Abstract
Background and AimsPrior work has examined cuticle function, composition and ultrastructure in many plant species, but much remains to be learned about how these features are related. This study aims to elucidate relationships between these features via analysis of cuticle development in adult maize (Zea mays L.) leaves, while also providing the most comprehensive investigation to date of the composition and ultrastructure of adult leaf cuticles in this important crop plant.MethodsWe examined water permeability, wax and cutin composition via gas chromatography, and ultrastructure via transmission electron microscopy, along the developmental gradient of partially expanded adult maize leaves, and analysed the relationships between these features.Key ResultsThe water barrier property of the adult maize leaf cuticle is acquired at the cessation of cell expansion. Wax types and chain lengths accumulate asynchronously over the course of development, while overall wax load does not vary. Cutin begins to accumulate prior to establishment of the water barrier and continues thereafter. Ultrastructurally, pavement cell cuticles consist of an epicuticular layer, and a thin cuticle proper that acquires an inner, osmiophilic layer during development.ConclusionsCuticular waxes of the adult maize leaf are dominated by alkanes and alkyl esters. Unexpectedly, these are localized mainly in the epicuticular layer. Establishment of the water barrier during development coincides with a switch from alkanes to esters as the major wax type, and the emergence of an osmiophilic (likely cutin-rich) layer of the cuticle proper. Thus, alkyl esters and the deposition of the cutin polyester are implicated as key components of the water barrier property of adult maize leaf cuticles.
Highlights
Plant epidermal cells of the shoot are covered by a hydrophobic layer, the cuticle (Esau, 1977), which forms the primary barrier between the plant’s air-exposed surfaces and the external environment
Almost all cell elongation occurred between 3 and 12 cm from the leaf base, with the highest cell expansion rate between 4 and 8 cm (Fig. 1D), where there is a local increase in Toluidine Blue O (TBO) permeability (Fig. 1A, B). These results indicate that the water barrier property of the adult maize leaf cuticle becomes fully established ~10 cm above the leaf base, coinciding with the completion of cell elongation and shortly before emergence of the leaf from the whorl
We examined the developmental origins of mature leaf cuticle ultrastructure, by TEM imaging of pavement cell cuticles at a series of 2-cm intervals along the developmental gradient of a partially expanded adult maize leaf 8
Summary
Plant epidermal cells of the shoot are covered by a hydrophobic layer, the cuticle (Esau, 1977), which forms the primary barrier between the plant’s air-exposed surfaces and the external environment. The cuticle limits non-stomatal water loss and gaseous exchanges, protects the plant from extreme temperatures, UV radiation and pathogens, provides mechanical strength, and prevents organ fusion during development (Kolattukudy, 2001; Nawrath, 2002). These functions of the cuticle allowed plants to survive in terrestrial habitats early in land plant evolution, with fossil evidence showing cuticles in the earliest known land plants (Bargel et al, 2006). Cutin is a polyester matrix composed mainly of glycerol and long-chain (C16 and C18) fatty acid monomers, usually having ω-linked functional groups and often containing mid-chain hydroxy and epoxy groups. The specific composition and quantities of cuticular wax classes may vary significantly across species, plant organs and developmental stages, and may undergo dynamic effects in response to growth conditions, physical disturbance or damage, and genetic manipulation (Jenks et al, 2001; Jetter et al, 2006; Kosma et al, 2009)
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