O-METHYLTRANSFERASE ACTIVITY, LIGNIN CONTENT, AND METHOXYLATED FLAVONES IN HEALTHY AND PHOMA-TRACHEIPHILIA-INFECTED LEAVES OF LEMON SAPLINGS

O-Methyltransferase activity and lignin content were studied in young leaves of lemon (Citrus limon Burm.) saplings, using both healthy leav es and those infected with the fungus Phoma tracheiphila (Petri) Kanz. and Gik. (a Mal-secco disease agent). Caffeic acid and quercetin were used as enzyme substrates. The highest O-methyltransferase activity w ith quercetin was observed on day 2 and with caffeic acid on day 16 fo llowing inoculation. The leaves of healthy and infected plants did not show any significant difference in lignin content throughout the expe riment (42 h). However, in the infected plants, both mature, rough lea ves and stems were considerably richer in lignin than those in healthy plants. Analyses for content and composition of polymethoxylated flav ones in lemon leaves showed that the Mal-secco infection resulted not only in a flavone concentration increase but in de novo formation of a n unidentified phenolic compound in a considerable amount as well.