Oil-resin glands in Velloziaceae flowers: structure, ontogenesis and secretion

Abstract

Many Velloziaceae flowers present conspicuous glands, whose taxonomic value has already been highlighted. However, until now, their micromorphology, anatomy and ultrastructure have not been investigated, nor have the natures and possible functions of their exudates. Our aim was to investigate distribution, ontogenesis, structure, and secretion mechanisms of glands of Barbacenia flava and Vellozia intermedia and to discuss their possible ecological functions. Samples were prepared according to standard methods for investigations of plant anatomy, scanning electron microscopy, and transmission electron microscopy. Histochemical tests were performed, and focal field observations were made in the study site. The capitate stalked glands on the pedicel, tepals and hypanthium are covered by a sticky secretion that is released in the gland head through the outer periclinal cell walls and cuticle. Secretions are produced in the epidermal and subepidermal cells that contain structural components typical of mixed, mainly lipophilic secretions. Bacteria were found inside the oil-resin gland cells of both species. The Meliponina bees Trigona spinipes and Tetragonisca angustula were observed collecting resin from both species, but were not involved in pollination. Our observations clearly indicate that flower glands of B. flava and V. intermedia are oil-resin secreting and remain active in secretion from very young buds, through to immature fruit. New, smaller glands replace senescent glands by divisions near the base of the original stalk cells. Oil-resin glands have a number of different, but important functions, including the interaction with Meliponina bees, protection against water loss and high temperatures by ultraviolet screening, and anti-desiccant properties.

Structure and functioning of oil cavities in the shoot apex of Metrodorea nigra A. St.-Hil. (Rutaceae)

“…The epithelial cells of mature oil glands of M. nigra share a number of common features with other metabolically active cells, such as a high density of ribosomes, a large nucleus-tocytoplasm volume ratio, and relatively small vacuoles (Fahn 1979;Evert 2006). In addition, the presence of endoplasmic reticulum tubular elements, leucoplast, and well-developed mitochondria with osmiophilic granulations has been described in glands producing terpenes (Turner et al 1999;Machado et al 2006;Paiva et al 2008;Rodrigues et al 2011aRodrigues et al , 2011bRodrigues and Machado 2012;Lange and Turner 2013;Turner and Lange 2015;Sá-Haiad et al 2015;Possobom et al 2015;Sadala-Castilho et al 2016). The close spatial relationship of plastids with the endoplasmic reticulum, as observed in the oil cavity of M. nigra, is another feature that is commonly reported for terpene glands (Sá-Haiad et al 2015 and literature therein).…”

Floral resins of Philodendron adamantinum (Araceae): secretion, release and synchrony with pollinators

“…The organelle composition of the epithelial cells of the canals of P. adamantinum, composed predominantly of plastids, mitochondria and smooth endoplasmic reticulum, is compatible with the synthesis of terpene resins, as observed in the secretory structures of these resins in other plant species (Gilliland et al 1988;Langenheim 2003;Rodrigues et al 2011;Sadala-Castilho et al 2016).…”

Florivory in twoChamaecristaspecies: Are secretory trichomes effective against florivores?

“…According to Meira et al (2014), the trichomes of Chamaecrista dentata, section Absus, secrete an oil-resin. In Vellozia intermedia and Barbacenia flava in the study area, the calyx and pedicel are covered with oil-resin glands; the stingless bees T. spinipes and Tetragonisca angustula actively collect this resin, although their visits do not result in pollination (Sadala et al, 2016). Although T. spinipes is often observed damaging the flowers of C. catharticoides (Silva, 2020), we have never recorded resin collection by these bees.…”

“…Our results showed that in C. catharticoides and C. cathartica , the oil‐resin glands are directly involved in protection against herbivory. However, for V. intermedia , other benefits such as reduced desiccation, protection against ultraviolet rays, increased light reflection, and lowered internal temperature were suggested for the oil‐resin glands, and protection against herbivory was considered secondary (Sadala‐Castilho et al, 2016).…”