Ozone effects on high light-induced photoinhibition in Phaseolus vulgaris

In this study the response to photoinhibition of photosynthesis and subsequent recovery was examined in plants of Phaseolus vulgaris L. cultivar 'Pinto' exposed to charcoal-filtered air or to ozone (O3) at 150 nL L−1 either for 3 h, or for 5 h. The responses were analysed using chlorophyll fluorescence imaging and by conventional fluorometry. Compared to control plants maintained in charcoal-filtered air, in plants exposed for 3 h to O3 and then subjected to high light treatment, the results show an increased tolerance to photoinhibition. Plants exposed to the same O3 concentration but for the longer 5-h period, were not tolerant to the photoinhibition treatment and, instead showed visible symptoms of damage (chlorosis and necrosis) clearly attributable to the longer O3 exposure. Here the detrimental effects of O3 aggravated the effects of the high light photoinhibitory treatment. The leaves exposed to the shorter O3 treatment (150 nL L−1 for 3 h) developed an ability to counteract the negative effects of a high light exposure probably because the O3 had activated an antioxidant system able to protect the photosynthetic machinery.