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Acta Botanica Brasilica

Print version ISSN 0102-3306On-line version ISSN 1677-941X

Acta Bot. Bras. vol.31 no.3 Belo Horizonte July/Sept. 2017

http://dx.doi.org/10.1590/0102-33062017abb0108 

Articles

Leaf glands of Banisteriopsis muricata (Malpighiaceae): distribution, secretion composition, anatomy and relationship to visitors

Lays Araújo Nery1 

Milene Faria Vieira2 

Marília Contin Ventrella1  * 

1Laboratório de Anatomia Vegetal, Departamento de Biologia Vegetal, Universidade Federal de Viçosa, 36570-000, Viçosa, MG, Brazil

2 Laboratório de Biologia Reprodutiva, Departamento de Biologia Vegetal, Universidade Federal de Viçosa, 36570-000, Viçosa, MG, Brazil

ABSTRACT

Leaf glands are common structures in Malpighiaceae and exhibit great morphological diversity, yet information on their anatomy, secretion and type of visitors remains scarce. The aim of this study was to describe the distribution, anatomical development and chemical and functional properties of leaf glands of Banisteriopsis muricata (Malpighiaceae). Leaves at different stages of development were collected and processed according to standard techniques for light and scanning electron microscopy. Secretion composition was determined by histochemical tests and test-strips, while gland funciton was determined by field observation of interactions with visitors. Leaf glands were located on the petiole and on the abaxial base of the leaf blade. The gland secretion was found to be a protein-rich nectar that was foraged upon by ants ( Solenopsis); it was found accumulated in subcuticular spaces without pores or stomata for its release. Leaf glands were found to develop from protoderm and ground meristem, and consisted of typical secretory epidermis, nectariferous parenchyma and vascularized subnectariferous parenchyma. Therefore, it can be concluded that the distribution, chemical nature of secretion and anatomy of leaf glands of B. muricata characterize them as EFNs, while foraging by ants indicate a mutualistic relationship that possibly protects the plant against herbivores.

Keywords anatomy; ants; extrafloral nectaries (EFNs); histochemistry; leaf glands; nectar; ontogeny

Introduction

The presence of secretory structures in vegetative and reproductive organs is common in the family Malpighiaceae ( Anderson 1979; 1990). In leaves, glands usually occur on the petiole and/or the abaxial surface of the blade, while in flowers oil-producing glands can occur on the sepals ( Judd et al. 1999). These calyx glands are present in most Neotropical species, but are only vestigial or absent in most Paleotropical species ( Anderson 1979; 1990; Judd et al. 1999). Within Malpighiaceae leaf glands are commonly known as extrafloral nectaries (EFNs), while calyx glands have been recognized as elaiophores ( Vogel 1990). These EFNs secrete sugar solution and are generally related to the attraction of patroller insects, predominantly ants ( Fahn 1979; Elias 1983; Nepi 2007). Elaiophores, on the other hand, secrete non-volatile oils ( Anderson 1990; Vogel 1990) and are related to the attraction of specific bee pollinators of the tribe Centridini, which are highly specialized in oil collection ( Anderson 1979; Buchmann 1987).

Extrafloral nectaries and elaiophores can be of taxonomic value in identifying genera ( Anderson 1990) and species ( Gates 1982; Machado et al. 2008) of the family Malpighiaceae. These glands are widely common, morphological diverse and important in ecological interactions in Neotropical and Paleotropical species of Malpighiaceae ( Anderson 1990). Extrafloral nectaries, which usually occur in pairs at the base of the leaf blade and petiole, are positioned analagously to elaiophores in sepals. The morphoanatomical similarity and analogous position between EFNs and elaiophores in Malpighiaceae indicate that these two secretory structures are homologous ( Anderson 1990). Although the leaf glands of Malpighiaceae have been described as EFNs because of the predominance of secretion rich in sugars ( Anderson 1990; Possobom et al. 2010), lipids were also identified in the secretion of leaf glands of Galphimia brasiliensis ( Castro et al. 2001). This evidence supports the hypothesis of homology between EFNs and elaiophores and the importance of these secretory structures to understanding aspects of the phylogenetic relationships of Malpighiaceae ( Castro et al. 2001).

