S03 - Session O1 - Is juglone really the only allelochemical in Jugla regia?

Authors: Aljaz Medic *, Metka Hudina, Jerneja Jakopic, Robert Veberic

Juglone is a characteristic compound of the Juglandaceae family. It is believed that the non-toxic precursors of juglone are washed from the leaves into the soil by rain, where they are oxidized to the toxic form of juglone. Since there are not many studies identifying these non-toxic precursors of juglone or other non-toxic naphthoquinones, the first objective was to identify and quantify the naphthoquinones as well as other phenolic compounds in different tissues of walnut ( Juglans regia L.) using a high-performance liquid chromatography coupled with mass spectrometry (HPLC-MS /MS). The HPLC-MS /MS allowed us to identify more than 100 different phenolic compounds in different walnut tissues. While no naphthoquinones were found in the edible part of walnut (pellicle and peeled kernels), naphthoquinones were present in all other tissues studied (leaves, petioles, bark, buds, roots, and husks). The second objective was to find out whether juglone is really the only naphthoquinone with allopathic effects in J. regia or whether there are other naphthoquinones that also exhibit allopathic properties. This was done by comparing pure juglone and J. regia leaf extract on seed germination, seedling growth, and secondary metabolites of selected crop vegetables and by comparing pure juglone and J. regia leaf extract on growth, yield, and secondary metabolites of selected crop vegetables in a hydroponic system using Nutrient Film Technique (NFT). The results indicated that juglone may not be the only allelochemical in J. regia and that the leaf extract contains one or more specific phenolic substances that may stimulate growth, germination and secondary metabolite production in some plant species and inhibit it in others. For future research, a more in-depth focus should be made in individual isolation of naphthoquinones and an assay testing them for their allopathic effects on other plants.