低叶绿素b高产水稻突变体及其光合特性的研究

最近发现了一个在田间条件下自然产生的低叶绿素b高产水稻突变体(Oryza sativa L. cv.Zhenhui 249),该突变体主要降低了外周捕光天线复合体的含量.这种变化主要表现在叶片全展前后,到叶片发育后期则接近野生型.与以往所研究的突变体不同的是,该突变体叶绿素b含量仅适量减少,因而不影响类囊体膜的稳定性.突变体的光合机构在叶片一生中较稳定,这可能表明突变减少了光系统截获的光能,相对提高了光能的利用率,减少了O-2的产生.     

一个黄绿色水稻突变体的光合作用特性

本文报道一个黄绿色水稻突变体光合器官结构和功能的某些特点,该突变体是作者通过花药培养得到的细胞核突变体。突变体叶片的叶绿素含量、叶黄素和β-胡萝卜素含量分别约为正常叶片的30％、40％和75％;chl a/chl b比值显著高于正常叶片。对SDS增溶的叶绿体片层叶绿素蛋白质复合物分析表明,突变体的捕光chl a/chl b蛋白质复合物极度减少,该复合物的chl a/chl b比值大于3。突变体的叶绿体明显缺乏基粒堆积,在日光下容易较快积累淀粉粒。突变体的叶绿体悬液有较高的铁氰化钾光还原活性。在2万lux日照强度下,突变体叶片同化二氧化碳的速率,以单位叶面积计算为正常叶片的75％,以单位叶绿素计算为正常叶片的185％。结果证明,叶绿体基粒结构与捕光chl a/b蛋白质含量正相关,它并非为光合作用基本过程的进行所必需。     

铈对黄瓜叶绿体叶绿素蛋白质复合物形成的影响

黄瓜（Ｃｕｃｕｍ ｉｓｓａｔｉｖｕｓＬ．）叶片叶绿体中铈（Ｃｅ）含量随Ｈｏａｇｌａｎｄ 培养液中ＣｅＣｌ３ 浓度的增加而增加。Ｃｅ 对黄瓜叶片Ｃｈｌａ／ｂ 比值的影响与光强度有关,当植株生长在强光下,对照和处理叶片的Ｃｈｌａ／ｂ 比值均为３．０７;但在弱光下对照叶片的Ｃｈｌａ／ｂ 比值为２．７２,而处理叶片为２．８６。这说明只有在弱光下Ｃｅ才对叶片色素的组分有影响,Ｃｅ 使叶片中的Ｃｈｌｂ 略有下降。Ｃｅ能促进叶绿体光系统Ⅰ叶绿素蛋白质复合物及１１０ ｋＤ多肽的形成,并使捕光叶绿素ａ／ｂ 蛋白质复合物及其２７ ｋＤ多肽的含量减少。     

水稻叶绿体基粒缺乏突变体的叶绿素蛋白质复合体分析

我们曾报道一个细胞核隐性基因控制的黄绿色水稻突变体。其叶片的叶绿素含量仅为正常品种叶片的1/3,Chla:Chlb比值很高;叶绿体缺乏基粒,即基粒数和每一基粒的片层数均很少;但以叶绿素量为基数的光合活性较高。为了认识色素含量、基粒结构和光合功能之间相互关系,对正常品种和突变体叶绿体膜的叶绿素蛋白质复合体作了比较分析。结果表明,突变体缺乏24KD的捕光叶绿素a/b蛋白质复合体,但富有28KD的叶绿素a蛋白质复合体CPa。从试验结果推论,叶绿体片层的垛叠和捕光叶绿素a/b蛋白质复合体的含量有正的相关,非垛叠片层则富有叶绿素a蛋白质复合体CPa;     

欧洲3种常见乔木幼苗在两种光环境下叶片的气体交换、叶绿素含量和氮素含量

在室内测定了分别栽培于全光照和20％光照条件下的垂枝桦Betulapendula,欧洲水青冈Fagussylvatica和欧洲白栎Quercusrobur幼苗叶片的光合作用－光响应曲线、叶片气孔导度、胞间二氧化碳浓度、水分利用效率,叶绿素含量和氮素含量,并分析叶片叶绿素含量和净光合速率的回归关系．20％光照条件引起净光合速率的光饱和点下降,叶片气孔导度和水分利用效率以及单位叶面积叶绿素含量降低,叶片的光合物质积累减少,但氮素含量上升．回归分析结果表明,叶片叶绿素含量与净光合速率成正相关．3种植物的幼苗对荫蔽条件有一定的适应性,其中B．pendula和Q．robur的耐荫能力比Fsylvatica强.     

