Depletion of phosphatidyl-glycerol head-group induces changes in oxygen evolution and protein secondary struc-tures of photosystem Ⅱ

The techniques of oxygen electrode polarogra-phy and Fourier transform infrared (FT-IR) spectroscopy were employed to explore the roles of polar head-group of phosphatidylglycerol (PG) molecules in the functional and structural aspects of photosystem Ⅱ (PS Ⅱ) through enzymatic approach. It was shown that the depletion of PG by treatment of phospholipase C (PLC) on PS Ⅱ particles caused the inhibition of oxygen evolving activity in PS Ⅱ. This effect also gave rise to changes in the protein secondary structures of PS Ⅱ, that is, an increase in a-helical conformation which is compensated by the loss of p-strand structures. It revealed that the head-group of PG molecules plays an important structural role in the maintenance of normal structure of PS Ⅱ proteins, which is required to maintain the appropriate physiological activity of the PS Ⅱ complex such as the oxygen evolving activity. It is suggested that there most probably exist hydrogen-bonding interactions between PG molecules and PS Ⅱ proteins.     

Depletion of phosphatidylglycerol head-group induces changes in oxygen evolution and protein secondary structures of photosystemⅡ

The techniques of oxygen electrode polarography and Fourier transform infrared (FT-IR) spectroscopy were employed to explore the roles of polar head-group of phosphatidylglycerol (PG) molecules in the functional and structural aspects of photosystemⅡ(PSⅡ) through enzymatic approach. It was shown that the depletion of PG by treatment of phospholipase C (PLC) on PSⅡ particles caused the inhibition of oxygen evolving activity in PSⅡ. This effect also gave rise to changes in the protein secondary structures of PSⅡ, that is, an increase in α-helical conformation which is compensated by the loss of β-strand structures. It revealed that the head-group of PG molecules plays an important structural role in the maintenance of normal structure of PSⅡ proteins, which is required to maintain the appropriate physiological activity of the PSⅡ complex such as the oxygen evolving activity. It is suggested that there most probably exist hydrogen-bonding interactions between PG molecules and PSⅡ proteins.     

Protection of phosphatidylcholine to photosystem Ⅱ membrane during heat treatment

Photosystem Ⅱ membrane was reconstituted with phosphatidylcholine (PC) with different kinds of fatty acyl chains and the protection of PC to photosystem Ⅱ (PS Ⅱ)membrane during heat treatment was investigated using oxygen electrode, variable fluorescence and circular dichroism (CD) spectroscopy. Heat treatment decreased the oxygen evolution rate and the F′v/Fm′ ratio of PS Ⅱ membrane and influenced CD spectra of PS Ⅱ membrane, but PC inhibited the effect of heat treatment on the oxygen evolution rate, the F′v/F′m ratio and CD spectra of PS Ⅱ membrane. The results indicate that PC can protect PS Ⅱ membrane against heat treatment and the alterations in the unsaturated fatty acid extent in PC can cause the changes of the protection ability.     

Co-oxidation of arsenic(Ⅲ) and iron(Ⅱ) ions by pressurized oxygen in acidic solutions

The co-oxidation of As(Ⅲ) and Fe(Ⅱ) in acidic solutions by pressured oxygen was studied under an oxygen pressure between 0.5 and2.0 MPa at a temperature of 150℃. It was confirmed that without Fe(Ⅱ) ions, As(Ⅲ) ions in the solutions are virtually non-oxidizable by pressured oxygen even at a temperature as high as 200℃ and an oxygen pressure up to 2.0 MPa. Fe(Ⅱ) ions in the solutions did have a catalysis effect on the oxidation of As(Ⅲ), possibly attributable to the production of such strong oxidants as hydroxyl free radicals(OH·) and Fe(IV) in the oxidation process of Fe(Ⅱ). The effects of such factors as the initial molar ratio of Fe(Ⅱ)/As(Ⅲ), initial pH value of the solution, oxygen pressure, and the addition of radical scavengers on the oxidation efficiencies of As(Ⅲ) and Fe(Ⅱ) were studied. It was found that the oxidation of As(Ⅲ) was limited in the co-oxidation process due to the accumulation of the As(Ⅲ) oxidation product, As(V), in the solutions.     

