Transfer cells in trichomatous nectary in Adenocalymma magnificum (Bignoniaceae)

Abstract

Transfer cells are specialized cells that play an important role where there are high energy costs due to facilitation of transmembrane flow of solutes. This study aimed to investigate the ontogenesis, histochemistry and ultrastructure of glandular trichomes focusing on stalk cells and their possible transfer function. Samples of prophylls of axillary buds, calyces of flowers in anthesis, and flower buds in different stages of development were collected, fixed and processed according to the common methods of microscopy. The glandular trichomes are composed of a secretory head with its cells in columnar format. The stalk is formed by two layers of cells, with the upper layer composed of cuboidal cells where the wall starts to thicken at the beginning of the pre-secretory phase. The secretion is heterogeneous, releasing glucose, other carbohydrates, lipids and phenolic compounds, with two types of release -eccrine and granulocrine. These trichomes are functionally termed as nectaries. The stalk cells appear as transfer cells since they have a thicker anticlinal wall with irregular ingrowths. The presence of transfer cells in the nectaries suggests a high specialization because it improves transport capacity of nectar and compensation in the high energy expenditure for its production and release.

Nectar trichome structure of aquatic bladderworts from the section Utricularia (Lentibulariaceae) with observation of flower visitors and pollinators

“…Fahn 1979a, b; Durkee 1983; Razem and Davis 1999; Wist and Davis 2006; Nepi 2007). However, it should be underlined that the most published observations were performed on the non-trichome nectarines, and data about trichome nectary ultrastructure are scarce and based on a few taxa only ( Lonicera —Fahn and Rachmilevitz 1970; Abutilon —Robards and Stark 1988; Hibiscus —Sawidis et al 1987, 1989; Platanthera —Stpiczyńska et al 2005; Cyclanthera —Nepi 2007; Adenocalymma —Gama et al 2016). In nectar-secreting trichromes, e.g.…”

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

“…subcuticular space, the volume of the nectar is defined by the extent of the cuticle that covers the gland and, naturally, the expandability of the cuticle. Nectar accumulation beneath the cuticle was reported by Pacini et al (2003), Gama et al (2016) and Nepi (2007), the latter of which explained some modes of nectar release. This process of nectar release was described by Wunnachit et al (1992) who stated: "cuticle became distended by secretion of nectar (…) no cuticular pores were observed and the nectar must tear the cuticle".…”

“…It should be noted that the fact that the subcuticular space does not extend beyond the limits of the gland (Rocha et al 2009;Possobom et al 2015;Gama et al 2016) allows us to infer that pectinases, which are responsible for the weakening of the pectin layer and the consequent displacement of the cuticle, act on secretory cells and not neighboring cells. If this were not the case, the subcuticular space would tend to expand beyond the limits of the gland due to cuticular resistance.…”

“…This view is very interesting and we must consider that cuticles, due to their lipidic nature, are sufficiently plastic in order to restore their integrity after the release of any secretory products or after any other kind of mechanical damage. Some nectaries possess lipid droplets inside secretory cells even when lipid was not detected in the nectar (Paiva & Machado 2006;Gama et al 2016). Thus, the role of lipids inside nectary cells during the cuticle restoration process needs to be investigated.…”

Morphology and histochemistry of glandular trichomes in Hyptis villosa Pohl ex Benth. (Lamiaceae) and differential labeling of cytoskeletal elements

“…The folds of the cell walls increase the surface of the plasmalemma and may favor the process of release of secretion (Gunning & Pate 1969;Evert 2006), facilitating the exchanges between the symplast and apoplast (Gunning & Pate 1969;Pate & Gunning 1972). Following Gama et al (2016), the presence of transfer cells in secretory tissues can improve the capacity of transport of the secretion, compensating the spending of the secretion production. This suggests some type of evolution of the transfer cells molded by physiological selection pressures, facilitating the short distance transport (Gunning & Pate 1969).…”