C_3植物的C_4光合途径

人类主要的粮食作物小麦、水稻、大豆等均为C_3植物,由于C_4光合途径显著优于C_3途径,因此,优化C_3作物拥有C_4光合途径特征的研究一直在探究中。综述了C_3植物的C_4光舍碳途径的发现、运行机制、诱发因素等,总结了改造C_3植物光合效率的方法并做了简单展望。     

C3、C4和C3-C4中间型植物的进化

介绍了有关C3、C4和C3-C4中间型植物进化的形态学、生理学、分子生物学、遗传学等方面的证据;推断地球上首先出现C3植物,然后是C3-C4中间类型植物,最后出现C4植物.     

C3植物中C4途径的研究进展

综述了C3植物中C4途径的发现及研究现状;阐述了C3植物中C4途径的几种作用机理;根据C3植物中C4途径的存在,探讨了改造C3植物的遗传特性;并展望了这一领域的研究前景。     

海北高寒草甸生态系统研究定位站没有发现C4植物——来自于稳定性碳同位素的证据

通过对海北高寒草甸生态系统研究站25个科、70个属、102种植物叶片的稳定性碳同位素的测定,以确定植物群落的光合型。结果表明,所测定的102种植物的稳定性碳同位素比值(δ^13C)介于-28．24‰和-24．84‰之间,说明这102种植物均属于C3植物,无C4植物或CAM植物。植物这种光合型的分布与该生态系统中的环境因子密切相关,是低温、强辐射等环境因素长期作用的结果,也反映了植物对这种特殊环境的适应。     

C3与C4植物的环境调控

环境条件决定着不同光合类型植物的地理分布范围和区域 ,一般来说 ,C4 植物分布于高温、强光的环境而 C3植物分布于阴凉、湿润的环境 ,且 C4 比 C3植物光合速率高。但环境条件影响着不同光合类型植物的光合潜能的发挥 ,C4 植物在高温、强光、干旱条件下所表现出来的优势在其它环境条件下未必就显现出来。环境条件甚至可以引起 C3、C4 光合途径间的相互转化 ,这使得目前几种鉴别植物光合类型的方法出现不一致的结果。因此 ,在判断植物的光合类型时 ,要注意多种手段的综合利用 ,同时注意植物所处环境条件的影响。     

差别分析方法在鉴别C3,C4植物中的应用——以中国东北样带（NECT） …

判别分析是多元统计分析中判断个体所属类型的一种重要方法。以中国东北样带（ＮＥＣＴ）作为研究平台,利用判别分析鉴别植物光合功能型。采用国际上先进的植物光合测定系统ＬＣＡ４便携式光合仪和ＣＩＤ－２０３便携式嘿面积仪在野外所测定的植物生理生态参,选取５１个来自Ｃ３功能群的植物种和１５个来自Ｃ４功能群的植物种构建判别模型,进行光合碳同化途径的判别。     

新的C4及CAM光合途径植物

以稳定性碳同位素比(δ~(13)C)鉴别禾本科、莎草科、苋科和萝摩科共46种植物的光合作用途径,发现了36种新的C_4植物(δ~(13)C-10.43到-13.66‰)和1种CAM植物(δ~(13)C-15.24‰)。根据Hattersley区分C_4植物三种亚类型的不同δ~(13)C值,提出在36种C_4中有8种具δ_(13)C值-10.4到-10.9‰者是NADP-ME型,6种具δ~(13)C值-13‰左右的是NAD-ME型,其余种类可能是NADP-ME或PCK型。     

几种C4和CAM植物光合亚途径的鉴别

C_4.植物鼠尾粟(Sporobolus indicus),金色狗尾草(Setaria glauca)、细叶结缕草(zoysia tenuifolia)、千金子(Leptochloa chinensis)和 CAM 植物芦荟(Aloe vera)属PEP 羧激酶亚型。C_4双子叶植物飞扬草(Euphorbia hirta)则为 NAD 苹果酸亚型。前面4种 PEP 羧激酶型的 C_4草本植物的维管束鞘细胞叶绿体呈均匀分布,与已知的该型的离心排列不同。认为这可为 C_4植物三种光合亚型的演化关系提供新的证据。     

