The role of plastids and assimilate transport system in the control of plant development

Phylogenetic and ontogenetic relationships between the plastids, cell endoplasmic reticulum, and plant transport communication have been reviewed. The initiating role of plastids (endosymbionts) in the origin of endoplasmic reticulum (buffer zone of endosymbiogenesis) has been shown, as well as a similar role of endoplasmic reticulum in the development of transport communication of xylem and phloem. Plastids, sugars and transport system for their distribution can be interpreted as leading sections in the mechanism of developmental control: gene expression of nuclear genome and genome of organelles, cell and tissue differentiation, and plant morphogenesis. The conflict between the bulk of plant genome and low percentage of its realization is explained as a result of limitation of the nuclear genome realization by plastid genome. The concept of development as applied to plant ontogenesis has been critically analyzed. The possibilities of the concept correction by with the help of symbiogenetic hypothesis are discussed.     

麻疯树小孢子发育的研究

用透射电镜观察了麻疯树(Jatropha curcas L.)小孢子发育的超微结构。小孢子母细胞时期内质网和质体较多;减数分裂和四分体时期,细胞处于明显的代谢活跃状态,细胞器丰富,主要有内质网、线粒体、质体、高尔基体和球状体;在小孢子发育早期和晚期,线粒体和内质网仍较丰富;小孢子经过高度的不对称分裂后,形成较大的营养细胞和较小的生殖细胞,营养细胞中细胞器数量明显减少,含大量的淀粉和脂类物质,生殖细胞中脂类物质丰富;表皮、药室内壁和中层细胞在小孢子母细胞和四分体时期淀粉粒丰富,小孢子时期明显减少,绒毡层从小孢子母细胞至小孢子发育晚期的细胞器都很丰富,主要为内质网、质体和线粒体,为二胞花粉发育奠定基础。     

The ultrastructural features and division of secondary plastids

Plastids in heterokonts, cryptophytes, haptophytes, dinoflagellates, chlorarachniophytes, euglenoids, and apicomplexan parasites derive from secondary symbiogenesis. These plastids are surrounded by one or two additional membranes covering the plastid-envelope double membranes. Consequently, nuclear-encoded plastid division proteins have to be targeted into the division site through the additional surrounding membranes. Electron microscopic observations suggest that the additional surrounding membranes are severed by mechanisms distinct from those for the division of the plastid envelope. In heterokonts, cryptophytes and haptophytes, the outermost surrounding membrane (epiplastid rough endoplasmic reticulum, EPrER) is studded with cytoplasmic ribosomes and connected to the rER and the outer nuclear envelope. In monoplastidic species belonging to these three groups, the EPrER and the outer nuclear envelope are directly connected to form a sac enclosing the plastid and the nucleus. This nuclear-plastid connection, referred to as the nucleus-plastid consortium (NPC), may be significant to ensure the transmission of the plastids during cell division. The plastid dividing-ring (PD-ring) is a conserved component of the division machinery for both primary and secondary plastids. Also, homologues of the bacterial cell division protein, FtsZ, may be involved in the division of secondary plastids as well as primary plastids, though in secondary plastids they have not yet been localized to the division site. It remains to be examined whether or not dynamin-like proteins and other protein components known to function in the division of primary plastids are used also in secondary plastids. The nearly completed sequencing of the nuclear genome of the diatom Thalassiosira pseudonana will give impetus to molecular and cell biological studies on the division of secondary plastids.     

