The presence of cutan limits the interpretation of cuticular chemistry and structure: Ficus elastica leaf as an example

Abstract

Plant cuticles have been traditionally classified on the basis of their ultrastructure, with certain chemical composition assumptions. However, the nature of the plant cuticle may be misinterpreted in the prevailing model, which was established more than 150 years ago. Using the adaxial leaf cuticle of Ficus elastica, a study was conducted with the aim of analyzing cuticular ultrastructure, chemical composition and the potential relationship between structure and chemistry. Gradual chemical extractions and diverse analytical and microscopic techniques were performed on isolated leaf cuticles of two different stages of development (i.e. young and mature leaves). Evidence for the presence of cutan in F. elastica leaf cuticles has been gained after chemical treatments and tissue analysis by infrared spectroscopy and electron microscopy. Significant calcium, boron and silicon concentrations were also measured in the cuticle of this species. Such mineral elements which are often found in plant cell walls may play a structural role and their presence in isolated cuticles further supports the interpretation of the cuticle as the most external region of the epidermal cell wall. The complex and heterogeneous nature of the cuticle, and constraints associated with current analytical procedures may limit the chance for establishing a relationship between cuticle chemical composition and structure also in relation to organ ontogeny.

Cuticle Structure in Relation to Chemical Composition: Re-assessing the Prevailing Model

“…The multi-functional character of the cuticle is achieved by a heterogeneous structural and chemical nature ( Khayet and Fernández, 2012 ) which may additionally vary between e.g., species, genotypes, organs, developmental stages, plant physiological status, or environmental conditions during growth (e.g., Knoche et al, 2004 ; Szakiel et al, 2012 ; Nawrath et al, 2013 ; Fernández et al, 2014a ; Guzmán-Delgado et al, 2016 ).…”

“…From a chemical viewpoint, the cuticle is formed by an array of compounds with different physico-chemical properties (see Figure 1 as an example of common cuticle constituents). These compounds can be waxes, cutin and/or cutan, polysaccharides, phenolics and mineral elements ( España et al, 2014 ; Guzmán et al, 2014a ; Guzmán-Delgado et al, 2016 ). Cuticular waxes are a mixture of compounds, such as long-chain fatty acids, alcohols, alkanes, esters or triterpenoids ( Jetter et al, 2006 ).…”

“…In recent decades, substantial progress has been made for characterizing the mechanisms of wax synthesis and export ( Samuels et al, 2008 ; Kunst and Samuels, 2009 ), cutin monomer synthesis and assembly (e.g., Li-Beisson et al, 2009 ; Domínguez et al, 2010 ; McFarlane et al, 2010 ; Girard et al, 2012 ; Yeats et al, 2012 ), and structural and chemical responses of the cuticle to biotic and abiotic stress factors (e.g., Bessire et al, 2007 ; Isaacson et al, 2009 ; Kosma et al, 2009 ), also in relation to different stages of organ development (e.g., España et al, 2014 ). However, many aspects of cuticle structure in relation to chemical composition ( Guzmán et al, 2014a ; Guzmán-Delgado et al, 2016 ) remain unclear e.g., cuticle genesis, or cuticular component synthesis and transport ( Bird, 2008 ; Pollard et al, 2008 ; Khayet and Fernández, 2012 ; Domínguez et al, 2015 ).…”

Cuticular Lipids as a Cross-Talk among Ants, Plants and Butterflies

“…This wax heterogeneity is also observed among plant species or genotypes, as well as between organs belonging to the same individual or even within ontogeny phases, and can be influenced by physiological or environmental conditions (e.g., [95,100,101,102]). Despite this variation, some wax pattern or even single compound (e.g., Δ-6 fatty acids in the Ranunculaceae [103]) are found to be typical of certain plant groups, to such an extent that epicuticular compounds have been successfully used in plant chemotaxonomy of different families including angiosperms [104,105,106,107] and gymnosperms [14].…”

Sensing vegetation canopies in the thermal domain

“…Additionally the multi-functional properties of the cuticle, due to its heterogeneous structure and chemical nature (Khayet and Fernández 2012), may additionally vary between e.g. species, genotypes, plant physiological status as well as environmental conditions during growth Fernández et al 2014;Guzmán-Delgado et al 2016;Knoche et al 2004;Szakiel et al 2012), and could consequently affect the emissivity spectra.…”