Seed priming and foliar application with jasmonic acid enhance salinity stress tolerance of soybean (Glycine max L.) seedlings

Background: Jasmonic acid (JA) is an important molecule, has a regulatory effect on many physiological processes in plant growth and development under abiotic stress. This study investigated the effect of 60 μM of JA as priming (P) at 15 °C in darkness for 24 h, foliar (F) and/or their combination effect (P+F) on two soybean cultivars (Nannong 99-6 (salt tolerant) and Lee 68 (salt sensitive)) under salinity stress (100 mM NaCl).

Results: Salinity stress reduced seedling growth and biomass as compared to that in the control condition. Priming and foliar application with JA and/or their combination significantly improved water potential, osmotic potential, water use efficiency (WUE) and relative water content (RWC) of both cultivars under salinity stress. Similarly, the priming, foliar application with JA and/or their combination significantly improved the net photosynthetic (Pn) by 68.03%, 59.85% and 76.67%; transpiration rate (Tr) by 74.85%, 55.10% and 80.26%; stomatal conductance (gs) by 69.88%, 78.25% and 26.24%; intercellular CO₂ concentration (Ci) by 61.64%, 40.06% and 65.79% and total chlorophyll content (Chl) by 47.41%, 41.02% and 55.73%, respectively under salinity stress as compared to the untreated seedlings. Soybean plants primed, sprayed with JA or treated with their combination enhanced the chlorophyll fluorescence, which was damaged by salinity stress. JA treatments improved abscisic acid (ABA), gibberellic acid (GA) and JA levels by 60.57%, 62.50% and 52.25%, respectively under salt stress as compared to those in the control condition. The transcriptional levels of the FeSOD, POD, CAT and APX genes increased significantly in the NaCl-stressed seedlings irrespective of JA treatments. Moreover, JA treatment resulted in a reduction of Na⁺ concentration and an increase of K⁺ concentrations in the leaf and root of both cultivars regardless of salinity stress. Monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR) and proline contents decreased in the seedlings treated with JA under salinity stress, whereas the ascorbate (AsA) content increased with JA treatment combined with NaCl stress.

Conclusion: The application of 60 μM JA improved plant growth by regulating the interaction between plant hormones and hydrogen peroxide (H₂ O₂ ), which may involved in auxin signaling and stomatal closing under salt stress. These methods could efficiently protect early seedlings and alleviate salt stress damage and provide possibilities to be used for improving soybean growth and inducing tolerance against excessive soil salinity. This article is protected by copyright. All rights reserved.

Keywords: antioxidant enzymes; gene expression; jasmonic acid; priming; salinity stress; soybean.