Protection of phosphatidyl-choline to photosystem II membrane during heat treatment

Photosystem II membrane was reconstituted with phosphatidylcholine (PC) with different kinds of fatty acyl chains and the protection of PC to photosystem II (PS II) membrane during heat treatment was investigated using oxygen electrode, variable fluorescence and circular dichro-ism (CD) spectroscopy. Heat treatment decreased the oxygen evolution rate and the F'v/Fm' ratio of PS II membrane and influenced CD spectra of PS II membrane, but PC inhibited the effect of heat treatment on the oxygen evolution rate, the F'v/F'm ratio and CD spectra of PS II membrane. The results indicate that PC can protect PS II membrane against heat treatment and the alterations in the unsaturated fatty acid extent in PC can cause the changes of the protection ability.     

Thermal stability of oxygen evolution in photosystem Ⅱ core complex in the presence of digalactosyl diacylglyceroli

The influence of digalactosyldiacylglycerol (DGDG), one of the photosynthetic membrane lipids, on heat inactivation of the process of oxygen evolution has been studied in vitro in photosystem Ⅱ (PSⅡ) core complex. It was found that the temperature of semi-inactivation of oxygen evolution in the complex increased from 40.0 to about 43.0℃ in the presence of DGDG with 5-min heat treatment in the dark. Furthermore, when PSⅡ core complex was incubated for 5 min at 45.0℃, the oxygen evolution in the complex was completely lost, whilst the DGDG-complexed PSⅡ core complex still retained a 16% of activity (100% for 25.0℃). In addition, a 1-h incubation at 38.0℃ inactivated absolutely the oxygen evolution for the PSⅡ core complex. By contrast, there remained about 20% of activity (zero time for 100%) for the complex in the presence of DGDG under the same condition. These results indicate a new role of DGDG in the protection of PSⅡ core complex against the deleterious effects of temperature. It was most likely that DGDG-mediated stability toward thermal denaturation of oxygen evolution in PSⅡ core complex is due to the protective effect of DGDG on the release of the 33 kD protein from PSⅡ core complex.     

Induction of Apoptosis in Purified Nuclei from Tobacco-Suspension Cells by Cytochrome b6／f Complex

An apoptotic cell-free system containing cytosol and nuclei from normally cultured tobacco suspension cells was used to show that a spinach chloroplast preparation can induce apoptosis in nuclei, evidenced by DNA electrophoresis and fluorescence microscopy observations, Further study showed that the chloroplast preparation or its pellet (thylakoid membrane) after hypoosmotic or supersonic treatment still exhibited the apoptosis-inducing activity, but the supernatant had no effect, which indicates that the apoptosisinducing effector in the chloroplast preparation is water-insoluble. The induction of apoptosis by chloroplast preparation could be attenuated by Ac-DEVD-CHO, the specific inhibitor of Caspase-3, implying involvement of a Caspase-3-1ike protease during the process. Furthermore, extensive apoptosis in nuclei was induced by cytochrome b6/f on the thylakoid membrane, indicating that this important cytochrome complex may have an important role in the chloroplast-related apoptotic pathway.     

Phosphatidylglycerol effect on oxygen-evolving activity in Ca2+-depleted photosystem Ⅱ

The effect of anionic phosphatidylglycerol (PG) on oxygen evolution in a photosystem Ⅱ (PSⅡ) particle depleted of Ca2+ (designated dCaPSⅡ) has been investigated. The major finding is the observation of a new role of PG in the PSⅡ function. That is, PG restores nearly the lost oxygen evolution in dCaPSⅡ particle owing to Ca2+ depletion to the levels in intact PSⅡ. Furthermore, there is a stimulation of oxygen-evolving activity in the dCaPSⅡ complexed with PG in the presence of exogenous CaCl2, which PG enhances increasingly oxygen evolution with increasing CaCl2 concentration. It is suggested that PG-induced oxygen evolution recovery of dCa PSⅡ particle results from resumption of normal structure in protein by PG effect, whereas the enhancement of oxygen evolution in complex subject to CaCl2 is ascribed to the optimization of such a structure due to coordination complex formation of Ca2+ ions with PG.     

