The Effect of Cadmium on Photosystem II in Spinach Chloroplasts

Cadmium ions, as an environmental pollution factor, significantly inhibited the photosynthesis especially, photosystem Ⅱ activity in isolated spinach chloroplasts. The presence of 5 mmol/l Cd2+ inhibited the O2-evolution to 53%. Cd2+ reduced the activity of photoreduction of DCIP and the variable fluorescence of chloroplasts and PSⅡ preparation. The inhibited DCIP photoreduction activity could only be restored slightly by the addition of an artificial electron donor of PSII, DPC, and the inhibited variable fluorescence could not be obviously recovered by the addition of NH2OH, another artificial electron donor of PSⅡ. It is considered that, besides the oxidizing side of PSI1, Cd2+ could also inhibit directly the PSⅡ reaction center. The inhibitory effect of Cd2+ on the whole chain electron transport (H2O→MV) was more serious than on O2-evolution (H2O→DCMU). It is suggested that the oxidizing side of PSⅡ is not the only site for Cd2+ action. There may be another site inhibited by Cd2+ in the electron transport chain between PSⅠ and PSⅡ.     

Effects of Water Stress on Energy Transduction in Chloroplasts

Water stress inhibited the photosynthetic O2 evolution rate of wheat leaves. It was shown that water stress decreased the electron transport rate, the activities of photophosphorylation and, coupling factor, and, the synthesis of ATP in chloroplasts. PS Ⅱ electron transport was more senstitive to water stress than PS Ⅰ. The reduction in photophosphorylation activity might be the results of reduction in electron transport rate and coupling factor activity, as well as the uncoupling effect of water stress on chloroplasts. The uncoupling effect could be due to the inhibition of light induced proton translocation in chloroplasts.     

Effects of Cucumber Mosaic Virus Infection on Photosynthetic Activities of Tobacco Leaves and Chloroplasts

Changes in photosynthetic activities were studied with tobacco (Nicotiana tabacum L.) leaves and chloroplasts infected by cucumber mosaic virus (CMV) at the top, middle and bottom located leaves. Net photosynthetic rate was reduced at all three positioned leaves, with the maximum reduction occurring at the top leaves (31.9% of control). The infected chloroplasts showed a reduction in electron transport rates of the whole chain electron transport, photosystem Ⅱ (PSⅡ) and photosystem Ⅰ (PSⅠ). Since the decline in the whole chain electron transport (15.6% of control, H2O→MV) closely paralleled the decline in PSⅡ activity (20.9% of control, H2O→PBQ), the inhibition of the latter was probably responsible for the overall decrease. Chlorophyll a fluorescence measurements showed a variable reduced fluorescence yield (Fv/Fo) which indicated that PSⅡ was impaired and the CO2 assimilation was disturbed by CMV infection. Fluorescence emission spectra at 77 K indicated that energy distribution between PSⅡ and PSⅠ was affected. F686/F734 of infected leaves and chloroplasts increased and the greatest increase (331.1% of control ) was found in the top leaves. These data may conclude that the infection inhibited mainly the PSⅡ activity.     

Structural and Functional Analysis of Chloroplast Membrane Using Trypsin and Chymotrypsin as Structural Modifiers

(1) Similar results were obtained after controlled digestion of spinach chloroplasts with trypsin and chymotrypsin, but the specificity of digestion of chymotrypsin differed from that of trypsin. Trypsin weakly uncoupled photosynthetic electron transport but chymotrypsin did not. (2) Both changes of DCIP and Fecy reduction activity and the recovery of CCCP inhibition by electron donors of PSⅡ during proteolytic enzyme digestion showed that trypsin not only affected oxidizing side and reducing side of PSⅡ, but also partially inactivated the reaction center of PSⅡ. (3) The effects of CCCP on photosynthetic electron transport in chloroplasts digested with trypsin and chymotrypsin indicated the probable presence of "channel" in PSⅡ. These results support the interpretation that there is a fine structure in PSⅡ membrane. Modification of the protein components of PSⅡ in the membrane might alter their function.     

