Investigating physiological and biochemical

2.3. Salt tolerance traits in plants 
2.3.1. Physiological traits of salt tolerance 
Laborious and time consuming efforts of conventional breeding to increase 
salinity tolerance in plants depend on existing variability in genetic makeup. In 
addition, to change a single trait which is controlled by multiple genes is very difficult. 
So, these constraints compel scientific community to take advantage of using 
advanced knowledge in plant physiological responses during salt stress tolerance. 

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According to Noble and Rogers (1992), using physiological responses as screening 
criteria can be successful in pragmatic selection for agronomic traits. When plants are 
exposed to salinity, both glycophytes and halophytes evolve some mechanisms 
through which they save them from salt damage. 
2.3.1.1. Entry of ions into the roots 
Roots are the only plant organs which are firstly and directly exposed to increased 
salt concentrations in root zone and/or in growth media. Plant and environmental 
factors change the ion uptake rate among plant species. These factors include plant 
species/genotype, plant growth stage, temperature, light intensity and relative 
humidity. Reduction in plant growth due to root zone salinity ultimately reduces the 
plant vigor and hence the plant yield.
Two types of pathways are adopted by plants to take up ions/salts from the root 
zone or growth media. These include symplast and apoplast. Symplast requires 
expenditure of energy in the form of ATP and is an active process while apoplast 
requires the concentration gradient and is a passive process. Osmotic potential 
provides the force for ion uptake and plants can regulate the uptake of Na
+
and/or Cl
-
ions by using this force. Different transport proteins are also involved in uptake of 
different ions (Na
+
, K
+
) under normal as well as saline conditions as described by 
Garciadebleas et al. (2003).