Ammonia-induced structural changes of the oxygen-evolving complex in photosystem II as revealed by light-induced FTIR difference spectroscopy

Light-induced Fourier transform infrared difference spectroscopy has been applied to studies of ammonia effects on the oxygen-evolving complex (OEC) of photosystem II (PSII). We found that NH(3) induced characteristic spectral changes in the region of the symmetric carboxylate stretching modes (1450-1300 cm(-1)) of the S(2)Q(A)(-)/S(1)Q(A) FTIR difference spectra of PSII. The S(2) state carboxylate mode at 1365 cm(-1) in the S(2)Q(A)(-)/S(1)Q(A) spectrum of the controlled samples was very likely upshifted to 1379 cm(-1) in that of NH(3)-treated samples; however, the frequency of the corresponding S(1) carboxylate mode at 1402 cm(-1) in the same spectrum was not significantly affected. These two carboxylate modes have been assigned to a Mn-ligating carboxylate whose coordination mode changes from bridging or chelating to unidentate ligation during the S(1) to S(2) transition [Noguchi, T., Ono, T., and Inoue, Y. (1995) Biochim. Biophys. Acta 1228, 189-200; Kimura, Y., and Ono, T.-A. (2001) Biochemistry 40, 14061-14068]. Therefore, our results show that NH(3) induced significant structural changes of the OEC in the S(2) state. In addition, our results also indicated that the NH(3)-induced spectral changes of the S(2)Q(A)(-)/S(1)Q(A) spectrum of PSII are dependent on the temperature of the FTIR measurement. Among the temperatures we measured, the strongest effect was seen at 250 K, a lesser effect was seen at 225 K, and little or no effect was seen at 200 K. Furthermore, our results also showed that the NH(3) effects on the S(2)Q(A)(-)/S(1)Q(A) spectrum of PSII are dependent on the concentrations of NH(4)Cl. The NH(3)-induced upshift of the 1365 cm(-1) mode is apparent at 5 mM NH(4)Cl and is completely saturated at 100 mM NH(4)Cl concentration. Finally, we found that CH(3)NH(2) has a small but clear effect on the spectral change of the S(2)Q(A)(-)/S(1)Q(A) FTIR difference spectrum of PSII. The effects of amines on the S(2)Q(A)(-)/S(1)Q(A) FTIR difference spectra (NH(3) > CH(3)NH(2) > AEPD and Tris) are inverse proportional to their size (Tris approximately AEPD > CH(3)NH(2) > NH(3)). Therefore, our results showed that the effects of amines on the S(2)Q(A)(-)/S(1)Q(A) spectrum of PSII are sterically selective for small amines. On the basis of the correlations between the conditions (dependences on the excitation temperature and NH(3) concentration and the steric requirement for the amine effects) that give rise to the NH(3)-induced upshift of the 1365 cm(-)(1) mode in the S(2)Q(A)(-)/S(1)Q(A) spectrum of PSII and the conditions that give rise to the altered S(2) state multiline EPR signal, we propose that the NH(3)-induced upshift of the 1365 cm(-1) mode is caused by the binding of NH(3) to the site on the Mn cluster that gives rise to the altered S(2) state multiline EPR signal. In addition, we found no significant NH(3)-induced change in the S(2)Q(A)(-)/S(1)Q(A) FTIR difference spectrum at 200 K. Under this condition, the OEC gives rise to the NH(3)-stabilized g = 4.1 EPR signal and a suppressed g = 2 multiline EPR signal. Our results suggest that the structural difference of the OEC between the normal g = 2 multiline form and the NH(3)-stabilized g = 4.1 form is small.     

