CHARACTERISTICS OF FLORAL NECTARY AND NECTAR OF COMMON BUGLOSS (Anchusa officinalis L.)

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1 Vol. 51 No Journal of Apicultural Science 25 CHARACTERISTICS OF FLORAL NECTARY AND NECTAR OF COMMON BUGLOSS (Anchusa officinalis L.) El bieta Weryszko-Chmielewska, Miros³awa Chwil Department of Botany, Agricultural University, Akademicka 15, Lublin, Poland. elzbieta.weryszko@ar.lublin.pl Received 06 April 2007; accepted 17 July 2007 S u m m a r y This study was pointed to the distribution, micromorphology of nectary and nectar secretion of Anchusa officinalis L. flowers. Observations of floral nectary structure were carried out with a scanning electron microscope (SEM). The mass of nectar produced over a flower's life span and sugars concentration in the nectar were determined. Flowers of Anchusa officinalis were eagerly visited by honeybees. The gland of Anchusa officinalis that secretes nectar is located at the base of the ovary and consists of 4 parts. No stomata were found in the epidermis of the nectary. The secretion of nectar proceeded through outer cell walls of the epidermis. Some cells with collapsed walls resembled the stomata. Flowers secreted nectar with sugars concentration of 61%, and the sugar yield of 10 flowers accounted for 4.69 mg. Keywords: floral nectary, micromorphology, nectar mass, sugar concentration, sugar efficiency, Anchusa officinalis L., Boraginaceae. INTRODUCTION Common bugloss Anchusa officinalis L. (Boraginaceae) is a plant commonly occurring in various regions of Poland (Rutkowski 2006, Zaj¹c and Zaj¹c 2001). It overgrows roadsides, hills, railway embankments and ruderal sites. Flowers have a radial corolla, red-violet at the beginning and change into violet-blue during blooming. The corolla reaches 6-15 mm in diameter with a tube length of 5-7 mm. Large, hairy throat scales close the inlet into the corolla's tube. The blooming stage of the flowers spans from April till September (Rutkowski 2006). Roots and flowers of common bugloss are used in the dyeing industry. Roots were used to produce a dark purple dye, whereas flowers obtained a yellow dye (Nowiñski 1983, Pogorzelec 2006). Common bugloss is believed to be a medicinal herb (Sarwa 2001), however recently, due to the content of toxic alcalloids: lycopsamine and 7-acetyllycopsamine, it has been withdrawn from therapeutics (Sadowska 2004). It is also used as an important cosmetic plant (Hlava et al 1984) and as an ornamental plant in sunlit gardens in a strip of higher plants. In addition, it is included as an apicultural plant providing nectar and pollen (Rawski 1948, Maurizio and Grafl 1969, Ko³towski 2006, Pogorzelec 2006). This study was aimed at determining the nectar secretion of Anchusa officinalis L. flowers under conditions of the city of Lublin as well description the morphological traits of the floral nectary of this species. MATERIAL AND METHODS Analyses of the nectar secretion of Anchusa officinalis L. flowers were carried out at the Botanical Garden of the Maria Sk³odowska-Curie University in Lublin in the years using the method of

2 26 Jab³oñski and Szklanowska (1979). The nectar was collected at 9:00 a.m., three times in four samples in the full blooming stage of plants. One sample was made of the nectar mass originating from the entire life span of flowers. Microscopic analyses referred to the structure of the floral nectary. For observations of the surface of nectary epidermis in a scanning electron microscope (SEM), fragments of flowers were fixed and the plant material was prepared according to the method described by Weryszko-Chmielewska (2003). RESULTS Flowers of Anchusa officinalis (Fig. 1) were eagerly visited by honeybees. A plate-like dark blue part of the corolla petals, with whitish or light-pink throat scales, was an attractant to insects. The adaxial surface of the petals was dull and slightly velvet. It resulted from the presence of conoidal hair which densely covered it (Fig. 2). The structure of hair occurring on the surface of corolla petals and its density may be an adaptive trait to pollination by specified groups of insects. Fig. 2. Segment of adaxial surface of corolla petal, with visible densely arranged coniform hair. Bar = 30 µm. Fig. 1. Flowers of Anchusa officinalis visited by a honeybee. Fig. 3. Four-segment ovary (o) with a nectary (n) at the base. Bar = 300 µm. The nectary gland of Anchusa officinalis consisted of 4 parts, accompanying the base of particular segments of the ovary (Fig. 3). Each segment of nectary surrounded the basal segment of the ovary from the outside, thus forming a noticeable protrusion growing out beyond the ovary. Nectariferous tissue formed some whole with the ovary and was separated from it