Differentiation and Ultrastructure of the Protophloem Sieve Elements of Minor Veins in the Maize Leaves: Changes in the Protoplast

Protophloem sieve element differentiation in the minor veins of the maize ( Zea mays L. ) leaves was first evidenced as an increase of the wall thickness, which began in the comers of the cell and then extended to other parts of the wall, and the appearance of long rough endoplasmic reticulum cistemae distributed throughout the cytoplasm, and then the presence of characteristic crystalloid inclusions within the plastids. As differentiation progressed, long cisternae of rough endoplasmic reticulum appeared to transform into shorter forms and eventually aggregated into small stacks, losing their ribosomes during the process. The nuclei degenerated, although frequently persisted until very late in differentiation the stages of maturation, as darkly stained amorphous aggregates surrounded by double nuclear envelope or only inner membrane of nuclear envelope. Subsequently, the nuclear envelope collapsed and became discontinuous. At the beginning of nuclear degeneration the perinuclear spaces were partly dilated and sometimes the outer nuclear envelope in the dilated portions then ruptured, and was accompanied by the disappearance of the cytoplasmic portion near it. During the peried of nuclear degeneration, in addition to the endoplasmic reticulum, plastids and mitochondria underwent structural modification, while components such as ribosomes, cytoplasmic ground substances, vacuoles and dictyosomes disintegrated and disappeared. At maturity, the surviving protoplasmic components, including plasmalemma, mitochondria, small stacked smooth endoplasmic reticulum and P-type plastids with crystalloids, became parietal in position. As differentiation of adjacent metaphloem sieve elements proceeded, the protoplasmic components of the mature protophloem sieve elements progresively degenerated and finally obliterated.     

Cytochemical Localization of Adenosine Triphosphataes Activity During Cytomixis in Pollen Mother Cells of David Lily and Its Relation to the Intercellular Migrating Chromatin Substance

Standard lead precipitation procedures have been used to examine the localization of ATPase activity during cytomixis in pollen mother cells of Lilium davidii var. willmottiae (Wilson) Roffill. Before cytomixis, cells at this stage of development show ATPase activity on plasma membrane, in the endoplasmic reticulum, dictyosomes, plastids, plasmodesmata, and in part of the groundplasm; however, there is no ATPase activity on the chromatin and nucleolus. During cytomixis, the chromatin substance begin to transfer from one cell to an adjacent cell, reaction product indicating ATPase activity is observed associated with the chromatin and nucleolus. ATPase activity is also found with the cistenae of both endoplasmic reticulum and dictyosomes, and some plastids. There is no deposition of ATPase reaction product associated with the plasm membrane and intercellular spaces. After cytomixis, the chromatin is little or no deposition of enzyme reaction product. ATPase activity, however, is consistenlly found within the intercellular space and on the plasm membrane, and also occur in the endoplasmic reticulum, dictyosome and plastid. The presence or absence of ATPase activity in the cell structure of pollen mother cells before, during or after eytomixis is discussed in relation to the active uptake or export of water for short-distance transport. It is also suggested that the intensive ATPase activity in the nucleus during cytomixis of pollen mother cells is evidence for a transport system involved in the active movement of the intercellular migrating ebromatin substance.     

Ultrastructural Aspects of the Glandular Cells from the Secretory Trichomes and from the Cell Suspension Cultures of Achillea millefolium L. ssp. millefolium

The ultrastructure of the glandular cells of the floret secretorytrichomes from Achillea millefolium L. ssp. millefolium (yarrow)was examined before and after anthesis and compared with theultrastructure of the cells from the cell suspension culturesobtained from the same plant. The profuse tubular structuresobserved in the plastids of the glandular cells of the trichomesduring the pre-secretory stage were much reduced in the secretorystage and showed an osmiophilic content. Some endoplasmic reticulumprofiles could be seen adjacent to the plastids. Later in thesecretory stage, the secretion appeared in the periplasmic spacebetween the cells of the upper tiers and in the sub-cuticularspace. Finally the secretion was released by rupture of thecuticle. At the lag phase, the cells from the cell suspensioncultures of yarrow were characterized by the presence or plastidswith tubular structures, similar to those observed in the plastidsof the trichomes in the pre-secretory stage. By the end of thelag phase accumulations of starch were observed inside the plastids.At the beginning of the exponential phase, the tubular structuresof the plastids started to show an osmiophilic content and theaccumulations of starch were still present. At the end of thisphase starch disappeared from the plastids and only osmiophilictubular structures were observed. Rough endoplasmic reticulumas well as smooth endoplasmic reticulum profiles were frequentlyin close association with plastids and mitochondria. At thestationary phase a very large vacuole filled the cells, andin the remaining cytoplasm some endoplasmic reticulum profilesand osmiophilic droplets were observed.Copyright 1994, 1999Academic Press Achillea millefolium L. spp. millefolium, yarrow, ultrastructure, trichomes, glandular cells, plant cell suspension cultures     

