Effects of insecticide acetamiprid on photosystem II (PSII) activity of Synechocystis sp. (FACHB-898)

Effects of insecticide acetamiprid on photosystem II (PSII) activity of Synechocystis sp. were investigated by a variety of in vivo chlorophyll fluorescence tests. Acetamiprid exposure increased the proportion of inactivated PSII reactive centers (PSII_X) and led to loss of active centers (PSII_A). High concentration (1.0 mM) acetamiprid decreased amplitude of the fast phase and increased the slow phase of fluorescence decay during reoxidation. The electron transport after Q_A was hindered by high concentration acetamiprid and more Q_A had to be reoxidized through S₂(Q_AQ_B)⁻ charge recombination. Acetamiprid decreased the density of the active reaction centers, electron transport flux per cross section and the performance of PSII activity but had little effect on dissipated energy flux per reaction center, antenna size and the maximum quantum yield for primary photochemistry (F_v/F_m). The target site of acetamiprid toxicity to the PSII of Synechocystis sp. was electron transfer on the acceptor side.     

Maize resistance to northern corn leaf blight is potentiated by nickel

Northern corn leaf blight (NCLB), caused by Exserohilum turcicum, is one of the most devastating diseases affecting maize yield worldwide. A foliar spray of nickel (Ni) to potentiate maize resistance against NCLB was investigated by examining alterations in the photosynthetic apparatus (leaf gas exchange and chlorophyll [Chl] a fluorescence parameters), production of ethylene and reactive oxygen species as well as activities of defence and antioxidant enzymes. Mycelial growth of E. turcicum was inhibited by Ni in vitro. Inoculated plants sprayed with Ni exhibited higher foliar Ni concentration, reduced NCLB symptoms, and lower concentrations of malondialdehyde and hydrogen peroxide. In inoculated leaves of plants not sprayed with Ni, concentrations of Chl a, Chl b, and carotenoids were lower and the photosynthetic apparatus was impaired at the biochemical level due to high NCLB severity. The activities of antioxidant enzymes were not affected by Ni, except an increase in glutathione reductase activity for noninoculated plants sprayed with Ni. High lipoxygenase and polyphenoloxidase activities, lower ethylene production, as well as elevated production of phenolics and lignin helped decrease NCLB severity in the leaves of Ni-sprayed plants.     

Phytoplasma [Stolbur-subgroup (Bois Noir-BN)] infection inhibits photosynthetic pigments, ribulose-1,5-bisphosphate carboxylase and photosynthetic activities in field grown grapevine (Vitis vinifera L. cv. Chardonnay) leaves

In this work we have studied the influence of phytoplasma-induced grapevine yellows (yellowing) on some features of the thylakoids from field grown grapevine (Vitis vinifera L. cv. Chardonnay) leaves. Changes in photosynthetic pigments, soluble proteins, ribulose-1,5-bisphosphate carboxylase, photosynthetic activities and thylakoid membrane proteins were investigated. The level of total chlorophyll and carotenoids, on a unit fresh weight basis, showed a progressive decrease in phytoplasma infected leaves. Similar results were also observed for total soluble proteins and ribulose-1,5-bisphosphate carboxylase activity. When various photosynthetic activities were followed in isolated thylakoids, phytoplasma infection caused marked inhibition of whole chain and photosystem (PS) II activity. Smaller inhibition of PSI activity was observed even in severely infected leaves. The artificial exogenous electron donors, DPC and NH₂OH significantly restored the PSII activity in both mild and severely infected leaves. The same results were obtained when F_v/ F_m was evaluated by Chl fluorescence measurements. The marked loss of PS II activity in infected leaves was evidently due to the loss of 33, 28–25, 23, 17 and 10 kDa polypeptides. This conclusion was confirmed by immunological studies showing that the content of the 33 kDa protein of the water-splitting complex was diminished significantly in infected leaves. Phytoplasma infection induced a fast degradation of LHCP II which became visible as yellowish colour in leaves.     

