ABA Metabolism and Signaling in Fleshy Fruits - Abscisic Acid: Metabolism, Transport and Signaling - page 264

of ripening (Coombe and Hale 1973 ; Coombe 1976 ; Inaba et al. 1976 ; Scienza
et al. 1978 ; Palejwala et al. 1985 ; Cawthon and Morris 1982 ; Davies et al. 1997 ).
Endogenous ABA levels are minimal 1 week prior to veraison and the application
of exogenous ABA to grape berries can markedly accelerate the ripening process,
including the rapid accumulation of sugars and anthocyanins (Coombe and Hale
1973 ; Inaba et al. 1976 ; Palejwala et al. 1985 ; Kataoka et al. 1982 ; Matsushima
et al. 1989 ; Jeong et al. 2004 ). It is now widely accepted that ABA is a key factor
in the regulation of diverse events during grape berry ripening including colora-
tion, sugar accumulation, acid decline and flesh softening (Yu et al. 2006 ; Wheeler
et al. 2009 ; Gambetta et al. 2010 ; Koyama et al. 2010 ; Giribaldi et al. 2010 ; Gagn￩
et al. 2011 ; Nicolas et al. 2014 ).
In addition to studies in grape berries, considerable progress has been made
recently in understanding the role of ABA in other non-climacteric fruits and envi-
ronmental factors that alter ABA levels. For example, water deficit treated straw-
berry ( Fragaria x ananassa ) fruits have higher ABA levels, as well as reduced berry
size, altered sugar/acid ratios, which affect the taste and levels of health-related
compounds (phenolic and antioxidant compounds, Terry et al. 2007 ). Indeed, there
is considerable physiological and molecular evidence to suggest an important role
for ABA in the regulation of strawberry fruit ripening: (1) exogenous application of
ABA or dimethyl sulfoxide (DMSO, an ABA biosynthesis accelerator) significantly
promotes fruit ripening, whereas fluridone (an ABA biosynthesis inhibitor) markedly
inhibits fruit ripening; (2) silencing of FaNCED1 , a key ABA biosynthesis gene in
strawberry fruit, results in a reduction in endogenous ABA levels and delayed rip-
ening; (3) exogenous ABA rescues the uncolored phenotype of FaNCED1 -RNAi
fruits, in which FaNCED1 expression has been suppressed using an RNA interfer-
ence (RNAi) strategy (Jia et al. 2011 ). The importance of ABA in strawberry fruit
development was also confirmed by silencing of the ʲ -glucosidase gene FaBG3 ,
which is involved in ABA synthesis, since the encoded protein hydrolyzes an ABA
glucose ester to release active ABA (Li et al. 2013 ). These findings together with
other studies indicate that ABA as a key regulator of strawberry fruit ripening (Kano
and Asahira 1981 ; Manning 1994 ; Perkins-Veazie 1995 ; Jiang and Joyce 2003 ; Terry
et al. 2007 ; Jia et al. 2011 ; Li et al. 2013 ). However, it should be noted that in addi-
tion to its role in grape berry and strawberry ripening, ABA has been found to influ-
ence diverse processes of characteristics in other fleshy fruit species, including the
development of astringency in persimmon ( Diospyros kaki ) fruit (Akagi et al. 2012 ),
citrus peel development (Romero et al. 2012 ), and cherry ( Prunus species) fruit mat-
uration (Ren et al. 2010 ).
In addition to non-climacteric fruits, it is also now clear that ABA can regulate
fruit development and ripening in climacteric fruits. For example, it was reported
that application of ABA to detached tomato fruits substantially advances the onset
of ripening (Mizrahi et al. 1975 ), which raises that possibility that ABA may also
act to promote tomato fruit ripening in vivo. A role for ABA regulating tomato
fruit development was indicated by studies of an ABA deficient tomato mutant
( high - pigment 3 ) that accumulates 30 % more carotenoids, has an increased num-
ber of fruit plastids and a higher lycopene content (Galpaz et al. 2008 ) than wild