Plastids are cell organelles that, beside other functions, have the capability to store carotenoids in specialized structures, which may vary among the different plant species, tissues or according to the carotenoid complement. Fruits are an important source of carotenoids, and during ripening, chloroplasts differentiate into chromoplasts that are able to accumulate large amounts of carotenoids, rendering then the characteristic fruit coloration. Whereas lycopene or β-carotene may accumulate as crystal in the chromoplasts of some fruit, other xanthophyll-accumulating fruits differentiate plastoglobuli as a preferred system to enhance carotenoids stability and storage. Visualization of plastid ultrastructure and their transformation during ripening or in fruit of contrasting coloration are fundamental objectives within carotenoids research in fruits. Therefore, in this chapter, we describe a protocol for the visualization and analysis of plastid ultrastructure by transmission electron microscopy (TEM), specially designed and adapted to fruit tissues.
Keywords: Carotenoids; Chloroplast; Chromoplast; Citrus fruits; Plastids; Plastoglobuli; Transmission electron microscopy.