Photosynthetic activity and membrane polypeptide composition of supergranal chloroplasts from plant tissue cultures containing a viruslike particle

Tissue culture cells of Streptanthus tortuosus (Kell.) var. orbiculatus (Greene) Hall (Cruciferae), having a viruslike particle in their nucleoli, the STV cell line, contain “supergranal” chloroplasts. Freeze-fracture studies of chloroplasts of a control cell line, which lacks the viruslike particles, reveal two complementary faces similar to those observed in spinach chloroplasts. Replicas of freeze-fractured STV supergranal chloroplasts, however, show that one membrane face (B) contains widely spaced 80 Å particles and the other face (C) is essentially smooth. Isolated STV supergranal chloroplasts lack photosystem II activity as indicated by their inability to reduce dichlorophenolindophenol and are unable to reduce NADP with electrons from photosystem II or from ascorbate-reduced dichlorophenolindophenol. However, partial photosystem I activity is indicated by the reduction of methyl viologen with electrons from dichlorophenolindophenol-ascorbate. This supports the concept that there is not a direct correspondence between grana formation and photosystem II activity. Electrophoresis shows that all of the major polypeptide bands present in the STV supergranal chloroplasts are also present in the control chloroplast membranes. One band, molecular weight 33,000, is present in a greatly increased amount in the STV supergranal chloroplast membranes and may be associated with grana stacking.     

ULTRASTRUCTURE OF THE SHOOT APEX OF TOMATO (LYCOPERSICON ESCULENTUM)

The vegetative shoot apical meristem of tomato (Lycopersicon esculentum Mill.) was examined at the ultrastructural level. The meristem consisted of a surface layer that was different from the rest of the meristem and was unique among the dicotyledonous species. The cells of the surface layer contained large distal vacuoles with relatively large electron-dense inclusions, proplastids with membrane-bound inclusions (MB), and differentiating chloroplasts. In addition, periclinal and oblique divisions were observed in the surface layer cells along with anticlinal divisions. The cells of the subsurface layers contained small vacuoles with fewer inclusions as well as proplastids of various shapes but without MB. Differentiating chloroplasts were not observed in these cells, but autophagic vacuoles at various stages of development were present. The normal complement of cell inclusions, e.g., the mitochondria, golgi bodies, endoplasmic reticulum (ER), ribosomes, and microtubules were observed in subsurface layers, and in many cells the ER was observed to be continuous with the outer membrane of the nuclear envelope and with the plasmalemma. Further below in the meristem, cells contained both the proplastids and differentiating chloroplasts with MB. In the latter, the outer membrane of the MB was found to be continuous with the developing lamellae, suggesting that MB probably serve as the storage centers for lamellae membranes. Near the base of the meristem, in the pith-rib meristem, enlarged cells containing large vacuoles and differentiated chloroplasts were present.     

Ultrastructure Changes Induced by Stem Nematodes in Hypocotyl Tissue of Alfalfa

Scarified seeds of Medicago sativa L. ''Ranger'' and ''Lahontan'' alfalfa were allowed to imbibe water for 36 hr and then were inoculated with stem nematodes, Ditylenchus dipsaci Kühn. Seedlings were grown in sterilized Provo sand at 20 C and hypocotyl sections harvested at 1, 3 and 7 days. Evidence from electron micrographs indicated that cells of noninfected control plants contained normally developing chloroplasts bearing stroma, thylakoids, starch grains and plastoglobuli. The cytoplasm contained a nucleus, endoplasmic reticulum, vacuoles, mitochondria, ribosomes and dictyosomes. No morphological symptoms of nematode infection were observed in infected plants of either Ranger of Lahontan alfalfa 1 day after inoculation. Electron micrographs of tissue from the infected plants, however, indicated more osmiophilic bodies (lipid bodies) per cell than did the noninfected control, with more lipid bodies present in Ranger than in Lahontan. Three and 7 days after planting, swollen hypocotyls could be seen; the degree of swelling was greater in Ranger than in Lahontan. Electron micrographs of infected tissues indicated that both cultivars were undergoing the same kind of damage. Injured organelles were endoplasmic reticulum, chloroplasts and the nucleus. Histochemical staining indicated no changes in the middle lamellae.     

