Recombinant PsbF from Synechococcus sp. PCC 7002 forms β:β homodimeric cytochrome b559

All organisms with oxygenic photosynthesis contain two photosystems:photosystem Ⅰ(PSⅠ)and photo-systemⅡ(PSⅡ),The minimal photosystem Ⅱ particles which are photochemically active contain three subunits:D1,D2 and cytochrome b559 (Cyt b559),The function of Cyt b559 remains unclear,We have successfully overxpressed the psbF gene,encoding the β subunit of Cyt b559,from a marine cyanobacterium Synechoccous sp.PCC 7002 as a fusion gene and obtained a redox-active from of Cyt b559,When the N-terminal GST protein of the fusion gene product was removed with thrombin ,the PsbF protein was still redox-active,suggesting that the recombinant PsbF can form dimer in Escherichia coli.The absorption spectra of either the oxidized from or the reduced form of both GST fusion protein and the purified PsbF dimer and the difference Spectra between the two forms are the same as that of the Cyt b559 isolated from the higher plants .Redox titration analysis of recombinant PsbF showed that the mid-point redox potential of the recombinant Cyt b559 was approximately 50 mV, which is close to the low potential of Cyt b559 ,The results are helpful to the understanding of locatlization and function of Cyt b559 on thylakoid membranes.Ⅰ     

脱落酸对小麦幼苗光合及抗氧化酶的影响

研究了短期和长期外源脱落酸(ABA)处理对小麦幼苗CO2同化作用、羧化效率、光合CO2响应以及抗氧化酶等的影响.外源ABA处理能提高小麦叶片光合速率,但使气孔导度、胞间CO2浓度和羧化效率略有降低.ABA处理能够提高小麦光合对CO2的响应.无论是长期还是短期ABA处理都能够不同程度提高小麦抗氧化酶(CAT、SOD、POD)活性,且对SOD影响最明显.结果表明,ABA处理可能主要通过提高小麦抗氧化酶活性从而增强对环境胁迫的抗性,且长期处理效果好于短期处理.     

苏铁耐旱、抗寒及光合生理特性研究

采用干旱胁迫及人工模拟冷冻试验 ,进行苏铁耐旱、抗寒及光合生理特性研究 ,结果表明 :不同年龄苏铁的耐旱性、抗寒性及光合生理指标存在明显差异 ,随苏铁叶龄增加 ,苏铁叶片水势、冻害敏感指数和 NR活力下降 ,蒸腾速率、自然饱和亏和叶绿素含量增加 ,苏铁耐旱及抗寒性增强 ;苏铁水分及光合生理指标对干旱胁迫反应敏感 ,随干旱胁迫加剧 ,苏铁叶片水势、蒸腾速率、叶绿素、NR活力及净光合速率下降 ,而自然饱和亏增大 ,以适应胁迫环境 ,使苏铁表现出较强的抗旱性和生命力。     

New structure model of oxygen-evolving center and mechanism for oxygen evolution in photosynthesis

So far, many important questions and problems concerning the structure and mechanism of photosynthetic oxygen evolution are still unsolved. On the basis of recent achievements in this field, a new structure model is proposed whereby two H2O molecules bind asymmetrically to two manganese ions (Mn1Ⅱ and Mn4Ⅲ) at the open end of "C" shaped cluster and keep rather large distance. Two histidine residues coordinate to the other two manganese ions in higher oxidation state (Mn2Ⅳ and Mn3Ⅳ ) through their nitrogen atoms of the imidazole. Cl bound as terminal ligand to Mn4Ⅲl is connected to Ca, and the latter is needed to maintain the special configuration of two Mn2O2 units by bridged-oxo and bridged-carboxylate ligands. The whole structure of oxygen evolution center is asymmetry. A new mechanism for oxygen evolution invokes predictions of asymmetric oxidation of two H2O molecules, dynamic structural changes of oxygen e-volving center and indirect proton transport, etc. Only in S2 state, could Mn1Ⅳ = O. intermediate with high oxidation potential be formed. The S2→S3 process occurs with significant structural changes, as well as intramolecular and intermolecular hydrogen transfer. The S3 state corresponds to intermediate of Mn1Ⅳ-O… H… O-Mn4Ⅳ . During S3→ [S4] →S0, the O-O bond is formed only in S4 state. The change of nucleophilic interaction between Cl and manganese ions different oxidation states has consequence for the significant structural changes in H2O oxidation process.     

麻栎光合作用的特性及其对CO2倍增的响应

研究了 1 2年生麻栎的光合作用特性、净光合速率的日变化及其对CO2 倍增的响应。结果表明 :( 1 )麻栎叶片的光饱和点约为 1 2 0 0 μmol/ (m2 ·s) ,光补偿点约为 50 μmol/ (m2 ·s) ,表观光量子效率为 0 .0 2 5mol/mol。麻栎叶片CO2 补偿点为 60 μmol/mol,CO2 饱和点为1 2 0 0 μmol/mol,叶片的羧化效率为 0 .0 2 ,麻栎为喜光的C3植物 ;( 2 )麻栎叶片的净光合速率日变化在生长初期和末期为单峰曲线 ,其走势与光合有效辐射走势一致 ;而在生长盛期为双峰曲线 ,净光合速率在中午出现了明显的下降 ;( 3 )主成份分析表明 ,影响麻栎净光速率的主导因子在生长初期是光强和叶室CO2 浓度 ,在生长盛期是饱和蒸汽压差和温度 ,在生长末期是饱和蒸汽压差和相对湿度 ;( 4 )CO2 倍增条件下 ,麻栎叶片净光合作用速率平均增幅为 89.1 7%。     

