ABSTRACT
Abstract. Overaccumulation of proline has been reported in numerous plant species growing in extreme environments including high soil salinity. Proline is widely regarded as a multifunctional stress-regulated molecule. Strong correlations between proline accumulation and plant osmotic and salt stress tolerance have been documented in different species. Recently, an emphasis has also been given in dissecting its role in offsetting cellular imbalances and maintaining cellular homeostasis during abiotic stresses. Several attempts have been made to increase the accumulation of this versatile proteinogenic amino acid in plants by transferring genes associated with proline metabolism and for finding the correlation between accumulation and
osmotic and salt tolerance in transgenic plants. In recent times, several attempts were made to overexpress various proline biosynthetic pathway genes such as Δ1-pyrroline-5-carboxylate synthetase (P5CS), pyrroline-5-carboxylate reductase (P5CR), and ornithine-δ-aminotransferase (OAT) (involved in synthesis) and to downregulate proline dehydrogenase (ProDH) and pyrroline-5-carboxylate dehydrogenase (P5CDH) (associated with proline degradation) to enhance osmotic and salinity stress tolerance. This chapter focuses on the current understandings of various aspects and the roles proline play not only in imparting osmotic and salt stress tolerance to plants but also in developmental activities.