Glyphosate uncouples gas exchange and chlorophyll fluorescence

BACKGROUND: Changes in chlorophyll fluorescence have often been advocated as a sensitive biomarker of plant stress, assuming that any kind of plant stress serious enough to affect plant growth will also affect photosynthesis. Glyphosate affects photosynthetic electron transport indirectly by inhibiting sink processes. The question is how fast this inhibition can be observed on CO₂ assimilation and ultimately on chlorophyll fluorescence? RESULTS: Experiments measuring CO₂ assimilation, conductance and chlorophyll fluorescence using four Kautsky curve parameters on barley (Hordeum vulgare L.) exposed to increasing doses of glyphosate showed a total cessation of CO₂ fixation and conductance without significant changes in chlorophyll fluorescence. The decrease in CO₂ fixation and conductance was significant 1 day after spraying and corresponded well to the decrease in biomass 5–7 days after spraying. CONCLUSION: A total cessation of CO₂ assimilation can take place without affecting chlorophyll fluorescence. Hypotheses concerning what happens to the energy from the photosynthetic apparatus that is not used for CO₂ assimilation are discussed. The results question the use of chlorophyll fluorescence as a universal indicator of stress on photosynthetic processes. Also, they demonstrate that changes in gas‐exchange parameters are more sensitive biomarkers for glyphosate toxicity compared with chlorophyll fluorescence. Copyright © 2010 Society of Chemical Industry     

尖孢镰刀菌侵染对马铃薯光合效率和叶绿素荧光参数影响

为研究枯萎病对马铃薯光合特性的影响,在幼苗期接种尖孢镰刀菌Fusarium oxysporum后,统计抗病品种陇薯10号和感病品种新大坪的病情指数,并测定叶绿素含量、光合及荧光参数。结果表明,尖孢镰刀菌侵染30 d后马铃薯表现出枯萎病症状,叶绿素含量显著降低,其中叶绿素a含量降幅最大,抗病品种陇薯10号比对照降低9.64%,感病品种新大坪比对照降低14.24%。尖孢镰刀菌侵染后马铃薯光合效率显著降低,侵染30 d后,抗病品种陇薯10号净光合速率比对照降低39.56%,感病品种新大坪比对照降低47.13%。病株的光响应曲线参数光补偿点、暗呼吸速率和表观量子效率都显著提高;而光饱和点和最大净光合速率都显著低于对照,表明尖孢镰刀菌侵染缩小了马铃薯对光能的利用有效范围。病株CO2响应曲线参数CO2饱和点、最大净光合速率和羧化效率分别显著低于对照;病株CO2补偿点和光呼吸速率反而升高,说明碳同化过程受到尖孢镰刀菌的限制。暗适应下的初始荧光、最小荧光、最大荧光、PSII最大光化学效率、光适应下PSII最大光化学效率及实际光化学效率、光化学猝灭系数、非光化学猝灭系数和光合电子传递速率均显著低于对照,...     

Uncoupling and inhibition properties of 3,4-seco-friedelan-3-oic acid isolated from Maytenus imbricata

3,4-Seco-friedelan-3-oic acid was isolated from Maytenus imbricata (Celastraceae). At low concentrations it inhibited non-cyclic electron transport and ATP synthesis in spinach chloroplasts, i.e., it behaved as a Hill reaction inhibitor, and at high concentrations it acts as an uncoupler by enhancing uncoupled electron transport and Mg²⁺-ATPase activity. 3,4-Seco-friedelan-3-oic acid did not inhibit PSII electron transport from DPC to DCPIP_ox and photosystem I activity, but it enhanced from TMQH₂ to MV, corroborating its action as uncoupler. It inhibits electron flow through PSII from water to sodium silicomolybdate. The whole results indicate that the 3,4-seco-friedelan-3-oic acid target is at the OEC complex enzyme, the donor side of PSII. The fluorescence decay data shows the formation of the K-band, which match this result, acting as inhibitor at the donor side of PSII and it as an uncoupler.     

Inhibition of photosystem II in spinach chloroplasts by trachyloban-19-oic acid

The effect of trachyloban-19-oic acid isolated from Iostephane heterophylla (Asteraceae), was investigated on several photosynthetic activities in spinach thylakoids. The results indicated that this compound inhibited ATP synthesis and uncoupled electron transport, as well as basal and phosphorylating electron flow. Therefore, trachyloban-19-oic acid acts as Hill reaction inhibitor. This compound did not affect photosystem I activity but inhibited uncoupled photosystem II electron flow from H₂O to DCPIP, and has not effect on electron flow from H₂O to SiMo, indicating that the site of inhibition of this compound is at the level of Q_A-Q_B. Chlorophyll a fluorescence measurements confirm the behavior of this diterpene as Q_A-Q_B inhibitor, and in the other hand, this results indicate that a perturbation in the thylakoid membranes at the level of LHC II occurs.     

