The formation and development of cellulose-synthesizing linear terminal complexes (TCs) in the plasma membrane of the marine red algaErythrocladia subintegra Rosenv.

Summary The formation and development of linear terminal complexes (TCs), the putative cellulose synthesizing units of the red algaErythrocladia subintegra Rosenv., were investigated by a freeze etching technique using both rotary and unidirectional shadowing. The ribbon-like cellulose fibrils ofE. subintegra are 27.6 ± 0.8 nm wide and only 1–1.5 nm thick. They are synthesized by TCs which are composed of repeating transverse rows formed of four particles, the TC subunits. About 50.4 ± 1.7 subunits constitute a TC. They are apparently more strongly interconnected in transverse than in longitudinal directions. Some TC subunits can be resolved as doublets by Fourier analysis. Large globular particles (globules) seem to function as precursor units in the assembly and maturation of the TCs. They are composed of a central hole (the core) with small subunits forming a peripheral ridge and seem to represent zymogenic precursors. TC assembly is initiated after two or three gobules come into close contact with each other, swell and unfold to a nucleation unit resembling the first 2–3 transverse rows of a TC. Longitudinal elongation of the TC occurs by the unfolding of globules attached to both ends of the TC nucleation unit until the TC is completed. The typical intramembranous particles observed inErythrocladia (unidirectional shadowing) are 9.15 ± 0.13 nm in diameter, whereas those of a TC have an average diameter of 8.77 ± 0.11 nm. During cell wall synthesis membranes of vesicles originating from the Golgi apparatus and which seem to fuse with the plasma membrane contain large globules, 15–22 nm in diameter, as well as tetrads with a particle diameter of about 8 nm. The latter are assumed to be involved in the synthesis of the amorphous extracellular matrix cell wall polysaccharides. The following working model for cellulose fibril assembly inE. subintegra is suggested: (1) the ribbon-like cellulose fibril is synthesized by a single linear TC; (2) the number of glucan chains per microfibril correlates with the number of TC subunits; (3) a single subunit synthesizes 3 glucan chains which appear to stack along the 0.6 nm lattice plane; (4) lateral aggregation of the 3-mer stacks leads to the crystalline microfibril.Dedicated to Prof. Dr. Dr. h.c. Eberhard Schnepf on the occasion of his retirement     

The supramolecular organization of red algal cell membranes and their participation in the biosynthesis and secretion of extracellular polysaccharides: a review

Summary The relationship between the supramolecular organization of red algal cell membranes and the biosynthesis and secretion of the cell wall skeletal and matrix polysaccharides is reviewed. Freeze-fracture studies have revealed that organized macromolecular structures — linear terminal complexes and tetrads — are present on the plasma membrane and on membranes of the endomembrane system. The linear terminal complexes seem to be involved in the biosynthesis, assembly, and orientation of the cellulose microfibrils and the tetrads in the synthesis of the matrix polysaccharides. It is shown how the research on the supramolecular organization of cell membranes has increased the knowledge on the biosynthesis and secretion of the extracellular crystalline and non-crystalline polysaccharides in red algae. In this review, the progress to date is discussed.Dedicated to Prof. Dr. Dr. h.c. Eberhard Schnepf on the occasion of his retirement     

Mikrospektralphotometrische Untersuchungen zum Speichermechanismus des amphoteren OxazinfarbstoffsPrune pure durch die lebende pflanzliche Zelle

