ABSTRACT
Osmolytes are low-molecular-weight organic metabolites that do not disturb normal plant metabolic activities and help plants cope with various stresses. Plant physiologists distribute osmolytes in four broad categories viz., 1- amino acids (e.g., proline, glutamine and ornithine), 2- quaternary ammonium compounds (e.g., glycinebetaine), 3- sugars (e.g., sucrose) and 4- sugar alcohol or polyols (e.g., mannitol and sorbitol). Accumulation of osmolytes is almost ubiquitous in the plant kingdom. In normal circumstances, osmolytes regulate cell turgor, modulate the cell signaling system and stabilize the chloroplast membrane structure. Similarly, during stress, osmolytes prevent water loss through osmotic adjustment, maintain membrane integrity in plant cells and scavenge radicals, thus increasing antioxidative status and mitigating osmotic and oxidative stress. Hence, osmolytes accumulation is one of the earliest and most successful strategies used by plants to combat environmental stress.
