Proline Accumulation and Oxidative Stress: Diverse Roles and Mechanism of Tolerance and Adaptation Under Salinity Stress

Osmotic stress caused by salinity is one of the major abiotic factors limiting crop productivity because it affects almost all plant functions. The complex regulatory processes of plant salt adaptation involve control of water flux and cellular osmotic adjustment via biosynthesis of osmoprotectants such as proline. “Proline,” a low-molecular compatible solute, accumulation leads to a decrease in cell osmotic potential which permits osmotic adjustment and stabilization and protection of membranes from damaging effects of salt/osmotic stresses. Free proline has been suggested as a metabolic measure of stress and is suggested to play an important role as an organic osmolyte and may be part of a general adaptation to water stress through water retention and prevention of dehydration. Proline has a diverse role in plant system, such as it can protect proteins and enzymes by stabilizing their structures and preventing aggregation during refolding and serve as a sink for the nitrogen from nitrogenous compounds derived from the net loss of protein, and lastly it may represent merely a manifestation of the damaging effects of stress. Cell membrane stability under salt stress is considered to be a major component in water stress tolerance, and proline might perform a protective function by scavenging reactive oxygen species (ROS). Therefore, the present chapter focuses on the recent advances in understanding proline signalling networks of biotechnological relevance in plant salt tolerance and adaptation.