Colleters in Rubiaceae from forest and savanna: the link between secretion and environment

Abstract

This study aims to investigate colleters' secretory function, on cellular level, in Rubiaceae species from contrasting environments looking to explore the association between secretion and environment. We collected samples from eight species of Rubiaceae growing in forest and savanna having standard-type colleters with diverse histochemistry (hydrophilic, lipophilic and mixed secretions) and processed for both conventional and cytochemical study under transmission electron microscopy (TEM). The standard colleters, although similar in morphology and anatomy, exhibited marked differences on cellular level, especially in the abundance and topology of Golgi bodies, endoplasmic reticulum and plastids when comparing forest and savanna species. These differences were clearly aligned with the chemical nature of the secretions they produce, with predominance of hydrophilic secretions in forest species and lipophilic or mixed secretions in savanna species. The combination of methods in electron microscopy revealed the sites of synthesis and intracellular compartmentation of substances, the mechanisms of their secretion from the protoplast and confirmed the involvement of the outer walls of the epithelial cells in the elimination of exudates to the gland surface. Our study suggests a potential environment-associated plasticity of the secretory cells of standard-type colleters in modulating their secretory function performance.

Flower nectar trichome structure of carnivorous plants from the genus butterworts Pinguicula L. (Lentibulariaceae)

“…Such a structure has been described in the cells of various nectary types in many species (e.g. Stpiczyńska 2003;Wist and Davis 2006;Rocha and Machado 2009;Antoń and Kamińska 2015;Weryszko-Chmielewska and Chwil 2016) as well as in other plant glandular structures-osmophores (García et al 2007;Płachno et al 2010;Kowalkowska et al 2012Kowalkowska et al , 2014Kowalkowska et al , 2017Paiva et al 2019), collectors (Tresmondi et al 2017) and trichomes, which produce a lipophilic secretion (Machado et al 2017;Muravnik et al 2019). Interestingly, we found polysaccharide micro-canals in the cuticular layer of the spur papillae.…”

More than Scales: Evidence for the Production and Exudation of Mucilage by the Peltate Trichomes of Tillandsia cyanea (Bromeliaceae: Tillandsioideae)

“…Plant mucilages usually present hygroscopic features, exhibiting changes in their aspect and volume in response to the presence of moisture [ 16 , 45 , 47 , 64 , 65 , 66 ]. Furthermore, mucilaginous secretions displaying a fibrillar aspect were recorded in many similar secretory systems [ 16 , 35 , 46 , 67 ].…”

How does the nectar of stomata-free nectaries cross the cuticle?

“…According to Jeffree (2006), cuticular pores capable of functioning as pathways for the passage of fluid are practically confined to secretory cells in higher plants, and despite the possible presence of these pores, the release of secretion may still require the rupture of the cuticle. However, Tresmondi et al (2017) presented evidences that secretion crosses the cuticle by micro-channels, without breaking the cuticle in some colleters.…”

“…These hydrophilic pathways into the cuticular layer have been described for some nectaries, such as those of Platanthera chlorantha (Orchidaceae) (Stpiczynska 2003), Galanthus nivalis (Amaryllidaceae) (Weryszko-Chmielewska & Chwil 2016), nectary spurs of four representatives of Ranunculaceae (Antón & Kaminska 2015) and several other examples in the literature, mostly in stomata-free floral nectaries. Similar cuticular canals, which are polysaccharide material from cell wall protruded inside the cuticular layers, seems to act increasing the porosity of the cuticle and, consequently, constituting pathways for the secretion release in colleters (see Tresmondi et al 2017).…”