Giuliana Lombardo

Mycoplasma development and cell alterations in white clover affected by clover dwarf an electron microscopy study

SummaryThe presence of mycoplasma has been demonstrated in the phloem of leaves of white clover (Trifolium repens L.) affected by clover dwarf. Mycoplasma-like bodies were found both in parenchyma and companion cells and in sieve elements.In young parenchyma and companion cells mycoplasma-like bodies appeared as round or oval particles with high ribosomal content, delimited by a ribosome-bearing membrane. Their diameter ranged between 50 and 400 nm. In mature sieve elements they were larger, more pleomorphic, and showed a central clear area containing presumed DNA filaments. Budding and dividing forms were sometimes seen among them.The main alterations found in the infected cells were: increased ribosome content, dilation of the perinuclear space, degeneration of mitochondria and chloroplasts, and cytoplasmic vacuolation. Many cells appeared completely disrupted and their content was replaced by a great number of pleomorphic mycoplasma.

Tapetal Ultrastructural Changes During Pollen Development. III. Studies on Gentiana Acaulis

SUMMARYIn Gentiana acaulis, where the anthers are elongated and mature in a scalar way. the tapetal cells are intermingled with pollen grains and possess simultaneously spherical cytoplasmic bodies, sporopollenin bodies (« orbicular bodies ») and grey bodies. The contemporaneous presence of such bodies is probably related to the fact that the cell walls of the tapetal cells disappear and therefore they can migrate towards anther zones which are already mature.

Tapetal Ultrastructural Changes During Pollen Development. I. Studies on Antirrhinum Maius

SUMMARYAnther sections of Antirrhinum maius in various stages of development have been examined with the electron microscope and the ultrastructural modifications of the tapetal cells have been followed during the development of the pollen grains. Characteristic of the early stages of development is the presence of a great number of intensely proliferating Golgi bodies and of spherical bodies, located in the perinuclear space in proximity of the plasmalemma and in the endoplasmic reticulum. They are bounded by a single membrane on which ribosomes are regularly ranged facing the body cavity. Probably the bodies located in the perinuclear space play a role in the nuclear-cytoplasmic information exchanges, while those in connection with the endoplasmic reticulum seem to be simply related to an enhanced endoplasmic reticulum activity. In the late tetrad stage a second body population appears. These bodies are spherical, electrondense and without bounding membrane. They are located at the cell periphery toward...

Peroxidase Activity and Gametophytic Incompatibility: Bud-Pollination in Petunia Hybrida

SUMMARYThe presence and distribution of peroxidase activity has been examined in non-, self- and cross-pollinated bud styles, in relation to the well-known bud pseudo-self-compatibility. No peroxidase activity is present in the apoplastic space of non-pollinated and cross-pollinated young styles. Self-pollination causes the appearance of peroxidase activity in the apoplastic space of the transmitting tissue region where the pollen tubes elongated, indicating that bud pistils are able to recognize «incompatible» pollen tubes and to react to their growth. A similar interaction between pollen tubes and transmitting tissue cells was observed in cross- and self-pollinated pistils regarding the utilization of cellular reserves. Bud pseudo-self-compatibility is explained by the lack in non-pollinated bud styles of the apoplastic peroxidase activity observed in adult non-pollinated pistils. A key role is proposed for the apoplastic peroxidase activity present in non-pollinated styles in the incompatibility reacti...

Tapetal Ultrastructural Changes During Pollen Development. II. Studies on Pelargonium Zonale and Kalanchoë Obtusa

SUMMARYThe ultrastructure of the tapetal cells was studied in Kalanchoe obtusa and Pelargonium zonale. In an early stage of development the most characteristic feature was the presence of many spherical bodies bounded by a single membrane and containing cytoplasmic material. These bodies were localized in dilations of the ER and in the perinuclear space. In later stages, when the pollen was mature, the tapetal cells of Pelargonium contained many « grey » bodies and their plasmalemma was in close connection with the sculptures of the pollen grains.

