Genetic and molecular responses of legumes in a changing environment - Legumes Under Environmental Stress: Yield, Improvement and Adaptations - page 208

pigments like xanthophylls are produced in greater
quantities to ensure the availability of antioxidants for
the plant (González-Cruz & Pastenes, 2012). Other
secondary metabolites like flavonoids are produced to
help the plant survive cold stress (Petrussa et al., 2013).
Keeping in view the diversity of responses produced,
a number of genes are positively regulated in response
to a cold stress. Among these the principal genes include
the cold regulated ( cor ), low temperature induced ( lti )
and cold-inducible ( kin ) genes (Mantri et al., 2012;
Bakht et al., 2013; Pang et al., 2013). The cold resistance
mechanisms are not always dependent upon the ABA
pathway to exert their effects. ABA has been observed
to be transiently increased under low temperature stress
conditions. However, the levels of endogenous ABA are

not significant enough to produce a stress response
alone. The DRE and rd29 act as response elements in
case of a cold-induced stress (Pirzadah et al., 2014).
C-repeat elements (CRTs) and low temperature respon-
sive elements have been observed to interact with the
DRE in exerting their cold neutralizing properties in
many plants (Humphreys & Gasior, 2013). As in case of
drought, the DREB elements involved belong to the
DREB 2 class (Nayak et al., 2009). They are responsible
for inducing specific gene expression of elements that can
respond to cold. Moreover, transgenic plants containing
the cor , lti and kin genes have been observed to develop
significant tolerance to the freezing temperatures
(Theocharis et al., 2012; Bakht et al., 2013; Castonguay
et al., 2013; Pang et al., 2013). Another group of response
elements known as sensitivity to freezing (sfr) have
been implicated in interacting with the DRE and its pro-
moter regions. Two more genes, HOS1 and HOS2 , are
considered to be negative regulators of signals generated
in response to freeze stress (Ishitani et al., 1997). Cold
shock domain proteins (CSDPs) are involved in the
induction of freezing tolerance in leguminous plants
(Theocharis et al., 2012).
An increase in intracellular calcium levels has been
observed in response to a sudden drop in temperature. It
has been hypothesized that Ca 2+ plays an important role
in signal transduction mechanisms. These genetic and
molecular changes in the plant are responsible for
inducing cold tolerance in the susceptible plants. Proline,
an amino acid derivative, is involved in osmoprotection
and reduction of reactive oxygen species. Many genes
( cor , lti , kin , erd ) produce proteins that act as dehydrins
(Arumingtyas et al., 2013). Some of these dehydrins have
been positively correlated with tolerability to cold stress by
increasing membrane stability and cryoprotection. Among
the various osmolytes stored by legumes to survive cold

Table 12.3 Genetic bases for induction of tolerance to
environmental stress factors.

Stress factor Genes regulated

Salt stress HVA, SOD, catalase, Ast, HSP, SSP, Akt, ITR, TIP

Osmotic stress CDPK/CPK, CBL, MAPK, PKS, HOG, SPK, ABRE

Cold stress HOS, RAV, CBF, LOS, ABRE, Rd, Cor

Abbreviations: ABRE: ABA-responsive element; Akt/KAT, K + selective
ion channels; Ast, aspartate aminotransferase; CBF, C-repeat binding
factors; CBL, calcineurin B-like; CDPK/CPK, calcium-dependent protein
kinases; Cor, cold regulated genes; H/LOS, high/low expression of
osmotically responsive genes; HOG, high-osmolarity glycerol response;
HSP, heat-shock proteins; HVA, late embryogenesis abundant protein
gene (barley derived); ITR, myo -inositol transporter; MAPK,
mitogen-associated protein kinases; PKS, plant type III polyketide
synthase; RAV, related to ABI3/VP (transcription factors); Rd,
dehydration responsive elements; SOD, superoxide dismutase; SPK,
calcium-dependent seed-specific protein kinase; SSP, salt shock
proteins; TIP, tonoplast intrinsic protein.

Low
temperature

Transcription
modi cation

Photosynthesis
regulation

Cytoplasmic
Ca ++

ROS
scavenging

Plant

Membrane
stabilization

Cryoprotectants

Cold
tolerance

Figure 12.3 Cellular changes involved in developing cold tolerance in legumes.