Foliar application of plant growth regulators such as 5-aminolevulinic acid (5-ALA) is an alternative way to improve antioxidant capacity and tolerance of stressed plants by affecting the physiological and biochemical process. This research was aimed to assess the effects of 5-ALA on some phytochemical and biochemical characteristics of Fagopyrum esculentum under different levels of salinity stress. A pot study in a factorial experiment based on randomized complete block design with three replications was conducted to assay the effect of foliar application of 5-ALA (0, 20, 40, and 60 µM) on physiological traits of F. esculentum under salinity stress (0, 25, 50, and 75 mM NaCl). The activities of antioxidant enzymes (phenylalanine ammonia-lyase, peroxidase, catalase, and superoxide dismutase) and the accumulation of H2O2, malondialdehyde, osmolytes, and phenolic compounds were increased with intensifying the salinity stress. The rutin content as the main flavonoid of leaves showed three times increasing under severe salinity stress. Salinity stress through decreasing photosynthesis pigments content, Rubisco enzyme activity, and stomatal conductance caused a reduction in photosynthesis rate and seed yield of stressed plants. Exogenously applied 5-ALA ameliorated the adverse effects of salinity via reduction of Na+ translocation to shoot, improving the ratio of K+/Na+, and increasing the osmolyte compounds, flavonoids content as well as plant antioxidant capacity. Increasing the water content of leaves, chlorophyll and carotenoids content, stomatal conductance, Rubisco activity, and photosynthesis rate in response to 5-ALA consequently enhanced the seed yield. Taken together, the results of the present study showed that F. esculentum can resist the 25 mM NaCl without any reduction in seed yield, and exogenous application of 40 µM 5-ALA could mitigate the salt toxicity via enhancement of antioxidant and photosynthesis capacity of treated plants under saline condition.

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