花后干旱对冬小麦光合、抗氧化特性和C4光合酶活性的影响

干旱是限制小麦增产最主要的非生物胁迫之一。为探究不同抗旱性冬小麦品种对花后干旱的响应,本试验以干旱敏感型品种“京冬18”和抗旱型品种“农大211”为材料,调查了花后干旱及复水后冬小麦的旗叶光合特性、丙二醛含量、抗氧化酶活性、渗透调节物质含量以及各器官C4光合酶活性的变化。结果表明：花后干旱显著降低了“京冬18”的千粒重,而对“农大211”的千粒重无显著影响;与“京冬18”相比,“农大211”在干旱胁迫下叶片的SPAD值和净光合速率相对较高,F_v/F_m值相对稳定,丙二醛含量的增幅相对较小,SOD和POD活性及可溶性蛋白和脯氨酸含量的增幅相对较大;穗部(颖壳和籽粒)C4光合酶(PEPC、NADP-ME和PPDK)活性高于旗叶,且在干旱胁迫下被诱导增强;复水后,各项指标得到不同程度的恢复;相关分析表明,花后干旱下穗部C4光合酶活性增幅与旗叶脯氨酸含量及抗氧化酶活性增幅呈显著正相关。综上,花后干旱胁迫降低了小麦旗叶光合能力,加速了膜脂过氧化和叶绿素降解,最终影响到籽粒产量;抗旱性较强的品种在干旱胁迫下通过增强穗部C4光合酶活性、旗叶渗透调节及抗氧化能...     

C4水稻,我们的新挑战

自从上个世纪60年代末C4光合途径发现以来,人们对工程改造现有C3粮食作物使之具有C4光合能力进行了大量努力。目前,大量分子、生理和基因组水平研究的进展和证据表明,该目标将可能在10～15年之内实现。本综述结合目前国际C4研究的现状,详述了该领域目前所涉各项研究内容的理论依据。我们首先总结过去的经典杂交实验,然后论证新一代测序技术与C4光合研究模式系统狐尾草（Setaria viridis）的发展极大的促进了我们对C4光合特征遗传发育相关基因的发现与鉴定。最后,我们强调虽然C4光合工程改造的研究目前已在世界各国大规模展开,但其最终成功仍有赖于不同国家研究基金及私立慈善基金的大力和长期共同资助。     

贺谈老百岁华诞

谈家桢教授是国际著名遗传学家,我国现代遗传学的奠基人之一,他也是一位卓越的教育家和社会活动家。 1909年9月15日,谈家桢先生出生于浙江宁波。他就读于苏州东吴大学,1930年获理学学士学位。随后赴北京燕京大学攻读硕士学位,导师是我国现代遗传学奠基人之一的李汝祺教授,1932年获硕士学位。经导师推荐,谈家桢先生赴美国深造,师从当代遗传学宗师摩尔根,在遗传学家杜布赞斯基的指导下完成博士研究生学业,于1936年获美国加州理工学院哲学博士学位。     

Complement components C5 and C7: recombinant factor I modules of C7 bind to the C345C domain of C5

Studies reported over 30 years ago revealed that latent, nonactivated C5 binds specifically and reversibly to C6 and C7. These reversible reactions are distinct from the essentially nonreversible associations with activated C5b that occur during assembly of the membrane attack complex, but they likely involve some, perhaps many, of the same molecular contacts. We recently reported that these reversible reactions are mediated by the C345C (NTR) domain at the C terminus of the C5 alpha-chain. Earlier work by others localized the complementary binding sites to a tryptic fragment of C6 composed entirely of two adjacent factor I modules (FIMs), and to a larger fragment of C7 composed of its homologous FIMs as well as two adjoining short consensus repeat modules. In this work, we expressed the tandem FIMs from C7 in bacteria. The mobility on SDS-polyacrylamide gels, lack of free sulfhydryl groups, and atypical circular dichroism spectrum of the recombinant product rC7-FIMs were all consistent with a native structure. Using surface plasmon resonance, we found that rC7-FIMs binds specifically to both C5 and the rC5-C345C domain with K(D) approximately 50 nM, and competes with C7 for binding to C5, as expected for an active domain. These results indicate that, like C6, the FIMs alone in C7 mediate reversible binding to C5. Based on available evidence, we suggest a model for an irreversible membrane attack complex assembly in which the C7 FIMs, but not those in C6, are bound to the C345C domain of C5 within the fully assembled complex.     