Effect of Elevated CO2 on the Primary Conversion of Light Energy of Alfalfa Photosynthesis

In studying the mechanism of increase in alfalfa (Medicago sativa L. ) photosynthesis under elevated atmospheric CO2, it was found that the capacity of chloroplasts for light absorption was greater, the potential activity and efficiency of primary conversion of light enlergy of PS Ⅱ , quantum yield of PS Ⅱ electron transport, and activation capacity of PS Ⅰ were stimulated, photochemical quenching coefficient was increased and non-photochemical quenching coefficient was decreased under elevated atmospheric CO2.     

Photosynthetic Functions of Rice Improved by 2,3-eroxypropionate

The photosynthetic functions of rice were obviously improved by pretreatment with 150 ppm 2,3-epoxypropionate. The activity of Photosystem Ⅱ (PSⅡ) and the efficiency of primary conversion of light energy of PSⅡ detected either with intact leaves or chloroplasts were enhanced by pretreatment of 2,3-cpoxypropionate. Electron transport rate of PSⅡ, Photosystem Ⅰ (PSⅠ) and the whole chain in chloroplasts were higher than those in untreated ones. It was also confirmed that the capacity of excitation energy distribution between PSⅡ and PSI which was regulated by Mg2+ or phosphorylation of chloroplast membrane proteins in pretreated rice was larger than that in the control. From these results it can be predicted that 2,3-epoxypropionate will have some prospect for practical application to rice production.     

Differential changes in the electron transport properties of thylakoid membranes during aging of attached and detached leaves, and of isolated chloroplasts

Abstract. Aging of chloroplasts both in vivo and in vitro causes a considerable loss in the 2,6-dichlorophenol indophenol (DCPIP)-Hill reaction with water as electron donor. The loss can be reduced by exogenous electron donors like diphenyl carbazide (DPC). suggestive of aging-induced damage of the oxygen evolving system. Aging also brings about a considerable loss in methylviologen (MV) reduction mediated by Photosystem I (PS I) of chloroplasts with an ascorbate-DCPIP couple as the electron donating system.
The loss in the electron transport ability of the plastids is faster during in vitro compared to in vivo aging of the chloroplasts.
Light protects the photo-electron transport ability of chloroplasts during aging of intact leaves in contrast to its action during aging of the isolated organelles.     

Changes of Photochemical Activities and Photosynthetic Electron Transport of Chloroplasts in the Course of Ageing

Chloroplasts were isolated from Spinacia olerecea L. and Doblichos lablab L. Chloroplasts suspension was stored in refrigerator at 5–8 ℃. Photochemical activities and chlorophyll content of chloroplasts at different times of storage were deter- mined. The results can be summarized as follows: 1. In the course of chloroplasts ageing, the lost of K3Fe(CN)6 photo reduction activity was more than that of DCPIP photoreduction activity. 2. The activity of K3Fe(CN)6 photoreduction during storage began to decrease markedly after 12 hours, but activity of DCPIP photoreduction began to decrease markedly after 24 hours. 3. The DCPIP photoreduction activity of aged chloroplasts was stimulated by the addition of 1.5-diphenylcarbazide. 4. Destruction of oxidized side of PSⅡ was earlier and higher than that of the other side (from the active center of PSⅡ to the reduced side of PSⅠ). 5. During chloroplasts ageing, the decrease of chlorophyll content was less than the rate of decrease of photochemical activities.     

Damage of PSII by Sulfite

The photoreduction of DCIP by PSⅡ pasticles isolated from spinach leaves was inhibited by sulfite and the degree of inhibition was increased with the increase of sulfite concentration. The site of sulfite damage was on the oxidation side. In dark, electron flow from H2O to DCIP and from DPC to DCIP was not affected by sulfite. With certain concentrations of sulfite, the damage to PSⅡ particle varied with time of sulfite treatment and the mechanism of the damage might be related to the discretion of 33 kD polypeptide from thylakoid membrane and the leakage of Mn. Sulfite did not specifically damage the newly prepared thyla- koid, but this was the case with aged thylakoid. The rate of DCIP photoreduction decreased as the aging process was prolonged. Decrease in Mn content correlated with the decrease of DCIP photoreduction. Especially in the presence of EDTA, with the decrease of Mn, the rate of electron transport was severely reduced.     

