Peroxidases are involved in biosynthesis and biodegradation of β‐thujaplicin in fungal elicitor‐treated Cupressus lusitanica cell cultures

Summary• Here, collaboration between peroxidases and H 2 O 2 in biosynthesis and biodegredation of β‐thujaplicin in elicited Cupressus lusitanica was investigated.• The accumulation of a phytoalexin, β‐thujaplicin, in C. lusitanica cell cultures can be stimulated by a yeast elicitor. A transient low peak was followed by a high level lasting for 2 d, and then a decrease, while peroxidases were activated to a high level just when amounts of β‐thujaplicin decreased. In vitro tests revealed that horseradish peroxidase can transform c . 80% of β‐thujaplicin in the presence of H 2 O 2 , and the culture medium was also able to transform β‐thujaplicin.• A transient production of H 2 O 2 occured in the cell cultures immediately after elicitation, following a increase in NAD(P)H‐oxidase activity. This H 2 O 2 production may mediate the elicitor‐induced accumulation of β‐thujaplicin, because inhibiting H 2 O 2 production or removing H 2 O 2 from the cell cultures suppressed elicitor‐induced β‐thujaplicin accumulation, while exogenously applied H 2 O 2 or H 2 O 2 generation system can stimulate β‐thujaplicin accumulation.• Both NAD(P)H oxidase inhibitors and peroxidase inhibitors partially inhibited NAD(P)H‐dependent O 2 − and H 2 O 2 production. In‐gel assay of peroxidase and superoxide anion synthase activity demonstrated that peroxidase isoforms have NAD(P)H‐dependent superoxide anion synthase activity. These results suggest that peroxidases can act as superoxide anion synthases to contribute to genecation of H 2 O 2 that promotes β‐thujaplicin production in elicited C. lusitanica cell cultures.