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After exposure to 80 ppb of ozone for a single 4 h period, a significant reduction in photosynthetic activity was rapidly induced in two cultivars of Phaseolus vulgaris, cv. Pinto, O3-sensitive and cv. Groffy, O3-resistant. Pinto displayed a strong and irreversible reduction in Amax accompanied by stomatal closure and an increase in intercellular CO2 concentration. The fluorescence parameters indicated that the electron transport around PSII had been altered. The increase in non-photochemical quenching was related to an energy dissipation through non-radiative mechanisms. Photosynthesis was also reduced in the cv. Groffy, but the effect was reversible with time. Groffy showed alteration in the photochemical functioning of the thylakoids and specific disturbances of the water-splitting enzyme system of PSII, but these alterations disappeared only 20 h after the end of fumigation. Recovery of photosynthetic ability was more delayed with time and needed 7 d to show values similar to the controls. Physiological tools, such as gas exchange and chlorophyll fluorescence, play a major role in the early detection of environmental stress such as O3 pollution, and in distinguishing the responses between cultivars with different O3-sensitivity.
Guidi et al. (Wed,) studied this question.