What happens with phloretin in plants? – Phloretin real-time effects and post-treatment metabolism in treated Arabidopsis seedlings

Abstract

Phloretin, phenolic compound found exclusively in Apple trees, possesses bioherbicidal potential towards other plant species. Our recent studies emphasized phloretin phytotoxic action towards model plant Arabidopsis [Arabidopsis thaliana (L.) Heynh.] as a consequence of disturbed auxin homeostasis in roots and disrupted normal leaf cell function due to chloroplast ultrastructural changes and decreased chlorophyll a and b levels. Given the known phloretin reactivity that results from its flexible dihydrochalcones structure, this study aimed to elucidate phloretin direct effects on the root plasma membrane, as well as phloretin post-treatment metabolism in Arabidopsis plants. Electrophysiological measurements were performed to assess real-time response of root plasma membrane to exogenously applied phloretin. Exposing Arabidopsis roots to a 250 µM phloretin resulted in rapid and significant depolarization of the root membrane potential with amplitude of about 47mV that confirmed high sensitivity of Arabidopsis to phloretin treatment. Reverse-phase liquid chromatography with mass spectrometry (LC-MS) was used to evaluate post-treatment metabolism of phloretin in Arabidopsis seedlings grown on 500 µM phloretin enriched medium for 10 days. Analyses revealed that phloretin underwent intensive glycosylation within plant tissues. Dominant peaks from treated plants showed a palette of phloretin derivatives mainly mono- and di-glycosides. Their quantity was significantly higher than in control plants, suggesting high uptake and metabolic interconversion of phloretin as an attempt of phloretin detoxification and/or preparation for vacuolar sequestration.