ELIPs – Light-induced stress proteins

Exposure of plants to light intensities higher than those required to saturate photosynthesis leads to a reduction in photosynthetic capacity. This effect is known as photoinhibition. Photoinhibition is followed by destruction of carotenoids, bleaching of chlorophylls and increased lipid peroxidation due to damage by oxygen-derivatives. The oxygen concentration in chloroplasts in the light is high because of oxygen production by photosystem II (PSII). This can result in the release of reactive intermediates of reduced dioxygen such as superoxide radicals, hydroxyl radicals, hydrogen peroxide or singlet oxygen. In order to maintain their normal function under light stress conditions, chloroplasts have developed multiple repair and protection systems. The induction of specific light stress proteins, the ELIPs (for early light-induced proteins) can be considered to be part of these protective responses. The accumulation of ELIPs under light stress conditions is correlated with the photoinactivation of PSII, degradation of the D_l-protein of PSII reaction centre and changes in the level of pigments. Futhermore, the accumulation of ELIPs in the thylakoids is strictly controlled by the pigment content, especially by chlorophylls. Isolation of ELIPs in a native form and analysis of pigments bound to these proteins revealed that ELIPs can bind chlorophyll a and lutein. These data indicate that ELIPs might represent unique chlorophyll-binding proteins which have a transient function(s) during light stress. A transient 'pigment-carrier' function is postulated for ELIPs.     

Redox signalling and the structural basis of regulation of photosynthesis by protein phosphorylation

In photosynthesis in chloroplasts and cyanobacteria, redox control of thylakoid protein phosphorylation regulates distribution of absorbed excitation energy between the two photosystems. When electron transfer through chloroplast photosystem II (PSII) proceeds at a rate higher than that through photosystem I (PSI), chemical reduction of a redox sensor activates a thylakoid protein kinase that catalyses phosphorylation of light-harvesting complex II (LHCII). Phosphorylation of LHCII increases its affinity for PSI and thus redistributes light-harvesting chlorophyll to PSI at the expense of PSII. This short-term redox signalling pathway acts by means of reversible, post-translational modification of pre-existing proteins. A long-term equalisation of the rates of light utilisation by PSI and PSII also occurs: by means of adjustment of the stoichiometry of PSI and PSII. It is likely that the same redox sensor controls both state transitions and photosystem stoichiometry. A specific mechanism for integration of these short- and long-term adaptations is proposed. Recent evidence shows that phosphorylation of LHCII causes a change in its 3-D structure, which implies that the mechanism of state transitions in chloroplasts involves control of recognition of PSI and PSII by LHCII. The distribution of LHCII between PSII and PSI is therefore determined by the higher relative affinity of phospho-LHCII for PSI, with lateral movement of the two forms of the LHCII being simply a result of their diffusion within the membrane plane. Phosphorylation-induced dissociation of LHCII trimers may induce lateral movement of monomeric phospho-LHCII, which binds preferentially to PSI. After dephosphorylation, monomeric, unphosphorylated LHCII may trimerize at the periphery of PSII.     

Chloroplast genome differences between Paspalum dilatatum Poir and the related species P. notatum Flugge

 Chloroplast DNA (cpDNA) of Paspalum dilatatum and P. notatum was digested singly or in combination with the restriction endonucleases PstI, PvuII, SalI, KpnI and XhoI. Data obtained from filter hybridization experiments with barley and wheat cpDNA probes were used to construct restriction site maps of the chloroplast genomes of the Paspalum species. The cpDNA fragments were ordered into a circular configuration of approximately 139.3 kbp that contained two inverted repeat regions of approximately 23 kbp and a small and large single-copy region of approximately 11 kbp and 83 kbp, respectively. The cpDNA maps showed that P. dilatatum and P. notatum shared a large number of restriction sites with the proportion of shared restriction sites S=0.90. No restriction site differences were detected in the KpnI maps. Eight species-specific restriction site differences that could be used to identify the cytoplasm of each Paspalum species were identified in the PstI, PvuII, SalI, and XhoI cleavage maps. The overall structural organization of the Paspalum cpDNAs is rather similar to those of most cpDNAs from other plants. The results presented in this study will be of value for exploring further phylogenetic relationships within the genus Paspalum. Received: 27 February 1997 / Accepted: 7 March 1997     

