**3. Mechanism and their responses to the salt tolerance in rice**

The potential of irrigation water and soil were affected by the accumulation of salts which interfere the uptake of water into plant from soil and presence of higher concentration of Na in soil solution will affected the uptake of some essential nutrients such as K and Ca in root zone [40]. If concentration of Na and Cl reach threshold level, some specific toxicities will alter the water relation [5]. The plants develop the some of the mechanism to grown in salinity condition. The mechanism are such as osmotic stress and osmolytes, ion exclusion, inclusion and compartmentation, antioxidant response and hormonal regulation.

#### **3.1 Mechanism of salt tolerance: osmotic stress and osmolytes**

When plants are grown under salinity condition, the plants adjust the losing of water and their potential and it will lead to decrease in osmotic potential, turgor and express the signal that trigger the adaptive responses [41]. The recovery period, osmotic potential and hydraulic conductivity of the membranes is reduced. By the accumulation of the organic and inorganic solutes and the plant turgidity is recovered after the tissue growth occur [5]. In osmotic adjustment, the cell wall elasticity was changed with decrease in RWC (Relative Water Content) and increase water content in the apoplast which decrease the salinity consequences by maintaining turgidity of the tissue. The organic osmolytes used to maintaining the osmotic potential in plants and prevent the salinity effects [42]. When salinity stress occurs, the osmolytes will synthesized and osmolyte biosynthesis and accumulation is important for the salinity tolerance. But the osmolyte biosynthesis may vary based on the plant age and rate of stress occur [43]. The most abundant and compatible

#### *Understanding the Responses, Mechanism and Development of Salinity Stress Tolerant Cultivars… DOI: http://dx.doi.org/10.5772/intechopen.99233*

osmolytes such as proline and glycine-betaine coming under the organic osmolytes [26]. Proline synthesis is enhanced under salinity [44]. Proline act as a reactive oxygen scavenger, redox buffer and molecular chaperone and stabilizes membranes and proteins under stress conditions [45]. Glycine-betaine involve in protection of enzymes and membrane structures [46].
