Antibodies against Fungal Conidia and Antibiotics Inhibit Phenylalanine Ammonia-Lyase Activation in Citrus

Antibodies raised against Trichoderma harzianum conidia prevented accumulation of Phenylalanine ammonia-lyase (PAL, E.C. 4.3.1.5.) in Citrus. The observed effect of the antibodies is produced by a delay in the formation of the fungal germination tube. An increase of PAL activity of ca. 7 fold in C. limon and C. sinensis seedlings, and of ca. 2 fold in C. paradisii seedlings was found, as an hypersensitive response to inoculation with T. harzianum conidia. This increase in activity was due to «de novo« synthesis of the enzyme as demonstrated by the effect of protein-synthesis inhibitors and by immunotitration.