Intracellular Transport and Elimination of Resin from Epithelial Duct-cells of Pinus halepensis

The ultrastructure of the resin secreting cells of root ductsof young Pinus halepensis seedlings was studied. It is suggestedthat the endoplasmic reticulum (ER) in addition to taking partin resin synthesis also plays a role in transporting the resinfrom the plastids, mitochondria and nuclear envelope to theplasmalemma. By fusing with the plasmalemma the ER releasesthe resin to the outside of the protoplast. The resin producedin the ground cytoplasm and by the Golgi apparatus seems tobe eliminated by plasmalemma invaginations. Pinus halepensis, resin secretion, root ducts, endoplasmic reticulum     

ULTRASTRUCTURE OF TETRASPOROGENESIS IN THE CORALLINE ALGA HALIPTILON CUVIERI(RHODOPHYTA)1

Tetrasporogenesis begins with the formation of the tetra-sporocyte, an elongate, apparently wall-less, cell containing few organelles. The tetrasporocyte rapidly elongates and a distinctive cell wall forms before the onset of meiosis. During this elongation phase there is also an increase in the number of plastids and mitochondria. The meiotic tetrasporocyte is characterized by extensive development of perinuclear endoplasmic reticulum (PNER) and peripheral endoplasmic reticulum (PER) and during the latter stages of sporogenesis by internuclear endoplasmic reticulum. Immediately next to the nuclear envelope the inter-cisternal spaces of the PNER are filled with very electron dense material and the PNER cisternae are quite narrow, while further away from the nucleus the PNER cisternae dilate. Throughout meiosis there is continued replication of plastids and mitochondria as well as synthesis of starch and the formation of Golgi-derived vesicles with very osmiophilic contents. Cytokinesis begins with the formation of striated thickenings on the inside of the tetrasporocyte wall, at the sites where the cleavage furrow, produced by infurrowing of the plasmalemma, will be formed. Early in cytokinesis the PER disappears and is replaced by osmiophilic vesicles and mitochondria. Tubular plasmalemma invaginations of 27–30 nm width also appear during the early stages of tetraspore wall formation. The ultra-structure of the early stages of tetraspore germination is also described.     

Structure of the Needles in the Early Phases of Development in Pinus ponderosa P. et C. Lawson with Special Reference to Plastids

Before they emerged from the fascicular sheath, the tissuesof young needles of Pinus ponderosa P. et C. Lawson alreadyshowed some characteristics typical of mature needles. The organelles,particularly the plastids, had undergone different development.The plastids in different types of cell varied in their ultrastructureand in association with the endoplasmic reticulum (ER). A sheathof ER was observed around the amoeboid plastids in epidermalcells, epithelial cells of resin ducts and maturing transfusiontracheids whereas there was no ER sheath around the young mesophyllchloroplasts, the fusiform chloroplasts in some transfusiontracheids and the proplastids in xylem and phloem cells. Thecontent of chlorophyll (a+b) was 0·85 g kg^-1 dry matterand chlorophyll a/b ratio was 2·70. The needles may becomephotosynthetically active whilst still within the fascicularsheaths.Copyright 1993, 1999 Academic Press Pinus ponderosa, ponderosa pine, needle structure, needle ontogeny, plastids, endoplasmic reticulum     

