Salicylic acid prevents the damaging action of stress factors on wheat plants

Abstract

We investigated the effect of salicylic acid (SA) on plant resist-ance to environmental stress factors. Treatment of wheat plants with 0.05 mM SA increased the level of cell division within the apical meristem of seedling roots which caused an increase in plant growth. Phytohormones are known to play a key role in plant growth regulation. It was found that the SA treat-ment caused accumulation of both ABA and IAA in wheat seedlings. How-ever, the SA treatment did not influence cytokinin content. We suppose, that the protective and growth promoting effects of SA are due to the phenomenon described above. The SA treatment reduced the damaging action of salinity and water deficit on seedling growth and accelerated a restoration of growth processes.Treatment with SA essentially diminished the alteration of phyto-hormones levels in wheat seedlings under salinity and water deficit. The SA treatment prevented the decrease in IAA and cytokinin content completely which reduced stress-induced inhibition of plant growth. Also, high ABA levels were maintained in SA treated wheat seedlings which provided the development of antistress reactions, for example, maintenance of proline ac-cumulation. Thus protective SA action includes the development of antistress programs and acceleration of normalization of growth processes after removal stress factors.

Full text

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SALICYLIC ACID PREVENTS THE DAMAGING ACTION
OF STRESS FACTORS ON WHEAT PLANTS
A. R. Sakhabutdinova, D. R. Fatkhutdinova, M. V. Bezrukova, F. M. Shakirova*
Institute of Biochemistry and Genetics, Ufa Scientific Centre Russian Academy of
Sciences, 69 pr. Octyabrya, 450054, Ufa, Russia
Summary. We investigated the effect of salicylic acid (SA) on plant resist-
ance to environmental stress factors. Treatment of wheat plants with 0.05mM
SA increased the level of cell division within the apical meristem of seedling
roots which caused an increase in plant growth. Phytohormones are known
to play a key role in plant growth regulation. It was found that the SA treat-
ment caused accumulation of both ABA and IAA in wheat seedlings. How-
ever, the SA treatment did not influence cytokinin content. We suppose, that
the protective and growth promoting effects of SA are due to the phenomenon
described above. The SA treatment reduced the damaging action of salinity
and water deficit on seedling growth and accelerated a restoration of growth
processes.Treatment with SA essentially diminished the alteration of phyto-
hormones levels in wheat seedlings under salinity and water deficit. The SA
treatment prevented the decrease in IAA and cytokinin content completely
which reduced stress-induced inhibition of plant growth. Also, high ABA
levels were maintained in SA treated wheat seedlings which provided the
development of antistress reactions, for example, maintenance of proline ac-
cumulation. Thus protective SA action includes the development of antistress
programs and acceleration of normalization of growth processes after removal
stress factors.
Keywords: Salicylic acid, salinity, water deficit, abscisic acid, indoleacetic acid,
cytokinins
Abbreviations: SA – salicylic acid; ABA – abscisic acid; IAA – indoleacetic
acid; PEG – polyethylene glycol
*Corresponding author, e-mail: shakirova@anrb.ru
BULG. J. PLANT PHYSIOL., SPECIAL ISSUE 2003, 314–319

