甜菊叶愈伤组织诱导过程中叶绿体的超微结构变化

观察了甜菊(Stevia rebaudiana Bertoni)叶外植体愈伤组织诱导过程中叶绿体的超微结构变化。结果表明,当叶外植体转移到培养基上培养后,叶绿体的片层结构逐渐退化。在叶绿体发生退化的过程中伴有叶绿体出芽和原质体的形成。推测新产生的原质体来自叶绿体产生的芽状体。而叶绿体本身最后完全解体消失。叶绿体超微结构的这种变化与高度液泡化的叶肉细胞脱分化至分生状态是平行的。随着培养的进行,分生状态的细胞发生液泡化变为薄壁细胞时,在愈伤组织表层的细胞中,质体重新形成片层结构,而内部细胞的质体则充满淀粉粒。     

红花组织培养中细胞分化的超微结构研究

红花子叶脱分化及愈伤组织形成的超微结构研究揭示：处于脱分化过程中的细胞代谢极其活跃。贮藏的脂类在诱导的初期即被利用,伴随细胞脱分化的同时,叶绿体了同样经历一个脱分化的过程,内膜肿胀解体,同时质体分裂或出芽增殖。转移到分化培养基后,叶绿体细胞逐渐恢复,分化成熟,处于脱分化的细胞以及愈伤组织细胞中,常可以观察到处于质膜与细胞之间的所谓壁旁体的囊泡结构,对壁旁体可能的功能以及叶绿体脱分化的原因进行了讨论     

甜菊组织培养物中叶绿体的超微结构与脱分代

含有叶绿体的甜菊（Ｓｔｅｖｉａｒｅｂａｕｄｉａｎａ）愈伤组织细胞转移至新鲜培养基后,导致光合片层的逐渐减少或消失,最后叶绿体脱分化形成原质体样的结构。超微结构观察表明,光合片层的减少或消失与降解及叶绿体分裂特别是不均等缢缩分裂而致基质组分和类囊体膜稀释有关。这一过程并不完全同步,一些质体含有少量正常的片展而另一些质体含有退化的片层甚至片展结构完全消失。细胞的一个明显特点是细胞器大多聚集在细胞核附近,细胞质增加并向细胞中央伸出细胞质丝。同时可观察到原质体。培养７ｄ后,许多细胞呈分生状态,细胞质富含细胞器,充满了细胞的大部分空间。此时细胞中的质体大多呈原质体状态。在细胞生长的稳定期,质体内膜组织成基质基粒片层,同时质体核糖体增加。文中讨论了高度液泡化细胞脱分化与细胞中叶绿体脱分化的关系。     

沙冬青冬季叶绿体的超微结构特征

沙冬青在冬季的叶肉细胞中有丰富的叶绿体,经常聚集在一起,相互重叠,相互嵌合,有的还相互融合。大部分叶绿体为凸透镜形,其余叶绿体主要为Ｖ形,蝶形、连婴形和哑铃形。它被膜不光滑,常凹凸不平,甚至出现突起和内陷。类囊体十分发达,质体小球很多,但淀粉粒缺乏。大部分叶绿体形态结构正常,有的还在出芽和分裂。少数叶绿体与此不同,有的还在出芽和分裂。少数叶绿体与此不同,它们已经衰老,其中一些正在解体或已经解体。     

高度抗寒植物冬季线粒体的电镜观察

冬季沙冬青叶肉我线粒体相当丰富,常常位于叶绿体出芽和分裂处,在质膜大量内隐形成管状细胞的附近和含有颗粒状物质、膜状物质或特殊内含和的周围也随时可见了线粒体也经常与微体和叶绿体在一起。有时甚至还不同程度地被内多所包围。沙冬青叶肉细胞中的的线粒一般灯承圆形,被膜清晰完整,嵴丰富,基质电子度较高。有时基质中有小泡或电子密度很高的颗粒和内含物,个别线粒体的基质中学有类髓样体结构。文中讨论了沙冬青线粒体的形     