Chloroplast ultrastructure,photosynthetic apparatus activities and production of steviol glycosides in <Emphasis Type="Italic">Stevia rebaudiana in vivo</Emphasis> and <Emphasis Type="Italic">in vitro</Emphasis>

The accumulation of steviol glycosides (SGs) in cells of Stevia rebaudiana Bertoni both in vivo and in vitro was related to the extent of the development of the membrane system of chloroplasts and the content of photosynthetic pigments. Chloroplasts of the in vitro plants, unlike those of the intact plants, had poorly developed membrane system. The callus cells grown in the light contained proplastids of almost round shape and their thylakoid system was represented by short thylakoids sometimes forming a little number of grana consisting of 2–3 thylakoids. In cells of the etiolated in vitro regenerants and the callus culture grown in the dark, only proplastids practically lacking the membrane system were observed. All the chloroplasts having developed thylakoids and forming at least a little number of grana were equipped with photochemically active reaction centers of photosystems 1 and 2. Leaves of in vivo plants accumulated greater amount of the pigments than leaves of the in vitro plants. In both the callus culture grown in the light and the etiolated in vitro regenerants, the content of the pigments was one order of magnitude lower than that in leaves of the intact plants. The callus tissue grown in the dark contained merely trace amounts of the pigments. Leaves of the intact and the in vitro plants did not exhibit any significant differences in photosynthetic O₂ evolution rate. However, photosynthetic O₂ evolution rate in the callus cells was much lower than that in the differentiated plant cells. The in vitro cell cultures containing merely proplastids did not practically produce SGs. However, after transferring these cultures in the light, both the formation of chloroplasts and the production of SGs in them were detected.     

Structure and development of the upper haustorium in the parasitic flowering plant Cuscuta japonica (Convolvulaceae)

The anatomical and ultrastructural development of the haustorium of the Cuscuta japonica, a holoparasitic angiosperm, growing on the host plant Impatiens balsamina was studied. After the shoot tips of light-grown parasite seedlings contacted the host, the upper haustorium (external to the host organ) developed through three main successive stages of the haustorial initials, the meristem, and the endophyte primoridium (EP) within the middle layer of the cortex of the parasite stem. The haustorial initial cells were characterized by abundant starch-bearing amyloplasts and mitochondria with an expanded intermembrane space. The meristem cells had numerous large chloroplasts with well-developed thylakoids, reflecting the capability for photosynthesis. Commonly, all three stages of haustorial cells contained conspicuous, large nuclei with enlarged nucleoli and dense cytoplasm including many other organelles, indicating a very active metabolism. In the final stage of upper haustorium development, the meristem cells differentiated into the EP, a host-penetrating tissue. The primordium had smaller file cells at the proximal end and elongate digitate cells at the distal end. The file cells divided actively, while the digitate cells contained abundant chloroplasts, dictyosomes, rough endoplasmic reticulum, and other organelles, suggesting that the EP was cytohistologically well organized for penetration into the host tissue.     

THE ULTRASTRUCTURE OF CARPOSPOROGENESIS IN THE MARINE HEMIPARASITIC RED ALGA ERYTHROCYSTIS SACCATA1

The ultrastructure of carposporogenesis for Erythrocystis saccata is described. The fusion and gonimoblast cells contain few organelles, and chloroplasts are in a proplastid state, with pit plugs between gonimoblast cells dissolving early in development. Carpospore development may be separated into 3 stages, the first stage being characterized by the appearance of straight-profiled dictyosomes, fibrous vesicles, and an increase of discoid thylakoids within the chloroplasts. During the second, stage the dictyosomes assume a curved profile and striped vesicles are formed by the endoplasmic reticulum. The third stage is initiated by the disappearance of striped vesicles and the appearance of straight-profiled dictyosomes secreting vesicles with cores. Mature carpospores consist of many cored vesicles, fibrous vesicles, and floridean starch grains. A single wall layer surrounds each carpospore since the carposporangial wall becomes incorporated into a mucilaginous matrix surrounding the spores.     

ULTRASTRUCTURE OF CARPOSPOROGENESIS IN THE PARASITIC RED ALGA FAUCHEOCOLAX ATTENUATA SETCH. (RHODYMENIALES,RHODYMENIACEAE)

Carpospore differentiation in Faucheocolax attenuata Setch. can be separated into three developmental stages. Immediately after cleaving from the multinucleate gonimoblast cell, young carpospores are embedded within confluent mucilage produced by gonimoblast cells. These carpospores contain a large nucleus, few starch grains, concentric lamellae, as well as proplastids with a peripheral thylakoid and occasionally some internal (photosynthetic) thylakoids. Proplastids also contain concentric lamellar bodies. Mucilage with a reticulate fibrous substructure is formed within cytoplasmic concentric membranes, thus giving rise to mucilage sacs. Subsequently, these mucilage sacs release their contents, forming an initial reticulate deposition of carpospore wall material. Dictyosome vesicles with large, single dark-staining granules also contribute to wall formation and may create a separating layer between the mucilage and carpospore wall. During the latter stages of young carpospores, starch is polymerized in the perinuclear cytoplasmic area and is in close contact with endoplasmic reticulum. Intermediate-aged carpospores continue their starch polymerization. Dictyosomes deposit more wall material, in addition to forming fibrous vacuoles. Proplastids form thylakoids from concentric lamellar bodies. Mature carpospores are surrounded by a two-layered carpospore wall. Cytoplasmic constituents include large floridean starch granules, peripheral fibrous vacuoles, mature chloroplasts and curved dictyosomes that produce cored vesicles which in turn are transformed into adhesive vesicles. Pit connections remain intact between carpospores but begin to degenerate. This degeneration appears to be mediated by microtubules.     