铯对小麦叶片光合特性影响的研究

随着环境中铯(Cs)污染日益恶化,铯对生物毒害作用的研究受到越来越多的关注.为了探讨铯对植物光合作用的影响,在石英砂和Hoagland营养液培养体系下,从三叶期开始用浓度为0、0.5、1、5、10、20 mmol·L-1的133Cs+[CsCl]处理小麦(Triticum aestivum L.)幼苗.在处理后的第0、7、14、21、28 d时,检测小麦光合特性的改变.结果表明:用0.5 mmol·L-1和1 mmol·L-1低浓度133Cs+处理7 d后,小麦叶片的叶绿素含量、叶圆片放氧活性、类囊体膜电子传递活性均显著高于对照;但随133Cs+浓度的增加及处理时间的延长,这些参数的数值均显著下降.此外,光合系统II(PSII)活性的下降速率高于光合系统I(PSI)下降速率,说明PSII相对于PSI更容易受到133Cs+的胁迫伤害.这些结果表明133Cs+对小麦的毒害效应受时间和浓度的双重制约.低浓度133Cs+可以促进小麦光合作用,而高浓度133Cs+则显著抑制小麦光合作用.     

不同盐分在不同浓度条件下对玉米幼苗基础生理效应的研究

用一系列含同摩尔Ｎａ＾＋浓度的ＮａＣｌ、Ｎａ２ＣＯ３、Ｎａ２ＳＯ４溶液以及用磷酸中和至ＰＨ值与含同摩尔Ｎａ＾＋浓度的ＮａＣｌ溶液的ＰＨ值相等的Ｎａ２ＣＯ３溶液处理生长期为３０天的玉米幼苗。处理一周后,测定离子含量、渗透势、光合性能和叶绿素含量等各项生理指标。结果表明：在同摩尔Ｎａ＾＋浓度条件下,玉米幼苗在ＮａＣｌ、ＮａＣＯ３和Ｎａ２ＳＯ４胁迫下产生胁变的顺序为：Ｎａ２ＣＯ３〉ＮａＣｌ〉Ｎａ２ＳＯ４     

新疆高光强条件下小麦群体光合能力的研究

对新疆大陆性气候条件下春小麦群体光合能力进行研究,结果表明:新疆小麦在相同的光强下具有较高的群体表观净光合速率,具有较高的光合生产潜力,其CAP的值在-15~45μmol.m-2.s-1,与山东小麦群体光合能力比较,群体光补偿点相近,光饱和点高出1.5~3.0万lx,CAP最大值在拔节期高出4~7μmol.m-2.s-1,开花期高出6~10μmol.m-2.s-1;温光效应分析表明,光强是影响新疆春小麦群体光合能力主导生态因子,中午光强超过光饱和点是造成群体光合“午休”现象的重要原因。     

华北落叶松冠层光合生理特性的空间异质性

【目的】森林生产力取决于树冠的整体光合能力,而树冠不同部位的光合作用具有差异性。深入了解华北落叶松冠层内光合作用的差异,为冠层水平模拟和准确估算森林生产力提供依据。【方法】采用Li-6400便携式光合仪对山西省太岳山20年生和40年生华北落叶松不同层次和不同方位的光合生理特性进行研究。【结果】20年生华北落叶松树冠中上层与下层的净光合速率(P_n)差异显著(P<0.05),而不同方位上的P_n差异不显著; 40年生华北落叶松树冠上、中、下3个层次的P_n差异显著(P<0.05),不同方位上的P_n差异也不显著。影响20年生华北落叶松树冠P_n的主要因子是羧化效率(V_c)、胞间CO₂浓度(C_i)、蒸腾速率(T_r); 影响40年生华北落叶松树冠P_n的主要因子是V_c、气孔导度(G_s)、水汽压亏缺(p_VPD)。20年生和40年生华北落叶松树冠不同层次、不同方位叶绿素a、叶绿素b和总叶绿素含量差异不显著。【结论】冠层光合空间异质性是冠层水平模拟和估算森林生产力时必须考虑的因素,这对于从单木到林分的尺度推演和模型拟合具有重要的意义。     

Relationships between D1 protein, xanthophyll cycle and photodamage-resistant capacity in rice (Orysa sativa L.)

Relationships between D1 protein, xanthophyll cycle and subspecific difference of photodamage-resistant capacity have been studied in O. japonica rice varieties 02428 and 029 (photoinhibition-tolerance) and O. indica rice varieties 3037 and Palghar (photoinhibition-sensitivity) and their reciprocal cross F1 hybrids after photoinhibitory treatment. It was shown that PSⅡ photochemical efficiency (Fv /Fm) decreased, and xanthophyll cycle from violaxanthin (V), via anaxanthin (A), to zeaxanthin (Z) was enhanced and non-photochemical quenching (qN) increased accordingly in SM-pretreated leaves of rice when the synthesis of D1 protein was inhibited, and that there was a decrease in qN and, as a result, more loss of D1 protein and a big decrease in Fv /Fm in DTT-pretreated leaves when xanthophyll cycle was inhibited. O. japonica subspecies had a higher maintaining capacity of D1 protein and a decrease of Fv /Fm in a more narrow range, and exhibited more resistance against photodamage, as compared with O. indica subspecies. The above physiological indexes in reciprocal cross F1 hybrids, though between the values of their parents, were closer to maternal lines than to paternal lines. Experimental results support the concept that the turnover capacity for D1 protein is an important physiological basis of photoinhibition-tolerance, and will provide the physiological basis for selection of the photoinhibition-tolerant parents and develop a new approach to breed hybrids with high photosynthetic efficiency.