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1.
The division of chloroplasts in Trebouxia potteri was studiedby electron microscopy. At the beginning of chloroplast division,vesicles with fine fibrils (FVs) and ER attach to the isthmusof the chloroplast. Then, filaments appear around the isthmusparallel to the direction of constriction and seem to contractin order to decrease the diameter of the isthmus. It is suggestedthat the FVs are involved in the formation of the filamentsand that the ER is involved in the contraction of the filaments.At the final stages of the division of the chloroplast, thefilaments decompose. FVs are partially surrounded and decomposedby lysosomal sheets. For the next cycle of division of the chloroplast,the recovery of substances from decomposed filaments by functionalFVs seems a realistic possibility. chloroplast division, division apparatus, division cycle, transmission electron microscopy, Trebouxia potteri 相似文献
2.
Division of Chloroplasts in a Green Alga, Trebouxia potteri 总被引:1,自引:0,他引:1
The division of chloroplasts in Trebouxia potteri was studiedby electron microscopy. At the beginning of chloroplast division,vesicles with fine fibrils (FVs) and ER attach to the isthmusof the chloroplast. Then, filaments appear around the isthmusparallel to the direction of constriction and seem to contractin order to decrease the diameter of the isthmus. It is suggestedthat the FVs are involved in the formation of the filamentsand that the ER is involved in the contraction of the filaments.At the final stages of the division of the chloroplast, thefilaments decompose. FVs are partially surrounded and decomposedby lysosomal sheets. For the next cycle of division of the chloroplast,the recovery of substances from decomposed filaments by functionalFVs seems a realistic possibility. chloroplast division, division apparatus, division cycle, transmission electron microscopy, Trebouxia potteri 相似文献
3.
The division of chloroplasts in a green alga, Pediastrum duplex,was studied by electron microscopy. Cells were treated for observationwith the freeze-substitution method. Fibrils, or fibrous belts,which we had observed previously at the dividing constrictionsof chloroplasts in Trebouxia potteri were not visible in Pediastrum,even though the method of preparation was the same for bothsets of samples. Microtubules (MTs) and the septum seem notto participate directly in the division of the single chloroplastin Pediastrum cells. Many thin fibrils, 720 nm in diameter,attached to, or protruding from, the surface of the dividingconstriction were seen. These fibres were less densely distributedat the constrictions of non-dividing chloroplasts. It is suggestedthat these fibrils are involved in the divison of chloroplastsin Pediastrum duplex. Cell wall, chloroplast division, freeze-substitution, intermediate fibres, Pediastrum duplex, transmission electron microscopy 相似文献
4.
Fujiwara MT Hashimoto H Kazama Y Abe T Yoshida S Sato N Itoh RD 《Plant & cell physiology》2008,49(3):345-361
Chloroplast division comprises a sequence of events that facilitatesymmetric binary fission and that involve prokaryotic-like stromaldivision factors such as tubulin-like GTPase FtsZ and the divisionsite regulator MinD. In Arabidopsis, a nuclear-encoded prokaryoticMinE homolog, AtMinE1, has been characterized in terms of itseffects on a dividing or terminal chloroplast state in a limitedseries of leaf tissues. However, the relationship between AtMinE1expression and chloroplast phenotype remains to be fully elucidated.Here, we demonstrate that a T-DNA insertion mutation in AtMinE1results in a severe inhibition of chloroplast division, producingmotile dots and short filaments of FtsZ. In AtMinE1 sense (overexpressor)plants, dividing chloroplasts possess either single or multipleFtsZ rings located at random intervals and showing constrictiondepth, mainly along the chloroplast polarity axis. The AtMinE1sense plants displayed equivalent chloroplast phenotypes toarc11, a loss-of-function mutant of AtMinD1 which forms replicatingmini-chloroplasts. Furthermore, a certain population of FtsZrings formed within developing chloroplasts failed to initiateor progress the membrane constriction of chloroplasts and consequentiallyto complete chloroplast fission in both AtMinE1 sense and arc11/atminD1plants. Our present data thus demonstrate that the chloroplastdivision site placement involves a balance between the opposingactivities of AtMinE1 and AtMinD1, which acts to prevent FtsZring formation anywhere outside of the mid-chloroplast. In addition,the imbalance caused by an AtMinE1 dominance causes multiple,non-synchronous division events at the single chloroplast level,as well as division arrest, which becomes apparent as the chloroplastsmature, in spite of the presence of FtsZ rings. 相似文献
5.
