Floral nectary and osmophore of Epipactis helleborine (L.) Crantz (Orchidaceae)

Abstract

The analysis of flowers collected at different stages of anthesis provides strong evidence to conclude that the shell-shaped hypochile and the knobs of epichile form a nectary. The scent comes from the aromatic constituents of nectar and the epichile tissue and the apices of all tepals (osmophores). The comparison between pollinated and unpollinated flowers revealed that the anthesis of unpollinated flowers lasted up to the 16th day. The nectariferous secretory cells formed single-layered epidermis and several layers of underlying parenchyma built by small, isodiametric cells with thin walls and dense cytoplasm, relatively large nuclei, supplied by collateral vascular bundles. During the floral lifespan, the residues of secreted material were higher on the hypochile cells. The lipoid-carbohydrate material and lipid globules in the cell walls and in the cytoplasm were localised. The abundance of starch grains was observed at the beginning of anthesis and their gradual reduction during the flower lifespan. At the end of anthesis in unpollinated flowers, the lipoid-carbohydrate-phenolic materials have been demonstrated. The phenolic material was the same as in plastoglobuli. The features such as irregular plasmalemma, the secretory vesicles that fuse with it, fully developed dictyosomes, numerous profiles of ER indicate vesicle-mediated process of secretion. The substances could be transported by vesicles to the periplasmic space via granulocrine secretion and then to the external surface. Both micro-channels and slightly developed periplasmic space were visible in the hypochile epidermis. This is the first time for anatomical survey of secretory tissue in pollinated and unpollinated flowers of E. helleborine.

Comparative studies on structure of the floral nectaries and the abundance of nectar production of Prunus laurocerasus L.

“…The extensive system of mitochondrial inner membranes, the endoplasmic reticulum with varied arrangement of tubules and the numerous transporting vesicles observed near the plasmalemma in the present study suggest granulocrine nectar secretion. A similar mode of nectar secretion is characteristic for many species of various genera (Chwil and Chwil 2012; Ojeda et al 2014; Kowalkowska et al 2018). The floral nectaries exhibited expanded ER cisterns and large vesicles associated mainly with the cis -side of dictyosomes.…”

“…The secretion was transported inside the vesicular structures and, next, through the fusion of vesicles with the plasmalemma, the excretion was accumulated in the subcuticular space. The irregular outline of the plasmalemma with numerous vesicles determined the granulocrine secretion of nectar into the periplasmic space and then onto the outer surface (Chwil and Chwil 2012; Kowalkowska et al 2012, 2015, 2018).…”

Taxonomic traits in the microstructure of flowers of parasitic Orobanche picridis with particular emphasis on secretory structures

“…Similar types of plastids were present in nectary cells in representatives of other families, e.g. Orchidaceae (De Melo et al 2010;Kowalkowska et al 2018) and Sapinadaceae (Weryszko-Chmielewska and Chwil 2017). The large amounts of smooth and rough ER profiles visible in the glandular parenchyma may have been involved in the synthesis of lipid and protein substances, respectively, and/or mediated the production and transport of nectar.…”

Systems analyses of key metabolic modules of floral and extrafloral nectaries of cotton

“…The nectariferous parenchyma is composed of small isodiametric cells with densely-staining cytoplasm, and closely packed papillae glands, which are composed of a single basal cell, variable number of stalk cells, and terminal head cells protruding from the epidermis (Bernardello et al, 2007; Eleftheriou and Hall, 1983a; Fahn, 1979; Findlay et al, 1971b; Kronestedt et al, 1986; Lattar et al, 2018; Sawidis et al, 1987; Wergin et al, 1975). Large phenolic ‘dense’ bodies and calcium oxalate crystals form in all four nectaries and based on their postulated functionality in nectaries of other plant taxa, such as Glycine , Linaria , Epipactis , Heliocarpus , Luehea , Ekebergia , and Anacardium , they may confer protection from herbivory (Horner et al, 2003; Jachuła et al, 2018; Kowalkowska et al, 2018; Lattar et al, 2018; Tilney et al, 2018; Tölke et al, 2018).…”

“…During active nectar secretion, the cuticle of the papillae head cells separates from the cell wall and the newly formed subcuticular space, which fills with nectar; microchannels or fractures develop in the cuticle to facilitate the release of nectar from the nectary. This phenomenon commonly occurs in the trichomatic nectaries of a variety of other species, included within Malvaceae (Findlay et al, 1971b; Haratym and Weryszko-Chmielewska, 2017; Kowalkowska et al, 2018; Kronestedt et al, 1986; Lattar et al, 2018; Plachno et al, 2018; Sawidis et al, 1987). Based on previous observations of Abutilon hydridum floral nectary papillae, the cuticular channels may function as valves, releasing discrete droplets of nectar once hydrostatic pressure exceeds a threshold (Findlay et al, 1971b).…”