Role of abscisic acid in legumes under abiotic stress - Legumes Under Environmental Stress: Yield, Improvement and Adaptations - page 154

( lec2 ) - have excessive starch accumulation but almost
no storage protein or lipid accumulation (Harada, 2001).
The DE-ETIOLATED 1 ( DET1 )/ FUS2 , FUS3 and LEC1
loci are also negative regulators of some light responses
that are enhanced by sugars, such as anthocyanin
accumulation, such that the (derepressed) mutant
seeds are abnormally pigmented. This effect is greatly
enhanced by some of the abi mutations. Additional
interactions between ABA and light signalling during
seed development are reflected in the dependence on
DET1, FUS3 and LEC1 for adequate accumulation of
ABI3 protein (Gampala et al., 2001). Taken together,
these results suggest that the regulators ABI3, ABI4,
ABI5, DET1, FUS3 and LEC1 may all participate in the
ABA signalling cascade under different environ-
mental conditions. These regulators may also participate
in sugar accumulation during seed development.
Furthermore, exogenous ABA applied to grains leads to
the accumulation of carbohydrates, thus accelerating
the filling process. In addition, Grappin et al. (2000)
reported that the application of fluridone reduced the
activity of enzymes associated with starch synthesis. In
soybean experiments, where stress was of short dura-
tion, the application of ABA immediately increased
carbohydrate amounts at the flowering period in shoots
of the ABA-treated plants as compared to controls; the
difference in shoots disappeared at harvest because of
increased carbohydrate remobilization (21%) to the
seed in the ABA-treated plants (Travaglia et al., 2009).
This effect has been also reported in rice (Yang et al.,
2004) and by Moreno (2009) who found that ABA
stimulates carbon translocation from source to sink.
Thus, these studies confirm the participation of ABA in
promoting source-to-sink transport of assimilates dur-
ing the stage of seed filling. Additionally, treatment with
ABA did not affect the quality of seeds, an important
characteristic since seed quality is one of the key aspects
for farming success. On the other hand, ABA mediates
amino acid and proline accumulation. Khadri et al.
(2006) showed that pretreatment of plants with ABA
prevented or reduced amino acid and proline produc-
tion under salt stress. In this regard, Trotel-Aziz et al.
(2000) have proposed that proline accumulated under
adverse environmental conditions is rapidly reduced
when those conditions are alleviated. The results of
Khadri et al. (2006) suggest that in common bean ABA
exogenously applied has a central function in the plant's
adaptive response to salt stress.

10.8 aBa mediating the expression
of abiotic stress-responsive genes

ABA can modify plant cells' transcriptome by upregulat-
ing or downregulating several genes, termed ABA-
responsive genes. Such genes encode transcription factors
and enzymes, hydrophilic proteins, etc. (Yamaguchi-
Shinozaki & Shinozaki, 2006). ABA-responsive genes or
their products are believed to orchestrate various cellular
and physiological responses to ABA. Consistent with this
idea, numerous studies have illustrated the ABA-
responsive transcriptome from some species (Cuming
et al., 2007; Richardt et al., 2010). In this regard, Seki et al.
(2002a) identified 299 ABA-responsive genes, 155 of
which were upregulated under drought stress conditions.
ABA treatment of guard cells revealed 64 differentially
expressing genes (Leonhardt et al., 2004). Using microar-
ray techniques, Seki et al. (2002b), Kreps et al. (2002) and
Kawaguchi et al. (2004) identified 27 genes that were
induced under water deficit stress; they were classified
into six functional categories: metabolism, transport,
signalling, transcription, hydrophilic proteins and
unknown proteins (Bray, 2004). Therefore, the activation
of regulatory components for stress perception leads to
the production of effector molecules that are directly
involved in alleviating stress. Regulatory components are
represented by transcription factors and signal transduc-
tion components such as kinases and phosphatases
(Yamaguchi-Shinozaki & Shinozaki, 2006). There is a
group of stress-responsive genes whose expression is
ABA-independent; these encode the DREB1 (cold) and
DREB2 (salt, dehydration) families of proteins (Liu et al.,
1998; Nakashima et al., 2000). The ABA-dependent
pathway is mainly associated with a subfamily of basic
leucine zipper (bZIP) class transcription factors called
ABRE-binding factors, or ABFs (Choi et al., 2000; Uno
et al., 2000). Other transcription factors involved in the
abiotic stress response have been reported (Yamaguchi-
Shinozaki & Shinozaki, 2006).
Transcriptome analysis under water-deficit stress has
also been performed in various other species, like Populus
trichocarpa and Populus euphratica, maize, chickpea and
wheat (Brosche et al., 2005; Andjelkovic & Thompson,
2006; Mantri et al., 2007; Talame et al., 2007). In the
model legume Lotus japonicus , a gene encoding for beta-
glucosidase, which hydrolyses glycosides of abscisic acid
to generate free ABA, was highly induced during water
deficit (Betti et al., 2012). Overexpression of this enzyme