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under stress to enhancement of the barrier properties of cell walls and consequent
inhibition of the entry of toxic ions into the internal tissues of roots.
In a joint pretreatment of wheat seedlings with SA and fluridone there was
observed an inhibition of cell wall lignification (Tables
1
,
2
), resulting in the
prevention of SA-induced inhibition of cadmium entrance into root tissues
(Table
3
), which, in turn, indicates the involvement of endogenous ABA in the
regulation of this protective mechanism by salicylic acid.
Therefore, for the first time inhibition analysis allowed to obtain experimental
evidence indicating in favor of the key role of endogenous ABA in the regulation
of SA-induced protective mechanisms making an important contribution to the
development of resistance of wheat
seedlings exposed to the toxic ions of
cadmium.
3.2 Sodium Chloride Salinity
Salinity caused by increased content of soluble salts in soil is one of the most
widely spread abiotic stress factors resulting in significant inhibition of plant
growth and decline in crop productivity, with sodium chloride being the most
detrimental (Munns and Tester
2008
; Cambrolle et al.
2011
).
The decline in cell growth processes is due to dehydration resulting from
osmotic effect of salts accumulating in the root zone and due to toxic effect of
sodium and chloride accumulation in the plant tissues causing great damaging
effect on the most important physiological processes and cell membrane integrity
(Munns and Tester
2008
; Nazar et al.
2011
). It is necessary to emphasize that
plants are able to develop a broad spectrum of protective reactions aimed on
diminishing the detrimental effects of salinity (Flowers
2004
; Munns and Tester
2008
). Stress hormone ABA, whose fast and significant accumulation is a char-
acteristic response to salinity, makes an important contribution to protective
reactions (Rock et al.
2010
; Shakirova et al.
2010
). At the same time attention is
drawn to the similarity in the several of the plant responses to sodium chloride
salinity and cadmium stress.
We have previously reported that pretreatment with SA did not prevent, but
significantly reduced the salinity-induced transient accumulation of ABA in wheat
plants, suggesting that the maintenance of increased content of ABA in SA-pre-
treated plants plays an important regulatory role in the manifestation of the pro-
tective effect of SA (Shakirova
2007
). To estimate the importance of maintaining
increased level of endogenous ABA in the manifestation of the protective effect of
SA on wheat seedlings under salt stress there was also used fluridone in the
experiments. Like cadmium, salinity stress also caused a rapid reversible accu-
mulation of ABA in untreated plants, whereas in pre-treated with SA seedlings
increase of ABA level was much lower. This is reflected in the fact that SA-
pretreated wheat seedlings are characterized by lower levels of stress-induced
accumulation of WGA (Fig.
10
a), as well as of osmoprotectant proline (Fig.
10
b),
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