Transcription of plant defence genes in response to UV light or fungal elicitor

The synthesis of secondary metabolites in response to stress conditions has been implicated as a major defence response of higher plants¹. Cell suspension cultures of parsley (Petroselinum hortense) have been studied extensively as a model system and shown to respond to UV irradiation and treatment with fungal elicitor by the synthesis of flavonoids and furanocoumarins, respectively^2,3. The induced synthesis of these compounds might afford the plant protection against the respective environmental hazards, because flavonoids strongly absorb UV light and furanocoumarins possess fungitoxic properties⁴. The production of each class of compound is preceded by the induction of groups of coordinately regulated enzymes^2,5-8, based on rapid changes in amounts and activities of the corresponding messenger RNAs^9,10. We now report that these changes are due to transient increases in the transcription rates of the respective genes, which indicates that gene activation has an important role in UV and disease resistance in higher plants.