The number and distribution pattern of dictyosomes in cellsof a green alga,Closterium ehrenbergii, were examined by fluorescencemicroscopy. Dictyosomes absorbed the fluorescent dye, DiOC6(3) intensely, and strongly radiated fluorescent light. Dictyosomeswere distributed in the cytoplasm along the longitudinal chloroplast-ridges.They began to divide synchronously at a premitotic stage whenthe chloroplast started to divide, and duplicated in numberbefore the cell divided by a transverse septum. Approximatelythe same number of dictyosomes entered each daughter cell. Thedictyosomes never migrated freely in the cytoplasm but migrateda short distance after division. Cell cycle; Closterium ehrenbergii; division of dictyosomes; fluorescence microscopy; Golgi apparatus; vital staining 相似文献
6.
Confocal laser scanning microscopy was utilized to compare the chloroplast morphology and ontogeny among five strains of the
green alga Asterochloris. Parsimony analysis inferred from the rDNA ITS sequences confirmed their placement in three distinct lineages: Asterochloris phycobiontica, Trebouxia pyriformis and Asterochloris sp. Examination by confocal microscopy revealed the existence of interspecific differences in the chloroplast ontogeny of
Asterochloris; this was based upon either specific chloroplast structures observed in a single species, or on the differential timing of
particular ontogenetic sequences. The occurrence of flat parietal chloroplasts prior to cell division, considered as a basic
morphological discriminative character of Asterochloris, was clearly associated with the process of aplanosporogenesis. By contrast, chloroplast transformation prior to the formation
of autospores proceeded simply by the multiple fission of the chloroplast matrix in the cell lumen.
Presented at the International Symposium Biology and Taxonomy of Green Algae V, Smolenice, June 26–29, 2007, Slovakia. 相似文献
7.
8.
Studies on the vegetative life cycle of Chlamydomonas reinhardi Dangeard in synchronous culture I. Some characteristics of the cell cycle 总被引:1,自引:0,他引:1
Cells of Chlamydomonas reinhardi Dangeard were grown synchronouslyunder a 12 hr light-12 hr dark regime. Time courses of nucleardivision, chloroplast division, "apparent cytokinesis" and zoosporeliberation were followed during the vegetative cell cycle inthe synchronous culture. Liberation of zoospores occurred atabout 2324 hr after the beginning of the light periodat 25°C. Four zoospores were produced per mother cell underthe conditions used. At lower temperatures, the process of zoosporeliberation as well as length of the cell cycle was markedlyprolonged, but the number of zoospores produced per mother cellwas approximately the same. At different light intensities,lengths of the cell cycle were virtually the same, while thenumber of zoospores liberated was larger at higher rather thanat lower light intensities. During the dark period, nuclear division, chloroplast divisionand apparent cytokinesis took place, in diis order, and proceededless synchronously than did the process of zoospore liberation.When the 12 hr dark period was replaced with a 12 hr light periodduring one cycle, the time of initiation as well as the durationof zoospore liberation was litde affected in most cases, whereasnuclear division, chloroplast division and apparent cytokinesiswere considerably accelerated by extended illumination. Whenalgal cells which had been exposed to light for 24 hr were furtherincubated in the light, zoospore liberation started much earlierand proceeded far less synchronously, compared with that under12 hr light-12 hr dark alternation. (Received October 12, 1970; ) 相似文献
9.
