Improving ATPase and PPase activities, nutrient uptake and growth of salt stressed ajowan plants by salicylic acid and iron-oxide nanoparticles.

KEY MESSAGE: Salicylic acid and iron-oxide nanoparticles alleviated salt toxicity and improved plant growth by stimulating the activities of H+-ATPase and H+-PPase and preventing nutrient imbalance. Two factorial experiments were undertaken in a greenhouse during 2018 and 2019, to evaluate the impacts of SA (1 mM) and nano-Fe2O3 (3 mM) sprays at 7 leaves and flowering stages on vacuolar H+-pumps, growth and essential oil of salt-subjected (0, 4, 8 and 12 dS m-1 NaCl) ajowan plants. Measurements of plant traits were started at about 12 days after the last foliar spray and continued up to maturity. The H+-ATPase and H+-PPase activities and root ATP content were enhanced under low salinity, but higher salinities reduced these parameters. Rising salinity enhanced Na uptake and translocation, endogenous SA and DPPH activity, while reduced K+/Na+ ratio and nutrients uptake, leading to a reduction in plant biomass. Treatment with SA, nano-Fe2O3 and their combination improved H+-pumps activities and ATP content in roots and leaves. The SA-related treatments caused the highest activities of H+-pumps in roots, but Fe-related treatments resulted in the highest activities of these pumps in leaves. Increasing H+-pumps activities reduced sodium uptake and translocation and enhanced nutrients uptake. Foliar treatments, especially SA + nano-Fe2O3 augmented endogenous SA, DPPH activity, and plant growth in salt-stressed plants. Essential oil contents of vegetative and inflorescence organs under severe salinity and seeds under moderate and severe salinities were enhanced. Maximum essential oil was obtained from seeds of SA + nano-Fe2O3-treated plants, which was strongly correlated with endogenous SA and DPPH. Nevertheless, the SA + nano-Fe2O3 was the best treatment for diminishing salt toxicity and improving ajowan plant growth and essential oil production.