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Investigations of the micromorphology of flowers and the structure of nectaries in Chamomilla recutita L. (Rausch.) were carried out with the use of stereoscopic, light, scanning and transmission electron microscopy. Biseriate glandular trichomes consisting of 5-6 cell layers were found on the surface of the corollas of ray and disc florets. Accumulation of secretion within the subcuticular space was accompanied by degradation of trichome cells. Secretion release followed rupture of the cuticle in the apical part of the trichome. The ovary of the ray florets exhibited characteristic ribs covered with epidermis composed of radially elongated palisade cells. Nectariferous glands were present only in the disc florets. The ring-like nectary (93×163 µm; height x diameter) was located above the inferior ovary. The gland structure was formed by single-layer epidermis and 5-8 layers of specialised nectariferous parenchyma. Nectar was released via modified 15-20 µm wide stomata. The guard cells were slightly elevated above the surface of the other epidermal cells or were located slightly below them. The stomatal cells were characterised by small external and internal cuticular ledges. No vascular bundles were observed in the nectary. The gland was supplied by branches of vascular bundles reaching the style and ending at the nectary base. The nectariferous tissue was formed by isodiametric cells with a diameter of 11-20 µm. The cell interior was filled with electron dense cytoplasm containing a large nucleus, numerous pleomorphic plastids, mitochondria with a distinct system of cristae, Golgi bodies, ER profiles, and ribosomes. The plastid stroma was characterised by presence of pastoglobuli, intraplastid tubules, and lighter zones. Several small vacuoles were found in each cell. Plasmodesmata were visible in the walls of some cells. Lighter periplasmic space in which apoplastic transport of nectar might take place was observed between the plasmalemma and the cell wall. The presence of an osmiophilic substance in the intercellular spaces additionally corroborates this assumption.
Micromorphology and distribution of glandular and non-glandular trichomes on the above-ground organs of Inula helenium L. were investigated using light and scanning electron microscopy (SEM). Two types of biseriate glandular trichomes, i.e. sessile and stalk hairs, and non-glandular trichomes were recorded. Sessile glandular trichomes were found on all examined I. helenium organs (with their highest density on the abaxial surface of leaves and disk florets, and on stems), whereas stalk glandular trichomes were found on leaves and stems. Sessile trichomes were characterised by a slightly lower height (58–103 µm) and width (32–35 µm) than the stalk trichomes (62–111 µm x 31–36 µm). Glandular hairs were composed of 5–7 (sessile trichomes) or 6–9 (stalk trichomes) cell tiers. Apical trichome cell tiers exhibited features of secretory cells. Secretion was accumulated in subcuticular space, which expanded and ruptured at the top, and released its content. Histochemical assays showed the presence of lipids and polyphenols, whereas no starch was detected. Non-glandular trichomes were seen on involucral bracts, leaves and stems (more frequently on involucral bracts). Their structure comprised 2–9 cells; basal cells (1–6) were smaller and linearly arranged, while apical cells had a prozenchymatous shape. The apical cell was the longest and sharply pointed. Applied histochemical tests revealed orange-red (presence of lipids) and brow colour (presence of polyphenols) in the apical cells of the trichomes. This may suggest that beside their protective role, the trichomes may participate in secretion of secondary metabolites.