竹节海棠叶外植体脱分化启动的细胞学观察

竹节海棠叶外植体接种于MS+6-BA1ppm+NAA0.1ppm培养基上。外植体脱分化启动过程中,表皮及叶肉细胞主要以劈裂的无丝分裂方式进行分裂:最初核延伸为纺锤形,核仁大而明显,使整个核的轮廓呈“眼”状;随着核的中部出现裂缝,核断开成为两部分,稍后,由原来的母细胞形成两个子细胞。由于核分裂前向细胞中央移动的距离及断裂时断裂面的不同,从而造成细胞团内细胞大小悬殊及分裂面严重混乱的不等分裂现象。文中对栅栏组织细胞脱分化启动后重复进行无丝分裂形成梯状细胞团的现象也进行了讨论。     

甜菊组织培养物中叶绿体的超微结构与脱分化

含有叶绿体的甜菊愈伤组织细胞转移至亲鲜培养基后,导致光合片层的逐渐减少或消失,最后叶绿体脱分化形成原体样的结构。超微结构观察表明,光合片层的减少或消失与降解及叶绿体分裂特别是不均等缢缩分裂而致基质组分和类囊体膜稀释有关,这一过程并不完全同步,一些质体含有少量正常的片支厕国一些质体有退化的片层对片导全消失。细胞的一个明显特点是细胞器大多聚细胞核附近,细胞质增加并向细胞中央伸出细胞质丝,同时可观察到质     

番茄叶组织培养中愈伤组织形成和器官发生的细胞学和微形态学研究

以番茄叶外植体为材料,研究了不同的生长素和细胞分裂素及其浓度配比对叶外植体培养行为的影响;同时,利用细胞学和扫描电子显微镜技术观察了愈伤组织形成和器官发生过程。结果表明,不同种类及浓度配比的生长素和细胞分裂素直接影响愈伤组织的物理状态、大小和形成的速度以及器官分化的频率和速度。叶外植体切口处的叶肉细胞,维管薄壁细胞和维管束上方的少数叶肉细胞首先启动脱分化而开始分裂,这些细胞的活跃分裂和分化导致在外植体表层形成由薄壁细胞、维管组织和无分化状态的表层分生细胞团组成的愈伤组织。而不定芽则通过愈伤组织的薄壁细胞再次脱分化和再分化活动而形成,为“外起源”。认为存在由植物激素决定的“无分化活性”和“有分化活性”二种性质的愈伤组织。     

珊瑚豆果实成熟过程中叶绿体转化为杂色体的研究

珊瑚豆 (Solanum pseudo- capsicum var.diflorum (Vell.) Bitter)果实成熟过程中 ,果实颜色的变化和叶绿素含量降低及类胡萝卜素含量增长相符合。对果实中叶绿体转化为杂色体进行了电镜观察。早期绿色果实的特点是叶绿体具典型的基粒 -基粒间类囊体结构。在黄绿色果实时期叶绿体类囊体系统解体 ,代之以少数非叶绿素的单个类囊体和积累大的嗜锇的质体小球。质体转变为所谓的原质体。这表明叶绿体在果实成熟中的脱分化过程。当果实达到黄色阶段 ,这些质体所含的质体小球开始从中央形成质体小管的结构。最初质体小球中央变为半透明 ,认为是质体累积胡萝卜素的开始。随着质体小球的延长 ,小管从小球中伸出。这些小管围以电子致密的膜 ,中央是半透明的轴心。与此同时 ,在质体基质中出现一系列发育不同阶段的小泡 ,似乎是形成新的质体小球的过程。在成熟的橙色和橙红色果实中的杂色体中只包含无数小管和小的质体小球。质体小管在数量和长度上增长 ,充满成熟的杂色体。无数质体小球分布在小管之间的空间中。成熟杂色体从脱分化的原质体的重建是真正的再分化过程。可以作出结论 ,珊瑚豆果实叶绿体转化为杂色体实质上是一个脱分化和再分化过程     