STRATIFICATION AND SUBSEQUENT BEHAVIOR OF PLANT CELL ORGANELLES

Living excised roots of pea were centrifuged at 20,000 g for 24 hours, and the behavior of organelles was followed by electron microscopy at various intervals after centrifugation. With these forces, organelles are not perceptibly or irreversibly damaged, nor is the viability of the whole root destroyed. Organelles stratify generally in the order of lipid (centripetal pole), vacuoles, smooth endoplasmic reticulum and dictyosomes, proplastids (without starch), mitochondria, rough endoplasmic reticulum, proplastids with starch. The nucleus distends from the vacuolar region to the extreme centrifugal pole of the cell, while the chromatin and nucleolus seek the centrifugal pole of the nucleus. During the redistribution of organelles the rough endoplasmic reticulum is among the first to reorient, and possible explanations for this are discussed. Mitochondria can be stretched elastically many times their original length, but proplastids seem fairly rigid. Small vacuoles, forced together during centrifugation, apparently may fuse to form a large unit. Lipid droplets, on the other hand, tend to remain separate. Dictyosomes and smooth endoplasmic reticulum layer in the same region of the centrifuged cell, indicating a density similarity between these two organelles.     

细叶黄芪叶肉原生质体发育早期几种细胞器的变化

在细叶黄芪叶肉原生质体发育早期,细胞器的变化较大。离体培养4h后,线粒体的嵴和基质物质开始增加。培养3—5天后,线粒体的数量增加5倍以上,此时可见大部分线粒体围绕细胞核分布。在培养24h后,高尔基体开始发育,它们主要分布在细胞质周边区域。多糖细胞化学染色表明,高尔基体内沉积着大量嗜银物质。培养1天后,粗面内质网开始发育。培养3天时,部分叶绿体边缘出现一些空隙结构。随着叶绿体内膜结构的消失,淀粉粒增大,叶绿体逐渐转变为造粉质体。     

ULTRASTRUCTURE OF DIFFERENTIATED CELLS IN HIGHER PLANTS

Esau , Katherine . (U. California, Santa Barbara.) Ultrastructure of differentiated cells in higher plants. Amer. Jour. Bot. 50(5): 495–506. Illus. 1903.—This paper reviews the rather meager information on differences between meristematic and fully differentiated cells of higher plants at the ultrastructural level. It includes personal observations on differentiated cells in Cucurbita maxima and Vitis vinifera, particularly those of the phloem tissue. The structures considered and illustrated by means of electron micrographs are vacuoles, the nucleus, mitochondria, the endoplasmic reticulum, dictyosomes, plasmodesmata, and, briefly, plastids.     

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。     

An ultrastructural and cytochemical investigation of the colonial green algaPediastrum tetras during zoospore formation

Summary Ultrastructural changes during zoospore formation and aggregation into motile, aggregating zoospores were examined in the colonial green algaPediastrum tetras. Developing zoospores are characterized by irregularly shaped nuclei, presence of peripheral networks of rough endoplasmic reticulum, chloroplasts with tightly apposed thylakoids and dictyosome cisternae which are compressed and reduced in size. A single membrane bound organelle with a fine granular matrix of moderate electron density of diameter ranging from 0.2 m to 0.6 m and associated with chloroplasts, mitochondria and endoplasmic reticulum was found only in adult cells. Although this organelle has the morphology of a microbody, it did not stain with 3,3-diaminobenzidine (DAB) at pH 9.6 or pH 7.6, whereas mitochondrial membranes stained. No DAB staining was observed along the cell wall or the plasma membrane of zoospores, or associated with endoplasmic reticulum, plastid membranes or dictyosomes.     

