Salicylic Acid and Calcium Signaling Induce Physiological and Phytochemical Changes to Improve Salinity Tolerance in Red Amaranth ( Amaranthus tricolor L.)

Amaranth ( Amaranthus tricolor L.) is a plant that is rich in vitamins, minerals, and phytochemicals. It is grown as a leafy vegetable in marginal environments, but high salinity levels in the soil can have a detrimental effect on its growth. These deleterious effects of salinity can be alleviated by exogenously applying signaling compounds such as salicylic acid (SA) and calcium (Ca), which can improve plant adaptation to stressful conditions. The present study evaluated the physiological and phytochemical responses of red amaranth ( Amaranthus tricolor L.) to foliar-applied salicylic acid (SA; 0.005 mM) and calcium (CaSO 4 ·2H 2 O; Ca, 2.5 mM) either alone or in combination (SA + Ca) under conditions of 100 mM NaCl salinity. The set-up was placed under greenhouse condition from May to October 2017. Treatments without salinity and applied with SA or Ca were used as controls for comparison. Salinity stress reduced the growth and biomass, total chlorophyll contents, and increased electrolyte leakage with Na + and Cl − accumulation in shoot and roots. Nonetheless, exogenous applied SA and/or Ca 2+ reduced the adverse effects of salinity by modulating growth, Na + exclusion from roots, and increased total phenolics, flavonoids, and antioxidant activity in red amaranth. The combined application of salicylic acid and calcium can be a better strategy for improving the salinity tolerance of amaranth under salt-stressed conditions.