Investigating physiological and biochemical

2.3.1.3 Na
+
/K
+
 ratio 
High concentration of exchangeable Na
+
is present in saline and/or sodic 
condition which increases the Na
+
/K
+
or Na
+
/Ca
2+
ratio in soil. Under such conditions, 
plants take more Na
+
and ultimately uptake of K
+
and Ca
2+
is greatly reduced. 
Venkata et al. (2012) claimed that of the several parameters (such as biomass 
production, quantities of proline, glycine betaine, sulphates, etc.) tested initially, only 
Na
+
and Na
+
/K
+
ratio showed significant and consistent (over seasons) correlation 
with salinity tolerance. They found that in pearl millet (Pennisetum glaucum L.), 
hybrids involving two poor general combiners produced better salt tolerant type 
except for stem Na
+
/K
+ 
where a combination of such parents yielded moderately 
tolerant hybrids. Natarajan et al. (2005) concluded that high yielding salt tolerant 
accessions of rice maintained a low Na
+
/K
+
ratio and higher grain yield. Similarly, 
Kaya et al. (2012) noted that salt tolerant linseed genotypes had low Na
+
/K
+
ratio and 
low Na
+
concentration than salt sensitive genotypes. Rezaei et al. (2010) observed 
that salinity tolerance in rapeseed cultivar Kristina was associated to a restriction of 
Na
+
absorption at the root level. Khan et al. (2009) investigated that wheat genotypes 
with higher concentration of proline, Na
+
/K
+
ratio and chlorophyll contents were 
found salt tolerant under saline conditions. It was found that high K
+
uptake over Na
+
caused salt tolerance in maize (Akram et al., 2010), in wheat (Munns and James, 2003) 
and barley (Wenxue et al., 2003). Thus keeping in view the above review, Na
+
/K
+
ratio can be suggested as an important criteria for screening genotypes under saline 
conditions (Wenxue et al., 2003; Natarajan et al., 2005; Khan et al., 2009; Akram et 
al., 2010; Rezaei et al., 2010; Kaya et al., 2012; Venkata et al., 2012). However, it is 
very important to separate cytosolic K
+
/Na
+
ratio from the tissue ratio as traditional 
tissue analysis for Na
+
content, based on acid tissue digestion followed by 
AA-spectroscopic analysis, used as a basis to determine K
+
/Na
+
ratio in plant tissues, 

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42 
cannot account for Na
+
compartmentation in the vacuole. This diminishes the 
predictive value of the K
+
/Na
+
ratio in plant tissues to screen plants for salt tolerance 
(Chen et al., 2005).