Expression and characterization of the C345C/NTR domains of complement components C3 and C5

Complement components C3, C4, and C5 are members of the thioester-containing alpha-macroglobulin protein superfamily. Within this superfamily, a unique feature of the complement proteins is a 150-residue-long C-terminal extension of their alpha-subunits that harbors three internal disulfide bonds. Previous reports have suggested that this is an independent structural module, homologous to modules found in other proteins, including netrins and tissue inhibitors of metalloproteinases. Because of its distribution, this putative module has been named both C345C and NTR. To assess the structures of these segments of the complement proteins, their relationships with other domains, and activities as independent structures, we expressed C345C from C3 and C5 in a bacterial strain that permits cytoplasmic disulfide bond formation. Affinity purification directly from cell lysates yielded recombinant C3- and C5-C345C with properties consistent with multiple intramolecular disulfide bonds and high beta-sheet contents. rC5-, but not rC3-C345C inhibited complement hemolytic activity, and surface plasmon resonance studies revealed that rC5-C345C binds to complement components C6 and C7 with dissociation constants of 10 and 3 nM, respectively. Our results provide strong evidence that this binding corresponds to the previously described reversible binding of C5 to C6 and C7, and taken together with earlier work, indicate that the C5-C345C module interacts directly with the factor I modules in C6 and C7. The high binding affinities suggest that complexes composed of C5 bound to C6 or C7 exist in plasma before activation and may facilitate assembly of the complement membrane attack complex.     

Co-function of C3-and C4-photosynthetic pathways in C3, C4 and C3-C4 intermediate Flaveria species

The potential for C₄ photosynthesis was investigated in five C₃-C₄ intermediate species, one C₃ species, and one C₄ species in the genus Flaveria, using ¹⁴CO₂ pulse-¹²CO₂ chase techniques and quantum-yield measurements. All five intermediate species were capable of incorporating ¹⁴CO₂ into the C₄ acids malate and aspartate, following an 8-s pulse. The proportion of ¹⁴C label in these C₄ products ranged from 50–55% to 20–26% in the C₃-C₄ intermediates F. floridana Johnston and F. linearis Lag. respectively. All of the intermediate species incorporated as much, or more, ¹⁴CO₂ into aspartate as into malate. Generally, about 5–15% of the initial label in these species appeared as other organic acids. There was variation in the capacity for C₄ photosynthesis among the intermediate species based on the apparent rate of conversion of ¹⁴C label from the C₄ cycle to the C₃ cycle. In intermediate species such as F. pubescens Rydb., F. ramosissima Klatt., and F. floridana we observed a substantial decrease in label of C₄-cycle products and an increase in percentage label in C₃-cycle products during chase periods with ¹²CO₂, although the rate of change was slower than in the C₄ species, F. palmeri. In these C₃-C₄ intermediates both sucrose and fumarate were predominant products after a 20-min chase period. In the C₃-C₄ intermediates, F. anomala Robinson and f. linearis we observed no significant decrease in the label of C₄-cycle products during a 3-min chase period and a slow turnover during a 20-min chase, indicating a lower level of functional integration between the C₄ and C₃ cycles in these species, relative to the other intermediates. Although F. cronquistii Powell was previously identified as a C₃ species, 7–18% of the initial label was in malate+aspartate. However, only 40–50% of this label was in the C-4 position, indicating C₄-acid formation as secondary products of photosynthesis in F. cronquistii. In 21% O₂, the absorbed quantum yields for CO₂ uptake (in mol CO₂·[mol quanta]^-1) averaged 0.053 in F. cronquistii (C₃), 0.051 in F. trinervia (Spreng.) Mohr (C₄), 0.052 in F. ramosissima (C₃-C₄), 0.051 in F. anomala (C₃-C₄), 0.050 in F. linearis (C₃-C₄), 0.046 in F. floridana (C₃-C₄), and 0.044 in F. pubescens (C₃-C₄). In 2% O₂ an enhancement of the quantum yield was observed in all of the C₃-C₄ intermediate species, ranging from 21% in F. ramosissima to 43% in F. pubescens. In all intermediates the quantum yields in 2% O₂ were intermediate in value to the C₃ and C₄ species, indicating a co-function of the C₃ and C₄ cycles in CO₂ assimilation. The low quantum-yield values for F. pubescens and F. floridana in 21% O₂ presumably reflect an ineffcient transfer of carbon from the C₄ to the C₃ cycle. The response of the quantum yield to four increasing O₂ concentrations (2–35%) showed lower levels of O₂ inhibition in the C₃-C₄ intermediate F. ramosissima, relative to the C₃ species. This indicates that the co-function of the C₃ and C₄ cycles in this intermediate species leads to an increased CO₂ concentration at the site of ribulose-1,5-bisphosphate carboxylase/oxygenase and a concomitant decrease in the competitive inhibition by O₂.Abbreviations PEP phosphoenolpyruvate - PGA 3-phosphoglycerate - RuBP ribulose-1,5-bisphosphate     

