Investigating physiological and biochemical

2.2.2. Ion toxicity 
Under salt stress, when plants are unable to stop entry of toxic ions into their 
body and/or over-accumulate toxic ions like Na
+
, Cl
-
, SO
4
2-
, HCO
3
-
, ion toxicity may 
occurs. Ion toxicity reduces the productivity of plants and hence causes crop failure. 
However, plant response to ion toxicity differs and varies with species (Dogan et al., 
2010). Not all crops are equally affected by ion toxicity and some crops and woody 
plant species are more sensitive than others.
In plants, ion toxicity mostly occurs in older leaves where toxic ions (Na
+
and Cl
-
) 
accumulate and cause leaf death. When salt build up in the cytoplasm surpasses the 
compartmentation of toxic ions in vacuoles, it reduces the activity of different 
enzymes and hence leads to injury and death of leaves (Munns 2002, 2005; Munns et 
al, 2006). This death of leaves ultimately reduces the overall photosynthetic area and 
hence production of photosynthates and their supply is badly affected. This leads to 

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the disturbance of plant carbon balance to maintain growth and physiological 
processes (Munns, 2002; Ulfat et al., 2007).
High Na
+
interferes with K
+
and Ca
2+
nutrition and stomatal regulation, while 
high Cl
-
concentration reduces photosynthetic capacity due to chlorophyll degradation 
in barley (Tavakkoli et al., 2011). 
Sibole et al. (1998) 
strongly suggested that bean is 
extremely sensitive to Na
+
. Ulfat et al. (2007) found that high Na
+
concentration in 
leaves inhibits photosynthesis in different Brassica napus cultivars. 
Slabu et al. 
(2009) 
concluded that for faba bean (Vicia faba) grown at high NaCl concentration, 
Na
+
is the primary toxic ion, because it interferes with K
+
uptake and disrupts efficient 
stomatal regulation resulting in unproductive water loss and necrosis whereas Cl
-
induces toxicity symptoms due to chlorophyll degradation. Control of Cl
-
transport 
and Cl
-
exclusion from shoots is correlated with salt tolerance in many species,