Ethylene-dependent activity of phenylalanine ammonia-lyase and lignin formation in cucumber roots exposed to phenolic allelochemicals
Barbara Politycka
Seedling roots of cucumber were subjected to allelochemical stress by treating them with 0.1 mM solutions of ferulic, p-coumaric, p-hydroxybenzoic and vanillic acids. In the experiment the influence of derivatives of cinnamic acid (ferulic and p-coumaric acids) on the activity of phenylalanine ammonia-lyase (E.C. 4.3.1.5.) (PAL), lignin content, and cucumber root growth was compared to that of benzoic acid (p-hydroxybenzoic and vanillic acids. Roots treated with ferulic and p-coumaric acids were found to have an increased activity of PAL, a higher lignin content, and lower growth indices. No similar effect was recorded in the case of p-hydroxybenzoic and vanillic acids. The application of ethylene synthesis inhibitor, (aminooxy) acetic acid (AOA), cancelled out the effect of ferulic and p-coumaric acids on the activity of PAL. Lignin content in roots treated with ferulic acid remained on the control level when using the inhibitor, while that in roots treated with p-coumaric acid increased. The obtained results suggest that an increase in the activity level of PAL induced by the action of ferulic and p-coumaric acids, depended on ethylene synthesis. A consequence of changes in the studied enzyme activity was an increased lignin content, and in the case of p-coumaric acid also a direct participation of that compound in their synthesis. A consequence of the above changes was inhibition of the growth of cucumber roots treated with ferulic and p-coumaric acids.
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