osmotic stress (Rahnama et al. 2010). Damage to photosynthetic pigments, stomatal
aperture, etc. under salinity leads to overproduction of reactive oxygen species like
H 2 O 2 , O 2
À (Saed-Moucheshi et al. 2014). ROS leads to the degradation of proteins,
inactivation of enzymes, etc., thereby leading to cellular damages and even leads to
cell death. Reduced shoot and root weight and yield due to decline in photosynthesis
under salinity have been well documented in many plants like strawberry (Yaghubi
et al. 2016), turfgrasses (Sekar 2016), tomato (Rivero et al. 2014), etc. Under ionic
stress, more influx of Na
+ occurs in place of K
+ ion and Cl
À decreases NO 3
À
acceptance that interrupts the normal ion balance and hampers the major functions
performed by the plant, majorly photosynthesis. The expulsion of Na
+ from leaves
results in salinity tolerance as reported in rice (Haq et al. 2010), barley (Shavrukov
et al. 2010), etc. Plants differ greatly in showing resistance to salinity due to the
difference in their internal organisations. After understanding the mechanism underlying salinity tolerance, researches have started exploring the solution to this problem. In this regard, they identified phytohormones as a major signalling molecule in
plants playing a crucial role in stress responses (Sharma et al. 2005; Shaterian et al.
2005). Javid et al. (2011) presented an extensive review describing the role of
different phytohormones in alleviating salinity stress. The phytohormones reported
by them include abscisic acid, indoleacetic acid, cytokinins, gibberellic acid,
brassinosteroids, jasmonates, salicylic acid, etc. After going through the literature,
we found salicylic acid and jasmonic acid to be more significant in alleviating
salinity stress. A lot of reports are available where jasmonic acid (Qiu et al. 2014;
Ahmad et al. 2018) and salicylic acid (Idrees et al. 2012; Liu et al. 2016) when
exogenously supplied to plants results in reduced damage by salinity.
9.3
Role of Phytohormones in Plants
Plants have the inherent capability to sense and respond against these adverse stress
conditions usually by modulating their internal cellular metabolic processes. Such
modulation in metabolic processes is possible due to the presence of signalling
molecules in plants that are able to sense the stress factors prevailing in the plant’s
environment and activate the signal transduction pathway that signals the plant to
modify its physiological and biochemical processes in order to cope up with the
stress conditions. In view of this, phytohormone acts as a major signalling molecule
that perceives signals from the plant’s niche and produces required modifications in
cellular processes such as changes in the activity of ion-channels, protein
modifications, protein degradation and gene expression. Auxin (IAA), Cytokinins
(CKs), Abscisic acid (ABA), Ethylene (ET) and Gibberellins (GAs) are the major
classical phytohormones and recently, Salicylic acid (SA) and Jasmonates (JAs) are
also included in the list of phytohormones (Fig. 9.3). Recent researches have shown
the potential of salicylic acid (SA), jasmonic acid (JA) and its derivative methyl
jasmonate (MeJ) to reduce the negative impact of abiotic stress in plants and
enhances the stress tolerance capacity of a plant under abiotic stresses (Walia et al.
9 Phytohormones: A Promising Alternative in Boosting Salinity Stress Tolerance in. . .
283
aperture, etc. under salinity leads to overproduction of reactive oxygen species like
H 2 O 2 , O 2
À (Saed-Moucheshi et al. 2014). ROS leads to the degradation of proteins,
inactivation of enzymes, etc., thereby leading to cellular damages and even leads to
cell death. Reduced shoot and root weight and yield due to decline in photosynthesis
under salinity have been well documented in many plants like strawberry (Yaghubi
et al. 2016), turfgrasses (Sekar 2016), tomato (Rivero et al. 2014), etc. Under ionic
stress, more influx of Na
+ occurs in place of K
+ ion and Cl
À decreases NO 3
À
acceptance that interrupts the normal ion balance and hampers the major functions
performed by the plant, majorly photosynthesis. The expulsion of Na
+ from leaves
results in salinity tolerance as reported in rice (Haq et al. 2010), barley (Shavrukov
et al. 2010), etc. Plants differ greatly in showing resistance to salinity due to the
difference in their internal organisations. After understanding the mechanism underlying salinity tolerance, researches have started exploring the solution to this problem. In this regard, they identified phytohormones as a major signalling molecule in
plants playing a crucial role in stress responses (Sharma et al. 2005; Shaterian et al.
2005). Javid et al. (2011) presented an extensive review describing the role of
different phytohormones in alleviating salinity stress. The phytohormones reported
by them include abscisic acid, indoleacetic acid, cytokinins, gibberellic acid,
brassinosteroids, jasmonates, salicylic acid, etc. After going through the literature,
we found salicylic acid and jasmonic acid to be more significant in alleviating
salinity stress. A lot of reports are available where jasmonic acid (Qiu et al. 2014;
Ahmad et al. 2018) and salicylic acid (Idrees et al. 2012; Liu et al. 2016) when
exogenously supplied to plants results in reduced damage by salinity.
9.3
Role of Phytohormones in Plants
Plants have the inherent capability to sense and respond against these adverse stress
conditions usually by modulating their internal cellular metabolic processes. Such
modulation in metabolic processes is possible due to the presence of signalling
molecules in plants that are able to sense the stress factors prevailing in the plant’s
environment and activate the signal transduction pathway that signals the plant to
modify its physiological and biochemical processes in order to cope up with the
stress conditions. In view of this, phytohormone acts as a major signalling molecule
that perceives signals from the plant’s niche and produces required modifications in
cellular processes such as changes in the activity of ion-channels, protein
modifications, protein degradation and gene expression. Auxin (IAA), Cytokinins
(CKs), Abscisic acid (ABA), Ethylene (ET) and Gibberellins (GAs) are the major
classical phytohormones and recently, Salicylic acid (SA) and Jasmonates (JAs) are
also included in the list of phytohormones (Fig. 9.3). Recent researches have shown
the potential of salicylic acid (SA), jasmonic acid (JA) and its derivative methyl
jasmonate (MeJ) to reduce the negative impact of abiotic stress in plants and
enhances the stress tolerance capacity of a plant under abiotic stresses (Walia et al.
9 Phytohormones: A Promising Alternative in Boosting Salinity Stress Tolerance in. . .
283