Despite the great morphological diversity and the associated taxonomic and ecological value assigned to leaf glands in Malpighiaceae ( Elias 1983), anatomical studies have been restricted to certain genera such as Banisteriopsis ( Araújo & Meira 2016) , Heteropteris, Peixotoa ( Machado et al. 2008), Galphimia ( Castro et al. 2001) and Diplopterys ( Possobom et al. 2010). Moreover, aspects of the ontogenetic development of these leaf glands are unknown. In most cases, only the occurrence of these leaf glands is reported, as for Banisteriopsis muricata ( Gates 1982). For this Neotropical species, a liana with a broad distribution among all biomes of Brazil ( Mamede 2012), there remains a lack of information evaluating leaf glands from structural and functional points of view. Furthermore, the integrated study of the distribution, development and anatomy of these foliar glands, as well as of their secretion profile of and interactions with visitors, are important for better understanding the ecology of the species and its interactions with other organisms.

Considering the foregoing, the aim of this study was to characterize the leaf glands of B. muricata and its relationship with visitors in order to address the following questions: 1) What is the distribution, and the ontogenetic and structural patterns of these leaf glands? 2) What is the chemical profile of the secretion? 3) Who are the visitors of leaf glands and how does foraging occur?

Materials and methods

Plant material and collection area

Leaves at different developmental stages (leaf primordia to fully expanded leaves) were collected from five specimens of Banisteriopsis muricata (Cavanilles) Cuatrecasas in a natural population in Estação de Pesquisa, Treinamento e Educação Ambiental (EPTEAM) Mata do Paraíso (20º48’08.4”S and 42º51’50.9”W), a forest fragment located in Viçosa, state of Minas Gerais, Brazil. The vegetation of the area is defined as semideciduous forest ( Veloso 1991), and is included within the Atlantic Forest domain ( Rizzini 1997). A voucher specimen was deposited in the Herbarium of the Universidade Federal de Viçosa (VIC), under n. 36941.

Gland distribution

Ten leaves (from the 5th to 6th node) of five individuals of B. muricata (n=50) were collected in the field and the glands counted using a stereoscopic microscope (Zeiss, Göttinger, Germany), coupled to a digital camera (AxioCam ERc 5S, Zeiss, Göttinger, Germany) and an image capture program (AxioVision Rel. 4.8, Zeiss, Göttinger, Germany).

Light microscopy (LM)

Structural analysis

Shoot meristems and fragments of the base of petiole and leaf blade (from 1st to 5th node) were used to study anatomy and the development of leaf glands. The material was fixed in 2.5 % glutaraldehyde in phosphate buffer 0.05 M, pH 7 for 24 hours, dehydrated in an ethanol series and stored in 70 % ethanol ( Johansen 1940). Subsequently, samples were dehydrated in an ascending ethanol series and embedded in methacrylate (Historesin, Leica, Heidelberg, Germany) according to Paiva et al. (2011). The samples were transverselly and longitudinally sectioned with a automatic rotary microtome (model RM2155, Leica Microsystems Inc., Deerfield, USA) at 5µm-thick, stained with toluidine blue, pH 4.4 ( O'Brien et al. 1964) and mounted under cover slip with synthetic resin (Permount, Fisher Scientific, Pittsburgh, USA).

Histochemical analysis

To study the nature of the secretion, fresh or fixed leaf samples (5th node) were used and mature glands were sectioned using a table microtome (LPC, Rolemberg e Bhering Comércio e Importação Ltda, Belo Horizonte, Brazil). Methacrylate-embedded samples were also used and sectioned as described above. The following reagents were used to test the secretion: sudan black B ( Pearse 1980), sudan IV ( Johansen 1940), neutral red ( Kirk 1970) and auramine O ( Heslop-Harrison 1977) for lipids; Nile blue sulfate ( Cain 1947) for acid and neutral lipids; NADI reagent ( David & Carde 1964) for essential oils and oleoresins; ferric chloride (Johansen 1940) for total phenolics, Wagner reagent ( Furr & Mahlberg 1981) for alkaloids, lugol ( Johansen 1940) for starch, periodic acid-Schiff reagent (PAS) ( McManus 1948) for neutral polysaccharides, coriphosphine O ( Ueda & Yoshioka 1976) for pectins and xylidine Ponceau ( Vidal 1970) for proteins. A control was conducted simultaneously for each test, according to the specifications of each respective author.

