apparatus against photoinhibition. No apparent difference of chloroplast ultrastructure was found between Chl b-less mutants and WT plants grown under low, LI (180 μmol m⁻² s⁻¹) and high, HI (700 μmol m⁻² s⁻¹) irradiance. However, swollen chloroplasts and slight dilation of thylakoids occurred in both mutants and the WT grown under LI followed by MV treatment. These typical symptoms of photooxidative damage were aggravated as plants were exposed to HI. Distorted and loose scattered thylakoids were observed in particular in the Chl b-less mutants. A greater extent of photoinhibition and photooxidation in these mutants indicated that the susceptibility to HI and oxidative stresses was enhanced in the photosynthetic apparatus without Chl b most likely as a consequence of a smaller antenna size.     

Changes in leaf protein and pigment contents and photosynthetic activities during senescence of detached maize leaves: influence of different ultraviolet radiations

Senescence induced loss in pigments and proteins of detached maize (Zea mays L. cv. Col) leaves was significantly enhanced on the exposure of leaves to different ranges of ultraviolet (UV) radiation. Compared to UV-A (320-400 nm) and UV-B (280-320 nm), the UV-C (200-320 nm) was the most damaging for the pigments and macromolecules. A severe decline in photosystem (PS) 2 mediated photoreduction during senescence of detached leaves exposed to UV irradiation suggested a damage of the system. The PS1 mediated photoreduction of methylviologen with 2,6-dichlorophenol indophenol as electron donor was stimulated by UV-A and UV-B radiations, suggesting a reorganisation of the PS1 complex. These results were fortified by the values of fast and slow kinetics of chlorophyll (Chl) a fluorescence transients. This revised version was published online in June 2006 with corrections to the Cover Date.