Comparative Account of Nectary Structure in Hexisea imbricata (Lindl.) Rchb.f. (Orchidaceae)

Abstract

Background and Aims Despite the number of orchid species that are thought to be pollinated by hummingbirds, our knowledge of the nectaries of these orchids is based solely on a single species, Maxillaria coccinea (Jacq.) L.O. Williams ex Hodge. Nevertheless, it is predicted that such nectaries are likely to be very diverse and the purpose of this paper is to compare the nectary and the process of nectar secretion in Hexisea imbricata (Lindl.) Rchb.f. with that of Maxillaria coccinea so as to begin to characterize the nectaries of presumed ornithophilous Neotropical orchids.Methods Light microscopy, transmission electronmicroscopy and histochemistry were used to examine the histology and chemical composition of nectary tissue and the process of nectar secretion in H. imbricata.Key Results and Conclusions The nectary of H. imbricata has a vascular supply, is bound by a single-layered epidermis with few stomata and comprises two or three layers of subepidermal secretory cells beneath which lie several layers of palisade-like parenchymatous cells, some of which contain raphides or mucilage. The secretory cells are collenchymatous and their walls have numerous pits with associated plasmodesmata. They contain the full complement of organelles characteristic of secretory cells as well as intravacuolar protein bodies but some of the secretory epidermal cells, following secretion, collapse and their anticlinal walls seem to fold. Nectar secretion is thought to be granulocrine and, following starch depletion, lipid droplets collect within the plastids. The nectar accumulates beneath the cuticle which subsequently forms swellings. Finally, nectar collects in the saccate nectary spur formed by the fusion of the margins of the labellum and the base of the column-foot. Thus, although the nectary of H. imbricata and M. coccinea have many features in common, they nevertheless display a number of important differences.

Studies on the ultrastructure of a three-spurred fumeauxiana form of Anacamptis pyramidalis

“…The proximity of SER and plastids were also pointed out in studies of the ultrastructure of the nectary spur of Limodorum abortivum (Pais and Figueiredo 1994) and P. bifolia (Stpiczyńska 1997). A dense osmiophilic material and tubular structures had been reported in plastids occurring in the nectaries of other orchid species (Pais and Figueiredo 1994;Stpiczyńska and Matusiewicz 2001;Stpiczyńska et al 2004Stpiczyńska et al , 2005 and from glandular trichomes involved in terpenoid synthesis (Cheniclet and Carde 1985;Turner et al 2000), in which the plastids were also in close association with ER.…”

Ontogênese, anatomia e ultra-estrutura dos nectários extraflorais de Hymenaea stigonocarpa Mart. ex Hayne (Fabaceae - Caesalpinioideae)

“…A observação destes compostos em maior quantidade no início da fase secretora, mostra que a planta oferece recompensa em uma forma mais energética no momento de maior suscetibilidade ao ataque de herbívoros, ou seja, quando as folhas estão em processo de expansão e diferenciação. A presença de lipídios na composição do néctar é comum e citada para nectários de diversas espécies (Baker et al 1978;Fahn 1979;1988;2000;Stpiczynska et al 2005).…”

“…ex Hayne, tais como núcleo volumoso, citoplasma denso, abundância de retículo endoplasmático, dictiossomos ativos, mitocôndrias, dentre outras, são relatadas para diversos nectários e indicativas de alta atividade metabólica (Fahn 1979;Durkee 1983;Fahn 1988;Stpiczynska et al 2005). Para Lüttge (1971), o pequeno desenvolvimento do vacuoma está relacionado ao intenso metabolismo destas células.…”

Poplar Extrafloral Nectaries: Two Types, Two Strategies of Indirect Defenses against Herbivores

“…They contain an epidermis in addition to a nectar and a subnectary parenchyma (Stpiczy nska et al, 2005;Wist and Davis, 2006;Kaczorowski et al, 2008;Wenzler et al, 2008;Fig. 2A).…”

“…Nectaries in general consist of three components: epidermis with or without stomata or trichomes; specialized parenchyma that produces or stores nectar; and a subnectary parenchyma composed of bigger cells more loosely packed (Stpiczy nska et al, 2005;Kaczorowski et al, 2008). Detailed studies have shown that decreases in herbivory rates associated with EFN secretion result from mechanical leaf damage, jasmonic acid (JA) production, and/or volatile emission Linsenmair et al, 2001;Mathews et al, 2007;Radhika et al, 2008).…”