Impact of Salicylic Acid on the Transport and Distribution of Sugars in Plants - Salicylic Acid: Plant Growth and Development - page 83

2 Effect of Salicylic Acid on the Content of Sugars in Plants
In recent years, a series of observations show the dependence of carbohydrate
accumulation in plant cells and tissues on SA. In most of these experiments,
spraying the leaves of seedlings and even of adult plants with a SA-containing
solution altered the sugar content in the above— and underground organs. The
total carbohydrate content in the plant increased, especially that of soluble sug-
ars—sucrose, glucose, and fructose (Khan et al. 2012 ; Mathur and Vyas 2007 ;
Shaaban et al. 2011 ; Kaveh et al. 2004 ; Ghasemzadeh and Jaafar 2012 ; Khodary
2004 ; Amin et al. 2007 , 2008 ; Sahar et al. 2011 ; Dong et al. 2011 ; Mostajeran and
Rahimi-Eichi 2009 ). This increase in sugar content in various plant organs was
positively correlated with accelerated growth in wheat (Shakirova et al. 2003 ), pea,
cucumber, (Farouk et al. 2008 ), common bean (Gharib and Hegazi 2010 ), and
groundnut (Jayalakshmi et al. 2010 ). In other experiments, SA also improved
germination and vigor of seeds (Gharib and Hegazi 2010 ), stem diameter, leaf and
stem dry weight, leaf area, and leaf index (Bayat et al. 2012 ). The cause for such
activation of growth processes might be due an increase in the turgor pressure in
the cells because of the accumulation of soluble sugars and other osmotically
active compounds, including proline and soluble proteins (Baghizadeh et al. 2009 ;
Khan et al. 2012 ). An increase in turgor pressure leads to the enhancement of cell
expansion (Morgan 1994 ). Healthy growth lead to higher biological yield with
bold grains with an increase in their length and diameter, their number and weight
per plant (Klessig and Malamy 1994 ; Mathur and Vyas 2007 ; Farouk and Osman
2011 ; Shaaban et al. 2011 ).
It should be noted that SA affects many of the physiological processes that
dependents on SA concentration, plant species, developmental stage, and func-
tional state, as well as environmental conditions. The data concerning SA impact
on plants are rather contradictory. For example, low SA concentrations enhanced
growth of soyabean (Gutierrez-Coronado et al. 1998 ), maize (Shehata et al. 2001 ),
and wheat plants (Shakirova et al. 2003 ; Iqbal and Ashraf 2005 , 2006 ), whereas
high concentrations caused an inhibitory effect on growth of tomato, lupine, wheat,
and maize plants (Haroun et al. 1998 ; Singh and Usha 2003 ; Abdel-Wahed et al.
2006 ). SA effects on sugar content are contradictory as well. Low SA concen-
trations (below 2.5 mM) increased markedly total sugar content in seeds; the
higher concentrations (above 5 mM) reduced it (Haroun et al. 1998 ; Shehata et al.
2001 ; Abdel-Wahed et al. 2006 ). High SA concentrations suppressed not only
sugar accumulation but also other processes—growth, yield and photosynthetic
rate (Amin et al. 2007 ).
Beneficial SA impact on plants is significantly manifested especially under
stress conditions (Hayat et al. 2010 ). It is known that, under most abiotic stress, the
accumulation of osmotically active compounds occurs, mainly soluble sugars,
proline, and soluble proteins (Maria et al. 2000 ; Al-Hakimi and Alghalibis 2007 ).
For example, at salinity (physiological drought) the content of these osmotica in
the cells is usually increased and the content of polysaccharides in the leaves