Effects of elevated ozone on chlorophyll a fluorescence in symptomatic and asymptomatic leaves of two tomato genotypes

Two different genotypes of Lycopersicon esculentum Mill. (cv. Cuor di Bue, O-3-sensitive and line 93.1033/1, O-3-resistant) were treated with a single dose of ozone (150 mm(3) m(-3) for 3 h). The PS 2 activity was examined by measurements of chlorophyll a fluorescence on symptomatic and asymptomatic leaves. Symptoms were evident on the 4(th) leaves from the bottom, in both genotypes, while the 2(n) leaves of the line 93.1033/1 were asymptomatic. In these leaves, the net photosynthetic rate (P-N) did not change even if the F-v/F-m ratio significantly decreased. A strong reduction in P-N, mostly due to the stomatal closure, was observed in Cuor di Bue. The non photochemical quenching coefficient (q(NP)) and the degree of PS 2 reaction centres closure (1-q(P)) were higher, while the quantum efficiency of PS 2 photochemistry (Phi(PS2)) and quantum efficiency of excitation energy capture (Phi(exc.)) were lower in O-3 treated leaves of both genotypes. The limitation of photosynthesis was shown also by a decrease in the parameter %P, which diminished compared to controls in both genotypes. The response of the two genotypes for the energy fraction dissipated as thermal energy in the PS 2 antennae (%D) was similar. The fraction of %P remained lower during the recovery in symptomatic leaves of the resistant line as compared to the controls, whereas %X, which represents the amount of light energy that is not utilized in photochemistry or dissipated in the PS 2 antennae, significantly rose in the asymptomatic leaves of this line and in both the leaves of Cuor di Bue. From data obtained we concluded that ozone affected the plants independently on the appearance of visible symptoms of injury because the leaves without visible symptoms of both the genotypes were negatively influenced.