Vitamins in Fleshy Fruits - Fruit Ripening: Physiology, Signalling and Genomics - page 134

carotenoid biosynthetic genes encoding
GGPS, PSY and CRTISO is specifi cally
upregulated in the fruit to sustain the
carotenoid accumulation. Remarkably,
similar upregulation of carotenoid gene
expression during fruit ripening has been
found in other fruits, not only in pepper
(Hugueney et al. , 1996), another
Solanaceae species, but also in satsuma
mandarin (Ikoma et al. , 2001), papaya
(Devitt et al. , 2010), palm fruit (Tranbarger
et al. , 2011) and gac (Hyun et al. , 2012). In
papaya, a chromoplast-specifi c lycopene
cyclase expressed during fruit ripening
leads to the formation of the provitamin A
E -carotene and E -cryptoxanthin in the
yellow-fl eshed fruit, whilst a mutation
reducing its functionality is probably
responsible for lycopene accumulation in
the red-fl eshed cultivars (Devitt et al. ,
2010). Conversely in tomato, which
normally accumulates lycopene, up-
regulation of a lycopene E -cyclase gene in
the Beta ( B ) mutant results in E -carotene
accumulation in fruits (Ronen et al. , 2000).
Ripening is a complex process. In
climacteric fruits, ethylene plays a key role
in initiating and coordinating ripening-
associated changes, including carotenoid
accumulation. The strong upregulation of
the PSY and PDS genes during tomato fruit
ripening are under the control of ethylene,
whilst regulation of the cyclase involved in
E -carotene formation is ethylene in-
dependent (Alba et al. , 2005). Light and
temperature are among the main factors
regulating carotenoid accumulation in the
fruit (Gautier et al. , 2008). The regulation
of carotenoid biosynthesis by light has
been well studied thanks to the large
number of tomato mutants affected in the
level and type of carotenoids in the fruit.
Both phytochromes and cryptochromes are
involved (Alba et al. , 2000; Fraser et al. ,
2009). In addition, the involvement of the
light signal transduction components in
the regulation of carotenoid accumulation
in tomato fruit has raised considerable
interest in recent years (Lieberman et al. ,
2004; Liu et al. , 2004; Wang et al. , 2008;
Enfi ssi et al. , 2010). Both carotenoid gene
transcription and plastid biogenesis are

affected when this pathway is deregulated,
leading to enhanced carotenoid accumu-
lation in the fruit, together with increased
levels of ascorbate and other phyto-
nutrients (Enfi ssi et al. , 2010). Increased
plastid number due to enhanced plastid
division has also been linked to the
increased accumulation of carotenoids in a
tomato ABA-defi cient mutant (Galpaz et
al. , 2008), illustrating the close relation-
ships between carotenoid and phyto-
hormone biosynthesis and regulation.

8.3 Vitamin E Biosynthesis and
Regulation in Fleshy Fruits

Vitamin E comprises several lipid-soluble
compounds, termed tocochromanols, com-
posed of a polar chromanol head group and
a lipophilic polyprenyl side chain (Mène-
Saffrané and DellaPenna, 2009). Toco-
pherols have a saturated phytil-derived
side chain, whilst tocotrienols have an
unsaturated geranylgeranyl-derived side
chain. Tocopherol and tocotrienol each
consist of four isoforms ( D , E , J and G ),
which are differentiated by the position
and number of the methyl groups on the
chromanol ring. Tocochromanols are only
found in photosynthetic organisms, and in
plants are found exclusively in plastids.
The most abundant tocochromanol found
in plants is tocopherol, whilst tocotrienol is
less widespread and is found mostly in
monocot seeds and in fruits.

8.3.1 Role of vitamin E in humans and plants

Vitamin E defi ciency is responsible for
several human pathologies, but clinical
evidence for vitamin E defi ciencies is rare,
except in conditions in which the
metabolism of vitamin E is disturbed
(FAO/WHO, 2004). Vitamin E can be
obtained from plant and animal sources. In
humans, as a lipid-soluble antioxidant, its
major role is to protect polyunsaturated
fatty acids and other cellular components
(DNA, proteins) from oxidation by free
radicals. Like provitamin A, vitamin E