Phenylalanine ammonia-lyase and hydroxycinnamate: CoA ligase in maize mesocotyls inoculated with Helminthosporium maydis or Helminthosporium carbonum

Abstract

Phenylalanine ammonia-lyase (E.C. 4.3.1.5) (PAL) and hydroxycinnamate:CoA ligase (E.C. 6.2.1.12) activities were measured in extracts from maize mesocotyls resistant and susceptible to Helminthosporium maydis and resistant to H. carbonum. CoA ligase activity increased in response to infection with H. maydis in both the resistant and susceptible cultivars. Activity began to increase between 6 and 9 h after inoculation and in the resistant cultivar continued to increase throughout a 48-h period. In susceptible cultivars activity ceased to increase at approximately 12 h after inoculation. The results demonstrate that the increase in CoA ligase activity is detectable as early as the onset of penetration by the fungus. No significant change in PAL activity was observed in either resistant or susceptible combinations with H. maydis, suggesting that PAL and CoA ligase are not coordinately regulated in interactions involving this fungus. Neither enzyme was found to change as a result of inoculation of any cultivar with H. carbonum.