Wound response characteristics as related to phenylpropanoid enzyme activity and lignin deposition in resistant and susceptible Populus tremuloides inoculated with Entoleuca mammata (Hypoxylon mammatum)

Green internodal stem tissues of glasshouse grown Populus tremuloides were either wounded or wound-inoculated with Entoleuca mammata (Hypoxylon mammat um) and assayed for phenylalanine ammonia-lyase (PAL), caffeic acid - o-met hyltransferase (CA-OMT), and cinnamyl - alcohol dehydrogenase (CAD) activit y over a 96-h period. Lignin deposited in response to the treatments was an alyzed by the Klason and the pyrolysis - gas chromatographic (GC) - mass sp ectroscopy (MS) methodologies. The wound-inoculated treatment resulted in a wound morphology congruent with a typical resistant and susceptible respon se to E. mammata. Wounding alone resulted in no morphological differences b etween the two genotypes. In wound-inoculated stem tissue PAL and CAD activ ities were substantially higher in the resistant relative to the susceptibl e genotype. Total Klason lignin was similar for both genotypes; however, py rolysis-GC-MS analysis revealed a difference in the lignin monomeric compos ition between the two genotypes, with the susceptible genotype accumulating higher levels of hydroxyphenyl units relative to the resistant genotype. I t is concluded that differences in PAL and CAD activity and the synthesis o f distinct phenylpropanoid monomers distinguish the resistant from the susc eptible aspen genotype. Alterations in boundary zone formation due to the d ifferential synthesis of phenylpropanoid monomers and its effect on compart mentalization of the pathogen are discussed.