Images were obtained with a light microscope (AX-70 TRF, Olympus Optical, Tokyo, Japan) coupled to a digital camera (Zeiss AxioCam HRc, Göttinger, Germany) and the Axion Vision image capture program. Fluorochrome analysis and autofluorescence were performed using the same equipment and a epifluorescence system with UV filter (WU: 340-380 nm), dichroic mirror (400 nm) and barrier filter (420 nm).

Scanning electron microscopy (SEM)

To observe the micromorphological characteristics of the leaf glands at different stages of development, fragments were fixed in 2.5 % glutaraldehyde as described above and dehydrated in an ethanol series, CO2 dried to critical point (CPD 020, Bal-Tec, Balzers, Liechtenstein) and fixed on supports for metal deposition with gold (Sputter Coater equipment, FDU 010, Bal-Tec, Balzers, Liechtenstein). Observation and image capture were made using a Zeiss LEO 1430 VP scanning electron microscope (Cambridge, England).

Test-strip analysis of secretion

Branches of B. muricata were collected and kept in buckets with water and covered with plastic bags for 12 hours in the laboratory to prevent evaporation of secretion. Test-strips were used (Combur Test, Roche) to determine presence of glucose, nitrites and protein in the secretion.

Leaf glands visitors

During field sampling, observations were made throughout the day to determine the diversity and relationships of insect visitors to the studied species. The collection of visitors was carried out during the course of two weeks, with sampling in the morning (08 to 09 h) and afternoon (16 to 17 h), time periods when there were greater frequencies of insect visits to the leaves. The collected visitors were preserved in 70 % ethanol and identified by Julio Cezar Mario Chaul (Laboratório de Ecologia de Comunidades, Departamento de Entomologia, UFV).

Results

Location

Leaf glands of B. muricata were found located on the abaxial surface of the base of the leaf blade and on the petiole ( Fig. 1A); they are minute (≤ 0.03mm), greenish and morphologically similar to one another. The number of glands ( Fig. 1B) varies from one to thirteen on the abaxial side of the leaf blade, and none, one or two opposite glands on the petiole. The glands are pedunculated protuberances on the leaf and have dilated apical regions ( Fig. 1C-D). Secretion may be present and observed as a translucent drop in the central zone of the gland ( Fig. 1C).

Figure 1 Distribution of leaf glands of Banisteriopsis muricata and its visitors. A. General view of a branch. Black arrows indicate the presence of ants. B. Detail of the basal third of the leaf blade. C. Gland of the petiole. D. Ant ( Solenopsis sp.) foraging on a gland. White arrows indicate leaf glands. lg: leaf gland; sc: secretion. Scale bars = 100 mm (A), 0.05 mm (B, D), 0.01 mm (C). 

Ontogeny

The glands of the leaf blade and petiole are similar in their development and anatomy. The initial structures of the glands appear early in leaf development. The glands develop on the abaxial surface of the leaf primordia, which have protoderm with cubical cells, ground meristem with polyhedral cells ( Fig. 2A) and procambial strands. Initial protodermal cells with dense cytoplasm and prominent nuclei undergo anticlinal divisions, becoming juxtaposed in a columnar fashion ( Fig. 2B). Concomitantly, the cells of the ground meristem undergo divisions in different planes, which permit the identification of the site of leaf gland formation ( Fig. 2B). The continued proliferation of protoderm and ground meristem cells results in the elevation of the glandular primordium above the leaf surface ( Fig. 2C-D). The apical portion of the gland becomes enlarged and initiates the differentiation of the glandular tissues ( Fig. 2E). Differentiation of protodermal cells results in a uniseriate secretory epidermis that is restricted to the central region of the glands, and composed of elongated and overlapping cells with thin walls, dense cytoplasm and evident nuclei ( Fig. 2E-F). The other epidemal cells of the gland are cuboid, less bulky and accumulate phenolic compounds ( Fig. 2F). Ground meristem cells differentiate into nectariferous and subnectariferous parenchyma. The nectariferous parenchyma is located bellow the glandular epidermis and comprises three to four layers of isodiametric, voluminous and thin-walled cells with dense cytoplasm, diminished vacuoles and conspicuous nuclei ( Fig. 2F). The subnectariferous parenchyma extends to the stalk of the gland and is composed of several layers of bulkier, thick-walled and vacuolated cells, and more conspicuous intercellular spaces ( Fig. 2F). Xylem and phloem cells, arising from the branch of vascular bundles of the leaf, cross the subnectariferous parenchyma and border the nectariferous parenchyma ( Fig. 2F-G). The secretory epidermis is glabrous, but leaf trichomes develop at the base of the glands and partially overlying the peduncle ( Fig. 2G-H). Cells containing phenolic compounds are already present in the leaf primordia as well as in the nectariferous and subnectariferous parenchyma and associated with vascular tissues in the gland peduncle ( Fig. 2F-G). Calcium oxalate druses are abundant in parenchyma cells around the vascular tissue of the gland ( Fig. 2F-G). The secretion accumulates in subcuticular spaces of secretory epidermis ( Fig. 2G). No stomata or pores are observed in the secretory epidermis ( Fig. 2I-J), but it is possible to observe secretion deposited on the intact nectariferous surface ( Fig. 2J).

