Ultrastructure of Osmophores in Restrepia (Orchidaceae)

Abstract

Osmophores ofthe myophilous genus Restrepia (Orchidaceae) were studied developmentally at the ultrastructural level. They are located at petal apices and on the adaxial surface of the dorsal sepal apex. Up to and through anthesis a dense, osmiophilic exudate is synthesized probably in endoplasmic reticulum or in plastids of papillose epidermal cells, and then appears to be transported through the plasmalemma by granulocrine elimination. As the exudate is amassed, the cuticle ruptures to form numerous pores that extend from the cell wall. Mitochondria and amyloplasts are especially abundant at anthesis. From anthesis to post-anthesis, lipid droplets appear in the cytoplasm and vacuoles of epidermal cells, and frequency of cell organelles drops markedly with increasing vacuolation.

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

“…This last character and the amount of sER in the epidermal cells of P. caerulea was also found in the osmophores of orchids (Curry, 1987;Pridgeon and Stern, 1983;Stern et al, 1987;Stpiczynska, 1993), in the presumed osmophoric hairs of Cypripedium spp. (Swanson et al, 1980) and in the glandular trichomes of Teucrium scorodonia (Sevinate-Pinto and Antunes, 1991).…”

“…Starch is the frequent energy reserve in osmophores, but lipids also occur (Vogel, 1990). Lipid substances, abundant in osmophores (Curry, 1987;Pridgeon and Stern, 1983;Stpiczynska, 1993Stpiczynska, , 2001, have been presumed to be the physical counterpart of the secreted fragrance (Curry, 1987;Pridgeon and Stern, 1983;Stern et al, 1987). This conjecture is based on the presumption that terpenes accumulate in that form (Kisser, 1958;Schnepf, 1969;cited in Pridgeon and Stern, 1983).…”

“…Stpiczynska (1993) reports about a swollen surface cuticle near agglomerations of secretion and Pridgeon and Stern (1983) and Stern et al (1987) show aggregations of osmiophilic material in the outer region of the apoplast, features comparable to the swollen wall and high electron-dense zone beneath the cuticle of P. caerulea during anthesis. Similar processes of the epidermal cells' outer wall extending into the cuticle in P. suberosa were found by Stern et al (1987); Lyshede (1978) observed microchannels in the epidermal outer walls through which wax precursors were interpreted to pass.…”

“…Vesicles in such location were observed in osmophores by Pridgeon and Stern (1983), Stern et al (1987) and Stpiczynska (1993Stpiczynska ( , 2001, but eccrine secretion also occurs in fragrance tissues of other orchids (Vogel, 1990). Both epidermal and subepidermal cells seem to produce and store.…”

“…Pridgeon and Stern (1983) and Stpiczynska (2001) documented cuticular pores. When there are no pores or ectodesmata, other pathways exist: low-molecular-weight terpenes can pass through cellulose and cutin (Vogel, 1990), certain wax-covered cuticles allow the passage of volatiles (Goodwin et al, 2003), lipids could pass through the wall as moieties and reassemble on the cuticle (Davies et al, 2003), wax precursors could be carried across the wall within the hydrophobic cavity of lipid transfer proteins or by hydrophobic domains of constitutive proteins (Kunst and Samuels, 2003).…”