Ultrastructural Characteristics of Spore Germination in the Moss Dawsonia Superba

The attachment of certain Agrobacterium species to moss protonema was examined by scanning electron microscopy. The bacteria cultured with the moss adhered to the protonemal filaments of Pylaisiella selwynii and Funaria hygrometrica throughout the fixation and washing procedure prior to examination. The number of bacteria adhering per unit length of filament did not correlate with the ability of four species (A. tumefaciens, A. rubi, A. rhizogenes, A. radiobacter) to induce gametophore formation in P. selwynii. Little difference was found between the number of A. tumefaciens on P. selwynii or on F. hygrometrica, and although this bacterial species induced gametophores on P. selwynii, it had no effect on F. hygrometrica. A. rhizogenes, which is capable of inducing rhizoid formation on both P. selwynii and F. hygrometrica without physical attachment, did associate with filaments of both mosses. Larger numbers of A. tumefaciens and A. rubi, which induce gametophores or callus, were associated with the spore and germ tube of P. selwynii than were A. rhizogenes or A. radiobacter which do not initiate these changes. These results suggest that the germ tube may constitute the site where effective attachment occurs. The number of A. tumefaciens adhering to P. selwynii was greatest at 2–6 h after addition and then decreased by 26 h, raising the possibility that some bacteria lyse following attachment. None of the bacteria adhered to the gametophore walls of either moss, indicating that a change in cell wall surface may occur. The four species of Agrobacterium differed in their orientation when adhering to the moss. These results suggest that the process of bacterial adherence to higher plant cells in Agrobacterium infection is similar to that which we observe in mosses and which leads to developmental changes.

mentioning

confidence: 99%

Adherence of Agrobacteria to Moss Protonema and Gametophores Viewed by Scanning Electron Microscopy

Spiess

Turner

Mahlberg

et al. 1977

Protonemal Organization and Growth in the Moss Dawsonia Superba: Ultrastructural Characteristics

DeMaggio

Stetler

1977

Self Cite

The elongating, tip cell of the protonema of Dawsonia superba is characterized by a variety of organelles distributed uniformly over the length of the cell. Chloroplasts, vacuoles, mitochondria and dictyosomes are present in the terminal portion of the cell. Dictyosomes are abundant throughout the cell and their production of vesicles is pronounced. Stratification of the cytoplasm and exclusion of organelles from the tip are not observed. The orientation of microtubules and microfibrils follows the pattern observed in filamentous fern prothallia. Microtubules are not observed at the tip of the protonema, but microfibrils are abundant and randomly oriented. While microtubules and microfibrils in lower regions of the apical dome are arranged randomly, more basally they assume an axial arrangement.

The Ultrastructure of Phycopeltis (Chroolepidaceae: Chlorophyta). I. Sporopollenin in the Cell Walls

Good

Chapman

1978

Electron microscope observations on Phycopeltis epiphyton, a subaerial green alga found growing on the leaves of vascular plants and bryophytes, revealed the presence of a densely staining material within the inner and outer zones of the cell walls. This material resists acetolysis, is degraded by chromic acid, is unaffected by ethanolamine and exhibits secondary fluorescence when stained with the fluorochrome Primuline. These characteristics, together with infrared absorption spectra indicate that, on the basis of currently accepted criteria, the densely staining material is a sporopollenin and that it is a major component of the cell wall. Tests for cellulose, chitin, and lignin were negative, and little if any silica is present. It is suggested that negative results in tests for cellulose may be due to a masking effect by the sporopollenin. Comparison of the fine structure of the cell walls of P. epiphyton, pollen grains, and algal cells (known to contain sporopollenin) supports the suggestion that sporopollenin deposition on “unit membranes” is universal. Morphological similarity among sporopollenin lamellae in P. epiphyton, pollen grains, spores of land plants, and the trilaminar sporopollenin sheath in Chlorella, Scenedesmus, and Pediastrum indicates that the structures may be analogous. As in pollen grains, sporopollenin may provide protection against desiccation and parasitism. It may also be involved in the adhesion of Phycopeltis to host plants and in the adhesion between adjacent filaments of the thallus.