Role of Aminolevulinic Acid in Mediating Salinity Stress Tolerance in Sunflower (Helianthus annuus L.)

The 5-aminolevulinic acid (5-ALA), an antioxidant, has been widely reported to participate in coping with different abiotic stresses. Among which, salinity greatly impacts the sunflower (Helianthus annuus L.) growth and production. The effect of 5-ALA spray (7.62 mM) was assessed to endure the adverse effect of salt stress on sunflower by using two cultivars of sunflower, namely, FH-751 and FH-675. Some morphological and physio-biochemical attributes were measured to observe the positive effects of 5-ALA. Foliar application of the 5-ALA enhanced the shoot fresh weight (33.91% to 34.53%), shoot and root dry weight (28.22% to 45.61%), shoot length (14.7% to 15.54%), number of the leaves (13.72% to 14.28%), leaf area (17.56% to 30.41%), and the first internode length (16.66% to 26.50%). Moreover, chlorophyll contents, soluble proteins, free proline, soluble sugar, glycine betaine, catalase and superoxide dismutase activity, phenolic and ascorbic acid contents, as well as shoot and root potassium, calcium, and K + /Na + ratio were also increased. In terms of root and shoot fresh and dry weights, root length, number of leaves, leaf area, enzymatic and non-enzymatic antioxidants, and ROS species, FH-751 cultivar outperformed FH-675. Overall, sunflower FH-751 cultivar showed better biochemical and morpho-physiological responses to salt stress compared to FH-675 which therefore proved more tolerant to salt stress. So, the 5-ALA foliar application can be used as beneficial approach in improving productivity and growth of sunflower cultivars under salt stress.