Steady state levels of free radicals in tomato fruit exposed to drought and ozone stress in a field experiment

The influence of drought and elevated ozone levels on the free radical contents of fruit from tomato has been investigated by electron paramagnetic resonance (EPR) spectroscopy. Under water deficit no differences in the signal intensity were observed between drought-stressed and control fruits, or between different harvests, from the same variety, whereas a reduction in the stomatal conductance of leaves under water deficit indicated a physiological effect of the drought stress on plants. One of the varieties investigated (Lycopersicon esculentum cv. Kremser Perle) generally showed higher radical levels than the other two. For relatively short periods of stress (≤ 20 d), the free radical contents of fruits that had received moderate ozone exposure were significantly higher than in fruits grown in filtered chambers with charcoal filtered air. However, all fruits had similar free radical levels after ~25 d of ozone fumigation.