The perturbation of the endomembrane network of the chlamydomonad alga Gloeomonas by the herbicide isopropyl N-phenyl carbamate (IPC)

Abstract. The highly complex and symmetric endomembrane network of the chlamydomonad alga, Gloeomonas kupferri , can be disrupted by the herbicide, isopropyl N-phenyl carbamate (IPC). Upon incubation with IPC for between 30 min and 1 h, curling of the dictyosomes, proliferation of small vesicles from the trans face and swelling of the peripheral vacuolar complex takes place. Longer treatments result in degeneration of dictyosome cisternae into vesicular masses and the formation of supervacuolar complexes. Enzyme cytochemistry revealed that endomembrane 'marker' enzymes are altered/inhibited by IPC. A second but striking I PC-induced effect is the production of branched, fibrillar inclusions in the cell nucleus. A discussion of I PC-induced affects on ion regulation and microtubule/MTOC distribution in the cell is presented.     

Plant cell extension: structural implications for the origin of the plasma membrane

Abstract. The proposal that rapidly elongating plant cells cannot maintain plasma membrane synthesis by means of the normal endomembrane system has been examined in elongating segments of Avena sativa coleoptiles. Segments were sampled and fixed for electron microscopy, before and after elongation on auxin solutions. Mean cell extensions, cytoplasmic volumes, dictyosomc numbers, and vesicle sizes and numbers were determined. It was shown that there are sufficient dictyosomes present to sustain the vesicle production necessary for the observed plasma membrane extension.     

FINE STRUCTURE OF CALONEIS AMPHISBAENA (BACILLARIOPHYCEAE)1

The structure of the motile pennate diatom Caloneis amphisbaena Cleve is described, with emphasis on the lateral, lobed pyrenoid with neither a limiting membrane nor penetration by thylakoids, an interphase nucleus with centers of condensed chromatin, paired dictyosomes, and mitochondria cradled within the chambers of the valve. Microfilaments forming two bundles which lie beneath each raphe slit are of the same size and appearance as actin microfilaments associated with other motile systems.     

Multiplication of the dictyosome during the formation of autospores in the green alga Chlorococcum infusionum

Numerical changes in dictyosomes during the formation of autospores in a green alga, Chlorococcum infusionum, were investigated by electron microscopy. Two dictyosomes were seen near the nucleus in young vegetative cells. Four dictyosomes were seen in large mononucleate cells which appeared to enter mitosis soon. Binucleate cells contained 4 or 8 dictyosomes, the latter number being found in the large binucleate cells. Large tetranucleate cells contained 16-25 dictyosomes in each cell. Dictyosomes consisted of about 4 cisternae with a diameter of 0.4-0.6 micron in mono- to tetranucleate cells. Cytokinesis began with the formation of the septa during the third nuclear division, and 16 cells were finally formed. Dictyosomes did not increase in number in 8- and 16-nucleate cells. In septum-forming cells, dictyosomes were 0.6-1.0 microns in diameter, with 6-9 cisternae. A single dictyosome was included in each of the 16 resultant cells. These observations suggest that the dictyosomes multiply in association with the multiplication of the nuclei without correlation with formation of the cell wall or cytokinesis.     

The golgi-mediated scale production in the marine haptophycean alga Ochrosphaera neapolitana Schussnig

Abstract

Some ultrastructural features of cells of the marine haptophycean alga, Ochrosphaera neapolitana Schussnig in the palmelloid stage were examined. Chloroplasts which are contained in a compartment isolated from the cytoplasm by ER profiles and nuclear envelope, display trilamellated thylakoids running along the major axis. The stalked pyrenoid with inner bilamellated thylakoids, protrudes in a large membrane-bounded vacuole. Other structures, as the haptonematic and flagellar bases, autophagic vacuoles and mitochondria, are typical of the chrysophycean and haptophycean genera so far investigated.

The Golgi apparatus is represented by a single dictyosome composed of stacked cisternae fonctioning in a way that they form organic scales which constitute the main part of the cell covering. The scales, build up of microfibrils disposed parallel each to other, lie in cisternal lumina of the dictyosomal maturing face; scaly cisternae are numerous in the peripheral cytoplasm and are observed merging in the plasma membrane and discharging the content outside the protoplast.