显脉金花茶的光合生理特性研究

采用LI-6400便携式光合测定系统(Li-Cor Inc., USA)对显脉金花茶光合特性进行研究。结果表明：(1)在夏季,显脉金花茶叶片的P_n日变化呈单峰曲线,最高峰出现在中午11：00。其最大净光合速率（P_max）为3.81 μmol·m^-2·s^-1、光饱和点（LSP）为459.9 μmol·m^-2·s^-1、光补偿点（LCP）为6.9 μmol·m^-2·s^-1。显脉金花茶的光饱和点和光补偿点都比较低,表明其是一种阴生植物。（2）在控制光照强度和温度的条件下,CO₂浓度小于800 μmol·mol^-1,P_n几乎呈直线上升,升高CO₂浓度可使显脉金花茶的净高合速率增大,提高了叶片对光能的利用率。其叶片CO₂饱和点(CSP)大约在1 200 μmol·mol^-1左右,CO₂的补偿点（Г^*）为70.1 μmol·mol^-1,最大羧化速率（V_cmax）为17.5 μmol·m^-2·s^-1,最大电子传递速率（J_max）为40 μmol·m^-2·s^-1。     

槟榔胚培养

1植物名称槟榔(Areca catechu L.)。2材料类别幼胚。3培养条件(1)启动培养基:MS 5%(V/V)椰子水 40g·L-1蔗糖 1g·L-1活性碳 0.55%琼脂;(2)生长培养基:MS BA1mg·L-1(单位下同) NAA0.5 5%(V/V)椰子水 4     

氰戊菊酯在茶叶和茶汤中的残留动态及最大残留限量评价

在生长均匀的茶园喷施氰戊菊酯(fenvalerate),采摘施药后2 h和1 h、2 h、3 h、5 h、7 h、9 h、14 h、21天的茶树鲜叶加工成绿茶,用气相色谱法测定成茶、茶汤和茶渣中反式氰戊菊酯和顺式氰戊菊酯的含量,研究了氰戊菊酯在成茶、茶汤中的残留动态。结果表明:反式氰戊菊酯和顺式氰戊菊酯在成茶中的残留水平随施药间隔天数的增加呈下降趋势,20 mL/667 m2施药剂量下,分别由施药当天2 h的9.40 mg/kg和17.51 mg/kg减小到第21天的1.07 mg/kg和1.53 mg/kg,消解幅度为88.62%和91.26%,40 mL/667 m2施药剂量下,分别由施药当天2 h的20.37 mg/kg和38.67 mg/kg减小到第21天的1.94 mg/kg和3.06 mg/kg,消解幅度为90.49%和92.09%。茶汤中氰戊菊酯含量(y)与成茶中氰戊菊酯含量(x)呈二项式函数关系,反式氰戊菊酯的函数关系为y=-0.0007x2 0.0242x,顺式氰戊菊酯的函数关系为y=-0.0002x2 0.0114x。按我国标准饮茶摄入的氰戊菊酯占每日允许摄入量的0.049%,足以达到保护人体健康水平的要求。而按欧盟的标准,饮茶摄入的氰戊菊酯占每日允许摄入量的0.0019%,即在10-5水平上,这样的风险水平已接近对非阈效应化学物质的风险控制水平(10-6)。     

一氧化氮参与调节盐胁迫诱导的玉米幼苗脱落酸积累

以三叶一心期的玉米幼苗为实验材料,研究了盐胁迫下玉米幼苗根尖和叶片中一氧化氮（NO）和脱落酸（ABA）积累之间的关系。结果表明,盐胁迫下玉米幼苗NO和ABA的含量均增加,用NO供体硝普钠（Sodium nitroprusside,SNP）处理时,ABA含量亦增加,且累积的时间较盐胁迫下早。用NO合成的抑制剂L-NAME （Nω-nitro-L-arginine methyl ester hydrochloride）和NaN,处理时,可减弱盐胁迫诱导的ABA含量的增加,用NO清除剂cPTIO处理时,这种盐胁迫诱导的ABA增加减少。推测盐胁迫下产生的NO参与调节ABA的积累及逆境下植物的防御反应。     

广西稀有濒危植物迁地保护评价

从迁地保护的内容、适应性、有效性等方面对桂林植物园迁地保护稀有濒危植物进行评价,结果表明:迁地保护的稀有濒危植物科学性强,96%以上的物种有科学记录,除了银杏等少数几个种属于“保护性收集”外,其它都是“具有保护意义的收集”;75%的种适应或基本适应迁移地的环境,原分布于广西的种明显比分布于广西区外的种适应性更强。按照最小存活种群的标准,该园有73种稀有濒危植物迁地保护有效。     

拟南芥MT-II过量表达提高抗旱性(英文)

