Presumed domatia are actually extrafloral nectaries on leaves of Anacardium humile (Anacardiaceae)

Abstract

Presumed domatia are actually extrafloral nectaries on leaves of Anacardium humile (Anacardiaceae), a species from the Brazilian savannah, is associated with foraging ants, which leads to the description of the structure of its leaves as domatia. However, the ants collect secretions on the leaves, a phenomenon that inspired us to elucidate this structure. To this end, we conducted an analysis of the distribution, micromorphology, anatomy and histochemistry of these supposed domatia. They are located in the axil of thicker leaf veins and are composed of glandular trichomes which exude glucose; they are, therefore, described here as extrafloral nectaries (EFNs). The nectariferous trichomes are located at the same level as the other epidermal cells on young leaves, while in mature leaves they were found in depressions of the leaf blade. The secretory activity of EFNs is limited to juvenile phases, becoming degenerated in mature leaves. Carbohydrates and lipophilic compounds were detected in the produced secretion. It can be concluded that the presence of ants foraging leaves to collect from EFNs indicates a mutualistic interaction, with the plant providing a sugar resource to the ants in return for protection against herbivory since they are present in developing leaves. Key words: Cashew, extrafloral nectary, glandular trichomes, histochemistry, nectar. ResumoSupostas domácias foliares de Anacardium humile (Anacardiaceae) são na realidade nectários extrafloraisAnacardium humile, uma espécie do cerrado brasileiro, está associada a formigas forrageadoras, o que leva à descrição da estrutura presente em suas folhas como domácias. No entanto, as formigas coletam a secreção das folhas, um fenômeno que inspirou este estudo, que visa justamente elucidar esta estrutura. Por esta razão, foi realizada uma análise da distribuição, micromorfologia, anatomia e histoquímica das supostas domácias. Elas estão localizadas nas axilas das nervuras foliares de maior calibre e são compostas por tricomas glandulares. Os tricomas exsudam glicose, portanto, são descritos aqui como nectários extraflorais (NEFs). Os tricomas nectaríferos estão localizados no mesmo nível que as células da epiderme em folhas jovens, enquanto, nas folhas maduras, foram encontradas nas depressões da lâmina foliar. A atividade secretora nos NEFs é limitada a fases juvenis, degenerando em folhas maduras. Carboidratos e substâncias lipofílicas foram detectados na secreção produzida. Pode-se concluir que a presença de formigas forrageando folhas para coleta nos NEFs indica uma interação mutualística, com a planta fornecendo recursos para as formigas em troca de proteção contra herbivoria, uma vez que as mesmas estão presentes em folhas ainda em desenvolvimento. Palavras-chave: Caju, nectário extrafloral, tricomas glandulares, histoquímica, néctar.

Flora of Anacardium (Anacardiaceae) in the state of Pará, Brazil

“…In view of the anatomical similarities between the structures observed by us for Anacardium amapaense, A. giganteum, A. microsepalum, A. occidentale, A. parvifolium, and A. spruceanum, and the extrafloral nectaries (EFNs) described by Lacchia et al (2016) for A. humile, we believe that what we observed are also EFNs.…”

“…The presence of domatia in Anacardium was indicated by Mitchell (1992), due to their similarity to mite domatia found in other genera of Anacardiaceae. However, subsequent works identified these structures as EFNs in Anacardium humile (Lacchia et al 2016) and A. occidentale (Wunnachit et al 1992;Rickson & Rickson 1998). Studies carried out with other families of angiosperms have already reported an association between EFNs and domatia (Leroy et al 2008;Weber et al 2012;Marazzi et al 2019), which could be the case for the species analyzed here, although field observations and histochemical tests are needed to support this hypothesis.…”

“…Information on leaf color is based on dried material. The terminology used follows Radford et al (1974), Mitchell & Mori (1987), Mitchell (1992) (especially for the orifices located in the axils of secondary veins on the abaxial surface), Pirani (2003), and Lacchia et al (2016). When necessary, descriptions were complemented with data from additional material.…”

Development, structure, and secretion of leaf colleters in Clusia criuva Cambess. subsp. criuva (Clusiaceae)

“…This corroborates the primary function of colleters in producing secretions that protect young organs during their development (Lersten & Horner 1968;Lersten 1974;Fahn 1979) and/or that promote the lubrication of the stem meristem, minimizing friction of the developing leaf tissues and preventing dehydration (Fahn 1979;Thomas 1991;Mayer et al 2011;Silva et al 2012;Mayer et al 2013). Proteins are involved in the defense against fungal activity and attack of pathogens (Klein et al 2004;Miguel et al 2006) and are commonly reported in the secretion of colleters (González & Tarragó 2009;Coelho et al 2013;Dalvi et al 2014;Lacchia et al 2016;Pinheiro et al 2019).…”

Pericarp ontogeny of Tapirira guianensis Aubl. (Anacardiaceae) reveals a secretory endocarp in young stage

“…These nectaries are already present in flowers and are maintained in the fruits, improving the viability and seed dispersal. None of these structures are exclusive to secreting fruits but basically occur in the whole plant (Lacchia & Carmello-Guerreiro 2009;Lacchia et al 2016a;2016b).…”