The aim of the study was to investigate the structure and topography of endogenous secretory tissues of Inula helenium L. By using light and electron microscopy, morphological and anatomical observations of stems, leaves and rhizomes were made. It was shown that in the stems secretory cavities were situated in the vicinity of phloem and xylem bundles. The number of the reservoirs reached its maximum value (34) at shoot flowerig termination, whereas the cavities with the largest diameter were observed at full flowering stage (44.6 µm). In the leaf petioles and midribs, the reservoirs also accompanied the vascular bundles, and their number and size increased along with the growth of the assimilation organs. Observations of the cross sections of the rhizomes revealed the presence of several rings of secretory reservoirs. The measurements of the cavities showed that as a rule the reservoirs with a larger dimension were located in the phelloderm, whereas the smallest ones in the xylem area. The secretory cavities located in the stems and leaves developed by schizogenesis, whereas the rhizome reservoirs were probably formed schizolisygenously. The cells lining the reservoirs formed a one - four-layered epithelium. Observed in TEM, the secretory cells of the mature cavities located in the rhizomes were characterised by the presence of a large central vacuole, whereas the protoplast was largely degraded. Fibrous elements of osmophilic secretion and numerous different coloured vesicles could be distinguished in it. The cell walls formed, from the side of the reservoir lumen, ingrowths into the interior of the epithelial cells. Between the cell wall and the plasmalemma of the glandular cells, a brighter periplasmatic zone with secretory vesicles was observed.
Due to the presence of secondary metabolites exhibiting pharmacological activity, the flowers of Rosa rugosa Thunb. have found application in traditional and folk medicine. The essential oil obtained from them is also considered to be a phytoncide. The morphological and anatomical characters of glandular trichomes located on the sepals of R. rugosa were studied by light and scanning electron microscopy. Using histochemical tests, the type of secretion produced in the trichomes was determined and its contents were compared with the secretion produced by the papillae on the petals. It was found that multicellular glandular trichomes, having the features of colleters, and non-glandular trichomes were located on the abaxial epidermis, while only non-glandular trichomes were situated on the adaxial epidermis. The stalk cells of the glandular trichomes are arranged in multiple rows, whereas the epidermal cells of the head are arranged radially. The capitate trichomes were classified into two types: short and long trichomes. The largest density of glandular trichomes was recorded in the basal abaxial epidermis and in the middle part of the sepals. During the initial stages of bud development, the glandular hairs were green colored, whereas in the next development stages they changed the color to red. The histochemical tests used allowed us to find that the trichomes on the sepals and the papille on the petals produced lipid substances, polyphenols, tannins, and flavonoids. Sesquiterpenes were found only in the secretion of the glandular hairs on the sepals.
The flowers of Viola × wittrockiana Gams. emit odorous compounds. The glands found in the flowers, responsible for the production of essential oils, are most frequently distributed on the petals of the corolla. They include papillae – conical epidermal cells. The structure of the epidermis and the internal tissues of the petals of V. × wittrockiana were examined using light, fluorescence and scanning electron microscopy. Papillae were found to occur in the epidermis on both sides of all the petals (spurred, lateral and upper), but they were much longer in the adaxial epidermis. Different-sized droplets of lipid nature, which are essential oils, were present in the papillae. They were also observed on the outer surface of the walls of these cells. Moreover, in the adaxial epidermis there were areas of flattened cells with a characteristic structure, being probably secretory glands. The present study shows that differently-structured cells of both the abaxial and adaxial epidermis participate in the release of odorous compounds by the flowers of V. × wittrockiana. These different structures may produce varied scents in terms of their quality.
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In plants belonging to the Ranunculaceae the floral nectaries may differ in origin, location in the flower, shape and structure. In many cases they are defined as modified tepals or modified stamens. The nectary organs in this family are frequently termed "honey leaves," and staminodial origin is attributed to them. Gynopleural and receptacular nectaries are rarely found in Ranunculaceae. To date there are no reports on the structure of the nectary organs in plants of the genus Pulsatilla. We used light and scanning electron microscopy to study the location and structure of the nectaries in Pulsatilla slavica and P. vulgaris flowers. The staminodial nectaries were found to be nectar-secreting organs. The number of stamens per flower (102-398) increases with plant age. The share of staminodes is 12–15%. The staminodes are composed of a filament and a modified head. They are green due to the presence of chloroplasts in the epidermal and parenchymal cells. The parenchymal cells are in a loose arrangement. Stomata (3–20), through which nectar exudation occurred, were found only in the abaxial epidermis of the staminode head. The stomata are evenly distributed and have well-developed outer cuticular ledges. Some of them are immature during nectar secretion, with their pores covered by a layer of cuticle. During the activity of the nectariferous organs in the flowers, primary (on the staminode surface) and secondary nectar (at the base of tepals) are presented. The staminodes of the two Pulsatilla species show similar structural features and have similar shares in the androecium.
