Effects of exogenous application of citrulline on prolonged water stress damages in hyssop (Hyssopus officinalis L.): Antioxidant activity, biochemical indices, and essential oils profile

This study examined the effects of exogenous citrulline (control, 1 and 2 mM) and water availability (100%, 50% and 25% WA) on antioxidant attributes and essential oil constituents of Hyssopus officinalis L. in two successive harvests. Hyssop tolerantly responded to water deficiency by well-promoted antioxidant enzymes (i.e., superoxide dismutase, and catalase), strong DPPH-scavenging activity, and increasing polyphenols; however, the essential oil content was negatively reduced by water stress. External citrulline further increased the activity of antioxidant enzymes. Citrulline application at 2 mM under severe water stress could also improve essential oil (EO) content in the first and second harvests by about 15 and 30%, respectively. Furthermore, under severe drought, citrulline at 2 mM could obtain the highest yield of isopinocamphone (47%) as the main component of EO. The results showed the high potential of this novel applied metabolite agent to be used in a well-fulfilled production of this medicinal plant.

Keywords: 1,1-Diphenyl-2-picrylhydrazine (PubChem CID: 74358); Aluminum (III) Chloride (PubChem CID: 6451240); Antioxidant activity; Cinnamic Acid (PubChem CID: 444539); Citrulline (PubChem CID: 9750); Compatible solutes; Foliar treatment; Gallic Acid (PubChem CID: 370); Hydrogen Peroxide (PubChem CID:784); Hyssopus officinalis L.; Isopinocamphone; Quercetine (PubChem CID:5280343); Thiobarbituric Acid (PubChem CID:2723628).