Visualization of β-carotene and starch granules in plant cells using CARS and SHG microscopy

Journal article, 2010

Information on the content and bioavailability of provitamin A carotenoids, such as beta-carotene, in plant foods is of great interest due to the widespread vitamin A deficiency in developing countries. While the amount of beta-carotene can readily be quantified with analytical techniques, there is limited information on beta-carotene morphology in native plant materials. Here, we introduce nonlinear microscopy for three-dimensional, label-free imaging of carotenoids in fresh and thermally treated plant tissues, providing quantitative information at single-aggregate level and detailed insight into their distribution. Carotenoids in orange-fleshed sweet potato (OFSP), carrot, and mango were visualized by coherent anti-Stokes Raman scattering (CARS) microscopy and, in the case of OFSP, related to the plant-matrix morphology by simultaneous second-harmonic generation (SHG) microscopy of starch granules. Sizes, shapes, densities, and location of different types of carotenoid bodies were quantified. While OFSP and carrot showed heterogeneous rod-shaped bodies with high carotenoid densities indicated by higher CARS signals, the carotenoid-filled lipid droplets in mango appeared as homogeneous low-density aggregates of rounded shape. In addition, beta-carotene densities and morphologies in OFSP were studied after thermal processing, showing that the bodies remain intact despite significant changes of the surrounding starch granules.