Ultrastructure of the Pollen Grain and Taxonomy

Abstract The fine structure of mature pollen grains of several Monocotyle-dons and Dicotyledons plants was studied at the electron microscope. It was observed that inside the pollen grain each generative cell is always clearly separated from romaining cytoplasmic portions. The ways by which the generative cell is delimited are vary in systematically different plants. There may be either a cell wall, quite similar to the one MARUYAMA (1965) reported in the pollen of Tradescantia paludosa. He believed, it to be of a pectocellulosic nature, or a passage from a wall to a two-layered membrane. Multiple membranes, or simply two-layered ones have also been found. These different structures seems to be related to the possible evolutionary trends of the pollen grain. The most primitive forms have grains with an evidently walled generative cell, while in the more evolued ones, there is only a two layered membrane. The fact that in both Monocotyledons and Dicotyledons the generative cell in the more primitive specie...

Electron-Cytochemical Localization of Peroxidase in Self- and Cross-Pollinated Styles of Primula Acaulis

SUMMARYPrimula acaulis is characterized by an heteromorphic incompatibility. Through electron microscopic techniques, based on the DAB cytochemical reaction, it has been possible to detect the presence of peroxidase in the intercellular spaces and in the cell walls of the stylar transmitting tissue. Peroxidase has been observed only in self-pollinated styles, that is after ilegitemate crosses. This fact suggests that peroxidase may be linked with incompatibility responses.

Microsporogenesis of the feathers (fertile branches derived from annual buds) in Vitis vinifera, cv Picolit giallo

Abstract Using light and electron microscopy, we have studied the microsporogenesis and tapetal development of the feathers in two different low producing clones of Picolit giallo (sp. Vitis vinifera). In these clones while the productivity of the main branches (fertile branches originated from buds, formed in the previous year, that remained silent during the winter) is very low, that of the feathers (fertile branches derived from annual buds) is always normal. The microsporogenesis and tapetal development proceed normally in almost all the examined anthers; it is remarkable that at the tetrad stage the tapetal cells appear well structured without any degeneration symptom, unlike what observed for the main branches. Moreover in most of the mature anthers the pollen grains are numerous, pleinty of organelles and show sometimes thickenings in the callose layer under their wall. The tapetal cells of these anthers have disappeared. Only in few anthers we observed the presence of collapsed pollen grains and t...

An Ultrastructural Study of the Localization of Sowbane Mosaic Virus

SUMMARYIn sowbane plants infected with sowbane mosaic virus (SOMV), virus particles were found in great amount in the mesophyll and xylem. They were present not only in the cytoplasm, but also in the vacuole of parenchyma cells and differentiating tracheids of minor veins. The tonoplast of virus-containing cells showed alterations, such as increased electron density and formation of convolutions bulging into the vacuole. Virus-containing cells were rich in peroxisomes and fat bodies.

Stylar peroxidases and heteromorphic incompatibility reactions in Primula acaulis Hill («thrum» morph)

SUMMARYIn non-, self- and cross-pollinated styles of Primula acaulis «thrum» morph, the distribution of apoplastic peroxidase activity has been investigated, by means of the cytochemical treatment with diaminobenzidine. Apoplastic peroxidase activity was detected throughout the transmitting tract (at the «neck» region level) in non- and self-pollinated styles. The enzyme has been related to the predisposition of incompatible pollen tube rejection, no appreciable differences in enzyme distribution having been found between non- and self-pollinated styles since, in this morph, incompatible pollen tubes hardly ever reach the stylar neck. Compatible intermorph pollination caused the disappearance of apoplastic peroxidase activity in the central portion of the transmitting tract, where pollen tubes elongated, utilizing the reserves of the stylar cells, which appeared highly degenerate. Stylar apoplastic peroxidases seem then to play a role in heteromorphic incompatibility responses.