Regulation mechanism of exogenous ALA on growth and physiology of Leymus chinensis   (Trin.) under salt stress

Salt stress is one of major problem hampering plant growth and development to a significant level. In present study, 5-aminolevulinic acid (ALA) was exogenously applied to Leymus chinensis (Trin.) Tzvel. plants at various concentrations (10, 50, and 100 mg L^-1) to assess its effects on morphology, physiology, and biochemistry under salt stress conditions (150 mmol NaCl L^-1) as compared with control. The results indicated that salt stress substantially impaired growth, physiology and biochemistry of L. chinensis plants; nonetheless, ALA application alleviated the adverse effects of salt stress. Application of ALA improved the leaf length, leaf area, leaf conductance, plant dry biomass, water contents, and root activity of L. chinensis under stress and no stress conditions. Additionally, biosynthesis of chlorophyll, carotenoids, free proline, soluble sugars and proteins of L. chinensis plants was also increased following ALA application as compared to control, under salt stress conditions. Moreover, we also observed an enhanced activity of antioxidant defense system in L. chinensis in response to ALA application. ALA elevated the activity of enzymatic antioxidants viz. ascorbate peroxidase (APX), glutathione reductase (GR), superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) significantly scavenged reactive oxygen species thus reduced the accumulation of malondialdehyde (MDA) under salt stress as compared to control under both normal and stressed conditions. The effect of ALA on all growth and biochemical attributes was concentration dependent and application of 50 as well as 100 mg L^-1 ALA proved better. The results concluded that salt stress tolerance in L. chinensis plants can be increased by exogenously applied ALA at appropriate concentration. It was suggested that L. chinensis plants were treated with ALA application of 50-100 mg L^-1 was more beneficial under both normal and saline conditions.

Keywords
5-Aminolevulinic acid (ALA); antioxidant enzymes; growth; Leymus chinensis; salt stress