百合花粉母细胞间细胞融合期间腺苷三磷酸酶活性的细胞化学定位及其与染色质胞间转移的关系

用标准的磷酸铅沉淀的细胞化学方法,对百合花粉母细胞间染色质穿壁运动期间及其前后三个时期中的腺苷三磷酸酶(ATP 酶)活性进行了超微结构的定位。结果表明:(1)在穿壁前,ATP 酶活性主要定位于质膜、胞间连丝及细胞间隙;在内质网、高尔基体、质体和某些局部的基质(groundplasm)中,也表现有 ATP 酶活性反应的产物;但在染色质和核仁中,一般都没有这种反应。(2)在穿壁时,染色质从一个细胞穿壁转移到另一个相邻细胞,同时看到染色质和核仁内出现密集的 ATP 酶活性反应产物;在内质网和高尔基体的腔内以及质体的片层上也产生明显的 ATP 酶活性反应;而在质膜、胞间连丝及细胞间隙内 ATP 酶活性明显降低,甚至看不到明显的活性反应。(3)在穿壁后,质膜及细胞间隙中又产生明显的 ATP 酶活性反应产物,但核内染色质上的 ATP 酶活性则显著降低,而核仁内则仍有较高的活性。同前二个时期一样,内质网、高尔基体和质体上的 ATP 酶仍表现明显的活性反应。最后讨论了三个不同发育时期 ATP 酶活性及其分布部位的改变与染色质胞间转移的关系。     

DNA synthesis and cytoplasmic differentiation in tapetal cells of normal and cytoplasmically male sterile lines of Petunia hybrida

Summary A new method is described by which tapetal cells may be isolated from anthers of cytoplasmic male sterile (CMS) and fertile lines of Petunia hybrida. Using a combination of stereometry and Feulgen densitometry it has been possible to chart DNA synthesis and nuclear division with great precision within these cells. Results are presented which show CMS lines both to synthesize far less DNA than the fertiles and also to undergo less cell division. These differences in DNA kinetics and cytokinesis are obvious long before any differences between sterile and fertile lines may be detected in the meiocyte mass. In addition to these difference in nuclear behaviour, the tapetal cells of CMS lines also synthesize far lower levels of rough endoplasmic reticulum than do their fertile counterparts. Again, this difference is evident at a very early stage of anther development when all other cell components, including mitochondria and plastids, appear normal. These data are discussed in terms of the very special differentiation undergone by tapetal cells in angiosperms, and the conclusions drawn are considered in the perspective of current hypotheses proposed to explain the operation of CMS.     

Cytological changes associated with induction of anthraquinone synthesis in photoautotrophic cell suspension cultures of Morinda lucida

Differences in subcellular structures between anthraquinone-producing and non-producing cells were investigated using photoautotrophic and photoheterotrophic cell suspension cultures of Morinda lucida. Irregular or distorted plastids containing starch grains were observed in the anthraquinone-producing cells, together with a highly elongated rough endoplasmic reticulum. The possible participation of plastids and rough endoplasmic reticulum in the anthraquinone biosynthesis is discussed.     

Role of the nuclear envelope in synthesis, processing, and transport of membrane glycoproteins

The outer nuclear membrane is morphologically similar to rough endoplasmic reticulum. The presence of ribosomes bound to its cytoplasmic surface suggests that it could be a site of synthesis of membrane glycoproteins. We have examined the biogenesis of the vesicular stomatitis virus G protein in the nuclear envelope as a model for the biogenesis of membrane glycoproteins. G protein was present in nuclear membranes of infected Friend erythroleukemia cells immediately following synthesis and was transported out of nuclear membranes to cytoplasmic membranes with a time course similar to transport from rough endoplasmic reticulum (t 1/2 = 5-7 min). Temperature-sensitive mutations in viral membrane proteins which block transport of G protein from endoplasmic reticulum also blocked transport of G protein from the nuclear envelope. Friend erythroleukemia cells and NIH 3T3 cells differed in the fraction of newly synthesized G protein found in nuclear membranes, apparently reflecting the relative amount of nuclear membrane compared to endoplasmic reticulum available for glycoprotein synthesis. Nuclear membranes from erythroleukemia cells appeared to have the enzymatic activities necessary for cleavage of the signal sequence and core glycosylation of newly synthesized G protein. Signal peptidase activity was detected by the ability of detergent-solubilized membranes of isolated nuclei to correctly remove the signal sequence of human preplacental lactogen. RNA isolated from the nuclear envelope was highly enriched for G protein mRNA, suggesting that G protein was synthesized on the outer nuclear membrane rather than redistributing to nuclear membranes from endoplasmic reticulum before or during cell fractionation. These results suggest a mechanism for incorporation of membrane glycoproteins into the nuclear envelope and suggest that in some cell types the nuclear envelope is a major source of newly synthesized membrane glycoproteins.     

