Combined Stresses in Plants: Physiological, Molecular, and Biochemical Aspects

110 I. M. Ahmed et al.

Oliver et al. 2011 ). In barley root, the metabolite profiling was analyzed in response
to drought (Sicher et al. 2012 ), and combined stress of high temperature and drought
(Rizhsky et al. 2004 ). Metabolome changes were also reported in cultivated barleys
in response to salt stress (Widodo et al. 2009 , Wu et al. 2013 ). In these context, sev-
eral categories of genes which respond to the stress could be differentiated (Fig. 5.3):
genes that encode protective but metabolically inactive polypeptides, such as dehy-
drins, chaperones (including proteases), genes for metabolic pathways leading to the
synthesis of low-molecular osmolytes which increase stress tolerance, radical scaven-
gers, or compounds with both functions, and regulatory proteins such as transcription
factors, protein kinases, phospholipase C, or 14-3-3 proteins.
Most of the drought- and salt-tolerance genes belong to large gene families with
high-sequence similarity distribute in a genome, which brings difficulty in identify-
ing the specific locus for a specific function. More recently, genomic technologies
have provided high-throughput integrated approaches (Bartels and Sunkar 2005 ) to
investigate global gene expression responses not only to drought but also to other

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Fig. 5.3 Stress tolerance factors produced in adaptive responses of a barley plant to drought and
salinity stress. CBF C-repeat binding factor, MYB myeloblastosis oncogenes, LEA late embryo-
genesis abundant, INA ice nucleation-active protein, MYC v-myc avian myelocytomatosis viral
oncogene homolog, bZIP basic leucine zipper, MAPK mitogen-activated protein kinase, MAPKK
mitogen-activated protein kinase kinase, HVA1 ABA-inducible protein PHV A1, WRKY c-terminal
wrky domain, NAC nascent polypeptide-associated complex protein