Polyphenols - Fruit Ripening: Physiology, Signalling and Genomics - page 168

Chinese bayberry and red-skinned pear
(Takos et al. , 2006a; Feng et al. , 2010; Niu
et al. , 2010).

position in fruits during ripening (Ojeda et
al. , 2002; Castellarin et al. , 2007; Ollé et
al. , 2011). In particular, under water defi cit
stimulating hydroxylation and metho-
xylation of the fl avonoid B-ring, the
anthocyanin profi le of water-stressed ber-
ries shifts towards purple/blue pigments
(Castellarin et al. , 2007). Conversely, the
fl avan-3-ol and fl avonol composition of
grape berry is only slightly affected by
water stress (Kennedy et al. , 2002; Ojeda et
al. , 2002; Castellarin et al. , 2007).

Hormones
In strawberry, the central role of abscisic
acid (ABA) was recently demonstrated
directly, as RNA interference-mediated
silencing of an ABA receptor gene led to
the inhibition of anthocyanin production
(Jia et al. , 2011). Grape berries treated with
ABA at the onset of ripening showed an
increased accumulation of anthocyanins
associated with increased expression of
the anthocyanin structural genes tested and
of the regulatory gene VvMYBA1 (Jeong et
al. , 2004). By contrast, in grape, there is
little effect of ABA on PA synthesis and
gene expression (Koyama et al. , 2010;
Lacampagne et al. , 2010).
Auxins appear to have the opposite
effect to ABA, delaying anthocyanin
accumulation in grape berries (Davies et al. ,
1997). The treatment of berries at veraison
with the auxin 2,4-dichlorophenoxyacetic
acid reduced the anthocyanin level in
berries. Similar results were seen when
naphthaleneacetic acid was sprayed on to
Cabernet Sauvignon berries at veraison
(Jeong et al. , 2004).
Ethephon, an analogue of ethylene,
increases stilbene accumulation when
sprayed on grapevine (Belhadj et al. ,
2008a), and, in groundnuts, stilbene bio-
synthetic genes are induced by ethylene
(Chung et al. , 2001). Methyl jasmonate was
shown to stimulate stilbene and antho-
cyanin production by grapevine cell
culture (Belhadj et al. , 2008b). Spraying
with the ethylene-releasing compound
2-chloroethylphosphonic acid enhanced
anthocyanin accumulation and expression
of several structural genes in grape (El-
Kereamy et al. , 2003), but ethylene did not
affect expression of VvMYBA transcription
factors (Tipa-Umphon et al. , 2007).

Biotic stress
Phenolics are said to be involved in
defence against biotic stresses. Induction of
the stilbene pathway after pathogen
infection is one of the main responses
described and has been particularly
studied on grapevine, where accumulation
of stilbenes is signifi cantly induced after
infection with powdery mildew (Fung et
al. , 2008), downy mildew (Adrian et al. ,
1997) or grey mould (Langcake and
McCarthy, 1979). Bilberry infection by a
fungal endophyte ( Paraphaeosphaeria sp.)
and a pathogen ( Botrytis cinerea ) resulted
in increased concentrations of fl avan-3-ols
and quercetin derivatives (Koskimäki et al. ,
2009). Applications of elicitors like
benzothiadiazole and methyl jasmonate
have been described as promoting the
accumulation of stilbenes, anthocyanins,
fl avonols and PAs of grape skins (Iriti et al. ,
2004, 2005; Ruiz-Garcia et al. , 2012).
In strawberry fruits, benzothiadiazole
induced the accumulation of fl avan-3-ols,
anthocyanins and kaempferol derivatives
(Hukkanen et al. , 2007).

9.4.2 Changes during development

Fruit polyphenol composition varies
throughout growth and ripening. In most
cases, unripe fruits have higher levels of
phenolic compounds than ripe fruits. PAs
are in general synthesized during the early
fruit development stages, for example in
grape berries (Kennedy et al. , 2000),
strawberries (Carbone et al. , 2009) and

Hydric status
Water stress can greatly increase the
content and alter the anthocyanin com-