315
Introduction
Salicylic acid is (SA) is an endogenous growth regulator of phenolic nature, which
participates in the regulation of physiological processes in plants. SA, for example,
plays a role of natural inductor of thermogenesis in Arum lily, induces flowering in a
range of plants, controls ion uptake by roots and stomatal conductivity (Raskin, 1992).
There are experimental data indicating participation of SA in signal regulation of gene
expression in the course of leaf senescence in Arabidopsis (Morris et al., 2000) More-
over SA might serve as a regulator of gravitropism (Medvedev and Markova, 1991),
inhibition of fruit ripening (Srivastava and Dwivedi, 2000) and of other processes.
During the last 20 years this substance drew the attention of researchers due to
its ability to induce systemic acquired resistance (SAR) in plants to different pathogens,
which is manifested in the appearance of pathogenesis related proteins (PR), while
SA is considered to serve as a signal in the induction of expression of these genes
(Metraux, 2001)
At the same time at present considerable interest has been aroused by the ability
of SA to produce a protective effect on plants under the action of stress factors of dif-
ferent abiotic nature. Thus convincing data have been obtained concerning the SA-
induced increase in the resistance of wheat seedlings to salinity (Shakirova and Bez-
rukova, 1997), and water deficit (Bezrukova et al., 2001), of tomato and bean plants
to low and high temperature (Senaratna et al., 2000), as well as the injurious action
of heavy metals on rice plants (Mishra and Choudhuri, 1999).
The important role of SA in protecting is probably played by its ability to induce
expression of genes coding not only for PR-proteins but also for example the extensin
gene in Arabidopsis plants (Merkouropoulos et al., 1999). There are data about SA
induced synthesis of heat shock proteins in tobacco plants (Burkhanova et al., 1999)
and accumulation of wheat lectins (Shakirova and Bezrukova, 1997), fast activation
of 48-kD protein kinase in suspension cell culture of tobacco at osmotic stress (Miko-
lajczyk et al., 2000). This suggests the involvement of SA in realization of different
antistress programs. However, the way of signal regulation of plant resistance to un-
favorable factors of environment induced by SA are still not clear.
The aim of the present work was to study the character of changes in hormonal
systems induced by SA in wheat plants under stress conditions.
Materials and methods
The object of investigation were 4-d-old plants of Triticum aestivum L. cv. Saratov-
skaya 29. Treatment of wheat seedlings with a concentration of SA optimal for seed-
ling growth (0.05 mM) have been used. For this purpose after washing of seeds with
tap water they were soaked in 0.05 mM SA solution for 3h and then dried in a desic-
Salicylic acid prevents the damaging action of stress factors on wheat plants

316
cator over CaCl2. Then, after excision of endosperm 3-d-old seedlings were transferred
into glasses, containing 2% sucrose, incubated for 24h for withdrawal of wounding
stress (Shakirova et al., 1993), and then 4-d-old seedlings were transferred to a mixture
of 2% sucrose and NaCl or PEG at different concentration. Plants incubated on 2%
sucrose solution served as a control in all these experiments.
Growth was estimated on the basis of changes in fresh weight of 30–50 wheat
seedlings.
Assay of free ABA, IAA and cytokinin was carried out with the help of rabbit
antibodies specific to each class of phytohormone and secondary antirabbit antibodies
labeled with peroxidase. The procedure of succession of phytohormone extraction and
immunoassay has been described earlier (Kudoyarova et al., 1990; Shakirova et al.,
1994). The data on cytokinin measurement presents three samples of zeatin derivatives
immunoreactive to antiserum raised against zeatin riboside (Kudoyarova et al., 1990).
Proline content was determined according to the method of Bates (Bates et al., 1973).
The experiments were repeated at least three times.
Results and discussion
Dynamics of phytohormone level in plants under salinity and water deficit
Unfavorable environmental factors lead to sharp changes in the balance of phytohor-
mones associated with not only accumulation of ABA, but also with a decline in the
level of growth activating hormones such as IAA and cytokinins (Zholkevich and Pus-
tovoytova, 1993; Jackson, 1997) As can be seen from Fig. 1a and 1b, incubation of
seedlings on the medium containing 2% NaCl or 18% PEG resulted in transitory ac-
0
0.5
1
1.5
2
2.5
3
Proline, µM / f. w.
Control
1%NaCl
2%NaCl
4%NaCl
SA
SA+1%NaCl
SA+2%NaCl
SA+3%NaCl
a
0
0.5
1
1.5
2
2.5
Proline, µM / f. w.
Control
10% PEG
15% PEG
SA
SA+10% PEG
SA+15% PEG
b
Fig. 1. The effects of seed presowing treatment with SA and salinity (a), water deficit (b) on proline
content in 4-d-old wheat seedlings. 4-d-old seedlings were subjected to the influence of NaCl and PEG
for 24 h
A. R. Sakhabutdinova et al.