3 Vol. 51 No Journal of Apicultural Science 27 Fig. 4. Fragment of the surface of nectary (n) epidermis Fig. 5. Fragments of secretory Fig. 8. Fragments of secretory Fig. 6. Fragments of secretory Fig. 9. Fragments of secretory Fig. 7. Fragments of secretory only with a minute hollow. The height of the ovary together with the nectary reached 566 µm, whereas the height of the nectary Fig. 10. Fragments of secretory gland reached ca. half of that value. The mean radial thickness of the nectary accounted for 79 µm. The thickness of the nectary constituted 14% of the diameter covering the pistil ovary and nectariferous tissue.

4 28 Abundance of nectar secretion by Anchusa officinalis flowers. Table 1 Year of study Mass of nectar per 10 flowers (mg) Sugars concentration in nectar (%) min. - max. x min. - max. x Mass of sugars per 10 flowers (mg) x Cells of nectary epidermis were of a size similar to that of cells of ovary epidermis (Fig. 4). When analyzed under a scanning electron microscope they were multi-angle, slightly elongated and isodiametric with sizes ranging from 10 to 15 µm. The external wall of most of the cells was convex and was characterized by smooth cuticula (Figs. 5, 7, 8, 9). Between this type of cells there were cells with collapsed walls, usually in the central part (Figs. 6-10), which may point to their adaptation facilitating nectar secretion. No stomata were observed in the epidermis of nectary. It indicates that nectar secretion proceeded through the outer walls of the epidermis cells. Some cells with collapsed walls resembled the stomata (Figs. 6, 7, 9). Flowers of Anchusa officinalis secreted nectar with a high concentration of sugars ranging from 59 to 65%, with the mean value accounting for 61%. Ten flowers of Anchusa officinalis secreted ca. 8 mg of nectar and their sugar efficiency reached 4.69 mg (Table 1). DISCUSSION The study demonstrated that flowers of Anchusa officinalis were eagerly visited by honeybees, which has also been confirmed by other authors (Maurizio and Grafl 1969, Pogorzelec 2006). They are also a source of food for bumble bees which prefer large plants of that species, providing abundant secretion of nectar (Dreisig 1995). In turn, Andersson (1988) claims that more visits of bumble bees were recorded on small plants of common bugloss than on the large flowers of that species. Ko³towski (2006) also reports that single plants of common bugloss are often occupied by bumble bees and solitary bees. Floral nectaries of common bugloss are located beneath the base of the ovary and are characterized by large sizes as compared with that part of the flower, since their height constitutes ca. half the height of the ovary. In this species, the shape of the nectary is similar to that described by Stpiczyñska (2003) in Symphytum officinale (Boraginaceae). No stomata were found in epidermis of Anchusa nectary, whereas they occurred in high numbers in the nectarines of other species of that family: in Symphytum officinale (Stpiczyñska 2003) and in Myosotis sylvatica (Weryszko-Chmielewska 2003). This indicates that nectar secretion in Anchusa proceeds through the surface of cell walls of nectary epidermis in which typical hollows were observed which might facilitate nectar exudation. The calculated mean mass of nectar secreted by a single flower of Anchusa officinalis reached 0.77 mg. The concentration of sugars in nectar accounted for ca. 61%. In turn, the mass of sugars obtained from nectar of a single flower reached 0.47 mg. This value is considerably lower compared to values reported for that spe-

