不同类型玉米发育籽粒中淀粉合成及相关酶活性比较

以普通玉米、爆裂玉米、甜玉米和糯玉米为试材,分析和比较不同类型的玉米品种之间籽粒发育过程中淀粉合成及相关酶活性的变化。结果表明,淀粉合成速率和蔗糖合成酶(SS)、可溶性淀粉合成酶(SSS)、束缚态淀粉合成酶(GBSS)、淀粉分支酶(SBE)、去分支酶(DBE)活性都呈单峰曲线变化。30～40 DAP,普通玉米的SS活性显著高于其他3种类型;类型间平均和最大SSS活性水平的顺序为普通玉米>糯玉米>爆裂玉米>甜玉米;30～40 DAP,普通玉米GBSS活性最高,糯玉米GBSS活性最低;20～40 DAP,糯玉米SBE活性最高;甜玉米的DBE活性很低,并且在40 DAP完全丧失。淀粉合成速率与SS、SSS、GBSS和SBE活性相关程度比较高,与腺苷二磷酸葡萄糖焦磷酸化酶(AGP酶)和DBE活性相关不显著。推测AGP酶虽然为淀粉合成提供直接前体ADPG,但可能SS活性过低致使其限速作用比AGP酶的还强,AGP酶潜在的限速作用无法表现,SS成为玉米籽粒淀粉合成的限速因子。GBSS对直链淀粉积累起重要的促进作用;SSS和SBE对支链淀粉积累起重要的促进作用。     

鲜食糯玉米采后糖代谢相关酶活性变化

鲜食糯玉米采后腺苷二磷酸葡萄糖焦磷酸化酶（ADPGPPase）、尿苷二磷酸葡萄糖焦磷酸化酶（UDPGPPase）、束缚态淀粉合成酶（GBSS）、淀粉脱分支酶（DBE）等活性均呈现单峰曲线变化,第1～2天出现峰值然后略有下降;可溶性淀粉合成酶（SSS）活性呈较大幅度上升趋势,活性远高于采收初期;淀粉分支酶（SBE）在第3天出现极高峰值。与20℃贮藏温度相比,采后0℃低温贮藏可增强UDPGPPase活性,促进蔗糖降解;降低SSS和GBSS活性,延缓淀粉合成进程;抑制SBE活性,增强DBE活性,促进直链淀粉生成。     

玉米种子发育过程中直链淀粉积累规律的分析

淀粉是玉米种子的主要组成成分,它包括直链淀粉和支链淀粉。支链淀粉的合成需要淀粉合成酶、分支酶和脱支酶的共同作用,而直链淀粉的合成则是在颗粒结合型淀粉合成酶的作用下进行的。颗粒结合型淀粉合成酶基因的突变造成玉米种子的腊质（糯性）表型。与支链淀粉合成的分子机制的研究相比,目前对玉米种子中直链淀粉合成的分子机制了解相对较少。以野生型黄早4玉米自交系和突变体糯玉米为实验材料,研究了种子不同发育时期直链淀粉的积累规律。通过碘染色的方法,观察了玉米种子发育过程中淀粉积累的形态变化。定量分析表明,从授粉后10d至25d,黄早4种子中直链淀粉的含量逐渐增加,同时颗粒结合型淀粉合成酶（GBSS）的活性逐渐提高;而在糯玉米中,直链淀粉和GBSS活性均未检测到。进而,通过RT-PCR方法,从黄早4种子中分离出编码GBSSI的cDNA片段。在授粉后10d至25d的玉米胚乳中均可检测到GBSSI的表达,而在胚中直到授粉后25d才检测到该基因表达的微弱信号。在糯玉米种子中没有检测到该基因的表达。研究结果表明,在玉米种子发育过程中,GBSSI基因的表达通过控制GBSS的合成,最终控制直链淀粉的合成。研究工作为理解玉米种子中直链淀粉合成的分子机制提供了重要信息。     

淀粉分支酶和去分支酶编码基因的功能

淀粉分支酶(SBE)和淀粉去分支酶(DBE)是直接参与淀粉生物合成的5类酶中的2类分支点形成支链淀粉,后者水解葡萄糖苷链中α(1-6)糖苷键.文章概述了已克隆的编码SBE和DBE同种型编码基因及其在体内外的表达特征,并提出DBE多聚体酶的结构和功能将成为淀粉粒起始形成研究中的起点,SBEⅠ和SBEⅡ表达调控是支链淀粉分子改良的途径的看法.     