玉米叶片细脉及其鞘细胞个体发育的超微结构研究

用透射电镜观察了玉米（ＺｅａｍａｙｓＬ．）叶片细脉原形成层及束鞘的起源,早期发育和超微结构,细脉及束鞘的发生与基本分生组织中层３个紧邻的细胞有关,位于中间的细胞发生平周分裂分别产生１个原形成层原的细胞,１个近轴端鞘细胞前体和１个远轴鞘细胞前体,位于两侧的细胞其中１个直接分化为侧向鞘细胞前体,另１个则经历１次垂周分裂产生另一侧向鞘细胞前体和１个叶肉细胞前体,后再分裂产生２个叶肉细胞,随着原形成层细     

ROLE OF MULTIPLE FTSZ RINGS IN CHLOROPLAST DIVISION UNDER OLIGOTROPHIC AND EUTROPHIC CONDITIONS IN THE UNICELLULAR GREEN ALGA NANNOCHLORIS BACILLARIS (CHLOROPHYTA,TREBOUXIOPHYCEAE)1

Chloroplasts of the unicellular green alga Nannochloris bacillaris Naumann cultured under nutrient‐enriched conditions have multiple rings of FtsZ, a prokaryote‐derived chloroplast division protein. We previously reported that synthesis of excess chloroplast DNA and formation of multiple FtsZ rings occur simultaneously. To clarify the role of multiple FtsZ rings in chloroplast division, we investigated chloroplast DNA synthesis and ring formation in cells cultured under various culture conditions. Cells transferred from a nutrient‐enriched medium to an inorganic medium in the light showed a drop in cell division rate, a reduction in chloroplast DNA content, and changes in the shape of chloroplast nucleoids as cells divided. We then examined DNA synthesis by immunodetecting BrdU incorporated into DNA strands using the anti‐BrdU antibody. BrdU‐labeled nuclei were clearly observed in cells 48 h after transfer into the inorganic medium, while only weak punctate signals were visible in the chloroplasts. In parallel, the number of FtsZ rings decreased from 6 to only 1. When the cells were transferred from an inorganic medium to a nutrient‐enriched medium, the number of cells increased only slightly in the first 12 h after transfer; after this time, however, they started to divide more quickly and increased exponentially. Chloroplast nucleoids changed from punctate to rod‐like structures, and active chloroplast DNA synthesis and FtsZ ring formation were observed. On the basis of our results, we conclude that multiple FtsZ ring assembly and chloroplast DNA duplication under nutrient‐rich conditions facilitate chloroplast division after transfer to oligotrophic conditions without further duplication of chloroplast DNA and formation of new FtsZ rings.     

FtsZ ring formation at the chloroplast division site in plants

Among the events that accompanied the evolution of chloroplasts from their endosymbiotic ancestors was the host cell recruitment of the prokaryotic cell division protein FtsZ to function in chloroplast division. FtsZ, a structural homologue of tubulin, mediates cell division in bacteria by assembling into a ring at the midcell division site. In higher plants, two nuclear-encoded forms of FtsZ, FtsZ1 and FtsZ2, play essential and functionally distinct roles in chloroplast division, but whether this involves ring formation at the division site has not been determined previously. Using immunofluorescence microscopy and expression of green fluorescent protein fusion proteins in Arabidopsis thaliana, we demonstrate here that FtsZ1 and FtsZ2 localize to coaligned rings at the chloroplast midpoint. Antibodies specific for recognition of FtsZ1 or FtsZ2 proteins in Arabidopsis also recognize related polypeptides and detect midplastid rings in pea and tobacco, suggesting that midplastid ring formation by FtsZ1 and FtsZ2 is universal among flowering plants. Perturbation in the level of either protein in transgenic plants is accompanied by plastid division defects and assembly of FtsZ1 and FtsZ2 into filaments and filament networks not observed in wild-type, suggesting that previously described FtsZ-containing cytoskeletal-like networks in chloroplasts may be artifacts of FtsZ overexpression.     

