Salicylic Acid-Mediated Abiotic Stress Tolerance - Salicylic Acid: Plant Growth and Development - page 192

2.3.2 Role of Exogenous and Endogenous Salicylic Acid During Salt
Stress
It has been shown that SA could provide multiple stress tolerance, namely drought,
chilling and heat to bean and tomato plants when applied in aqueous solution or as
soil drenches (Senaratna et al. 2000 ). Similarly, soaking wheat seeds in SA
solution provided protection against not only drought, but also salinity stress
(Hamada and Al-Hakimi 2001 ). Long-term incubation of tomato plants in low
concentration of salicylic acid enabled plants to tolerate salt stress caused by
100 mM NaCl (Tari et al. 2002 ).The application of exogenous SA appeared to
induce a pre-adaptive response to salt stress in barley plants, leading to the pro-
tection of photosynthetic pigments and the maintenance of membrane integrity,
which was reflected in an improvement in plant growth (El-Tayeb 2005 ). Fur-
thermore, foliar spray with SA significantly decreased the lipid peroxidation
induced by NaCl and improved plant growth. This alleviation of NaCl toxicity was
related to a decrease in the Na content and increases in K and Mg contents,
and also to increase the activity of SOD, CAT, glutathione peroxidase (GPX)
and dehydroascorbate reductase and in the ascorbate and glutathione contents
(He and Zhu 2009 ). The stress-induced accumulation of active oxygen species and,
therefore, the level of SOD and peroxidase (POD) activity in the roots of young
wheat seedlings pre-treated with SA were significantly lowered than in untreated
plants, indicating that these enzymes contribute to the protective effect of SA on
plants under conditions of salination (Sakhabutdinova et al. 2004 ). SA pre-treat-
ment also provided protection against salinity due to the increased activity of
aldose reductase, GST and APX enzymes, to improve photosynthetic performance
and to the accumulation of osmolytes, such as sugars, sugar alcohol or proline in
tomato plants (Tari et al. 2002 , 2004 , 2010 ; Szepesi et al. 2005 , 2008a , b ; Gémes
et al. 2008 ) and in Salvia officinalis L. (Sahar et al. 2011 ). A high ABA level was
also maintained in wheat seedlings treated with SA. The SA-induced increase in
ABA might contribute to the pre-adaptation of plants to stress, since ABA is
known to have a key role in inducing the synthesis of a range of stress proteins
ensuring the development of antistress reactions, for example, the maintenance of
proline accumulation (Sakhabutdinova et al. 2004 ).
By contrast, SA may promote the formation of ROS in the photosynthetic
tissues of Arabidopsis plants during salt stress and osmotic stress. Recent results
also suggest that the decrease of intracellular K + concentration and K + /Na + ratio is
a common phenomenonin triggering programmed cell death by lethal concentra-
tions of salicylic acid and NaCl (Poór et al. 2012a ). The widespread necrotic
lesions observed on the shoots of wild-type plants after NaCl or mannitol treat-
ments were not exhibited by NahG plants incapable of SA accumulation (Borsani
et al. 2001 ). Investigations on Arabidopsis transgenic lines and mutants, including
snc1 (with a high level of SA), NahG (with a low level of SA), npr1-1 (with SA
signalling blockage) andsnc1/NahG (expression of nahG in the snc1 background),
and on wild type plants showed that SA deficit or signalling blockage in Ara-
bidopsis plants was favourable to salt adaptation, while a high accumulation of SA