Induction of phenylalanine ammonia-lyase gene expression by paraquat and stress-related hormones in Rehmannia glutinosa.

Rehmannia glutinosa is a medicinal herb that is tolerant to the non-selective herbicide paraquat. Acteoside, a phenolic compound present in the plant, has been shown to inhibit paraquat. To understand regulation of the phenylpropanoid pathway that produces the acteoside moiety, we isolated a phenylalanine ammonia-lyase (PAL) cDNA clone (RgPAL1) and used it to examine PAL expression. The deduced 712 amino acid sequence of the open reading frame contains the conserved active site and potential phosphorylation sites of other plant PALs. RgPAL1 mRNA was detected in the leaves, flowers and roots of healthy plants, and the level of the mRNA was higher in leaves than in flowers and roots. RgPAL1 mRNA was induced in leaves by paraquat, H2O2, UV light, wounding, yeast extract, jasmonic acid and ethephon. The transcript level and enzyme activity increased gradually from 6 to 24 h after exposure to paraquat or jasmonic acid. Induction of RgPAL1 by paraquat and stress-related phytohormones suggests that it is involved in the regulation of the phenylpropanoid pathway under oxidative stress.