Involvement of ethylene in growth inhibition of cucumber roots by ferulic and p-coumaric acids

Derivatives of hydroxycinnamic acid are widely known as allelochemical agents, which reduce the plant growth. However, molecular basis of inhibitory action of these compounds are unknown. Our earlier studies showed that two derivatives of hydroxycinnamic acid (ferulic and p-coumaric acids) reduce the cucumber growth. Ethylene may also participate in this inhibitory effect, because symptoms of ethylene stress syndrome i.e. increase in phenylalanine ammonia-lyase activity and enhanced lignin synthesis were observed. The aim of this study was to check the role of ethylene in growth retardation of cucumber roots by ferulic and p-coumaric acids.

Cucumber seedlings were subjected to allelochemical stress by treating their roots with 0.5 mM solutions of ferulic and p-coumaric acids. Production of ethylene by cucumber seedlings, the increase in phenylalanine ammonia-lyase activity and lignin synthesis as well as the reduction in growth indices of cucumber roots were observed. Using the inhibitors of ethylene synthesis and phenylalanine ammonia-lyase activity, no inhibitory effect of ferulic and p-coumaric acids was observed. The results indicate that ethylene participates in the retardation of cucumber root growth by these phenolic compounds.