小麦旗叶黄化转绿突变体的生理分析及细胞学研究

叶色突变体是研究植物光合作用机理的理想材料。该研究以小麦旗叶黄化转绿突变体LF2090及其野生型H_261为材料,对其主要农艺性状、光合色素含量、光合参数和叶绿体超微结构进行比较分析。结果显示:突变体在旗叶黄化期叶绿素b含量显著降低,叶绿体结构基本正常,光合速率无显著变化;在旗叶转绿期,突变体叶绿素b相对含量提高,但各色素含量均显著下降,叶绿体内基粒大部分消失,细胞间CO_2浓度及光合速率均显著下降。研究表明,叶绿素a与叶绿素b间的比例变化导致突变体旗叶叶片颜色发生由黄转绿的变化;突变体LF2090旗叶气孔部分关闭是该突变体光合速率降低和农艺性状较差的主要原因,同时色素含量降低导致叶绿体结构的改变也影响着旗叶的光合效率。     

黄化油菜突变体Cr3529子叶类囊体膜光谱性质研究

以发育10d的黄化油菜突变体为材料,分析了突变体油菜子叶类囊体膜的色素含量、室温吸收光谱、叶绿素荧光发射和激发光谱以及蛋白内源荧光光谱的变化。数据显示：与野生型相比,突变体油菜子叶类囊体膜的光合色素Chl α和Chl b含量均减少．但Chl α／b比值升高;突变体油菜子叶类囊体膜叶绿素捕光能力和受激发能力均下降,且较依赖于Chl α捕光并将光能激发传递给PSⅡ反应中心;突变体油菜子叶类囊体膜的蛋白内源荧光也明显异于野生型。进一步表明突变体油菜子叶类囊体膜蛋白组成发生了改变。     

高粱浅绿叶突变体sll1的农艺性状和生理生化特性

通过EMS诱变野生型高粱BTx623种子获得浅绿叶突变体sll1(Sorghum Light-green Leaf 1)。以野生型BTx623为对照,进行成熟期农艺性状调查和苗期生理生化指标测定。结果表明,突变体sll1茎粗和穗柄长与BTx623相比没有显著差异,而株高、穗长、粒数和千粒重均低于BTx623,存在极显著差异,且抽穗期延迟15~20 d。苗期叶片叶绿素测定结果显示,突变体sll1叶绿素a、叶绿素b和总叶绿素含量均极显著低于BTx623,其中叶绿素b含量只有野生型的1/10,推测该突变体是叶绿素b减少型突变体。突变体sll1蛋白总量显著低于BTx623,但脯氨酸含量以及超氧化物歧化酶、过氧化物酶和过氧化氢酶活性均极显著高于BTx623,说明突变体sll1具有较强的渗透调节能力和清除活性氧的能力以维持自身正常生长。     

一个新的玉米黄绿叶突变体ygl-m的初步研究

在田间选育系谱过程中发现了一份黄绿叶突变体ygl-m,该突变体叶片在苗期自发地表现黄绿色,待植株长到6周大左右植株叶片开始恢复绿色,最后整个植株叶片都恢复正常的绿色。苗期ygl-m与野生型植株B73相比,叶片总叶绿素、叶绿素a、叶绿素b含量均显著下降,叶绿素a/b比值显著升高;苗期叶片叶绿体中基粒类囊体片层较少,排列不规则,结构松散。遗传分析表明,突变体ygl-m的黄绿叶表型由隐性单基因控制。本研究将为开展ygl-m基因的分子标记定位和进一步探讨其利用潜力奠定基础。     

杂交水稻及其亲本光合特性的研究 Ⅰ．功能叶片叶绿素含量、叶绿素－蛋白复合物及诱导荧光动力学

研究了杂交水稻青优１５９和广优四号及其亲本功能叶片的光合速率、叶绿素含量、叶绿素－蛋白复合物及诱导荧光动力学特性．这二个杂交水稻的光合速率分别高于其亲本,其超亲优势分别为１８．７２％和１８．２％,平均优势分别为２９．６％和２６．２％．杂交水稻功能叶片的叶绿素－蛋白复合物在６５０ｎｍ和６７５ｎｍ处光密度扫描峰面积具有明显的杂种优势,并与光合速率之间有较密切的正相关关系;叶绿素诱导荧光动力学特征参数Ｆｖ／Ｆｍ和Ｆｖ／Ｆｏ比值超过其高值亲本,具有杂种优势;杂交水稻功能叶片的叶绿素含量没有明显的杂种优势,光合速率与叶绿素含量之间没有明显的相关关系。而杂交水稻功能叶片的叶绿素ａ／ｂ比值均低于其亲本,并且叶绿素ａ／ｂ比值与光合速率呈较为密切负相关．     

