Structure–function relationships of the plant cuticle and cuticular waxes — a smart material?

Abstract

This paper is part of The EvansAbstract. The cuticle is the main interface between plants and their environment. It covers the epidermis of all aerial primary parts of plant organs as a continuous extracellular matrix. This hydrophobic natural composite consists mainly of the biopolymer, cutin, and cuticular lipids collectively called waxes, with a high degree of variability in composition and structure. The cuticle and cuticular waxes exhibit a multitude of functions that enable plant life in many different terrestrial habitats and play important roles in interfacial interactions. This review highlights structure-function relationships that are the subjects of current research activities. The surface waxes often form complex crystalline microstructures that originate from self-assembly processes. The concepts and results of the analysis of model structures and the influence of template effects are critically discussed. Recent investigations of surface waxes by electron and X-ray diffraction revealed that these could be assigned to three crystal symmetry classes, while the background layer is not amorphous, but has an orthorhombic order. In addition, advantages of the characterisation of formation of model wax types on a molecular scale are presented. Epicuticular wax crystals may cause extreme water repellency and, in addition, a striking self-cleaning property. The principles of wetting and upto-date concepts of the transfer of plant surface properties to biomimetic technical applications are reviewed. Finally, biomechanical studies have demonstrated that the cuticle is a mechanically important structure, whose properties are dynamically modified by the plant in response to internal and external stimuli. Thus, the cuticle combines many aspects attributed to smart materials.

Attachment force of the beetle Cryptolaemus montrouzieri (Coleoptera, Coccinellidae) on leaflet surfaces of mutants of the pea Pisum sativum (Fabaceae) with regular and reduced wax coverage

“…The field or garden pea P. sativum is an annual herb with pinnately compound leaves, which in leafy types consist of two stipules at the base of the leaf, one or more pairs of opposite, broad and ovate petiolulate leaflets, several pairs of tendrils and a single or compound terminal tendril (Aichele and Schwegler 2000). The plant originated from the Mediterranean area and Middle East (wild genotypes P. humile J.I.…”

“…Additionally, microscopically small crystals, protruding from the film, cause the pruinosity or powdery appearance of the surface in many plant species (Barthlott et al 1998). Such pruinose surfaces contribute prominently to the mechanical strength of the tissue, to the protection against harmful radiation, to the limitation of uncontrolled water loss or leaching from interior and foliar uptake, to the control of water status, to the cueing of host-pathogens/ insects recognition and epidermal cell development, to the reduction of contamination and pathogen attack, and to the promoting or preventing insect attachment and locomotion (see reviews by Barthlott 1990 andBargel et al 2006).…”

MYB107 and MYB9 Homologs Regulate Suberin Deposition in Angiosperms

“…It is characteristically comprised of a cutin polymer, consisting of long-chain fatty acids and glycerol, which is embedded with very long chain fatty acid waxes (Heredia, 2003;Bargel et al, 2006). The cutin polymer and embedded waxes are typically translucent, allowing photosynthesis, while also providing a strong water proofing barrier, and are thus crucial to the plant's terrestrial survival (Bargel et al, 2006;Isaacson et al, 2009;Chen et al, 2011a). While control of water movement can be considered the principal role of the cuticle, additional roles include structural support and protection against pathogen infection and herbivory Chen et al, 2011a).…”

Exploiting Natural Variation to Uncover an Alkene Biosynthetic Enzyme in Poplar

“…As such, the cuticle serves important roles in nonstomatal water loss prevention, defense against pathogens and insects, and plant development (Bernard and Joubès, 2013;Bargel et al, 2006). The cuticle is made of cutin, a polymeric matrix of oxygenated lipids and waxes, a complex mixture predominated by fatty acid (FA)-derived metabolites, interspersed with triterpenoids, flavonoids, and phenolic lipids (Haslam and Kunst, 2013;von Wettstein-Knowles, 2012).…”