Investigating physiological and biochemical

2.2.3. Nutrient imbalance 
Under salinity, not only the homeostasis of Na
+
but also Ca
2+
and K
+
ions are 
disturbed (Borsani et al., 2003; Xue and Liu, 2008). Na
+ 
and/or Cl
-
concentrations 
often exceed those of most macronutrients by one or two orders of magnitude, and by 
even more in the case of micronutrients. Therefore, high concentrations of Na
+
and 
Cl
-
in the soil solution may depress nutrient-ion activities and produce extreme ratios 

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37 
of Na
+
/Ca
2+
, Na
+
/K
+
, Ca
2+
/Mg
2+
, and Cl
-
/NO
3
-
. As a result, the plant becomes 
susceptible to osmotic and specific-ion injury as well as to nutritional disorders that 
may result in reduced yield or quality. Nutrient imbalances can result in salt-stressed 
plants in various ways. Imbalances may result from the effect of salinity on nutrient 
availability, competitive uptake, transport or partitioning within the plant or may be 
caused by physiological inactivation of a given nutrient resulting in an increase in the 
plant's internal requirement for that essential element (Grattan and Grieve, 1994). 
Under normal conditions, cytosolic K
+
/Na
+
ratio is fairly high, enabling normal 
cell metabolism. Under saline conditions, K
+
/Na
+
ratio falls dramatically (Maathuis 
and Amtmann, 1999) due to excessive Na
+
accumulation in the cytosol and increased 
K
+
leakage from the cell, resulting from NaCl induced membrane depolarization 
under saline conditions (Zhu, 2000; Shabala, 2000; Shabala et al., 2003; Chen et al., 
2005; Cuin et al., 2008). Sodium ion enters the cytosol via non-selective cation 
channels and depolarizes the membrance, provoking K
+
loss via outward-rectifying 
K
+
channels (KORC) and non-selective outward rectifying channels (NORC). The 
activity of plasma membrane H
+
-ATPase opposes NaCl induced membrane 
depolarization and its related K
+
efflux. Besides, it fuels the Na
+
/H
+
antiport, further 
improving the cytosolic Na
+
/K
+
ratio (Zepeda-Jazo et al., 2008). Salt stress increases 
the uptake of some micronutrients like Fe, Mn, Zn, and Cu in some crop plants 
(Villora et al., 2000).