Plant Syst Evol (2016) 302:585–599 DOI 10.1007/s00606-016-1287-5 ORIGINAL ARTICLE Oil-resin glands in Velloziaceae flowers: structure, ontogenesis and secretion 1 2 1 Rachel Sadala-Castilho • Silvia R. Machado • Ba´rbara Sa´-Haiad • Heloisa A. Lima1 Received: 24 October 2015 / Accepted: 18 February 2016 / Published online: 11 March 2016 Ó Springer-Verlag Wien 2016 Abstract Many Velloziaceae flowers present conspicu- V. intermedia are oil-resin secreting and remain active in ous glands, whose taxonomic value has already been secretion from very young buds, through to immature fruit. highlighted. However, until now, their micromorphology, New, smaller glands replace senescent glands by divisions anatomy and ultrastructure have not been investigated, nor near the base of the original stalk cells. Oil-resin glands have the natures and possible functions of their exudates. have a number of different, but important functions, Our aim was to investigate distribution, ontogenesis, including the interaction with Meliponina bees, protection structure, and secretion mechanisms of glands of Bar- against water loss and high temperatures by ultraviolet bacenia flava and Vellozia intermedia and to discuss their screening, and anti-desiccant properties. possible ecological functions. Samples were prepared according to standard methods for investigations of plant Keywords Barbacenia flava Á Campos Rupestres Á anatomy, scanning electron microscopy, and transmission Endophytic bacteria Á Meliponina Á Ultrastructure Á Vellozia electron microscopy. Histochemical tests were performed, intermedia and focal field observations were made in the study site. The capitate stalked glands on the pedicel, tepals and hypanthium are covered by a sticky secretion that is Introduction released in the gland head through the outer periclinal cell walls and cuticle. Secretions are produced in the epidermal Plant resins are compounds consisting mainly of terpenes and subepidermal cells that contain structural components and phenols. Primarily, they are materials produced by typical of mixed, mainly lipophilic secretions. Bacteria vegetative organs contained in canals or pockets from were found inside the oil-resin gland cells of both species. which they ooze if the plant suffers some mechanical The Meliponina bees Trigona spinipes and Tetragonisca damage. Resins appear to function against predation, in angustula were observed collecting resin from both spe- vegetative tissues, and are also good water repellents. cies, but were not involved in pollination. Our observations Many bees collect resins exuding from vegetative tissues clearly indicate that flower glands of B. flava and and carry it to their nests, where it is worked into a coating for the nest walls (Simpson and Neff 1983). The presentation of floral resin as a reward to female Handling editor: Marlies Sazima. bees of Apidae and Megachilidae has so far been reported & Rachel Sadala-Castilho in Dalechampia (Euphorbiaceae), Clusia, Chrysochlamys [email protected] and Tovomitopsis (Clusiaceae) and Clusiella (Calophyl- ´ 1 laceae) (Sa-Haiad et al. 2015 and references therein). In the Departamento de Botaˆnica, Quinta da Boa Vista, process of collecting floral resin, bees are dusted with Universidade Federal do Rio de Janeiro, Museu Nacional, Rio de Janeiro, RJ 22940-040, Brazil pollen and so become effective pollinators (Kearns and Inouye 1993). Floral resins are more easily worked by 2 Departamento de Botaˆnica, Instituto de Biocieˆncias, Universidade Estadual Paulista, Caixa Postal 510, Botucatu, bees, and also more predictable than vegetative resins SP 18618-000, Brazil (Simpson and Neff 1983). 123 586 R. Sadala-Castilho et al. Members of Velloziaceae are typical elements of odouriferous flowers of V. intermedia, anthesis is also Brazilian Campos Rupestres (Giulietti and Pirani 1988), a diurnal, and the tepals are white at the base, changing neotropical vegetation complex, endemic to Brazil, and gradually to blue/violet, towards the apex (Fig. 1c, d). located on rocky mountaintops (from 900 to over 2000 m Voucher specimens were deposited in the herbarium of asl), mainly in the Cerrado and Caatinga provinces of the the Museu Nacional, Universidade Federal do Rio de Brazilian Shield (Alves et al. 2014a). Many Velloziaceae Janeiro (R). flowers present conspicuous glands, distributed on the pedicel, hypanthium and tepals. Our preliminary observa- Structural and ultrastructural studies tions show that secretions are produced throughout flower and fruit development. Such secretory structures have been Four stages of the developing flowers of both B. flava and described as capitate glandular trichomes (Sazima 1978; V. intermedia were considered: stage 1, very young flower Sajo et al. 2010), and most recently as