Ultrastructure of the corona of scented and scentless flowers of Passiflora spp. (Passifloraceae)

Abstract

To know thoroughly the structure and function of the corona of Passiflora, the anatomy and ultrastructure of two species were analysed in relation to the emission of odour perceivable by humans: a scented one, P. caerulea L., and a scentless one, P. suberosa L. Both species exhibited secretory tissue, whose cells were characterised by dense cytoplasm, numerous mitochondria and vacuoles. Evidence of granulocrine secretion was detected. Nevertheless, there were differences concerning some cytological structures: P. suberosa lacked smooth endoplasmic reticulum (sER) and starch but had large and many lipidic globules, while P. caerulea had few dictyosomes, scarce lipidic content, a greater proportion of sER/rough endoplasmic reticulum (rER) and amyloplasts. The cellular features of P. caerulea correspond with those of fragrance tissues. The secretion appearance and quantity were also different between both species: P. caerulea exhibited sparse drops on the cuticle in contrast to P. suberosa, which secrets a wax-like material. If this is the final product of the secretory process or just a vehicle that contributes to the emission of volatile compounds, as occurs in certain osmophores, needs further confirmation with chemical analysis. Results are discussed in the context of the pollination syndromes of each species and their florivores.