G. Deichgräber

Food uptake and the fine structure of the dinophytePaulsenella sp. an ectoparasite of marine diatoms

SummaryMotile dinospores ofPaulsenella attach to a host diatom frustule, form a feeding tube, drive it between epi- and hypocingulum, pierce the host plasmalemma and suck up host cytoplasm gradually. This mode of endocytosis (“myzocytosis”) implies that the host plasmalemma is not ingested and that the host cytoplasm within the food vacuole is bounded only by the vacuolar membrane. The feeding tube is formed by the emergence of a preformed “microtubular basket” consisting of plates of microtubules. At its entrance into the cell body the feeding tube channel is surrounded by an electron-dense ring. Similar “sphincters” enclose the two exits through which the two flagella emerge. These sphincters are composed of microfibrils which reveal a cross striation when the fixative does not contain calcium ions. The flagellar bases as well as the internal part of the feeding tube are surrounded by a common cavity which is in open connection also with the ampullae of the pusule. The light and electron microscopical observations do not support the assumption that food uptake is driven by a flow of the membrane of the feeding tube channel caused by an interaction with the microtubular basket (as postulated for food uptake inSuctoria) but rather by an hydrostatic gradient which might be caused by rhythmical ion pumping and be based on the existence of the common cavity and the sphincters. Myzocytosis is inhibited by cytochalasin B.—The fine structure of dinospores and trophonts, especially with respect to the cell covering, the amphiesma, and the en- and excystment, is described.

Morphogenetic processes inAttheya decora (Bacillariophyceae, Biddulphiineae)

The valva of the diatomAttheya decora is formed within a silica deposition vesicle which enlarges centrifugally by the fusion of small vesicles. The silica deposition vesicle can already be seen when the spindle has not yet disappeared completely. Valva formation seems to begin with the shaping of an organic matrix within a silica deposition vesicle. Later, this material silicifies. The complicated shape of the labiate process is preformed by the silica deposition vesicle, the inner membrane of which is associated with electron dense material on both faces. The horns are formed when the expanding silica deposition vesicle has reached the cell corners. They are elaborated without participation of microtubules. Swelling of local depositions of polysaccharides seems to provide the forces that spread the silicified horns during daughter cell separation and to cause the local „spontaneous plasmolyses“ under the valva and along the cell flanks in the region of the intercalary bands. The inner organic wall layers and the organic continuations of the intercalary bands are formed on the surface of the plasmalemma; each of the continuations is produced simultaneously with the intercalary band belonging to it and becomes attached to the latter when the silica deposition vesicle opens.

Development and ultrastructure of the marine, parasitic Oomycete,Lagenisma coscinodisci Drebes (Lagenidiales): Formation of the primary zoospores and their release

SummaryZoosporogenesis inLagenisma begins after the final nuclear division by the development of “encystment vesicles” which presumably are derived from Golgi vesicles. The sporangial wall is secreted simultaneously. Initially, the encystment vesicles have an internal coat of fine ribs which becomes a uniform mass during the complicated invagination of the vesicles. When the sporangial wall is complete the protoplast cleaves centripetally by means of narrow “cleavage cisternae” apparently coming from the distal face of the dictyosomes and being detached by interposing ER cisternae. The cleavage cisternae fuse with each other and with the plasmalemma to which they are often parallel. Narrow cytoplasmic compartments are then cut off and swell to become “separation vesicles” which lie between the developing zoospores but later disintegrate. Basal bodies develop from procentrioles after the final nuclear division and elongate into flagella (without participation of a flagellar vesicle) when cleavage is complete. The mastigonemes are formed within the ER, mature within the peripheral elements of the dictyosomes near the flagellar bases and appear to be extruded after the elongation of the flagellum. Structurally, especially in the organization of the flagellar root apparatus, the zoospores resemble primary zoospores of other Oomycetes. They become motile within the zoosporangium but seem to be driven out by means of additional unknown forces.—Formation of the encystment vesicles and the manner of cleavage are compared with those of other Oomycetes and general aspects ofLagenisma zoosporogenesis are discussed.