淀粉含量不同的玉米自交系籽粒淀粉积累及其关键酶活性

以2个高淀粉和2个低淀粉玉米自交系为材料,分析了玉米籽粒淀粉的动态积累规律,同时对高低淀粉玉米籽粒灌浆过程中淀粉生物合成关键酶活性的动态变化及其与淀粉积累动态的相关性进行讨论分析。研究结果表明:灌浆过程中4个自交系淀粉含量变化趋势均呈sigmoid型曲线。灌浆过程中ADPG-PPase(腺苷二磷酸葡萄糖焦磷酸化酶)、SSS(可溶性淀粉合成酶)、GBSS(颗粒结合淀粉合成酶)活性均呈单峰曲线变化,峰值都出现在20～30DAP(授粉后天数)。2个高淀粉自交系的Q酶(淀粉分支酶)活性也呈单峰曲线变化,峰值也出现在20DAP,而2个低淀粉自交系的Q酶活性则呈双峰曲线变化,2个峰值分别出现在15～20DAP和30～35DAP。4个自交系籽粒淀粉的积累速率与各自交系ADPG-PPase、SSS和GBSS的活性变化呈极显著正相关。各自交系关键酶活性之间,ADPG-PPase、SSS和GBSS三者间活性变化呈极显著正相关,这3种酶活性变化与Q酶活性变化也呈不同程度的正相关。     

玉米灌浆期水分差异供应对籽粒淀粉积累及其酶活性的影响

利用普通玉米(Zay mays)‘掖单22’和高油玉米‘高油115’,研究了灌浆期水分差异供应对籽粒淀粉及其组分积累、相关酶活性动态变化的影响。结果表明,两种类型玉米淀粉积累和酶活性动态变化趋势基本一致,但对水分的反应有差异。缺水提高了‘掖单22’籽粒中淀粉、支链淀粉含量,而直链淀粉含量下降,‘高油115’则是籽粒中的淀粉含量、支链淀粉和直链淀粉含量提高;充分供水使淀粉及其组分产量提高;叶片中蔗糖合成酶(SS)、磷酸蔗糖合成酶(SPS)活性随水分供应水平而提高,尤其在授粉后10~30 d增幅更加明显。充分供水明显提高籽粒中腺苷二磷酸葡萄糖焦磷酸化酶(ADPG-PPase)、尿苷二磷酸葡萄糖焦磷酸化酶(UDPG-PPase)、可溶性淀粉合成酶(SSS)和淀粉粒结合淀粉合成酶(GBSS)活性,缺水使籽粒中酶活性下降较早且迅速;SPS、ADPG-PPase、SSS酶活性对缺水反应比较敏感。     

作物淀粉生物合成与转基因修饰研究进展

淀粉是高等植物中碳水化合物的主要贮藏形式 ,也是粮食作物产品的最主要成分。淀粉虽然都由直链淀粉和枝链淀粉组成 ,但在不同作物中两者的比例和枝链淀粉结构的存在很大差异。现已明确 ,直链淀粉是在颗粒结合淀粉合成酶 (granule boundstarchsynthase,GBSS)催化下合成的 ,而枝链淀粉是四种酶共同作用的结果 ,它们分别是腺嘌呤 -葡萄糖焦磷酸化酶 (ADP glucosepyrophosphorylase ,AGP) ,可溶性淀粉合成酶 (solublestarchsynthase ,SSS) ,淀粉分枝酶 (starchbranchingenzyme ,SBE)和脱分枝酶 (starchdebranchingenzyme ,DBE)。一方面 ,在不同作物中 ,这些酶本身存在多种形式 ,如在玉米胚乳中 ,AGP有大亚基和小亚基之分 ,SBE又可分BE1,BEIIa ,BEIIb 3种 ,SSS也可分为SSI和SSIII(或SSIIa)两种 ,而DBE也有异淀粉酶 (isoamylase)和限制性糊精酶 (pullu lanase)两种。另一方面 ,控制特定酶的基因 ,在不同作物甚至在同一种作物的不同品种中也可能存在不同的复等位基因 ,如籼稻和粳稻的GBSS分别由蜡质基因Wxa 和Wxb 控制 ,两者编码的GBSS活性差异显著。此外 ,环境条件也可通过影响基因的转录使酶的含量或催化性能发生变化。迄今 ,国内外已获得多种马铃薯和水稻的转基因材料 ,对淀粉合成进行修饰 ,试图培育优质品     

