Early development of epiphytic roots: perspectives based on the composition of the velamen cell wall

Abstract

The velamen, a root structure of some epiphytic species for water uptake, usually is stratified epidermis consisting of dead cells. In general, its cell walls exhibit variation during development, including in thickness and amount and type of impregnated substances. These changes result in diverse physical and chemical properties that can serve in water and nutrient uptake, as well as in mechanical support and protection. On this basis, the main objective of the current study was to describe the composition of the cell walls of the velamen during the development of the roots of four species of Cattleya. Anatomical, histochemical and immunocytochemical analyses were performed with samples (n=3 individuals per species) of meristematic, developing, and mature regions of the root. The development of the primary wall led to the deposition of pectins as highly methylesterified homogalacturonans, which were demetihylesterified with maturation of the velamen. The deposition of lipids (and subsequently lignins) in velamen cells marked a transition stage to the formation of the secondary wall, which gives rigidity to the tissue. For the first time, we showed that the deposition of lipids and lignins began close to the exodermis in the direction of the epivelamen.

Vegetative anatomy and endorrhizal fungal morphology of an endangered medicinal plant Gloriosa superba L.

“…The velamen in G. superba could help in the uptake of water and nutrients, reduce water loss, and protect the underlying cortex under stressful environmental conditions (Moreira & Isaias, 2008; Pridgeon, 1987). The deposition of lignin in the cell walls of velamen as evidenced by autofluorecence in G. superba suggests accelerations of the development of the secondary walls contributing to the stiffness of the tissue (Kitin et al, 2020; Lana et al, 2021). The uniseriate exodermis comprising of long cells, single‐layered endodermis and pericycle and parenchymatous cortex in G. superba resemble the root anatomy of Colchicum kurdicum of Colchicaceae (Kahraman & Celep, 2010).…”