Budowa nektarnika ostrogowego u Dendrobium finisterrae Schltr. (Dendrobiinae, Orchidaceae)

To date, the structure of the nectary spur of Dendrobium finisterrae has not been studied in detail, and the present paper compares the structural organization of the floral nectary in this species with the spurs of other taxa. The nectary spur of D. finisterrae was examined by means of light microscopy (LM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). It is composed of a single layer of secretory epidermis and several layers of small and compactly arranged subepidermal secretory cells. The secretory cells have thick cellulosic cell walls with primary pits. The secretory tissue is supplied by vascular bundles that run beneath in ground parenchyma and are additionally surrounded by strands of sclerenchymatous fibers. The flowers of the investigated species displayed morphological features characteristic of bee-pollinated taxa, as they are zygomorphic, creamy-green coloured with evident nectar guides. They also emit a weak but nice scent. However, they possess some characters attributed to bird-pollinated flowers such as a short, massive nectary spur and collenchymatous secretory tissue that closely resembles the one found in the nectaries of certain species that are thought to be bird-pollinated. This similarity in anatomical organization of the nectary, regardless of geographical distribution and phylogeny, strongly indicates convergence and appears to be related to pollinator-driven selection

Nectar resorption and translocation in Cucurbita pepo L. and Platanthera chlorantha Custer (Rchb.)

Nectar resorption and sugar translocation were studied in Cucurbita pepo (Cucurbitaceae) and Platanthera chlorantha (Orchidaceae) by micro-autoradiography. In both species, nectar was resorbed in pollinated and unpollinated flowers and ovules developing into seeds were found to be the main sugar sink. In C. pepo, the mobility of resorbed sugars in pollinated female flowers was higher than in unpollinated ones; male flowers showed lower mobility of resorbed sugar. In P. chlorantha, radioactivity was detected in pollinated flowers below and above labelled unpollinated ones: the nearer the flower, the stronger the accumulation of label in developing fruits

Nectary structure in Symphyglossum sanguineum [Rchb.f.] Schltr. [Orchidaceae]

Ornithophily occurs in a great number of orchid species but despite this, researchers have largely neglected to investigate their nectaries. The aim of this study is to describe the nectary structure of Symphyglossum sanguineum, a species presumed to be pollinated by hummingbirds. The nectary is located at the free margins of auricles, which form a channel for the passage of nectar. The nectary, which consists of a single-layered epidermis and 2-3 layers of subepidermal cells, is supplied by collateral, vascular bundles. The nectary cells of S. sanguineum, like those of other ornithophilous orchids, have thick cellulose cell walls. A remarkable feature of these nectary cells is the dissolution of the middle lamella and the subsequent separation of epidermal cells. It is possible that this latter process facilitates the flow of the nectar to the nectary surface. The cuticle covering the nectary epidermis has micro-channels, but unlike the other species of ornithophilous orchids studied to date, it neither becomes disrupted nor detached from the epidermal cells. Abundant mitochondria, lipid droplets and smooth endoplasmic reticulum (SER) with an osmiophilic material are present in the cytoplasm of nectary cells. Some plastids with few lamellae contain numerous vesicles and osmiophillic globules whereas others accumulate starch. SER lamellae are often closely associated with plastids and the contents of the former organelles closely resemble osmiophillic globules. Secretory vesicles are common, especially near the outer, tangential wall indicating that granulocrine secretion possibly occurs in S. sanguineum.Ornitofilia występuje u wielu Orchidaceae, lecz nektarniki storczyków zapylanych przez ptaki rzadko są przedmiotem badań. Celem niniejszej pracy było zbadanie struktury nektarników Symphyglossum sanguineum, gatunku przypuszczalnie zapylanego przez kolibry. Nektarnik w kwiatach S. sanguineum znajduje się na wolnych krawędziach auriculi, które są wytworem warżki. Auricule tworzą kanal, przez który przesącza się nektar na powierzchnię labellum. Nektarnik zbudowany jest z jednowarstwowej epidermy i 2-3 warstw komórek subepidermalnych. Jest on zaopatrywany przez kolateralne wiązki przewodzące. Komórki nektarnika S. sanguineum mają grube celulozowe ściany komórkowe. Charakterystyczną cechą nektarnika jest rozpuszczenie blaszek środkowych w ścianach niektórych komórek epidermy wydzielniczej, co powoduje ich rozsunięcie. Przypuszczalnie proces ten ułatwia przesączanie się nektaru na powierzchnię nektarnika. Kutykula pokrywająca komórki epidermy wydzielniczej ma mikrokanaliki, lecz w przeciwieństwie do komórek nektarników innych dotąd badanych ornitofilnych storczyków, nie pęka ani też nie tworzy uwypukleń pod wpływem wydzielanego nektaru. Cytoplazma komórek wydzielniczych zawiera liczne mitochondria, krople lipidowe i gładkie retikulum endoplazmatyczne (SER) wypełnione osmofilnym materiałem. Niektóre plastydy w komórkach nektarnika mają nieliczne tylakoidy i pęcherzyki oraz osmofilne globule, podczas gdy w innych plastydach znajdują się ziarna skrobi. Błony SER są w kontakcie z plastydami, a osmofilny materiał zawarty w SER przypomina ciemno wybarwione globule w plastydach. Liczne pęcherzyki wydzielnicze w sąsiedztwie ściany komórkowej wskazują na możliwość sekrecji pęcherzykowej

