The mystery element: building a variable plant cuticle

The plant cuticle seems to be quite a hot topic at the moment. In a recent post I discussed how Penny von Wettstein-Knowles investigated the multifunctional roles of the cuticle in barley in a paper published in Annals of Botany. Now, variation in the composition of the protective plant cuticle comes under the spotlight. In their paper also now out in Annals of Botany, Jana Leide and colleagues from Germany and the Netherlands examine the composition of leaf cuticles of several angiosperm species. The differences they find highlight that plant cuticles are compositionally variable, possibly linking to different requirements of the different species they survey. The data they collect also gives clues as to how some of the complex components of the plant cuticle may be made – a system about which much remains unknown.

The plant cuticle is a multifunctional structure, providing protection from water loss, nutrient leaching, herbivorous insects and electromagnetic radiation, amongst other functions. Likely related to its multifunctionality is its molecular complexity. Appreciation of this complexity has increased with advances in the molecular techniques that can be used to analyse the plant cuticle over recent decades. One slightly mysterious components of the plant cuticle is cutan, which is often left behind after other components of the cuticle have been extracted in biochemical analyses. Cutan appears to increase the strength of the plant cuticle, and is found in a variety of flowering plant species as well as in some non-flowering species. To find out more about the composition of cutan and how this may vary between plant species, Leide and colleagues examine the cutan content of four plant species. Surprisingly, although all four of the species they examine have previously been reported to contain cutan, Leide and colleagues only find it in two of the species using their methods – Agave americana and Clivia miniate.

These results indicate that cutan presence may be more variable between plant species than was previously thought. The authors speculate that the difference between this result and previous studies is due to the refined extraction technique that they use, and this will likely be of interest to other researchers thinking about the plant cuticle in a variety of different contexts. Interestingly, some data presented in this paper indicates that the cutan of C.miniate may be of different structure to that of A.americana. This highlights a question likely to be of interest in the future – whether different cutan content and structure may be used by different plant species to create cuticles of differing properties. As Leide and colleagues state: ‘The cuticular composition of A.americana and C.miniata leaves might be responsible for a specific cuticle ultrastructure, possibly representing adaptations of the cuticular barrier properties to environmental conditions’.

How plants make cutan is unclear compared to other cuticle components. However, Leide and colleagues find that the building blocks of cutan resemble some of the other wax components found in the cuticle. This indicates that they may be made by the same or similar biochemical pathways. Making an additional cuticle component in some plant species may therefore be spun out of existing components and pathways. This is possibly a clever way for plants to produce variable cuticle compositions suiting their particular requirements without having to produce elaborate new biochemical pathways from scratch. This study highlights that there is still much to understand in how the variability of the plant cuticle may support different requirements of different plant species, and how this variability may be produced.