Genetic and molecular responses of legumes in a changing environment - Legumes Under Environmental Stress: Yield, Improvement and Adaptations - page 205

ultimately, help in neutralizing the stress conditions
(Patel et al., 2012). The overexpression of myo -inositol
and IAA in response to salt stress has been studied in a
number of legumes including chickpea and cacao
(Fraire-Velázquez & Balderas-Hernández 2013; Kaur
et al., 2013; Li et al., 2013). In this way, the genetically
controlled cellular responses assist in responding to a
physical constraint through the involvement of a wide
range of tissues and mediators.

prime importance. MAPKs have been identified in a
number of plants, including legumes, and are consid-
ered pivotal in rendering tolerance against the abiotic
stress factors including salt and water constraints. A
MAPK isolated from Pisum sativum (PsMAPK) has been
identified as possessing significant homology with yeast
proteins involved in glycerol accumulation (Ahmad
et al., 2012). The increased levels of glycerol in the plant
body can help in controlling and regulating the overall
water and osmolyte levels. Moreover, plant serine/thre-
onine kinases display a high sequence homology with
DBF-2, glycogen synthase kinase (GSK) and calcineurin
genes that are involved in providing tolerance against
salt and osmotic imbalances in the growth environment
in legumes (Akio Kido et al., 2011; Wang et al., 2013).

12.4.4 regulatory elements
The stress response elements or mediators encoded by
specific regulator genes help the plant to respond to a
stress stimulus by altering various steps in signal trans-
duction pathways or by affecting the effector molecules/
pathways. Ultimately they are linked to providing
assistance in salt and osmotic regulation in plants. They
act as modulators of transcription or translation and are
classified on the basis of the interaction between the
transcription factors and the promoter regions of stress
response genes. They either specifically or non-specifi-
cally respond to the stress conditions. Abscisic acid is
one of the main chemical players in this regard. It may
be activated and regulated by a variety of different ele-
ments. Dehydration responsive protein, rd22, for
example is activated in the case of salt and osmotic stress
conditions (Wang et al., 2012). Interaction between the
rd22 gene and the corresponding regulatory elements,
both cis and trans regulators, results in the transcrip-
tional activation of a number of pathways. A series of
genetic interactions, including those with the Ca 2+ -
dependent protein kinases and DNA binding proteins,
are responsible for the efficient response to stress factors.
Apart from ABA, a number of other genetic factors
might be involved in regulation of responses to salt and
osmotic stress in leguminous plants. The Salt Overly
Sensitive ( SOS ) genes encodes the salt response ele-
ments that are mediated by K + exchange across the
plasma membrane (Hill et al., 2013). Regulation of these
genes helps in controlling the transmembrane osmotic
transport in plant cells. Moreover, the dehydration
response element (DRE) proteins are involved in
binding to the ethylene responsive elements and are,
hence, involved in controlling the response to salt and
osmotic stress (Mizoi et al., 2013).
Among the plant regulatory elements possessing
the ability to directly control the stress responses,
mitogen-activated protein kinases (MAPKs) are of

12.5 Genetic and molecular responses
to drought

An important stress factor that significantly affects the
yield of legumes is insufficiency of water to maintain
growth and homeostasis. Legumes respond to drought in
a similar manner as they respond to saline stress, and
usually the same genetic and molecular players are
involved. This is mainly because both physical constraints
tend to induce similar changes in the plant body, i.e.
increased turgor pressure, changes in ionic concentra-
tions and alterations in cellular morphology. Abscisic
acid, proline, glycine betaine and sugars are the main
drought response elements (Allario et al., 2012; Z. Yang
et al., 2012).
General mechanisms similar to those observed with
other environmental restraints, are followed in case of
drought stress. Figure 12.2 manifests the cascade of
events occurring in leguminous plants in response to a
drought stress. A number of osmosensors, which
function to interpret changes in the water levels avail-
able to the plant, have been identified. Of significant
importance among these are the ATHK type osmosen-
sors (Kumar et al., 2013b). Once the signal has been
detected, a series of signalling molecules (proteins) are
activated. MAPK, phosphatases and phospholipases are
the most important enzymes in this respect. These then
interact with the effector cells to produce specific
changes in the plant body (Table 12.2).
Physiologically, legumes respond to a drought threat
by adopting either an escape or an avoidance