Ultrastructural studies on the process of aloin production and accumulation in Aloe arborescens (Asphodelaceae) leaves

Aloin, a kind of anthraquinone, is a chemical component in Aloe leaves used in medicine. The processes of aloin production, transport and storage were studied with a transmission electron microscope using the lead acetate precipitate method for ultracytochemical localization of aloin in the leaf of Aloe arborescens Mill. Results showed that aloin was produced in the plastids of the assimilating tissue, transported through the plastid membrane to the surrounding endoplasmic reticulum and enveloped in the vesicles by the endoplasmic reticulum elements. The vesicles approached, and later fused with, the plasmalemma, released their contents into the apoplast through exocytosis and finally, reached the vascular bundle sheath by apoplastic translocation. Aloin was transported to the internal tangential wall of the vascular bundle sheath cell through endoplasmic reticulum vesicles, and reached the cytoplasm of the aloin cell by means of plasmodesmata. Finally, aloin was stored in the vacuole of the cell in which it was produced.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 150 , 241–247.     

木立芦荟叶内芦荟素的超微细胞化学研究

使用醋酸铅溶液对木立芦荟叶的药用成分芦荟素进行细胞化学定位,在透射电镜下探讨芦荟素产生、转运和贮藏的过程。结果表明:芦荟素由同化薄壁组织产生,质体的类囊体为其合成部位。通过质体膜形成的小泡转移到周围的内质网,以后内质网小泡与质膜融合:或质体小泡直接与质膜融合。通过胞吐作用将芦荟素释放到质膜外,经质外体途径到达维管束的鞘细胞。在鞘细胞中, 芦荟素经内质网小泡转移至内切向壁,由胞间连丝运输到芦荟素细胞的细胞质,最终贮藏在芦荟素细胞的液泡中。     

植物不饱和脂肪酸的生物合成及调控

不饱和脂肪酸是植物细胞中的一类重要代谢物质,是组成细胞膜的主要成分,对调节细胞的生理功能起着重要作用。不饱和脂肪酸也是人类必须的一类营养物质,对健康发挥着重要作用。因此,研究植物不饱和脂肪酸的合成和调控机制具有着重要的理论和现实意义。不饱和脂肪酸的合成主要发生在质体和内质网,由一系列编码基因控制,并受到外在环境胁迫及发育的调控。本研究综述了近年来不饱和脂肪酸合成和调控机制相关的一些研究进展,解析了不饱和脂肪酸合成的一些关键基因,以期为将来利用相关基因进行种质创新,从而实现改良食用油品质或提升植物的抗性育种提供思路和实践。     

Structure and development of sieve cells in the primary phloem ofPinus resinosa

Summary The primary phloem consists mostly of sieve cells. Procambial cells and very young sieve cells contain all the components characteristic of young nucleate cells. Increase in wall thickness, which is relatively limited, constitutes the first indication of sieve-cell differentiation. During the period of wall thickening, the plastids develop starch grains and then fibrillar inclusions. Eventually the internal lamellae of the plastids collapse. The plastids do not form crystalline inclusions. As the sieve cell approaches maturity, an extensive network of smooth, tubular endoplasmic reticulum (ER) appears and then becomes mostly parietal in distribution. At maturity, large aggregates of this ER occur at the sieve areas. These aggregates are interconnected longitudinally by the parietal network of ER. In addition to the ER, the mature, plasmalemma-lined primary sieve cell contains a degenerate nucleus, with intact nuclear envelope, plastids, and mitochondria. Dictyosomes, ribosomes, and vacuoles are lacking. P-protein is not present at any stage of development.This work was supported by U.S. National Science Foundation grants GB 8330 and GB 31417 to R. F.Evert.     