5 Vol. 51 No Journal of Apicultural Science 29 cies by Demianowicz et al. (1963), i.e mg, as well as by Ko³towski (2006), i.e. 1-2 mg. That author evaluated the apiarian value of Anchusa officinalis as good. In contrast, Rawski (1948) determined nectar secretion by that taxonomic unit as medium. Pogorzelec (2006) points to the great diversification of nectar secretion by Anchusa depending on soil conditions and emphasizes that in field cultivation it secretes remarkably more nectar than in natural conditions. In turn, the mass of sugars secreted by the flower of common bugloss, due to their high concentration in nectar, was considerably higher in the plants examined as compared to the mass of sugars contained in nectar of Symphytum officinale (0.33 mg) described by Stpiczyñska (2003). Despite considerable apiarian values of common bugloss, attention should be given to its toxic properties that may also refer to its nectar. Toxic alcalloids of that species are assumed to be able to penetrate into the human body with consumed honey originating from nectar of that plant (Sadowska 2004). REFERENCES Andersson S. (1988) Size-dependent pollination efficiency in Anchusa officinalis (Boraginaceae): causes and consequences. Oecologia 76(1): Demianowicz Z., Jab³oñski B., Ostrowska W., Szybowski S. (1963) Wydajnoœæ miodowa wa niejszych roœlin miododajnych w warunkach Polski. Pszczeln. Zesz. Nauk. 2: Dreisig H. (1995) Ideal free distributions of nectar foraging bumblebees. Oikos 72(2): Hlava B., Starý F., Pospíšil F., Krejèová Z. (1984) Roœliny kosmetyczne. PWRiL, Warszawa. Jab³oñski B., Szklanowska K. (1979) Propozycje zmiany metody badañ nektarowania roœlin. Pszczeln. Zesz. Nauk. 23: Ko³towski Z. (2006) Wielki atlas roœlin miododajnych. Przeds. Wydawn. Rzeczypospolita SA. Maurizio A., Grafl I. (1969) Das Trachtpflanzenbuch. Ehrenwirth Verlag, München. Nowiñski M. (1983) Dzieje upraw i roœlin leczniczych. PWRiL, Warszawa. Pogorzelec M. (2006) Roœliny miododajne. Wyd. S¹decki Bartnik, Nowy S¹cz. Rawski M. (1948) Po ytki pszczele. Cz. III. Wartoœæ po ytkowa roœlin dzikich i uprawnych. Wydaw. Ex Libris, Warszawa. Rutkowski L. (2006) Klucz do oznaczania roœlin naczyniowych Polski ni owej. Wydawnictwo Naukowe PWN, Warszawa. Sadowska A. (2004) Rakotwórcze i truj¹ce substancje roœlinne. SGGW, Warszawa. Sarwa A. (2001) Wielki leksykon roœlin leczniczych. Ksi¹ ka i Wiedza, Warszawa. Stpiczyñska M. (2003) Sekrecja nektaru w kwiatach ywokostu lekarskiego (Symphium officinale L.) i jego sk³ad chemiczny. Acta Agrobot. 56 (1-2): Weryszko-Chmielewska E. (2003) Morphology and anatomy of floral nectary and corolla outgrowths of Myosotis sylvatica Hoffm. (Boraginaceae). Acta Biol. Crac. Ser. Bot. 45(1): Zaj¹c A., Zaj¹c M. (Red.) (2001) Atlas rozmieszczenia roœlin naczyniowych w Polsce. Wydaw. Pracownia Chorologii Komputerowej Instytutu Botaniki UJ i Fundacji dla UJ, Kraków.

6 30 CHARAKTERYSTYKA NEKTARNIKÓW KWIATOWYCH I NEKTARU FARBOWNIKA LEKARSKIEGO (Anchusa officinalis L.) Weryszko-Chmielewska E., Chwil M. S t r e s z c z e n i e W pracy zbadano po³o enie i mikromorfologiê nektarników oraz obfitoœæ nektarowania kwiatów Anchusa officinalis L. Obserwacje struktury nektarników przeprowadzono w skaningowym mikroskopie elektronowym (SEM). Okreœlono masê nektaru wyprodukowanego w ci¹gu ca³ego ycia kwiatu oraz zawartoœæ cukrów w nektarze. Kwiaty Anchusa officinalis by³y chêtnie oblatywane przez pszczo³y. Gruczo³ nektarnikowy Anchusa officinalis po³o ony by³ u podstawy zal¹ ni i sk³ada³ siê z 4 czêœci. W epidermie nektarnika nie stwierdzono obecnoœci aparatów szparkowych. Sekrecja nektaru odbywa³a siê za poœrednictwem zewnêtrznych œcian komórek epidermy. Niektóre komórki z zapadniêtymi œcianami komórkowymi przypomina³y aparaty szparkowe. Kwiaty wydziela³y nektar o koncentracji cukru 61%, a ich wydajnoœæ cukrowa z 10 kwiatów wynosi³a 4,69 mg. S³owa kluczowe: nektarnik kwiatowy, mikromorfologia, masa nektaru, koncentracja cukrów, wydajnoœæ cukrowa, Anchusa officinalis L., Boraginaceae.