The problem of plant osmotic stress tolerance is one of the most complicated. Wild type plants developed various protective mechanisms to mitigate detrimental effects of salt and water stresses. But the necessity of cultural plants with higher levels of stress tolerance becomes critical. Therefore, the investigation of tolerant genotypes (natural or experimentally obtained) makes a significant contribution to the detection of new tolerance determinants.

It is known, that free proline accumulation occurs in plant tissues during various osmotic stresses. This event is considered to be a common biological response to a wide range of biotic and abiotic stresses. Plants accumulate proline to mitigate stress detrimental effects. Proline lends increased viability to suffered plants. This amino acid is a cellular compatible osmolyte that protects enzymes against inactivation. It may serve as an energy supply for utilization during period of reparation. The activation of proline synthesis and inhibition of its oxidation retain proline level. There are two pathways of proline synthesis. The first one developed with the participation of Δ-pyrroline-5-carboxylate synthase (P5CS); the alternative pathway of proline biosynthesis is catalyzed by Orn-δ-aminotransferase (OAT). The proline degradation is the reverse process and catalyzed by Proline dehydrogenase (PrDH).