317
cumulation of ABA and a progressive decline in cytokinins as well as small decrease
in the level of IAA.
Presowing treatment with SA (Fig. 2c and 2d) completely prevented salinity-in-
duced and water deficit-induced declines in the concentration of IAA and cytokinins
in seedlings and reduced accumulation of ABA, which might be a prerequisite for ac-
celeration of growth resumption of wheat seedlings after withdrawal of stressor from
the medium. Alongside this, maintaining a comparatively high level of ABA under
stress conditions in plants pretreated with SA is of primary importance from our point
of view since ABA might serve an important regulating factor in SA-induced unspe-
cific plant resistance. Since proline is one of the important components of defence
reactions of plants to salinity (Kuznetsov and Shevyakova, 1999), it might be expected
that pretreatment with SA contributes to accumulation of this amino acid under stress
through maintaining an enhanced level of ABA in seedlings.
0
50
100
150
200
250
% of control
a-SA
0
50
100
150
200
% of control
ABA
IAA
Cytokinins
b-SA
0
50
100
150
200
1.5 5 7
Time, h
% of control
c+SA
0
50
100
150
200
3 7 11 24
Time, h
% of control
d+SA
Fig. 2. The effects of salinity (a, c) or water deficit (b, d) on phytohormonal balance of wheat
seedlings pretreated with 0.05mM SA. 4-d-old seedlings were subjected to the influence of
2%NaCl and 18%PEG for 7h.
Salicylic acid prevents the damaging action of stress factors on wheat plants

318
The effect of SA on concentration of proline under salinity and water deficit
Salinity and water deficit induces accumulation of proline in seedlings (Fig. 1). These
data suggests that proline is an important component in the spectra of SA-induced
ABA-mediated protective reactions of wheat plants in response to salinity and water
deficit, which contribute to a reduction of injurious effects of stress factors and ac-
celeration of restoration processes during the period after action of stress, which might
be a manifestation of the protective action of SA on wheat plants.
The effect of presowing treatment with SA on growth of seedlings
subjected to salinity and water deficit
Salinity and water deficit result in a decline in metabolic activity of plant cells, which
should be inevitably reflected in inhibition of their growth. Action of 2% NaCl or
18% PEG on 4-d-old wheat seedlings led to noticeable and almost equal extent of
inhibition of growth of plants both treated and not treated with SA, however, since
by the moment of the start of experiment seedlings pretreated with SA had greater
biomass (72mg per seedling) compared to control (64 mg per seedling), even after
the action of 2% NaCl or 18% PEG this characteristic was still higher (68 mg per
seedling) than in control not treated with salt and PEG plants (66mg per seedling).
Consequently, although presowing treatment with SA does not prevent negative
effects of 2% NaCl and water deficit on growth of plants, it nevertheless, in general,
noticeably reduces its injurious effect as compared to control plants.
The data presnted in total indicate overall that presowing treatment of wheat seeds
with SA contributes to the increase in the resistance of plants to stress factors of en-
vironment and ABA serves as a rmediator in the manifestation of the protective action
of SA. SA-treatment induces a sharp accumulation of ABA, which in turn is an inducer
of a wide spectra of antistress reactions in plants, which is why it is likely that the
effect of SA on the increase of ABA lies at the root of the preadaptive action of SA
to possible stress situations. Maintaining a high level of ABA in SA-treated plants
under stress contributes to protective reactions aimed to decrease its injurious effect
on growth and acceleration of growth resumption.
Acknowledgements: This work was supported by RFBR-Agidel, Grant No 02-04-
97919 and Integracia, No Ya 0108.
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