两种穗型冬小麦籽粒淀粉积累动态及其有关酶活性变化

花后25d内,大穗型品种豫麦66籽粒中淀粉积累比多穗型品种豫麦49慢,但花后25d后情况则相反。2个品种籽粒中淀粉积累速率的变化均呈单峰曲线,豫麦49峰值出现在花后15～20d,而豫麦66峰值则出现在花后20～25d。灌浆期豫麦66和豫麦49籽粒中蔗糖合成酶(SS)活性变化呈单峰曲线,峰值分别出现在花后20d和15d,整个灌浆期内豫麦66籽粒中SS活性高于豫麦49;2个品种籽粒中腺苷二磷酸葡萄糖焦磷酸化酶(AGPP)和淀粉分支酶(SBE)活性变化均呈单峰曲线,峰值出现在花后20d,而可溶性淀粉合成酶(SSS)活性变化则呈双峰曲线,峰值分别出现在花后10d和20d,且第二个峰值显著高于第一个。相关分析表明,SS、AGPP、SSS和SBE是影响小麦籽粒淀粉积累的关键酶。     

RNAi沉默淀粉分支酶基因SEEI对玉米直链淀粉合成的影响

淀粉分支酶(SBE)是淀粉合成的限速酶.为了研究SBEI沉默对直链淀粉合成的影响,克隆了玉米(Zea mays)淀粉分支酶SBEI基因片段,构建了S8EI的RNAi表达载体pBAC418,用基因枪将其导入玉米自交系幼胚愈伤组织,经木糖筛选获得了7株转化再生植株.利用FAD2 intron和xylA基因探针对T<,0>代再生玉米植株进行DNA dot blot和PCR-Southern检测,证实5株为阳性植株,其中4株正常结实.SBEI基因沉默对阳性再生玉米株系籽粒的含油量没有显著影响;蛋白质含量显著高于受体对照;总淀粉含量与对照相比无显著差异,转基因株系直链淀粉含量平均提高了9.8%.     

RNAi沉默淀粉分支酶基因SBEI对玉米直链淀粉合成的影响

淀粉分支酶(SBE)是淀粉合成的限速酶。为了研究SBEI沉默对直链淀粉合成的影响, 克隆了玉米(Zea mays)淀粉分支酶SBEI基因片段, 构建了SBEI的RNAi表达载体pBAC418, 用基因枪将其导入玉米自交系幼胚愈伤组织, 经木糖筛选获得了7株转化再生植株。利用FAD2 intron和xylA基因探针对T₀代再生玉米植株进行DNA dot blot和PCR-Southern检测, 证实5株为阳性植株, 其中4株正常结实。SBEI基因沉默对阳性再生玉米株系籽粒的含油量没有显著影响; 蛋白质含量显著高于受体对照; 总淀粉含量与对照相比无显著差异, 转基因株系直链淀粉含量平均提高了9.8%。     

Spectral karyotyping of the human colon cancer cell lines SW480 and SW620

The cell lines SW480 and SW620, derived from different stages of colon carcinoma in the same patient, have been used for a number of biochemical, immunological, and genetic studies on colon cancer. A comparative analysis of their karyotypes may identify chromosomal aberrations that might represent markers for metastatic spread. In the present study spectral karyotyping (SKY) was applied to these two colon cancer cell lines. Compared to previously reported G-banded karyotypes, 9 (SW480) and 7 (SW620) markers were identical, 3 (SW480) and 3 (SW620) markers could be redefined, 5 (SW480) and 8 (SW620) markers were newly identified, and 4 (SW480) and 5 (SW620) of the previous described markers could not be confirmed. The redefined aberrations include very complex rearrangements, such as a der(16) t(3;16;1;16;8;16; 1;16;10) and a der(18)t(18;15;17)(q12; p11p13;??) in SW620 and a der(19)t(19;8;19;5) in SW480, that have not been identified by conventional banding techniques. The resulting chromosome gains (5q11-->5q15, 7pter-->q22, 11, 13q14-->qter, 20pter-->p12, X) and losses (8pter-->p2, 18q12-->qter, Y) found in both SW480 and SW620 were in good agreement with those frequently described in colorectal tumors as primary changes in the stem cell. Abnormalities found exclusively in SW620 cells only (gains of 5pter-->5q11, 12q12-->q23, 15p13-->p11, and 16q21-->q24 and losses of 2pter-->2p24, 4q28-->qter, and 6q25-->qter) can be viewed as changes that occurred in a putative metastatic founder cell.     

