Luigi Brighigna

Programmed-cell-death events during tapetum development of angiosperms

SummaryProgrammed-cell-death events in the tapetum of two angiosperms (Lobivia rauschii Zecher andTillandsia albida Mez et Purpus) are described by ultrastructural methods. Tapetum degradation appears to be a type of programmed cell death, with the cellular remnants necessary for pollen development, acting as products of holocrine secretion. Diagnostic features of apoptosis during tapetum development are: general shrinkage of the whole cell and the nuclei; condensation of the chromatin at the periphery of the internal nuclear membrane; the enlargement of the endoplasmicreticulum cisternae to circumscribe portions of the cytoplasm; the persistence of mitochondria together with microfilament bundles until the last stages of tapetal degeneration.

Megasporogenesis and programmed cell death in Tillandsia (Bromeliaceae)

The degeneration of three of four meiotic products is a very common process in the female gender of oogamous eukaryotes. In Tillandsia (and many other angiosperms), the surviving megaspore has a callose-free wall in chalazal position while the other three megaspores are completely embedded in callose. Therefore, nutrients and signals can reach more easily the functional megaspore from the nucellus through the chalazal pole with respect to the other megaspores. The abortion of three of four megaspores was already recognized as the result of a programmed cell death (PCD) process. We investigated the process to understand the modality of this specific type of PCD and its relationship to the asymmetric callose deposition around the tetrad. The decision on which of the four megaspores will be the supernumerary megaspores in angiosperms, and hence destined to undergo programmed cell death, appears to be linked to the callose layer deposition around the tetrad. During supernumerary megaspores degeneration, events leading to the deletion of the cells do not appear to belong to a single type of cell death. The first morphological signs are typical of autophagy, including the formation of autophagosomes. The TUNEL positivity and a change in morphology of mitochondria and chloroplasts indicate the passage to an apoptotic-like PCD phase, while the cellular remnants undergo a final process resembling at least partially (ER swelling) necrotic morphological syndromes, eventually leading to a mainly lipidic cell corpse still separated from the functional megaspore by a callose layer.

Programmed cell death in the nucellus of Tillandsia (Bromeliaceae)

Abstract We report the ultrastructural aspects and histochemical assay regarding the degenerating nucellar cells of Tillandsia during early female gametophyte development. Nucellar cells degeneration was observed to start during the somatogenesis of the gametophyte. Ultrastructural features of degenerating process and TUNEL assay indicated that the nucellar cells death mechanism is genetically controlled. Mitochondria and cytoplasmic vesicles persisted until cell degeneration was completed. This feature represens a peculiar aspect of the PCD mechanism in this specific case.

Structural and ultrastructural characterization of Selaginella lepidophylla, a desiccation-tolerant plant, during the rehydration process

Summary Selaginella lepidophylla is a pteridophyte resurrection plant from Central America deserts that has been studied hitherto only for microphyll ultrastructure and photosynthetic activity during rehydration. With the present work the anatomy and cell ultrastructures have been examined during progressive rehydration. Light microscope observations clearly showed the maintenance in the dry condition of chloroplasts although in a crushed form, of chlorophyll content, and the restoration of the normal anatomical structures in stem and microphylls after the complete rehydration process. Electron microscope analyses permitted us to observe a gradual reorganization in the different cells of stem and microphylls of all the cytoplasmic components including the membrane systems present either in the protoplasm or in the organelles. In particular, the chloroplasts appeared to be able to newly accumulate starch, and then to recover the normal photosynthetic capacity. Therefore, it is possible to say that S. lepidophylla retains in the dry condition the cell structures in a well conserved state or, at least, in a functional state by protective mechanisms that permit a total reorganization of the cells after rehydration. This statement is further supported by the absence of any structural disruption effects in the rehydrated cells of S. lepidophylla .

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...

Ultrastructural studies on bicellular pollen grains of Tillandsia seleriana Mez (Bromeliaceae), a neotropical epiphyte

Abstract The ultrastructure and ontogeny of bicellular pollen in Tillandsia seleriana Mez (Bromeliaceae) before anther dehiscence has been here investigated. The development, after the first mitosis, is described to consist in three stages. The aim of the present report, which is part of a more extensive study on the reproductive mechanisms in the genus, is to compare the development of the male gametophyte of Tillands with information available from other an-giosperms. Aspects on water, starch and soluble carbohydrate contents of the pollen of T. seleriana are discussed in the light of the current ecological classification of pollens. The generative cell did not show any plastid in its cytoplasm, hence plastid inheritance in Tillandsia is confirmed as totally maternal (Lycopersicon type). Contrarily to other pollen grains, those of T. seleriana maintain a considerable amount of starch in the vegetative cell until dehiscence. The inulin test was negative, indicating that T. seleriana pollen lacks of Fructans. Pollen only with starch is subjected to faster dehydration and, probably, cannot be transported at long distance. The ecological adaptive plasticity of genus Tillandsia, is confirmed also by morphological characters that appear to be typical both of the partially dehydrated and partially hydrated pollen in T. seleriana. This situation is, probably, a plesiomorphic character that permitted to genus Tillandsia to differentiate species well adapted to arid environments and others living in mesic forests.

Peculiar Adaptations of the Plasma-Membrane in the Sucking-Scale's Dome Cell of Tillandsia Usneoides

SUMMARYCarrying on the ultrastructural analysis of the sucking apparatus in Tillandsiae, this work construes the absorption process associated with the dynamic properties of the plasma-membrane macromolecular constituents in the dome-shaped cell.A ropheocytotic mechanism of the absorption is pointed out, supported by the presence of a great number of mitochondria, which does not differ substantially from DOLZMANNS pinocytotic view. Also the presence of numerous active dictyosomes is made clear.

Ultrastructural aspects of the hypanthial epithelium of Selenicereus grandiflorus (L.) Britton & Rose (Cactaceae)

Summary The epithelium of the basal part of the inside floral tube (hypanthium) of Selenicereus grandiflorus (L.) Britton & Rose was investigated with ultrastructural and cytochemical methods, while a Gas Chromatography/Gas Mass analysis was performed on the secretion products of this flower tissue. Despite its position (frequently occupied by “classical” nectaries in many representatives of Cactaceae) the cells of the investigated epithelium show features that are typical of cells involved prevailingly in lipidic production. Lipids are stored in the big vacuole which fills almost the whole cell in the last developmental stage. The secretion is of holocrine type and probably started by the mechanical action of the pollinator itself. However sugars conveying from the underlying parenchyma towards the epithelium and a strong PAS-positive reaction at the vacuolar level was observed. These observations suggest also an important presence of carbohydrates in the last products. The formation of subcuticular spaces indicates also an eccrine type of secretion. The results obtained with Gas Chromatography/Gas Mass analysis indicate the production of some phenols, that we link to flower scent. This is the first report on oils producing flowers among Cactaceae and the first for nocturnal flowers.

Observations on a Singular Mitochondrial Structure in the Dome-Shaped Cell of Tillandsia Usneoides

SUMMARYThe electron-dense zones visible in the mitochondria of the absorption apparatus found in Tillandsia usneoides, were considered to be aggregates of genetic material and macromolecules, in relation to the mitochondrias synthetic capabilities connected to their growth and duplication. Characteristic mitochondrial duplication by constriction were observed very frequently in connection with the typical absorption apparatus found in Tillandsiae.

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...