Acibenzolar-S-methyl primes cell wall strengthening genes and reactive oxygen species forming/scavenging enzymes in cucumber after fungal pathogen attack

Expression profiles for major cell wall strengthening genes, lignin peroxidase (LPO), callose synthase (CALS), caffeoyl-CoA 3-O-methyl transferase (CCOAMT) and cinnamyl alcohol dehydrogenase (CAD) as well as reactive oxygen species forming and scavenging genes namely, Cu/Zn superoxide dismutase (Cu/Zn SOD) and catalase (CAT) genes were examined in cucumber during acibenzolar-S-methyl (ASM) induced systemic resistance against anthraconse disease caused by Colletotrichum orbiculare. The time course study revealed early increased expressions of LPO, CALS and Cu/Zn SOD genes, while transcripts of CCOAMT, CAD and CAT remained unchanged. The early gene expression of LPO and CALS coincided with subsequent deposition of lignin and callose which generally occurs within 24 h after inoculation of the fungal pathogen on ASM treated plants. SOD enzyme activities were increased after 24 h of treatment and enhanced CAT activity was noticed at 12 and 48 h after treatment in inoculated plants. These results reveal that only certain cell wall strengthening genes (LPO and CALS) and the production and scavenging of ROS processes are involved in systemic acquired resistance induced by ASM in cucumber.