Floral structure of two species of Bulbophyllum section Cirrhopetalum Lindl.: B. weberi Ames and B. cumingii (Lindl.) Rchb. f. (Bulbophyllinae Schltr., Orchidaceae)

Agnieszka K Kowalkowska,Sławomir Turzyński,Natalia Wiśniewska,Małgorzata Kozieradzka-Kiszkurno

doi:10.1007/s00709-016-1034-3

Abstract

Flowers of Bulbophyllum weberi and B. cumingii are characterized by fly-pollinated features. The secretory activity was described in dorsal sepals in both species (putative osmophores), petals in B. weberi (possible osmophores) and adaxial surface of lips in both species. In the cells of dorsal sepals and petals of B. weberi proteins, dihydroxyphenols, lipids and starch grains were detected, in lateral sepals—lipids. Whereas in dorsal sepal of B. cumingii only lipids and starch grains were noted, in lateral sepals—proteins and dihydroxyphenols and in petals—proteins and starch grains. The lips in both species differed histochemically and ultrastructurally. The epidermal cells of lip groove in B. weberi contained lipids, proteins, starch grains in cytoplasm, dihydroxyphenols in vacuoles and pectic acids/mucilage on surface. Whereas in B. cumingii—few lipids, starch grains, no proteins, no dihydroxyphenols and no mucilage were noted. Ultrastructurally, in B. weberi, the secretory material was present on surface and vesicles building into plasmalemma, while in B. cumingii—cell wall ingrowths and microchannels in cuticle. The osmiophilic irregular materials and globular, osmiophilic globules in B. weberi are probably tannin-like materials. For the first time, we described the cell wall ingrowths in Bulbophyllum species: in lip of B. cumingii and petals of B. weberi.

Highlights

Bulbophyllum Lindl. is a large, pantropical genus, containing about 2200 species, distributed from Continental Africa, Madagascar, East Indian Islands, Asia, Australia and the tropical Pacific islands to the Neotropics
Raspberry ketone was detected as the major fragrance compound in Bulbophyllum apertum ssp. verrucosum being attracted to Bactrocera species sensitive to this ketone (Tan and Ritsuo 2005)
The conspicuous idioblasts with raphides emerged from the tissue on the whole outer dorsal sepal surface (Fig. 1f–j), visible in scanning electron microscopy (SEM) as elevated groups of cells (Figs. 2a, 3e)

Summary

Introduction

Bulbophyllum Lindl. is a large, pantropical genus, containing about 2200 species, distributed from Continental Africa, Madagascar, East Indian Islands, Asia, Australia and the tropical Pacific islands to the Neotropics. Madagascar and New Guinea are the main centres of diversity (Pridgeon et al 2014) Their flowers are dull cream or yellow-green to purple-brown, frequently spotted and hirsute, with mobile labella and appendages, emitted fruity or malodorous and carrion-like scents (Tan and Nishida 2000, 2005; Tan et al 2002). Whereas the sapromyiophilous pollination syndrome embraces dark flowers (brown, purple, greenish, often with great depth), emitting the putrescent odour containing sulphur compounds (Feinstein et al 2009; van der Pijl and Dodson 1966). In fruit fly-pollinated Bulbophyllum species, methyl eugenol (aromatic compound) and ketones have been identified as key chemical components in plant-pollinator interaction. In B. cheiri methyl eugenol acts as sex pheromone precursor for males of Bactrocera species during pollination (Tan et al 2002; Nishida et al 2004). The unpleasant urine-like odour in sapromyiophilous Bulbophyllum variegatum could be ascribed to indole, p-cresol, 2-heptanone (Arctander 1994; Dobson 2006) and nitrogenous and sulphur compounds (Humeau et al 2011)

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