Natural diterpene β-lactone derivative as photosystem II inhibitor on spinach chloroplasts

α,7β-Dihydroxyvouacapan-17β-oic acid (1) was isolated from Pterodon polygalaeflorus Benth. Then, (1) was modified to obtain 6α-hydroxyvouacapan-7β,17β-lactone (2). Inhibition properties of both (1) and (2) were evaluated in spinach chloroplasts. Only compound (2) inhibited non-cyclic electron transport and ATP synthesis, i.e., (2) behaved as a Hill reaction inhibitor. Compound (2) did not affect photosystem I (PSI) activity but it did inhibit electron flow through PSII. Analysis of the partial PSII reactions from water to DCPIP_ox, water to silicomolybdate, and diphenylcarbazide to DCPIP_ox allowed locating inhibition sites at (i) the oxygen-evolving complex (OEC) and (ii) the redox enzymes of the electron transport chain, in the span of P₆₈₀ to Q_A. Chlorophyll a fluorescence measurements confirmed the action site for (2).     

Photochemical damage and comparative performance of superoxide dismutase and ascorbate peroxidase in sugarcane leaves exposed to paraquat-induced oxidative stress

The physiological responses of sugarcane (Saccharum officinarum L.) to oxidative stress induced by methyl viologen (paraquat) were examined with respect to photochemical activity, chlorophyll content, lipid peroxidation and superoxide dismutase (SOD) and ascorbate peroxidase (APX) activities. Thirty-day-old sugarcane plants were sprayed with 0, 2, 4, 6 and 8 mM methyl viologen (MV). Chlorophyll fluorescence was measured after 18 h and biochemical analyses were performed after 24 and 48 h. Concentrations of MV above 2 mM caused significant damage to photosystem II (PSII) activity. Potential and effective quantum efficiency of PSII and apparent electron transport rate were greatly reduced or practically abolished. Both chlorophyll and soluble protein contents steadily decreased with MV concentrations above 2 mM after 24 h of exposure, which became more pronounced after 48 h, achieving a 3-fold decrease. Insoluble protein contents were little affected by MV. Oxidative stress induced by MV was evidenced by increases in lipid peroxidation. Specific activity of SOD increased, even after 48 h of exposure to the highest concentrations of MV, but total activity on a fresh weight basis did not change significantly. Nondenaturing PAGE assayed with H₂O₂ and KCN showed that treatment with MV did not change Cu/Zn-SOD and Mn-SOD isoform activities. In contrast, APX specific activity increased at 2 mM MV but then dropped at higher doses. Oxidative damage induced by MV was inversely related to APX activity. It is suggested that the major MV-induced oxidative damages in sugarcane leaves were related to excess H₂O₂, probably in chloroplasts, caused by an imbalance between SOD and APX activities, in which APX was a limiting step. Reduced photochemical activity allowed the early detection of the ensuing oxidative stress.     

Pesticides-induced depression of photosynthesis was alleviated by 24-epibrassinolide pretreatment in Cucumis sativus L