Geminiviruses: a tale of a plasmid becoming a virus

Background  

Geminiviruses (family Geminiviridae) are small single-stranded (ss) DNA viruses infecting plants. Their virion morphology is unique in the known viral world – two incomplete T = 1 icosahedra are joined together to form twinned particles. Geminiviruses utilize a rolling-circle mode to replicate their genomes. A limited sequence similarity between the three conserved motifs of the rolling-circle replication initiation proteins (RCR Reps) of geminiviruses and plasmids of Gram-positive bacteria allowed Koonin and Ilyina to propose that geminiviruses descend from bacterial replicons.     

Testing a Primary and a Secondary Endpoint in a Group Sequential Design

Summary We consider a clinical trial with a primary and a secondary endpoint where the secondary endpoint is tested only if the primary endpoint is significant. The trial uses a group sequential procedure with two stages. The familywise error rate (FWER) of falsely concluding significance on either endpoint is to be controlled at a nominal level α. The type I error rate for the primary endpoint is controlled by choosing any α‐level stopping boundary, e.g., the standard O'Brien–Fleming or the Pocock boundary. Given any particular α‐level boundary for the primary endpoint, we study the problem of determining the boundary for the secondary endpoint to control the FWER. We study this FWER analytically and numerically and find that it is maximized when the correlation coefficient ρ between the two endpoints equals 1. For the four combinations consisting of O'Brien–Fleming and Pocock boundaries for the primary and secondary endpoints, the critical constants required to control the FWER are computed for different values of ρ. An ad hoc boundary is proposed for the secondary endpoint to address a practical concern that may be at issue in some applications. Numerical studies indicate that the O'Brien–Fleming boundary for the primary endpoint and the Pocock boundary for the secondary endpoint generally gives the best primary as well as secondary power performance. The Pocock boundary may be replaced by the ad hoc boundary for the secondary endpoint with a very little loss of secondary power if the practical concern is at issue. A clinical trial example is given to illustrate the methods.     

Vegetation as a component of a non-nested hierarchy: a conceptual model

Abstract. A general conceptual model of vegetation based on hierarchy theory is presented. The model emphasizes that prediction of vegetation requires consideration of both mechanisms of vegetation change and the constraints within which it occurs. The mechanisms of vegetation change are the responses to and effects upon their surroundings of individual plants. The most general constraints upon vegetation are aspects of the environment not affected by vegetation over successional time, and the pool of species within dispersal range. Examples of such environmental factors include macroclimate and soil parent material. In some cases, vegetation may alter important labile environmental factors such as soil nutrient and water availability. Some vegetation compositions appear to be resistant to changes in the general constraints. Due to both sources, there are multiple possible vegetation compositions given the same general constraints. Disturbance is defined as an abrupt change in the constraints on the vegetation resulting in a change in the vegetation's state or dynamics. Both the recognition of disturbance and the distinction between independent and labile environmental factors depend on the spatial and temporal scale of observation. For example, a particular wildfire at a given stand may be a disturbance, whereas at a larger scale of observation the same event may contribute to the wildfire regime, part of the constraints at that scale. Similarly, levels of soil organic matter may constrain vegetation over short time scales, due to influencing availability of water and nutrients. Over long time scales, the vegetation itself is a primary determinant of soil organic matter content. This model contains elements of both the initial, holistic theory of vegetation and recent, reductionistic approaches. It reiterates the need to considerboth mechanisms and constraints, stressed by contemporary and earlier workers. Hierarchy theory provides new insights concerning sufficient conditions for prediction, possible limits on predictability, and appropriate research strategy.     

Heating of a Local Region of a Branching Streamer as a Starting Point of a Space Leader and a Negative-Leader Step

Plasma Physics Reports - Localized plasma formations called space leaders are observed in streamer coronas of negative leaders of long laboratory sparks. The main leader completes a step when the...     

Transformation of a psychrotrophic bacterium with a plasmid from a mesophile

The psychrotrophic bacteriumBacillus psychrophilus was transformed with the broadhost-range plasmid pC194. The ability of the transformant to express chloramphenicol (CAM) resistance and the possible effects of such expression on the physiology of the psychrotroph were examined. The transformant exhibited growth rates, filament formation at elevated temperatures, synthesis of cold shock proteins and cold acclimation proteins, similar to the parentalB. psychrophilus.