Dictyosomal activity is evidenced morphologically by massive vesicle production. Three kinds of membrane-bounded vesicles were identified in the present material: i) inner-granulated vesicles, arising from the maturation face; ii) coated vesicles, scattered in the cytoplasm or at the periphery of the golgi body, and iii) dense-cored vesicles, present in the proximity of the maturation face. The possible functional relationships related to scale production and assembly outside the protoplast, and between the nucleus and dictyosome are discussed.     

The distribution of membrane-bound 14-3-3 proteins in organelle-enriched fractions of germinating lily pollen

Proteins of the 14-3-3 family show a broad range of activities in plants, depending on their localisation in different cellular compartments. Different organelle membranes of pollen grains and pollen tubes of Lilium longiflorum Thunb. were separated simultaneously using optimised discontinuous sucrose density centrifugation. The obtained organelle-enriched fractions were identified as vacuolar, Golgi, endoplasmic reticulum and plasma membranes, according to their marker enzyme activities, and were assayed for membrane-bound 14-3-3 proteins by immunodetection. 14-3-3 proteins were detected in the cytoplasm as well as in all obtained organelle fractions but were also released into the extracellular medium. In pollen grains, much more plasma membrane-bound 14-3-3 proteins were detected than in the PM-enriched fraction of pollen tubes, whereas the level of Golgi- and ER-associated 14-3-3 proteins was similar in pollen grains and tubes. This shift in the localisation of membrane-associated 14-3-3 proteins is probably correlated with a change in the major function of 14-3-3 proteins, e.g., perhaps changing from initiating pollen grain germination by activation of the PM H +-ATPase to recruitment of membrane proteins via the secretory pathway during tube elongation.     

A STARCH GRAIN-MITOCHONDRION-DICTYOSOME ASSOCIATION IN BATRACHOSPERMUM(RHODOPHYTA)1

In Batrachospermum sirodotii Skuja the dictyosome-mitochondrion association, commonly reported in other red algae, includes a floridean starch grain during periods of intense dictyosomal activity. Such an organellar assemblage may serve to provide the most efficient means of energy flow during periods of peak dictyosomal activity.     

The Symplechosome: a Unique Cell Organelle of some Basidiomycetes*

An unusual cell organelle of some basidiomycetes, the symplechosome, is described and illustrated in detail using Saccoblastia farinacea as an example. Symplechosomes are structurally similar, but not identical to “classical” dictyosomes of green plants and animals. As is typical for dictyosomes, each symplechosome consists of a stack of platelike cisternae. The central portions of the symplechosome-cisternae are flattened, and adjacent cisternae are separated in the mid-region by an intercisternal space of constant width. In contrast to dictyosomes, the intracisternal spaces are completely obliterated in the central area, and hexagonally arranged bars extend between adjacent cisternae. Identical bars often connect the symplechosomes with mitochondria. Symplechosomes are highly complex-structured organelles which differ significantly from the simple individual Golgi cisternae or “Golgi bodies” observed in asco- and basidiomycetes.     

Ultrastructure of Trimastix pyriformis (Klebs) Bernard et al.: similarities of Trimastix species with retortamonad and jakobid flagellates.

Trimastix pyriformis (Klebs 1893) Bernard et al. 1999, is a quadriflagellate, free-living, bacterivorous heterotrophic nanoflagellate from anoxic freshwaters that lacks mitochondria. Monoprotist cultures of this species contained naked trophic cells with anterior flagellar insertion and a conspicuous ventral groove. Bacteria were ingested at the posterior end of the ventral groove, but there was no persistent cytopharyngeal complex. The posterior flagellum resided in this groove, and bore two prominent vanes. A Golgi body (dictyosome) was present adjacent to the flagellar insertion. The kinetid consisted of four basal bodies, four microtubular roots, and associated fibers and bands. Duplicated kinetids, each with four basal bodies and microtubular root templates, appeared at the poles of the open mitotic spindle. Trimastix pyriformis is distinguishable from other Trimastix species on the basis of external morphology, kinetid architecture and the distribution of endomembranes. Trimastix species are most similar to jakobid flagellates, especially Malawimonas jakobiformis, and to species of the retortamonad genus Chilomastix. Retortamonads may have evolved from a Trimastix-like ancestor through loss of "canonical" (easily seen with electron microscopy) endomembrane systems and elaboration of cytoskeletal elements associated with the cytostome/cytopharynx complex.