The phytotoxicities of nine pesticides (paraquat, fluazifop-p-butyl, haloxyfop, flusilazole, cuproxat, cyazofamid, imidacloprid, chlorpyrifos, and abamectin) at practical dosages on photosynthesis were investigated in cucumber (Cucumis sativus L. cv. Jinyan No. 4) by gas exchange and chlorophyll fluorescent measurements. Plants treated with paraquat showed the severest phytotoxic symptom with the highest reduction in net photosynthetic rate (Pn), while other pesticides except flusilazole inhibited Pn to various degrees. The inhibition of Pn by cuproxat was accompanied by declines both in stomatal conductance (Gs) and intercellular CO₂ concentration (Ci), whereas decreased Pn for the cyazofamid was associated with increased Ci. For other 6 pesticides, however, inhibition of Pn was accompanied by decrease in Gs, while Ci was increased or unaffected. Paraquat almost completely inhibited the maximal quantum efficiency of PSII (F_v/F_m), while other pesticides had no significant effect on F_v/F_m. Quantum efficiency of PSII (Φ_PSII) was significantly reduced by paraquat, fluazifop-p-butyl, and chlorpyrifos and the reduction was mostly attributed to decrease in photochemical quenching coefficient (qP). In comparison, Φ_PSII was not significantly affected by haloxyfop, flusilazole, cyazofamid, imidacloprid, and abamectin. Non-photochemical quenching (NPQ) was suppressed by paraquat and haloxyfop, while apparent upregulation was evident after exposure to other pesticides. Interestedly, inhibitions of Pn were alleviated by 24-epibrassinolide (EBR) pretreatment, as for the pesticides examined in this study except paraquat and flusilazole. EBR pretreatment also increased Φ_PSII and qP. It is likely that EBR enhanced the resistance of cucumber seedlings to pesticides by increasing CO₂ assimilation capacity and activities of antioxidant enzymes.     

新型解毒剂T对异噁草松造成玉米药害的缓解作用

通过测定植株叶绿素含量与荧光光谱特征动态变化，分析除草剂异FDB8草松和解毒剂T 对玉米植株的生理作用。随着除草剂浓度升高，叶绿素浓度下降，单位叶绿素荧光强度比不 断上升，而解毒剂T可缓解上述伤害。     

The influence of <Emphasis Type="Italic">Aphanomyces cochlioides</Emphasis> on selected physiological processes in sugar beet leaves and yield parameters

Alterations in some physiological processes in source leaves of sugar beet—such as chlorophyll and carbohydrate concentrations, stomatal conductance, rate of net photosynthesis and transpiration, and activity of the photosynthetic apparatus during root interaction with Aphanomyces cochlioides, were investigated. The influence of time of infection on plant health, yield quality and quantity was also examined. Plants were infected at different times of their growth period: on the sowing day and 4 or 8 weeks after sowing. A variation treatment, with non-pelleted seeds infected on the sowing day, was also analyzed. The experiment showed that development of disease symptoms depends on the time of infection and seed protection. A significant root yield decrease was observed in case of late infection, as compared to the yield of plants infected on the sowing day. The fresh weight of leaves was significantly increased where there was late infection. The infected plants showed a lower content of K⁺, Na⁺ and α-amino-N than did the controls. Infection by A. cochlioides induced chlorophyll degradation mostly in older leaves with the occurrence of natural senescence processes. Chlorophyll fluorescence parameters indicated that the photosynthetic apparatus of younger leaves was more sensitive to pathogen infection, when compared to older ones. The photochemical efficiency of photosystem II was reduced in young leaves mainly due to disturbance of the water-splitting system. In plants grown from non-pelleted seeds a strong impairment of PSII was observed only in those leaves which developed during early pathogen infection. In young leaves of plants infected in the fourth week after sowing, inhibition of the rate of net photosynthesis was correlated with the increase in intercellular CO₂ concentration, indicating some disturbance in the carbon assimilation phase. In mature leaves of late infected plants the reduction of photosynthesis net rate was associated with a decrease of stomatal conductance and an increase of diffusion resistance to CO₂ and H₂O, which was also the cause of the transpiration rate inhibition. When the leaves developed during early infection, an increase of specific leaf weight and accumulation of carbohydrates was observed. In mature leaves of non-protected plants infected on the sowing day, the recovery of all physiological processes was observed together with a diminution of disease symptoms.     

Growth, photosynthetic pigments and photosynthetic activity during seedling stage of cowpea (Vigna unguiculata) in response to UV-B and dimethoate

