Activity and gene expression analysis of polyphenol oxidase enzyme in juglon applied cucumber seedlings

Allelopathy refers to the natural interactions between plants that a plant appear to affect another plant by producing a specific chemical. Many members of the walnut (Juglandaceae) family produce an allelochemical called juglone (5-hydroxy-1,4-naphthoquinone). Juglon occurs naturally in many parts of these plants. Although few plant species are tolerant to juglone and can grow near walnut trees, some susceptible plants may be affected negatively from walnut trees. The effects of juglon on the activities of oxidant enzyme polyphenol oxidase have been examined in leaves and root of cucumber (Cucumis sativus L.). Furthermore, the effect of the juglon on the expression of the genes encoding these enzymes has been examined. The cucumber seeds were germinated in the control (distilled water) medium and juglone solutions containing 0.01 mM, 0.1 mM, 0.25 mM and 0.5 mM juglone respectively. Root and stem parts of feedlings emerging from germinated seeds were separated and total protein and total RNA isolations were made. Enzyme activity assays were performed using the specific substrate of the enzyme of interest. Real-time PCR was used to analyze changes in gene expression. Juglone has inhibited growth of cucumber root and shoot without affecting germination. Enzyme activities and gene expression of Polyphenol oxidase were increased by juglone.