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

Agnieszka K Kowalkowska,Agnieszka T Krawczyńska,Patrycja Guzanek,Michalina Pawłowicz

doi:10.1007/s00709-018-1274-5

Agnieszka K Kowalkowska, Agnieszka T Krawczyńska + Show 2 more

Open Access

https://doi.org/10.1007/s00709-018-1274-5

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Journal: Protoplasma	Publication Date: Jun 9, 2018
Citations: 20	License type: open-access

Affiliation: University of Gdańsk, Warsaw University of Technology

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.

Highlights

The plant nectaries diverse greatly in topography, anatomy, ultrastructure and secretion processes
As we did not observe significant differences on histochemical and ultrastructural level from two localities, we focused on comparison between pollinated and unpollinated flowers
The secretory cells in hypochile and knobs formed singlelayered 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, which reflect the nature of nectaries (Nepi 2007)

Summary

Introduction

The plant nectaries diverse greatly in topography, anatomy, ultrastructure and secretion processes. The chemical analysis of the nectar in E. helleborine revealed that the main components are eugenol, 2,6-dimethoxy-4-(2-propenyl)phenol (methoxyeugenol), ethanol and 4-hydroxy-3-methoxybenzaldehyde (vanillin) (Jakubska et al 2005b). The hypothetical plant-pollinator interaction is divided in E. helleborine into two steps: the first insect reaction on long-distance attractant—scent, i.e. vanillin, furfural, ethanol, eugenol and their derivatives; the second alimentary short-distance attractant—nectar with narcotic constituents, i.e. morphinian derivatives and indole derivatives, caused the disorientation of flights known as Bsluggish^ pollinators effect (Jakubska et al 2005b)

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