Treatment of dark-grown gherkin seedlings with dichlobenil (2,6-dichlorobenzonitrile) causes an increase in the phenylalanine ammonia-lyase (PAL) activity in the hypocotyl. This is explained by the following mechanism. Hydroxycinnamic acids, end products of the pathway in which PAL is a key enzyme, are normally mainly present in cell compartments separated from compartments containing phenol oxidizing enzymes such as peroxidases and phenol oxidases. Dichlobenil increases the permeability of membranes for hydroxycinnamic acids, making these acids available for the oxidizing enzymes. This results in the deposition of lignin-like material and in the decrease in the concentration of soluble hydroxycinnamic acids. In its turn this leads to derepression of PAL synthesis and/or diminished inactivation of PAL resulting in a higher PAL level.