Katarina Šoln, Nada Žnidaršič and Jasna Dolenc Koce
University of Ljubljana, Biotechnical faculty, Dept. of Biology, Večna pot 111, SI-1000 Ljubljana, Slovenia
Japanese knotweed (Fallopia japonica) and Bohemian knotweed (F. ×bohemica) are invasive alien plants that according to the novel weapon hypothesis inhibit growth of their neighbours by allelopathy (Hierro and Callaway, 2003). The main target of knotweed´s allelopathic compounds is the primary root of a tested plant (Dolenc Koce and Šoln, 2018). The aim of our study was to evaluate the effect of knotweed rhizome extracts on morphological and biochemical characteristics of radish roots. Radish seeds were exposed to knotweed extracts in a range of concentrations (0.5%–10%). After seven days, biochemical markers of oxidative stress were examined, and morphological and ultrastructural characteristics of root cells were analysed using light and transmission electron microscopes.
Root growth of the treated radish was strongly inhibited, whereas shoots were not affected. Roots were shorter and thicker due to changes of cell shape and size in the cortex. Knotweed extracts exhibited a strong effect on the root cap cells: cell membrane, mitochondria and endoplasmic reticulum ultrastructure was affected and some cells were completely disintegrated. The ultrastructure of apical root meristem was also affected, one of the changes was increase in the amount of vacuoles. Biochemical characteristics of oxidative stress (enzymatic and non-enzymatic antioxidants, lipid peroxidation) changed according to the control treatment. Staining with diaminobenzidine showed the increased synthesis of hydrogen peroxide in roots.