Measuring the Nanomechanical Properties of Tomato Cuticles Using Atomic Force Microscopy

Tomato plant (Solanum lycopersicum) consist of an outer skin surface called cutin. The cutin has two components: polymeric cutin and a mixture of waxes. Tomato fruit is subjected to stresses from environmental, biotic, and mechanical factors, leading to decreased crop yield and economic losses. It is important to understand the fundamental links between chemical composition and biomechanical properties of tomatoes. This project assesses the influence of cutin deposition on the nanomechanical properties of the tomato cuticle using Atomic Force Microscopy (AFM). The Young’s modulus of the glossy surface of dewaxed and waxy tomato outer cuticles from wild type (M82) and two RNAi-silenced cultivars (deficient in cutin synthase enzymes CUS1 and CUS2) were compared under controlled humidity (60%). The results were used to investigate if inhibition of the expression of the CUS1 and the CUS2 genes would result in significant differences in the elasticity of tomato cuticles. A downward trend in Young's modulus (M82, CUS2 and CUS1) was observed for the glossy surface of the dewaxed samples. This indicated that the elasticity of tomato cuticle is positively correlated to cutin deposition within the sample. Higher cutin deposition in the sample leads to higher values for the Young’s modulus. However for the waxy samples, CUS1 and CUS2 displayed a higher Young's modulus than M82. It was concluded that in the absence of epicuticualr waxes, as compared with the wild-type M82 cultivar, cutin deficiency in CUS1 and CUS2 contributes to a lower resistance to deformation and decreased stiffness of the cuticles in the absence of waxes. However, for the waxy samples the scenario is quite the opposite, with CUS2 and CUS1 having higher Young’s modulus values than M82. This trend can be attributed to the higher proportion of waxes to cutin in the CUS-silenced cuticles. In the future, these results will be correlated with findings from NMR and mass spectroscopy to better understand the underlying changes in chemical composition that produce cultivar-specific differences in nanomechanical performance.