Tip Cell Growth and the Frequency and Distribution of Particle Rosettes in the Plasmalemma: Experimental Studies in Funaria Protonema Cells

SummaryComparingFunaria protonema tip cells of different age and of experimentally modified growth rate (by changing the light-dark-regime, by application of colchicine and of D2O and by plasmolysis) we found that the site and intensity of growth are related closely to the distribution and frequency of particle rosettes in the PF of the plasma membrane. The results confirm previous suggestions that the rosettes are involved in cellulose fibril formation and that they have a rather short life time (about 10–15 minutes,Reisset al. 1984). The appearance of rosettes seems to depend on the exocytosis of Golgi vesicle containing wall matrix material. Morphometric calculations suggest that each Golgi vesicle may incorporate one rosette into the plasmalemma in caulonema tip cells.

Structure, function, and development of the peristome of the moss,Rhacopilum tomentosum, with special reference to the problem of microfibril orientation by microtubules

SummaryThe movement of the outer peristome teeth of the sporangium of the moss,Rhacopilum tomentosum, is driven by different swelling velocities of the outer (“plates”) and inner (“ridges”) wall thickenings due to suberin-like substances and wax-lamellae which enclose the ridges. The plates do not contain suberin-like material. The hydrophobic materials are secreted with the participation of smooth tubular ER.—When the local wall thickenings of the peristome teeth are formed, microtubules are concentrated along the plasmalemma in the thickening regions. They run along the crest of the developing plates (i.e., normal to the long axis of the tooth) and parallel to the long axis in the ridge cells. The wall thickenings are composed of layers of parallel microfibrils and of matrix substances. With a few exceptions microtubules and microfibrils have different directions. Golgi vesicles, subsurface ER and coated regions in the plasmalemma also are involved in cell wall formation. The function of the microtubules is discussed.

Development of cell wall appendages inAcanthosphaera zachariasi (Chlorococcales): Kinetics, site of cellulose synthesis and of microfibril assembly, and barb formation

SummaryThe investigation of the formation of cell wall appendages inAcanthosphaera by means of light and electron microscopy and by the use of dyes which interfere with microfibril assembly resulted in several observations which are helpful to an understanding of the formation of normal cell walls. The barbs are built up in the ER, pass through the Golgi apparatus, and are extruded exocytotically after cytokinesis, a remarkable example of the secretion of a structured product. Each cellulose microfibril in a spike develops in a distinct pit of the plasmalemma. The pits are aggregated in a pit field, generating one spike, and are closely adjacent to a basal vesicle which might have morphogenetic and/or regulatory functions. The pits are the site of cellulose synthesis; here the plasmalemma is conspicuously thickened. As shown directly and by the application of Calcofluor white and Congo red, the microfibrils assemble at a certain distance from the plasma membrane,i.e. cellulose synthesis and microfibril assembly are separated by a gap. It is discussed whether single glucan chains or small bundles of them are released from the plasmalemma. The elongation rate of the spikes indicates that about 1000 glycosidic linkages per glucan chain per minute are formed.

Structure and formation of fibrillar mucilages in seed epidermis cells

SummaryThe seed epidermis cells ofCollomia grandiflora Dougl. contain a mucilage with an amorphous and a fibrillar component. The elementary fibrils are very long and usually measure about 2.0 2.5 nm in thickness after negative staining but more than 5 nm in thin sections. They seem to consist of cellulose but are stained also with aniline blue; the emitted fluorescence light is polarized. The elementary fibrils are surrounded by the amorphous component of the mucilage and are loosely associated to form mucilage strands and, more densely, a massive spiral (or rings) which is embedded in the mucilage. During mucilage formation, microtubules run parallel with the elementary fibrils, both are oriented circumferentially. Microtubules are dense in regions where mucilage strands are formed and especially frequent where the spiral is being produced. Within the outer cell wall of the epidermis cells, lacuna-like spaces develop underneath the cuticle. They become partly filled with stacks of electron transparent lamellae, embedded in an electron dense material and resemble layers of waxes but are thicker than common “wax layers”.

Herbicide Induced Changes in Wheat Chloroplast Ultrastructure and Chlorophyll a/b Ratio

Summary Wheat plants (Triticum aestivum L. cv. Kolibri) treated with the photosynthesis inhibiting herbicide methabenzthiazuron (N-(benzothiazol-2-yl)-N,N′-dimethylurea) responded by a decreased chlorophyll a/b ratio and an increased proportion of grana to stroma lamellae. The concentration of soluble reducing sugars was simultaneously reduced, but the concentrations of soluble amino acids and soluble proteins were increased. These results are integrated into the results from earlier experiments with methabenzthiazuron treated wheat plants, and the correlations with the available evidence on chloroplast ultrastructure in photosynthetically inhibited and in shaded plants are discussed.