Labellar anatomy and secretion in Bulbophyllum Thouars (Orchidaceae: Bulbophyllinae) sect. Racemosae Benth. & Hook. f.

• DOI: 10.1093/aob/mcu153
• Publication Date: 2014-08-13T21:38:36Z
• Authors: Kevin L. Davies; Malgorzata Stpicz...
• Keywords: Orchidaceae; Hook; Sect

Floral secretions are common in Bulbophyllum Thouars, and the labella of a number Asian species said to produce rich lipids that act as food rewards for insect pollinators. Although some these reports based on simple histochemical tests, much greater anecdotal and, hitherto, neither ultrastructure labellum nor secretory process has been investigated detail. Furthermore, sophisticated approaches have generally not applied. Here, both labellar structure four sect. Racemosae Benth. & Hook. f., namely careyanum (Hook.) Spreng., B. morphologorum Kraenzl., orientale Seidenf. wangkaense Seidenf., compared with those unequivocal lipid-secreting orchids. Labellar, tissue was using light microscopy, scanning electron transmission microscopy histochemistry. The adaxial median longitudinal groove contained comprising palisade-like epidermal cells, similar certain Oncidiinae However, cells their gave positive results mainly protein mucilage, organelle complement consistent involved mucilage synthesis. Sub-cuticular accumulation secretion resulted cuticular distension blistering. sub-epidermal layer isodiametric parenchyma starch like Lipids were confined cuticle, hardly any intracellular lipid droplets observed. It is proposed produced by dictyosomes present cells. Mucilage precursors may also be same organelles thought pass along symplast via plasmodesmata into adjoining which contain abundant arrays rough endoplasmic reticulum. they become chemically modified form protein-rich, mucilaginous that, following vesicle-mediated transport across cytoplasm, traverses cell wall accumulates blisters formed from distended cuticle. Rupture releases onto surface. species, there evidence traverse cuticle pores, micro-channels permit passage fragrance. Hydrolysis probably generates carbohydrate together mitochondria, energy required process. This anatomical organization resembles found lipid-secreting, Neotropical Oncidiinae, but since chemical composition different, taxa occur separate continent different pollinators, parallelism floral anatomy likely.