The micromorphology of the nectaries and of other elements of the flower was examined by scanning electron microscopy (SEM). The anatomy of the nectaries was determined using light microscopy (LM). The inflorescences of A. platanoides comprise flowers included in two categories: functionally male and female. Nectaries of similar structure are found in both types of these flowers. The nectary gland located on the surface of the receptacle belongs to interstaminal nectaries. It has the form of a fleshy ring situated between the petals and the pistil. The bases of the staminal filaments are located in the depressions of the nectary. The outer diameter of the nectary reaches ca. 5 mm, while the thickness of this gland’s tissues is 400-700 µm. In the epidermis of the nectary gland, there are numerous, evenly distributed stomata through which nectar release occurs. The stomata function asynchronously. In some stomata, we could observe nectar drops flowing out and a layer of this secretion around the stomata. The secretory parenchyma of the nectary is composed of several layers of thick-walled cells, whereas the ends of the vascular bundles with xylem and phloem elements are situated in the subglandular parenchyma. Chloroplasts are found both in the epidermal cells and in the glandular parenchyma cells and photosynthesis can take place in them due to the nectary’s good exposure to light. The presence of starch grains was found in the chloroplasts; they can be energy material for nectar production.
Floral nectaries of Inula helenium L. only occurred in disc florets and were situated above the inferior ovary. The shape of the investigated glands (five-armed star with rounded tips and deep incisions - observed from above) clearly differed from the shape of the nectaries of other Asteraceae, also the height of nectary was much lower (129 µm). The glandular tissue of the nectaries of elecampane was composed of a single-layered epidermis and 5--9 layers of secretory cells. Nectar was released through modified stomata, mainly arranged in the top part of the gland. The secretory cells were characterised by granular cytoplasm and the presence of a large, often lobate, cell nucleus. In the cytosol, numerous amoeboid plastids, mitochondria, Golgi bodies and ribosomes were present. In small vacuoles, myelin-like structures, fibrous material and vesicles with the content of substances which can be secretion, were observed. The plastid stroma showed different electron density and the presence of internal tubules and plastoglobules. Vesicular extensions forming bright zones were visible between the membranes of the nuclear envelope. Adjacent to the plasmalemma, as well as between the plasmalemma and the cell wall, secretory vesicles occurred, indicating the granulocrine mechanism of nectar secretion.
Badano cechy morfologiczne i anatomiczne oraz związane z ultrastrukturą komórek nektarników Achillea millefolium z rodziny Asteraceae. Obecność nektarników stwierdzono tylko w kwiatach rurkowatych u podstawy szyjki słupka. Zbadano mikromorfologię nektarników w SEM, przeprowadzono obserwacje struktury w mikroskopie świetlnym i transmisyjnym elektronowym. Określono liczbę warstw budujących gruczoł, wielkość oraz kształt komórek epidermy i komórek gruczołowych. Analizowano ultrastrukturę komórek wydzielniczych. Dyskoidalny gruczoł nektarnikowy oglądany z góry miał kształt pięciokąta o wysokości 181,5 µm i średnicy 299,4 µm. Zbudowany był z jednowarstwowej epidermy oraz średnio z 6 warstw komórek wydzielniczych. Komórki gruczołowe były większe (27 µm) od komórek skórki (22 µm), różny był także kształt komórek w obu tkankach. Sekrecja nektaru odbywała się przez zmodyfikowane aparaty szparkowe. Komórki aparatów szparkowych były wyniesione ponad powierzchnię pozostałych komórek tkanki okrywającej oraz wyróżniały się większymi rozmiarami. Nektarniki zaopatrywane były przez wiązki waskularne biegnące od szyjki słupka, które kończyły się u podstawy nektarnika, nie wnikając w głąb gruczołu. Badane w TEM komórki epidermy nektarnika krwawnika charakteryzowały się obecnością dużych jąder komórkowych, licznych piastydów, mitochondriów oraz wakuol z depozytami włóknistej wydzieliny oraz pęcherzykowatymi strukturami. W komórkach tkanki wydzielniczej nektarnika obserwowano elektronowo gęstą cytoplazmę, liczne plastydy, mitochondria, aparaty Golgiego oraz rozległą sieć retikulum endoplazmatycznego.
