Sebastian Antoń

Comparative floral spur anatomy and nectar secretion in four representatives of Ranunculaceae.

Nectaries are common in Ranunculaceae. These secretory structures, however, have not been studied in detail despite their importance in plant-animal interactions, and data relating to the structure of nectary spurs, which are so characteristic of several genera of this family, remain scarce. In order to redress this imbalance, we sought, in the present paper, to analyze the anatomical and ultrastructural organization of the nectary spurs of four representatives of Ranunculaceae, i.e., Aconitum lycoctonum L., Aquilegia vulgaris L., Consolida regalis Gray, and Delphinium elatum L. Nectary spurs were examined using light, fluorescence, scanning electron, and transmission electron microscopy. The floral nectaries of A. lycoctonum and A. vulgaris are situated at the apices of the spurs, whereas in C. regalis and D. elatum, the nectary is located along the floor surface of the spurs. Nectar in C. regalis and D. elatum is exuded through micro-channels in the cuticle, whereas in A. lycoctonum and A. vulgaris, it is released by means of cell wall disruption, indicating that the method of nectar secretion here is holocrine. Structurally, the nectary of all four investigated species is quite similar, and its cells are typical of nectar-producing cells described in the literature. It is proposed that in A. lycoctonum and A. vulgaris, disruption of the cell wall and the release of the entire cell contents into the spur cavity contribute to the composition of the nectar that the latter contains, enriching it with cytoplasmic components. We conclude that the manner of nectar exudation may vary considerably between closely related plant species, regardless of their geographical origin and phylogeny.

The Flowering, Pollen Production, and Insect Visitors in the Ornamental Shrub Potentilla Fruticosa L. (Rosaceae)

Summary Urban areas have a specific ecological environment and may help to sustain local pollinator populations by the cultivation of different ornamental plants with entomophilous flowers. This yearlong study examined the flowering pattern, abundance of flowering, pollen production as well as insect visitation of two cultivars of the ornamental shrub Potentilla fruticosa L. (‘Maanleys’ and ‘Blink’), grown in Lublin; a city in south-eastern Poland. P. fruticosa ‘Maanleys’ bloomed from the middle of May to the first decade of September and P. fruticosa ‘Blink’ from June until October. The pattern of diurnal flowering was similar for both cultivars and showed plasticity in the season. Flowers opened most intensively in the morning hours, and 80 - 90% of the daily installment of newly opened flowers expanded by 8.00 h GMT +2h. A delay in the peak of diurnal flowering was noted between the spring/summer and summer/autumn periods. The most intense blooming fell in the 2nd month of flowering. The mass of pollen produced per flower depended on both the number of anthers and the efficiency of archesporial tissues. The pollen output varied from 1.4 to 7.2 mg per 10 flowers (‘Maanleys’) and from 2.6 to 4.5 mg per 10 flowers (‘Blink’). The mass of pollen produced per individual shrub was substantially related to the abundance of blooming. The average estimated pollen productivity in the full flowering phase was low; 1 g (‘Maanleys’) and 1.5 g (‘Blink’) per 10 m2 of shrub crown. The flowers of Potentilla fruticosa attracted numerous insects, mainly solitary bees (33 - 43%), dipterans (31 - 42%), lepidopterans (4 - 14%), bumblebees (3 - 15%), and honey bees (3 - 4%). The Potentilla fruticosa ‘Maanleys’ and ‘Blink’ are propagated for specific ornamental arrangements and due to a long flowering period may be used in small urban courtyards for both decorative value and as a pollen delivering plants. Streszczenie Uprawa różnych gatunków entomofilnych roślin ozdobnych w terenach zieleni miejskiej istotnie wpływa na utrzymanie lokalnych populacji owadów zapylających. W niniejszej pracy przedstawiono wyniki wieloletnich badań dotyczących obfitości i dynamiki kwitnienia, wydajności pyłkowej oraz oblotu kwiatów przez owady dwóch ozdobnych odmian Potentilla fruticosa L. (‘Maanleys’ oraz ‘Blink’) uprawianych na terenie Lublina. Przeciętnie kwitnienie P. fruticosa ‘Maanleys’ rozpoczynało się w połowie maja i trwało do pierwszej dekady września, natomiast termin kwitnienia P. fruticosa ‘Blink’ przypadał w okresie od czerwca do października. Dzienna dynamika rozkwitania była podobna w przypadku obu odmian. W ciągu dnia szczyt rozkwitania obserwowano o godz. 8.00 (GMT +2h), gdy rozkwitało od 80 - 90% wszystkich kwiatów, ale wystąpiło nieznaczne opóźnienie dziennego rytmu kwitnienia w okresie lato/jesień w stosunku do okresu wiosna/lato. Masa pyłku produkowanego w kwiatach zależała od liczby wykształcanych pręcików oraz efektywności tkanki archesporialnej. Wydajność pyłkowa z 10 kwiatów ‘Maanleys’ wahała się w granicach 1,4 - 7,2 mg, zaś 10 kwiatów ‘Blink’ produkowało 2,6 - 4,5 mg pyłku. Średnia wydajność pyłkowa w pełni kwitnienia była stosunkowo niska i wyniosła 1,0 g (‘Maanleys’) oraz 1,5 g (‘Blink’) na każde 10 m2 powierzchni krzewów. Kwiaty badanych odmian P. fruticosa zwabiały owady, głównie: pszczoły samotnice (33 - 43%), muchówki (31 - 42%), motyle (4 - 14%), trzmiele (3 - 15%) oraz pszczołę miodną (3 - 4%). Z uwagi na długi okres kwitnienia oraz walory dekoracyjne, krzewy P. fruticosa ‘Maanleys’ oraz ‘Blink’ mogą być wykorzystywane w założeniach zieleni miejskiej, stanowiąc równocześnie uzupełnienie pokarmu pyłkowego dla owadów.

