The photosynthesis response, antioxidant systems and lipid peroxidation were studied in leaves from spinach plants (Spinacia oleracea L.)
in response to ozone fumigation, ambient air and charcoal filtered air treatments. The photosynthetic activity was tested through gas exchange
and chlorophyll a fluorescence measurements. Ambient air and ozone fumigation caused a decrease in the photosynthetic rate (25% and 63%,
respectively) mainly due to a reduced mesophyll activity, as evidenced by the increased intercellular CO2 concentration. These data agree with
a large reduction in the non-cyclic electron flow (7% and 16%), a lower capacity to reduce the quinone pool and a higher development of
non-photochemical quenching upon high O3 concentration. The results suggest that the oxidative stress produced, together with the
stimulation of superoxide dismutase (SOD, EC 1.15.1.1) and ascorbate peroxidase (APX, EC 1.11.1.11) activities and the increase in lipid
peroxidation (20% and 36%, respectively), generated an alteration of the membrane properties.