Figure 2 Ontogeny of the leaf glands of Banisteriopsis muricata. Photomicrographs of cross sections of leaf primordia and leaves stained with toluidine blue (A-G) and scanning electromicrographs (H-J). A-G, I-J. Leaf blade. H. Petiole. A. Leaf primordium before the emergence of the first gland cells. B. Leaf primordium with the first cellular divisions in the protoderm and ground meristem (black arrows). C-E. Developing leaf glands with progressive increase in number and size of cells. F-J. Differentiated leaf glands. G, J. Differentiated leaf glands with the cuticle dilated by the accumulation of secretion (white arrow). H-J. Note that there are no stomata or pores in the secretory epidermis and trichomes only surround the glands. cu: cuticle; dr: druse; ep: epidermis; gm: ground meristem; np: nectariferous parenchyma; pc: phenolic cell; pd: protoderm; sc: secretion; se: secretory epidermis; sp: subnectariferous parenchyma; ss: subcuticular space; tr: trichome; vt: vascular tissue. Scale bars = 25 μm (A-D), 100 μm (E-J). 

Histochemistry and chemical features of secretion

The histochemical tests ( Tab. 1) carried out on leaf glands confirm that the secretion accumulates in subcuticular spaces ( Fig. 3). Fresh glands are green and possess chloroplasts throughout the nectariferous and subnectariferous parenchyma (not shown). Methacrylate-embedded glands not exposed to any reagent or dye exhibit translucent or slightly yellowish cells and translucent secretion ( Fig. 3A). A thick cuticle is evidenced by autofluorescence ( Fig. 3B), the black color of Sudan black B ( Fig. 3C) and the yellow-green secondary fluorescence emitted by neutral red fluorochrome ( Fig. 3D), but no lipids were identified in the subcuticular secretion. The secretory epidermal cells and subcuticular secretion possess pectins, highlighted by orange secondary fluorescence emitted by coriphosphine fluorochrome ( Fig. 3E). Neutral polysaccharides were also found in the secretory epidermis and in the secretion, as shown by magenta staining with PAS ( Fig. 3F). Polysaccharides in the secretory epidermis cells and secretion, as well as phenolic compounds in nectariferous parenchyma cells, were confirmed by purple and green coloration with toluidine blue, respectively ( Fig. 3G). Proteins were identified by xylidine Ponceau in the secretory cells and mainly in secretion accumulated in the subcuticular space ( Figure 3H). The test-strip analysis of the secretion confirmed the presence of proteins, as identified in the histochemical tests, and also indicated the presence of glucose. Therefore, the secretion of leaf glands is a mixture of glucose, proteins and pectins. The secretion produced in each EFN was so minimal that it was not possible to measure its volume.

Table 1 Histochemical characterization of the leaf glands of Banisteriopsis muricata

Chemical compounds Reagent Reaction
Cuticle Secretion Secretory epidermis Nectariferous parenchyma
Lipids Sudan IV + - - -
Sudan black B + - - -
Neutral red + - - -
Auramine O + - - -
Terpenoids NADI reagent + - - -
Phenolic compounds Ferric chloride - - + +
Alkaloids Wagner reagent - - - -
Carbohydrates Polysaccharides PAS - ++ + -
Starch Lugol - - - -
Pectins Ruthenium red - + + -
Coriphosphine O - ++ + +
Proteins Xylidine Ponceau - ++ + +

+ positive reaction; - negative reaction.