FtsZ在钝顶螺旋藻形态建成中的作用

为了研究细胞骨架蛋白FtsZ在螺旋藻形态建成中的作用,通过PCR克隆了ftsZ基因并进行原核表达,对表达的融合蛋白进行了纯化。通过免疫小鼠制备了FtsZ的多克隆抗体。分别用Western blot和免疫荧光技术检测螺旋藻不同形态藻丝体中ftsZ的表达和定位。结果表明,在两株不同螺旋藻Spirulina platensisFACHB869和FACHB882中,ftsZ在直线形藻丝体中的表达量都高于螺旋形藻丝体。免疫荧光定位结果显示,FtsZ蛋白在藻细胞中呈环状分布于细胞膜上,且这种环状结构在直线形藻丝体中排列较密而在螺旋形藻丝体中排列疏松。ftsZ在不同形态藻丝体中的表达量和细胞定位差异说明,细胞骨架蛋白FtsZ可能通过改变细胞刚性而参与螺旋藻形态建成。     

An integrated physiological and genetic approach to the dynamics of FtsZ targeting and organisation in a moss, Physcomitrella patens

Plant FtsZ (filamentous temperature-sensitive Z) proteins are regarded as descendants of prokaryotic cell division proteins. We could show previously that four FtsZ isoforms of the moss Physcomitrella patens assemble into, and interact in, distinct structures inside the chloroplasts and in the cytosol. Their organisation and localisation patterns indicate an involvement in chloroplast and cell division and in the maintenance of chloroplast shape and integrity. The cellular processes of chloroplast division and maintenance of chloroplast shape were disturbed either by application of the beta-lactam antibiotic ampicillin or by a mutation that presumably affects signal transduction of the plant hormone cytokinin. When cells of these plants were analysed microscopically, there was no indication that cytosolic functions of FtsZ proteins were affected. Furthermore, FtsZ proteins continued to build three-dimensional plastoskeleton networks, even in considerably enlarged or malformed chloroplasts. On the other hand, macrochloroplast formation promoted the localisation of FtsZ proteins in filaments that emanate from the plastids and, therefore, most likely represent stromules. Annular FtsZ structures that are regarded as essential components of the division apparatus were absent from macrochloroplasts of ampicillin-treated cells. Thus, the distribution of FtsZ proteins after inhibition of chloroplast division further strengthens our hypothesis on the functions of distinct isoforms. In addition, the results provide further insight into the regulation of protein targeting and dynamics of plastoskeletal elements.     

Plant FtsZ1 and FtsZ2 expressed in a eukaryotic host: GTPase activity and self-assembly

Plants and algae contain the FtsZ1 and FtsZ2 protein families that perform specific, non-redundant functions in plastid division. In vitro studies of chloroplast division have been hampered by the lack of a suitable expression system. Here we report the expression and purification of FtsZ1-1 and FtsZ2-1 from Arabidopsis thaliana using a eukaryotic host. Specific GTPase activities were determined and found to be different for FtsZ1-1 vs. FtsZ2-1. The purified proteins readily assembled into previously unreported assembly products named type-I and -II filaments. In contrast to bacterial FtsZ, the Arabidopsis proteins do not form bundled sheets in the presence of Ca²⁺.     

Chloroplast division in higher plants requires members of two functionally divergent gene families with homology to bacterial ftsZ.

