Viscoelastic matrix (cutin) of plant cuticle protects fruit from cracking by fibrillar components capable of passive realignment when placed in tension.

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Plant cuticles play a key role in a plant's interaction with the environment and in controlling organ expansion because "the lipid cuticle layer is deposited on the surface of outer epidermal cell walls and modifies the chemical and mechanical nature of these cell walls" (Domíngueza et al. 2011: 77). The cuticle is made up of polysaccharides and flavenoids that contribute to the nature of its stiffness. Compared to the rest of the epidermal cells, the cuticle is much less flexible. Harder cuticles help protect against fungal pathogens more efficiently than softer ones. Stiffness can be modulated by a plant's ability to realign its fibrils in the direction of an applied force. In other words, plants better at opposing the force through their fibril alignment are able to maintain their stiffness under stress. The properties of cuticles (that is their stiffness and strength) can be altered by temperature and humidity. For example, fruit tends to go bad more often when kept out in the heat because the cuticle becomes degraded thus allowing external factors to penetrate its surface. Understanding the mechanical properties of the cuticle could lead to fruits that last longer on the shelves and better withstand attack from animal and fungal pests. Edit Summary

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"Most if not all mechanical tests performed on the cuticle are uniaxial tests: stresses applied on only one axis. Nevertheless, plants or plant organs are subjected in vivo to stresses applied on more than one dimension, even when growth preferentially occurs in one axis due to different growth rates or turgor pressures. Equipment allowing biaxial tests that apply the same or differential stresses on each axis and are able to work with both cuticle and peel (cuticle plus epidermal cells) would be desirable for approximating the in vivo conditions of some fruits, especially bell peppers, tomatoes, cherries, etc., where surface cracks produce signi?cant economical losses. In this sense, two-dimensional rheological properties of grape berries in vivo have been studied with the aid of an injection tester that used water to increase internal pressure, and allowed the correlation of fruit skin strain with splitting susceptibility[86]…Clearly, information from biaxial mechanical analyses, though still in its infancy, will be a step forward in the comprehension of in vivo plant cuticle mechanics. Additionally, the development of theoretical models that integrate the mechanical information of cuticle and epidermis into an ideal fruit will also advance our knowledge on the subject. Little progress has been made on this topic and only recently a mathematical model that describes the rheological behavior of isolated tomato cuticles from experimentally measured properties was formulated [88]" (Domíngueza et al. 2011: 83).

Journal article
An overview on plant cuticle biomechanicsPlant ScienceMay 7, 2011
Eva Domínguez, Jesús Cuartero, Antonio Heredia

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