305,195 research outputs found
Nectar resorption and pollination economy
No full textThe nectaries and nectar of three species (Helleborus bocconei, Cucurbita pepo and Linaria vulgaris) that differ in ecological, cytological and physiological characteristics are compared. Nectar is resorbed in Cucurbita pepo and Linaria vulgaris, but in different ways and at different rates. Nectar secretion and resorption, if any, are discussed in terms of the economics of the plant and environmental conditions
Nectar biodiversity: a short review
No full textNectaries differ in many aspects but a common feature is some kind of advantage for the plant conferred by foraging of consumers which may defend the plant from predators in the case of extrafloral nectaries, or be agents of pollination in the case of floral nectaries. This minireview is concerned mainly with floral nectaries and examines the following characteristics: position in flower; nectary structure; origin of carbohydrates, aminoacids and proteins; manner of exposure of nectar; site of nectar presentation; volume and production of nectar in time; sexual expression of flower and nectary morphology; nectar composition and floral sexual expression; variability of nectar composition; fate of nectar; energy cost of nectar production. The species of certain large families, such as Brassicaceae, Lamiaceae and Asteraceae, resemble each other in nectary organisation; other families, such as Cucurbitaceae and Ranunculaceae, have various types of organisation. A scheme is presented to illustrate factors influencing nectary and nectar biodiversity
Floral nectar production in Helleborus foetidus L.: an ultrastructural study
No full textThe floral nectaries of Helleborus foetidus were studied using scanning and transmission electron microscopy as well as light microscopy. Nectaries are tubular and consist of an external epidermis, a photosynthesizing parenchyma, large branches of vascular tissue, a nectar-producing parenchyma and an internal epidermis. The external epidermis is characterized by thick outer walls and thin cuticle. Cells of the photosynthesizing parenchyma are characterised by the presence of chloroamyloplasts. The nectar-producing parenchyma consists of small cells with lobed nucleus, several small vacuoles and numerous undifferentiated elongated plastids. These cells contain lipid bodies, Golgi membranes and rough endoplasmic reticulum, and are connected by numerous plasmodesmata. Parenchyma cells around the sieve elements contain some amyloplasts. The outer cell wall of the internal epidermis displays a small thinned area with a pinch inside. The cuticle is very thick, and consists of a globular structure evident especially in its proximal part. Secretion takes place only in the inner basal region of the nectary cup. The surface of the internal epidermis is devoid of secreting structures. The fracture point of the cuticle and underlying cell wall is the mechanism of nectar release, nonetheless epidermal cell death is not apoptotic. This holocrine secretion is coupled with a more common merocrine secretion through which nectar accumulates in the subcuticular spaces. The consequence of the combined manner of secretion is an enriched “nectar soup” crucial in the interaction with pollinators and yeasts during winter flowering
Nectary structure, nectar secretion patterns and nectar composition in two Helleborus species
No full textThe morphological and cytological characteristics of nectaries of Helleborus foetidus and H, bocconei during the secretory period are reported. The nectaries are derived from modified petals and secrete nectar continuously for about 20 days; they consist of a single layered epidermis, nectar-producing parenchyma and photosynthesizing parenchyma. Nectar secretion is holocrine and the nectar is released by rupture of the wall and cuticle of each epidermal cell. The nectaries of the two species differ in number and external morphology. In H. foetidus, secretion begins before anthesis and secretion Fate decreases with nectary age. In H. bocconei it begins on the day of anthesis and proceeds ata constant rate. The nectar has a high sugar content, mainly sucrose, and also contains lipids and proteins
Successful treatment with leflunomide of arthritis in systemic sclerosis patients
No full textSystemic sclerosis (SSc) is a connective tissue disease clinically characterized by different degrees of skin fibrosis and visceral organ involvement Joint involvement with severe synovitis during SSc is relatively uncommon. About 11% of SSc patients present with arthritis at disease onset , usually characterized by mono-oligoarthritis, responsive to steroid therapy
Shopping in green: FUTURIBILE con-BATTENTE
No full textLa gestione degli spazi urbani aperti rappresenta una questione cruciale nella governance delle città dopo la pandemia. Nell’accezione comune, il tema dell’abitare viene posto come una prerogativa dello spazio confinato della casa, mentre il tema ”abitare la città” richiede oggi un impegno di studio e di analisi che, pur misurandosi su livelli disciplinari diversi, sia per lo meno pari al livello di approfondimento e di dettaglio a cui è giunto, dagli anni del movimento moderno e fino ai nostri giorni, il tema della casa.
La questione abitativa oggi più che mai investe, più che lo spazio individuale già di per sé controllato e sicuro, la dimensione collettiva ovvero quegli spazi di relazione che risultano elementi “mediatori” tra la casa e la città. Proprio sulle relazioni tra costruito e spazi aperti si gioca una parte della “qualità della vita” che noi immaginiamo; e proprio su questi spazi si propone un’indagine puntuale che, partendo dalla questione climatica come componente fondamentale del benessere abitativo urbano, tende a far coincidere dimensione, forma, uso, controllo climatico come una complessità di requisiti innegabilmente collegati fra loro.
L’indagine fa percepire un’ipotesi di lavoro sulla città basato più su una strategia di “agopuntura” piuttosto che pervasiva. Questo vuol dire immaginare una rete di “luoghi urbani”, ciascuno con le proprie specificità, che formano un sistema riconoscibile e identificabile, parte di un progetto rigenerativo
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Holocrine secretion and cytoplasmic content of Helleborus foetidus L. (Ranunculaceae) nectar
No full textWe used electron microscopy to investigate the fine structure of nectary secretions of Helleborus foetidus. During the secretion period, epidermal cells of nectaries discharge the whole contents of the cytoplasm into the nectary cavity. The external wall of the cell breaks, releasing the cytoplasm as a dense aggregate that later disperses in the nectary cavity. Cell components, such as chromatin, plastids, mitochondria, lipid droplets and membranes, were found in the nectar of H. foetidus, evincing the complex nature of the secreted material. These results confirm that nectar secretion in H. foetidus is of the holocrine type. © 2008 German Botanical Society and The Royal Botanical Society of the Netherlands
Analisi matematica di architetture ed opere d'arte
No full textIn questo lavoro mostriamo i risultati di una sperimentazione didattica proposta prevalentemente a studenti del primo anno di Architettura del Politecnico di Torino, nell’ambito all’interno del corso di Istituzioni di Matematiche. Dopo aver scelto l’immagine di un panorama, della mappa di un insediamento urbano o di un’opera d’arte, lo scopo era quello di cogliere alcune linee fondamentali della gura e dedurne, grazie all’uso di GeoGebra, le equazioni matematiche partendo da funzioni elementari e trasformandone i gra ci con traslazioni, omotetie, ribaltamenti, per approssimarle al meglio. Il lavoro ha permesso un uso dinamico e applicato della Matematica all’arte
Dipendenza economica da Pechino e voto alle Nazioni Unite. Il caso sudamericano
No full textAfter decades of intense growth, today Beijing is considered able to harness its economic power to gain influence and advance its strategic interests on a global scale. In the Western Hemisphere too – particularly in South America – China now plays a crucial role both commercially and financially. Using the concept of economic dependence as the main explanatory variable, the article intends to verify whether and to what extent the trade and financial relationship with Beijing has translated for South American countries into greater convergence in terms of foreign policy, measured on the basis of the voting behaviour at the UNGA
- …
