Induction of ascorbate peroxidase activity in stressed pine (Pinus sylvestris L.) needles: a putative role for ethylene

Ascorbate peroxidase (EC 1.11.1.11) was studied in chemically stressed pine (Pinus sylvestris L.) needles, and the possible role of ethylene in its regulation was evaluated. Ascorbate peroxidase activity was induced both in detached and intact pine needles in response to H₂O₂ and Na₂S₂O₅ treatment through de novo protein synthesis. Both 1-aminocyclopropane-1-carboxylic acid, a direct precursor of ethylene, and ethephon, an artificial ethylene-releasing compound, caused an activation of ascorbate peroxidase which was effectively suppressed by inhibitors of protein synthesis. Chemical stress-dependent increase in ascorbate peroxidase activity was abolished by inhibitors of both ethylene biosynthesis (aminooxyacetic acid) and ethylene action (silver thiosulfate). It appears that both ethylene and H₂O₂ are involved in the control of ascorbate peroxidase induction in stressed pine needles, ethylene being a modulator rather than an inducer of the response.