Investigating of biochemical and physiological responses of Lepidium sativum to methyl jasmonate foliar application and water deficit stress

IntroductionSeveral environmental factors affect growth, development, and finally crop yield. Water scarcity is one of the environmental stresses that has destructive and harmful effects on the growth stages of plants, their organ structure and activity, eventually causing oxidative stress by disturbing the balance between the production of reactive oxygen species and the plant’s antioxidant defense system. In this regard, the induction of drought tolerance in plants is prominent from both theoretical and practical points of view. The application of plant growth regulators for survival, production of biomass, and yield in plants could be a promising approach that allows the farming of plants in the extension of cultivation fields and the increase of species diversity in natural and agricultural ecosystems. Methyl jasmonate (MeJA) is one of the compounds that is effective in causing tolerance and resistance to water scarcity in plants. Due to the role of jasmonic acid in drought tolerance induction in plants under stress conditions and considering the importance of Lepidium sativum in human nutrition, the main purpose of the present study was to investigate the effects of water scarcity and the foliar application of MeJA on the enzymatic antioxidant defense system, membrane stability and osmotic regulators. The mechanisms underlying drought tolerance are crucial for enhancing plant resilience and agricultural sustainability.Materials and methodsTo evaluate the effect of MeJA foliar spraying on some physiological indices and antioxidant enzymes activity of Lepidium sativum under water scarcity conditions, an experiment was conducted in a factorial arrangement based on a complete block design with three replications in the research greenhouse of the Bardsir Faculty of Agriculture, Shahid Bahonar University of Kerman, in 2022. The experimental treatments included the exogenous application of MeJA (0 (control), 50, and 100 μM) and irrigation level (100 and 50% of field capacity). Spraying distilled water and foliar application of MeJA concentrations on the leaves of the garden cress plant were applied based on the design plan, two times a week, and approximately 30 ml of MeJA was sprayed on each plant. Plant water depletions were determined by weighing the pots.         Results and discussionThe results showed that water scarcity caused a significant decrease in the amount of protein and an increase in the peroxidation content of membrane lipids, accompanied by the leakage of electrolytes. Although under water scarcity, the activity of antioxidant enzymes including superoxide dismutase(SOD), catalase (CAT), glutathione peroxidase (GPX), and ascorbate peroxidase (APX), as well as osmotic regulators consisting of proline content and soluble sugars increased by approximately 59.2, 74.3, 62.8, 62.7, 77.5, and 40.3%, respectively, as compared to the control plants, it was determined that the inhibition of ROS was beyond the tolerance of garden cress. Therefore, reducing the content of MDA (36.2%) and ion leakage (26.7%) and increasing the protein content by 23.5% through the induction of plant defense mechanisms, including amelioration of antioxidant enzyme activity and osmolytes, has been effective only by spraying the concentration of 100 µmol MeJA in garden cress under water scarcity conditions. MeJA exogenous application markedly ameliorated the water scarcity tolerance by increasing the activities of antioxidant enzymes and compatible osmolytes.ConclusionBased on the obtained results, it can be concluded that MeJA as a messenger molecule by increasing the activities of enzymatic antioxidants (SOD, CAT, GPX and APX) and increment osmotic regulators (proline and soluble sugars) in the cell led to decrease in lipids peroxidation and reduce in MDA content, which caused cell membrane stability, decline in ion leakage, and raising dry weight under water scarcity conditions. Therefore, it seems that the application of methyl jasmonate in modern agriculture can be a crucial step towards achieving agricultural sustainability in the country.