Evidence for the dual role of floral secretory cells in Bulbophyllum

Floral epidermal cells of most species of Bulbophyllum Thouars studied to date produce both lipid-rich foodrewards and fragrance. Since fragrances largely consist of terpenoids and have an affinity for lipophilic stains, the simultaneous presence of lipid-rich food-rewards frustrates identification of fragrance-secreting cells by conventional histochemistry. Furthermore, since both lipid-rich food-rewards and fragrances are probably synthesized by a similar complement of organelles, interpretation of TEM images can prove difficult. All members of section Racemosae Benth. & Hook. f. investigated to date, however, are unusual in their secretion of a predominantly proteinaceous food-reward, and lipids are seemingly absent. This might enable their use as models for the identification and characterization of fragrance-secreting tissues and organelles. Three members of sect. Racemosae were chosen, namely Bulbophyllum dissitiflorum Seidenf., B. lilacinum Ridl. and B. tricorne Seidenf. & Smitinand. All produced food-rewards. Of these, one (B. dissitiflorum) lacked fragrance and was used as a control, whereas the remaining two species produced fragrance. Having established that the food-reward was mainly proteinaceous in each case, and did not test positively for lipid, we undertook further histochemical investigations, as well as light microscopy, SEM and TEM. Specialized palisade-like epidermal cells of all species contained protein bodies and rough endoplasmic reticulum consistent with the production and secretion of a protein-rich food-reward. Cuticular pores were also present. In fragrant species, these cells also contained abundant smooth endoplasmic reticulum, oil droplets and many, well-developed, spherical plastids with numerous plastoglobuli, similar to those found in the osmophores (fragrance-producing structures) of other orchids. Indeterminate, osmiophilic cytoplasmic inclusions were also present. By contrast, the non-fragrant species lacked oil droplets and other osmiophilic inclusions and the plastids were scant, poorly developed, often elongate or irregular in shape and contained few plastoglobuli. Smooth endoplasmic reticulum was also less frequent. Since food-rewards tested negatively for lipid, it is probable that any oil droplets present were involved in fragrance production, especially since they were absent from the non-fragrant species. Thus, the unusual absence of lipids from the food-rewards of sect. Racemosae provided a rare opportunity, permitting, for the first time, the unraveling of these two secretory processes (food-reward and fragrance) in Bulbophyllum and clearly demonstrating the plasticity of these cells and their dual role in secretion

