carotenoid production [8, 9]. Amyloplasts are starch-storing plastids found in seed, roots and tubers (wheat, maize, potato, cassava)
and in general contain relatively low levels of carotenoids, mainly
xanthophylls (i.e., lutein, zeaxanthin, and violaxanthin)
[8, 10]. Etioplasts are developed in dark-grown plants and usually
contain small amounts of photosynthetic carotenoids, primarily
lutein and violaxanthin, as well as the chlorophyll precursor protochlorophyllide [11]. Chloroplasts are the typical plastids found in
green photosynthetic tissues (leaves and immature fruits) while the
synthesis of carotenoids is believed to occur in their envelop and in
the thylakoid membrane [12–14]. The formation of a lipoprotein
complex between chlorophyll and carotenoids allows the accumulation of large amounts of carotenoids in the chloroplasts. Lutein,
β-carotene, violaxanthin and neoxanthin are the most abundant
carotenoids in chloroplast [14]. Finally, chromoplast are specialized
plastid with large capacity to synthetize and accumulate massive
amounts of carotenoids, and then providing particular coloration
to specialized tissue, such as flowers or fruits [9, 15, 16].
Chromoplasts in most tissues contain plastoglobuli, which are
lipid body structures accumulating carotenoids. Moreover, other
types of carotenoid-accumulating structures may also be found
inside the chromoplast, which determine their classification as
globular, tubular, fibrillary, crystalline, and membranous [9, 15].
Globular chromoplasts are characterized by abundant plastoglobule, and are characteristics of many fruits such as mango (Mangifera indica), yellow papaya (Carica papaya), tomato (Solanum
lycopersicum) [17], saffron stigma [18] and citrus [19, 20]. Globular
chromoplasts usually contain lutein, β-cryptoxanthin, and
β-carotene as major carotenoids [21]. Crystalline chromoplasts
typically accumulate large amount of lycopene and β-carotene, as
red/orange crystals and are abundant in tomato [17] and carrot
(Daucus carota) [22]. Interestingly, while all-trans-β-carotene is
deposited as crystalline, its cis isomers are in globular chromoplasts
[23]. Membranous chromoplasts are typified by the large amount
of condensed multi-layer membrane structures, as shown in orange
cauliflower [24]. Fibrillar chromoplasts contain spindle-shaped
structures with numerous tubules arranged in bundles, as in yellow
papaya [21]. In general, fruits with low carotenoid content do not
differentiate plastids of define any structure, whereas fruit accumulating uncommon carotenoids develop uncommon structures. The
high heterogeneous nature or plasticity of the carotenoidsequestering substructures in the chromoplasts is determinant of
the diversity and the levels of carotenoids accumulating in different
plant tissues.
The diversity in coloration and in the carotenoid content and
composition in the peel and pulp of citrus fruits, provide an excellent system for the morphological and structural analysis of plastid
diversity into the chromoplast and the relation with the carotenoid
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Joanna Lado et al.
and in general contain relatively low levels of carotenoids, mainly
xanthophylls (i.e., lutein, zeaxanthin, and violaxanthin)
[8, 10]. Etioplasts are developed in dark-grown plants and usually
contain small amounts of photosynthetic carotenoids, primarily
lutein and violaxanthin, as well as the chlorophyll precursor protochlorophyllide [11]. Chloroplasts are the typical plastids found in
green photosynthetic tissues (leaves and immature fruits) while the
synthesis of carotenoids is believed to occur in their envelop and in
the thylakoid membrane [12–14]. The formation of a lipoprotein
complex between chlorophyll and carotenoids allows the accumulation of large amounts of carotenoids in the chloroplasts. Lutein,
β-carotene, violaxanthin and neoxanthin are the most abundant
carotenoids in chloroplast [14]. Finally, chromoplast are specialized
plastid with large capacity to synthetize and accumulate massive
amounts of carotenoids, and then providing particular coloration
to specialized tissue, such as flowers or fruits [9, 15, 16].
Chromoplasts in most tissues contain plastoglobuli, which are
lipid body structures accumulating carotenoids. Moreover, other
types of carotenoid-accumulating structures may also be found
inside the chromoplast, which determine their classification as
globular, tubular, fibrillary, crystalline, and membranous [9, 15].
Globular chromoplasts are characterized by abundant plastoglobule, and are characteristics of many fruits such as mango (Mangifera indica), yellow papaya (Carica papaya), tomato (Solanum
lycopersicum) [17], saffron stigma [18] and citrus [19, 20]. Globular
chromoplasts usually contain lutein, β-cryptoxanthin, and
β-carotene as major carotenoids [21]. Crystalline chromoplasts
typically accumulate large amount of lycopene and β-carotene, as
red/orange crystals and are abundant in tomato [17] and carrot
(Daucus carota) [22]. Interestingly, while all-trans-β-carotene is
deposited as crystalline, its cis isomers are in globular chromoplasts
[23]. Membranous chromoplasts are typified by the large amount
of condensed multi-layer membrane structures, as shown in orange
cauliflower [24]. Fibrillar chromoplasts contain spindle-shaped
structures with numerous tubules arranged in bundles, as in yellow
papaya [21]. In general, fruits with low carotenoid content do not
differentiate plastids of define any structure, whereas fruit accumulating uncommon carotenoids develop uncommon structures. The
high heterogeneous nature or plasticity of the carotenoidsequestering substructures in the chromoplasts is determinant of
the diversity and the levels of carotenoids accumulating in different
plant tissues.
The diversity in coloration and in the carotenoid content and
composition in the peel and pulp of citrus fruits, provide an excellent system for the morphological and structural analysis of plastid
diversity into the chromoplast and the relation with the carotenoid
236
Joanna Lado et al.