富含巯基的植物II型金属硫蛋白(MT)对植物抵抗重金属胁迫具有重要作用,其中一个可能机制是金属硫蛋白可能猝灭重金属引起的氧化胁迫。利用转MT-II基因和野生型拟南芥(Arabidopsis thaliana)植株来对比研究MT在胁迫过程中通过清除氧自由基,特别是H2O2而对植物抗旱性的影响。研究表明,转基因型拟南芥能有效维持体内氧化—还原势,减少MDA的产生,从而缓解干旱胁迫引起的伤害,提高抗旱性。     

Identification of Critical Regions in Human SAMHD1 Required for Nuclear Localization and Vpx-Mediated Degradation

The sterile alpha motif (SAM) and HD domain-containing protein-1 (SAMHD1) inhibits the infection of resting CD4+ T cells and myeloid cells by human and related simian immunodeficiency viruses (HIV and SIV). Vpx inactivates SAMHD1 by promoting its proteasome-dependent degradation through an interaction with CRL4 (DCAF1) E3 ubiquitin ligase and the C-terminal region of SAMHD1. However, the determinants in SAMHD1 that are required for Vpx-mediated degradation have not been well characterized. SAMHD1 contains a classical nuclear localization signal (NLS), and NLS point mutants are cytoplasmic and resistant to Vpx-mediated degradation. Here, we demonstrate that NLS-mutant SAMHD1 K11A can be rescued by wild-type SAMHD1, restoring its nuclear localization; consequently, SAMHD1 K11A became sensitive to Vpx-mediated degradation in the presence of wild-type SAMHD1. Surprisingly, deletion of N-terminal regions of SAMHD1, including the classical NLS, generated mutant SAMHD1 proteins that were again sensitive to Vpx-mediated degradation. Unlike SAMHD1 K11A, these deletion mutants could be detected in the nucleus. Interestingly, NLS-defective SAMHD1 could still bind to karyopherin-β1 and other nuclear proteins. We also determined that the linker region between the SAM and HD domain and the HD domain itself is important for Vpx-mediated degradation but not Vpx interaction. Thus, SAMHD1 contains an additional nuclear targeting mechanism in addition to the classical NLS. Our data indicate that multiple regions in SAMHD1 are critical for Vpx-mediated nuclear degradation and that association with Vpx is not sufficient for Vpx-mediated degradation of SAMHD1. Since the linker region and HD domain may be involved in SAMHD1 multimerization, our results suggest that SAMHD1 multimerization may be required for Vpx-mediation degradation.     

尾叶桉人工林生物量和生产力的研究

按径级标准木法测定了尾叶桉（Ｅｕｃａｌｙｐｔｕｓ ｕｒｏｐｈｙｌｌａ）器官生物量,建立了林木器官干重（ｗ）与胸径和树高（Ｄ＾３Ｈ）关系的相对生长方程,进而计算出尾叶桉林分的生物量和生产力。结果表明：东门林场１０年生尾叶桉人工林平均生物量为１４４．８５ｔ ｈｍ＾２,各器官生物量的在小序列为：干材（７１．６９％）〉根（１４．２１％）〉皮）７．９９％）〉枝（４．７１％）〉叶（４．７１％）〉叶（１．４０％     

High-resolution crystal structure reveals a HEPN domain at the C-terminal region of S. cerevisiae RNA endonuclease Swt1

Swt1 is an RNA endonuclease that plays an important role in quality control of nuclear messenger ribonucleoprotein particles (mRNPs) in eukaryotes; however, its structural details remain to be elucidated. Here, we report the crystal structure of the C-terminal (CT) domain of Swt1 from Saccharomyces cerevisiae, which shares common characteristics of higher eukaryotes and prokaryotes nucleotide binding (HEPN) domain superfamily. To study in detail the full-length protein structure, we analyzed the low-resolution architecture of Swt1 in solution using small angle X-ray scattering (SAXS) method. Both the CT domain and middle domain exhibited a good fit upon superimposing onto the molecular envelope of Swt1. Our study provides the necessary structural information for detailed analysis of the functional role of Swt1, and its importance in the process of nuclear mRNP surveillance.