Figure 3 Leaf glands of Banisteriopsis muricata submitted to different histochemical tests. (A-H) Photomicrographs of methacrylate-embedded material. A. No application of dyes or reagents. B. Autofluorescence. C. Sudan black B; black color indicates lipids. D. Neutral red; yellow-green secondary fluorescence indicates lipids. E. Coriphosphine; orange secondary fluorescence indicates pectins. F. Periodic acid/Schiff reagent (PAS); magenta staining indicates neutral polysaccharides. G. Toluidine blue; purple color indicates polysaccharides. H. Xylidine Ponceau; reddish color indicates proteins. cu: cuticle; dr: druse; np: nectariferous parenchyma; pc: phenolic cell; se: secretory epidermis; * secretion. Scale bars = 25 μm. Please see the PDF version for color reference. 

Visitors

Ants of the genera Solenopsis, Pheidole and Camponotus were observed foraging leaves and branches of B. muricata. However, only individuals of Solenopsis were observed making direct contact with the glands ( Fig. 1D). The behavior of these ants involves approaching the glands and projecting the front legs and antennae onto them, and then passing the appendages rapidly on the surface of the glands. Bristles were observed in the forepaws and the antenna, indicating that these structures are used to "scan" the surface of glands and collect secretion. After foraging, the legs and antennae touch, as if the ants are cleaning them, and then borugh to touch the mouthparts, which seems to be a behavior of deposition of the glandular secretion.

Discussion

The distribution of the leaf glands of Banisteriopsis muricata varies among different leaves, similar to that observed in other species of Malpighiaceae ( Castro et al. 2001; Machado et al. 2008). The occurrence of eglandulated leaves and leaves with two to four pairs of glands in the basal third of leaf blade and petiole have been previously described for B. muricata ( Gates 1982), but this was not exactly the pattern found in the present study. In addition to eglandulated leaves, the present study found B. muricata to also possess leaves with a highly variable number of glands (1-13), as in other Malpighiaceae ( Anderson 1990). The difference between these accounts can be justified by the small size of the glands and the difficulty in observing them with the naked eye, as was done by Gates (1982).

The presence of numerous small glands, as in B. muricata, may represent an advantageous strategy compared to other species that have leaves with a small number of large glands. Some of these glands can be injured and lose functionality, and having a greater number can act as a compensatory mechanism ( Subramanian & Inamdar 1985). Variaiton in location and abundance of glands on the leaf blade favor ant patrolling across the entire leaf in search of nectar, and favoring organ protection against attack by herbivorous insects ( Bentley 1977; Paiva & Machado 2006). In addition, the small volume of secretion of each leaf gland in B. muricata would also be compensated by the abundance of glands on the leaf, favoring the continued the production of secretion necessary to attract and reward ants ( Paiva et al. 2007), and thus ensuring the protection of young leaves and buds.

These glands are cup-shaped with a short peduncle, a discoidal apical portion and a slightly concave secretory surface, which characterize them as “high type” according to the classification of Elias (1983). Similar morphology has been observed in the leaf glands of other species of Banisteriopsis ( Machado et al. 2008; Araújo & Meira 2016), but in yet others the leaf glands are sessile (Machado et al. 2008). The leaf glands of Banisteriopsis muricata possess a secretory surface that is restricted to the central region of the gland, which is common in some species of Banisteriopsis ( Araújo & Meira 2016) and Galphimia brasiliensis ( Castro et al. 2001), but not in other Malpighiaceae, such as Peixotoa reticulata ( Machado et al. 2008).

The secretion of leaf glands of B. muricata is a mixture of water, glucose, pectins and proteins. The presence of glucose in the secretion confirms the nectariferous nature of these glands ( Bentley 1977; Fanh 1979). Thus, the leaf glands of B. muricata can be considered extrafloral nectaries (EFNs) and the secretion as nectar. Moreover, the absence of lipids in the secretion dismisses the possibility of these leaf glands acting as elaiophores, as suggested by Castro et al. (2001). These authors identified lipids in the secretion of the leaf glands of Galphimia brasiliensis by histochemical tests, but they did not provide images and so these results can not be verified.

Pectins and water form a mucilaginous phase and, consequently, increase the viscosity of nectar ( Nepi 2007), which may be a mechanism for regulating secretion release ( Paiva 2016). The proteins found in the nectar of EFNs of B. muricata may be crucial to the establishment of mutualistic relationships between individual plants and various animals ( Fahn 1979; Roshchina & Roshchina 1993; Heil 2011).

