Effects of Tropospheric Ozone on Potato Plants Protected by the Antioxidant Diphenylamine (DPA)

To assess the protective effects of diphenylamine (DPA) on yield, DPA- and non-DPA-treated plants of potatoes (Solanum tuberosum cv. Agria) were exposed to ambient air at a rural site in Spain. Concentrations of ambient ozone were high at the site. Untreated plants served as controls. The DPA treatments did not have a significant effect on Chl content. The treatment with DPA (0.2 M) caused a significant increase of fresh weight production and tuber number of the potato plants in both years of study (32 and 47% in 2002 and 9 and 27% in 2003). Changes in the activity of antioxidant enzymes guaiacol peroxidase (GPX) and glutathione reductase (GR) in the leaves were determined in control and DPA-treated plants. The GPX activity in the leaves was significantly lower in the treated plants. GR was also lower, but not significantly, in the treated plants. The highest correlation between enzyme activity and yield was found in the case of GPX. The protective effect of DPA was related inversely to peroxidase activity. This is the first report demonstrating markedly enhanced yield and reduction of peroxides of potentially harmful O3 by DPA as a mechanism for protecting plants against noxious oxidative stress from the environment.