Nectary and gender-biased nectar production in dichogamous Chamaenerion angustifolium (L.) Scop. (Onagraceae)

In dichogamous plants, nectar characteristics (i.e. nectar amount and its composition) can differ between sexual phases. In the present study, we investigated the structural organization of the floral nectary, nectar production and carbohydrate composition in the protandrous Chamaenerion angustifolium (L.) Scop. (Onagraceae). The receptacular nectary consisted of an epidermis with numerous nectarostomata, several layers of photosynthetic secretory parenchyma, and subsecretory parenchyma. Nectariferous tissue was not directly vascularized and starch grains were rarely observed in the secretory cells, occurring exclusively in the guard cells of modified stomata. The nectar was released via nectarostomata. The floral nectar was hexose rich (32.8/39.1/28.1% glucose/fructose/sucrose) and the total concentration was constant throughout the anthesis (47% on average). However, contrasting patterns in nectar amount and carbohydrate composition between the floral sexual phases were observed. On average, female‐phased flowers produced 1.4‐fold more nectar than male‐phased flowers, and although the nectar was sucrose rich during the male phase, it was hexose rich during the female phase, suggesting sucrose hydrolysis.

Pollination biology and breeding system in five nocturnal species of Oenothera (Onagraceae): reproductive assurance and opportunities for outcrossing

The capacity to produce seed, both by selfing and outcrossing, or mixed mating strategies, is considered a mechanism for overcoming unpredictable pollinator availability. In the present study, we investigate breeding system, insect visitations and the role of insect visitors in the pollination of five species of Oenothera subsect. Oenothera. Field experiments showed that autonomous selfing occurs at bud stage, prior to the opening of the flower. Control flowers showed similar seed set to hand-pollinated flowers, whereas emasculated flowers and those subject to open pollination set fewer seed. These results are consistent with the hypothesis that the investigated Oenothera exhibit a great capacity for autonomous selfing and that selfing is selected in order to provide reproductive assurance. Although flowers were visited mostly by nocturnal lepidopterans, these insects did not precipitate pollination and are thus considered nectar thieves. Conversely, analysis of pollen loads and behavior during foraging by diurnal insect visitors revealed that honeybees and bumblebees are the probable pollinators. We conclude that production of flowers capable of autonomous selfing at bud stage, followed by anthesis and opportunities for outcrossing, probably improves the invasive potential of these Oenothera in Europe, together with a rapid increase in their populations, even when pollinators are scarce.

Morphology of Anemone sylvestris L. flower (Ranunculaceae)

Abstract During the monitoring of populations of Anemone sylvestris L. (Ranunculaceae), a protected species in Poland, we found that the seed set is impaired. The flower is considered an adaptation that has coevolved to achieve effective pollination and successful fertilization. Therefore we have focused on the morphological and anatomical characteristics of the flowers of A. sylvestris L. as a prelude to the study of the species’ pollination biology and plant breeding system. The large size of the flower (50.6 ± 16.4 mm in dimensions) and its bowl shape fulfil both the biotic pollination syndrome and the aerodynamic requirements for pollen dispersal and capture. The opening and closing of the perianth provide a shelter for beetles. The odourless perianth, absence of nectar, scarcity of pollen (approximately 200 000 pollen grains per flower) and its traits - small size (axis P = 18.52 ± 1.0 μm; E = 16.59 ± 0.9 μm), lack of balsam on the exine surface, starch accumulation in more than 95% of pollen grains correspond to the specialization in anemophily. The stigma is papillous, the dense hairs are situated between single carpels indicating adaptation to capturing dry pollen and specialization in the wind pollination syndrome. The flower of A. sylvestris is an example for an intermediate form between entomophily and anemophily, i.e. a secondary and more advanced feature among Ranunculaceae.