低氧抑制C2C12细胞的体外分化

目的:研究低氧环境对C2C12细胞分化的影响,为探讨肌肉的发生和骨骼肌的损伤修复机理提供理论依据.方法:培养C2C12细胞,分别在常氧和低氧(3%O2)条件下诱导分化.免疫细胞化学方法检测成肌细胞终末分化的标志蛋白MI-IC(肌球蛋白重链)的表达;Western blot检测MHC以及MRFs(成肌调控因子)的表达.结果:在常氧条件下诱导分化的C2C12细胞融合形成肌管并表达MHC蛋白,而在低氧条件下培养的C2C12细胞几乎很少融合形成肌管并表达MHC蛋白;同时低氧下调了C2C12细胞中MRFs的表达.结论:低氧抑制了C2C12细胞的体外分化.     

Formation of Desacetylcephalosporin C in Cephalosporin C Fermentation

The origin of desacetylcephalosporin C in cephalosporin C fermentation broths was investigated. Esterase activity was detected in cell-free extracts of Cephalosporium acremonium, but these extracts failed to deesterify cephalosporin C. When cephalosporin C was added to sterile and inoculated fermentation media, the antibiotic decayed at nearly identical rates. The formation of desacetylcephalosporin C during the fermentation was measured by quantitative chromatography and by the incorporation of valine-1-(14)C into the molecule. The rate constants obtained from the results of these experiments were equivalent to those for the decay of cephalosporin C in sterile and inoculated media. The data demonstrate that desacetylcephalosporin C is produced by nonenzymatic hydrolysis of cephalosporin C.     

13C isotope fractionation during rhizosphere respiration of C3 and C4 plants

Stable carbon isotopes are used extensively to partition total soil CO₂ efflux into root-derived rhizosphere respiration or autotrophic respiration and soil-derived heterotrophic respiration. However, it remains unclear whether CO₂ from rhizosphere respiration has the same δ¹³C value as root biomass. Here we investigated the magnitude of ¹³C isotope fractionation during rhizosphere respiration relative to root biomass in six plant species. Plants were grown in a carbon-free sand-perlite medium inoculated with microorganisms from a farm soil for 62 days inside a greenhouse. We measured the δ¹³C value of rhizosphere respiration using a closed-circulation 48-hour CO₂ trapping method during 40~42 and 60~62 days after sowing. We found a consistent depletion in ¹³C (0.9~1.7‰) of CO₂ from rhizosphere respiration relative to root biomass in three C₃ species (Glycine max L. Merr., Helianthus annuus L. and Triticum aestivum L.), but a relatively large depletion in ¹³C (3.7~7.0‰) in three C₄ species (Amaranthus tricolor L., Sorghum bicolor (L.) Moench and Zea mays L. ssp. mays). Overall, our results indicate that CO₂ from rhizosphere respiration is more ¹³C-depleted than root biomass. Therefore, accounting for this ¹³C fractionation is required for accurately partitioning total soil CO₂ efflux into root-derived and soil-derived components using natural abundance stable carbon isotope methods.     

Genetics of complement C4. Two homoduplication haplotypes C4S C4S and C4F C4F in a family

Summary A family in which two homoduplicated C4 haplotypes (or supergenes) segregate is described. One haplotype C4F ^* 3 C4F ^*2.2 is composed of two C4F alleles and the other C4S ^* 5.1 C4S ^*1 of two C4S alleles. The C4F duplication haplotype is a partial inhibitor of the Rodgers antigen, and judged from our family and population material, it seems to be rather frequent and associated with HLAB ^*35, Bf ^* F, and HLAD/DR ^*1. The C4S duplication haplotype is Rg(a-) and is not identified in individuals without another S, Ch(a+) variant.This work was supported by grant No 12-1727 from the Danish Medical Research Council