Salicylic Acid: An Update on Biosynthesis and Action in Plant Response to Water Deficit and Performance Under Drought - Salicylic Acid: Plant Growth and Development - page 8

2012 ; Saruhan et al. 2012 ). Plant resistance to water deficit may be the result of
two strategies responsible for surviving the stress: strategy of avoiding dehydration
and strategy of tolerance dehydration (Levitt 1980 ). In the strategy of avoiding
dehydration an important role is played by osmotic adjustment involving the
accumulation of osmolytes, which lower cell water potential to prevent dehydra-
tion (Farooq et al. 2010 ). The protective action of SA during water deficit in many
plants was demonstrated by the accumulation of different osmolytes such as
sugars, sugar alcohol and proline, responsible for osmotic adjustment (Szepsi et al.
2005 ; Umebese et al. 2009 ; Farooq et al. 2010 , Bidabadi et al. 2012 ). The
improvement of leaf water status under water deficit through preventing dehy-
dration of leaves as a result of osmotic adjustment as well the restriction of
reduction stomatal conductance by the application of SA plays a positive role in
maintaining photosynthetic activity and reducing damage. Closure of the stomatal
aperture prevents water loss, but it also limits the uptake of carbon dioxide and
influences on the decrease of photosynthetic rate, which exerts a harmful effect on
the growth and productivity of plants (Pinheiro and Chaves 2011 ). Moreover, the
limitation of CO 2 assimilation may affect the accumulation of ROS and H 2 O 2
because the reductive power (NADPH) developed in the light phase of photo-
synthesis is not utilized in the phase, independent of light (Jaspers and Kangasjärvi
2010 ; Miller et al. 2010 ; Gill and Tuteja 2010 ). Plant pre-treatment with 0.5 mM
SA, one day before water deficit imposition increased sensitivity to drought
because it caused a decrease of stomatal conductance and net rate of photosyn-
thesis and increased damage of cell membranes (Németh et al. 2002 ). Moreover,
Borsani et al. ( 2001 ) found that SA application enhanced the generation of ROS in
leaves of Arabidopsis thaliana and increased development of stress symptoms
under water deficit conditions. However, SA reduced the damage of cell mem-
branes in cucumber, rice, wheat, barley, Satureja hortensis, banana and maize,
exposed to water deficit (Bandurska and Stroi´ski 2005 ; Baninasab 2010 ; Farooq
et al. 2010 ; Bidabadi et al. 2012 ; Saruhan et al. 2012 ; Yazdanpanah et al. 2011 ).
SA ameliorates the water deficit induced injuries by increasing proline content
which protects cell membranes against the harmful effects of ROS (Bandurska and
Stroinski 2005 ; Baninasab 2010 ). The alleviating effect of SA on cell membrane
functioning under water deficit conditions can also be associated with the acti-
vation of the synthesis of soluble phenolics and anthocyanins, which protect leaf
tissue from oxidative damage (Farooq et al. 2010 ). The application of exogenous
SA may also alleviate the damaging effect of water deficit by up-regulation the
activity of antioxidant system. The increased activity of antioxidant enzymes with
simultaneous reduction in H 2 O 2 production and lipid peroxidation level was noted
under water deficit conditions in plants pre-treated with SA, at various concen-
trations through root, seed soaking or foliar spray (Horváth et al. 2007 ; Korkmaz
et al. 2007 ; Daneshmand et al. 2009 , Farooq et al. 2010 ; Kadioglu et al. 2011 ;
Bidabadi et al. 2012 ; Saruhan et al. 2012 ).