Mariarosa Palandri

Ultrastructural Features of the Tillandsia Usneoides L. Absorbing Trichome During Conditions Moisture and Aridity

SUMMARYThe ultrastructure of the whole cellular system which forms the absorbing trichome of Tillandsia usneoides L. was studied under conditions of water stress and moisture. Cytological modification which are associated with so special a modality of functioning, were identified. The trichome is tipically divided into two parts: the «shield» whose cells form a central disk and a wing; the «stalk» whose structure includes a dome cell, two intermediate cells and two foot cells. All the walls of the absorbing system cells did not show any differences under the two physiological conditions assayed. No differences were observed also between the cytoplasm of the «shield» cells in the two experimental conditions. However, the cytoplasm of the central disk cells remained vital implying that they play an active role under both conditions, in this portion of the trichome, as regards the choise of nutrient solutions. The most important ultrastructural aspects were offered by the cytoplasm of «stalk» cells under bot...

Characterization of the seed reserves in Tillandsia (Bromeliaceae) and ultrastructural aspects of their use at germination

Abstract The nature and the use of the reserves accumulated in the seed of Tillandsia, a markedly epiphyte genus, are especially important in consideration of the subsequent seedling development. As a matter of fact, the embryo radicle degenerates precociously without emerging at the germination and the sole function of the root system is that of anchoring to the substratum. The present cytochemical and ultrastructural study carried out on mature seeds has highlighted the presence of proteins and lipids, in both the endosperm and in the cotyledon, which are both well–developed; in addition, the endosperm contains starch and calcium oxalate. At germination the reserves, broken–down by enzymes, are absorbed by the cotyledon in whose epidermis ultrastructural modifications, correlated with this austorial function, appear. A part of the nutrients absorbed is initially stored in the large vacuoles, of aleuronic origin, of the cotyledon parenchyma. The result is a water uptake. It is in this manner that the water and necessary nutrient needs of the seedling are satisfied during early development.

Ultrastructure of the Placental Epithelium in Tillandsia and its Modification in Connection to Anthesis

SUMMARYThe epithelium cells lining the placental lobes of three species of Tillandsia are investigated under both light and electron microscope.The fine structure of the cells, fixed before anthesis, shows that an intense metabolic activity is in progress anticipating the phase of secretory activity. The secretion process starts after anthesis, and is mediated by the Golgi apparatus; it releases polysaccharides whose nature is at least partly acid which determine a development of the wall-membrane apparatus similar to that observed in transfer cells. Further the abundance of polysomes, associated with a well developed endoplasmic reticulum, reveals that synthesis of proteins is involved. These proteins may enter partly into the composition of the Golgi secretion product and partly be of enzymatic nature. Such proteins may be secreted to the outside by eccrine process, as suggested by breaking up of the vacuoles and by the morphology of the wall-membrane apparatus. The increase both in extension and thickn...

Ultrastructural Modifications in Cotyledonous Leaves of Ricinus Communis L. During Aging

SUMMARYThe ultrastructural variations observed in Ricinus communis L. cotyledonous leaves during aging have been studied. Various samples up to the 65th day of age, shortly before the fall of the cotyledon itself, were taken. The ultrastructural variations found in various cellular organelles are described. As already observed by other authors in various plants, the most impressive modifications concerned the chloroplasts. Amongst these of particular note is the presence in the senescent cotyledons of vesicles the membranes of which are clearly continuous with those of the thylakoids. These vesicles, which seem to include portions of matrix, draw near to one another absorbing the contacting membranes and seem to give origin to very elongated vesicular formations. The presence inside the vesicles of starch, plastoglobules and DNA fibers supports the hypothesis that portions of matrix are included in them. The plastoglobules of the last samples have various degrees of electron-opacity. It is suggested that ...

Structural comparison between free and anchored roots in Tillandsia (Bromeliaceae) species.

SUMMARYThe loss of the absorbing function by aerial roots observed in Tillandsia (Bromeliaceae) is a display of extremely specialized epiphytism. The roots of the «atmospheric» Tillandsia usually anchor the plant to the support: however, some of these roots grow free. The structure of both free and anchoring roots is compared in this paper. Analyses by SEM, TEM and LM were carried out on the atmospheric species: T. latifolia Meyen, T. macdougalli Smith. The following features emerged: in the rootcap of both adhering and free roots the dead and degenerating cells remain to form a protective cover; no ultrastructural differences can be noted. In contrast, the underlying living rootcap cells show ultrastructural differences. In the free roots and in the non contact side of the anchored roots the rootcap cells appear to be involved in a utilization process of the cytoplasmic content of the outer degenerating cells; in the adhering side of the anchored roots they show large cytoplasmic zones which appear to be...

Cytological aspects of the hypocotyl correlated to the behavior of the embryo radicle of Tillandsia atmospheric species

SUMMARYGenerally in Bromeliaceae, as in all monocotyledons, upon germination of the seed, the embryo radicle grows very little. In the atmospheric species of Tillandsia, not even this minimal growth occurs. In the adult stage, these species use special hairs as their sole absorbing organ. The present work analyses the morphological and cytochemical events that are responsible for the lack of growth in the embryo radicle. Ultrastructural analysis and specific stainings for light microscopy highlighted a special area (that we have called the «constriction zone») in the median region of the hypocotyl-root axis of embryos of T. flabellata Back. and T. schiedeana Steud., both atmospheric species. During the final phase of seed maturation, the cells of the aforesaid zone thickened their walls by means of materials that, at least in part, consisted of acid polysaccharydes and neutral lipids. These materials were derived from the fused contents of characteristic cytoplasmic vesicles. Due to the presence of hydrop...

Possible Origin and Significance of the Content of Some Vacuoles in the Pollen Grain of Tillandsia Caput-Medusae Morr. (Bromeliaceae)

SUMMARYA possible origin of the content of at least some vacuoles occurring in the vegetative cytoplasm of Tillandsia caput-medusae pollen prior to the anthers dehyscence is here suggested. The significance of this process is briefly discussed and represented by diagram.

Unusual Mitochondria in Coenocytic Alga Halimeda Tuna

SUMMARYThe structure of the mitochondria found in the cytoplasm of the coenocytic alga Halimeda tuna (Ell. et Sol.) Lamour. is described. The material was examined with the electron microscope following glutaraldheyde-osmium tetroxide fixation. Generally these organelles show an amoeboid elongated form with the laminar cristae parallely arranged to its main axis. Frequently a swelling of the central zone is noted; in that case the cristae run very closely to the inner mitochondrial membrane. Sometimes in the middle portion of the matrix, that is less electron-dense, bundles of parallel tubules 230 A in diameter, are observed. The probable space arrangement of this type of mitochondria is diagramatically shown. It is also pointed out the resemblance of such mitochondria with similar ones described in certain animal tissues.