Ekofizjologiczne aspekty reabsorpcji nektaru

A number of approaches, both direct and indirect, have shown that nectar is reabsorbed by numerous plant species, irrespective of the age or sex of the flower. Furthermore, reabsorption occurs regardless of whether or not the flower has been pollinated. Reabsorption helps to maintain concentration of nectar and their viscosity and thereby encourages continued visits by pollinators. Conversely, the capacity to vary concentration of nectar sugars may confer evolutionary advantage by encouraging visits by more than one kind of pollinator and this is particularly important in regions where there is a paucity of pollinators. A further important role of nectar reabsorption is the maintenance of the energy equilibrium of the plant. A number of studies have shown that nectar production involves considerable energy expenditure requiring as much as 37% of the plant's daily production of energy by photosynthesis. The increased metabolic costs incurred by the plant during nectar production and secretion can reduce its growth and reproduction during the following season. Reabsorption of nectar that has not been collected by pollinators enables the plant to conserve at least some of the energy reserved for the secretion of nectar. Sugars reabsorbed from nectar can be re-used for the development of fruit and ovules - processes which demand large quantities of sugar. Despite convincing evidence for the reabsorption of nectar, few detailed studies have addressed the transport and incorporation of reabsorbed sugars. One of the questions that remain to be answered is 'What is the cellular basis for nectar reabsorption by the nectary?'.Nektar jest resorbowany w kwiatach roślin z różnych rodzin botanicznych, między innymi Apiaceae, Brassicaceae, Cucurbitaceae, Combretaceae czy Orchida- ceae. Reabsorbcja nektaru spełnia kilka niezwykle ważnych funkcji i występuje niezależnie od stadium kwitnienia, płci kwiatu czy zapylenia. W kwiatach typu otwartego, reabsorpcja cukrów umożliwia regulację koncentracji, która wzrasta na skutek parowania wody z nektaru. Z kolei w kwiatach innych roślin możliwość zmiany koncentracji nektaru stanowi pewną adaptację do zapylania przez szersze spektrum gatunków, co jest niezwykle ważne w sytuacjach deficytu zapylaczy w środowisku. Inne funkcje resorpcji nektaru dotyczą energetycznego bilansu roślin. Wyniki niektórych badań wykazują, że produkcja nektaru wymaga dużego nakładu energii metabolicznej i może pochłaniać dziennie do 37% energii uzyskanej z fotosyntezy. Dlatego też niektóre rośliny odzyskują przynajmniej część energii wydatkowanej na produkcję i sekrecję nektaru poprzez reabsorpcję cukrów, jeśli nektar nie jest pobrany podczas zapylenia. Cukry te rośliny wykorzystują głównie jako materiały zapasowe w rozwijających się owocach i nasionach, które są silnymi akceptorami asymilatów. Mechanizm reabsorpcji nektaru na poziomie komórkowym wymaga dalszych szczegółowych badań

Porównanie budowy osmoforów w kwiatach Stanhopea graveolens Lindley i Cycnoches chlorochilon Klotzsch (Orchidaceae)

The structure of the osmophores in Stanhopea graveolens and Cycnoches chlorochilon was studied by means of light microscopy (LM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The scent glands are located in the basal part of the labellum. The surface of the osmophores is wrinkled or rugose, which increases the area of fragrance emission. On the surface of the epidermis, remnants of secretion are noticeable in S. graveolens, but these are absent in C. chlorochilon. The osmophore tissue is composed of secretory epidermal cells and several layers of subepidermal parenchyma, and it is supplied by vascular bundles that run in ground parenchyma. The secretory cells have large nuclei, a dense cytoplasm with numerous ER profiles, lipid droplets, and plastids with a substantial amount of starch, which are probably involved in the synthesis of volatile substances. In the cell walls of the osmophore cells, numerous pits with plasmodesmata occur that are likely to take part in symplastic transport of the scent compounds. The structure of the osmophores is similar in both investigated species. Both S. graveolens and C. chlorochilon are pollinated by euglossine bees, and such similarity results from adaptation to effective scent emission and attraction of pollinators.W niniejszej pracy badano strukturę osmoforów w kwiatach Stanhopea graveolens Lindley oraz Cycnoches chlorochilon Klotzsch wykorzystując mikroskopię świetlną (LM), skaningową elektronową (SEM) oraz transmisyjną elektronową (TEM). Gruczoły wydzielające zapach zlokalizowane są u podstawy warżki. Powierzchnia osmoforów jest pomarszczona lub brodawkowata, co ułatwia emisję substancji zapachowych. W SEM na powierzchni epidermy u S. graveolens widoczne są pozostałości wydzieliny, natomiast u C. chlorochilon pomimo tego, że wydzielina pokrywa warżkę świeżych kwiatów, to w SEM nie jest widoczna. Tkanka osmoforowa jest utworzona z komórek wydzielniczych epidermy oraz kilku warstw subepidermalnych komórek miękiszowych i jest zaopatrywana przez wiązki przewodzące zlokalizowane w miękiszu zasadniczym. Komórki wydzielnicze mają duże jądro, gęstą cytoplazmę, ER, krople lipidowe oraz plastydy z ziarnami skrobi. W ścianach komórek osmoforów znajdują się liczne jamki z plazmodesmami, które przypuszczalnie biorą udział w symplastycznym transporcie związków zapachowych. Osmofory badanych gatunków mają bardzo podobną budowę anatomiczną. Zarówno S. graveolens jak i C. chlorochilon są zapylane przez pszczoły Euglossine, natomiast podobieństwa w strukturze ich osmoforów wynikają z przystosowania do efektywnego wydzielania zapachu, a tym samym skutecznego zwabiania zapylaczy