glandular emer- buds (27 and 33 mm long, respectively; green tepals); gences (Montserrat and Mello-Silva 2013). The taxonomic stage 2, flower buds (46 and 52 mm long; with yellow and value of these glands has been highlighted by Mello-Silva violet tepals, respectively); stage 3, freshly open flowers; (1995). Although there are a number of studies that focus stage 4, senescent flowers. Ten replicate samples of each on the taxonomy, reproductive biology and floral anatomy stage were collected for anatomical (five samples) and of the Velloziaceae species (Mello-Silva 1995, 2004, 2005; ultrastructural studies (five samples). Alves et al. 2014b; Sazima and Sazima 1990; Jacobi and For light microscopy, samples were fixed in 4 % Del Sarto 2007; Menezes 1973, 1980, 1988), none have formaldehyde ? 2.5 % glutaraldehyde in 0.05 M sodium investigated the morphology, anatomy and ultrastructure of phosphate buffer, pH 7.2 (Gahan 1984), dehydrated in an these glands, nor have the nature and possible functions of ethanol series, embedded in HistoresinÒ (Leica, Wetzlar, their exudates been discussed. Germany) in accordance with the manufacturer’s recom- In this study, we identify the oil-resin nature of the mended procedure, and sectioned with glass knives at secretion from the glands present in the flowers of Bar- 1–3 lm on a RM2255 (Leica) rotary microtome. The bacenia flava Mart. ex Schult. and Schult.f. and Vellozia sections were stained with toluidine blue O (Feder and intermedia Seub., and we also describe the origin, structure O’Brien 1968). Measurements and photomicrographs were and lifespan of these glands. Based on the interactions with obtained using an Olympus BX-51 microscope (Olympus, stingless bees (subtribe Meliponina) and the extreme con- Tokyo, Japan) with the image-capture system Q color5 and ditions of the habitats where these species live, we discuss Image-ProExpress software (Media Cybernetics Inc., Sil- the possible ecological functions of these structures. We ver Spring, Maryland, USA). also report the presence of endophytic bacteria inside the Histochemical tests were carried out to detect the pres- oil-resin gland cells. ence of lipophilic compounds using Sudan III and IV (Jensen 1962); starch using Lugol (Langeron 1949); sugars using Fehling’s reagent (Maclean and Ivemey-Cook 1952); Materials and methods phenolic compounds using potassium dichromate (Gabe 1968); proteins using xylidine Ponceau (Cortelazzo and Study site and taxa Vidal 1991; Amaral et al. 2001); mucilage using ruthenium red (Langeron 1949); polysaccharides, using the periodic This study was conducted at the Parque Estadual de Ibiti- acid–Schiff’s reagent reaction (Taboga and Vilamaior poca, located within the municipality of Lima Duarte, 2013); lignin using phloroglucin ? HCl (Johansen 1940); Minas Gerais State, SE Brazil (between 21°4001500– cellulose and suberin using iodated zinc chloride (Jensen 21°4303000S and 43°5203500–43°5401500W). The predominant 1962); and resin using copper acetate (Johansen 1940). vegetation in the park is characteristic of Campo Rupestre. For scanning electron microscopy (SEM), samples were The climate is altitude tropical, mesothermal, with cold, fixed in glutaraldehyde (2.5 % with 0.1 M phosphate buf- dry winters (June to September) and high-rainfall summers fer, pH 7.3), post-fixed with 0.5 % osmium tetroxide in the (December to March). The annual rainfall, 2248 mm, is same buffer, dehydrated in an ethanol series, critical-point also high (Rodella and Tarifa 2002). dried using a Balzers Union CPD 020 critical-point dryer Barbacenia flava and Vellozia intermedia are herba- with CO2, gold coated using a Bal-Tec SCD 050 vacuum ceous and occur on rocky and sandy outcrops. Their sputter-coater and examined using a FEI QUANTA 200 flowers are trimerous, pedicellate, actinomorphic, perfect, microscope (FEI, Hillsboro, OR, USA). epigynous, with three, fused carpels and septal nectaries. In For transmission electron microscopy (TEM), samples B. flava, the anthesis is diurnal, the flowers are pale-yellow, were fixed in glutaraldehyde (2.5 % with 0.1 M phosphate odourless and functionally tubular (Fig. 1a, b). In the buffer, pH 7.3) and left overnight at 4 °C. They were then 123 Oil-resin glands in Velloziaceae 587 Fig. 1 Barbacenia flava (a, b); Vellozia intermedia (c, d): a flower in lateral view, b detail of the glands on the outer surface of the hypanthium; c flower in frontal view; d detail of the glands on the outer surface of the hypanthium post-fixed with 1 % osmium tetroxide in the same buffer peduncle, densely concentrated on the hypanthium surface, for 2 h at room temperature, dehydrated in a graded series and in specific areas on the tepals. In B. flava, such glands of acetone solutions and embedded in Araldite resin. occur