Zusammenfassung Elektrophorese-, spektralphotometrische und Ausschüttelversuche mit hydrophoben Solventien ergeben, daßPrune pure in der wässerigen Lösung, je nach dem pH-Wert, als einwertiges Kation, Zwitterion und Anion vorliegt. Im stark sauren Bereich (H₂SO₄) kann es noch als zweiwertiges Kation auftreten. Das Farbbasenmolekül ist nur in hydrophoben Lösungsmitteln nachzuweisen.Mit Zunahme der Farbstoffkonzentration in einer wässerigen Lösung (pH7) verschiebt sich das Absorptionsmaximum von = 640 nm nach = 580 nm. Diese Verschiebung beruht sehr wahrscheinlich auf einer Assoziation der Zwitterionen.In polaren Lösungsmitteln verschiebt sich das Absorptionsmaximum desPrune pure mit zunehmender Polarität in den längerwelligen Bereich.Rutin bedingt eine negative Metachromasie.Plasma und Zellkern der Oberepidermis vonAllium- cepa- Schuppenblättern zeigen nach Vitalfärbung mitPrune pure übereinstimmend ein breites Absorptionsmaximum bei 575 nm. Die Färbungsintensität übt keinen Einfluß auf die Lage des Maximums aus.Die mitPrune pure gefärbten vollen Zellsäfte der Unterepidermis besitzen ein Absorptions-maximum bei 675 nm.Aus der Lage der Absorptionsmaxima und der Form der Absorptionskurven wird geschlossen, daßPrune pure von Plasma und Zellkern als Farbbasenmolekül in apolaren Lipoiden gespeichert wird. Auf Grund der Dissoziationskonstante des Farbstoffs kannPrune pure nur von vollen Zellsäften aufgenommen werden. In den Unterepidermiszellen liegt eine Bindung an zellsafteigene Flavonole vor.

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Microspectrophotometric investigations into the mechanism of accumulation of the amphoteric oxacin dyePrune pure by the living plant cell

Summary Electrophoretic, spectrophotometric and shake out experiments withPrune pure show that in aqueous solution the dye is present according to pH as a univalent cation, zwitterion or anion. In strongly acid solutions (H₂SO₄) it may be present, too, as a bivalent cation. The dye base molecule is demonstrable only in hydrophobic solvents.In aqueous solution (pH 7.0) the absorption maximum shifts from = 640 nm to = 580 nm when the concentration of the dye is increased. The shift probably is due to an association of zwitterions.In polar solvents the absorption maximum ofPrune pure shifts towards the long wave area with increasing polarity of the solvent.Rutin causes negative metachromasy.After vital staining withPrune pure both the plasma and the nucleus of cells from the upper epidermis of scale leaves ofAllium cepa show a broad absorption maximum at 575 nm. The staining intensity has no influence over the position of the maximum.The full cell saps of cells from the lower epidermis give an absorption maximum at 675 nm when stained withPrune pure.From the position of the absorption maxima and the shape of the absorption curves it is concluded thatPrune pure is accumulated by the plasma and the nucleus as the dye base molecule into apolar lipoids.According to the dissociation constant ofPrune pure the dye can only be accumulated by ful cell saps. In cells of the lower epidermis it is bound to flavonoles present in the cell sap.

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Herrn Professor Dr. H.Drawert danke ich für die Unterstützung dieser Arbeit und für anregende Diskussionen; dem Deutschen Akademischen Austauschdienst (DAAD) bin ich für die Gewährung eines Stipendiums dankbar. Das UMSP I stellte die Deutsche Forschungsgemeinschaft zur Verfügung.     

Development of mestome sheath cells in leaves ofAegilops comosa var.thessalica

Summary The development of mestome sheath cells ofAegilops comosa var.thessalica was studied by electron microscopy. Anatomical and cytological observations show that this grass belongs to the C₃ or non-Kranz plants. In the asymmetrically thickened walls of mestome sheath cells a suberized lamella is present. This lamella is deposited asynchronously. In the midrib and the large lateral bundles it appears first in the outer and inner walls and usually later in the radial walls. In the small lateral bundles its appearance is delayed in the inner walls of those cells situated on the xylem side. At maturity the suberized lamella is observed in all cell walls; however, in the small lateral bundles it is partly or totally absent from the walls of some cells situated on the xylem side. Tertiary wall formation is asynchronous as well, for it generally follows the deposition pattern of the suberized lamella.During the development of the mestome sheath cells microtubules show marked changes in their number and orientation, being fewer and longitudinal during suberin deposition. Dictyosomes are very active and may be involved in primary and tertiary wall formation. Endoplasmic reticulum cisternae are abundant and partly smooth, while plasmalemmasomes may function to reduce the plasmalemma extension. However, cytoplasmic structures that are clearly involved in suberin synthesis could not be identified.Suberized lamellae react strongly with silver hexamine. This is probably due to post-fixation with osmium tetroxide.On the basis of structural characteristics the mestome sheath may be regarded as an endodermis (cf., alsoFahn 1974). The significance of this view for water and assimilate exchange between the mesophyll and the bundle is discussed.This report represents a portion of a doctoral dissertation.     