An Arabidopsis ctpA homologue is involved in the repair of photosystem II under high light

A T-DNA insertion mutant AtctpA1 was identified to study the physiological roles of a carboxyl-terminal processing protease (CtpA) homologue in Arabidopsis. Under normal growth conditions, disruption of AtctpA1 did not result in any apparent alterations in growth rate and thylakoid membrane protein components. However the mutant plants exhibited increased sensitivity to high irradiance. Degradation of PSII reaction center protein D1 was accelerated in the mutant during photoinhibition. These results demostrated that AtctpA1 was required for efficient repair of PSII in Arabidopsis under high irradiance.     

在酸性溶液中加压氧化三价砷离子和二价铁离子

The co-oxidation of As(III) and Fe(II) in acidic solutions by pressured oxygen was studied under an oxygen pressure between 0.5 and 2.0 MPa at a temperature of 150°C. It was confirmed that without Fe(II) ions, As(III) ions in the solutions are virtually non-oxidizable by pressured oxygen even at a temperature as high as 200°C and an oxygen pressure up to 2.0 MPa. Fe(II) ions in the solutions did have a catalysis effect on the oxidation of As(III), possibly attributable to the production of such strong oxidants as hydroxyl free radicals (OH·) and Fe(IV) in the oxidation process of Fe(II). The effects of such factors as the initial molar ratio of Fe(II)/As(III), initial pH value of the solution, oxygen pressure, and the addition of radical scavengers on the oxidation efficiencies of As(III) and Fe(II) were studied. It was found that the oxidation of As(III) was limited in the co-oxidation process due to the accumulation of the As(III) oxidation product, As(V), in the solutions.     

Trichloroacetate affects the EPR SignalⅡslow and SignalⅠin the thylakoid of Chlamydomonas reinhardtii

One electron paramagnetic resonance (EPR) signal, named SignalⅡslow, originates from the oxidized Tyrosine 160 (YDo) of D2 polypeptide of photosystemⅡ reaction center. After adding high concentration trichloroacetate (TCA) to the Chlamydomonas reinhardtii thylakoid suspension, this signal was abolished in a minute. Treatment of TCA also removes a few of polypeptides, including three extrinsic polypeptides of oxygen-evolving complex, from the thylakoid membrane. Based upon the analysis of the microenvironment around YD with a three-dimensional model, it is indicated that relatively high hydrophobicity of this microenvironment may be the essential prerequisite for TCA to affect YD. It has been observed that TCA treatment also retards the decay of the SignalⅠ, produced by the oxidized reaction center chlorophyll dimer (P700+) of photosys- temⅠ.     

雌雄异型异熟青钱柳幼龄林开花习性及交配系统分析

青钱柳为典型的雌雄异型异熟树种,包括雌花先熟个体(雌先型,PG)和雄花先熟个体(雄先型, PA)两种交配型。同一交配型内雌雄花期错开而交配型间雌雄花同步的开花生物学特性可能对青钱柳种子产量和质量有重要影响。为了解青钱柳群体的交配系统,对江苏溧阳陶峰和安徽红琊山林场的7年生青钱柳人工林群体进行了连续2 a花期物候学观测,包括林分中交配型的比例、不同交配型的雌雄开花顺序、开花持续时间及花期相遇特点。结果表明:受环境条件的影响,青钱柳花期为4月下旬至5月下旬,有一定波动; 雌、雄花期持续时间分别为9～19 d(最长21 d)和2～9 d。在人工林幼龄群体中,开花植株有2类共5种表现型,其中两性植株包括雌先型(PG)、雄先型(PA)和同步型(SC),单性植株包括雌株(F)和雄株(M); 观察发现幼林群体中雌株居多,两性植株比例较小。2015年溧阳陶峰青钱柳人工林中开花率达到73.2%,两性植株占28.8%,PA和PG比例1:1.2; 而红琊山林场的开花率仅为38.6%,其中16.7%为两性植株,PG比例较高。连续2 a的定株观察还表明:开花表现型的变化主要为单性植株转变为两性植株; PA和PG表达稳定,极少发生逆转; 两性植株中,有52.2%的植株上雌、雄花期完全错开,而47.8%的植株上雌、雄花花期有部分(少量全部)重叠。相关分析表明,开花状况与母树胸高断面积显著相关,显著性大小顺序为雌先型﹥雄先型﹥雄株﹥雌株﹥未开花植株。多重比较表明:两性植株的平均胸高断面积与单性植株、未开花植株差异显著; 开花植株中雌先型、雄先型和雄株平均胸高断面积差异不显著,但三者与雌株存在显著差异。由此推测青钱柳开花与否和开花表现型明显受植株营养积累的影响。     