Dynamics of localization and protein composition of plastid nucleoids in light-grown pea seedlings

Summary Localization and protein composition of plastid nucleoids was analyzed in light-grown pea seedlings at various stages of leaf development. In young plastids of unopened leaf buds, nucleoids were abundant and localized in the periphery of plastids, whereas, in mature leaves, chloroplasts contained nucleoids within narrow spaces restricted by thylakoids or grana. The migration of nucleoids into the interior of plastids preceded the formation of grana, and hence, the maturation of the photosynthetic apparatus. The protein composition of nucleoids was considerably different in young plastids and mature chloroplasts. Polypeptides with a molecular mass of 70–100 kDa predominated in the nucleoids of young plastids, whereas polypeptides with molecular mass of 20–30 kDa were abundant in the nucleoids of mature chloroplasts. Immuno-blot analysis with antibodies against the nucleoids of young plastids identified various polypeptides that were significantly more abundant in the nucleoids of young plastids than in the nucleoids of mature chloroplasts. These results demonstrate that plastid nucleoids are subject to dynamic changes in both localization and composition during the normal development of chloroplasts in the light.Abbreviations DAPI 4,6-diamidino-2-phenylindol - DiOC₆ 3,3-dihexyloxacarbocyanine iodide     

Chloroplast assemblage by mechanical stimulation and its intercellular transmission in diatom cells

Summary By touching a cell ofPleurosira laevis, a centric diatom, the chloroplasts in the cortical cytoplasm immediately migrate to the nuclear cytoplasm which is located at the center of the cell. The time required for migration, is about 10 s and that for restoration is about 15 min. The touch could be replaced by an electric stimulation. A 7 V pulse for 1 ms was required for the induction of chloroplast assemblage. To obtain chloroplast assemblage in 50% of the cells, the amount of time and voltage required were inversely proportional. Higher concentrations of KCl also induced chloroplast assemblage. Neither contact nor electric stimulation in Ca²⁺ free medium induced chloroplast assemblage. Verapamil, a Ca²⁺ channel blocker, in medium suppressed the chloroplast assemblage. Ca²⁺ ionophore caused the chloroplast assemblage. These results suggested that the depolarization of the plasma membrane was a trigger of the induction of chloroplast assemblage and the influx of Ca²⁺ to the cytoplasm through the channel was essential for this. The chloroplast assemblage was transmitted successively to the other cells of the filamentous colony, though these cells were linked only by a mucilaginous substance. Furthermore, the transmission occurred in cells which were placed separately. The maximum distance possible for this jumping transmission was 200 m in the culture medium. To search for the release of any chemical transmitter, contact stimulation was applied to one cell at the middle of a filamentous colony which was placed in water streaming along the axis of the filament. Chloroplast assemblage was induced more in downstream cells than in upstream ones. This result suggested the existence of some substance which mediated the transmission of the stimulation.     

Anatomy and ultrastructure of the sporophyte of Takakia ceratophylla (Bryophyta)