Ultrastructural changes of cell organelles inArabidopsis stems after gamma irradation

We examined ultrastructural changes of the cell organelles ofArabidopsis stems in response to gamma irradiation. Seedlings treated with 0 to 5 Gy developed normally, while height growth in plants exposed to 50 Gy was significantly inhibited. Based on TEM observations, the chloroplasts were extremely sensitive to such irradiation. In particular, the thylakoids were heavily swollen, some portions of the mitochondria and endoplasmic reticulum were structurally altered, and the plasmalemma had pulled away from the cell wall in places. However, no ultrastructural changes in cell organelles occurred at doses of 0 to 5 Gy.     

AN ULTRASTRUCTURAL STUDY OF CHLOROPLAST STRUCTURE AND DEDIFFERENTIATION IN TISSUE CULTURES OF STREPTANTHUS TORTUOSUS (CRUCIFERAE)

Cells of Streptanthus tortuosus callus tissue contain chloroplasts when cultured in a liquid medium in the light. Similar cells grown in the dark contain proplastids that fail to develop prolamellar bodies but do contain a complex of loosely-associated membranes. When green, light-grown cultures are cut into small pieces and subcultured to a fresh culture medium, they become bleached even though maintained under the same illumination. The fine structure of the chloroplasts and the chlorophyll content of the cells indicate a dedifferentiation of the chloroplasts to a proplastid state during the early culture period. The changes in the ultrastructure of the plastids are paralleled by a dedifferentiation of the vacuolate cells to a less differentiated, meristematic state. Subsequent growth in the light results in a re-formation of chloroplasts and an increase in the chlorophyll content of the cells. The period of chloroplast redevelopment is associated with the re-formation of large central vacuoles in the cultured cells. Invaginations of the inner membrane of the plastid envelope occur at all stages of plastid development and are not lost during the period of grana degeneration. The proplastids formed from the dedifferentiation of the chloroplasts contain a large number of these invaginations and the redevelopment of grana is associated with a change in the electron density of the invaginating membranes. The degradation of the chlorophyll-containing membranes of the grana occurs during a period of rapid cytoplasmic synthesis induced by the fresh supply of nutrients in the culture medium. These results suggest that the high levels of nutrients may act directly on the chloroplasts and cause their dedifferentiation or that the rapid cell growth induced by the nutrients may cause a degradation of the membrane proteins in the grana of the chloroplasts and an incorporation of the released amino acids into non-plastid components of the cytoplasm.     

The effect of abscisic acid on cold tolerance and chloroplasts ultrastructure in wheat under optimal and cold stress conditions

The effect of abscisic acid (0.1 mM) on cold tolerance of leaf cells and ultrastructure of chloroplasts in wheat (Triticum aestivum L.) under optimal (22 °C) and cold stress conditions (4 °C) was studied. Results indicated that exogenous abscisic acid induces a rise in the cold tolerance of wheat along with a number of significant ultrastructural changes in chloroplasts both at 22 and at 4 °C. Some of them (increase in density of chloroplasts stroma, formation of “distorted” and “dilated” thylakoids, appearance of invaginations, changes in the shape of chloroplasts and increase of their dimension owing to the stroma area) were common to the two types of treatments. At the same time, the character of changes in the membrane system of plastids was temperature specific, i.e. if at 22 °C the hormone caused a considerable increase in the length of photosynthetic membranes in chloroplast owing the length of both appressed and non-appressed membranes of thylakoids, then in cold stress conditions observed an increase in the number of grana and the length of appressed membranes of thylakoids. These results suggested that the rise in the cold tolerance of abscisic acid-treated plants is associated with the ultrastructural reorganization of chloroplasts aimed to defense plant cells against chilling injury and to maintain the activity of the photosynthetic system.     

Ultrastructure and development of nonarticulated laticifers in seedlings ofEuphorbia maculata L.

The ultrastructure of nonarticulated laticifers in the seedlings ofEuphorbia maculata was studied at various developmental stages. The apical regions of the seedling laticifers growing intrusively contained large nuclei with mainly euchromatin and dense cytoplasm possessing various and many organelles such as rich ribosomes, several small vacuoles, giant mitochondria with dense matrices, rough endoplasmic reticulum, dictyosomes, and proplastids. This result suggested that the apical regions of laticifers were metabolically very active. Laticifers in seedlings at the first-leaf developmental stage did not contain latex particle. In seedlings at second-leaf growth stage, the laticifer cells contained numerous and elongated small vacuoles. These vacuoles appeared to arise by dilation of the endoplasmic reticulum and frequently possessed osmiophilic or electron-dense latex particles. The small vacuoles fused with the large vacuole occupying the central portion of the subapical region of laticifers, and then the latex particles were released into the large central vacuole. The latex particles varied in size and were lightly or darkly stained. Proplastids with a dense matrix and a few osmiophilic plastoglobuli were filled with an elongated starch grain and thus were transformed into amyloplasts. Latex particles were initially produced in the laticifers after seedlings had developed their second young leaves. In seedlings at forth-leaf stage, latex particles with an alveolated rim were found in the laticifers.     

