Other Hormonal Signals during Ripening - Fruit Ripening: Physiology, Signalling and Genomics - page 216

later in development may indicate a
possible role in delaying ripening, but
there is no direct evidence that they
perform this function during 'normal'
development.

accumulation was inhibited (Fan et al. ,
1998). Ripening of blackberries, considered
to be non-climacteric fruit, was enhanced
by MeJA treatment as measured by antho-
cyanin content, soluble solids content and
acid levels (Wang et al. , 2008). As well as
effects on ethylene and polyamine
synthesis, jasmonate application to fruit on
the plant, detached fruit or culture cells
can infl uence the synthesis of secondary
metabolites, such as anthocyanins, caroten-
oids, chlorophyll, sesquiterpines, tannins
and stilbenes (Pérez et al. , 1993; Kondo et
al. , 2000; Wang et al. , 2008; D'Onofrio et
al. , 2009). From the above, it can be seen
that, although jasmonates infl uence
ripening in some cases, clear proof of a role
for endogenous jasmonates in the control
of fl eshy fruit ripening is still lacking.

12.2.6 Jasmonates

Jasmonates are involved in a number of
processes but are most commonly
associated with plant defence responses
(Browse, 2009), and the evidence for their
being involved in the control of fruit
ripening is not extensive. Endogenous
levels of jasmonates have been measured
only in the fruits of a small number of
species and in some reports with a lack of
labelled standards. In experiments
involving apples and tomatoes, jasmonic
acid levels were higher than methyl
jasmonate (MeJA) levels and both peaked
in concentration just before the climacteric
ethylene burst, which suggests a possible
involvement in ripening in these fruits
(Fan et al. , 1998). In other reports where
the levels of various forms of jasmonates
were measured in non-climacteric fruits
such as grape skins (Kondo and Fukuda,
2001), and in the fl esh of sweet cherry
(Kondo et al. , 2000) and strawberry
(Gansser et al. , 1997), jasmonate levels
were higher early in development and
decreased to be low at ripening with little
or no increase during ripening. The
reported effects of jasmonate application to
fruits are mixed. In both climacteric and
non-climacteric fruits, there is evidence of
a jasmonate-induced ethylene production
(Fan et al. , 1998; Mukkun and Singh,
2009), but reduced ethylene production
has also been reported (Ziosi et al. , 2008).
In peach, exogenous jasmonates have been
reported to enhance the rate of ripening
(Janoudi and Flore, 2003) or delay it (Ziosi
et al. , 2008). When ripening was delayed in
jasmonate-treated fruit, ethylene bio-
synthesis was repressed and overall
polyamine levels were increased (Ziosi et
al. , 2009). Curiously, in mature green
tomato discs, ethylene production was
increased by MeJA treatment but lycopene

12.2.7 Polyamines (PAs)

The biosynthesis of PAs, such as
putrescine, spermidine and spermine, is
well understood in plants (Liu et al. , 2006).
In developing fruits, putrescine is the most
abundant species, spermine is usually the
least abundant (e.g. Kushad et al. , 1988;
Shiozaki et al. , 2000; Mehta et al. , 2002). In
a range of species, the levels of free PAs are
high early in fruit development, at around
the time of rapid cell division and
expansion (Kushad et al. , 1988: Shiozaki et
al. , 2000). In a number of fruits, the levels
of free PAs decline after this early stage to
be low during ripening (Mehta et al. , 2002;
Valero et al. , 2002; Liu et al. , 2006),
suggestive of a possible role as a ripening
inhibitor. There are some exceptions to this
pattern of PA accumulation, however, as
increases at around the time of ripening
have been observed, although their
signifi cance has not been explored fully
(Martínez-Madrid et al. , 1996; Valero et al. ,
2002). Microarray analysis in grape berries
has indicated that PA biosynthetic gene
expression increases at around the time of
ripening initiation (Deluc et al. , 2007;
Fortes et al. , 2011).
A number of reports indicate that PA
application (or higher endogenous levels)