Ultrastructure of the differentiating zygotospores of Porphyra leucosticta (Rhodophyta)

The ultrastructure of zygotosporogenesis is described for the red alga Porphyra leucosticta Thuret. Packets of eight zygotosporangia, each packet derived from a single carpogonium are interspersed among vegetative cells. Zygotospore differentiation in Porphyra can be separated into three developmental stages. (i) Young zygotospores exhibit a nucleus and a large centrally located, lobed plastid with pyrenoid. Mucilage is produced within concentric membrane structures during their dilation, thus resulting in the formation of mucilage sacs. Subsequently, these sacs release their contents, initiating the zygotospore wall formation. Straight‐profiled dictyosomes produce vesicles that also provide wall material. During the later stages of young zygotospores, starch polymerization commences, (ii) Medium‐aged zygotospores are characterized by the presence of fibrous vacuoles. These are formed from the ‘fibrous vacuole associated organelles’. The fibrous vacuoles finally discharge their contents. (iii) Mature zygotospores are recognized by the presence of numerous cored vesicles produced by dictyosomes. Cored vesicles either discharge their contents or are incorporated into the fibrous vacuoles. There is a gradual reduction of starch granules during zygotospore differentiation. Mature zygotospores are surrounded by a fibrous wall, have a large chloroplast with pyrenoid and well‐depicted phycobilisomes but are devoid of starch granules.     

Ultrastructural studies on the secretory cavities ofCitrus deliciosa ten. II. Development of the essential oil-accumulating central space of the gland and process of active secretion

Summary Oil glands ofCitrus deliciosa are multicellular secretory structures, globular to oval in shape, in the centre of which an essential oil-accumulating space is formed. Opening of this space begins from a single cell. It undergoes lysis which later extends to the neighbouring gland cells.Secretory material in form of droplets is produced in plastids, from where it is transported to the parietal cytoplasm of the secretory cells via numerous ER-elements. After fusion of the ER-membranes with the plasmalemma, the exudate reaches the apoplast, through which it is driven to the central cavity of the gland.Peripheral cells of the secretory complex are modified into a protective sheath with thick walls and large vacuoles, while their plastids are differentiated from leucoplasts into typical amyloplasts.     

Occurrence of the putative microfibril-synthesizing complexes (linear terminal complexes) in the plasma membrane of the epiphytic marine red algaErythrocladia subintegra Rosenv.

Summary Cells of thalli at different developmental stages of the epiphytic marine red algaErythrocladia subintegra have been studied by freeze-etching. It was found that the plasma membrane exhibits linear microfibril-termnal synthesizing complexes (TCs), randomly distributed consisting of four rows of linearly-arranged particles (average diameter of particles 8.6 nm); each row of TCs consists of 5–33 particles (average 15). The TCs were observed on both fracture faces (PF and EF) but more clearly on the PF face. These structures appear to span both the outer and inner leaflets of the plasma membrane (transmembrane complexes)-The TCs have stable width (35 nm) and vary in length (41–311 nm, average 181 nm). The TCs subunits are highly ordered arrays forming a semicylinder. The average density of TCs on the PF face is 5.5TC/m². The microfibrils are randomly distributed and have a mean width of 39.4 nm (ranging from 16 to 70 nm). Many TCs are associated with the ends of microfibrils and microfibril imprints. The structural characteristics of linear TCs in the red algaErythrocladia are compared with those of the so far investigated Chlorophyta spp. All results favour the suggestion that TCs in the plasma membrane ofErythrocladia cells are involved in the biosynthesis, assembly and orientation of microfibrils.