In vivo and in vitro effects of ethephon on some oxidative enzymes in spinach leaves

In vivo and in vitro effects of ethephon, an ethylene-generating compound, on some oxidative enzymes; polyphenol oxidase (PPO, 1.10.3.1), peroxidase (POD, 1.11.1.7) and catalase (CAT, 1.11.1.6) in spinach leaves were investigated. The plants were grown under controlled conditions in sand culture in 60 days. Ethephon was applied as two doses at 0.1 and 1 mM. The leaves were harvested in the first and fifth days after ethephon treatment. In order to determine the effect of ethephon on the enzymes in vitro, the enzymes from leaves in control group were partially purified. In vivo, PPO activities were increased significantly at both concentrations whereas significant enhancement of POD activity was determined only at 1 mM. CAT activity was significantly reduced by ethephon through time. In vitro, POD and CAT activities increased slightly at 0.033 and 0.33 mM ethephon concentrations, as PPO activity did not increase at the same concentrations. But these activities of enzymes decreased significantly at 33.3 mM of ethephon concentration for POD and PPO and 26.6 mM for CAT. As a result, the increase of activity for PPO and POD or decrease of activity for CAT in vivo may be caused by not direct inhibition or activation of enzymes but a mechanism at transcriptional level induced by ethylene.