Characterization of active oxygen-producing proteins in response to hypo-osmolarity in tobacco and Arabidopsis cell suspensions: identification of a cell wall peroxidase.

The oxidative response induced by hypo-osmolarity is characterized in tobacco and Arabidopsis cells in order to identify the corresponding active oxygen-producing proteins. The pharmacological profiles of the oxidative responses were clearly different in the two plant materials, leading to the identification of distinct active oxygen producers in tobacco and Arabidopsis cells. In tobacco cells, a 100 kDa protein, localized in the plasma membrane, was demonstrated to produce active oxygen in the presence of NADPH. This production can be activated by fatty acids and is strongly depressed by diphenylene iodonium, as measured by an in vivo response. In Arabidopsis, 30 kDa and 34 kDa proteins localized in the cell wall were shown to be able to produce active oxygen in the presence of cofactors and the production is prevented by peroxidase inhibitors, as is the in vivo response. The two purified proteins were identified by mass spectrometry and both correspond to the peroxidase gene At5g64120.