Plant cuticle

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Water beads on the waxy cuticle of kale leaves

A plant cuticle is a protecting film covering the outermost skin layer (epidermis) of leaves, young shoots and other aerial plant organs (aerial here meaning all plant parts not embedded in soil or other substrate) that have no periderm. The film consists of lipid and hydrocarbon polymers infused with wax, and is synthesized exclusively by the epidermal cells. [1]

Description

Anatomy of a eudicot leaf

The plant cuticle is a layer of lipid polymers impregnated with waxes that is present on the outer surfaces of the primary organs of all vascular land plants. It is also present in the sporophyte generation of hornworts, and in both sporophyte and gametophyte generations of mosses[2] The plant cuticle forms a coherent outer covering of the plant that can be isolated intact by treating plant tissue with enzymes such as pectinase and cellulase.

Composition

The cuticle is composed of an insoluble cuticular membrane impregnated by and covered with soluble

hydrophobic aliphatic compounds, hydrocarbons with chain lengths typically in the range C16 to C36.[7]

Cuticular wax biosynthesis

Cuticular wax is known to be largely composed of compounds which derive from very-long-chain fatty acids (VLCFAs), such as aldehydes, alcohols, alkanes, ketones, and esters.[8][9] Also present are other compounds in cuticular wax which are not VLCFA derivatives, such as terpenoids, flavonoids, and sterols,[9] and thus have different synthetic pathways than those VLCFAs.

The first step of the biosynthesis pathway for the formation of cuticular VLCFAs, occurs with the de novo biosynthesis of C16 acyl chains (palmitate) by chloroplasts in the mesophyll,[1] and concludes with the extension of these chains in the endoplasmic reticulum of epidermal cells.[9] An important catalyzer thought to be in this process is the fatty acid elongase (FAE) complex.[8][9][10]

To form cuticular wax components, VLCFAs are modified through either two identified pathways, an acyl reduction pathway or a

reductase converts VLCFAs into primary alcohols, which can then be converted to wax esters through a wax synthase.[9][10] In the decarbonylation pathway, aldehydes are produced and decarbonylated to form alkanes, and can be subsequently oxidized to form secondary alcohols and ketones.[8][9][10] The wax biosynthesis pathway ends with the transportation of the wax components from the endoplasmic reticulum to the epidermal surface.[9]

Functions

The primary function of the plant cuticle is as a water permeability barrier that prevents evaporation of water from the epidermal surface, and also prevents external water and solutes from entering the tissues.

biomimetic
technical materials.

Dehydration protection provided by a maternal cuticle improves offspring fitness in the moss Funaria hygrometrica

angiosperms the cuticle tends to be thicker on the top of the leaf (adaxial surface), but is not always thicker. The leaves of xerophytic plants adapted to drier climates have more equal cuticle thicknesses compared to those of mesophytic
plants from wetter climates that do not have a high risk of dehydration from the under sides of their leaves.

"The waxy sheet of cuticle also functions in defense, forming a physical barrier that resists penetration by virus particles, bacterial cells, and the spores and growing filaments of fungi".[13]

Evolution

The plant cuticle is one of a series of

innovations, together with stomata, xylem and phloem and intercellular spaces in stem and later leaf mesophyll tissue, that plants evolved more than 450 million years ago during the transition between life in water and life on land.[11] Together, these features enabled upright plant shoots exploring aerial environments to conserve water by internalising the gas exchange surfaces, enclosing them in a waterproof membrane and providing a variable-aperture control mechanism, the stomatal guard cells, which regulate the rates of transpiration
and CO2 exchange.

References

  1. ^
    environmental stresses
    . In: Plant Cuticles. Ed. by G. Kerstiens, BIOS Scientific publishers Ltd., Oxford, pp 83-108
  2. ^
    PMID 23471009
    .
  3. ^ Holloway, PJ (1982) The chemical constitution of plant cutins. In: Cutler, DF, Alvin, KL and Price, CE The Plant Cuticle. Academic Press, pp. 45-85
  4. ^ Stark, RE and Tian, S (2006) The cutin biopolymer matrix. In: Riederer, M & Müller, C (2006) Biology of the Plant Cuticle. Blackwell Publishing
  5. ^ Tegelaar, EW, et al. (1989) Scope and limitations of several pyrolysis methods in the structural elucidation of a macromolecular plant constituent in the leaf cuticle of Agave americana L., Journal of Analytical and Applied Pyrolysis, 15, 29-54
  6. ^ Jetter, R, Kunst, L & Samuels, AL (2006) Composition of plant cuticular waxes. In: Riederer, M & Müller, C (2006) Biology of the Plant Cuticle. Blackwell Publishing, 145-181
  7. ^ Baker, EA (1982) Chemistry and morphology of plant epicuticular waxes. In: Cutler, DF, Alvin, KL and Price, CE The Plant Cuticle. Academic Press, 139-165
  8. ^
    PMID 23893170
    .
  9. ^
    PMID 12467640
    .
  10. ^
    PMID 24692420
    .
  11. ^
    ISBN 9780120059058
    .
  12. S2CID 37872229
    .
  13. ISBN 978-0130819239
    .
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