Floral nectary ultrastructure of Prunus persica (L.) Batch cv. Forastero (Newcomer), an Argentine peach

 Flowers of Prunus persica (L.) Batch. cv. Forastero have an orange toral nectary. The nectariferous tissue was formed by densely packed parenchyma cells (secretory cells) and an epidermis with hairs and modified stomata. The epidermal cells were highly vacuolated with a striated cuticle. The ultrastructure of these cells contained a cytoplasm with endoplasmic reticulum, plastids, mitochondria and dictyosomes. Sub-epidermal cells were barely vacuolated and their ultrastructure was similar to that of the epidermal cells. Differences were observed only in the endoplasmic reticulum, which is organized in a parallel configuration. Plasmodesmata were found between adjacent secretory cells and between secretory and epidermal cells. An electron dense secretion occurred in the intercellular spaces and between the external tangential wall and the cuticle of the epidermal cells. According to the ultrastructural observations, the sugar solution could be passed through the symplast or the apoplast. The nectar could be exuded from the stomata and the micro-channels of the cuticle covering the epidermal cells. Received July 7, 2002; accepted September 24, 2002 Published online: June 2, 2003     

Initiation and ultrastructure of a reptilian fibroblast cell line obtained from cutaneous fibropapillomas of the green turtle,Chelonia mydas

Summary Two fibroblastic cell lines were established from explants of fibropapillomas of each of two different green turtles (Chelonia mydas). These cells, designated GTFP (Green Turtle Fibropapilloma), were subcultured approximately 30 times at 30°C in Eagle’s minimal essential media supplemented with 2 to 10% fetal bovine serum. The ultrastructural morphology of the cultured fibroblasts is described. The cells contained abundant rough endoplasmic reticulum, polyribosomes, and mitochondria; collagen fibrils were visible in the extracellular space. No viruslike particles or evidence of other pathogenic agents could be demonstrated by electron microscopy in any of the cultured cells examined. Supported in part by a grant from Sea World Research Institute, Hubbs Marine Research Center, San Diego, California 92109, and the Chelonia Institute, Arlington, Virginia 22209. Published as University of Florida, College of Veterinary Medicine, Journal Series no. 192.     

Ultrastructural changes in the MP3 neuron of the mollusk Lymnaea stagnalis after cryopreservation of the isolated brain

Investigation of a possibility of long-term storage of frozen (-196 degrees C) viable neurons and nervous tissue is one of the central present day problems. In this study ultrastructural changes in neurons of frozen-thawed snail brain were examined as a function of time. We studied the influence of cryopreservation, cryoprotectant (Me2SO), cooling to 4-6 degrees C, and a prolonged incubation in physiological solution at 4-6 degrees C on dictyosomes of Golgi apparatus, endoplasmic reticulum (ER) cisternae and mitochondria. It has been found that responses of these intracellular structures of cryopreserved neurons to the above influences are similar: dissociation of Golgi dictyosomes, swelling of endoplasmic reticulum cisternae and mitochondrial cristae. Both freezing-thawing and cryoprotectant were seen to cause an increase in the number of lysosomes, liposomes, myelin-like structures, and to form large vacuoles. The structural changes in molluscan neurons caused by cryopreservation with Me2SO (2 M) were reversible.     

ULTRASTRUCTURE OF GLANDULAR OVARIAN TRICHOMES OF CYPRIPEDIUM CALCEOLUS AND C. REGINAE (ORCHIDACEAE)

Trichomes on the orchid ovary are a possible site of synthesis and secretion of the floral scent. Scanning electron microscopy of these trichomes shows a bulbous cell on a two-celled stalk. Thin sections of the tip cell revealed the morphology of an active, secretory cell with unusual coated vesicles in the extra-cellular deposition. Abundant smooth endoplasmic reticulum (ER) aggregated beneath the plasma membrane in the apical region of the cell and the limited dictyosomes in the cell suggest direct secretion by ER. Numerous lipid droplets are present in the apical area. Plastids, found only in the basal region of this cell, are more round in profile than typical chloroplasts and contain only a few unstacked thylakoids and a limited membranous reticulum. In addition to the normal plastid envelope, a double layer of membrane (probably ER) is tightly appressed to each dense, starch-free plastid. Highly specialized morphology and subcellular localization of organelles suggest the secretory nature of these trichomes.