Environmental Engineering Reference
In-Depth Information
1.
I
NTRODUCTION
The adverse environments which can bring about disastrous damages to plants are
multiple, including drought, salinity, mineral deficiency, extreme temperature and so on
(Ashraf, 2009). Scientists throughout the world spare no efforts to study and assess the
influences of all the stresses on plants and large amount of discoveries have been acquired.
The effects of the salinity on plants therein attract more attention than others (Allakhverdiev
et al., 2000; Zhu, 2001). The adverse impacts imposed by salt stress are osmotic stress, ionic
stress, nutrient imbalance and the production of reactive oxygen species and the plants would
display the declining in growth, development and photosynthesis rate, sometimes even death
in the end (Ashraf and Foolad, 2007). Among all the influences, the osmotic and ionic
stresses are the dominating and fundamental ones. The osmotic stress is duo to the high
concentration of the salinity in the soil which hampers the roots to absorb water from the soil.
And the ionic stress is because of the high concentration of salts within plants (Munns and
Tester, 2008).
As is well known, the osmotic stress is always accompanied with drought stress under
which physiological drought often occurs, yet it can also be induced by salt stress (Yan et al.,
2013). Under salt stress, the water potential of the soil is reduced by the large quantity of ions,
so it is very difficult for the roots to take up enough water to maintain natural physical
development (Parida and Das, 2005). Under this circumstance, the stomatal conductance
reduced immediately and transiently (Wieland Fricke, Akhiyarova, Veselov, and
Kudoyarova, 2004). Moreover, related researches on halophyte such as
R. mucronata
,
Urochondra setulosa
,
S. salsahave
have demonstrated that the water potential and
transpiration rate reduced along with the increasing salt concentration (Aziz and Khan, 2001;
Gulzar et al., 2003; Lu et al., 2002). To accommodate the water balance, plants can also
reduce the loss of the water and lower water potential through the accumulation of the
compatible solutes. The compatible solutes are organic and low molecular metabolites, and at
the same time they do not harass the normal cellular order (Agarwal et al., 2012). The
common and effective compatible solutes include proline, glycinebetaine, polyols, fructans,
trehalose, sucrose, and mannitol and so on (Agarwal et al., 2012; Ashraf and Foolad,
2007Ashraf and Akram, 2009). In addition, genes of many osmolytes have also been
identified, cloned and introduced into plants,
producing a certain number
of transgenic plants
with enhanced resistance.
With a great deal of ions mainly Na
+
and Cl
-
entering into intracellular, the ion
homeostasis of the cell is disturbed, manifesting high concentration of Na
+
and Cl
-
, and
alterations in Na
+
/K
+
rate and disordered metabolism (Apse and Blumwald, 2007). The Na
+
is
able to compete with K
+
to bind to the plasma membrane obstructing the sorption of K
+
,
which plays very important roles in protein synthesis, osmotic adjustment and cytosolic ion
homeostasis (Zhu, 2003).
It has been reported that the replacement of the K
+
by Na
+
can lead to a forfeit of the
chloroplast functions bringing about the wild loss of water (Slabu, Zörb, Steffens, and
Schubert, 2009). While the good news is that the plants have acquired a plethora of different
mechanisms to adapt to the salt stress.
Among them, control of the ion exchange and xylem loading is the key (Munns and
Tester, 2008), moreover maintaining a high-activity of H
+
-ATPase is consider another