Structural and functional stability of isolated intact chloroplasts

The effect of in vitro ageing on the ultrastructure, electron transport, thermoluminescence and flash-induced 515 nm absorbance change of isolated intact (type A) chloroplasts compared with non-intact (types B and C) chloroplasts was studied.When stored in the dark for 18 h at 5°C, the structural characteristics of intact and non-intact chloroplasts were only slightly altered. The most conspicuous difference between the two was in the coupling of the electron transport which was tighter and more stable in intact chloroplasts. Under dark-storage the activity of PS 2* decreased and the -20°C peak of thermoluminescence increased at the expense of the emission at +25°C. These changes were less pronounced in the intact chloroplasts. PS 1 activity and the flash-induced 515 nm absorbance change were not affected by dark-storage.When kept in the light (80 W m^-2 (400–700 nm) for 1 h at 5°C), the thylakoid system of chloroplasts rapidly became disorganized. Although the initial activity of electron transport was much higher in intact chloroplasts, after a short period of light-storage the linear electron transport and the electron transport around PS 2 decreased in both types of preparations to the same low level. These changes were accompanied by an overall decrease of the intensity of thermoluminescence. PS 1 was not inhibited by light-storage, while the flash-induced 515 nm absorbance change was virtually abolished both in preparations of intact and non-intact chloroplasts.The data show that in stored chloroplast preparations intactness cannot be estimated reliably either by the FeCy test or by inspection under the electron microscope. These tests should be cross-checked on the level and coupling of the electron transport.     

Photosynthetic Electron Transport During Senescence of the Primary Leaves of Phaseolus vulgaris L.: II. THE ACTIVITY OF PHOTOSYSTEMS ONE AND TWO, AND A NOTE ON THE SITE OF REDUCTION OF FERRICYANIDE

The activity of photosystems one and two (PS I and PS II) wasmeasured in chloroplasts isolated from the primary leaves ofPhaseolus vulgaris. During foliar senescence, the rates of electrontransport through PS I and PS II declined by approximately 25%and 33% respectively. These losses of activity could not accountfor the decrease of 80% in the rate of coupled, non-cyclic electrontransport during senescence. It is therefore suggested thatan impairment of electron flow between the photosystems limitednon-cyclic electron transport in chloroplasts from older leaves.In this study the activity of PS II was measured using oxidizedp-phenylenediamine as the electron acceptor, and trifluralinas an inhibitor of electron transport between PS II and PS I.In chloroplasts from young leaves the reduction of ferricyanidewas a measure of non-cyclic electron transport, but in preparationsfrom older leaves ferricyanide received a large proportion ofelectrons from PS II.     

A single step separation of PS 1, PS 2 and chlorophyll-antenna particles from spinach chloroplasts

After solubilization of photosynthetic membranes by digitonin, three main protein pigment complexes were isolated by electrophoresis with deoxycholate as detergent.The band with the slowest mobility, fraction 1, had PS 1 activity and was devoid of PS 2 activity. This fraction was four times enriched in P700 when compared with chloroplasts. Fraction 1 had little chl b, a long wavelength absorption maximum in the red, a maximum of low temperature emission fluorescence at 730nm, and a circular dichroism spectrum characteristic of PS 1 enriched fraction.Fraction 2 exhibited a PS 2 activity and no PS 1 activity. It was enriched five times in PS 2 reaction centre and had little chl b and carotenoids. The absorption maximum was at 674 nm and the low temperature fluorescence emission maximum was at 700 nm. Fraction 2 might be useful PS 2 enriched particle because of the great stability of this fraction with regard to photochemical activity and also rapidity and simplicity of its preparation.Fraction 3, which had the fastest migration, was devoid of photochemical activities; It was rich in chl b and had the fluorescence and the circular dichroism spectrum characteristic of an antenna complex.Abbreviations PS 1 (2) photosystem 1 (2) - chl chlorophyll - car carotenoid - Q primary plastoquinone electron acceptor - P700 primary electron donor of PS 1 - P680 primary electron donor of PS 2 - K₃Fe(CN)₆ potassium ferricyanide - DCMU dichlorophenyldimethylurea - DCPIP dichlorophenolindophenol - DPC diphenyl-carbazide     

Mg2+对生长在不同光强下的小麦叶绿体光合功能的影响

研究结果表明,Mg~(2+)对生长在不同光强度下的小麦叶绿体光合功能有不同影响。与生长在低光强(2×10~8勒克斯)下的小麦叶绿体相比,Mg~(2+)更加明显地降低从生长在高光强(2×10~4勒克斯)下的小麦所分离的叶绿体的吸收光谱在红区和蓝区的吸收峰值;但它更大幅度地提高后者在低温(77K)下的PSⅡ相对荧光产量(F_(687))与PSⅠ相对荧光产量(F_(742))的比值,PSⅡ活性和PSⅡ原初光能转化效率。实验结果证明,更高的光强度可能有利于叶绿体形成更多可流动的LHC-Ⅱ和LHC-Ⅰ。     

