Chapter 18
Visualization of Carotenoid-Storage Structures in Fruits
by Transmission Electron Microscopy
Joanna Lado, Jaime Zacarias, Marı ´a Jesu ´ s Rodrigo, and Lorenzo Zacarı ´as
Abstract
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.
Key words Carotenoids, Citrus fruits, Chloroplast, Chromoplast, Plastids, Plastoglobuli, Transmission electron microscopy
1 Introduction
Carotenoids are a group of tetraterpenoid pigments synthetized in
the plastids of plants and in some algae, fungi, and bacteria [1].
They are responsible for the attractive coloration of flowers, fruits,
and other tissues in many plant species and also play critical roles in
human nutrition and health [2–4].
Accumulation of carotenoids in plants is the result of a fine
balance between biosynthesis, degradation, and their accumulation
in specialized structures, the plastid [5]. During plant development
and tissue differentiation, there are substantial changes in the number of plastids and in their structure and functionality that may
determine the capacity for carotenoid storage. Various types of
plastids can be identified in plant cells, such as proplastids, amyloplasts, etioplasts, chloroplasts, and chromoplasts [6, 7]. All these
types of plastids, except proplastids, possess the capacity for
Manuel Rodrı ´guez-Concepcio ´ n and Ralf Welsch (eds.), Plant and Food Carotenoids: Methods and Protocols,
Methods in Molecular Biology, vol. 2083, https://doi.org/10.1007/978-1-4939-9952-1_18,
© Springer Science+Business Media, LLC, part of Springer Nature 2020
235
Visualization of Carotenoid-Storage Structures in Fruits
by Transmission Electron Microscopy
Joanna Lado, Jaime Zacarias, Marı ´a Jesu ´ s Rodrigo, and Lorenzo Zacarı ´as
Abstract
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.
Key words Carotenoids, Citrus fruits, Chloroplast, Chromoplast, Plastids, Plastoglobuli, Transmission electron microscopy
1 Introduction
Carotenoids are a group of tetraterpenoid pigments synthetized in
the plastids of plants and in some algae, fungi, and bacteria [1].
They are responsible for the attractive coloration of flowers, fruits,
and other tissues in many plant species and also play critical roles in
human nutrition and health [2–4].
Accumulation of carotenoids in plants is the result of a fine
balance between biosynthesis, degradation, and their accumulation
in specialized structures, the plastid [5]. During plant development
and tissue differentiation, there are substantial changes in the number of plastids and in their structure and functionality that may
determine the capacity for carotenoid storage. Various types of
plastids can be identified in plant cells, such as proplastids, amyloplasts, etioplasts, chloroplasts, and chromoplasts [6, 7]. All these
types of plastids, except proplastids, possess the capacity for
Manuel Rodrı ´guez-Concepcio ´ n and Ralf Welsch (eds.), Plant and Food Carotenoids: Methods and Protocols,
Methods in Molecular Biology, vol. 2083, https://doi.org/10.1007/978-1-4939-9952-1_18,
© Springer Science+Business Media, LLC, part of Springer Nature 2020
235