Fujiwara Takayuki; Misumi Osami; Tashiro Kousuke; Yoshida Yamato; Nishida Keiji; Yagisawa Fumi; Imamura Sousuke; Yoshida Masaki; Mori Toshiyuki; Tanaka Kan; Kuroiwa Haruko; Kuroiwa Tsuneyoshi 《DNA research》2009,16(1):59-72
Previous cell cycle studies have been based on cell-nuclearproliferation only. Eukaryotic cells, however, have double membranes-boundorganelles, such as the cell nucleus, mitochondrion, plastidsand single-membrane-bound organelles such as ER, the Golgi body,vacuoles (lysosomes) and microbodies. Organelle proliferations,which are very important for cell functions, are poorly understood.To clarify this, we performed a microarray analysis during thecell cycle of Cyanidioschyzon merolae. C. merolae cells containa minimum set of organelles that divide synchronously. The nuclear,mitochondrial and plastid genomes were completely sequenced.The results showed that, of 158 genes induced during the S orG2-M phase, 93 were known and contained genes related to mitochondrialdivision, ftsZ1-1, ftsz1-2 and mda1, and plastid division, ftsZ2-1,ftsZ2-2 and cmdnm2. Moreover, three genes, involved in vesicletrafficking between the single-membrane organelles such as vps29and the Rab family protein, were identified and might be relatedto partitioning of single-membrane-bound organelles. In othergenes, 46 were hypothetical and 19 were hypothetical conserved.The possibility of finding novel organelle division genes fromhypothetical and hypothetical conserved genes in the S and G2-Mexpression groups is discussed. 相似文献
10.
Summary Uniseriate filaments of the freshwater red algaCompsopogon coeruleus were examined by transmission electron microscopy for details of vegetative organization and cell division with the goal of providing useful taxonomic characters. Each cell's single, complex chloroplast contains a peripheral encircling thylakoid, and unlike the vast majority of red algae, the cis-regions of dictyosomes are not consistently juxtaposed with mitochondria. These subcellular features, which are present in all examined genera in theCompsopogonales, Erythropeltidales, andRhodochaetales, along with certain unique reproductive characteristics, unify these three orders. During mitosis in uncorticated axial cells, a small, ring-shaped nucleus associated organelle (NAO) is located at each division pole, an intranuclear spindle comes to a moderately acute focus at the flattened, fenestrated metaphase-anaphase division poles and perinuclear ER partially encloses dividing nuclei, including a well-developed interzonal midpiece. The cleavage furrow penetrates the large, central vacuolar region to separate daughter nuclei. These cell division features most closely resemble the pattern described for the orderCeramiales. Our observations of vegetative and dividing cells ofC. coeruleus supplement the growing volume of evidence in favour of uniting all red algae into a single class without subclass designations.Abbreviations ER
endoplasmic reticulum
- IZM
interzonal midpiece
- MT
microtubule
- MTOC
microtubule organizing center
- NAO
nucleus associated organelle
- NE
nuclear envelope
- PER
perinuclear endoplasmic reticulum 相似文献
11.
Elisabeth Tschermak-Woess 《Plant Systematics and Evolution》1978,129(3):185-208
Chaenotheca brunneola is lichenized withDictyochloropsis splendida. Until now this member of theChlorococcales has been observed only twice and free-living. It reproduces by motionless daughter cells in the lichen thallus, but mainly by zoospores in the free-living state and under favourable conditions. Zoospore development has not been observed before and apparently depends on storage of starch which is repressed in the lichenized state. During zoospore activity this storage material is consumed. Zoospores possess two flagella which are inserted rather far apart from each other, one pulsating vacuole and a cup-shaped, not latticed chloroplast.Chaenotheca phaeocephala var.alpina, Ch. melanophaea andCh. chrysocephala are lichenized withTrebouxia. The phycobiont ofCh. chrysocephala, Trebouxia simplex, sp. n., differs from other sibs of the genus by the relative small size of the cells, the less marked differentiation of the chloroplast and certain details of cell division. 相似文献
12.
