Are the Effects of Jasmonic Acid on Ascorbate Biosynthesis and Ammonium-Metabolizing Enzyme Activities of Wheat Seedlings Dependent on the Phase of Salt Stress?

During salt stress, plant growth is severely impaired by osmotic stress in a first phase and by specific ion toxicity in a second phase. To minimize these deleterious effects, the development of suitable management practices needs to be developed. The present study was undertaken to check whether the jasmonic acid (JA)-mediated enhancement of salt tolerance could be linked to ascorbate (AsA) concentrations and $${\text{NH}}_4^ + $$ -metabolizing enzyme activities during the second phase of salt stress. To this end, wheat seedlings cv. Karim were submitted for four weeks to 100 mM NaCl, in the presence of 1 mM JA or AsA, and analyzed for their growth-related parameters and ascorbate content as well as $${\text{NH}}_4^ + $$ -metabolizing enzymes. Obtained results showed decreased shoots’ and roots’ dry weight production and relative water contents, associated to a noteworthy reduction in leaves’ and roots’ AsA concentrations, as well as glutamine synthetase (GS), glutamate synthase (GOGAT) and glutamate dehydrogenase (GDH) activities. Nevertheless, exogenously-supplied JA, although not affecting AsA concentrations, enhanced GS, GOGAT and GDH activities, resulting in a significant increase in all measured growth parameters. The supplementation of AsA to salt-stressed seedlings, although not affecting GS, GOGAT and GDH activities, enhanced plant growth. Overall, results of the current study indicate that the effects of JA and AsA supplementations on the activities of $${\text{NH}}_4^ + $$ -metabolizing enzymes depend on the phase of salt stress and that the JA-mediated enhancement of wheat seedlings’ tolerance to salt stress is not exerted, at the second phase, through AsA.