UV-B (0.4 W m⁻²) irradiation and dimethoate (100 and 200 ppm) treatments, singly and in combination, declined the growth, photosynthetic pigment contents and photosynthesis (O₂ evolution and CO₂-fixation) of cowpea (Vigna unguiculata). Contrary to this, low concentration of dimethoate (50 ppm) caused stimulation on these parameters, while together with UV-B it showed inhibitory effects. Carotenoids (Car) showed varied responses. It was found that carbon-fixation (¹⁴CO₂) was more sensitive to both the stresses than photosynthetic oxygen evolution. Photosynthetic electron transport activity was reduced by both the stresses, however, 50 ppm dimethoate besides inhibiting photosystem II (PSII) and whole chain activity, showed slight stimulation in photosystem I (PSI) activity. The individual effect of two stresses on PSII activity was probably due to interruption of electron flow at oxidation side of PSII which extended to its reaction center following simultaneous exposure. A similar trend was also noticed in case of CO₂ liberation (measured as ¹⁴CO₂ release) in light and dark. Results suggest that dimethoate (100 and 200 ppm) and UV-B alone caused heavy damage on pigments and photosynthetic activity of cowpea, leading to the significant inhibition in growth. Further, the interactive effects of both the stresses got intensified. However, low concentration (50 ppm) of dimethoate showed stimulation, but in combination, it slightly recovered from the damaging effect, caused by UV-B.     

Effect of phytoplasmal infection on photosystem II efficiency and thylakoid membrane protein changes in field grown apple (Malus pumila) leaves

We have studied the effect of the apple proliferation phytoplasmal infection on some features of the thylakoids from field grown apple (Malus pumila) leaves. Changes in photosynthetic pigments, soluble proteins, ribulose-1,5-bisphosphate carboxylase, nitrate reductase, photosynthetic activities and thylakoid membrane proteins were investigated. The level of total chlorophyll and carotenoids were reduced in phytoplasma-infected leaves. Similar results were also observed for soluble proteins and ribulose- 1,5-bisphosphate carboxylase activity. The in vivo nitrate reductase activity was significantly reduced in infected leaves. When various photosynthetic activities were followed in isolated thylakoids, phytoplasmal infection caused marked inhibition of whole chain and photosystem II activity while the inhibition of photosystem I activity was only marginal. The artificial exogenous electron donors, diphenyl carbazide and hydroxylamine significantly restored the loss of photosystem II activity in infected leaves. The same results were obtained when F_v/F_m was evaluated by chlorophyll fluorescence measurements. The marked loss of photosystem II activity in infected leaves could be due to the loss of 47, 33, 28–25, 23 and 17 kDa polypeptides. It is concluded that phytoplasmal infection inactivates the donor side of photosystem II. This conclusion was confirmed by immunological studies showing that the content of the 33 kDa protein of the water-splitting complex was diminished significantly in infected leaves.     

Extracellular ATP functions in alleviating the decrease of PSII photochemistry caused by the infection of Xanthomonas campestris pv. phaseoli

Extracellular ATP (eATP) can function as a signalling molecule to regulate a wide range of cellular processes. This present work investigated the role of eATP in mediating the change of PSII (photosystem II) photochemistry of the tissues of Phaseolus vulgaris leaves infected with Xanthomonas campestris pv. phaseoli (Xcp). Infection of the leaves with Xcp caused a significant decrease in the the PSII maximal photochemical efficiency (F_v/F_m), the maximum quantum efficiency of PSII photochemistry at illumination (F_v′/F_m′), the PSII operating efficiency (Φ_PSII), the rate of non‐cyclic electron transport through PSII (ETR), photochemical quenching (qP), and eATP level in the tissues of the infected leaves. At the same time, the levels of non‐photochemical quenching (qN) and the quantum yield of regulated energy dissipation of PSII (Y(NPQ)) were significantly increased. Application of exogenous ATP at 0·2 mm to uninfected leaves had no significant effect on any of the chlorophyll fluorescence parameters being measured. However, in the tissues of infected leaves, the application of exogenous ATP alleviated the decreases of the F_v/F_m, F_v′/F_m′, Φ_PSII, ETR, qP and eATP level, and also abolished the increases of qN and Y(NPQ). These results suggest that the change of PSII photochemistry by pathogen infection could be mediated by eATP.     