The EFNs of B. muricata differentiate early in the leaf primordia and remain active in expanded leaves. This pattern of development seems to guarantee indirect protection against herbivores for an extended period of time, since the glands do not show damage after foraging by ants. The ants found on the EFNs of B. muricata forage the gland in search of sugars for adult nutrition and protein for the nutrition of the larvae ( Bentley 1977). In B. muricata, only ants of the genus Solenopsis, attracted by nectars rich in sugars and amino acids ( Lanza et al. 1993; Ness et al. 2010; Byk & Del-Claro 2011), were observed foraging on the EFNs. However, patrolling by ants of other genera that did not forage on the EFNs, such as Pheidole and Camponotus, could also act to protect the plant by increasing the period and frequency of patrolling ( Bentley 1977).

The EFNs of B. muricata consist of secretory epidermis, nectariferous parenchyma and vascularized subnectariferous parenchyma, as is typical for EFNs of species of Malpighiaceae ( Machado et al. 2008; Possobom et al. 2010; Araújo & Meira 2016). The accumulation of secretion in the subcuticular spaces and the absence of stomata, or any other type of opening to release the secretion of EFNs of B. muricata, suggest that the elimination of nectar occurs gradually via permeability of the cuticle or by its rupture after foraging by ants. Curiously, no EFNs were observed with ruptured cuticles in B. muricata, which favors the former release mechanism over the latter. There is also the possibility that hydrophilic microchannels occur in the cuticle and favor the release of predominantly hydrophilic secretions by the apoplastic pathway ( Fahn 1988; Paiva 2016).

The nectariferous parenchyma of the EFNs of B. muricata is similar to that observed in other species of the genus Banisteriopsis ( Araújo & Meira 2016) and other genera of the family Malpighiaceae, such as Peixotoa ( Machado et al. 2008) and Diplopterys ( Possobom et al. 2010). Dense cytoplasm and conspicuous nuclei are cytological features of the nectariferous parenchyma cells of B. muricata, and secretory cells in general, indicating high tissue metabolic activity ( Fahn 1979). This suggests the participation of nectariferous parenchyma in the transformation of the solutions received from the vascular system that runs through the subnectariferous parenchyma to the final composition of the nectar ( Fahn 1979; Nepi 2007). Both the nectariferous parenchyma and the subnectariferous parenchyma of B. muricata EFNs are green, have chloroplasts and, consequently, photosynthetic activity, which corroborates the possibility of the local incorporation of photoassimilated products into the nectariferous secretion ( Vassilyev 2010). Highlighted in the subnectariferous parenchyma of the EFNs of B. muricata, are cells with phenolic compounds and cells containing calcium oxalate crystals, which are related to chemical ( Mandal et al. 2010) and mechanical ( Franceschi & Nakata 2005) protection, respectively, of this secretory structure. However, the presence of calcium oxalate crystals in nectaries, although common, has been interpreted differently. Fixation of calcium in crystals could represent a mechanism of physiological adaptation to control cellular calcium levels ( Franceschi & Nakata 2005; Paiva & Machado 2005), since at high concentrations, calcium ions are toxic to plants ( Franceschi & Nakata 2005).

Despite the presence of chloroplasts in the nectariferous parenchyma, there are no stomata throughout the epidermis of EFNs of B. muricata to maintain gas exchange and supply the photosynthetic process. However, the presence and abundance of calcium oxalate crystals could represent a source of carbon dioxide for the maintenance of the photosynthetic process under these conditions ( Tooulakou et al. 2016). These authors showed a new photosynthetic pathway that uses mesophyll calcium oxalate crystals as a CO2 source when stomata are closed, which provides adaptive advantages under drought conditions. This photosynthetic pathway could also occur in nectaries in general, where such crystals are so abundant.

Extrafloral nectaries may be vascularized by xylem and phloem ( Fahn 1979; Elias 1983), as in B. muricata and other species of Malpighiaceae ( Machado et al. 2008; Possobom et al. 2010; Araújo & Meira 2016), but they may also possess only one type of vascular tissue or no vascular tissues at all ( Fahn 1979; Paiva et al. 2007). The amount of vascular tissue in nectaries is considered proportional to their size ( Carlquist 1969) and to the volume of secretion produced ( Paiva et al. 2007). In the case of B. muricata, the reduced size of the EFNs may be the only factor explaination the small volume of secretion produced, since the proportion of vascular tissue in relation to the size of the EFNs is large.

