The Exogenously Applied 5-Aminolevulinic Acid (ALA) Mitigates Salt Stress in Tomato Plants

In this research, the effects of 5-aminolevulinic acid, as a key precursor in the biosynthesis of porphyrin compounds such as chlorophyll, in mitigating salt stress were studied in Lycopersicum esculentum mill. Salinity at three levels (0, 50 and 75 mM NaCl) and ALA treatment at three levels (0, 1 and 2 mM) were applied on plants of this species. Both levels of salt (50 and 75 mM) reduced shoot fresh weight (11, 13%), shoot dry weight (15, 20%), shoot length (13, 25%), leaf area (20, 27.5%), chlorophyll (22.5, 49%), protein (12.5, 33.5%) and K+ content (22.5, 55.5%), and increased lipid peroxidation (84, 117%), H2O2 level (60, 100%), proline (61, 110%) and soluble sugars content (8. 18%), and ascorbate (25, 50%) and glutathione pool (29, 43%) and Na+ content (500, 700%) respectively. 5-aminolevulinic acid application in both levels, increased the leaf area, the amount of chlorophyll, protein, proline and soluble sugars, and ascorbate and glutathione pool by reducing the amount of lipid peroxidation, H2O2 level and Na+ content. The K+ content was not affected by ALA application. These results suggested that application of 5-aminolevulinic acid (1 and 2 mM) improved plant growth under normal condition and increased tolerance of tomato plants to salinity stress via increasing the amount of osmolytes, non-enzymatic antioxidants and chlorophyll cencentration.