Photosynthetic Differences in Mustard Genotypes under Salinity Stress: Significance of Proline Metabolism

Aim: To determine the importance of proline in protection of photosynthetic capacity under salt stress in mustard cultivars (Brassica juncea L. Czern and Coss.).
Design of the Study: Mustard plants were grown with or without 100mM NaCl treatments.
Place and Duration of Study: The experimental work was carried out in the herbal garden of the Department of Botany, Jamia Hamdard, New Delhi, India under natural day/night conditions, between November to December, 2013.
Methodology: Plants were sampled at 30 days after seed sowing to determine physiological, biochemical and growth parameters.
Results: Salinity stress significantly reduced the studied photosynthetic parameters in all the cultivars. However, Pusa Jai Kisan with higher proline content better protected its photosynthesis and showed higher tolerance to salinity stress. Higher proline content was a result of increased N assimilation and increased synthesis of proline synthesizing enzymes, pyrolline-5-carboxylate synthetase and γ-glutamyl kinase while decrease of proline oxidase, the proline degrading enzyme. Higher inherent and salinity induced proline content in Pusa Jai Kisan was responsible for higher water relations, photosynthetic pigments and growth under salt stress.
Conclusion: Proline accumulation is an important strategy that plants operate to minimize the adverse effects of salinity stress on photosynthesis. Among all the cultivars proline content was maximum in Pusa Jai Kisan which led to comparatively higher osmotic potential and water potential, allowing the plants for higher intake of water and thereby resulting in increased stomatal opening and photosynthetic efficiency. Higher proline content resulted in lesser oxidative stress and consequently higher photosynthesis in Pusa Jai Kisan. The knowledge on the role of proline in protection of photosynthetic potential under salt stress could be exploited to develop tolerant line through intensive selection and breeding programs.