The division of plastids is critical for viability in photosynthetic eukaryotes, but the mechanisms associated with this process are still poorly understood. We previously identified a nuclear gene from Arabidopsis encoding a chloroplast-localized homolog of the bacterial cell division protein FtsZ, an essential cytoskeletal component of the prokaryotic cell division apparatus. Here, we report the identification of a second nuclear-encoded FtsZ-type protein from Arabidopsis that does not contain a chloroplast targeting sequence or other obvious sorting signals and is not imported into isolated chloroplasts, which strongly suggests that it is localized in the cytosol. We further demonstrate using antisense technology that inhibiting expression of either Arabidopsis FtsZ gene (AtFtsZ1-1 or AtFtsZ2-1) in transgenic plants reduces the number of chloroplasts in mature leaf cells from 100 to one, indicating that both genes are essential for division of higher plant chloroplasts but that each plays a distinct role in the process. Analysis of currently available plant FtsZ sequences further suggests that two functionally divergent FtsZ gene families encoding differentially localized products participate in chloroplast division. Our results provide evidence that both chloroplastic and cytosolic forms of FtsZ are involved in chloroplast division in higher plants and imply that important differences exist between chloroplasts and prokaryotes with regard to the roles played by FtsZ proteins in the division process.     

Manipulation of starch granule size distribution in potato tubers by modulation of plastid division

Starch granule size is an important parameter for starch applications in industry. Starch granules are formed in amyloplasts, which are, like chloroplasts, derived from proplastids. Division processes and associated machinery are likely to be similar for all plastids. Essential roles for FtsZ proteins in plastid division in land plants have been revealed. FtsZ forms the so-called Z ring which, together with inner and outer plastid division rings, brings about constriction of the plastid. It has been shown that modulation of the expression level of FtsZ may result in altered chloroplast size and number. To test whether FtsZ is also involved in amyloplast division and whether this, in turn, may affect the starch granule size in crop plants, FtsZ protein levels were either reduced or increased in potato. As shown previously in other plant species, decreased StFtsZ1 protein levels in leaves resulted in a decrease in the number of chloroplasts in guard cells. More interestingly, plants with increased StFtsZ1 protein levels in tubers resulted in less, but larger, starch granules. This suggests that the stoichiometry between StFtsZ1 and other components of the plastid division machinery is important for its function. Starch from these tubers also had altered pasting properties and phosphate content. The importance of our results for the starch industry is discussed.     

Chloroplast division machinery as revealed by immunofluorescence and electron microscopy

The division of chloroplasts (plastids) is critical for the viability of photosynthetic eukaryotes. Previously we reported on the chloroplast division apparatus, which consists of inner and outer double or triple rings (PD rings). Chloroplasts are assumed to arise from bacterial endosymbionts, while bacterial division is instigated by a bacterial cytokinesis Z-ring protein (FtsZ). Here we present immunofluorescence and electron-microscopic evidence of chloroplast division via complex machinery involving the FtsZ and PD rings in the higher plant Pelargonium zonale Ait. Prior to invagination, the FtsZ protein was attached to a ring at the stromal division site. Following formation of the FtsZ ring, the inner stromal and outer cytosolic PD rings appeared, signifying the initiation of invagination. The FtsZ ring and the PD rings were found at the leading edge of chloroplast constriction throughout division. During chloroplast division, neither the FtsZ nor the inner rings changed width, but the volume of the outer ring gradually increased. We suggest that the FtsZ ring determines the division region, after which the inner and outer PD rings are formed as a lining for the FtsZ ring. With the outer ring providing the motivating force, the FtsZ and inner PD rings ultimately decompose to their base components.     

鹤望兰组织培养与工厂化快繁程序的研究

将材料接种于诱导愈伤组织手芽的培养基上,培养２个月后,胚芽外植体下出现白色颗粒状的愈伤组织,４个月后愈伤组织上出现小芽丛。将小芽丛转入不加植物激素的ＭＳ培养基上,芽的生长加快,２个月左右可长成３－６ｃｍ高的丛小植株。将小植株切下,插入根培养基中,一般３５ｄ左右基部突出很小的白色根尖。