Chlorophyll fluorescence for visualizing the spatial and temporal spread of Phytophthora alni subsp. alni in alder bark tissue

The impact of alder Phytophthora (Phytophthora alni subsp. alni) on corticular photosynthetic metabolism was explored via measurements of chlorophyll fluorescence. Stem inoculation induced a sharp reduction of maximum (F_v/F_m) and effective quantum yield of PSII (). Observations of the axial and radial spread of the pathogen revealed that near to the point of inoculation and in the whole centre of the stem lesion F_v/F_m and of the cortex chlorenchyma decreased to almost zero, indicating tissue necrosis. Low values of F_v/F_m and were also found in some presymptomatic regions beyond the visible stem lesion. In contrast, substantial photosynthetic activity was found in uninvaded parts of the inoculated trees and in the control. These stem parts showed a marked light‐adapted quantum efficiency of PSII as well as marked electron transport rates in their bark tissues. Thus, corticular photosynthesis stayed unaffected in these stem parts supporting stem carbon balance. Chlorophyll fluorescence measurements in the field illustrated that stem infection with P. alni subsp. alni and the effect on the bark tissues is not only highly heterogeneous but also underlies very quick temporal changes, due to a rapid destruction of the photosynthetic apparatus. The results show that chlorophyll fluorescence measurements and fluorescence imaging are useful indicators of tissue infection caused by Phytophthora infection of bark tissues. Chlorophyll fluorescence measurements can be used to map and visualize the spatial as well as temporal spread of bark pathogens and can give a first indication of invasion of the host tissue beyond the visible lesion.     

Leaf tissue pigments and chlorophyll fluorescence parameters vary among sweet corn genotypes of differential herbicide sensitivity

Herbicide applications are meant to eliminate weed competition; however, herbicides may also impose abiotic stress on registered crops. Leaf tissue carotenoid pigments play vital roles in the photoprotection of photosynthetic membranes and contribute to non-photochemical quenching (NPQ) of excitation energy, both important to plant environmental stress tolerance. Our research objectives were to characterize leaf tissue pigments and chlorophyll fluorescence parameters following post-emergence herbicide applications (simulating an abiotic stress) to sweet corn (Zea mays var. rugosa) genotypes of differential herbicide sensitivities. Post-emergence herbicide applications of combinations of mesotrione (105 g ai/ha) and atrazine (560 g ai/ha) were applied to ‘Merit’ (sensitive), ‘Temptation’ (tolerant), and ‘Incredible’ (moderately sensitive) sweet corn genotypes. Leaf tissues were sampled after herbicide applications and measured for chlorophyll fluorescence parameters, and the same tissues were analyzed for carotenoid and chlorophyll pigments. Leaf pigments and chlorophyll fluorescence were not affected by any herbicide treatment; however, data revealed significant differences between genotypes for leaf tissue antheraxanthin, β-carotene, zeaxanthin, chlorophyll a/b ratios, and for values of F_o, F_m, F_v, and NPQ, with ‘Merit’ leaf tissue having higher values than the other two genotypes evaluated. Results demonstrate that genotypic sensitivities to certain post-emergence herbicides may be related to concentrations of photo-protective carotenoids in sweet corn leaf tissues.     

Phytoplasmas change the source–sink relationship of field-grown sweet cherry by disturbing leaf function

Changes in the function of field-grown sweet cherry leaves infected with phytoplasma were evaluated through the analysis of photosynthesis, respiration, carbohydrates and hormones. Phytoplasmal infection caused witches' broom, small leaves, leaf yellowing and leaf rolling. The photosynthesis of infected leaves was considerably reduced, and they were unable to produce sufficient carbohydrates for their own needs. In contrast, the starch content of infected leaves was significantly increased. These results demonstrate the change in the role of infected leaves from sources to sinks. Further analysis revealed that the photosynthetic decline was related to a significant decrease in photosynthetic pigments and to marked inactivation of photosystem II (PSII). Furthermore, the loss of PSII function was due to a decrease in chlorophyll content, reduction and closure of active reaction centers, and decline in photochemical efficiency.     

白粉病菌侵染对黄瓜叶片光合电子传递及其PSⅡ功能蛋白D1表达的影响

 本文研究了黄瓜(Cucumis sativus L.)感染黄瓜白粉病后,植物叶绿素含量、光合电子传递速率和光化学反应中心D1蛋白的变化。被感染的黄瓜叶片叶绿素含量降低,而且Chlb比Chla敏感。全链电子传递速率受到抑制,PSⅡ电子传递速率的变化与全链电子传递速率的变化趋势相似,但PSⅠ电子传递速率却未受到抑制。由于PSⅡ的光合反应中心D1蛋白含量变化与PSⅡ电子传递速率的变化类似,推测D1蛋白的表达量变化是引起电子传递活性波动的主要因素。