Plant cuticle

A plant cuticle is a protective cover on the outer skin of leaves, young shoots, and other parts of plants that grow above the ground.[1]

Plant cuticle
Water beads on a plant leaf, effect of plant cuticle.

A plant cuticle is a protective cover on the outer skin of leaves, young shoots, and other parts of plants that grow above the ground.[1]

It is made of lipids and hydrocarbon polymers mixed with wax. The plant's skin cells make it.[2] The plant cuticle can be removed from the rest of the plant by using enzymes like pectinase and cellulose.[3]

The plant cuticle is one of the things that plants developed over 450 million years ago when they moved from life in water to life on land. Along with other features like stomata, xylem and phloem, and spaces between cells, the cuticle helps plants save water. It acts like a waterproof covering, protecting the places where gases are moved. The stomatal guard cells, a kind of control mechanism, manage how much water evaporates and how much carbon dioxide gets exchanged.[4]

Structure

Structure of leaf tissue.

The cuticle is made up of a tough membrane filled with waxes. The main part of this membrane is a polyester polymer called cutin, made of special acids. Another component is a non-saponifiable hydrocarbon polymer called cutan. The membrane is loaded with waxes, and there are additional waxes on top of it, which are a mix of hydrophobic compounds. These compounds are often long chains of carbon atoms.[5]

Cuticular wax mainly consists of compounds derived from very-long-chain fatty acids (VLCFAs), like aldehydes, alcohols, alkanes, ketones, and esters. There are also other compounds not derived from VLCFAs, like terpenoids, flavonoids, and sterols.[6]

The process of making cuticular wax involves the creation of long acyl chains in chloroplasts, followed by extending these chains in the endoplasmic reticulum of epidermal cells. An important helper in this process is the fatty acid elongase (FAE) complex.[7][8]

To create cuticular wax, VLCFAs undergo two main pathways: an acyl reduction pathway and a decarbonylation pathway. In the acyl reduction pathway, VLCFAs turn into primary alcohols, which can then become wax esters through a wax synthase. In the decarbonylation pathway, aldehydes change into alkanes and can further transform into secondary alcohols and ketones. The process ends with transporting the wax components from the endoplasmic reticulum to the surface of the epidermis.[9][10]

In certain plants, especially in moss and vascular plants, having a protective cuticle from the parent plant helps the new plants survive better. In flowering plants, the cuticle is usually thicker on the upper side of the leaf, but not always. Plants in dry areas have more even cuticle thickness compared to plants in wet areas.[11]

Besides preventing water loss, the cuticle also acts as a defence. It makes a barrier that stops viruses, bacteria, and fungi from getting in.[12]

References

  1. ↑ Kolattukudy, PE (1996) Biosynthetic pathways of cutin and waxes, and their sensitivity to environmental stresses. In: Plant Cuticles. Ed. by G. Kerstiens, BIOS Scientific publishers Ltd., Oxford, pp 83-108
  2. ↑ RIDGE, IRENE (1997). "Plant Cuticles: an Integrated Functional Approach". The Journal of Agricultural Science. 128 (4): 499–501. doi:10.1017/s0021859697244436. ISSN 0021-8596.
  3. ↑ Budke, J. M.; Goffinet, B.; Jones, C. S. (2013-05-01). "Dehydration protection provided by a maternal cuticle improves offspring fitness in the moss Funaria hygrometrica". Annals of Botany. 111 (5): 781–789. doi:10.1093/aob/mct033. ISSN 0305-7364. PMC 3631323. PMID 23471009.
  4. ↑ Raven, J.A. (1977), "The evolution of vascular land plants concerning supracellular transport Processes", Advances in Botanical Research, vol. 5, Elsevier, pp. 153–219, doi:10.1016/s0065-2296(08)60361-4, ISBN 978-0-12-005905-8, retrieved 2024-02-01{{citation}}: CS1 maint: work parameter with ISBN (link)
  5. ↑ Jetter, Reinhard; Kunst, Ljerka; Samuels, A. Lacey (2006), "Composition of Plant Cuticular Waxes", Biology of the Plant Cuticle, Oxford, UK: Blackwell Publishing Ltd, pp. 145–181, doi:10.1002/9780470988718.ch4, ISBN 978-0-470-98871-8, retrieved 2024-02-01{{citation}}: CS1 maint: work parameter with ISBN (link)
  6. ↑ Brown, G.A.; Holloway, P.J. (1981). "Electron microscope histochemistry of plant cutins". Micron (1969). 12 (2): 193–194. doi:10.1016/0047-7206(81)90062-5. ISSN 0047-7206.
  7. ↑ Yeats, Trevor H.; Rose, Jocelyn K.C. (2013). "The Formation and Function of Plant Cuticles". Plant Physiology. 163 (1): 5–20. Bibcode:2013PlanP.163....5Y. doi:10.1104/pp.113.222737. ISSN 0032-0889. PMC 3762664. PMID 23893170.
  8. ↑ Yeats, Trevor H.; Rose, Jocelyn K.C. (2013). "The Formation and Function of Plant Cuticles". Plant Physiology. 163 (1): 5–20. Bibcode:2013PlanP.163....5Y. doi:10.1104/pp.113.222737. ISSN 0032-0889. PMC 3762664. PMID 23893170.
  9. ↑ JEFFREE, C.E.; BAKER, E.A.; HOLLOWAY, P.J. (1976), "Origins of the Fine Structure of Plant Epicuticular Waxes", Microbiology of Aerial Plant Surfaces, Elsevier, pp. 119–158, doi:10.1016/b978-0-12-215050-0.50008-4, ISBN 978-0-12-215050-0, retrieved 2024-02-01{{citation}}: CS1 maint: work parameter with ISBN (link)
  10. ↑ Kunst, L (2003). "Biosynthesis and secretion of plant cuticular wax". Progress in Lipid Research. 42 (1): 51–80. doi:10.1016/S0163-7827(02)00045-0. PMID 12467640.
  11. ↑ Budke, J. M.; Goffinet, B.; Jones, C. S. (2013-05-01). "Dehydration protection provided by a maternal cuticle improves offspring fitness in the moss Funaria hygrometrica". Annals of Botany. 111 (5): 781–789. doi:10.1093/aob/mct033. ISSN 0305-7364. PMC 3631323. PMID 23471009.
  12. ↑ Freeman, Scott (2002). Biological science. Upper Saddle River, New Jersey: Prentice Hall. ISBN 978-0-13-081923-9.

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