ABSTRACT
Proline accumulation is a common response in several plant species to a wide range of stresses including drought and salinity. Proline has multifaceted roles in plants as it protects cells from damage by acting as an osmoprotectant, antioxidant, and a source of energy to drive growth during recovery from stress. Moreover, it has an impact on several developmental processes during stress. Exogenous application of proline to plants imparts tolerance to both drought and salinity. Many transgenic plants and crops having higher amounts of proline have also shown enhanced tolerance to drought and salinity stress. Proline biosynthesis under drought and salt stress is regulated by both ABA-dependent and ABA-independent signaling. Many transcription factor (TF) families including WRKY, MYB, bZIP, and NAC are known to regulate the expression of proline biosynthetic enzymes under osmotic stress. Proline may also play a role in flowering and development both as a metabolite and a signaling molecule. In the present chapter, we summarize current information on proline biosynthesis and regulation, proline homeostasis and its importance during growth and development of plants under two major abiotic stresses: drought and salinity.
