Abstract
This micromorphological, chemical and ultrastructural study is a continuation of research conducted on the section Lepidorhiza. The Bulbophyllum echinolabium flowers comprised features that characterize a sapromyophilous syndrome, having large, glistening parts that emit an intense scent of rotten meat. The secretory activity was described in the hypochile (nectary in longitudinal groove and in the prickles) and the epichile (putative osmophore). The ultrastructural studies revealed a dense cytoplasm in the epidermis and subepidermal tissue with large nuclei and numerous mitochondria, the profiles of SER and RER, and dictyosomes. Large amounts of heterogeneous residues of secreted material (possibly phenolic) were present on the cuticle surface, similar to the unusual prominent periplasmic space with flocculent secretory material. The chemical analysis (GC/MS) of the scent profile of lips comprised carbohydrates and their derivatives (29.55% of all compounds), amino acids (1.66%), lipids (8.04%) and other organic compounds (60.73%). A great number of identified compounds are Diptera attractants (mainly Milichiidae, Tephritidae, Drosophilidae, Muscidae, Sarcophagidae, Tachinidae). The examination of visual and olfactory features indicates correlation between colour of flowers and the type of olfactory mimicry, where a dark colour labellum emits strong smell of rotten waste.
Highlights
This micromorphological, chemical and ultrastructural study is a continuation of research conducted on the section Lepidorhiza
Considering the presence of carbohydrates (29.55% in GC/MS), the profusion of starch grains (PAS) and a large amount of the secretory material on hypochile (TEM), we consider it nectar
Subcuticular spaces were present in two other species from the section Lepidorhiza (Wiśniewska et al 2018)
Summary
This micromorphological, chemical and ultrastructural study is a continuation of research conducted on the section Lepidorhiza. A anther-cap, an appendage of stelidium, ds dorsal sepal, e epichile, g gynostemium, gr groove (marked with white on b), h hypochile, k keel (marked with yellow on b), ls lateral sepal, pr prickle, pt petal, st stelidium median lip groove, which is a highly conservative lip feature among Bulbophyllum, in contrast to the nature of the secretion (Teixeira et al 2004; Nunes et al 2014; Kowalkowska et al 2015a; Wiśniewska et al 2018). An abundance of proteins detected in the labellum of both species is most likely associated with the unpleasant scent of the flowers, whereas the lipid-rich cuticular striations formed a thin wax layer on the epidermis which is presumably involved in the brilliance of floral tepals, strongly attracting flies (Kugler 1951, apud Meve and Liede 1994). The flowers of B. echinolabium imitate a highly unpleasant smell of rotten waste, which is characteristic of sapromyophilous flowers
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