At the ultrastructural level, cell division in Ochromonas danica exhibits several unusual features. During interphase, the basal bodies of the 2 flagella replicate and the chloroplast divides by constriction between its 2 lobes. The rhizoplast, which is a fibrous striated root attached to the basal body of the long flagellum, extends under the Golgi body to the surface of the nucleus in interphase cells. During proprophase, the Golgi body replicates, apparently by division, and a daughter rhizoplast, appears. During prophase, the 2 pairs of flagellar basal bodies, each with their accompanying rhizoplast and Golgi body, begin to separate. Three or 4 flagella are already present at this stage. At the same time, there is a proliferation of microtubules outside the nuclear envelope. Gaps then appear in the nuclear envelope, admitting the microtubules into the nucleus, where they form a spindle. A unique feature of mitosis in O. danica is that the 2 rhizoplasts form the poles of the spindle, spindle microtubules inserting directly onto the rhizoplasts. Some of the spindle microtubules extend from pole to pole; others appear to attach to the chromosomes. Kinetochores, however, are not present. The nuclear envelope breaks down, except, in the regions adjacent, to the chloroplasts; chloroplast ER remains intact throughout mitosis. At late anaphase the chromosomes come to lie against part of the chloroplast ER. This segment of the chloroplast ER appears to be incorporated as part of the reforming nuclear envelope, thus reestablishing the characteristic nuclear envelope—chloroplast ER association of the interphase cell. 相似文献
13.
Tsuneyoshi Kuroiwa 《Journal of plant research》1989,102(2):291-329
It has been established that organelles, such as mitochondria and plastids, contain organelle-specific DNA and arise from
the division of pre-existing organelles (e.g., Possingham and Lawrence, 1983). We propose that organelle DNAs, such as mitochondrial
DNA and plastid DNA are not naked in organellesin situ but are organized in each case to form an “organelle nucleus” with basic proteins (Kuroiwa, 1982). The concept of organelle
nuclei has changed our ideas about the division of organelles. Thus, the process of organelle division must be composed of
two main events: division of the organelle nucleus and organellekinesis (division of the other components of the mitochondrion
or plastid). The latter term has been adopted as an appropriate analogue of cytokinesis.
We were the first to identify the plastid-dividing ring (PD-ring), which is located in the cytoplasm close to the outer envelope
membrane at the constricted isthmus of dividing chloroplasts in the red algaCyanidium caldirum. The PD-ring is about 60 nm in width and 25 nm in thickness, and is a circular bundle of actin-like, fine filaments, each
about 4–5 nm in diameter. Since cytochalasin B, an inhibitor of polymerization of actin filaments, inhibits the formation
of the PD-ring and, thus, prevents subsequent division of chloroplasts, the PD-ring is thought to be a structure that is essential
for the division of plastids (plastidkinesis).
The behavior of the PD-ring during a cycle of chloroplast division can be classified into the following four stages on the
basis of morphological and temporal differences. The chloroplast growth stage: the small, spherical chloroplast increases
in volume and becomes a football-like structure, while the PD-ring from the previous division disappears. Formation of the
PD-ring: the somewhat electron-dense body (see below) is fragmented into many, somewhat electron-dense granules, which are
aligned along the equatorial region of the chloroplast and fine filaments are formed from the somewhat electron-dense granules
in the equatorial region. The fine filaments of the PD-ring align themselves according to the longest axis of their overall
domain, i.e., circumferentially. Contraction stage: a bundle of fine filaments begins to contract and generates a deep furrow.
Conversion stage: after chloroplast division, the remnants of the PD-ring are converted into somewhat electron-dense bodies.
Similar events occur during the second cycle of chloroplast division. Since similar structures are observed extensively in
the plastids of algae, moss and higher plants, the PD-ring appears to be an essential structure for the division of plastids
in plants. 相似文献
14.
