Other Hormonal Signals during Ripening - Fruit Ripening: Physiology, Signalling and Genomics - page 217

resulted in a delay of one or more ripening-
related parameters (Dibble et al. , 1988;
Liu et al. , 2006). This may be due partly to
the apparently antagonistic interaction
between PAs and ethylene (Harpaz-Saad et
al. , 2012). As with some other hormones,
such as jasmonates, more work is required
to fi rmly establish a role for PAs in the
control of ripening.

auxin application (Coombe and Hale, 1973;
Kondo et al. , 2004), and there are
numerous other examples to be found in
the literature (some have been discussed
above).
New technical processes, such as
microarray analyses, have been useful in
studying the wide-ranging changes in gene
transcript level during fruit development
(e.g. apple, Costa et al. , 2010; grape, Deluc
et al. , 2007; Fortes et al. , 2011; tomato,
Jones et al. , 2002; watermelon, Wechter et
al. , 2008). Using this type of approach a
number of examples of cross-talk between
signalling pathways (e.g. between ABA and
auxin, and ethylene and auxin) have also
been revealed following hormone appli-
cation (e.g. grape, Koyama et al. , 2010;
peach, Trainotti et al. , 2007). The sig-
nifi cant levels of cross-talk likely to occur
between hormone pathways during fruit
ripening has important implications for the
interpretation of experiments where a
hormone, or an inhibitor of its action, is
applied, or where the levels of a hormone
or the ability to perceive a hormone is
altered through transgenesis.
In addition to the cross-talk between
hormones during fruit development, it
should also be noted that there is cross-talk
between seeds and fl esh, and that their
maturation process appears to be linked.
An example of this and the involvement of
various hormones in this process can be
found in peach, where auxin, cytokinins
and GAs are proposed to be important
earlier in development, while ABA and
ethylene seem to be involved later (Bonghi
et al. , 2011).

12.2.8 Salicylic acid

Salicylic acid and methyl salicylic acid are
involved in signalling in plants, par-
ticularly in the induction of defence and
stress responses (Bari and Jones, 2009).
There is a good deal of information
regarding the effects of salicylic acid
application on fruit postharvest, where
treatment generally delays senescence
(Asghari and Aghdam, 2010). A limited
number of reports in grapes and tomatoes
suggest that salicylic acid application may
delay, or slow, ripening-associated changes
(Li et al. , 1992; Kraeva et al. , 1998; Wang et
al. , 2011). However, there is very little data
regarding the accumulation of salicylic
acid during fruit development and so a role
for salicylic acid during ripening is still
unproven.

12.3 Cross-talk during Fruit Ripening

There is an increasing amount of infor-
mation about cross-talk between different
signalling pathways during plant develop-
ment, and all of the hormones and some
sugars seem to be involved (Finkelstein
and Gibson, 2002; Rolland et al. , 2002;
Rashotte et al. , 2005; Weiss and Ori, 2007;
Teale et al. , 2008; Zhang et al. , 2009b).
Evidence for direct interactions in fruit is
limited, but it is increasingly obvious that
cross-talk occurs in fruit and is involved in
fruit ripening. At the simplest level, a
number of studies have shown that the
application of one hormone to a fruit
induces the synthesis of another; for
example, ethylene evolution in pre-
ripening grapes and pears was increased by

12.4 Summary

Despite the economic and social
importance of fruit and fruit products and
their health benefi ts, there are still large
gaps in our understanding of fruit ripening.
Clearly, hormones other than ethylene
are involved in the ripening of both
climacteric and non-climacteric fruits.
Much of the current evidence regarding the
action of various hormones is indirect,