In this study, morphogenesis and structure of the sporophyte of Takakia ceratophylla are characterized beginning with the late embryo and culminating in the fully dehisced capsule. Information is presented on the development, ultrastructure, and anatomy of the three organographic regions of the sporophyte, namely capsule, seta, and foot. Diagnostic features that identify Takakia as a moss include the gradual elongation of seta, persistence of an apical calyptra, expansion of the capsule after cessation of seta elongation, existence of a columella, monoplastidic meiosis, spore ultrastructure (including a perine layer deposited late in spore wall (development), and the structure of the foot. Commonalities with the capsule of the Andreaeopsida include sporogenous tissue that overarchs a central columella, absence of stomata, and lack of a peristome and operculum. Peculiarities of the genus are seen in the internal structure of the capsule, the disintegration of the columella with spore maturation, and the dehiscence of the capsule along a single, spiralled, longitudinal suture line. Passive spore dispersal through longitudinal splitting of the capsule occurs in andreaeopsid mosses, liverworts, hornworts, and seedless vascular plants. The precise mechanism of dehiscence along a spiralled suture is unparalleled in extant archegoniates but finds counterparts in ancestral land plants such as the pteridophyte Tortilicaulis.     

高山植物盘花垂头菊和唐古特乌头光合膜系统的超微结构研究

对生长在青藏高原东北部海拔高度为3700m处的盆花垂头（Cremanthodiumdiscoideum）和唐古特乌头（Aconitumtangutcum）叶肉细胞叶绿体光合膜系进行超微分析表明：叶绿体被膜异常,基拉片层叠垛程度小,基粒和基质类囊体肿胀严重。叶绿体超微结构上的这些特征,是青藏高原低气压、严寒和强辐射等生态条件综合作用的结果。     

甜菊愈伤组织分生区细胞中膜内含物的超微结构研究

生长在分化培养基上的甜菊（Ｓｔｅｖｉａ ｒｅｂａｕｄｉａｎａ）愈伤组织分生区细胞中存在双膜和多膜内含物。电镜观察表明,这些膜内含物是由一圈或多圈呈同民贺或卷绕状排列的内质网包围部分细胞质而形成的。双膜内含物内外层膜的靠细胞质表面有核糖体附着,而多膜内含物仅在其最外层潴泡的外膜上偶有和量核糖体附着。附着细胞液泡化程度的提高,多膜内含物通过液泡膜内陷而转移到液泡中或通过消化其中被包围的细胞质及内膜而转     

抗菌肽CM4抗K562癌细胞的超微结构研究

报道了家蚕抗菌肽CM4抗K562癌细胞的体外实验研究.结果表明：纯化后的家蚕抗菌肽CM4对培养的K562(人髓样白血病细胞)有很强的杀伤作用.用扫描和透射电镜观察超微结构以及用激光共聚集显微断层图像分析,表明微量纯化的抗菌肽CM4能使K562癌细胞产生一系列的病理变化,可造成细胞高度肿胀,膜与胞质分离,细胞器和膜结构排列紊乱,细胞表面微绒毛消失,出现不规则的孔洞,细胞骨架严重破坏,膜局部结构破裂,缺损,胞浆内容物大量外泄,最终细胞解体,崩解成碎片.     

枸杞胚性细胞分化的超微结构和ATP酶的细胞化学定位研究

枸杞的胚性细胞多由愈伤组织表层的薄壁细胞分化而来,与愈伤组织中未分化的细胞相比,胚性细胞呈卵圆形,细胞核大,核仁明显,细胞质浓厚并含有丰富的细胞器,细胞壁较薄,细胞间有胞间连丝相通;胚性细胞发育到晚期细胞壁加厚,胞间连丝逐渐消失,细胞核向一端偏移,有大液泡形成;胚性细胞的第一次分裂多为均等分裂,形成二细胞原胚,继续分裂形成多细胞原胚;组成多细胞原胚胚体的细胞核大,核形状不规则,细胞质浓厚,细胞器丰富,在质体中出现淀粉的积累。在胚性细胞发育的早期,ATP酶活性主要位于质膜上,随后在液泡内和细胞核中都出现ATP酶活性的分布;随着胚性细胞壁的加厚,细胞壁加厚处和细胞间隙中也出现ATP酶活性反应;当多细胞原胚形成后,ATP酶活性反应主要定位于液泡膜上。由此分析了结构特征、ATP酶活性定位变化与胚性细胞分化的关系。