Mechanism of Impatiens glandulifera Royle Allelopathy to Sinapis alba L. and Raphanus sativus L. Germination Is Through Oxidative Stress

<i>Impatiens glandulifera</i> Royle (<i>I. glandulifera</i>) in the EU presents a threat to the ecosystem, and is thus on the list of invasive alien species. The aim of this study was to clarify if an allelopathic effect of <i>I. glandulifera</i> involves the activation of oxidative stress in target plants. First, <i>I. glandulifera</i> leaf extract was prepared and levels of 2-hydroxy-1,4-naphtoquinone (2-HNQ) and 2-methoxy-1,4-naphthoquinone (2-MNQ), as main allelochemicals of <i>I. glandulifera</i>, determined by HPLC. Next, seeds of white mustard (<i>Sinapis alba</i>) or radish (<i>Raphanus sativus</i>) were exposed to the extract or to 2-MNQ (in the concentration range of 1-30 µg/mL) for 3 days and parameters of germination and oxidative stress were assessed. Both the leaf extract and 2-MNQ inhibited germination of white mustard and radish; however, the effect of 2-MNQ was more pronounced. Furthermore, the extract and 2-MNQ induced activation of antioxidative defense and caused oxidative damage to lipids and proteins in white mustard and radish seedlings. It was observed that radish seedlings were less susceptible to negative effect of <i>I. glandulifera</i> extract and 2-MNQ. This study's obtained results demonstrated that 2-MNQ is the main allelochemical of <i>I. glandulifera</i> and that the mechanism by which <i>I. glandulifera</i> and 2-MNQ induce negative effects to target plants involves oxidative stress. In addition, species-dependent susceptibility to <i>I. glandulifera</i> and 2-MNQ was shown.