Involvement of nitrate reductase in the ameliorating effect of 5-aminolevulinic acid on NaCl-stressed barley seedlings

Exogenous application of 5-aminolevulinic acid (ALA) is widely used to decrease the effect of different abiotic stresses in various crops while the nitrogen metabolism is a possible target of ALA in plants. We investigated the effect of exogenous ALA on growth, activity of nitrate reductase (NR; EC 1.6.6.1), synthesis of proline and ROS generation in seedlings of the salt-sensitive barley cultivar (Hordeum vulgare L. cv. Gonar). Obtained data indicated that the ALA (20, 40 and 80 mg L−1) increased elongation and leaf blade expansion of barley seedlings exposed to 150 mM NaCl as compared to control plants, which were not treated by ALA. NR gene (Nar1) expression, NR protein content and enzymatic activities increased in ALA-treated plants. ALA also induced accumulation of free proline and decreased generation of superoxide anion radicals. Overall, this study demonstrates that ALA effects on salt-stressed barley involves changes of NR activities both at transcriptional and translational levels and leads to complex physiological modifications, such as improvement of growth and antiradical defense.