ABA Regulation of the Cold Stress Response in Plants - Abscisic Acid: Metabolism, Transport and Signaling - page 335

perception in land plants, based on the observation that plants lacking the mem-
brane protein cyclic nucleotide gated calcium channel (CNGC) showed con-
stitutively high levels of Ca 2 + influx and impaired thermoperception in a moss
and in Arabidopsis (Finka et al. 2012 ). Moreover, a homologue of the synaptic
Ca 2 + -binding protein synaptotagmin (SYT1), which is a calcium sensor that can
prevent Ca 2 + -dependent membrane, damages in Arabidopsis protoplasts under
freezing conditions (Yamazaki et al. 2008 ). These results suggest the central
role of cytosolic calcium to trigger cold signalling. Ca 2 + may function through
calmodulin or Ca 2 + sensors to modulate the activation of downstream calcium-
dependent protein kinases (CPKs). Calcineurin B-like proteins (CBLs), one kind
of calcium sensors, were also shown to regulate expression of the CBF genes,
based on the observations that overexpression of CBL1 resulted in reduced
freezing tolerance, whereas cbl1 null mutants showed increased cold-induced
expression of stress genes and enhanced freezing tolerance (Albrecht et al.
2003 ; Cheong et al. 2003 ).
Several CBL-interacting protein kinases (CIPKs) and CPKs have been impli-
cated in the responses to ABA, cold, and high-salt stress. In Arabidopsis , the
expression of CIPK3 is strongly induced by cold stress and ABA treatment, but
not by drought stress. In addition, the expression of various cold-induced marker
genes is all significantly delayed in a cipk3 mutant, and the induction of ABA-
responsive genes is also significantly inhibited (Kim et al. 2003 ). Therefore,
CIPK3 may function as a cross talk node between signalling pathways for ABA,
cold, and other abiotic stresses. It has also been suggested that CIPK1 is a conver-
gence point for the ABA-dependent and ABA-independent stress responses. For
example, CIPK1 can interact with CBL1 and CBL9, resulting in the formation of
CBL1/CIPK1 and CBL9/CIPK1 complexes that mediate the ABA-independent
and ABA-dependent responses, respectively, during osmotic stress (D'Angelo
et al. 2006 ). Rice OsCDPK7 is a cold- and salt-inducible gene, and overexpression
of OsCDPK7 confers cold and salt/drought tolerance on rice plants (Abbasi et al.
2004 ). Collectively, these results indicate a central role for calcium in sensing and
transducing the cold and ABA signals.
17.6 ABA and ROS Under Cold Stress
The induction of ROS-scavenging systems is common to many stress pathways
including ABA and cold stress (Fujita et al. 2006 ). The roles of ROS in cold
stress are considered in two ways. On the one hand, excessive ROS levels are
toxic and can lead to lipid peroxidation, and ultimately, to oxidative stress. On
the other hand, increased ROS levels can also play a benefit signalling role and
activate scavenging enzyme systems to eliminate excess ROS in plants sub-
jected to low temperatures. Numerous studies have shown that ROS-scavenging
enzymes such as superoxide dismutase (SOD), ascorbate peroxidise (APX),
catalase (CAT), and glutathione peroxidise (GPX) are required for protection