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چکیده
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Plants respond to water deficit by adjusting many biochemical pathways that lead to synthesis of osmotically active metabolites and specific proteins that control scavenging of oxygen radicals and water flux. This study was carried out to elucidate the role of phenylethanoid glycosides (PhGs) as a part of primary and secondary metabolic networks responsive to water stress in Scrophularia striata. The 65-day-old seedlings of S. striata in Hoagland's solution were exposed to polyethylene glycol 6000 (˗0.5 bar) over a time course of 72 h. The observed data indicate that H2O2 content and activities of antioxidant enzymes such as catalase (CAT), guaiacol peroxidase (GPX) and superoxide dismutase (SOD) increased at all exposure times. Acteoside and echinacoside (two important PhGs as osmotic metabolites) were highly accumulated in the roots over the exposure time. A positive correlation was observed between PhGs, phenolic acids and flavonoids contents with phenylalanine ammonia-lyase (PAL) and tyrosine ammonia-lyase (TAL) activities which peaked at over the treatment time. Furthermore, water stress altered soluble sugars content (glucose, mannose, rhamnose and xylose) and free amino acids (phenylalanine, tyrosine and arginine) accumulation. Our observations corroborate that in S. striata, the increase of soluble sugars and free amino acids under osmotic stress not only serve as compatible solute but also with favoring PhGs and other phenolic compounds production can improve water stress tolerance.
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