Summary Changes in the lysosome structures were examined by electron microscopy during the formation of zoospores inTrebouxia potteri. Lysosomes in vegetative cells were homogeneously filled with electron-dense material. At the beginning of zoospore formation, lysosomes invaginated or evaginated to take up mitochondria, ER, or cytoplasmic ground plasma. The ingested organelles became disorganized within the lysosomes. During this disruption of these organelles, the lysosomal contents became heterogeneous, suggesting a decrease in the amount of enzymes within the lysosomes. Golgi bodies and ER seemed to be involved with the disruption of the organelles, probably supplying some substances necessary for the functioning of the lysosomes. Amount of electron-dense materials decreased and, finally, only one to three small spherical aggregates remained in the lysosomes. Then the lysosomes appeared to shrink via loss of watery substances or cutting off of electron-transparent regions. After these changes in lysosome structure, nuclei started to divide successively for formation of the zoospores. The possibility is proposed that the drastic cytoplasmic changes operated by lysosomes trigger the following morphogenetic events in the formation of zoospores.Abbreviations ER
endoplasmic reticulum
- TGN
trans Golgi network 相似文献
15.
Cell division and chloroplast replication in Heterosigma akashiwo(Hada) Hada occurred as separate synchronous events during thecell cycle when cells were subjected to light-dark regimes.Under three different photoperiodic cycles of 10L/14D (10 hlight/14 h dark), 12L/12D or 16L/8D, cell division began athour 1920 and finished at hour 2326 after theonset of the light period, while chloroplast replication beganat hour 2022 after the onset of the dark period. Almostall the cells divided only once in the 12L/12D cycle. The rateof increase in chloroplast number during one light-anddark cyclewas always equal to that in cell number in every photoperiodexamined. Light was essential for both cell division and chloroplast replication,but the minimum light period necessary for each event differed.When the light period was shorter than 6 h, no cell divisionoccurred; when it was shorter than 3 h, no chloroplast replicationoccurred. (Received February 26, 1987; Accepted June 17, 1987) 相似文献
16.
The timing and manner of disassembly of the apparatuses for chloroplast division (the plastid-dividing ring; PD ring) and
mitochondrial division (the mitochondrion-dividing ring; MD ring) were investigated in the red alga Cyanidioschyzon merolae De Luca, Taddei and Varano. To do this, we synchronized cells both at the final stage of and just after chloroplast and mitochondrial
division, and observed the rings in three dimensions by transmission electron microscopy. The inner (beneath the stromal face
of the inner envelope) and middle (in the inter-membrane space) PD rings disassembled completely, and disappeared just before
completion of chloroplast division. In contrast, the outer PD and MD rings (on the cytoplasmic face of the outer envelope)
remained in the cytosol between daughter organelles after chloroplast and mitochondrial division. The outer rings started
to disassemble and disappear from their surface just after organelle division, initially clinging to the outer envelopes at
both edges before detaching. The results suggest that the two rings inside the chloroplast disappear just before division,
and that this does not interfere with completion of division, while the outer PD and MD rings function throughout and complete
chloroplast and mitochondrial division. These results, together with previous studies of C. merolae, disclose the entire cycle of change of the PD and MD rings.
Received: 19 May 2000 / Accepted: 3 August 2000 相似文献
17.
The distribution, cytological organization and differentiationof non-articulated laticifers in the primary and mature tissuesof Calotropis gigantea (Linn.) R.Br., were studied by the useof optical and electron microscopy. Laticifers occur in thecortex, vascular bundle and pith of the plant axis. At the earliestdetectable stage a laticifer is a cell which undergoes rapidelongation and nuclear division. This results in a multinucleateelongated cell which undergoes further increase in length withgradual degeneration of the cytoplasm. At the electron microscopiclevel the presumptive laticifer cell shows increasing vacuolationwhich forms a large central vacuole. Simultaneously the cytoplasmicorganelles undergo degeneration by autophagic processes. Laternumerous vesicles can be observed in the large central vacuole,the remaining cytoplasm being pushed to a thin layer. Maturelaticifers show three types of spherical structures of whichthe highly electron dense globules are the latex particles. Calotropis gigantea (Linn.), R.Br., laticifers, ultrastructure, differentiation 相似文献
18.
