Coumarin impairs redox homeostasis in wheat aleurone layers

Many plant families produce coumarin (COU) and its derivatives as secondary metabolites via the phenylpropanoid biosynthetic pathway. This ubiquitous group of phytochemicals was shown to have diverse physiological effects on cellular, tissue, and organ levels. So far, research dealing with the hormonal like behavior of COU and its interaction with the activity and/or transport of phytohormones is very limited. In the current study, the impact of COU on redox homeostasis in aleurone layers of wheat grains was investigated. Aleurone layers were incubated in either 1000 μM COU or 5 μM gibberellic acid (GA₃) alone or in combination with 5 μM abscisic acid (ABA). Results revealed that both COU and GA₃ treatments induced the production of α-amylase but inhibited the activities of superoxide dismutase, catalase and ascorbate peroxidase. The downregulation of antioxidant enzymes that is provoked by COU and GA₃ was accompanied by significant accumulation of both H₂O₂ and malondialdehyde. In contrast with the effect of ABA, both COU and GA₃ treatments resulted in a significant reduction in cell viability as revealed by trypan blue staining. These results suggest that COU could disrupt the redox balance in aleurone layers through downregulation of the enzymatic antioxidant system. Therefore, the current study provides evidence for the gibberellin like activity of COU.