Salicylic Acid-Mediated Abiotic Stress Tolerance - Salicylic Acid: Plant Growth and Development - page 205

SA could alleviate the detrimental effects of hypoxia stress on plant growth and of
oxidative stress in the leaves of Malus robusta Rehd.by enhancing the antioxidant
defence system (Bai et al. 2009 ).
3 Salicylic Acid In Relation to Other Plant Hormones
Various hormones involved in plant defence mechanisms cross talk with SA where
both negative and positive interactions have been reported. Endogenous ABA
levels rise in several species when they are exposed to stress conditions (Veisz et al.
1996 ; Lee et al. 1997 ; Janowiak et al. 2002 ). The modes of cross talk between ABA
and SA are the subject of intensive research. SA treatment caused ABA accumu-
lation in the leaves of Hordeum spontaneum (Bandurska and Stroinski 2005 ) and
tomato plants (Szepesi et al. 2009 ). It was also found that SA treatment caused the
accumulation of both ABA and indoleacetic acid (IAA), but did not influence the
cytokinin (CK) content, while diminishing the changes in phytohormone levels in
wheat seedlings under salinity (Sakhabutdinova et al. 2003 ). In Panicum virgatum,
moderate water stress treatment decreased the endogenous SA contents, accom-
panied by an increase in the ABA content (Yasuda et al. 2008 ). Salt stress caused an
increase in the ABA and jasmonate (JA) content in Iris hexagona, while the levels
of IAA and SA declined (Wang et al. 2001 ). In salt-stressed soybean, the endog-
enous gibberellic acid (GA 3 ) and free SA contents decreased, while a significant
increase was observed in the endogenous ABA and JA contents (Hamayun et al.
2010 ). Furthermore, both heat and SA treatment caused a rapid increase in the level
of ABA, although this declined sharply, shortly afterwards (Wang et al. 2005 ).The
addition of SA or even that of ethylene (ET) precursor 1-aminocyclopropane-1-
carboxylic acid (ACC) or ABA to plants may also protect them from heat-induced
oxidative damage. It was demonstrated that the inhibition of ABA biosynthesis
caused a less serious loss of thermotolerance than the inhibition of SA biosynthesis
(Liu et al. 2006 ). In addition, the ethylene-insensitive mutant etr-1, the ABA-
insensitive mutant abi-1 and a transgenic line expressing nahG showed increased
susceptibility to heat (Larkindale and Knight 2002 ). Although, it was suggested that
the induction of several heat shock proteins (HSPs) by ABA may be one mechanism
whereby it confers thermotolerance (Pareek et al. 1998 ), it was later reported that
ABA and SA are involved in acquired thermotolerance separately from heat shock
protein induction (Larkindale et al. 2005 ).
An SA analogue, benzothiadiazole S-methylester (BTH), repressed NaCl-
induced ABA biosynthesis, while ABA or NaCl treatment antagonized BTH-
induced resistance to Pseudomonas syringae in Arabidopsis (Yasuda et al. 2008 ).
ABA signalling was also positively correlated with the susceptibility of Arabidopsis
to P. syringae (de Torres-Zabala et al. 2007 ). These results suggested an antagonistic
interaction between these two hormones, probably as a result of sharing common
intermediaries in the signalling pathway. Responses to both biotic and abiotic
stresses require significant amounts of energy for gene expression and metabolic