CHARACTERIZATION OF THE ROLE OF LIGNIFICATION IN DISEASE RESISTANCE

Department of Plant Science, University of Manitoba, Winnipeg, Manitoba R3T2N2, Canada

A pathogen infecting the corresponding host plant triggers several defence responses in the host plant. Lignin synthesis, a product of the phenylpropanoid pathway, is also an induced defence response in many plants. In this study, we have attempted to characterize the induction of Phenylalanine Ammonia Lyase (PAL -first enzyme in the phenylpropanoid pathway), Caffeicacid O-Methyltransferase (COMT) and Caffeoyl CoA O-Methyl transferase (CCOMT) lignin synthetic enzymes in the middle of the pathway)and Peroxidase (POX-final enzyme of the pathway) in wheat in response to Pyrenophora tritici-repentis infection. The enzyme activities were measured in resistant and susceptible cultivars at 0, 24, 48 and 72h post-inoculation. Maximum PAL activity was observed in leaves of both the cultivars at 48h post-inoculation while maximum COMT and CCOMT activities were observed in leaves of only the susceptible cultivar at 48h post-inoculation. Maximum COMT and CCOMT activities were observed in leaves of the resistant cultivar at 72h post-inoculation. Further, maximum POX activities were observed in leaves of both the cultivars at 72h post-inoculation. Higher levels of enzyme activities were observed in leaves of the susceptible cultivar, when the activites were expressed on a tissue weight basis. However, when the activities were expressed on the basis of lesion area, the resistant cultivar exhibited much higher levels of activity. Further, Northern and RT-PCR experiments are in progress to analyse the expression of PAL and POX genes.