Investigating physiological and biochemical

2.3.2. Biochemical traits of salt tolerance 
2.3.2.1. Synthesis of organic osmolytes 
Salinity causes water deficit or osmotic shock to the plants as a first symptom of 
stress condition. During this shock/stress, plants produce water potential gradient as a 
first reaction or strategy to cope with the new situation of stress. To create water 
potential gradient, plants synthesize organic compatible solutes, like proline, and 
glycinebetain in the cytoplasm. These solutes create sharp water potential gradient 
and help plants to take up water into the plant. They also protect and maintain the 
structure of the cell organelles and proteins (enzymes) without interfering with their 
activities and hence termed as osmoprotectants (Ashrafijou et al., 2010; Nabati et al., 
2011). Although osmotic adjustment is essential for adapting plants to soils with low 
water potential, but may bring penalties in terms of carbon allocation for the rapidly 
growing phase of fast growing plants such as wheat and barley (Munns, 1988). 
Compatible solute synthesis comes with an energy cost and hence involves a potential 
growth penalty (Munns and Tester, 2008). Lutts et al. (1996) found that proline did 
not take part in osmotic adjustment in salt stressed rice and its accumulation seemed 

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to be a symptom of injury rather an indicator of salt tolerance. Similarly, Colmer et al. 
(1995) found no significant affect of proline in salt tolerance in a wheat amphiploid. 
On the other hand, Petrusa and Winicow (1997) noted a rapid increase in proline 
contents in alfalfa and similar results were reported by Madan et al. (1995) in salt 
tolerant lines of B. juncea. Although the synthesis of these compounds occurs at the 
expense of plant growth, but may allow the plant to survive and recover from the 
period without water (Munns, 2011).