Nano-Anatase Relieves the Inhibition of Electron Transport Caused by Linolenic Acid in Chloroplasts of Spinach

Linolenic acid is an inhibitor of electron transport in chloroplasts of higher plants. It has obvious effects on the structure and function of chloroplasts. In the present paper, we investigated the nano-anatase relieving the inhibition of photoreduction activity and oxygen evolution caused by linolenic acid in spinach chloroplasts. The results showed that linolenic acid in various concentrations could obviously reduce the whole chain electron transport and the photoreduction activity of two photosystems, especially on the oxidative reside and reduce reside of photosystem II (PS II). After adding nano-anatase to chloroplasts treated by linolenic acid, the whole chain electron transport rate, the photoreduction activity of two photosystems, and the oxygen evolution rate were increased significantly, indicating that nano-anatase could obviously decrease the inhibition of linolenic acid on the electron transport, photoreduction activity, and oxygen evolution of spinach chloroplasts.     

Effect of temperature on senescing detached rice leaves: I. Photoelectron transport activity of chloroplasts

Detached rice(Oryza sativaL cv Mousouri)leaves were induced to senesce in darkness at 0°C(cold), 27°C(room temperature) and 40°C(heat). 2,6-dichlorophenol indophenol (DCPIP) Hill reaction activity of chloroplasts isolated from senescing leaves under all experimental temperatures with H₂O, Mn²⁺ or diphenyl carbazide (DPC) as electron donor declined during the period of incubation. Since DPC and Mn²⁺ augmented 2,6-dichlorophenol indophenol photoreduction by chloroplasts from senescing leaves, damage and/or change in the conformation of a site between H₂O and DCPIP in photosystem II (PS II) is suggested. Heat caused a faster decline of the Hill activity compared to cold or room temperature. However, cold treatment showed no significant effect on the photoelectron transport from H₂O to DCPIP compared with room temperature.     

Development of photosynthetic electron transport in Pinus silvestris

Photosynthetic electron transport activity has been measured in chloroplasts isolated from dark-grown seedlings of Pinus silvestris L. and in chloroplasts isolated from seedlings subjected to illumination for periods of up to 48 h. Activities of photosystem 2, photosystem 1 and photosystem 2 plus 1 have been measured. Chloroplasts isolated from dark-grown seedlings showed significant electron transport activity through both photosystems and through the entire electron transport chain from water to NADP. Illumination of the seedlings for only 5 min markedly promoted photosystem 2 activity. The artificial electron donor, diphenylcarbazide. promoted activity in chloroplasts from dark-grown seedlings and in chloroplasts from seedlings illuminated for up to 30 min. In comparison to photosystem 2 and overall electron transport from water to NADP, photosystem 1 activity increased only slightly during illumination. Measurements of electron transport and fluorescence kinetics have confirmed that photosynthetic electron transport capacity is limited on the water splitting side of photosystem 2 in dark-grown seedlings, whereas the primary and secondary electron acceptors of photosystem 2 are fully synthesized and functioning in darkness. Polyethylene glycol must be used as a protective agent when isolating photoactive chloroplasts from secondary needles of conifers. However, the presence of polyethylene glycol, when isolating chloroplasts from dark-grown pine cotyledons, caused a total inhibition of the activity of photosystem 2. The failure of others to show a substantial electron transport activity in chloroplasts from dark-grown Pinus silvestris might depend on their use of polyethylene glycol in the preparation medium and/or on their use of suboptimal reaction conditions for the electron transport measurements.     

