Modulation of proline metabolism under drought and salt stress conditions in wheat seedlings

Drought and salinity are the major environmental constraints that limit plant growth and productivity. In the present investigation, shoots of seven day old plantlets of nineteen wheat genotypes (PBW621, PBW660, PBW175, HD3086, WH1105, HD2967, C306, C273, C518, C591, Type 11, Excalibar, Gladius, Drysdale, Babax, Krichauff, Kharchia, Krl 1-4 and Krl 19) were evaluated for proline metabolism and its cross-talk with various biochemical parameters under water deficit, water withholding and salinity stress conditions. Principle component analysis categorized the genotypes into four groups: i.e. drought tolerant (Excalibar, Krichauff, Babax, Drysdale, Gladius and C306), salt tolerant (Kharchia, Typel 1, Krll-4 and Kr119), low stress tolerant (C273, C518 and C591) and susceptible (HD2967, PBW621, WH1105, HD3086, PBW660 and PBW175). Tolerant genotypes possessed increased proline content and 1,1 diphenyl-picryl hydrazyl (DPPH) radical scavenging activity along with the reduced magnitude of thiobarbituric acid reactive species in parallel with decreased H2O2 content. Proline accumulation in shoots of tolerant genotypes under stress conditions may be an adaptative strategy, as it supplies energy for growth and lowers the generation of free radicals and reduces the lipid peroxidation linked membrane damage resulting in their stabilization. Glutamate dehydrogenase might have played a dominant role in ammonium assimilation and glutamate biosynthesis, leading to an increased glutamate pool, which via pyrroline-5carboxylate synthetase activity led to enhanced proline accumulation in tolerant genotypes under stress conditions. Water withholding condition induced the stimulation of proline synthesis via increased glutamate dehydrogenase (GDH), pyrroline-5-carboxylate synthetase (P5CS) and pyrroline-5-carboxylate reductase (P5CR) activities with inhibition of oxidation via reduced proline dehydrogenase activity to a large extent as compared to water deficit and salt stress conditions. Our results highlight that in certain genotypes, GDH under water deficit, P5CS and PDH under salt stress and P5CR under water withholding stress condition were responsible for stress tolerance and could be used as a selectable marker.