高温胁迫对菠菜类囊体膜蛋白亚基和光谱特征的影响

研究了高温处理对菠菜类囊体膜蛋白亚基和光谱特征的影响.结果显示,高温处理后,内周天线CP43、放氧外周蛋白33 000降解明显,而外周天线LHC II发生聚集;随着处理温度的增高,菠菜类囊体膜的吸收光谱和荧光发射光谱明显下降,而且峰位发生蓝移,这说明高温处理破坏了类囊体膜的结构,影响到对光能的吸收.而35℃高温处理下,随着处理时间的延长,吸收光谱和荧光光谱也呈现下降趋势,但与不同温度处理相比,下降程度略缓,这说明类囊体膜在35℃长时间处理表现出的耐受性比在高温短时间处理条件强.     

Mg~(2+)-induced LHC Ⅱ aggregation in thylakoid membrane

Mg2+-induced changes in 77K fluorescence spectra of wheat thylakoid membranes were analyzed by a Gaussian deconvolution program. All spectra were fitted well with 7 Gaussian sub-bands. The sub-band areas for the LHC Ⅱ macroaggregate (F699) and PS Ⅱ (F685 and F695) were increased and those for the LHC Ⅱ trimer (F681) and PS Ⅰ (F729 and F740) were decreased by Mg2+ . Moreover, it was found that the sub-band area ratio for F699 over F681 was dramatically enhanced by Mg2+ by 1.72 times. It was concluded that the LHC Ⅱ trimer in thylakoid membranes could be aggregated and transformed into its macroaggregate by Mg2+ on a large scale. The possible implication of the Mg2+-induced LHC Ⅱ aggregation was also discussed .     

Phosphatidylglycerol effect on oxygen-evolving activity in Ca2+-depleted photosystem II

The effect of anionic phosphatidylglycerol (PG) on oxygen evolution in a photosystem II (PS II ) particle depleted of Ca²⁺ (designated d_CaPSII ) has been investigated. The major finding is the observation of a new role of PG in the PSII function. That is, PG restores nearly the lost oxygen evolution in d_caPS II particle owing to Ca²⁺ depletion to the levels in intact PS II. Furthermore, there is a stimulation of oxygen-evolving activity in the d_CaPSII complexed with PG in the presence of exogenous CaCl₂, which PG enhances increasingly oxygen evolution with increasing CaCl₂ concentration. It is suggested that PG-induced oxygen evolution recovery of d_Ca PS II particle results from resumption of normal structure in protein by PG effect, whereas the enhancement of oxygen evolution in complex subject to CaCl₂ is ascribed to the optimization of such a structure due to coordination complex formation of Ca²⁺ ions with PG.     

光照条件下Rose bengal处理对植物类囊体膜，PS II颗粒活性及多肽组分的影响

研究了Rose bengal处理对菠菜类囊体膜及PS II颗粒的叶绿素荧光发射光谱、蛋白质内源荧光发射光谱、DCIP光还原活性及多肽组分的影响。结果表明：单线态氧可改变类囊体膜的结构,并且可破坏PS II反应中心及LHC II中叶绿素分子的结合状态,引起类囊体膜PS II天线系统中的叶绿素捕光效率下降,还可引起光合电子传递能力下降和类囊体膜蛋白构象的改变,但至少在短时间内不会造成类囊体膜多肽组分的降解。     

Trichloroacetate affects the EPR Signal IIslow and Signal I in the thylakoid ofChlamydomonas reinhardtii

One electron paramagnetic resonance (EPR) signal, named Signal II_slow, originates from the oxidized Tyrosine 160 (Y_D) of D2 polypeptide of photosystem II reaction center. After adding high concentration trichloroacetate (TCA) to theChlamydomonas reinhardtii thylakoid suspension, this signal was abolished in a minute. Treatment of TCA also removes a few of polypeptides, including three extrinsic polypeptides of oxygen-evolving complex, from the thylakoid membrane. Based upon the analysis of the microenvironment around Y_D with a three-dimensional model, it is indicated that relatively high hydrophobicity of this microenvironment may be the essential prerequisite for TCA to affect Y_D. It has been observed that TCA treatment also retards the decay of the Signal 1, produced by the oxidized reaction center chlorophyll dimer (P700⁺) of photosystem I.