Therefore, it can be concluded that the distribution, chemical composition of the secretion and anatomy of leaf glands of B. muricata characterize them as EFNs, while foraging by ants of the genus Solenopsis indicate a mutualistic relationship that possibly protects the plant against herbivores.

Acknowledgements

The authors thank FAPEMIG for financial support in the form of a scholarship to LA Nery, and biologist JCM Chaul for help in identifying insect visitors collected in this study.

References

Anderson WR. 1979. Floral conservation in Neotropical Malpighiaceae. Biotropica 11: 219-223. [ Links ]

Anderson WR. 1990. The origin of the Malpighiaceae: the evidence from morphology. Memoirs of the New York Botanical Garden 64: 210-224. [ Links ]

Araújo JS, Meira RMSA. 2016. Comparative anatomy of calyx and foliar glands of Banisteriopsis C. B. Rob. (Malpighiaceae). Acta Botanica Brasilica 30: 112-123. [ Links ]

Bentley BL. 1977. Extrafloral nectaries and protection by pugnacious bodyguards. Annual Review of Ecology and Systematics 8: 407-427. [ Links ]

Buchmann SL. 1987. The ecology of oil flowers and their bees. Annual Review of Ecology and Systematics 18: 343-69. [ Links ]

Byk J, Del-Claro K. 2011. Ant-plant interaction in the Neotropical savanna: direct beneficial effects of extrafloral nectar on ant colony fitness. Population Ecology 53: 327-332. [ Links ]

Cain AJ. 1947. The use of Nile Blue in the examination of lipoids. Quarterly Journal of Microscopical Science 88: 383-392. [ Links ]

Carlquist S, 1969. Toward acceptable evolutionary interpretations of floral anatomy. Phytomorphology 19: 4. [ Links ]

Castro MA, Vega AS, Múlgura ME, 2001. Structure and ultrastructure of leaf and calyx glands in Galphimia brasiliensis (Malpighiaceae). American Journal of Botany 88: 1935-1944. [ Links ]

David R, Carde JP. 1964. Coloration différentielle dês inclusions lipidique et terpeniques dês pseudophylles du Pin maritime au moyen du reactif Nadi. Comptes Rendus Hebdomadaires dês Séances de l’Academie dês Sciences Paris D258: 1338-1340. [ Links ]

Elias TS. 1983. Extrafloral nectaries: their structure and distribution. In: Bentley B, Elias T. (eds.) The biology of nectaries. New York, Columbia University Press. p. 174-203. [ Links ]

Fahn A. 1979. Secretory tissues in plants. London, Academic Press. [ Links ]

Fahn A. 1988. Secretory tissues in vascular plants. New Phytologist 108: 229-257. [ Links ]

Franceschi VR, Nakata PA. 2005. Calcium oxalate in plants: formation and function. Annual Review Plant Biology 56: 41-71 [ Links ]

Furr M, Mahlberg PG. 1981. Histochemical analyses of lacticifers and glandular trichomes in Cannabis sativa. Journal of Natural Products 44: 153-159. [ Links ]

Gates B. 1982. Banisteriopsis, Diplopterys (Malpighiaceae). Flora Neotropica Monograph 30: 1-237. [ Links ]

Heil M. 2011. Nectar: generation, regulation and ecological functions. Trends in Plant Science 16: 191-200. [ Links ]

Heslop-Harrison Y. 1977. The pollen-stigma interaction: pollen-tube penetration in Crocus. Annals of Botany 41: 913-922. [ Links ]

Johansen DA. 1940. Plant Microtechnique. New York, McGraw-Hill Book Co. Inc. [ Links ]

Judd WS, Campbell CS, Kellogg EA, Stenvens PF. 1999. Plant Systematics: a phylogenetic approach. Sunderland, Sinauer Associates. [ Links ]

Kirk PW. 1970. Neutral red as a lipid fluorochrome. Stain Technology 45: 1-4. [ Links ]

Lanza J, Vargo EL, Pulim S, Chang YZ. 1993. Preferences of the fire ants Solenopsis invicta and S. geminate (Hymenoptera: Formicidae) for amino acid and sugar components of extrafloral nectars. Environmental Entomology 22: 411-417. [ Links ]

Machado SR, Morellato LPC, Sajo MG, Oliveira PS. 2008. Morphological patterns of extrafloral nectaries in woody plant species of the Brazilian cerrado. Plant Biology 10: 660-673. [ Links ]

