Impact of Salicylic Acid on the Transport and Distribution of Sugars in Plants - Salicylic Acid: Plant Growth and Development - page 84

(Khodary 2004 ; Sahar et al. 2011 ) and roots (Maria et al. 2000 ; Zahra et al. 2010 )
is reduced. SA treatment of plants subjected to salinity can induce further sugar
accumulation (see, for example, Aldesuquy et al. 2012 ; Khan et al. 2012 ). Similar
accumulation of soluble sugars under the influence of SA was observed also under
drought conditions (Loutfy et al. 2012 ).
In experiments where SA influence on growth and carbohydrate content under
unfavorable conditions was studied, the results were ambiguous as well. Along
with the enhancement of defensive responses, an increase in the content of os-
motica in the cells, induced by water deficit, was further enhanced by SA. How-
ever, in some experiments under salinity leaf spraying with SA, several days or
even several weeks before the analysis normalized the composition of carbohy-
drates. When salinity increased marked, after SA treatment the content of soluble
sugars and proline, decreased, relative control (salinity without SA treatment),
whereas the content of polysaccharides increased (Hussain et al. 2011 ; Khodary
2004 ). When the salinity declines the content of reducing sugars, SA treatment
stimulated their accumulation (Barakat 2011 ).
Differences in the direction of SA action on sugar content may be evidently
explained by the stress severity. In particular, the degree of salinity determined the
response of plant carbohydrate status to SA treatment. For example, experiments
performed on tomato plants, a relatively small increase in the salt content in the
root medium (25-50 mM NaCl) induced sugar accumulation but leaf treatment
with SA (0.5-1.5 mM) reduced their content. In contrast, the higher salt con-
centration (100 mM) suppressed sugar accumulation, whereas SA increased their
content. These experiments once again emphasize the ability of the SA to nor-
malize plant carbohydrate status (Zahra et al. 2010 ).
SA can exert no direct action but has an impact on the general plant preparation
to subsequent stress conditions (priming). Many workers have shown that seed
soaking for several hours in the solution with low SA concentrations (10 -6 -
10 -5 M) modified seedling growth and that of the adult plants even after months
(see for example Hayat et al. 2005 ; Al-Hakimi and Alghalibis 2007 ). In our
experiments, treatment of apical segments of maize roots with 10 -10 -10 -4 MSA
for several hours did not affect growth during the first day. However, on the second
day we observed growth activation at low SA concentrations (Burmistrova et al.
2009 ). The SA influence during the seed imbibition and at the early seedling
growth turned out to be a key factor for subsequent plant growth and yield. In such
cases, growth of both above— and underground organs is said to be accelerated
(Hayat et al. 2007 ). For example, two-month-old wheat plants, exposed to water
stress, exhibited a decrease in root and shoot dry mass. However, short-term seed
soaking in SA solution improved water content, growth and pigment contents in
the leaves (Aldesuquy et al. 2012 ). The seedlings developed from the seeds pre-
treated with SA were more tolerant to stressful conditions, in particular to infection
with pathogens (Khodary 2004 ; Yarullina et al. 2011 ). On infection with patho-
gens SA lead to defense gene expression and hypersensitive cell death in soybean
cells (Kawano 2003 ; Kawano and Furuichi 2007 ).