Floral features of two species of Bulbophyllum section Lepidorhiza Schltr.: B. levanae Ames and B. nymphopolitanum Kraenzl. (Bulbophyllinae Schltr., Orchidaceae)

Abstract

Two representatives of section Lepidorhiza, previously sometimes considered conspecific, Bulbophyllum levanae and Bulbophyllum nymphopolitanum, demonstrated both similarities and differences in floral features. There were significant differences in the length of sepals and micromorphological features of the labellum. In both species, osmophores are located on the extended apices of sepals and possibly on petals. An abundance of proteins in tepals is probably associated with the unpleasant scent of the flowers, whereas the thin wax layers on the epidermis are probably involved in the maintenance of the brilliance of floral tepals, which strongly attracts flies. In all tepals of both species, we noted the presence of dihydroxyphenolic globules in the cytoplasm after staining with FeCl. Comparison with ultrastructure results revealed that they were associated with plastids containing plastoglobuli. The most remarkable feature was the presence of a prominent periplasmic space in the epidermal cells of both investigated species. Furthermore, in the labellum of B. levanae, the cuticle contained microchannels. The combination of periplasmic space and microchannels has not previously been recorded.

Nectar Replaced by Volatile Secretion: A Potential New Role for Nectarless Flowers in a Bee-Pollinated Plant Species

“…A noteworthy feature of the disks from nectarless flowers was the coexistence of plastids with different inclusions, only lipids or combinations of carbohydrate and phenolic substances. The increase in the amount of different materials (lipid–carbohydrate–phenolic) within the plastids throughout anthesis, as here observed, has been demonstrated in Orchidaceae osmophores ( Wiśniewska et al, 2018 and references therein). The involvement of plastids in the synthesis of scent components, mainly terpenoids and phenolic compounds, has been broadly discussed ( Pridgeon and Stern, 1985 ; Stern et al, 1987 ; Pais and Figueiredo, 1994 ; Kowalkowska et al, 2012 ; Stpiczyńska and Davies, 2016 ; Wiśniewska et al, 2018 ).…”

“…Some authors, studying Orchidaceae species ( de Melo et al, 2010 ; Kowalkowska et al, 2012 , 2015 ; Wiśniewska et al, 2018 ), found that floral nectaries and osmophores are somewhat similar in structure and ultrastructure features, except that in the latter there is predominance of SER and low frequency of Golgi bodies. Therefore, abundance of globular mitochondria, SER with peripheral distribution and oil droplets in the cytosol and in amyloplasts, together with the scarce Golgi bodies here observed may be associated with fragrance production ( Curry et al, 1991 ; Stpiczyńska and Davies, 2016 ).…”

“…Although amyloplasts are common components of both nectaries and osmophores ( Nepi, 2007 ), the absence of starch has been recorded in osmophores in some orchid species ( Wiśniewska et al, 2018 ). Plastids lacking or having reduced starch grains in the epidermis and in the first subepidermal layers at recently opened nectarless flowers, as here observed, might be caused by their hydrolysis before anthesis (at an earlier stage than we sampled), as starch grains are utilized as energy source for scent production ( Stern et al, 1987 ; Vogel, 1990 ; Nepi, 2007 ; Pacini and Nepi, 2007 ; de Melo et al, 2010 ).…”

“…The emission of volatile substances is of short duration and is associated with the fast utilization of large amounts of starch grains ( Stern et al, 1987 ; Vogel, 1990 ; Pacini and Nepi, 2007 ; de Melo et al, 2010 ; Wiśniewska et al, 2018 ). In fact, essences were histochemically detected since the beginning of anthesis in nectarless flowers.…”

“…The involvement of plastids in the synthesis of scent components, mainly terpenoids and phenolic compounds, has been broadly discussed ( Pridgeon and Stern, 1985 ; Stern et al, 1987 ; Pais and Figueiredo, 1994 ; Kowalkowska et al, 2012 ; Stpiczyńska and Davies, 2016 ; Wiśniewska et al, 2018 ). Besides protection against herbivores, pathogens, and UV radiation ( Brillouet et al, 2013 ), phenolic compounds are known to occur in floral scent ( Jürgens and Dötterl, 2004 ; Jürgens et al, 2006 ; Steiner et al, 2011 ; Wiśniewska et al, 2018 ).…”