Numerous Plasmodesmata Research Articles

THE FINE STRUCTURE OF THE DIGESTIVE GLAND OF VENUS'S FLYTRAP

The digestive gland of Venus's flytrap has been studied by light and electron microscopy. Cells of the gland contain dense protoplasm comprised of relatively large nuclei, granular endoplasmic reticulum, osmiophilic vacuolar inclusions and numerous mitochondria, Golgi bodies and plastids. The vacuolar inclusions are predominantly protein but are also sudanophilic, therefore containing some lipid material. They are similar in appearance to aleurone grains. The nuclear envelope is a porous, double‐membrane structure, the pores of which are approximately 900 A and have a dense granular appearance. Plastids contain dense fine‐grained stroma, several thylakoids, osmiophilic globules and a tubular complex. Gland cell walls have many complex‐shaped protuberances extending into the cytoplasm providing a very large internal surface area. The stalk and basal cells contain numerous lipid globules and the common wall between the two cells is traversed by numerous plasmodesmata. In general the digestive gland fine structure is discussed in relation to its function.

Light- and electron-microscopical studies on the structure of salt glands of Tamarix aphylla L.

Cuttings of Tamarix aphylla were grown in various concentrations of NaCl. Salt glands on newly developed branches were sectioned and examined, both with the light- and with the electron-microscope. An electron-dense material appears in cuttings grown in all concentrations of NaCl at the anticlinal walls of the innermost pair of secretory cells and, to some extent, on the surface of the gland above the cuticle. In the glands of cuttings grown in high concentration of NaCl this material also appears in large quantities, not only on top of the gland but also beneath the cuticle at the region of the median anticlinal wall of the outermost pair of secretory cells. The material beneath the cuticle is connected to the electron-dense material on the outer surface of the cuticle via the secretory pores. It is suggested that this material is of pectic nature and forms a continuous system with the walls and wall protuberances of the secretory cells which are also very rich in pectic substances. As pectic substances absorb solutions easily they may enhance the transport of salt. Many proplastids, vacuoles with simple structure and others with infolded membranes as well as numerous mitochondria were observed in the secretory cells. In the walls between the collecting cells and the innermost secretory cells there are numerous plasmodesmata with characteristically arranged membranes.

Ultrastructural features of the salt gland of Tamarix aphylla L.

The salt gland in Tamarix is a complex of eight cells composed of two inner, vacuolate, collecting cells and six outer, densely cytoplasmic, secretory cells. The secretory cells are completely enclosed by a cuticular layer except along part of the walls between the collecting cells and the inner secretory cell. This non-cuticularized wall region is termed the transfusion are (RUHLAND, 1915) and numerous plasmodesmata connect the inner secretory cells with the collecting cells in this area. Plasmodesmata also connect the collecting cells with the adjacent mesophyll cells.There are numerous mitochondria in the secretory cells and in different glands they show wide variation in form. In some glands wall protuberances extend into the secretory cells forming a labyrinth-like structure; however, in other glands the protuberances are not extensively developed. Numerous small vacuoles are found in some glands and these generally are distributed around the periphery of the secretory cells in association with the wall protuberances. Further, an unusual structure or interfacial apparatus is located along the anticlinal walls of the inner secretory cells. The general structure of the gland including the cuticular encasement, connecting plasmodesmata, interfacial apparatus, and variations in mitochondria, vacuoles, and wall structures are discussed in relation to general glandular function.

A LIGHT‐ AND ELECTRON‐MICROSCOPIC SURVEY OF ALGAL CELL WALLS. I. PHAEOPHYTA AND RHODOPHYTA

Dawes, Clinton J., Flora M. Scott, and E. Bowler. (U. California, Los Angeles.) A light‐ and electron‐microscopic survey of algal cell walls. I. Phaeophyta and Rhodophyta. Amer. Jour. Bot. 48(10): 925–934. Illus. 1961.—An introductory survey of the structure of the cell walls of brown, red, and green algae, as seen under light and electron microscopes, has been completed. In the present paper (Part I) the structure of the thalli of the Phaeophyta and Rhodophyta is compared, and the occurrence of intercellular spaces, pitting, and microfibrillar patterns is discussed. A detailed comparison of the cell‐wall structure and growth of a brown alga, Dictyota flabellata, and of a red alga, Helminthocladia californica, is also presented. In Dictyota, typical of the brown algae, the microfibrillar pattern in the apical cells and in the adjacent cells of the thallus tip is reticulate. In mature cells, the microfibrils are dominantly parallel in orientation. Pits, which are fields of closely set pores, are distinctive. The microfibrils in the pit areas are masked by non‐fibrillar material. Helminthocladia, with a cell wall characteristic of the red algae, differs from Dictyota in that the microfibrillar pattern is reticulate at all ages of the cell and throughout the thallus. In the pit areas, the microfibrils are not masked by amorphous material. Pit connections, characteristic of the Florideae, can be divided into 2 major groups. Either the pit connection is an open channel between 2 adjacent cells, or it is composed of numerous plasmodesmata traversing a continuous, loose, microfibrillar wall. The techniques of the survey are emphasized in that fragmented cell walls were studied, and, also, chemically cleared material was constantly compared with fresh material under light and electron microscopes. It is concluded that the cell wall, as a taxonomic character, is of value only in delimiting the Phaeophyta and Rhodophyta.

Submicroscopic differentiation of plasmodesmata and sieve plates in Cucurbita

In the skeletal network of the youngest partition walls in parenchyma cells no plasmodesmata are visible (Fig. 2). These differentiate only later when the production of microfibrils, which is a continuous process, progresses (Figs. 3–5). Sometimes initiated plasmodesmata are covered and closed by the proceeding deposition of microfibrils (Fig. 6). Pits originate in that the development of the secondary wall is prevented on top of a local cluster of numerous plasmodesmata (Fig. 7). The formation of pores between sieve tubes is caused by an early discontinuation of fibril deposition in local fields of the transverse wall, while bars of tangential fibrillar strands are secreted between those localities (Figs. 8–10). Subsequently the bars are narrowed by active growth of a cytoplasmic plug which covers the area of the future pore (Figs. 10–12). If two adjacent cells differentiate sieve pores, the original network of the field will disappear so that open pores result (Figs. 12, 13). This is not the case if one-sided sieve plates are formed in contact with companion cells (Figs. 14–17).