ABSTRACT
Proline (Pro) is a primary protectant against osmotic stress which plays an important role in coordinating the osmotic potential between cytosol and vacuolar. The role of Pro in ion homeostasis at high salinity has been reported by several studies. The biosynthesis of Pro in plants is adjusted by either the glutamate pathway or the ornithine pathway. Pro catabolism occurs predominately in mitochondria by Pro dehydrogenase or Pro oxidase producing pyrroline-5-carboxylate (P5C) , which converted to glutamate by P5C dehydrogenase. Induction of osmotic stress is responsible for the oxidative stress caused by reactive oxygen species such as superoxide radical, hydrogen peroxide and hydroxyl radicals. Reports in the literature strongly suggest that exogenous Pro application with low concentration would be more efficient in inducing tolerance to abiotic stresses in different plant species. Most plant species naturally accumulate Pro and other compounds as major organic osmolytes subject to altered abiotic stresses.
