Outer Wall Material Research Articles

COMPARATIVE STUDIES ON THE CELL WALLS OF SEXUAL AND ASEXUAL BANGIA ATROPURPUREA (RHODOPHYTA). I. HISTOCHEMISTRY OF POLYSACCHARIDES1

ABSTRACTA comparative histochemical study of the nature and distribution of acidic and neutral cell wall polysaccharides was conducted on marine sexual and asexual filaments of the red alga Bangia atropurpurea (Roth) C. Ag. Outer and inner walls of this species were clearly partitioned according to staining and transmission electron microscopic characteristics. Neutral polysaccharides were detected in the outer coating (cuticle) but were absent from outer and inner walls of all filaments. Acidic polysaccharides were noted in the outer wall material but not in the inner wall layers of any filaments at any developmental stages. The major staining component of vegetative regions of sexual material and all regions of asexual filaments was a highly sulfated polymer. During sexual reproduction only there was a generalized change in the nature of the acidic component, characterized by a decrease in intensity of staining for sulfates in both male and female filaments and the appearance, in female filaments only, of polysaccharides which presumably were carboxylated. Spermatia attached to both male and female filaments in regions where sexual differentiation was initiated and where changes in the outer wall components commenced.

Ultrastructural study of promycelial development and basidiospore initiation in Ustilago maydis

Cytoplasm and walls of developing promycelia and basidiospores of Ustilago maydis were examined. The promycelial wall was derived from an inner wall layer of the teliospore. Small vesicles and probable Golgi cistemae appeared to be associated with promycelial extension. Some promycelial septa contained small pores; spherical vesicles, formed centripetally in the electron-transparent lamella at the center of the septa, appeared to be involved in promycelial fragmentation. An inner layer of the basidial wall gave rise to the wall of the developing basidiospore, and a collar of torn outer wall material surrounded the spore base. Spores were formed on short sterigmata. No significant vacuolation occurred in the promycelium during initial basidiospore formation, a feature unique among phragmobasidiomycetes examined thus far. The distribution of cytoplasmic organelles in the promycelium is like that seen in vegetative structures of other fungi.The placement of Ustilaginales in the basidiomycetes is supported by the layered walls and small pores in the promycelium. Derivation of the basidiospore wall and the migration of the nucleus into the basidiospore before mitosis resembled aspects of budding in basidiomycetous yeasts.

Fate of the plasma membrane of Saccharomyces cerevisiae during cell rupture.

Intact and homogenized yeast cells were studied in thin sections in the electron microscope to determine the fate of the plasma membrane during fractionation. Intact cells possess a unit-membrane plasma membrane closely appressed to the cell wall. After even slight physical damage following limited homogenization in dilute buffer, the plasma membrane collapses away from the wall while the intra-cytoplasmic membranes (ER, vacuolar, nuclear, mitochondrial) dilate and vesiculate. With prolonged homogenization, the plasma membrane fragments and vesiculates and becomes indistinguishable from the remains of the other membranes. Washed wall fractions consist of wall fragments with entrapped vesicles derived from all cellular membranes. Exhaustive digestion of the wall fraction with snail gut enzymes liberates some of the trapped vesicles and results in an undigested, non-membranous, inner layer of wall partially contaminated with outer wall material. Polyacrylamide gel electrophoresis indicates that proteins of the wall "membranes" are partially of mitochondrial origin.

ULTRASTRUCTURE AND INITIATION OF WALL PATTERN IN PEDIASTRUM BORYANUM

The reticulate pattern in the wall of Pediastrum boryanum emerges rapidly during wall formation following aggregation of the swarming zoospores to form the coenobium. Electron micrographs during colony formation show that microtubules, present during the motile phase and aggregation, are gone prior to wall formation and probably do not participate in wall pattern regulation. A single dictyosome lies adjacent to the nucleus and from blebs of the nuclear membrane receives vesicles at its forming face. Vesicles formed at the maturing face have not been observed to contribute to the cell wall. Electron‐lucent patches occur in the plasma membrane prior to wall formation. The first indication of a reticulate pattern in wall development is the deposition on the plasma membrane of interconnected plaques of outer wall material at the corners of hexagons. The sites of the plaques may correspond to clusters of ribosomes on endoplasmic reticulum underlying the plasmalemma. Following completion of the outer wall the thicker inner wall layer is deposited and within it the reticulate pattern of ridges is soon evident in tangential sections as strips of greater electron density. It is suggested that the pattern of the wall is templated by the plasma membrane.

Ultrastructure and Initiation of Wall Pattern in Pediastrum boryanum

The reticulate pattern in the wall of Pediastrum boryanum emerges rapidly during wall formation following aggregation of the swarming zoospores to form the coenobium. Electron micrographs during colony formation show that microtubules, present during the motile phase and aggregation, are gone prior to wall formation and probably do not participate in wall pattern regulation. A single dictyosome lies adjacent to the nucleus and from blebs of the nuclear membrane receives vesicles at its forming face. Vesicles formed at the maturing face have not been observed to contribute to the cell wall. Electron-lucent patches occur in the plasma membrane prior to wall formation. The first indication of a reticulate pattern in wall development is the deposition on the plasma membrane of interconnected plaques of outer wall material at the corners of hexagons. The sites of the plaques may correspond to clusters of ribosomes on endoplasmic reticulum underlying the plasmalemma. Following completion of the outer wall the thicker inner wall layer is deposited and within it the reticulate pattern of ridges is soon evident in tangential sections as strips of greater electron density. It is suggested that the pattern of the wall is templated by the plasma membrane.