Optical Coherence Tomography (OCT), a non-contact, non-destructive imaging technique, is becoming a popular tool in phytophotonics, helping to address research questions in plant biology and horticulture. However, the stationary nature of typical OCT systems compromises its non-destructive advantage since plants often need to be dissected for an analysis with a laboratory OCT system. Here we present a portable, low-cost OCT system that enables in-situ measurements of plants. We outline technical challenges encountered during the development and showcase initial measurements of different plant tissues.
The cuticle is a natural polymeric membrane that covers the surface of aerial organs (including fruit) of terrestrial plants. The cuticle membrane mainly consists of cutins, waxes, and polysaccharides and serves as a protective barrier against water movement, adverse environmental conditions and the invasion of pathogens. Fulfilling its barrier function requires an intact cuticle. During fruit development, the cuticle is stretched and heavily stressed as the fruits grow exponentially in phases. In apple fruit, cutin and wax are synthesized constitutively throughout development. The newly synthesized cutin is deposited on the cuticle’s inner side. This results in a gradient of age and strain in the cuticle from outside (older, more strained) to inside (younger, less strained). Wax is deposited mainly within the cutin network and fixes the elastic strain of the cutin network. Studies indicated that wax concentration among the different layers of the cutin also varies with more wax in the outer cuticular proper and less in the inner cuticle layer. As a result, the cuticle of mature apple fruits exhibits a complex micromechanical structure. Characterizing this structure poses challenges that cannot be overcome using conventional tensile testing methods. In this study, we employed a Brillouin scattering setup to investigate the micromechanical structure of the cuticle.
Plant cell walls are highly complex structures, which are adaptable to various environmental stresses. While many biochemical pathways have been discovered, cellular stress indicators are widely unknown. Here we demonstrate a label-free optical setup, that can map both mechanical properties and chemical composition in biological samples. We measured changes in mechanical stiffness and chemical response of rose leaf cells due to inoculation of the fungal disease Diplocarpon rosae. With this we are able to image fungal growth in a dynamical and high-resolution manner.
The arising 3D printing technologies open new possibilities for the production of optical devices, e.g. of optical waveguides. Using two-photon polymerization (2PP), arbitrary three-dimensional structures with resolution below the diffraction limit can be manufactured, thus allowing for new and versatile applications in photonics. Recent demonstration of phononic metamaterials using 2PP fabrication rely on homogeneous mechanical properties of the photopolymer. Thus, the state of polymerization can be used as process parameter to develop adaptable phononic crystals. Here we demonstrate an optical setup that combines Brillouin- and Raman-scattering experiments to measure the mechanical and chemical characteristics with respect to the polymerization state.
Hyperspectral imaging is a key technology for monitoring agricultural crops and vegetation. It can be used for health estimation and the early detection of disease symptoms in plants. This can help to reduce the use of pesticides by allowing targeted and early intervention. Cost-efficient hyperspectral imaging systems are necessary to meet the increasing demand for monitoring techniques for agricultural products. These systems usually suffer from sub-optimal image quality. Here we present a digital aberration correction for hyperspectral image data.
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