Role of osmolytes dynamics in plant metabolism to cope with salinity induced osmotic stress

Salinization is an ever-increasing problem that severely affects crop performance and finally agricultural production worldwide. This adverse effect of salinity on crop plants occurs in two phase i.e. ionic and osmotic phase. Plants accumulate osmolytes to combat with the osmotic phase of salinity. Osmolytes are polar, non-toxic, uncharged organic compatible solutes that are easily soluble in nature and do not cause any disturbance in normal cellular functions. Osmotic adjustment is crucial to maintain cell turgidity and membrane stability. Osmolytes also regulates the protein folding essential for mediating stress signalling mechanisms or pathways responsible for tolerance. Additionally, they help maintain thylakoid membrane stability, keeping the plants in photosynthetically active phase under stressed conditions. Osmolytes are broadly classified into three groups: ammonium containing compounds (polyamines and betaines), sugars, amino acids and sugar alcohols. In consideration of immense potential of plant osmolytes under salinity, the present review emphasized on the biosynthesis of various reported osmotically active substances and their involvement in different mechanisms or pathways responsible for salinity tolerance in crop plants.