Response to ozone in two lettuce varieties on chlorophyll a fluorescence, photosynthetic pigments and lipid peroxidation

The effect of different O-3 concentrations on two lettuce (Lactuca sativa L.) varieties (Valladolid and Morelia) was investigated through chlorophyll (Chi) a fluorescence parameters, photosynthetic pigments (Chi a, b and total carotenoid), lipid peroxidation and crop yield. Ozone fumigation caused: a decrease in maximum quantum yield of photosystem II (PSII) photochemistry (F-v/F-m) in mature leaves, a reduction in the non-cyclic electron flow (phi(PSII)) and a lower capacity to reoxidize the Q(A) Pool (q(P)). These reductions were significant in the Valladolid var. but not in the Morelia var. A significant decrease in Chi a, b and in the total carotenoids was observed in the Valladolid var. but not in the Morelia var. mainly under O-3 fumigation conditions. We observed that the NPQ parameter did not increase in parallel to the q(P) reduction seen in the Valladolid var. O-3 fumigation with respect to air charcoal filtered air conditions. This fact could be associated with a lower capacity for dissipation of non-radiative excess energy and it may be closely correlated with significant decreases in photosynthetic pigment concentration. A decrease in NPQ from air ozone-free to ozone fumigation in the Morelia var. can be explained by the need to maintain the photochemical quenching under O-3 stress. It may also be associated with a slight increase in photosynthetic pigments. The differences between the two varieties may indicate that the Valladolid var. is more susceptible to O-3 damage. (C) 2004 Elsevier SAS. All rights reserved.