Redundant function of two Arabidopsis COPII components, AtSec24B and AtSec24C, is essential for male and female gametogenesis

Anterograde vesicle transport from the endoplasmic reticulum to the Golgi apparatus is the start of protein transport through the secretory pathway, in which the transport is mediated by coat protein complex II (COPII)-coated vesicles. Therefore, most proteins synthesized on the endoplasmic reticulum are loaded as cargo into COPII vesicles. The COPII is composed of the small GTPase Sar1 and two types of protein complexes (Sec23/24 and Sec13/31). Of these five COPII components, Sec24 is thought to recognize cargo that is incorporated into COPII vesicles by directly interacting with the cargo. The Arabidopsis genome encodes three types of Sec24 homologs (AtSec24A, AtSec24B, and AtSec24C). The subcellular dynamics and function of AtSec24A have been characterized. The intracellular distributions and functions of other AtSec24 proteins are not known, and the functional differences among the three AtSec24s remain unclear. Here, we found that all three AtSec24s were expressed in similar parts of the plant body and showed the same subcellular localization pattern. AtSec24B knockout plant, but not AtSec24C knockdown plant, showed mild male sterility with reduction of pollen germination. Significant decrease of AtSec24B and AtSec24C expression affected male and female gametogenesis in Arabidopsis thaliana. Our results suggested that the redundant function of AtSec24B and AtSec24C is crucial for the development of plant reproductive cells. We propose that the COPII transport is involved in male and female gametogenesis in planta.     

Ultrastructure of microsporogenesis and microgametogenesis inArabidopsis thaliana (L.) Heynh. ecotype Wassilewskija (Brassicaceae)

Summary The process of microsporogenesis and microgametogenesis was studied at the ultrastructural level in wild-typeArabidopsis thaliana ecotype Wassilewskija to provide a basis for comparison with nuclear male-sterile mutants of the same ecotype. From the earliest stage studied to mature pollen just prior to anther dehiscence, microsporocyte/microspore/pollen development follows the general pattern seen in most angiosperms. The tapetum is of the secretory type with loss of the tapetal cell walls beginning at about the time of microsporocyte meiosis. Wall loss exhibits polarity with the tapetal protoplasts becoming located at a distance from the inner tangential walls first, followed by an increase in distance from the radial walls beginning at the interior edge and progressing outward. The inner tangential and radial tapetal walls are completely degenerated by the microspore tetrad stage. Unlike other members of the Brassicaceae that have been studied, the tapetal cells ofA. thaliana Wassilewskija also lose their outer tangential walls, and secretion occurs from all sides of the cells. Exine wall precursors are secreted from the tapetal cells in a process that appears to involve dilation of individual endoplasmic reticulum cisternae that fuse with the tapetal cell membrane and release their contents into the locule. Following completion of the exine, the tapetal cell plastids develop membranebound inclusions with osmiophilic and electron-transparent regions. The plastids undergo ultrastructural changes that suggest breakdown of the inclusion membranes followed by release of their contents into the locule prior to the complete degeneration of the tapetal cells.     

Mobile reticular organization of plastids and mitochondria in plant cells

Results of confocal, fluorescent and video microscopy of plant cell organelles and of stromule network uniting them are reviewed. The vast information on the structure of stromules, their mobility, proposed functions and development has been analyzed, in addition to factors stimulating and suppressing this development. Structural similarity between the network of stromules in living cells, observed by confocal fluorescence microscopy, and the endoplasmic reticulum, seen on micrographs of preparations fixed for electron microscopy is discussed. As a result of this discussion, a conclusion is made with regard to the identity of these endomembranous networks. The intercellular symplastic organization is shown for both networks in plant tissues. The existence of a common transport and trophic compartment is proposed that includes organelles, intercellular endoplasmic reticulum and its derivatives, phloem and xylem. The trophic system development might have been induced in the course of endosymbiogenesis with some bacterial precursors of organelles.