Phloretin, dihydrochalcone from apple tree, bursts antioxidant capacity of tested Arabidopsis seedlings

Abstract

Apple species are exclusively rich source of dihydrochalcones phloretin and phloridzin, phenolic compounds with elusive role in planta but suggested auto-allelochemical features related to ‘apple replant disease’ (ARD). Our recent study emphasized phytotoxic action of phloretin towards other plant species such as model plant Arabidopsis as a consequence of disturbed auxin homeostasis in roots and altered chloroplast structure and function. Since elevated production and accumulation of reactive oxygen species (ROS) in plant cells is the one of the most common effect of allelochemicals, this study aimed to analyze the antioxidant status of Arabidopsis seedlings treated with phloretin. Total phenolic content (TPC) and total antioxidant capacity (TAC), as well as antioxidant enzymes activities were determined spectrophotometrically in treated and control seedlings at 5th and 10th day after germination (DAG). TAC increased c.a. 280% and 200% relative to control at 5th and 10th DAG respectively, presumably due to highly elevated TPC in treated seedlings (c.a. 150%). At the same time, the activity of antioxidant enzymes significantly decreased. The activity of catalase (CAT) was reduced by c.a. 40% and guaiacol peroxidase (POD) activities by 93% and 47% at 5th and 10th DAG, respectively. The activity of superoxide dismutase (SOD) was reduced by 55% and 18% at 5th and 10th DAG, respectively. The burst of antioxidant capacity of phloretin treated Arabidopsis seedlings resulted in significantly decreased antioxidant enzymes activities presumably due to strong antioxidant properties of absorbed phloretin. However, phloretin inhibition of antioxidant enzymatic activity due to its direct interaction with enzymes is object of further investigation.