UV-C对紫杉针叶叶绿体膜脂过氧化及PSⅡ电子传递活性的影响

在实验室条件下,用12W·m^-2剂量的紫外线C(UV-C,254nm)辐射紫杉针叶离体叶绿体．结果表明。随辐射时间的延长,活性氧清除系统中类胡萝卜素(Car)、谷胱甘肽(GSH)含量和超氧化物歧化酶(SOD)活性有不同程度的下降;脂质过氧化产物丙二醛(MDA)含量和膜相对透性有不同程度的增加;光系统Ⅱ(PSⅡ)电子传递活性显著下降,这种下降与光合活性光(PAR)强度呈反比;叶绿素对UV-C辐射不敏感．根据以上结果推测,UV-C辐射诱导叶绿体膜脂过氧化是导致PSⅡ电子传递活性下降的原因之一．     

Effect of Pb ions on superoxide dismutase and catalase activities in leaves of pea plants grown in high and low irradiance

The role of irradiance on the activity of antioxidant enzymes: superoxide dismutase (SOD) and catalase (CAT) was examined in the leaves of Pisum sativum L. plants grown under low (LL) or high (HL) irradiance (PPFD 50 or 600 μmol m⁻² s⁻¹) and exposed after detachment to 5 mM Pb (NO₃)₂ for 24 h. The activities of both enzymes increased in response to LL compared with HL and no effect of Pb ions was observed. Photosystem (PS) 1 and PS 2 activities were also investigated in chloroplasts isolated from these leaves. LL lowered PS 1 electron transport rate and changes in photochemical activity of PS 1 induced by Pb²⁺ were visible only in the chloroplasts isolated from leaves of LL grown plants. PS 2 activity was influenced similarly by Pb ions at both PPFD. This study demonstrates that leaves of HL grown plants were less sensitive to lead toxicity than those from LL grown plants. Changes in electron transport rates were the main factors responsible for the generation of reactive oxygen species in the chloroplasts and as a consequence, in induction of antioxidant enzymes.     

Mechanism of inhibition by local anesthetics of electron transport at the donor site of the photosystem II

The mechanism of inhibition by local anaesthetics of the procaine group of electron transport at the donor site of photosystem II (PS II) from pea chloroplasts was investigated. It was found that besides the inactivation of the O2 release system the anaesthetics used at one order of magnitude lesser concentration exert an uncoupling effect. With a rise in pH the inhibiting activity increases; however, this process is not coupled with the protonophore effect but is due to the generation of a neutral form of the amine. The increment of the inhibiting activity of the anaesthetics in the course of deprotonation seems to be regulated by changes in the coefficient of distribution between the membrane and the aqueous phase. The rate of inactivation of the H2O-dissociating complex increases considerably upon illumination. Electron transport through PS II in anaesthetic-treated chloroplasts in restored by diphenylcarbaside, but not by hydroxylamine. It is concluded that the anaesthetics induce the inhibition by interacting with the electron carrier. The role of the Ca2+--calmodulin-like protein in the functioning of the electron transport chain of PS II is discussed.     

Photoinhibition and recovery of photosynthesis in leaves of Vitis berlandieri and Vitis rupestris

Photoinhibition of photosynthesis was studied in Vitis berlandieri and Vitis rupestris leaves under controlled conditions (irradiation of detached leaves to about 1900 micromol m(-2) s(-1)). The degree of photoinhibition was determined by means of the ratio of variable to maximum chlorophyll (Chl) fluorescence (Fv/Fm) and electron transport measurements. The potential efficiency of PS2, Fv/Fm declined, Fo increased significantly in leaves of V. berlandieri, while Fo decreased in V. rupestris. In isolated thylakoids, the rate of whole chain and PS2 activity markedly decreased in high light irradiated more in leaves of V. berlandieri than in leaves of V. rupestris. A smaller inhibition of PS1 activity was also observed in both leaves. In the subsequent dark incubation, fast recovery was observed in both leaves and reached maximum PS2 efficiencies similar to those observed in non-photoinhibited leaves. The artificial exogenous electron donors DPC, NH2OH and Mn2+ failed to restore the high light induced loss of PS2 activity in V. berlandieri leaves, while DPC and NH2OH significantly restored in V. rupestris leaves. It is concluded that high light inactivates on the donor side of PS2 and acceptor side of PS2 in V. rupestris and V. berlandieri leaves, respectively. Quantification of the PS2 reaction center protein D1 and 33 kDa protein of water splitting complex following high light exposure of leaves showed pronounced differences between V. berlandieri and V. rupestris leaves. The marked loss of PS2 activity in high light irradiated leaves was due to the marked loss of D1 protein and 33 kDa protein in V. berlandieri and V. rupestris leaves, respectively.