The presence of ruderal and mid-field vegetation promotes conservation of biodiversity and provides an additional source of food for insect pollinators. The white deadnettle is a common synanthropic plant visited frequently by various groups of insects, as it is a source of pollen and nectar. In 2012–2013, in the city of Lublin (Poland), signalling and food attractants in L. album flowers were analysed using light and scanning electron microscopy. The pipetting method was used for determination of nectar abundance in the flowers, and the content of sugars in the nectar was assessed with the use of an Abbe refractometer. It was found that the white dead-nettle flowers emitted a fragrance and were equipped with nectar guides, and the corolla and stamens had glandular trichomes and papillae secreting essential oils. On the stamens, there are also non-glandular trichomes, which play a role of pollen presenters. The nectary in the L. album flower has a shape of an irregular disc partly surrounding the base of the ovary. The content of sugars in the nectar was 43%. Sugar and honey yields per ha were calculated, and the values obtained were 153 kg and 191 kg, respectively.
Wild growing rose species are of great importance as a source of pollen for insects. Oil extracted from the petals of various Rosa species is used in perfumery, cosmetic industry, and therapeutics. In our study, we compared the flowering duration and flower lifespan, the number of stamens and pistils, the mass and size of pollen grains as well as the anatomical features of the petals of four Rosa species: R. canina, R. ×damascena, R. gallica, and R. rugosa. Moreover, we examined the pollen loads collected by bumblebees foraging on rose flowers in order to determine the attractiveness of pollen of this genus to insects. We showed the flower lifespan to vary (3.5–8 days) in the roses studied and revealed high variation in the number of stamens (82–260) and pistils (17–65) as well as in the mass of pollen produced. The flowers of R. rugosa produced the highest amount of pollen (26.7 mg per flower), while the flowers of R. canina the least (3.3 mg per flower), which is associated with differences in the number of stamens developed in the flowers between these species. The largest pollen grains were found in R. ×damascena and R. gallica. We demonstrated that R. ×damascena produces the thickest petals and that scent-emitting papillae found on the adaxial surface of the petals differ in size and shape in the rose species investigated.
The intensely fragrant flowers of the Rosa rugosa Thunb. have been applied in medicine, and food and cosmetic industries. The species is cultivated for production of rose essential oil (Oleum Rosae) from its flowers. R. rugosa petals secrete the largest quantities of essential oil. The aim of the study was to identify the characteristics of the epidermis of both sides of the petal and to observe whether adaxial and abaxial epidermal cells can secrete essential oil. The investigations were conducted using light and scanning electron microscopy. The analyses were focused on petal thickness and characteristics of the mesophyll. The study has demonstrated that only adaxial epidermal cells form conical papillae covered by massive cuticular striae. The surface of the papillae displayed remnants of a secretory substance. In turn, the inner walls of the abaxial epidermal cells were flat and covered by a striated cuticle, which exhibited various striation patterns. Fragrant substances stored under the cuticle caused local stretching thereof and disappearance of striation. The results of our observations allow a statement that the cells of the adaxial and abaxial epidermis of R. rugosa petals differ in terms of the structure and they secrete fragrant substances.
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