华西南十字花科新分类群

本文发表了十字花科2新种1新变种:巴郎山葶苈Draba balangshanica W.T.Wang, 泸定葶苈D.ludiugensis W.T.Wang, 小花毛果拟南芥Arabidopsis lasiocarpa var.micrantha W.T.Wang.     

A multiple adapter for the SW 25 rotor

An easily made adapter whose use increases threefold the analytical capacity of the Spinco SW 25 rotor is described. Two types of commercially available polypropylene tube can be used with the adapters. The SW 25 rotor can be loaded with three adapters carrying in all nine 4.8 ml tubes with 4.4 ml sucrose gradients or with a combination of adapters and standard 34 ml SW 25 cellulose nitrate tubes containing 25 ml gradients. Resolution of total E. coli RNA in the 4.4 ml (50–100 μg RNA) and 25 ml (500–1000 μg RNA) gradients is equivalent.     

Holocene carbon burial by lakes in SW Greenland

The role of the Arctic in future global change processes is predicted to be important because of the large carbon (C) stocks contained in frozen soils and peatlands. Lakes are an important component of arctic landscapes although their role in storing C is not well prescribed. The area around Kangerlussuaq, SW Greenland (66–68°N, 49–54°W) has extremely high lake density, with ∼20 000 lakes that cover about 14% of the land area. C accumulation rates and standing stock (kg C m⁻²), representing late- to mid-Holocene C burial, were calculated from AMS ¹⁴C-dated sediment cores from 11 lakes. Lake ages range from ∼10 000 cal yr  bp to ∼5400 cal yr  bp , and reflect the withdrawal of the ice sheet from west to east. Total standing stock of C accumulated in the studied lakes for the last ∼8000 years ranged from 28 to 71 kg C m⁻², (mean: ∼42 kg C m⁻²). These standing stock determinations yield organic C accumulation rates of 3.5–11.5 g C m⁻² yr⁻¹ (mean: ∼6 g C m⁻² yr⁻¹) for the last 4500 years. Mean C accumulation rates are not different for the periods 8–4.5 and 4.5–0 ka, despite cooling trends associated with the neoglacial period after 4.5 ka. We used the mean C standing stock to estimate the total C pool in small lakes (<100 ha) of the Kangerlussuaq region to be ∼4.9 × 10¹³ g C. This C stock is about half of that estimated for the soil pool in this region (but in 5% of the land area) and indicates the importance of incorporating lakes into models of regional C balance at high latitudes.     

Defective triglyceride biosynthesis in CETP-deficient SW872 cells

We previously reported that reducing the expression of cholesteryl ester transfer protein (CETP) disrupts cholesterol homeostasis in SW872 cells and causes an ∼50% reduction in TG. The causes of this reduced TG content, investigated here, could not be attributed to changes in the differentiation status of CETP-deficient cells, nor was there evidence of endoplasmic reticulum (ER) stress. In short-term studies, the total flux of oleate through the TG biosynthetic pathway was not altered in CETP-deficient cells, although mRNA levels of some pathway enzymes were different. However, the conversion of diglyceride (DG) to TG was impaired. In longer-term studies, newly synthesized TG was not effectively transported to lipid droplets, yet this lipid did not accumulate in the ER, apparently due to elevated lipase activity in this organelle. DG, shown to be a novel CETP substrate, was also inefficiently transferred to lipid droplets. This may reduce TG synthesis on droplets by resident diacylglycerol acyltransferase. Overall, these data suggest that the decreased TG content of CETP-deficient cells arises from the reduced conversion of DG to TG in the ER and/or on the lipid droplet surface, and enhanced TG degradation in the ER due to its ineffective transport from this organelle.