Mamede MCH. 2012. Banisteriopsis. Lista de Espécies da Flora do Brasil. Rio de Janeiro, Jardim Botânico do Rio de Janeiro. [ Links ]

Mandal SM, Chakraborty D, Dey S. 2010. Phenolic acids act as signaling molecules in plant-microbe symbioses. Plant Signaling & Behavior 5: 359-368. [ Links ]

McManus JFA. 1948. Histological and histochemical uses of periodic acid. Stain Technology 23: 99-108. [ Links ]

Nepi M. 2007. Nectary structure and ultrastructure. In: Nicolson SW, Nepi M, Pacini E. (eds.) Nectaries and nectar. Dordrecht, Springer. p. 129-166. [ Links ]

Ness J, Mooney K, Lach L. 2010. Ants as mutualists. In: Lach L, Parr CL, Abbott KL. (eds.) Ant ecology. Oxford, University Press. p. 97-114. [ Links ]

O’Brien TP, Feder N, McCully ME. 1964. Polycromatic staining of plant cell walls by toluidina blue O. Protoplasma 59: 368-373. [ Links ]

Paiva EAS. 2016. How do secretory products cross the plant cell wall to be released? A new hypothesis involving cyclic mechanical actions of the protoplast. Annals of Botany 117: 533-540. [ Links ]

Paiva EAS, Buono RA, Delgado MN. 2007. Distribution and structural aspects of extrafloral nectaries in Cedrela fissilis (Meliaceae). Flora 202: 455-461 [ Links ]

Paiva EAS, Machado SR. 2005. Role of intermediary cells in Peltodon radicans (Lamiaceae) in the transfer of calcium and formation of calcium oxalate crystals. Brazilian Archives Biology Technology 48: 147-153. [ Links ]

Paiva EAS, Machado SR. 2006. Ontogênese, anatomia e ultra-estrutura dos nectários extraflorais de Hymenaea stigonocarpa Mart. ex Hayne (Fabaceae - Caesalpinioideae). Acta Botanica Brasilica 20: 471-482. [ Links ]

Paiva EAS, Pinho SZ, Oliveira DMT. 2011. Large plant samples: how to process for GMA embedding? Methods in Molecular Biology 689: 37-49. [ Links ]

Pearse AGE. 1980. Histochemistry theorical and applied. Vol. 2. 4th. edn. Edinburgh, Churchill Livingston. [ Links ]

Possobom CCF, Guimarães E, Machado SR. 2010. Leaf glands act as nectaries in Diplopterys pubipetala (Malpighiaceae). Plant Biology 12: 863-870. [ Links ]

Rizzini CT. 1997. Tratado de fitogeografia do Brasil. Rio de Janeiro, Editora Âmbito. [ Links ]

Roshchina VV, Roshchina VD. 1993. The secretory function of higher plants. Berlin, Springer. [ Links ]

Subramanian B, Inamdar JA. 1985. Occurrence, structure, ontogeny and biology of nectaries in Kigelia pinnata DC. The Botanical Magazine 98: 67-73. [ Links ]

Tooulakou G, Giannopoulos A, Nikolopoulos D, et al. 2016. “Alarm photosynthesis”: calcium oxalate crystals as an internal CO2 source in plants. Plant Physiology 171: 2577-2585. [ Links ]

Ueda K, Yoshioka S. 1976. Cell wall development of Micrasterias americana, especially in isotonic and hypertonic solutions. Journal of Cell Science 21: 617-631. [ Links ]

Vassilyev AE. 2010. On the mechanisms of nectar secretion: revisited. Annals of Botany 105: 349-354. [ Links ]

Veloso HP, Rangel-Filho ALR, Lima JC. 1991. Classificação da vegetação brasileira, adaptada a um sistema universal. Rio de Janeiro, IBGE. [ Links ]

Vidal BC. 1970. Acid glycosaminoglycans and endochondral ossification: microespectrophotometric evaluation and macromolecular orientation. Cell Molecular Biology 22: 45-64. [ Links ]

Vogel S. 1990. History of Malpighiaceae in the light of pollination ecology. Memoirs of the New York Botanical Garden 55: 130-142. [ Links ]

Received: March 20, 2017; Accepted: May 29, 2017

* Coresponding author: ventrella@ufv.br

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