Histochemical analyses of the pseudopollen of ten species ofMaxillaria sectionGrandiflorae revealed that the main storageproduct is protein, although starch is usually also present.Lipids are rare in pseudopollen and thus do not seem to playan important role in attracting insects. In Maxillaria sanderiana,pseudopollen is formed by the fragmentation of multicellular,uniseriate trichomes, derived by the repeated division of asingle, papilla-like, basal secretory cell that contains well-developeddictyosomes, endoplasmic reticulum and mitochondria. At first,there is continuity of cytoplasm between adjacent componentcells of a trichome via plasmodesmata. During maturation, thecytoplasm retracts as the cell volume increases and the plasmodesmatabecome less obvious. Each component cell of the trichome eventuallycomprises a large protein body and a small amount of peripheralcytoplasm containing amyloplasts, a few small lipid bodies,mitochondria and a nucleus with nucleolus. Finally, the trichomeundergoes fragmentation, forming individual cells or chainsof cells of varying lengths. Light microscopy observations indicatea similar sequence in the other species examined. The occurrenceof pseudopollen in section Grandiflorae and alliance Splendensmay indicate that this character has evolved at least twicein Maxillaria. Copyright 2000 Annals of Botany Company Bees, farina, histochemistry, labellum, low-vacuum scanning electron microscopy, Maxillaria, Orchidaceae, pseudopollen, transmission electron microscopy, trichomes 相似文献
19.
Plastid-dividing Rings in Ferns 总被引:4,自引:1,他引:3
Plastid-dividing rings (PDs) are described for the first timein the ferns Ophioglossum, Gleichenia, Hymenophyllum, Trichomanes,Athyrium, Dryopteris, Ceratopteris and Pteridium. They are foundin the constricted isthmuses of undifferentiated plastids, amyloplasts,amylochloroplasts and chloroplasts in gametophytes and in arange of sporophytic tissues including apices, differentiatingleaf mesophyll and vascular parenchyma from roots, stems andleaves. Fern PDs comprise two concentric structures; a densegranular ring 60-100 nm wide adhering to the stromal face ofthe constriction and a smaller cytoplasmic annulus only 20-40nm wide. The diameters of the PD-containing constrictions, particularlythose in vascular parenchyma, where the outer component is usuallylacking, are extremely uniform (means of 177-188 nm in differentspecies and tissues) and closely in line with those in angiosperms.PDs in ferns differ from those previously described in othergroups of lands plants in that they are far more persistentand in multilobed plastids one is present at each constriction.The occurrence of multiple PDs in the giant plastids found inup to 30% of vascular parenchyma cells may be associated withorganelle fusion rather than division.Copyright 1993, 1999 AcademicPress Chloroplast division, division cycle, ferns, plastid-dividing rings, pteridophytes, transmission electron microscopy 相似文献
20.
The PALE CRESS gene (PAC) is essential for proper chloroplastand leaf development in Arabidopsis thaliana. The ability ofpac mutants to accumulate significantly more chlorophyll whengrown in low light conditions than in high light conditionssuggests that carotenoid deficiency is at least partly responsiblefor premature cessation of chloroplast development. In additionto accumulation of low levels of chlorophyll and carotenoidpigments,pac mutants are abscisic acid (ABA) deficient and havecharacteristics which may be explained by this deficiency. Theseinclude reduced seed viability and, in enclosed growth conditions,increased leaf growth. Plants transformed with an antisensePAC construct often bear viviparous embryos which may be symptomaticof a deficiency in ABA. Since carotenoids are precursors ofABA, a role for PAC in carotenoid biosynthesis is further supported.The nuclear-encoded, chloroplast-localized PAC protein has beenimplicated in the maturation of plastid-encoded mRNAs. Thus,PAC may affect the abundance of one or more chloroplast proteinswhich function in the synthesis or stability of carotenoids.Using thePROLIFERA gene as a marker for cell division, it isshown that cell division profiles in the pac shoot apex aredisrupted. pac leaves are relatively normal in size and shapedespite the light intensity-induced variability of leaf celldefects. Copyright 2000 Annals of Botany Company Abscisic acid, carotenoid, chloroplast development, leaf development, organismal theory, PALE CRESS,PROLIFERA , vivipary 相似文献